RADAR DEVICE

A radar apparatus includes: first radar circuitry, which, in operation, transmits a first transmission signal from a plurality of first transmission antennas; and second radar circuitry, which, in operation, transmits a second transmission signal from a plurality of second transmission antennas, in which a first interval of each Doppler shift amount applied to the first transmission signal transmitted from each of the plurality of first transmission antennas is different from a second interval of each Doppler shift amount applied to the second transmission signal transmitted from each of the plurality of second transmission antennas.

TECHNICAL FIELD

The present disclosure relates to a radar apparatus.

BACKGROUND ART

Recently, a study of radar apparatuses using a radar transmission signal of a short wavelength including a microwave or a millimeter wave that allows high resolution has been carried out. Further, it has been demanded to develop a radar apparatus which senses small objects such as pedestrians or falling objects in addition to vehicles in a wide-angle range (wide-angle radar apparatus) in order to improve the outdoor safety.

Examples of the configuration of the radar apparatus having a wide-angle sensing range include a configuration using a technique of receiving a reflected wave by an array antenna composed of a plurality of antennas (antenna elements), and estimating the direction of arrival (the angle of arrival) of the reflected wave using a signal processing algorithm based on received phase differences with respect to element spacings (antenna spacings) (Direction of Arrival (DOA) estimation). Examples of the DOA estimation include a Fourier method, and, a Capon method, Multiple Signal Classification (MUSIC), and Estimation of Signal Parameters via Rotational Invariance Techniques (ESPRIT) that are methods achieving higher resolution.

Further, there has been a proposed radar apparatus, for example, in which a transmitter in addition to a receiver is provided with a plurality of antennas (array antenna), and which is configured to perform beam scanning through signal processing using the transmission and reception array antennas (which may also be referred to as a Multiple Input Multiple Output (MIMO) radar) (e.g., see Non-Patent Literature (hereinafter referred to as “NPL”) 1).

CITATION LIST

Patent Literature

However, methods for a radar apparatus (e.g., MIMO radar) to sense a target object (or a target) have not been comprehensively studied.

One non-limiting and exemplary embodiment of the present disclosure facilitates providing a radar apparatus capable of accurately detecting a target object.

A radar apparatus according to one exemplary embodiment of the present disclosure includes: first radar circuitry, which, in operation, transmits a first transmission signal from a plurality of first transmission antennas; and second radar circuitry, which, in operation, transmits a second transmission signal from a plurality of second transmission antennas, in which a first interval of each Doppler shift amount applied to the first transmission signal transmitted from each of the plurality of first transmission antennas is different from a second interval of each Doppler shift amount applied to the second transmission signal transmitted from each of the plurality of second transmission antennas.

Note that these generic or specific exemplary embodiments may be achieved by a system, an apparatus, a method, an integrated circuit, a computer program, or a recoding medium, and also by any combination of the system, the apparatus, the method, the integrated circuit, the computer program, and the recoding medium.

According to one exemplary embodiment of the present disclosure, a radar apparatus is capable of accurately detecting a target object.

DESCRIPTION OF EMBODIMENTS

A MIMO radar transmits, from a plurality of transmission antennas (also referred to as “transmission array antenna”), signals (also referred to as “radar transmission waves” or “radar transmission signals”) that are multiplexed using Time Division Multiplexing (TDM), Frequency Division Multiplexing (FDM), or Code Division Multiplexing (CDM), for example. In addition, the MIMO radar receives signals (also referred to as “radar reflected waves” or “reflected wave signals”) reflected, for example, by an object around the radar using a plurality of reception antennas (also referred to as “reception array antenna”) to separate and receive the multiplexed transmission signals from reception signals. With this processing, the MIMO radar can extract propagation path responses indicated by the product of the number of transmission antennas and the number of reception antennas, and perform array signal processing using these reception signals as a virtual reception array.

Further, in the MIMO radar, it is possible to virtually enlarge the antenna aperture so as to enhance the angular resolution by appropriately arranging element spacings in the transmission and reception array antennas (see, for example, NPL 1).

The MIMO radar is roughly divided into a “monostatic configuration” and a “bistatic/multistatic configuration,” for example.

The monostatic configuration may, for example, be a configuration in which a radar transmitter (for example, including a plurality of transmission antennas and a high-frequency radio) and a radar receiver (for example, including a plurality of reception antennas and a high-frequency radio) are included in the same housing.

In the bistatic/multistatic configuration, for example, the radar transmitter and the radar receiver may be included respectively in different housings. For example, the bistatic/multistatic configuration is a configuration in which the respective housings are installed at distances apart from each other, and the radar transmitter and the radar receiver are connected to a controller that performs synchronization control. In the bistatic configuration, for example, a pair of the radar transmitter and the radar receiver are provided, and the radar transmitter and the radar receiver are disposed at distances apart from each other. The multistatic configuration is, for example, a configuration in which at least one or both of the radar transmitter and the radar receiver are plural. The multistatic configuration is disclosed in, for example, NPL 2.

For example, a radar apparatus having the monostatic configuration is capable of capturing radio waves (reflected waves) that are emitted to a target object and reflected in a backward direction (for example, in a radar transmission wave direction). Meanwhile, it is difficult for the radar apparatus having the monostatic configuration, for example, to capture a reflected wave when the radio wave is reflected in a direction different from the backward direction. In contrast to the above, the radar apparatus having the bistatic or multistatic configuration is capable of capturing a reflected wave depending on an installation position, for example, even when the radio wave is reflected in a direction different from the backward direction. For example, even in a case where a backward reflected wave is unlikely to be captured, such as a case where a target object such as a wall is inclined in an oblique direction with respect to the radar transmission wave direction, the radar apparatus having the multistatic configuration has a degree of freedom in the installation position of the radar receiver, and therefore, the reflected wave can be easily captured and the detection performance of the target object can be improved by devising the installation position of the radar receiver.

In the following, a non-limiting exemplary embodiment of the present disclosure focuses on a multistatic configuration. For example, in the non-limiting exemplary embodiment, the multistatic configuration using a plurality of MIMO radars having the monostatic configuration will be described. The multistatic configuration using a plurality of MIMO radars having the monostatic configuration may be referred to as a “mono- & multi-static configuration,” for example.

FIG.1illustrates an exemplary radar apparatus having the mono- & multi-static configuration in which radar #1 and radar #2 being MIMO radars having the monostatic configuration are used.

Radar #1 illustrated inFIG.1is, for example, a “first MIMO radar having the monostatic configuration” that outputs a radar transmission wave from radar transmission antenna group Tx #1 and receives a reflected wave from target object #1 by radar reception antenna group Rx #1 in the same housing (for example, path (1) illustrated inFIG.1).

Similarly, radar #2 illustrated inFIG.1is, for example, a “second MIMO radar having the monostatic configuration” that outputs a radar transmission wave from radar transmission antenna group Tx #2 and receives a reflected wave from target object #3 by radar reception antenna group Rx #2 in the same housing (for example, path (2) illustrated inFIG.1).

Further, the radar apparatus illustrated inFIG.1may perform an operation of transmitting a radar transmission wave from transmission antenna group Tx #1 of radar #1 and receiving a reflected wave from target object #2 by reception antenna group Rx #2 of radar #2 in addition to the operation as the MIMO radar with the first monostatic configuration described above. The radar apparatus performing this operation may be regarded as, for example, a “MIMO radar having a first multistatic configuration” (for example, path (3) illustrated inFIG.1).

Similarly, in addition to the operation as MIMO radar of the second monostatic configuration described above, the radar apparatus illustrated inFIG.1may perform an operation of transmitting a radar transmission wave from transmission antenna group Tx #2 of radar #2 and receiving a reflected wave from target object #2 at the reception antenna group Rx #1 of radar #1. The radar apparatus performing this operation may be regarded as, for example, a “MIMO radar having a second multistatic configuration” (for example, path (4) illustrated inFIG.1).

InFIG.1, path (3) and path (4) are assumed as similar paths. For example, the radar apparatus detects target object #2 in both directions of path (3) and path (4), thereby reducing erroneous detection due to multipath or the like and achieving enhancement in detection accuracy of the target object.

Further, for example, when target object #2 moves in the cross-range direction of radar #1 and radar #2 (for example, in a direction orthogonal to the direction corresponding to path (1) or path (2)), it is difficult for radar #1 and radar #2 to detect the Doppler velocity of target object #2. On the other hand, the cross-range direction of radar #1 and radar #2 in which target object #2 moves is different from the cross-range direction of the paths (for example, path (3) or path (4)) of the first or second multistatic configurations. Thus, the radar apparatus can detect the Doppler velocity of target object #2 by radar positioning with the multistatic configuration, and can also obtain an effect of facilitating detection of the target object as a mobile object.

For using a radar not only as the radar having the monostatic configuration, but also as the radar having the multistatic configuration, a synchronization controller that performs synchronization control between a plurality of radars having the monostatic configuration installed at distant positions may, for example, be used. For example, inFIG.1, when a Frequency modulated continuous wave (FMCW) signal (for example, a “chirp signal”) is used as the radar transmission wave, the synchronization controller may generate the chirp signal and supply a common chirp signal to radar #1 and radar #2. Thus, radar #1 and radar #2 can transmit the chirp signal common between radar #1 and radar #2, and can perform reception processing using the common chirp signal. Thus, radar #1 and radar #2 can be used as the radar of the monostatic configuration, and can also be used as the radar of the multistatic configuration composed of the transmission antenna of radar #1 and the reception antenna of radar #2 or of the transmission antenna of radar #2 and the reception antenna of radar #1.

As described above, the radar apparatus illustrated inFIG.1may generate the radar transmission signal in the synchronization controller and supply the radar transmission signal, which is the output of the synchronization controller, to radar #1 and radar #2 in common. For example, the radar apparatus can transmit the transmission signal from the first radar having the monostatic configuration and perform reception processing of the first radar having the monostatic configuration and reception processing of the second radar having the multistatic configuration. In addition, the radar apparatus can transmit the transmission signal from the second radar having the monostatic configuration, for example, and can perform reception processing of the second radar having the monostatic configuration and reception processing of the second radar having the multistatic configuration.

For example, when the first and second radars having the monostatic configurations operate simultaneously using the same radar transmission wave, interference may occur with each other. Accordingly, the interference may increase likeliness of erroneous detection or non-detection, thus deteriorating the positioning accuracy or the detection performance of the radars. To avoid this, for example, multiplexing transmission with application of time division (TDM), frequency division (FDM), or code division (CDM) is conceivable for the transmission of the radars with the multistatic configuration using the first and second radars of the monostatic configurations.

Examples of the radar having the multistatic configuration may include a configuration in which, inFIG.1, transmission from the transmission antenna (Tx #1) of radar #1 and reception by the reception antenna (Rx #2) of radar #2 (the multistatic configuration from radar #1 to radar #2) and transmission from the transmission antenna (Tx #1) of radar #2 and reception by the reception antenna (Rx #1) of radar #1 (the multistatic configuration from radar #2 to radar #1) are alternately switched in time division (hereinafter, referred to as “inter-multistatic time-division transmission”).

In the case of performing the inter-multistatic time-division transmission, for example, switching to transmission in the multistatic configuration from radar #2 to radar #1 takes place after completion of the transmission in the multistatic configuration from radar #1 to radar #2. Thus, the time required for the transmission processing is likely to increase.

For example, inFIG.1, a configuration is conceivable in which transmission in the multistatic configuration from radar #1 to radar #2 and transmission in the multistatic configuration from radar #2 to radar #1 are simultaneously performed (multiplexing transmission) at different frequencies (hereinafter referred to as “inter-multistatic frequency multiplexing transmission”).

When the inter-multistatic frequency multiplexing transmission is performed, for example, two chirp signals #1 and #2 having different center frequencies may be used as common signals. For the transmission processing, for example, chirp signal #1 may be transmitted from radar #1, and chirp signal #2 may be transmitted from radar #2.

Further, for the reception processing, for example, radar #1 may perform the reception processing of the monostatic configuration based on chirp signal #1 by a part of the reception antennas of radar #1, and perform the reception processing of the multistatic configuration based on chirp signal #2 by the remainder of the reception antennas of radar #1 since the frequencies of chirp signal #1 and chirp signal #2 are different from each other.

Similarly, for the reception processing, for example, radar #2 may perform the reception processing of the monostatic configuration based on chirp signal #2 by a part of the reception antennas of radar #2, and perform the reception processing of the multistatic configuration based on chirp signal #1 by the remainder of the reception antennas of radar #2.

Thus, simultaneous multiplexing transmissions can be performed between the multistatic configurations. Accordingly, the measurement time can be shorter than in the case of the inter-multistatic time-division transmission. On the other hand, for example, the reception processing of the multistatic configuration is performed by a part of the reception antennas of radar #1 or radar #2 in the inter-multistatic frequency multiplexing transmission, and therefore, the reception signal level is likely to be lowered or the angle measurement accuracy is likely to be deteriorated.

In the inter-multistatic frequency multiplexing transmission, a plurality of chirp signals that are common signals are used. In general, an expensive cable which focuses on a low loss property is used for a transmission line of the high-frequency signal, and thus, the system cost is likely to increase.

For example, inFIG.1, a configuration is conceivable in which transmission in the multistatic configuration from radar #1 to radar #2 and transmission in the multistatic configuration from radar #2 to radar #1 are simultaneously performed (multiplexing transmission) at the same frequency and with different codes (hereinafter referred to as “inter-multistatic code multiplexing transmission”).

When inter-multistatic code multiplexing transmission is performed, for example, a chirp signal having the same center frequency may be used as a common signal. For example, for the transmission processing, the radar apparatus may multiply each chirp signal by an orthogonal code (or a code having a correlation value of zero or almost zero with respect to another code) between transmission in the multistatic configuration from radar #1 to radar #2 and transmission in the multistatic configuration from radar #2 to radar #1, and transmit the chirp signal.

Further, with respect to the reception processing, the radar apparatus may perform demultiplexing processing on the multiplexed transmission signals using, for example, the codes used for transmission.

In the inter-multistatic code multiplexing transmission, for example, the code separation processing amount tends to increase. In addition, in the inter-multistatic code multiplexing transmission, inter-code interference occurs in a reflected wave from a target object with a relative velocity, which is likely to cause deterioration in positioning performance. In addition, when the inter-code interference is suppressed in the inter-multistatic code multiplexing transmission, the maximum Doppler that can be observed in the radar apparatus tends to be reduced.

Regarding the transmission of the radar with the multistatic configuration, the application of the multiplexing transmission to which time division, frequency division, or code division is applied has been described above.

In a non-limiting exemplary embodiment of the present disclosure, a method for improving the efficiency of target detection in the mono- & multi-static configuration is described. For example, the non-limiting exemplary embodiment of the present disclosure describes a multiplexing transmission method that enables inter-multistatic simultaneous multiplexing transmission, in addition to the monostatic configuration, and reduces the time required for radar distance measurement.

For example, in a non-limiting exemplary embodiment of the present disclosure, in addition to radar positioning with the monostatic configuration of radar #1 and radar #2 illustrated inFIG.1, radar positioning with the multistatic configuration from radar #1 to radar #2 and radar positioning with the multistatic configuration from radar #2 to radar #1 may be performed simultaneously. In this case, for example, Doppler Division Multiplexing (DDM) using different Doppler multiplexing intervals may be applied as inter-multistatic multiplexing transmission (hereinafter, also referred to as “inter-multistatic Doppler multiplexing transmission”).

Note that the radar apparatus according to an exemplary embodiment of the present disclosure may be mounted on a mobile entity such as a vehicle, for example. A positioning output (information on an estimation result) of the radar apparatus mounted on a mobile entity may be output to, for example, an Advanced Driver Assistance System (ADAS) that enhances collision safety or a control Electronic Control Unit (ECU) (not illustrated) such as an automated driving system, and may be used for vehicle-drive control or alarm call control.

In addition, the radar apparatus according to one exemplary embodiment of the present disclosure may be attached to a relatively high-altitude structure, such as, for example, a roadside utility pole or traffic lights. Such a radar apparatus can be utilized, for example, as a sensor of a support system for enhancing the safety of passing vehicles or pedestrians, or a suspicious person intrusion prevention system. Further, the positioning output of the radar apparatus may be output to, for example, a control apparatus (not illustrated) in the support system for enhancing the safety or the suspicious person intrusion prevention system, and may be used for alarm call control or abnormality detection control.

The use of the radar apparatus is not limited to the above, and the radar apparatus may also be used for other uses.

Further, the target object is an object to be detected by the radar apparatus, and includes, for example, a vehicle (including four wheels and two wheels), a person, a block, a curbstone, or the like.

Embodiments of the present disclosure will be described below in detail with reference to the drawings. In the embodiments, the same constituent elements are identified with the same numerals, and a description thereof is omitted because of redundancy.

The following describes a configuration of a radar apparatus (for example, MIMO radar configuration) having a transmitting branch in which multiplexed different transmission signals are simultaneously sent from a plurality of transmission antennas, and a receiving branch in which the transmission signals are separated and subjected to reception processing.

Further, by way of example, a description will be given below of a configuration of a radar system using a frequency-modulated pulse wave such as a chirp pulse (e.g., also referred to as chirp pulse transmission (fast chirp modulation)). However, the modulation scheme is not limited to frequency modulation. For example, an exemplary embodiment of the present disclosure is also applicable to a radar system that uses a pulse compression radar configured to transmit a pulse train after performing phase modulation or amplitude modulation on the pulse train.

The radar apparatus (or radar system) according to the present embodiment may include, for example, a plurality of radar sections (which corresponds to radar circuitry and is, for example, a MIMO radar). Further, the radar apparatus according to the present embodiment may include, for example, a synchronization controller (for example, corresponding to control circuitry) that performs synchronization control between a plurality of radar sections, and a positioning output integrator that integrates positioning outputs of the plurality of radar sections.

For example, radar apparatus1illustrated inFIG.2is a radar system including first radar section10(or expressed by radar section10-1) having a plurality of transmission/reception antennas (not illustrated), and second radar section10(or expressed by radar section10-2) having a plurality of transmission/reception antennas (not illustrated).

In radar apparatus1illustrated inFIG.2, synchronization controller20performs synchronization control between first radar section10and second radar section10. For example, synchronization controller20may generate a chirp signal or a reference clock signal (also referred to as a reference signal) as a common signal to first radar section10and second radar section10for synchronization control.

Here, the reference clock signal is, for example, a reference signal of a Voltage Controlled Oscillator (VCO) that generates a chirp signal, and is a high-frequency signal of about several tens to several hundreds MHz. Accordingly, in the case where the reference clock signal is used, a system cost can be lowered as compared with the case where the chirp signal (for example, GHz order) is used. Further, in the case where the reference clock signal is used, the chirp signal is generated individually in each of first radar section10and second radar section10. Thus, the coherence of the phases between first radar section10and second radar section10is not guaranteed, and the phase shift to such an extent as to drift to cause displacement is likely to occur. For example, radar apparatus1may measure and correct a drift component of the phase between first radar section10and second radar section10in advance.

For example, radar apparatus1may transmit a transmission signal from a plurality of transmission antennas of radar transmitter100-1of first radar section10. Radar apparatus1may perform positioning processing of target object #1, for example, by receiving a reflected wave signal by radar receiver200-1having a plurality of reception antennas of first radar section10, the reflected wave signal being the transmission signal of first radar section10reflected by target object #1 (not illustrated) (for example, radar positioning using the monostatic configuration).

Further, radar apparatus1may perform positioning processing of target object #2, for example, by receiving a reflected wave signal by radar receiver200-2having a plurality of reception antennas of second radar section10, the reflected wave signal being a transmission signal of first radar section10reflected by target object #2 (not illustrated) (for example, radar positioning using the multistatic configuration).

Similarly, for example, radar apparatus1may transmit a transmission signal from a plurality of transmission antennas of radar transmitter100-2of second radar section10. Radar apparatus1may perform positioning processing of target object #3, for example, by receiving a reflected wave signal by radar receiver200-2having a plurality of reception antennas of second radar section10, the reflected wave signal being the transmission signal of second radar section10reflected by target object #3 (not illustrated) (for example, radar positioning using the monostatic configuration).

Further, radar apparatus1may perform positioning processing of target object #2, for example, by receiving a reflected wave signal by radar receiver200-1having a plurality of reception antennas of first radar section10, the reflected wave signal being a transmission signal of second radar section10reflected by target object #2 (not illustrated) (for example, radar positioning using the multistatic configuration).

Note that the reception processing in first radar section10and second radar section10may be performed using, for example, a MIMO virtual antenna.

In the present embodiment, radar apparatus1may perform multiplexing transmission of the transmission signal from radar transmitter100-1of first radar section10and the transmission signal from radar transmitter100-2of second radar section10.

For example, each of first radar section10and second radar section10may include a first demultiplexer that demultiplexes, from the reception signal, the reflected wave signal for the transmission signal from radar transmitter100of the corresponding radar section, and a second demultiplexer that demultiplexes the reflected wave signal for the transmission signal from radar transmitter100of the other radar section.

Further, for example, each of first radar section10and second radar section10may include a first direction estimator that performs direction estimation using the signal demultiplexed by the first demultiplexer and a second direction estimator that performs direction estimation using the signal demultiplexed by the second demultiplexer.

InFIG.2, for example, positioning output integrator30may integrate positioning outputs from first radar section10(for example, a first positioning output and a second positioning output) and positioning outputs from second radar section10(for example, a first positioning output and a second positioning output) to perform positioning of the target object.

With such a configuration, radar apparatus1can receive the reflected wave from the target object at radar receiver200-1of first radar section10and radar receiver200-2of second radar section10, demultiplex the reception signal depending on whether the reception signal is a reflected wave of the transmission signal of the corresponding radar section or a reflected wave of the transmission signal of the other radar section, and appropriately perform the positioning processing based on the positional information of each of first radar section10and second radar section10. Further, radar apparatus1can also shorten the positioning time.

For example, inFIG.2, first radar section10and second radar section10may be disposed at locations apart from each other. In this case, radar apparatus1can be used as a radar of the so-called multistatic configuration. For example, positioning by the radar having the multistatic configuration in which the first transmission signal emitted from first radar section10is received by radar receiver200-2of second radar section10and positioning by the radar having the multistatic configuration in which the second transmission signal emitted from second radar section10is received by radar receiver200-1of first radar section10are simultaneously possible, and thus it is possible to shorten the positioning time.

Since first radar section10and second radar section10illustrated inFIG.2have the same configuration, they are collectively denoted and described as “radar sections10” thereinbelow, and different operations between first radar section10and second radar section10will be described distinctively.

FIG.3illustrates an exemplary configuration of radar apparatus1in which a frequency-modulated chirp signal is used as a radar transmission signal (also referred to as a radar signal or a radar transmission wave).

Radar apparatus1ofFIG.3includes, for example, a plurality of radar sections10(corresponding to, for example, first radar section10and second radar section10illustrated inFIG.2), synchronization controller20, and positioning output integrator30(not illustrated). InFIG.3, an exemplary configuration of one radar section10among the plurality of radar sections10is illustrated, and the illustration of other radar sections10is omitted.

Radar section10includes, for example, radar transmitter (corresponding to a transmission branch or radar transmission circuitry)100and radar receiver (corresponding to a reception branch or radar reception circuitry)200.

Radar transmitter100generates the radar transmission signal, for example, and transmits the radar transmission signal at a predetermined transmission period using a transmission array antenna including a plurality of transmission antennas102-1to102-Nt.

Radar receiver200receives reflected wave signals, which are radar transmission signals reflected by a target object (target) (not illustrated), using a reception array antenna composed of a plurality of reception antennas202-1to202-Na, for example. Radar receiver200performs signal processing on the reflected wave signals received at reception antennas202to, for example, detect the presence or absence of the target object, or estimate the directions of arrival of the reflected wave signals.

For example, synchronization controller20generates a chirp signal and supplies the generated chirp signal to the plurality of radar sections10.

[Exemplary Configuration of Synchronization Controller20]

Radar transmission signal generator301generates a radar transmission signal based on, for example, control by signal controller304. The generated radar transmission signal may be, for example, a predetermined frequency modulated wave (e.g., a frequency chirp signal or a chirp signal). Radar transmission signal generator301outputs the generated chirp signal to the plurality of radar sections10(for example, radar transmitter100).

Radar transmission signal generator301includes, for example, modulation signal generator302and VCO303. Hereinafter, the components of radar transmission signal generator301will be described.

Modulation signal generator302periodically generates, for example, saw-toothed modulation signals. The radar transmission period is herein represented by Tr.

VCO303generates a chirp signal based on the modulation signal output from modulation signal generator302, and outputs the chirp signal to radar transmitter100(for example, Doppler shifters101-1to101-Nt) and radar receiver200(mixer204described later) of radar section10.

Signal controller304controls generation of the radar transmission signal of radar transmission signal generator301(for example, modulation signal generator302and VCO303). For example, signal controller304may configure parameters (for example, modulation parameters) related to the chirp signal such that the chirp signal is transmitted Ne times for transmission periods Trper one radar positioning.

FIG.4illustrates an example of the chirp signal output from synchronization controller20. For example, radar apparatus1can detect a time variation of the positioning results of positioning the target object by transmitting the chirp signal generated by synchronization controller20and measuring, multiple times, the reflected wave being the chirp signal reflected by the target object. In the following description, each transmission period among Nctransmission periods Tris represented by index “m.” Here, “m” are integers of from 1 to Nc.

FIG.5illustrates an example of the chirp signal output from synchronization controller20.

As illustrated inFIG.5, the modulation parameters for the chirp signal may include, for example, center frequency fc, frequency sweep bandwidth Bw, sweep start frequency fcstart, sweep end frequency fcend, frequency sweep duration Tsw, and frequency sweep change rate Dm. Note that Dm=Bw/Tsw. Note also that Bw=fcend−fcstart, and fc=(fcstart+fcend)/2.

Frequency sweep time Tswcorresponds to, for example, a time range (also called a range gate) in which A/D sampled data is taken by A/D converter207of radar receiver200, which will be described later. Frequency sweep time Tswmay be set to an entire time section of the chirp signal as illustrated at (a) inFIG.5, or may be set to a partial time section of the chirp signal as illustrated at (b) inFIG.5, for example.

Note thatFIGS.4and5illustrate examples of up-chirp waveforms in which the modulation frequency gradually increases with time, but the present disclosure is not limited thereto, and down-chirp in which the modulation frequency gradually decreases with time may be applied. Similar effects can be obtained regardless of whether the modulation frequency is of up-chirps or down-chirps.

[Exemplary Configuration of Radar Transmitter100]

InFIG.3, radar transmitter100of radar section10includes, for example, Doppler shifters101-1to101-Nt and transmission antennas102-1to102-Nt (for example, Tx #1 to Tx #Nt). Radar transmitter100may include Nt transmission antennas102, and transmission antennas102may be connected to respective different Doppler shifters101.

To apply Doppler shift amount DOPn(q) to the chirp signal inputted from VCO303, each of Doppler shifters101of qth radar section10applies phase rotation Φn,qto the chirp signal for each transmission period Trof the chirp signal, and outputs the Doppler-shifted signal to transmission antenna102.

Here, “q” represents indices for identifying a plurality of radar sections10included in radar apparatus1, and may be, for example, q=1 or 2. Further, for example, the number of transmission antennas102in each qth radar section10may be the same or may be different. Hereinafter, the number of transmission antennas in qth radar section10will be referred to as “Nt(q)” (or simply “Nt”). Here, Nt(q)>1. In addition, n=1 to Nt(q).

For example, qth radar section10may perform output while applying predetermined phase rotations Φn,q(m) for applying respective different Doppler shifts to transmission antennas102used for the multiplexing transmission of the monostatic radar (an exemplary operation will be described later). Further, qth radar section10may perform output, for example, while applying predetermined phase rotations Φn,q(m) for applying Doppler shifts for providing different Doppler multiplexing intervals (also referred to as Doppler shift intervals or Doppler intervals) between radar sections10that perform the multiplexing transmission of the multistatic radar (an exemplary operation will be described later).

The signals outputted from Doppler shifters101are amplified to a predetermined transmission power and emitted into space from respective transmission antennas102(e.g., Tx #1 to Tx #Nt).

[Exemplary Configuration of Radar Receiver200]

InFIG.3, radar receiver200includes Na reception antennas202(for example, Rx #1 to Rx #Na), and serves as a component of an array antenna. Further, radar receiver200includes Na antenna system processors201, Constant False Alarm Rate (CFAR) sections210, Doppler demultiplexers211, and direction estimators212.

Here, the number of reception antennas202may be the same or may be different between qth radar sections10(for example, q=1 or 2). Hereinafter, the number of reception antennas in qth radar section10will be referred to as “Na(q)” (also referred to simply as “Na”). Here, Na(q)≥1.

Antenna system processors201may be provided to correspond respectively to Na(q) reception antennas202, for example. In addition, CFAR sections210, Doppler demultiplexers211, and direction estimators212may be provided in each of q radar sections10, for example, to correspond to one another.

Each of Na(q) reception antennas202receives a reflected wave signal being a radar transmission signal transmitted from each of the plurality of radar sections10and reflected by a target object (for example, a reflective object including a radar measurement target), and outputs the received reflected wave signal to corresponding antenna system processor201as a reception signal. For example, reception antenna202simultaneously receives a radar reflected wave corresponding to a monostatic configuration and a radar reflected wave corresponding to a multistatic configuration.

Each of antenna system processors201includes reception radio203and signal processor206.

Reception radio203includes mixer204and low pass filter (LPF)205. In reception radio203, mixer204mixes the received reflected wave signal (reception signal) with the chirp signal that is the transmission signal. Further, a beat signal having a frequency corresponding to a delay time of the reflected wave signal is extracted by passing an output of mixer204through LPF205. For example, as illustrated inFIG.6, a difference frequency between a frequency of the transmission signal (transmission frequency-modulated wave) and a frequency of the reception signal (reception frequency-modulated wave) is obtained as the beat frequency (or beat signal).

InFIG.3, Signal processor206of each antenna system processor201-z(where z=any one of 1 to Na) includes A/D converter207, beat frequency analyzer208, and Doppler analyzer209.

The signal (for example, beat signal) outputted from LPF205is converted into discretely sampled data by A/D converter207in signal processor206.

Beat frequency analyzer208performs, for each transmission period Tr, FFT processing on Ndatapieces of discretely sampled data obtained in a predetermined time range (range gate). Here, the range gate may set frequency sweep time Tsw. Signal processor206thus outputs a frequency spectrum in which a peak appears at a beat frequency dependent on the delay time of the reflected wave signal (radar reflected wave). In the FFT processing, for example, beat frequency analyzer208may perform multiplication by a window function coefficient such as the Han window or the Hamming window. The use of the window function coefficient can suppress sidelobes around the beat frequency peak.

When Ndatais not a power of 2, zero-padded data is included, for example, to obtain the data size of a power of 2 and the FFT processing can thus be performed. In such cases, the number of data including the zero-padded data may be regarded as Ndataand treated similarly regardless of whether or not Ndatais a power of 2.

Here, a beat frequency response obtained by the mth chirp pulse transmission of the chirp signal, which is outputted from beat frequency analyzer208in zth signal processor206, is denoted as “RFTz(fb, m).” Here, fbdenotes the beat frequency index and corresponds to an FFT index (bin number). For example, fb=0 to Ndata/2−1, z=an integer of from 1 to Na, and m=an integer of from 1 to NC. A beat frequency having smaller beat frequency index fbindicates a shorter delay time of the reflected wave signal (for example, a shorter distance to the target object).

In addition, beat frequency index fbmay be converted to distance information R(fb) using Expression 1 for the monostatic configuration and Expression 2 for the multistatic configuration. Thus, in the following, beat frequency index fbis also referred to as “distance index fb.”

Here, Bwdenotes a frequency sweeping bandwidth within the range gate for a chirp signal, and C0denotes the speed of light.

For example, when Ncis a power of 2, Doppler analyzer209of qth radar section10can apply FFT processing in the Doppler analysis. Here, the FFT size is Nc, and the maximum Doppler frequency at which no aliasing occurs and which is derived from the sampling theorem is +1/(2Tr). Further, the Doppler frequency interval of Doppler frequency index fsis 1/(Nc×Tr), and the range of Doppler frequency index fsis fs=—Nc/2, . . . , 0, . . . , and Nc/2-1.

By way of example, a description will be given of a case where Ncis a power of 2. When Ncis not a power of 2, zero-padded data is included, for example, to obtain the data size of a power of 2 and the FFT processing can thus be performed. In the FFT processing, Doppler analyzer209may perform multiplication by a window function coefficient such as the Han window or the Hamming window. It is possible to suppress sidelobes generated around the beat frequency peak by applying a window function.

For example, output VFTz,q(fb, fs) from Doppler analyzer209in zth signal processor206of qth radar section10is given by following Expression 3. Here, j is an imaginary unit, z is an integer of from 1 to Na, and q is 1 or 2. Note that the beat frequency response outputted from beat frequency analyzer208in qth radar section10is expressed as “RFTz,q(fb, m”). The same applies hereinafter.

The processing in each component of signal processor206has been described above.

InFIG.3, CFAR sections210perform CFAR processing (for example, adaptive threshold determination) using the outputs from Doppler analyzers209of first to Nath signal processors206to extract distance indices fb_cfarand Doppler frequency indices fs_cfarthat provide local peak signals. As illustrated inFIG.3, CFAR sections210may include, for example, first CFAR section210(also expressed as CFAR section210-1) corresponding to the monostatic configuration, and second CFAR section210(also expressed as CFAR section210-2) corresponding to the multistatic configuration.

For example, first CFAR section210selectively extracts local peaks of the reflected wave signals (reception signals) for the radar transmission signals of qth radar section10(the corresponding radar), which has the monostatic configuration, using outputs VFT1,q(fb, fs), VFT2,q(fb, fs), . . . , and VFTNa(q),q(fb, fs) of Doppler analyzers209of first to Na(q)th signal processors206. For example, first CFAR section210may perform the CFAR processing of performing the adaptive threshold determination after power addition at intervals matching the Doppler multiplexing intervals set for the radar transmission signals transmitted from qth radar section10, extract distance indices fb_cfarand Doppler frequency indices fsddm_cfarthat provide local peak signals, and output extracted distance indices fb_cfarand Doppler frequency indices fsddm_cfarto first Doppler demultiplexer211(an exemplary operation will be described later).

The radar transmitter having the monostatic configuration in first radar section10is radar transmitter100of first radar section10. Similarly, the radar transmitter having the monostatic configuration in second radar section10is radar transmitter100of second radar section10.

Further, for example, second CFAR section210selectively extracts local peaks of the reflected wave signals for the radar transmission signals of another radar section10different from qth radar section10(the corresponding radar), which has the multistatic configuration, using outputs VFT1,q(fb, fs), VFT2,q(fb, fs), . . . , and VFTNa(q),q(fb, fs) of Doppler analyzers209of first to Na(q)th signal processors206. For example, second CFAR section210may perform the CFAR processing of performing the adaptive threshold determination after the power addition at intervals matching the Doppler multiplexing intervals set for the radar transmission signals transmitted from radar section10other than qth radar section10, extract distance indices fb_cfarand Doppler frequency indices fsddm_cfarthat provide local peak signals, and output the extracted distance indices fb_cfarand Doppler frequency indices fsddm_cfarto second Doppler demultiplexer211(an exemplary operation will be described later).

The radar transmitter having the multistatic configuration in first radar section10is radar transmitter100of second radar section10. Similarly, radar transmitter100having the multistatic configuration in second radar section10is radar transmitter100of first radar section10.

Doppler demultiplexers211may include first Doppler demultiplexer211(also referred to as Doppler demultiplexer211-1) that performs Doppler demultiplexing processing using the outputs of Doppler analyzers209and first CFAR section210, and second Doppler demultiplexer211(also referred to as Doppler demultiplexer211-2) that performs Doppler demultiplexing processing using the outputs of Doppler analyzers209and second CFAR section210.

For example, first Doppler demultiplexer211of qth radar section10performs Doppler demultiplexing on the reflected wave signals for the radar transmission signals of qth radar section10(the corresponding radar), which has the monostatic configuration, using the outputs of first CFAR section210. Further, second Doppler demultiplexer211of qth radar section10performs Doppler demultiplexing on the reflected wave signals for the radar transmission signals of another radar section10that differs from qth radar section10(the corresponding radar), which has the multistatic configuration, using the outputs of second CFAR section210, for example.

For example, first Doppler demultiplexer211outputs information on the demultiplexed signal to first direction estimator212-1. Further, second Doppler demultiplexer211outputs, for example, information on the demultiplexed signal to second direction estimator212-2. The information about the demultiplexed signal may include, for example, a distance index and a Doppler frequency index corresponding to the demultiplexed signal (which may also hereinafter be referred to as demultiplexing index information). Further, Doppler demultiplexers211outputs the outputs from Doppler analyzers209to direction estimators212.

Hereinafter, an exemplary operation of qth Doppler demultiplexer211will be described together with an exemplary operation of Doppler shifters101and qth CFAR section210. For example, q=1 or 2 may hold true.

The operation of qth Doppler demultiplexer211is related to the operation of Doppler shifters101of radar transmitter100. Similarly, the operation of qth CFAR section210is related to the operation of Doppler shifters101of radar transmitter100.

Hereinafter, an exemplary operation of Doppler shifters101will be described, and an exemplary operation of qth CFAR section210and an exemplary operation of qth Doppler demultiplexer211will then be described.

[Method for Setting Doppler Shift Amount]

To begin with, an example of a method for setting the Doppler shift amount applied in Doppler shifters101will be described.

First to Nt(q)th Doppler shifters101of qth radar section10perform Doppler multiplexing transmission by applying respective different Doppler shift amounts DOPn(q) of predetermined Doppler multiplexing intervals Δfd(q) to the chirp signals inputted from synchronization controller20. At this time, Doppler multiplexing intervals Δfd(q) may satisfy the following setting conditions (1) and (2).(1) The Doppler multiplexing intervals may be set to different intervals between the plurality of radar sections10. For example, the intervals for respective Doppler shift amounts applied to the radar transmission signals transmitted from the plurality of transmission antennas102of first radar section10and the intervals for respective Doppler shift amounts applied to the radar transmission signals transmitted from the plurality of transmission antennas102of second radar section10may be different from each other (for example, Δfd(1) #Δfd(2)).(2) For example, the ratio between Δfd(1) and Δfd(2) may be set so as not to match an integer. For example, of Δfd(1) and Δfd(2), the ratio of the Doppler multiplexing interval having the larger value to the Doppler multiplexing interval having the smaller value may be different from the integer. For example, Δfd(1)/Δfd(2) or Δfd(2)/Δfd(1) may be set so as not to match the integer (so as to be different from the integer).

Hereinafter, an example of setting Doppler multiplexing interval Δfd(q) will be described.

In the following description, the number of Doppler multiplexing for qth radar section10will be referred to as “NDM(q),” and a description is given of a case of NDM(q)=Nt(q), but the present disclosure is not limited thereto. For example, radar section10may bundle some of the plurality of transmission antennas102to form a transmission beam for performing Doppler multiplexing transmission. In this case, NDM(q)<Nt(q). Here, m is an integer of from 1 to Nc. Further, for example, index n of Doppler shift amount DOPn(q) represents an index of the Doppler multiplexed signal, and n is an integer of from 1 to NDM(q). Also, NDM(q)>1 and q=1 or 2.

For example, Doppler shifter101may apply a predetermined phase rotation (e.g., ranging from 0 to 2π) to the chirp signal at every transmission period Tr.

Here, in Doppler analyzers209, the range of Doppler frequency fdin which no aliasing is generated and which is derived from the sampling theorem is from −1/(2Tr)≤fd<1/(2Tr). For example, even when the Doppler frequency exceeds the range of Doppler frequency fdin which no aliasing occurs, the range of Doppler frequency fdobserved in Doppler analyzers209is from −1/(2Tr)≤fd<1/(2Tr).

Therefore, for example, when Doppler shifter101applies the Doppler shift within the range of −1/(2Tr)≤fd<1/(2Tr), the maximum Doppler shift interval (for example, expressed as “Δfdmax”) for Nt(q) transmission antennas102(for example, the number equal to the Doppler multiplexing number) is Δfdmax=1/(TrNt(q))=1/(TrNDM(q)). For example, Doppler shifters101may set Δfd(1) and Δfd(2) to different intervals within the range up to Δfdmax. Accordingly, Doppler shifters101can set the Doppler shift within the range of 0 to 2π that is the phase rotation providing the Doppler shift.

For example, the Doppler multiplexing intervals of each of first radar section10and second radar section10may be set to Δfd(1)=1/(Tr×(NDM(1)+δ1)) and Δfd(2)=1/(Tr×(NDM(2)+δ2)), respectively.

Here, δ1, δ2≥0 and satisfies NDM(1)+δ1≠NDM(2)+δ2. Further, δ1and δ2may be set so that the ratio between NDM(1)+δ1and NDM(2)+δ2does not match an integer. With this setting, the Doppler multiplexing interval is different between the plurality of radar sections10(for example, between first radar section10and second radar section10) (Δfd(1)≠Δfd(2)), and the ratio between Δfd(1) and Δfd(2) does not match an integer.

Note that each of δ1and δ2may be a positive integer or a positive real number. For example, by setting δ1and δ2to positive integers, the processes in first CFAR section210and second CFAR section210, which will be described later, can be simplified. Descriptions are given below of a case where δ1and δ2are each set to zero or a positive integer. However, the present disclosure is not limited thereto, and positive real numbers may be set.

In addition, when supposed situations are mostly those in which radar apparatus1and the target object are both stationary, a configuration may be adopted in which parameters (for example, values such as Doppler multiplexing intervals Δfd(q) or δq) which, for example, cause the Doppler shift amounts to match each other between first radar section10and second radar section10are excluded in advance. For example, for all of n1and n2, the parameters may be set so as to satisfy following Expression 4:

By this setting, for example, Doppler shift amount DOPn1(1) applied to the radar transmission signal of first radar section10and Doppler shift amount DOPn2(2) applied to the radar transmission signal of second radar section10are set to values different from each other.

The parameter setting satisfying Expression 4 may be applied, for example, to situations in which both radar apparatus1and the target object are supposed to be mostly stationary. For example, when radar apparatus1and the target object are both stationary, a Doppler component is zero. Therefore, for example, even when the reflected wave signal for the radar transmission signal of first radar section10and the reflected wave signal for the radar transmission signal of second radar section10are included in the same distance index, Doppler shift amount DOPn(q) for each MIMO multiplexed transmission signal is different. Thus, radar apparatus1can demultiplex and receive both the reflected wave signals by utilizing the difference in detected Doppler components.

A description is given below of exemplary setting of Doppler shift amounts.

Setting Example 1

For example, when NDM(1) #NDM(2) and the ratio of NDM(1) to NDM(2) does not match an integer multiple, then Δfd(1)=1/(Tr×NDM(1)) and Δfd(2)=1/(Tr×NDM(2)) may be set. In this case, the above-described setting conditions of the Doppler multiplexing intervals are satisfied.

In this case, the Doppler multiplexing interval can be maximized within the range of −1/(2Tr)≤fd<1/(2Tr) of Doppler frequencies fdobserved by Doppler analyzers209. Therefore, for example, even in a case where the Doppler spectrum has a spread, such as a case where the moving speed of the target is not constant and has a component such as acceleration, the interference effect between the Doppler multiplexed signals can be reduced. For example, when a Doppler velocity observable by using non-uniformity of Doppler multiplexing intervals as disclosed in PTL 1 does not increase, the Doppler velocity is −1/(2Tr×NDM(1))≤fd<1/(2Tr×NDM(1)) or −1/(2Tr×NDM(2))≤fd<1/(2Tr×NDM(2)).

By way of example,FIG.7illustrates an example of Doppler shift setting of first radar section10(upper part ofFIG.7) and an example of Doppler shift setting of second radar section10(lower part ofFIG.7) in a case of NDM(1)=Nt(1)=3 and NDM(2)=Nt(2)=4. InFIG.7, Δfd(1)=1/(3Tr) (e.g., δ1=0) is set and Δfd(2)=1/(4Tr) (e.g., δ2=0) is set. For example, inFIG.7, Doppler shift amounts DOP1(1) and DOP1(2) assigned to first transmission antennas102(Tx #1) of first radar section10and second radar section10are set to values corresponding to Doppler frequency fd=0. For example, inFIG.7, at least one Doppler shift amounts match each other between first radar section10and second radar section10.

By way of another example,FIG.8illustrates an example of Doppler shift setting of first radar section10(upper part ofFIG.8) and an example of Doppler shift setting of second radar section10(lower part ofFIG.8) in the case of NDM(1)=Nt(1)=3 and NDM(2)=Nt(2)=4. InFIG.8as inFIG.7, Δfd(1)=1/(3Tr) (e.g., δ1=0) is set, and Δfd(2)=1/(4Tr) (e.g., δ2=0) is set. Further, inFIG.8, Doppler shift amounts DOPn1(1) and DOPn2(2) applied to respective transmission antennas102of first radar section10and second radar section10are set so that the Doppler shift amounts do not match each other between first radar section10and second radar section10(for example, so as to satisfy Expression 4).

Setting Example 2

For example, when NDM(1) #NDM(2) and the ratio of NDM(1) and NDM(2) matches an integer, then the above-described Doppler multiplexing interval setting conditions are satisfied when Δfd(1)=1/(Tr×(NDM(1)+1)) and fd(2)=1/(Tr×(NDM(2)+1)) are set, when Δfd(1)=1/(Tr×NDM(1)) and Δfd(2)=1/(Tr×(NDM(2)+1)) are set, or when Δfd(1)=1/(Tr×(NDM(1)+1)) and Δfd(2)=1/(Tr×NDM(2)) are set.

In this case, the Doppler multiplexing interval can be maximized within the range of −1/(2Tr)≤fd<1/(2Tr) of Doppler frequencies fdobserved by Doppler analyzers209. Therefore, for example, even in a case where the Doppler spectrum has a spread, such as a case where the moving speed of the target is not constant and has a component such as acceleration, the interference effect between the Doppler multiplexed signals can be reduced.

Further, for example, when the Doppler multiplexing intervals include a non-uniform part, the Doppler velocity observable by using the non-uniformity of the Doppler intervals is −1/(2Tr)≤fd<1/(2Tr) as disclosed in PTL 1.

By way of example,FIG.9illustrates an example of Doppler shift setting of first radar section10(upper part ofFIG.9) and an example of Doppler shift setting of second radar section10(lower part ofFIG.9) in a case of NDM(1)=Nt(1)=2 and NDM(2)=Nt(2)=4. InFIG.9, Δfd(1)=1/(3Tr) (e.g., § 1=1) is set and Δfd(2)=1/(4Tr) (e.g., δ2=0) is set. For example, inFIG.9, Doppler shift amounts DOP1(1) and DOP1(2) assigned to first transmission antennas102(Tx #1) of first radar section10and second radar section10are set to values corresponding to Doppler frequency fd=0. For example, inFIG.9, at least one Doppler shift amounts match each other between first radar section10and second radar section10.

Further, for example, regarding the Doppler shifts set for first radar section10illustrated inFIG.9, a Doppler shift for providing an interval of Δfd(1) is not assigned on the negative side and thus a non-uniform Doppler multiplexing interval portion is included. For example, the Doppler shift intervals set for first radar section10are set to one of intervals obtained by unequally dividing the Doppler frequency range to be subjected to the Doppler analysis.

By way of another example,FIG.10illustrates an example of Doppler shift setting of first radar section10(upper part ofFIG.10) and an example of Doppler shift setting of second radar section10(lower part ofFIG.10) in the case of NDM(1)=Nt(1)=2 and NDM(2)=Nt(2)=4. InFIG.10as inFIG.9, Δfd(1)=1/(3Tr) (e.g., δ1=1) is set, and Δfd(2)=1/(4Tr) (e.g., δ2=0) is set. Further, inFIG.10, Doppler shift amounts DOPn1(1) and DOPn2(2) applied to respective transmission antennas102of first radar section10and second radar section10are set so that the Doppler shift amounts do not match each other between first radar section10and second radar section10(for example, so as to satisfy Expression 4).

Further, for example, regarding the Doppler shifts set for first radar section10illustrated inFIG.10, a Doppler shift for providing an interval of Δfd(1) is not assigned on the negative side and thus a non-uniform Doppler multiplexing interval portion is included. For example, the Doppler shift intervals set for first radar section10are set to one of intervals obtained by unequally dividing the Doppler frequency range to be subjected to the Doppler analysis.

In the Doppler frequency domain, the position where no Doppler shift is assigned is not limited to the negative-side region as illustrated inFIGS.9and10, and may be a positive-side region.

Setting Example 3

For example, when NDM(1)=NDM(2), the above-described setting conditions for the Doppler multiplexing interval are satisfied when Δfd(1)=1/(Tr×NDM(1)) and Δfd(2)=1/(Tr×(NDM(2)+1)) are set, Δfd(1)=1/(Tr×(NDM(1)+1)) and Δfd(2)=1/(Tr×NDM(2)) are set, or Δfd(1)=1/(Tr×(NDM(1)+1)) and Δfd(2)=1/(Tr×(NDM(1)+2)) are set.

In this case, the Doppler multiplexing interval can be maximized within the range of −1/(2Tr)≤fd<1/(2Tr) of Doppler frequencies fdobserved by Doppler analyzers209. Therefore, for example, even in a case where the Doppler spectrum has a spread, such as a case where the moving speed of the target is not constant and has a component such as acceleration, the interference effect between the Doppler multiplexed signals can be reduced. Further, for example, when the Doppler multiplexing intervals include a non-uniform part, the Doppler velocity observable by using the non-uniformity of the Doppler intervals is −1/(2Tr)≤fd<1/(2Tr) as disclosed in PTL 1.

By way of example,FIG.11illustrates an example of Doppler shift setting of first radar section10(upper part ofFIG.11) and an example of Doppler shift setting of second radar section10(lower part ofFIG.11) in a case of NDM(1)=Nt(1)=2 and NDM(2)=Nt(2)=2. InFIG.11, Δfd(1)=1/(3Tr) (e.g., δ1=1) is set, and Δfd(2)=1/(4Tr) (e.g., δ2=2) is set. For example, inFIG.11, Doppler shift amounts DOP1(1) and DOP1(2) assigned to first transmission antennas102(Tx #1) of first radar section10and second radar section10are set to values corresponding to Doppler frequency fd=0. For example, inFIG.11, at least one Doppler shift amounts match each other between first radar section10and second radar section10.

Further, for example, regarding the Doppler shifts set for first radar section10illustrated inFIG.11, a Doppler shift for providing an interval of Δfd(1) is not assigned on the negative side and thus a non-uniform Doppler multiplexing interval portion is included. Further, for example, regarding the Doppler shifts set for second radar section10illustrated inFIG.11, two Doppler shifts for providing an interval of Δfd(2) are not assigned on the negative side and thus a non-uniform Doppler multiplexing interval portion is included. For example, the Doppler shift interval set for each of first radar section10and second radar section10is set to one of intervals obtained by unequally dividing the Doppler frequency range to be subjected to the Doppler analysis.

By way of another example,FIG.12illustrates an example of Doppler shift setting of first radar section10(upper part ofFIG.12) and an example of Doppler shift setting of second radar section10(lower part ofFIG.12) in the case of NDM(1)=Nt(1)=2 and NDM(2)=Nt(2)=2. InFIG.12as inFIG.11, Δfd(1)=1/(3Tr) (e.g., δ1=1) is set, and Δfd(2)=1/(4Tr) (e.g., δ2=2) is set. Further, inFIG.12, Doppler shift amounts DOPn1(1) and DOPn2(2) applied to respective transmission antennas102of first radar section10and second radar section10are set so that the Doppler shift amounts do not match each other between first radar section10and second radar section10(for example, so as to satisfy Expression 4).

Further, for example, regarding the Doppler shifts set for first radar section10illustrated inFIG.12, a Doppler shift for providing an interval of Δfd(1) is not assigned on the negative side and thus a non-uniform Doppler multiplexing interval portion is included. Further, for example, regarding the Doppler shifts set for second radar section10illustrated inFIG.12, two Doppler shifts for providing an interval of Δfd(2) are not assigned on the positive side and thus a non-uniform Doppler multiplexing interval portion is included. For example, the Doppler shift interval set for each of first radar section10and second radar section10is set to one of intervals obtained by unequally dividing the Doppler frequency range to be subjected to the Doppler analysis.

The example of setting the doppler shift amounts have been described above.

As described above, setting the Doppler multiplexing intervals for each of first radar section10and second radar section10is performed such that the above-described setting conditions for Doppler multiplexing intervals are satisfied. This setting of the Doppler multiplexing intervals makes it more likely for the Doppler components corresponding to the radar reflected waves (reception signals) for the radar transmission signals from first radar section10and second radar section10to appear at respective different positions within the range of −1/(2Tr)≤fd<1/(2Tr) of Doppler frequencies fdobserved by Doppler analyzers209, and facilitates demultiplexing the reflected wave signals corresponding to first radar section10and second radar section10from each other.

By way of example,FIG.13illustrates an example of outputs (for example, reception Doppler frequencies) of Doppler analyzers209in a case where reflected wave signals for radar transmission signals from first radar section10and second radar section10are received. InFIG.13, the vertical axis represents the distance axis, and the horizontal axis represents the Doppler frequency axis. Further, inFIG.13, Doppler components having high power are represented by arrows.

When the Doppler components corresponding to interval Δfd(1) or the Doppler components corresponding to an integer multiple of interval Δfd(1) are observed at distance index fb1 or fb2 illustrated inFIG.13, radar apparatus1can distinguish (or detect) that these Doppler components are reflected wave signals for the radar transmission signals transmitted from first radar section10.

Further, when the Doppler components corresponding to interval Δfd(2) or the Doppler components corresponding to an integer multiple of interval Δfd(2) are observed at distance index fb3 or fb4 illustrated inFIG.13, radar apparatus1can distinguish that these Doppler components are reflected wave signals for the radar transmission signals transmitted from second radar section10.

Further, when a Doppler component that matches interval Δfd(1) (or an integer multiple of Δfd(1)) and a Doppler component that matches the interval of Δfd(2) (or an integer multiple of Δfd(2)) are observed in a mixed manner at distance index fb5 illustrated inFIG.13, radar apparatus1can distinguish the reflected wave signals for the radar transmission signals transmitted from first radar section10and the reflected wave signals for the radar transmission signals transmitted from second radar section10, for example, based on the intervals of the Doppler components.

As described above, radar apparatus1can distinguish whether the observed Doppler components are the reflected wave signals for the radar transmission signals transmitted from the radar section of first radar section10or from second radar section10, based on the difference between the Doppler multiplexing intervals of the Doppler multiplexing transmissions in first radar section10and the Doppler multiplexing intervals of the Doppler multiplexing transmissions in second radar section10.

For example, Doppler shifters101may set the Doppler shift amount corresponding to each transmission antenna102using the Doppler multiplexing interval set as described above, and apply the phase rotation for applying the Doppler shift amount to the chirp signal at each chirp transmission period.

For example, nth Doppler shifter101of qth radar section10applies, to the mth chirp signal as input, phase rotation Φn,q(m) for applying Doppler shift amount DOPn(q) different for each nth transmission antenna102, and outputs the resultant signal. As a result, different Doppler shifts are applied to the transmission signals transmitted respectively from multiple transmission antennas102.

Here, n is an integer of from 1 to Nt(q), m is an integer of from 1 to Nc, and q is 1 or 2.

For example, phase rotations Φn,q(m) for applying Doppler shift amounts DOPn(q) for Doppler shift intervals Δfd(q) to the radar transmission signals transmitted from Nt(q) (e.g., Nt(q)=NDM(q)) transmission antennas102are expressed by following Expression 5. Expression 6 represents Doppler shift amounts DOPn(q) for Doppler shift intervals Δfd(q).

In the expression, Φ0is the initial phase and ΔΦ0is a reference Doppler shift phase. Note that α is a coefficient for offsetting the Doppler shift amount for each Doppler multiplexed signal and a real value may be used for the coefficient. For example, when α=1, the Doppler shift amount for the first Doppler multiplexed signal is zero.

For example, when Nt(1)=Nt(2)=3, ΔΦ0=0, Φ0=0, δ1=1, and δ2=2, the Doppler multiplexing intervals are set to Δfd(1)=1/(4Tr) and Δfd(2)=1/(5Tr). Further, for example, when α=1, Doppler shift amount DOPn(q) corresponding to nth transmission antenna102is expressed by following Expression 7:

Further, for example, phase rotations Φn,q(m) for applying Doppler shift amounts DOPn(q) different for nth (n=1, 2, 3) transmission antennas102to the mth chirp signal as input are expressed by following Expression 8:

For example, when first radar section10performs Doppler multiplexing transmission using number Nt of transmission antennas=3, first Doppler shifter101in first radar section10applies phase rotation Φ1,1(m) to the chirp signal inputted from synchronization controller20for each transmission period Tras shown in following Expression 9. The output of first Doppler shifter101is output from, for example, first transmission antenna102(Tx #1). Here, cp(t) denotes the chirp signal for each transmission period.

Further, as illustrated in following Expression 10, for example, second Doppler shifter101in first radar section10applies, for each transmission period Tr, phase rotation Φ2,1(m) to the chirp signal inputted from synchronization controller20. The output of second Doppler shifter101is output from, for example, second transmission antenna102(Tx #2).

Similarly, for example, as illustrated in following Expression 11, third Doppler shifter101in first radar section10applies, for each transmission period Tr, phase rotation Φ3,1(m) to the chirp signal inputted from synchronization controller20. The output of third Doppler shifter101is output from, for example, third transmission antenna102(Tx #3).

Further, for example, when second radar section10performs Doppler multiplexing transmission using number Nt of transmission antennas=3, first Doppler shifter101in second radar section10applies, for each transmission period Tr, phase rotation Φ1,2(m) to the chirp signal inputted from synchronization controller20, as illustrated in following Expression 12. The output of first Doppler shifter101is output from, for example, first transmission antenna102(Tx #1). Here, cp(t) denotes the chirp signal for each transmission period.

Further, for example, second Doppler shifter101in second radar section10applies phase rotation Φ2,2(m) to the chirp signal inputted from synchronization controller20, as illustrated in following Expression 13, for each transmission period Tr. The output of second Doppler shifter101is output from, for example, second transmission antenna102(Tx #2).

Similarly, for example, third Doppler shifter101in second radar section10applies phase rotation Φ3,2(m) to the chirp signal inputted from synchronization controller20for each transmission period Tras illustrated in following Expression 14. The output of third Doppler shifter101is output from, for example, third transmission antenna102(Tx #3).

The example of setting the doppler shift amounts has been described above.

Next, an exemplary operation of first CFAR section210, second CFAR section210, first Doppler demultiplexer211, and second Doppler demultiplexer211in qth radar section10corresponding to the operation of Doppler shifters101described above will be described.

[Exemplary Operation of First CFAR Section210]

For example, in order to receive the reflected wave signals for the radar transmission signals from radar transmitter100of qth radar section10, first CFAR section210of qth radar section10may perform the following operation.

For example, when δ1and δ2are set to values that differ from positive integers for Doppler shifters101, first CFAR section210may perform peak detection by, for example, searching, in the power addition values outputted from Doppler analyzers209of first to Na(q)th signal processors206, for a power peak that matches the Doppler shift intervals set for the radar transmission signals of qth radar section10for each distance index, and performing adaptive threshold processing (CFAR processing).

On the other hand, for example, when δ1and δ2are set to positive integers for Doppler shifters101, an interval of Δfd(q) or an interval of an integer multiple of Δfd(q) is used as an interval of the Doppler shift amounts. Here, q may be 1 or 2. Therefore, Doppler multiplexed signals can be detected as aliasing at an interval of Δfd(q) in the Doppler frequency domain of the outputs of Doppler analyzers209. By using such characteristics, for example, the operation of first CFAR section210can be simplified as follows.

For example, first CFAR section210of qth radar section10detects a Doppler peak by applying a threshold to a power addition value obtained by adding together the reception powers of the reflected wave signals for respective ranges (for example, ranges of Δfd(q)) within the Doppler frequency range that is outputted from Doppler analyzers209and subjected to the CFAR processing, the ranges corresponding to the intervals of the Doppler shift amounts applied respectively to the radar transmission signals.

For example, first CFAR section210performs the CFAR processing on the outputs from Doppler analyzers209of first to Na(q)th signal processors206by calculating power addition value PowerDDMq(fb, fsddm) obtained by adding power values PowerqFT(fb, fs) at the intervals of Δfd(q) (for example, corresponding to NΔfd(q)) as illustrated in following Expressions 15 and 16:

In the expressions, fsddm=−Nc/2, . . . , and −Nc/2+NΔfd(q)−1 and NΔfd(q)=round (Δfd(q)/(1/(TrNc). In addition, round(x) is an operator that rounds off real number x and outputs an integer value.

The operation in the CFAR processing may be based on the operation disclosed in NPL 3, for example, and detailed explanation of the exemplary operation is omitted.

Accordingly, the range of the Doppler frequencies subjected to the CFAR processing in first CFAR section210can be set (for example, reduced) to 1/(Nt(q)+δq)=1/(NDM(q)+δq) of the entire range (for example, the range of from —Nc/2 to Nc/2−1). It is thus possible to reduce the computational amount of the CFAR processing.

For example, first CFAR section210adaptively sets a threshold, and outputs, to first Doppler demultiplexer211, distance indices fb_cfar, Doppler frequency indices fsddm_cfar, and the reception power information (PowerFT(fb_cfar, fsddm_cfar+(ndm−1)×NΔfd(q))) that provide reception power greater than the threshold. In the expression, ndm is an integer of from 1 to NDM(q)+δq.

[Exemplary Operation of First Doppler Demultiplexer211]

First Doppler demultiplexer211performs the following operations, for example, based on distance indices fb_cfar, Doppler frequency indices fsddm_cfar, and the reception power information (PowerFT(fb_cfar, fsddm_cfar+(ndm−1)×NΔfd(q))) (ndm is an integer of from 1 to NDM(q)+δq)) inputted from first CFAR section210.

<(1) Case of δq=0>

For example, assuming that the Doppler velocity of the target object is −1/(2Tr×NDM(q))≤fd<1/(2Tr×NDM(q)), first Doppler demultiplexer211associates the Doppler shift amounts of the Doppler multiplexed signals to be transmitted with fsddm_cfar+(ndm−1)×NΔfd(q), and outputs, to first direction estimator212, the resulting demultiplexing index information (for example, fdemul_Tx#1(q), . . . , and fdemul_Tx#NDM(q)) of the Doppler multiplexed signals.

Here, fdemul_Tx#n(q) indicates the Doppler frequency index of the reflected wave signal for the radar transmission signal transmitted from nth transmission antenna102(Tx #n) of qth radar section10.

By way of example, a Doppler shift setting example illustrated inFIG.7in which NDM(1)=Nt(1)=3 and NDM(2)=Nt(2)=4 will be described. In this case, Δfd(1)=1/(3Tr) and Δfd(2)=1/(4Tr).

Here, it may be assumed that the Doppler frequencies of the reflected wave signals for the radar transmission signals transmitted from first radar section10, which are received by first radar section10, are −1/(2Tr×NDM(1))≤fd<1/(2Tr×NDM(1)). Therefore, inFIG.7, the demultiplexing index information (fdemul_Tx#1(1), fdemul_Tx#2(1), and fdemul_Tx#3(1)) of the Doppler multiplexed signals for fsddm_cfar+(ndm−1)×NΔfd(1)has a correspondence relation of fdemul_Tx#3(1)<fdemul_Tx#1(1)<fdemul_Tx#2(1). First Doppler demultiplexer211may, for example, output each of fsddm_cfar+(ndm−1)×NΔfd(1)(ndm is an integer of from 1 to 3) as fdemul_Tx#3(1), fdemul_Tx#1(1), and fdemul_Tx#2(1).

Similarly, it may be assumed that the Doppler frequencies of the reflected wave signals for the radar transmission signals transmitted from second radar section10and received by second radar section10are −1/(2Tr×NDM(2))≤fd<1/(2Tr×NDM(2)). Therefore, inFIG.7, the demultiplexing index information (fdemul_Tx#1(2), fdemul_Tx#2(2), fdemul_Tx#3(2), and fdemul_Tx#4(2)) of the Doppler multiplexed signals for fsddm_cfar+(ndm−1)×NΔfd(2)has a correspondence relation of fdemul_Tx#3(2)<fdemul_Tx#4(2)<fdemul_Tx#1(2)<fdemul_Tx#2(2) when 0≤fd<1/(2Tr×NDM(1)). In this case, first Doppler demultiplexer211may, for example, output each of fsddm_cfar+(ndm−1)×NΔfd(2)(ndm is an integer of from 1 to 4) as fdemul_Tx#3(2), fdemul_Tx#4(2), fdemul_Tx#1(2) and fdemul_Tx#2(2). In addition, inFIG.7, the demultiplexing index information (fdemul_Tx#1(2), fdemul_Tx#2(2), fdemul_Tx#3(2), and fdemul_Tx#4(2)) of the Doppler multiplexed signals for fsddm_cfar+(ndm−1)×NΔfd(2)has a correspondence relation of fdemul_Tx#4(2)<fdemul_Tx#1(2)<fdemul_Tx#2(2)<fdemul_Tx#3(2) when −1/(2Tr×NDM(1))≤fd<0). Here, first Doppler demultiplexer211may, for example, output each of fsddm_cfar+(ndm−1)×NΔfd(2)(ndm is an integer of from 1 to 4) as fdemul_Tx#4(2), fdemul_Tx#1(2), fdemul_Tx#2(2), and fdemul_Tx#3(2).

When a difference between the powers for NDM(q) Doppler frequency indices is larger than a predetermined value (for example, a threshold), first Doppler demultiplexer211may regard (or determine) that the components of the reception signal for the multistatic configuration are highly likely to be mixed, and may add an operation of removing a reception signal without outputting the reception signal to subsequent processing (for example, direction estimation processing).

<(2) Case of δq>0>

For example, it may be assumed that the Doppler velocity of the target object is −1/(2Tr)≤fd<1/(2Tr). Further, a large difference between, on one hand, the reception levels for top NDM(q) Doppler frequency indices of reception power and, on the other hand, the reception levels for δqDoppler frequency indices different from the top NDMDoppler frequency indices of reception power (for example, the difference being equal to or greater than the threshold) may be used. For example, first Doppler demultiplexer211compares the reception power information inputted from first CFAR section210and determines the Doppler frequency in the range of −1/(2Tr)≤fd<1/(2Tr). Note that an exemplary operation of first Doppler demultiplexer211is disclosed in, for example, PTL 1, and therefore description of the exemplary operation is omitted here.

For example, first Doppler demultiplexer211associates the Doppler shift amounts of the transmitted Doppler multiplexed signals with fsddm_cfar+(ndm−1)×NΔfd(q)based on the relation between δqDoppler frequency indices of a lower reception level and top NDMDoppler frequency indices of a higher reception power, and performs an output to first direction estimator212as demultiplexing index information (fdemul_Tx#1(q), . . . , and fdemul_Tx#NDM(q)) of the Doppler multiplexed signals.

Here, fdemul_Tx#n(q) indicates the Doppler frequency index of the reflected wave signal for the radar transmission signal transmitted from nth transmission antenna102(Tx #n) of qth radar section10.

By way of example,FIG.14illustrates an example of an output (for example, a reception Doppler frequency) of Doppler analyzer209in a case where a reflected wave signal with respect to a radar transmission signal from first radar section10is received. InFIG.14, the vertical axis represents the distance axis, and the horizontal axis represents the Doppler frequency axis.

For example, when the Doppler components corresponding to interval Δfd(1) or the Doppler components corresponding to an integer multiple of interval Δfd(1) are observed at distance index fb1 illustrated inFIG.14, first Doppler demultiplexer211can distinguish (for example, detect) that these Doppler components are reflected wave signals for radar transmission signals transmitted from first radar section10.

Further, for example, inFIG.14, δq(=1) Doppler frequency index for a lower reception level is indicated by mark “o,” and top NDM(=2) Doppler frequency indices of reception power are indicated by marks “x” and “Δ.” For example, since the Doppler components (mark “o” inFIG.14) that do not match the interval of Δfd(1) are uniquely determined in the range of −1/(2Tr)≤fd<1/(2Tr), first Doppler demultiplexer211can uniquely determine the Doppler velocity of the target object in the range of −1/(2Tr)≤fd<1/(2Tr).

Further, first Doppler demultiplexer211can determine the association between the Doppler frequencies and transmission antennas102, for example, based on the magnitude relationship between the Doppler frequency indices (mark “o” inFIG.14) that do not match the interval of Δfd(1) and other Doppler frequency indices (mark “x” inFIG.14) that match the interval of Δfd(1).

By way of example, a description will be given in which at distance index fb1 ofFIG.14, NDM(1)=Nt(1)=2, a radar transmission signal is transmitted by assigning Tx #1 to the Doppler frequency (mark “x” inFIG.14) higher by Δfd(1) than the Doppler frequency index (mark “o” inFIG.14), and a radar transmission signal is transmitted by assigning Tx #2 to the Doppler frequency (mark “Δ” inFIG.14) lower by Δfd(1) than the Doppler frequency index (mark “o” inFIG.14).

In this case, at distance index fb1 ofFIG.14, first Doppler demultiplexer211, for example, detects δq(=1) Doppler frequency index for a lower reception level (“o” inFIG.14), and can thus determine that the Doppler frequency (mark “x” inFIG.14) higher by Δfd(1) than the detected Doppler frequency corresponds to Tx #1 and the Doppler frequency (mark “Δ” inFIG.14) lower by Δfd(1) than the detected Doppler frequency corresponds to Tx #2.

Further, it is, for example, assumed that at distance index fb2 ofFIG.14, the same assignment of the Doppler multiplexed signals as at distance index fb1 is performed. In this case, for example, as is seen at distance index fb2 ofFIG.14, there may be a case where δq(=1) Doppler frequency index for a lower reception level (“o” inFIG.14) is lower by Δfd(1) than top NDM(=2) Doppler frequency indices of reception power. In this case, the Doppler frequency range that can be observed by Doppler analyzers209is a range of −1/(2Tr)≤fd<1/(2Tr), and the Doppler frequency (mark “Δ” inFIG.14) that is lower by Δfd(1) than δq(=1) Doppler frequency index (mark “o” inFIG.14) for a lower reception level can be observed with aliasing on the higher-frequency side. Since first Doppler demultiplexer211can assume the occurrence of such aliasing in advance, first Doppler demultiplexer211can, for example, detect δq(=1) Doppler frequency index (mark “o” inFIG.14) for a lower reception level, and can thus determine that the Doppler frequency (mark “x” inFIG.14) higher by Δfd(1) than the detected Doppler frequency for the lower reception level corresponds to Tx #1 and the Doppler frequency (mark “Δ” inFIG.14) even higher by Δfd(1) than the detected Doppler frequency for the lower reception level corresponds to Tx #2.

Likewise, it is, for example, assumed that also at distance index fb3 ofFIG.14, the same assignment of the Doppler multiplexed signals as at distance index fb1 is performed. In this case, for example, as is seen at distance index fb3 ofFIG.14, there may be a case where δq(=1) Doppler frequency index for a lower reception level (“o” inFIG.14) is higher by Δfd(1) than top NDM(=2) Doppler frequency indices of reception power. In this case, the Doppler frequency range that can be observed by Doppler analyzers209is a range of −1/(2Tr)≤fd<1/(2Tr), and the Doppler frequency (mark “x” inFIG.14) that is higher by Δfd(1) than δq(=1) Doppler frequency index (mark “o” inFIG.14) for the lower reception level can be observed with aliasing on the lower-frequency side. Since first Doppler demultiplexer211can assume the occurrence of such aliasing in advance, first Doppler demultiplexer211can determine that, for example, the Doppler frequency (mark “Δ” inFIG.14) lower by Δfd(1) than δq(=1) Doppler frequency index (mark “o” inFIG.14) for the lower reception level corresponds to Tx #2 and the Doppler frequency (mark “x” in FIG.14) even lower by Δfd(1) than the detected Doppler frequency for the lower reception level corresponds to Tx #1.

When the difference between the powers for top NDM(q) Doppler frequency indices of reception power is larger than a predetermined value (threshold), first Doppler demultiplexer211may regard (or determine) that signals of the reception signals of the multistatic configuration are highly likely to be mixed, and may add an operation of removing the reception signals without performing an output for subsequent processing (for example, direction estimation processing).

The exemplary operation of first Doppler demultiplexer211has been described above.

[Exemplary Operation of Second CFAR Section210]

For example, second CFAR section210of qth radar section10may perform the following operations in order to receive the reflected wave signal for the radar transmission signal from radar transmitter100of radar section10that differs from qth radar section10.

For example, when δ1and δ2are set to values that differ from positive integers for Doppler shifters101, second CFAR section210may perform peak detection by, for example, searching, in the power addition values outputted from Doppler analyzers209of first to Na(q)th signal processors206, for a power peak that matches the Doppler shift interval set for the radar transmission signal of radar section10different from qth radar section10for each distance index, and performing adaptive threshold processing (CFAR processing).

On the other hand, for example, when δ1and δ2are set to positive integers for Doppler shifters101, an interval of Δfd(q) or an interval of an integer multiple of Δfd(q) is used as an interval of the Doppler shift amounts. In this case, q may be 1 or 2. Therefore, Doppler multiplexed signals can be detected as aliasing at an interval of Δfd(q) in the Doppler frequency domain of the outputs of Doppler analyzers209. By using such characteristics, for example, the operation of second CFAR section210can be simplified as follows.

For example, second CFAR section210of qth radar section10detects a Doppler peak by applying a threshold to a power addition value obtained by adding together the reception powers of the reflected wave signals for respective ranges (for example, ranges of Δfd(qe)) within the Doppler frequency range that is outputted from Doppler analyzers209and subjected to the CFAR processing, the ranges corresponding to the intervals of the Doppler shift amounts applied respectively to the radar transmission signals.

Here, “qe” represents a radar number of radar section10that differs from qth radar section10. For example, “qe” may be 2 in the case of first radar section10(q=1), or “qe” may be 1 in the case of second radar section10(q=2).

For example, second CFAR section210performs the CFAR processing on the outputs from Doppler analyzers209of first to Na(q)th signal processors206by calculating power addition value PowerDDMqe(fb, fsddm) obtained by adding power values PowerqFT(fb, fs) at the intervals of Δfd(qe) (for example, corresponding to NΔfd(qe)) as illustrated in following Expression 17:

In the expressions, fsddm=−Nc/2, . . . , and −Nc/2+NΔfd(qe)−1 and NΔfd(qe)=round(Δfd(qe)/(1/(TrNc). In addition, round(x) is an operator that rounds off real number x and outputs an integer value.

The operation in the CFAR processing may be based on the operation disclosed in NPL 3, for example, and detailed explanation of the exemplary operation is omitted.

Thus, the Doppler frequency range on which the CFAR processing is performed in second CFAR section210can be set (e.g., reduced) to 1/(Nt(qe)+δqe)=1/(NDM(qe)+δqeof the entire range (e.g., the range of −Nc/2 to Nc/2−1), thereby reducing the computational amount of the CFAR processing.

For example, second CFAR section210adaptively sets a threshold, and outputs, to second Doppler demultiplexer211, distance indices fb_cfar, Doppler frequency indices fsddm_cfar, and the reception power information (PowerFT(fb_cfar, fsddm_cfar+(ndm−1)×NΔfd(qe))) that provide reception power greater than the threshold. Here, ndm is an integer of from 1 to NDM(qe)+δqe.

[Exemplary Operation of Second Doppler Demultiplexer211]

Second Doppler demultiplexer211performs the following operations based on, for example, distance indices fb_cfar, Doppler frequency indices fsddm_cfar, and the reception power information (PowerFT(fb_cfar, fsdm_cfar+(ndm−1)×NΔfd(qe))) (ndm is an integer of from 1 to NDM(qe)+δqe)) inputted from second CFAR section210.

<(1) Case of δqe=0>

For example, assuming that the Doppler velocity of the target object is −1/(2Tr×NDM(qe))≤fd<1/(2Tr×NDM(qe)), second Doppler demultiplexer211associates the Doppler shift amounts of the Doppler multiplexed signals to be transmitted with fsddm_cfar+(ndm−1)×NΔfd(qe), and outputs, to second direction estimator212, the resulting demultiplexing index information (for example, fdemul_Tx#1(qe), . . . , and fdemul_Tx#NDM(qe)) of the Doppler multiplexed signals.

Here, fdemul_Tx#n(qe) indicates the Doppler frequency index of the reflected wave signal for the radar transmission signal transmitted from nth transmission antenna102(Tx #n) of qeth radar section10.

By way of example, a Doppler shift setting example illustrated inFIG.7in which NDM(1)=Nt(1)=3 and NDM(2)=Nt(2)=4 will be described. In this case, Δfd(1)=1/(3Tr) and Δfd(2)=1/(4Tr).

Here, it may be assumed that the Doppler frequencies of the reflected wave signals for the radar transmission signals transmitted from second radar section10, which are received by first radar section10, are −1/(2Tr×NDM(2))≤fd<1/(2Tr×NDM(2)). Therefore, inFIG.7, the demultiplexing index information (fdemul_Tx#1(2), fdemul_Tx#2(2), fdemul_Tx#3(2), and fdemul_Tx#4(2)) of the Doppler multiplexed signals for fsddm_cfar+(ndm−1)×NΔfd(2)has a correspondence relation of fdemul_Tx#3(2)<fdemul_Tx#4(2)<fdemul_Tx#1(2)<fdemul_Tx#2(2) when 0≤fd<1/(2Tr×NDM(1)). In this case, second Doppler demultiplexer211may, for example, output each of fsddm_cfar+(ndm−1)×NΔfd(2)(ndm is an integer of from 1 to 4) as fdemul_Tx#3(2), fdemul_Tx#4(2), fdemul_Tx#1(2) and fdemul_Tx#2(2). In addition, inFIG.7, the demultiplexing index information (fdemul_Tx#1(2), fdemul_Tx#2(2), fdemul_Tx#3(2), and fdemul_Tx#4(2)) of the Doppler multiplexed signals for fsddm_cfar+(ndm−1)×NΔfd(2)has a correspondence relation of fdemul_Tx#4(2)<fdemul_Tx#1(2)<fdemul_Tx#2(2)<fdemul_Tx#3(2) when −1/(2Tr×NDM(1))≤fd<0). In this case, second Doppler demultiplexer211may, for example, output each of fsddm_cfar+(ndm−1)×NΔfd(2)(ndm is an integer of from 1 to 4) as fdemul_Tx#3(2), fdemul_Tx#4(2), fdemul_Tx#1(2) and fdemul_Tx#2(2).

Similarly, it may be assumed that the Doppler frequency of the radar reflected wave for the radar transmission signal transmitted from first radar section10received by second radar section10is −1/(2Tr×NDM(1))≤fd<1/(2Tr×NDM(1)). Therefore, inFIG.7, the demultiplexing index information (fdemul_Tx#1(1), fdemul_Tx#2(1), and fdemul_Tx#3(1)) of the Doppler multiplexed signals for fsddm_cfar+(ndm−1)×NΔfd(1)has a correspondence relation of fdemul_Tx#3(1)<fdemul_Tx#1(1)<fdemul_Tx#2(1). Second Doppler demultiplexer211may, for example, output each of fsddm_cfar+(ndm−1)×NΔfd(1)(ndm is an integer of from 1 to 3) as fdemul_Tx#3(1), fdemul_Tx#1(1), and fdemul_Tx#2(1).

When a difference between the powers for NDM(qe) Doppler frequency indices is larger than a predetermined value (for example, a threshold), second Doppler demultiplexer211may regard (or determine) that the reception signals for the monostatic configuration are highly likely to be mixed, and may add an operation of removing a reception signal without outputting the reception signal to subsequent processing (for example, direction estimation processing).

<(2) Case of δqe>0>

For example, it may be assumed that the Doppler velocity of the target object is −1/(2Tr)≤fd<1/(2Tr). Further, a large difference between, on one hand, the reception levels for top NDM(qe) Doppler frequency indices of reception power and, on the other hand, the reception levels of δqeDoppler frequency indices different from the top NDMDoppler frequency indices of reception power (for example, the difference being equal to or greater than the threshold) may be used. For example, second Doppler demultiplexer211compares the reception power information inputted from second CFAR section210and determines the Doppler frequency in the range of −1/(2Tr)≤fd<1/(2Tr). Note that an exemplary operation of second Doppler demultiplexer211is disclosed in, for example, PTL 1, and therefore description of the exemplary operation is omitted here.

When the difference between the powers of NDM(qe) Doppler frequency indices for the higher reception powers is larger than a predetermined value (threshold), second Doppler demultiplexer211may regard (or determine) that components of the reception signals of the monostatic configuration are highly likely to be mixed, and may add an operation of removing the reception signals without performing an output for subsequent processing (for example, direction estimation processing).

The exemplary operation of second Doppler demultiplexer211has been described above.

Next, an exemplary operation of first direction estimator212and second direction estimator212illustrated inFIG.3will be described.

[Exemplary Operation of First Direction Estimator212]

First direction estimator212of qth radar section10performs direction estimation processing on the target object based on, for example, the information inputted from first Doppler demultiplexer211(for example, distance indices fb_cfar(q) and the demultiplexing index information (fdemul_Tx#1(q), fdemul_Tx#2(q), . . . , and fdemul_Tx#Nt(q)) on the Doppler multiplexed signal).

For example, first direction estimator212performs the direction estimation processing by extracting the outputs of Doppler analyzer209based on distance indices fb_cfar(q) and the demultiplexing index information (fdemul_Tx#1(q), fdemul_Tx#2(q), . . . , and fdemul_Tx#Nt(q)) on the Doppler multiplexed signals, and generating qth virtual reception array correlation vector hq(fb_cfar(q), fdemul_Tx#1(q), fdemul_Tx#2(q), . . . , and fdemul_Tx#Nt(q)) of first direction estimator212as illustrated in following Expression 18. Here, for example, q=1, 2.

The qth virtual reception array correlation vector hq(fb_cfar(q), fdemul_Tx#1(q), fdemul_Tx#2(q), . . . , and fdemul_Tx#Nt(q)) of the first direction estimator includes Nt(q)×Na(q) elements that are the product of number Nt(q) of transmission antennas and number Na(q) of reception antennas as illustrated in Expression 18. The qth virtual reception array correlation vectors hq(fb_cfar(q), fdemul_Tx#1(q), fdemul_Tx#2(q), . . . , and fdemul_Tx#Nt(q)) are used in a process of performing direction estimation on the reflected wave signals from the target based on phase differences between respective reception antennas202. Here, z is an integer of from 1 to Na(q).

In Expression 18, hcal[b]is an array correction value for correcting a phase deviation and an amplitude deviation between transmission array antennas and reception array antennas. The character “b” is an integer of from 1 to (Nt(q)×Na(q)).

First direction estimator212of qth radar section10calculates a spatial profile by, for example, changing azimuth direction θuin direction estimation evaluation function values PH(θu, fb_cfar(q), fdemul_Tx#1(q) to fdemul_Tx#Nt(q)) within a predetermined angular range. First direction estimator212may extract a predetermined number of maximum peaks of the calculated spatial profile in descending order, and output the azimuth directions of the maximum peaks to positioning output integrator30as direction-of-arrival estimation values (for example, positioning outputs).

Note that, there are various methods with direction estimation evaluation function values PH(θu, fb_cfar(q), fdemul_Tx#1(q), . . . , and fdemul_Tx#Nt(q)) depending on direction-of-arrival estimation algorithms. For example, an estimation method using an array antenna disclosed in NPL 4 may be used.

For example, when Nt(q)×Na(q) virtual reception arrays are arranged linearly at equal intervals dH, a beamformer method can be expressed as following Expression 19. In addition to the beamformer method, techniques such as Capon, MUSIC, and the like are also applicable. In Expression 19, superscript H denotes the Hermitian transpose operator.

In Expression 19, aq(θu) represents direction vectors of the virtual reception arrays to an incoming wave in azimuth direction θuat center frequency fcof the radar transmission signal, and is expressed by Expression (20). In Expression 20, λ is the wavelength of the radar transmission signal (e.g., chirp signal) for center frequency fc, and λ=C0/fc.

Azimuth direction θuis a vector that is changed at predetermined azimuth interval β1in an azimuth range over which direction-of-arrival estimation is performed. For example, θumay be set as follows.

θu=θmin+uβ1, where integer u is 0 to NU

Here, floor(x) is a function that returns the largest integer value not greater than real number x.

Further, regarding the above-described example, the description has been given of the example in which first direction estimator212calculates the azimuth direction as the direction-of-arrival estimation value, but the present disclosure is not limited thereto, and a direction-of-arrival estimation in the elevation direction or a direction-of-arrival estimation in the azimuth direction and the elevation direction can also be performed by using MIMO antennas arranged in a rectangular grid pattern. For example, first direction estimator212may calculate the azimuth direction and the elevation direction as the direction-of-arrival estimation values and use them as the positioning outputs.

Through the above-described operations, first direction estimator212of qth radar section10may output, for example, as the positioning outputs, the direction-of-arrival estimation values for distance indices fb_cfar(q) and the demultiplexing index information (fdemul_Tx#1(q), fdemul_Tx#2(q), . . . , and fdemul_Tx#Nt(q)) of the Doppler multiplexed signals. Further, first direction estimator212may further output distance indices fb_cfar(q) and the demultiplexing index information (fdemul_Tx#1(q), fdemul_Tx#2(q), . . . , and fdemul_Tx#Nt(q)) of the Doppler multiplexed signal as the positioning outputs.

Further, distance indices fb_cfar(q) may be outputted after converted into distance information by using Expression 1.

The exemplary operation of first direction estimator212has been described above.

[Exemplary Operation of Second Direction Estimator212]

Second direction estimator212of qth radar section10performs direction estimation processing on the target object based on, for example, the information inputted from second Doppler demultiplexer211(for example, distance indices fb_cfar(qe) and the demultiplexing index information (fdemul_Tx#1(qe), fdemul_Tx#2(qe), . . . , and fdemul_Tx#Nt(qe)) on the Doppler multiplexed signals.

For example, second direction estimator212extracts the outputs of Doppler analyzers209based on distance indices fb_cfar(qe) and the demultiplexing index information (fdemul_Tx#1(qe), fdemul_Tx#2(qe), . . . , and fdemul_Tx#Nt(qe)) of the Doppler multiplexed signal, generates qeth virtual reception array correlation matrix Hqe(fb_cfar(qe), fdemul_Tx#1(qe), fdemul_Tx#2(qe), . . . , and fdemul_Tx#Nt(qe) of second direction estimator212as illustrated in following Expression 21, and performs the direction estimation processing. Here, for example, qe=1, 2.

In Expression 21, hcal[b]is an array correction value for correcting a phase deviation and an amplitude deviation between transmission array antennas and reception array antennas. The character “b” is an integer of from 1 to (Nt(qe)×Na(q)).

Second direction estimator212of qth radar section10calculates a spatial profile by, for example, changing azimuth direction θuin direction estimation evaluation function values PT×H(θu, fb_cfar(qe), fdemul_Tx#1(qe) to fdemul_Tx#Nt(qe)) of the transmission direction within a predetermined angular range. Second direction estimator212may extract a predetermined number of maximum peak directions of the calculated spatial profile in descending order, and output the transmission azimuth directions of the maximum peaks to positioning output integrator30as direction estimation values (for example, positioning outputs).

Note that, there are various methods with direction estimation evaluation function values PT×H(θu, fb_cfar(qe), fdemul_Tx#1(qe), . . . , and fdemul_Tx#Nt(qe)) depending on direction estimation algorithms. For example, an estimation method using an array antenna disclosed in NPL 4 may be used. For example, the beamformer method can be expressed as following Expression 22. In addition to the beamformer method, techniques such as Capon, MUSIC, and the like are also applicable. In Expression 19, superscript H denotes the Hermitian transpose operator.

In Expression 22, aTx(qe)(θu) represents a transmission array direction vector of the transmission antenna in qeth radar section10to an incoming wave in azimuth direction θuat center frequency fc.

Further, for the direction-of-arrival estimation, second direction estimator212of qth radar section10calculates a spatial profile by, for example, changing azi muth direction θRxin direction estimation evaluation function values PR×H(θu, fb_cfar(qe), fdemul_Tx#1(qe) to fdemul_Tx#Nt(qe)) of the reception direction within a predetermined angular range. Second direction estimator212may extract a predetermined number of maximum peak directions of the calculated spatial profile in descending order, and output the reception azimuth directions of the maximum peaks to positioning output integrator30as direction estimation values (for example, positioning outputs).

Note that, there are various methods with direction estimation evaluation function values PR×H(θu, fb_cfar(qe), fdemul_Tx#1(qe), . . . , and fdemul_Tx#Nt(qe)) depending on direction estimation algorithms. For example, an estimation method using an array antenna disclosed in NPL 4 may be used. For example, the beamformer method can be expressed as following Expression 23. In addition to the beamformer method, techniques such as Capon, MUSIC, and the like are also applicable. In Expression 19, superscript H denotes the Hermitian transpose operator.

In Expression 23, aRx(q)(θu) represents a reception array direction vector of the reception antenna in qth radar section10to an incoming wave in azimuth direction θuat center frequency fc.

Azimuth direction θuis a vector that is changed at predetermined azimuth interval β1in an azimuth range over which the direction estimation is performed. For example, θumay be set as follows.

θu=θmin+uβ1, where integer u=0 to NU

Here, floor(x) is a function that returns the largest integer value not greater than real number x.

Further, regarding the above-described example, the description has been given of the example in which second direction estimator212calculates the azimuth direction as the direction estimation value, but the present disclosure is not limited thereto, and a direction estimation in the elevation direction or a direction estimation in the azimuth direction and the elevation direction can also be performed by using MIMO antennas arranged in a rectangular grid pattern. For example, second direction estimator212may calculate the azimuth direction and the elevation direction as the direction estimation values and use them as the positioning outputs.

Through the above-described operations, second direction estimator212of qth radar section10may output, for example, as the positioning outputs, the transmission azimuth direction estimation values and reception azimuth direction estimation values for distance indices fb_cfar(qe) and the demultiplexing index information (fdemul_Tx#1(qe), fdemul_Tx#2(qe), . . . , and fdemul_Tx#Nt(qe)) of the Doppler multiplexed signals. Further, second direction estimator212may further output distance indices fb_cfar(qe) and the demultiplexing index information (fdemul_Tx#1(qe), fdemul_Tx#2(qe), . . . , and fdemul_Tx#Nt(qe)) of the Doppler multiplexed signal as the positioning outputs.

Further, distance indices fb_cfar(qe) may be outputted after converted into distance information by using Expression 2.

Here, the positions of first radar section10and second radar section10are known to radar apparatus1in advance. For example, when the positions of first radar section10and second radar section10are regarded as forcal points, the target object may be present on an elliptic curve which gives, by the sum of the distances from two focal points, a distance for the multistatic configuration as indicated by distance indices fb_cfar(qe) outputted from second direction estimator212.

Further, since the transmission azimuth direction of qeth radar section10and the reception azimuth direction of qth radar section10are estimated, second direction estimator212can determine the target-object position using a result of angle measurement. Second direction estimator212may output, for example, the estimation result of the target-object position in the radar having such a multistatic configuration. A method for estimating a target-object position in a radar having a multistatic configuration is described in, for example, NPL 5. Thus, a detailed description of the estimation method will be omitted.

The exemplary operation of second direction estimator212has been described above.

InFIG.2, positioning output integrator30integrates the positioning outputs of first direction estimator212and second direction estimator212from first radar section10and the positioning outputs of first direction estimator212and second direction estimator212from second radar section10, and performs positioning of the target object.

For example, positioning output integrator30may determine the type of the target object based on correspondence between a positioning result of second direction estimator212of first radar section10and a positioning result of second direction estimator212of second radar section10, which are the positioning results of the multistatic configuration. For example, positioning output integrator30may utilize the tendency that the correspondence is high for poles (metal poles) and the correspondence of a reflection point is low for target objects having a large horizontal dimension, such as a wall.

Further, for example, in a case where the detection areas overlap between the positioning outputs of first direction estimator212of first radar section10and the positioning outputs of first direction estimator212of second radar section10, which are the positioning results of the monostatic configuration, positioning output integrator30may output components of high correspondence between both estimation results. For example, positioning output integrator30may not output components of low correspondence between both of the estimation results. In this case, positioning output integrator30can remove multipath reflection or the like that becomes a virtual image.

Note that positioning output integrator30may output the positioning output (or the positioning result) to, for example, a control apparatus (ECU or the like) of the vehicle in the case of an in-vehicle radar, or to an infrastructure control apparatus in the case of an infrastructure radar, which are not illustrated.

As described above, in the present embodiment, radar apparatus1includes first radar section10that transmits radar transmission signals from a plurality of transmission antennas102, and second radar section10that transmits radar transmission signals from a plurality of transmission antennas102. Here, the Doppler multiplexing interval between the Doppler shift amounts applied respectively to the radar transmission signals transmitted from the plurality of transmission antennas102of first radar section10is different from the Doppler multiplexing interval between the Doppler shift amounts applied respectively to the radar transmission signals transmitted from the plurality of transmission antennas102of second radar section10.

Accordingly, radar apparatus1can demultiplex the reflected wave signals corresponding to the radar transmission signals of radar sections10from the reception signals, for example, based on the Doppler multiplexing intervals set in radar sections10. Therefore, radar apparatus1can simultaneously perform the radar positioning by the monostatic configuration of each of first radar section10and second radar section10, and in addition the radar positioning by the multistatic configuration from first radar section10to second radar section10and the multistatic configuration from second radar section10to first radar section10. In addition, radar apparatus1can shorten the radar positioning time as compared with the multistatic time-division transmission.

Further, in the present embodiment, Doppler multiplexing is used in the monostatic configuration and the multistatic configuration. Thus, radar apparatus1does not need to perform code separation processing, and thus the amount of demultiplexing operations can be reduced as compared with inter-multistatic code multiplexing transmission. Further, radar apparatus1does not use the inter-multistatic code multiplexing transmission. Thus, even a reflected wave from a target object having a relative speed does not cause inter-code interference.

Further, for example, radar apparatus1can expand the observable Doppler range (for example, can set the observable Doppler range to +1/(2Tr)) by performing Doppler aliasing determination using unequal-interval Doppler multiplexing, and can suppress reduction of the maximum Doppler observable by the inter-multistatic multiplexing transmission. For example, radar apparatus1can maintain the same observation range as the maximum Doppler in a case where a single transmission antenna is used.

Further, for example, when radar apparatus1is applied to a radar that performs vehicle periphery monitoring, the use of the multistatic configuration can be used even when the observable area of each radar section10does not overlap completely. Accordingly, an effect of reducing the number of radars (the number of radar sections10) in radar apparatus1can be expected. In addition, the multistatic configuration allows radar apparatus1to utilize reflection at different angles. Thus, for example, the performance of detecting a planar object such as a wall can be improved.

Further, in radar apparatus1, the radar having the multistatic configuration can observe a Doppler component of even a moving object in the cross-range direction for a radar having the monostatic configuration. Thus, detection of the moving object is facilitated.

In addition, in radar apparatus1, the number of chirp signals that are a common signal between a plurality of radar sections10may be one, and the present disclosure can be realized by a smaller number of chirp signals than in the case of the inter-multistatic frequency-division transmission. It is thus possible to reduce the system cost.

Variation 1 of Embodiment 1

In Embodiment 1 (for example,FIG.3), a chirp signal (an output signal of VCO303) is output from synchronization controller20, but the present disclosure is not limited thereto.FIG.15is a block diagram illustrating an exemplary configuration of radar apparatus1aaccording to Variation 1 of Embodiment 1. In radar apparatus1a, synchronization controller20amay output a low-frequency reference signal in reference signal generator401and output information on the timing of transmission period Trin signal controller402.

Each of a plurality of radar sections10a(for example, first radar section10aand second radar section10a) individually includes synchronization controller103including radar transmission signal generator301(for example, including modulation signal generator302and VCO303). Each of the plurality of radar sections10amay generate a chirp signal using the reference signal input from synchronization controller20a, for example, based on the information on the timing of transmission period Trinput from synchronization controller20a.

In the configuration illustrated inFIG.15, for example, there is a possibility that the phase between first radar section10aand second radar section10achanges like a drift. Therefore, a drift component of the phase may be corrected in advance in radar apparatus1a.

In general, an expensive cable which focuses on a low loss property is used for a transmission line for the high-frequency signal, and thus, the system cost is likely to increase. Contrastingly, the configuration according to Variation 1 of Embodiment 1 as illustrated inFIG.15makes the low-frequency reference signal less than or equal to about 100 MHz. It is thus not necessary to use the cable which focuses on the low loss property. Accordingly, the system cost can be reduced and radar apparatus1acan be realized with a simpler configuration.

Further, in the configuration illustrated inFIG.15, signal controller402may synchronously output the timing of transmission period Trsuch that the transmission period is the same between first radar section10aand second radar section10a, but the present disclosure is not limited thereto. For example, signal controller402may control the timing of transmission period Trso as to shift the transmission period by Δt between first radar section10aand second radar section10a. For example, the transmission timing of the radar transmission signal in first radar section10amay be different from the transmission timing of the radar transmission signal in second radar section10a.

The shift of the transmission timing between radar section10amay affect the distance measurement in a multistatic configuration. However, for example, shift amount Δt of the transmission timing is known to radar apparatus1a, and radar apparatus1acan thus maintain the accuracy of the distance measurement by correcting a distance measurement value.

In addition, for example, signal controller402may vary shift amount Δt of the transmission period per predetermined time, for example, per radar positioning (per Nctransmission measurement times for each transmission period Tr). For example, when a Doppler component of a reflected wave in the monostatic configuration and a Doppler component of a reflected wave in the multistatic configuration, which are present at the same distance component from radar apparatus1a, partially match each other, it is difficult for radar apparatus1ato properly demultiplex them from each other, and there is a possibility that the target object is undetected. On the other hand, since shift amount Δt of the transmission period is set to be variable, the transmission timings between the multistatic configurations are periodically shifted and the distances thereof are shifted, radar apparatus1acan prevent continuous non-detection of the target object and reduce the likelihood that the target object is undetected.

Note that the configuration of Variation 1 can be similarly applied to the following embodiments or variations, and the same effects can be obtained.

Variation 2 of Embodiment 1

FIG.16is a block diagram illustrating an exemplary configuration of radar apparatus1baccording to Variation 2 of Embodiment 1.

In Variation 2 of Embodiment 1, for example, radar transmitter100aincludes Doppler multiplexing controller104in addition to the configuration of radar transmitter100(FIG.3).

For example, Doppler multiplexing controller104may variably set the Doppler multiplexing interval between the multistatic configurations per predetermined time, for example, per radar positioning (per Nctransmission measurement times for each transmission period Tr). For example, at least one of the Doppler multiplexing intervals set for each of the plurality of radar sections10bof radar apparatus1bmay be variably set.

For example, when a Doppler component of a reflected wave in the monostatic configuration and a Doppler component of a reflected wave in the multistatic configuration, which are present at the same distance from radar apparatus1b, partially match each other, it is difficult for radar apparatus1bto properly demultiplex them from each other, and there is a possibility that the target object is undetected.

On the other hand, Doppler multiplexing controller104shifts the Doppler multiplexing intervals between the multistatic configurations periodically (for example, per radar positioning), thereby shifting the Doppler components (for example, the distance components). Therefore, in radar apparatus1b, it is possible to prevent continuous non-detection of the target object, and to reduce the likelihood that the target object is undetected.

Note that the configuration of Variation 2 can be similarly applied to the preceding or succeeding embodiments or variations, for example, and the same effects can be obtained.

Variation 3 of Embodiment 1

The description has been given of Embodiment 1 having the configuration and operation in which the radar having the monostatic configuration and the radar having the multistatic configuration perform simultaneous multiplexing to perform positioning. A description will be given of Variation 3 of Embodiment 1 having a configuration in which, for example, a plurality of radars having the monostatic configuration perform simultaneous multiplexing to perform positioning.

FIG.17is a block diagram illustrating an exemplary configuration of radar apparatus1caccording to Variation 3 of Embodiment 1.

Radar apparatus1cillustrated inFIG.17has a configuration in which, as compared with Embodiment 1 (FIG.3), second CFAR section210, second Doppler demultiplexer211, and second direction estimator212corresponding to the multistatic configuration are excluded from radar receiver200cof radar section10c.

For example, first radar section10cmay remove a reflected wave signal corresponding to a radar transmission signal transmitted from second radar section10c, based on a Doppler multiplexing interval set for first radar section10cand a Doppler multiplexing interval set for second radar section10c, and perform the direction estimation processing using the reflected wave signal corresponding to the radar transmission signal transmitted from first radar section10c. Similarly, second radar section10cmay remove the reflected wave signal corresponding to the radar transmission signal transmitted from first radar section10c, based on the Doppler multiplexing interval set for first radar section10cand the Doppler multiplexing interval set for second radar section10c, and perform the direction estimation processing using the reflected wave signal corresponding to the radar transmission signal transmitted from second radar section10c.

According to the configuration of radar apparatus1c, for example, a plurality of radar sections10chaving the monostatic configuration that uses radar transmission waves (for example, chirp signals) in the same frequency band may be disposed close to each other. For example, even when the reflected wave signal for the radar transmission signal of first radar section10cis inputted in second radar section10c, second radar section10cis able to demultiplex and not receive such a reflected wave signal by using different Doppler multiplexing intervals between neighboring radar sections10c. Thus, an interference-canceling effect can be obtained. Similarly, for example, even when the reflected wave signal for the radar transmission signal of second radar section10cis inputted in first radar section10c, first radar section10cis able to demultiplex and not receive such a reflected wave signal.

The configuration of Variation 3 can be similarly applied to, for example, the previous or subsequent embodiments or variations, and the same effects can be obtained.

Variation 4 of Embodiment 1

In Variation 4 of Embodiment 1, for example, the multiplexing transmission method may be switched between the multiplexing transmission method of Embodiment 1 (for example, multiplexing transmission based on the Doppler shift amount) and the other multiplexing methods.

For example, radar apparatus1may perform multiplexing transmission by temporally or periodically switching between the multistatic time-division transmission and the multiplexing transmission method of Embodiment 1.

In such a transmission method, the multiplexing transmission of Embodiment 1 is applied to some radar positioning. Thus, for example, the positioning time can be reduced as compared with a case where the inter-multistatic time-division transmission is applied to every radar positioning.

Further, in addition to the effects according to Embodiment 1, Variation 4 achieves a more preferable ratio of the desired signal (for example, the power of the transmission signal from first radar section10) to the interference power (for example, the power of the transmission signal from second radar section10) since simultaneous multiplexing is not performed in the inter-multistatic time-division transmission. As described above, erroneous detection can be reduced by temporally switching the multiplexing transmission methods of the plurality of radar sections10(for example, every positioning period).

The configuration of Variation 4 can be similarly applied to, for example, the previous or subsequent embodiments or variations, and the same effects can be obtained.

Variation 5 of Embodiment 1

In Variation 5 of Embodiment 1, synchronization controller20may be included in any one of the plurality of radar sections10(for example, first radar section10and second radar section10). Even in this case, the same effects as those of Embodiment 1 can be obtained.

FIG.18is a block diagram illustrating an exemplary configuration of radar apparatus1daccording to Variation 5 of Embodiment 1. InFIG.18, synchronization controller20is included in a housing of first radar section10d. Synchronization controller20may supply an output signal not only to radar transmitter100in first radar section10but also to second radar section10doutside first radar section10d.

Note that the present disclosure is not limited to the example illustrated inFIG.18, and for example, synchronization controller20may be included in a housing of second radar section10d, and the output signal of synchronization controller20may be supplied to first radar section10doutside second radar section10d(not illustrated).

The configuration of Variation 5 can be similarly applied to, for example, the previous or subsequent embodiments or variations, and the same effects can be obtained.

Variation 6 of Embodiment 1

The description has been given of Embodiment 1 in which each of the plurality of radar sections10(for example, first radar section10and second radar section10) has the monostatic configuration, but the present disclosure is not limited thereto. For example, at least one of the plurality of radar sections10may be a radar having the multistatic configuration (or bi-static configuration).

For example, each of the plurality of radar sections10may have a configuration in which radar transmitter100and radar receiver200are included in the same housing (for example, the monostatic configuration), or a configuration in which radar transmitter100and radar receiver200are included in respective different housings (for example, the multistatic configuration (or bi-static configuration)). Radar section10may have the multistatic configuration including, for example, a plurality of radar transmitters100and at least one radar receiver200(not illustrated).

FIG.19is a block diagram illustrating an exemplary configuration of radar apparatus1eaccording to Variation 6, as an example.

In the example illustrated inFIG.19, both first radar section10eand second radar section10edo not have the monostatic configuration, but are radars having the bi-static configuration. For example, in each of first radar section10eand second radar section10e, radar transmitter100and radar receiver200may be disposed at distances apart from each other. In this case, a signal from synchronization controller20may be inputted to each of radar transmitter100and radar receiver200of first radar section10e. Similarly, a signal from synchronization controller20may be inputted to each of radar transmitter100and radar receiver200of second radar section10e.

Regarding the operations of first radar section10eand second radar section10ein the configuration as illustrated inFIG.19, the operation of first direction estimator212(not illustrated inFIG.19) is different, and the operations of the other components may be the same, for example. For example, the direction estimation operation of first direction estimator212of radar receiver200in first radar section10eor second radar section10eis an operation of a radar having the multistatic configuration, and may thus be the same operation as the direction estimation operation described for second direction estimator212. Further, for example, Expression 2, which is a conversion equation for the multistatic configuration, may be used for converting beat frequency index fb(or the distance index) into distance information R(fb) in a positioning output of first direction estimator212.

The configuration of Variation 6 can be similarly applied to, for example, the previous or subsequent embodiments or variations, and the same effects can be obtained.

Variation 7 of Embodiment 1

The description given of Embodiment 1 is of the configuration and operation of simultaneous multiplexing transmission of the radar having the monostatic configuration and the multistatic configuration that uses the two radar sections of first radar section10and second radar section10. Here, the number of radar sections included in radar apparatus1(or the number of radar sections used for radar positioning) is not limited to two, and a larger number (three or more) of radar sections may be used. By increasing the number of simultaneous multiplexing, the effect of reducing the measurement time is further enhanced. Further, for example, positioning output integrator30can improve detection accuracy or reduce erroneous detection by using the positioning results of a larger number of radar sections.

By way of example, radar apparatus1fillustrated inFIG.20includes three radar sections10f. Hereinafter, operations different from those of Embodiment 1 will be described.

InFIG.20, first to Nt(q)th Doppler shifters101(not illustrated inFIG.20) of qth radar section10fperform Doppler multiplexing transmission of the chirp signals inputted from synchronization controller20by applying different Doppler shift amounts DOPn(q) to the chirp signals based on predetermined Doppler multiplexing intervals Δfd(q).

Further, for example, the Doppler multiplexing intervals between the plurality of radar sections10f(inFIG.20, between first radar section10f, second radar section10f, and third radar section10f) may be set to different intervals (for example, Δfd(1)≠Δfd(2)≠Δfd(3)).

Further, for example, the ratio between Δfd(1) and Δfd(2) may be set so as not to match an integer. For example, Δfd(1)/Δfd(2) or Δfd(2)/Δfd(1) may be set so as not to match an integer.

Further, for example, the ratio between Δfd(2) and Δfd(3) may be set so as not to match an integer. For example, Δfd(2)/Δfd(3) or Δfd(3)/Δfd(2) may be set so as not to match an integer.

Similarly, for example, the ratio between Δfd(3) and Δfd(1) may be set so as not to match an integer. For example, Δfd(3)/Δfd(1) or Δfd(1)/Δfd(3) may be set so as not to match an integer.

For example, each of second and third CFAR sections210of qth radar section10fperforms the CFAR processing by extracting reflected waves matching the Doppler multiplexing intervals for any one of the other two radar sections10fforming the multistatic radar.

For example, in first radar section10f, first CFAR section210performs the CFAR processing by extract a reflected wave matching Doppler multiplexing intervals Δfd(1) for first radar section10f. Second CFAR section210performs the CFAR processing by extracting a reflected wave that matches Doppler multiplexing intervals Δfd(2) for second radar section10f. Third CFAR section210performs the CFAR processing by extracting a reflected wave that matches Doppler multiplexing intervals Δfd(3) for third radar section10f.

Similarly, for example, in second radar section10f, first CFAR section210performs the CFAR processing by extracting a reflected wave that matches Doppler multiplexing intervals Δfd(2) for second radar section10f. Second CFAR section210performs the CFAR processing by extracting a reflected wave that matches Doppler multiplexing intervals Δfd(3) for third radar section10f. Third CFAR section210performs the CFAR processing by extracting a reflected wave that matches Doppler multiplexing intervals Δfd(1) for first radar section10f.

Similarly, for example, in third radar section10f, first CFAR section210performs the CFAR processing by extracting a reflected wave matching Doppler multiplexing interval Δfd(3) for third radar section10f. Second CFAR section210performs the CFAR processing by extracting a reflected wave that matches Doppler multiplexing intervals Δfd(1) for first radar section10f. Third CFAR section210performs the CFAR processing by extracting a reflected wave that matches Doppler multiplexing interval Δfd(2) for second radar section10f.

Thereafter, first Doppler demultiplexer211of qth radar section10fdemultiplexes and outputs a Doppler multiplexed signal based on an output of first CFAR section210, second Doppler demultiplexer211demultiplexes and outputs a Doppler multiplexed signal based on an output of second CFAR section210, and third Doppler demultiplexer211demultiplexes and outputs a Doppler multiplexed signal based on an output of third CFAR section210.

Further, first direction estimator212of qth radar section10fperforms azimuth estimation based on the output of first Doppler demultiplexer211and outputs a positioning result. Second direction estimator212performs azimuth estimation based on the output of second Doppler demultiplexer211and outputs a positioning result. Third direction estimator212performs azimuth estimation based on the output of third Doppler demultiplexer211and outputs a positioning result.

Third direction estimator212may perform, for example, the direction estimation processing and distance conversion of the distance index using a radar having a multistatic configuration, and output the positioning result.

The configuration of Variation 7 can be similarly applied to, for example, the previous or subsequent embodiments or variations, and the same effects can be obtained.

Embodiment 1 has been described in which the Doppler multiplexing is applied to the transmission multiplexing in the monostatic MIMO radar, but the present disclosure is not limited thereto, and the time division multiplexing may be applied. In the present embodiment, an operation performed in a case where the Doppler multiplexing is applied in a multistatic MIMO radar and time division multiplexing is applied in a monostatic MIMO radar will be described.

FIG.21is a block diagram illustrating an exemplary configuration of radar apparatus1gaccording to the present embodiment. InFIG.21, components that perform the same operations as those inFIG.3are denoted by the same reference numerals. Hereinafter, operations different from those of Embodiment 1 will be mainly described.

Radar apparatus1gillustrated inFIG.21may include, for example, a plurality of radar sections10g, synchronization controller20, and positioning output integrator30(not illustrated inFIG.21).FIG.21illustrates an exemplary configuration of one radar section10g.

InFIG.21, synchronization controller20includes, for example, radar transmission signal generator301including modulation signal generator302and Voltage-Controlled Oscillator (VCO)303, and signal controller304. Radar transmission signal generator301generates a radar transmission signal (for example, a predetermined frequency-modulated wave (chirp signal)) based on, for example, control by signal controller304, and outputs the generated radar transmission signal to a plurality of radar sections10g(for example, radar transmitters100g) constituting the multistatic configuration. The chirp signal outputted by synchronization controller20is also inputted to radar receiver200g(each mixer204). The operation of synchronization controller20may be the same as that of Embodiment 1.

In addition, inFIG.21, each of the plurality of radar sections10gmay perform time-division transmission of radar transmission signals to which different Doppler shift amounts are applied, from a plurality of transmission antennas102. Each of radar sections10gmay include, for example, radar transmitter100gand radar receiver200g. In the present embodiment, for example, the numbers of transmission antennas102(or transmission antennas102as used) included in each qth radar section10gmay be the same. In the following description, the number of transmission antennas in qth radar section10gmay be referred to as Nt(q) (or simply “Nt”). For example, Nt(1)=Nt(2) and Nt(q)>1.

[Exemplary Configuration of Radar Transmitter100g]

To apply Doppler shift amount DOPn(q) to the chirp signal inputted from VCO303, each of Doppler shifters101of qth radar section10gapplies phase rotation Φn,q(m) to the chirp signal for each transmission period Trof the chirp signal, and outputs the Doppler-shifted signal to switch106.

For example, qth radar section10gmay perform output while applying predetermined phase rotations Φn,q(m) for applying Doppler shifts for providing Doppler multiplexing intervals that differ between radar sections10gthat perform multistatic radar multiplexing transmission (an exemplary operation will be described later). Here, n is an integer of from 1 to Nt(q), and q is 1 or 2.

For example, antenna switching controller105controls switches106to switch transmission antennas102in a predetermined order for each transmission period Tr. In addition, antenna switching controller105outputs information on the antenna switching control to output switcher213of radar receiver200g.

For example, antenna switching controller105may set switch106corresponding to first transmission antenna102(Tx #1) to ON in the first transmission period, and set switches106corresponding to other transmission antennas102different from first transmission antenna102to OFF.

Further, for example, antenna switching controller105may set switch106corresponding to second transmission antenna102(Tx #2) to ON in the second transmission period, and set switches106corresponding to other transmission antennas102different from second transmission antenna102to OFF.

Antenna switching controller105may repeat the control (switching) of these switches106, set switch106corresponding to Nt(q)th transmission antenna102(Tx #Nt(q) to ON in the Nt(q)th transmission period, and set switches106corresponding to other transmission antennas102different from Nt(q)th transmission antenna102to OFF.

Further, for example, antenna switching controller105may set switch106corresponding to first transmission antenna102(Tx #1) to ON in a subsequent Nt(q)+1th transmission period, and set switches106corresponding to other transmission antennas102different from first transmission antenna102to OFF.

Antenna switching controller105may repeatedly perform the same antenna switching control hereinafter.

Switch106(SW) switches the states of ON and OFF based on, for example, control by antenna switching controller105. Here, when switch106is in the ON state, the transmission signal inputted from Doppler shifter101is outputted. On the other hand, when switch106is in the OFF state, the transmission signal inputted from Doppler shifter101is not outputted. Therefore, the output signal of Doppler shifter101is amplified to a predetermined transmission power and is emitted into space from corresponding transmission antenna102for which switch106is switched to the ON state. [Exemplary Configuration of Radar Receiver200g]

InFIG.21, radar receiver200gincludes Na reception antennas202(for example, Rx #1 to Rx #Na), and serves as a component of an array antenna. Radar receiver200gincludes Na antenna system processors201, CFAR sections210, Doppler demultiplexers211, and direction estimators212.

Here, the number of reception antennas202may be the same or may be different between qth radar sections10g(for example, q=1 or 2). Hereinafter, the number of reception antennas in qth radar section10gwill be referred to as “Na(q)” (also referred to simply as “Na”). Here, Na(q)≥1.

The operation of reception radio203of antenna system processor201is the same as that of Embodiment 1, and the description thereof is omitted.

The operations of A/D converter207and beat frequency analyzer208in signal processor206gof the antenna system processor201are the same as those in Embodiment 1, and the explanation thereof is omitted.

Output switcher213performs, for example, an operation associated with the switching operation of switch106performed by antenna switching controller105based on the control by antenna switching controller105of radar transmitter100g, and selectively switches a destination of an output of beat frequency analyzer208to one of Nt(q) Doppler analyzers209(for example, also represented by Doppler analyzers209-1to209-Nt(q)) for each transmission period Tr.

For example, when antenna switching controller105controls switches106so that switch106corresponding to first transmission antenna102(Tx #1) is set to ON and switches106corresponding to other transmission antennas102are set to OFF in the first transmission period, output switcher213outputs the output signal from beat frequency analyzer208to first Doppler analyzer209and does not output the output to other Doppler analyzers209.

Similarly, when antenna switching controller105controls switches106so that switch106corresponding to mth transmission antenna102(Tx #n) is set to ON and switches106corresponding to other transmission antennas102are set to OFF in the nth transmission period, output switcher213outputs the output signal from beat frequency analyzer208to nth Doppler analyzer209and does not output the output to other Doppler analyzers209. Here, n is an integer of from 1 to Nt(q).

The nth Doppler analyzer209(or Doppler analyzer209-n) of zth signal processor206gperforms Doppler analysis for each distance index fbbased on a beat frequency response for the transmission period in which a signal is transmitted from each transmission antenna102, among beat frequency responses RFTz(fb, 1), RFTz(fb, 2), . . . , and RFTz(fb, NC) obtained by NCchirp pulse transmissions of the chirp signals.

For example, in a case where the time-division transmission in which Nt(q) transmission antennas102cyclically switch from first transmission antenna102to Nt(q)th transmission antenna102for each transmission period Tris applied under the control of antenna switching controller105, Doppler analyzer209may apply Fast Fourier Transform (FFT) processing as illustrated in following Expression 24, and may output VFTn,z,q(fb, fs) as the output of nth Doppler analyzer209in zth signal processor206g. Note that Ndis an integer multiple of Nt(q), and may be set to, for example, Nd=Nc/Nt(q). Note that RFTz,q(fb, m) represents the beat frequency response outputted from beat frequency analyzer208in qth radar section10.

Here, the FFT size is Nd, and the maximum Doppler frequency at which no aliasing occurs and which is derived from the sampling theorem is ±1/(2TrNt(q)). Further, the Doppler frequency interval of Doppler frequency index fsis 1/(Nd×TrNt(q)), and the range of Doppler frequency index fsis fs=Nd/2, . . . , 0, . . . , and Nd/2−1.

By way of example, a description will be given of a case where Ndis a power of 2. When Ndis not a power of 2, zero-padded data is included, for example, to obtain the data size of a power of 2 and the FFT processing can thus be performed. In the FFT processing, Doppler analyzer209may perform multiplication by a window function coefficient such as the Han window or the Hamming window. It is possible to suppress sidelobes generated around the beat frequency peak by applying a window function.

InFIG.21, for example, first CFAR section210selectively extracts local peaks of reflected wave signals for radar transmission signals of qth radar section10g(corresponding radar), which has the monostatic configuration, using outputs VFTn,z,q(fb, fs) of first to Nt(q)th Doppler analyzers209of first to Na(q)th signal processors206g. For example, first CFAR section210may perform the CFAR processing of performing the adaptive threshold determination after power addition at intervals matching the Doppler multiplexing intervals set for the radar transmission signals transmitted from qth radar section10g, extract distance indices fb_cfarand Doppler frequency indices fsddm_cfarthat provide local peak signals, and output extracted distance indices fb_cfarand Doppler frequency indices fsddm_cfarto first Doppler demultiplexer211(an exemplary operation will be described later).

The radar transmitter having the monostatic configuration in first radar section10gis radar transmitter100gof first radar section10g. Similarly, the radar transmitter having the monostatic configuration in second radar section10gis radar transmitter100gof second radar section10g.

Further, for example, second CFAR section210selectively extracts local peaks of radar reflected waves (reception signals) for radar transmission signals of another radar section10gthat differ from qth radar section10g(corresponding radar), which is the multistatic configuration, using outputs VFTn,z,q(fb, fs) of first to Nt(q)th Doppler analyzers209of first to Na(q)th signal processors206g. For example, second CFAR section210may perform the CFAR processing of performing the adaptive threshold determination after the power addition at intervals matching the Doppler multiplexing intervals set for the radar transmission signals transmitted from radar section10gother than qth radar section10g, extract distance indices fb_cfarand Doppler frequency indices fsddm_cfarthat provide local peak signals, and output the extracted distance indices fb_cfarand Doppler frequency indices fsddm_cfarto second Doppler demultiplexer211(an exemplary operation will be described later).

The radar transmitter having the multistatic configuration in first radar section10gis radar transmitter100gof second radar section10g. Similarly, the radar transmitter having the multistatic configuration in second radar section10gis radar transmitter100gof first radar section10.

Next, the operation of qth Doppler demultiplexer211will be described together with the exemplary operation of Doppler shifters101and qth CFAR section210. For example, q=1 or 2 may hold true.

Doppler demultiplexers211of qth radar section10gmay include, for example, first Doppler demultiplexer211that performs Doppler demultiplexing on the reflected wave signals for the radar transmission signals from qth radar section10g(corresponding radar), which has the monostatic configuration, using the outputs of first CFAR section210and second Doppler demultiplexer that performs Doppler demultiplexing on the reflected wave signals for the radar transmission signals from another radar section10gdifferent from qth radar rsection10g, which has the multistatic configuration, using the outputs of second CFAR section210.

The operation of qth Doppler demultiplexer211is related to the operation of Doppler shifters101of radar transmitter100g. Similarly, the operation of qth CFAR section210is related to the operation of Doppler shifters101of radar transmitter100g.

Hereinafter, an exemplary operation of Doppler shifters101will be described, and an exemplary operation of qth CFAR section210and an exemplary operation of qth Doppler demultiplexer211will then be described.

[Method for Setting Doppler Shift Amount]

To begin with, an example of a method for setting the Doppler shift amount applied in Doppler shifters101will be described.

In the present embodiment, by the operation of antenna switching controller105and switches106, a radio wave is transmitted from each of transmission antennas102at each period of Nt(q)×Tr. First to Nt(q)th Doppler shifters101of qth radar section10gperform Doppler multiplexing transmission by applying respective different Doppler shift amounts DOPn(q) of predetermined Doppler multiplexing intervals Δfd(q) for respective Nt(q) transmission antennas102to the chirp signals inputted from synchronization controller20. At this time, Doppler multiplexing intervals Δfd(q) may satisfy the following setting conditions (1) and (2) as in Embodiment 1.(1) The Doppler multiplexing intervals between the plurality of radar sections10gmay be set to different intervals. For example, the intervals for respective Doppler shift amounts applied to the radar transmission signals transmitted from the plurality of transmission antennas102of first radar section10gand the intervals for respective Doppler shift amounts applied to the radar transmission signals transmitted from the plurality of transmission antennas102of second radar section10gmay be different from each other (for example, Δfd(1)≠Δfd(2)).(2) For example, the ratio between Δfd(1) and Δfd(2) may be set so as not to match an integer. For example, of Δfd(1) and Δfd(2), the ratio of the Doppler multiplexing interval having the larger value to the Doppler multiplexing interval having the smaller value may be different from the integer. For example, Δfd(1)/Δfd(2) or Δfd(2)/Δfd(1) may be set so as not to match the integer (so as to be different from the integer).

Hereinafter, an example of setting Doppler multiplexing interval Δfd(q) will be described.

In the following, a description is given of a case where the number of Doppler multiplexing of qth radar section10gis NDM(q)=Nt(q), but the present disclosure is not limited thereto. For example, radar section10gmay bundle some of the plurality of transmission antennas102to form a transmission beam for performing Doppler multiplexing transmission. Here, NDM(q)<Nt(q) holds true. Here, m is an integer of from 1 to Nc. Further, for example, index n of Doppler shift amount DOPn(q) is an integer of n=1 to Nt(q). Also, NDM(q)>1 and q=1 or 2.

For example, by the operation of antenna switching controller105and switches106, radio waves are transmitted from transmission antennas102for each of Nt(q)×Trperiods Tr, and Doppler shifters101may thus apply predetermined phase rotations (for example, ranging from 0 to 2π) for the chirp signals to Nt(q) transmission antennas102for each of Nt(q)×Trperiods.

Here, in Doppler analyzers209, the range of Doppler frequency fdin which no aliasing is generated and which is derived from the sampling theorem is from −1/(2Tr×NDM(q))≤fd<1/(2Tr×NDM(q)). For example, even when the Doppler frequency exceeds the range of Doppler frequency fdin which no aliasing occurs, the range of Doppler frequency fdobserved in Doppler analyzers209is −1/(2Tr×NDM(q))≤fd<1/(2Tr×NDM(q)).

Therefore, for example, when Doppler shifters101apply Doppler shifts within the range of −1/(2Tr×NDM(q))≤fd<1/(2Tr×NDM(q)), maximum Doppler shift interval Δfdmax with respect to Nt(q) transmission antennas102(for example, the number equal to the Doppler multiplexing number) is Δfdmax=1/(TrNt(q)Nt(q))=1/(TrNDM(q)NDM(q)). For example, Doppler shifters101may set Δfd(1) and Δfd(2) to different intervals within the range up to Δfdmax. Accordingly, Doppler shifters101can set the Doppler shift within the range of 0 to 2π that is the phase rotation providing the Doppler shift.

For example, the Doppler multiplexing intervals of each of first radar section10gand second radar section10gmay be set to Δfd(1)=1/(Tr×NDM(1)×(NDM(1)+δ1)) and Δfd(2)=1/(Tr×NDM(2)×(NDM(2)+δ2)), respectively.

Here, NDM(1)=NDM(2), and δ1, δ2≥0 hold true, and NDM(1)+δ1+NDM(2)+δ2is satisfied (e.g., δ1≠δ2). Further, δ1and δ2may be set so that the ratio between NDM(1)+δ1and NDM(2)+δ2does not match an integer. With this setting, the Doppler multiplexing interval between the plurality of radar sections10g(for example, between first radar section10gand second radar section10g) is different (Δfd(1) #Δfd(2)), and the ratio between Δfd(1) and Δfd(2) does not match an integer.

Note that each of δ1and δ2may be a positive integer or a positive real number. For example, by setting δ1and δ2to be positive integers, the processes in first CFAR section210and second CFAR section210, which will be described later, can be simplified. Descriptions are given below of a case where δ1and δ2are each set to zero or a positive integer. However, the present disclosure is not limited thereto, and positive real numbers may be set.

In addition, if supposed situations are mostly those in which radar apparatus1gand the target are both stationary, a configuration may be adopted in which parameters (for example, values such as Doppler multiplexing intervals Δfd(q) or δq) which, for example, cause the Doppler shift amounts to match each other between first radar section10gand second radar section10gare excluded in advance. For example, for all of n1and n2, the parameters may be set to satisfy following Expression 25.

By this setting, for example, Doppler shift amount DOPn1(1) applied to the radar transmission signal of first radar section10gand Doppler shift amount DOPn2(2) applied to the radar transmission signal of second radar section10gare set to values different from each other.

The parameter setting satisfying Expression 25 may be applied, for example, to situations in which both radar apparatus1gand the target are supposed to be mostly stationary. For example, when radar apparatus1gand the target are both stationary, a Doppler component is zero. Therefore, for example, even when the reflected wave signal for the radar transmission signal of first radar section10gand the reflected wave signal for the radar transmission signal of second radar section10gare included in the same distance index, Doppler shift amount DOPn(q) for each MIMO multiplexed transmission signal is different. Thus, radar apparatus1gcan demultiplex and receive both the reflected wave signals by utilizing the difference in detected Doppler components.

A description is given below of exemplary setting of Doppler shift amounts.

For example, in the case of NDM(1)=NDM(2), Δfd(1)=1/(Tr×NDM(1)×NDM(1)) and Δfd(2)=1/(Tr×NDM(2)×(NDM(2)+1)) may be set, Δfd(1)=1/(Tr×NDM(1)×(NDM(1)+1)) and Δfd(2)=1/(Tr×NDM(2)×NDM(2)) may be set, or Δfd(1)=1/(Tr×NDM(1)×(NDM(1)+1)) and Δfd(2)=1/(Tr×NDM(2)×(NDM(2)+2)) may be set. In this case, the above-described setting conditions of the Doppler multiplexing intervals are satisfied.

In this case, the Doppler intervals can be maximized within the range of −1/(2Tr×NDM(1))≤fd<1/(2Tr×NDM(1)) of Doppler frequencies fdobserved by Doppler analyzers209. Therefore, for example, even in a case where the Doppler spectrum has a spread, such as a case where the moving speed of the target is not constant and has a component such as acceleration, it is possible reduce a determination error in first Doppler demultiplexer211or second Doppler demultiplexer211.

By way of example,FIG.22illustrates a setting example of Doppler shifts for first radar section10g((a) ofFIG.22) and a setting example of Doppler shifts for second radar section10g((b) ofFIG.22) in the case of NDM(1)=Nt(1)=2 and NDM(2)=Nt(2)=2. InFIG.22, Δfd(1)=1/(6Tr) (e.g., § 1=1) is set, and Δfd(2)=1/(8Tr) (e.g., δ2=2) is set.

In addition, the operation of antenna switching controller105and switches106performed when NDM(1)=Nt(1)=2 and NDM(2)=Nt(2)=2 switches transmission antennas102used for the transmission of the radar transmission signals between odd-numbered transmission periods Trand even-numbered transmission periods Tr. For example, in first radar section10g, at odd-numbered transmission periods Tr(m=1, 3, 5, . . . ) as illustrated at the upper part at (a) ofFIG.22, switch106corresponding to Tx #1 is switched to the ON state (switch106corresponding to Tx #2 is switched to the OFF state), and radio waves are emitted from Tx #1. Further, at even-numbered transmission periods Tr(m=2, 4, 6, . . . ) as illustrated at the lower part at (a) ofFIG.22, switch106corresponding to Tx #2 is switched to the ON state (switch106corresponding to Tx #1 is switched to the OFF state), and radio waves are emitted from Tx #2.

Similarly, in second radar section10g, at odd-numbered transmission periods Tr(m=1, 3, 5, . . . ) as illustrated at the upper part at (b) ofFIG.22, switch106corresponding to Tx #1 is switched to the ON state (switch106corresponding to Tx #2 is switched to the OFF state), and radio waves are emitted from Tx #1. Further, at even-numbered transmission periods Tr(m=2, 4, 6, . . . ) as illustrated at the lower part at (b) ofFIG.22, switch106corresponding to Tx #2 is switched to the ON state (switch106corresponding to Tx #1 is switched to the OFF state), and radio waves are emitted from Tx #2.

Note that the switching order of transmission antennas102is not limited to this, and may be different switching orders. The same applies to the following description.

Further, by way of another example,FIG.23illustrates a setting example of the Doppler shifts for first radar section10g((a) ofFIG.23) and a setting example of the Doppler shifts for second radar section10g((b) ofFIG.23) in the case of NDM(1)=Nt(1)=2 and NDM(2)=Nt(2)=2. InFIG.23, Δfd(1)=1/(6Tr) (e.g., δ1=1) is set, and Δfd(2)=1/(8Tr) (e.g., δ2=2) is set.

Further, inFIG.23, Doppler shift amounts DOPn1(1) and DOPn2(2) applied to respective transmission antennas102of first radar section10gand second radar section10gare set so that the Doppler shift amounts do not match each other between first radar section10gand second radar section10g.

As described above, setting the Doppler multiplexing intervals for each of first radar section10gand second radar section10gis performed such that the above-described setting conditions for Doppler multiplexing intervals are satisfied. This setting of the Doppler multiplexing intervals makes it more likely for the Doppler components corresponding to the radar reflected waves (reception signals) for the radar transmission signals from first radar section10gand second radar section10gto appear at respective different positions within the range of −1/(2TrNDM(1))≤fd<1/(2TrNDM(1)) of Doppler frequencies fdobserved by Doppler analyzers209, and facilitates demultiplexing the reflected wave signals corresponding to first radar section10gand second radar section10gfrom each other.

By way of example,FIG.24illustrates an example of an output (for example, a reception Doppler frequency) of Doppler analyzer209in a case where reflected wave signals for radar transmission signals from first radar section10gand second radar section10gare received. InFIG.24, the vertical axis represents the distance axis, and the horizontal axis represents the Doppler frequency axis. Further, inFIG.24, Doppler components having high power are represented by arrows.

In the present embodiment, radar transmission signals are transmitted from a plurality of transmission antennas102while the transmission antennas are switched in a time-division manner, and different Doppler shifts are applied to the signals transmitted from respective transmission antennas102. Thus, for example, by adding together the powers of all the outputs of first to Nt(q)th Doppler analyzers209, radar apparatus1gcan detect one of Doppler multiplexing intervals Δfd(1) and Δfd(2) in the reception signals. For example, since the radar transmission signals are transmitted at Doppler multiplexing intervals different between first radar section10gand second radar section10g, radar apparatus1gcan distinguish whether the reception signals are reflected wave signals for the radar transmission signals from first radar section10gor from second radar section10gbased on the detected Doppler multiplexing intervals of the reception signals.

For example, when a Doppler component that matches the interval (e.g., 1/(6Tr) inFIG.24) of Δfd(1) or a Doppler component that matches an integer multiple of the interval of Δfd(1) is observed at distance index fb1 or fb2 illustrated inFIG.24, radar apparatus1gcan distinguish (or detect) that these Doppler components are reflected wave signals for the radar transmission signals transmitted from first radar section10g.

Further, when a Doppler component that matches the interval (e.g., 1/(8Tr) inFIG.24) of Δfd(2) or a Doppler component that matches an integer multiple of the interval of Δfd(2) is observed at distance index fb3 or fb4 illustrated inFIG.24, radar apparatus1gcan distinguish that these Doppler components are reflected wave signals for the radar transmission signals transmitted from second radar section10g.

Further, when a Doppler component that matches interval Δfd(1) (or an integer multiple of Δfd(1)) and a Doppler component that matches the interval of Δfd(2) (or an integer multiple of Δfd(2)) are observed in a mixed manner at distance index fb5 illustrated inFIG.24, radar apparatus1gcan distinguish the reflected wave signals for the radar transmission signals transmitted from first radar section10gand the reflected wave signals for the radar transmission signals transmitted from second radar section10g, for example, based on the intervals of the Doppler components.

As described above, radar apparatus1gcan distinguish whether the observed Doppler components are the reflected wave signals for the radar transmission signals transmitted from the radar section of first radar section10gor from second radar section10g, based on the difference between the Doppler multiplexing intervals of the Doppler multiplexing transmissions in first radar section10gand the Doppler multiplexing intervals of the Doppler multiplexing transmissions in second radar section10g.

For example, Doppler shifters101may set the Doppler shift amount corresponding to each transmission antenna102using the Doppler multiplexing interval set as described above, and apply the phase rotation for applying the Doppler shift amount to the chirp signal at each chirp transmission period.

For example, nth Doppler shifter101of qth radar section10gapplies, to the mth chirp signal as input, phase rotation Φn,q(m) for applying Doppler shift amount DOPn(q) different for each nth transmission antenna102, and outputs the resultant signal. As a result, different Doppler shifts are applied to the transmission signals transmitted respectively from multiple transmission antennas102.

Here, n is an integer of from 1 to Nt(q), m is an integer of from 1 to Nc, and q is 1 or 2.

For example, phase rotations Φn,q(m) for applying Doppler shift amounts DOPn(q) for Doppler shift intervals Δfd(q) to the radar transmission signals transmitted from Nt(q) (e.g., Nt(q)=NDM(q)) transmission antennas102are expressed by following Expression 26. Expression 27 represents Doppler shift amounts DOPn(q) for Doppler shift intervals Δfd(q).

In the expression, Φ0is the initial phase and ΔΦ0is a reference Doppler shift phase. Note that α is a coefficient for offsetting the Doppler shift amount for each Doppler multiplexed signal and a real value may be used for the coefficient. For example, when α=1, the Doppler shift amount for the first Doppler multiplexed signal is zero.

Expression 26 represents the phase rotations in the case of time-division transmission of Nt(q) transmission antennas102cyclically switched from the first transmission antenna to the Nt(q)th transmission antenna for each transmission period Trbased on the control of antenna switching controller105, but the present disclosure is not limited thereto. Floor[x] represents the floor function outputting the minimum integer less than or equal to real number x.

For example, when Nt(1)=Nt(2)=3, ΔΦ0=0, Φ0=0, δ1=1, and δ2=2, the Doppler multiplexing intervals are set to Δfd(1)=1/(12Tr) and Δfd(2)=1/(15Tr). Further, for example, when α=1, phase rotations Φn,q(m) for applying Doppler shift amounts DOPn(q) different for nth (n=1, 2, 3) transmission antennas102to the mth chirp signal as input are expressed by following Expression 28:

For example, when first radar section10gperforms Doppler multiplexing transmission using number Nt of transmission antennas=3, first Doppler shifter101in first radar section10gapplies phase rotation Φ1,1(m) to the chirp signal inputted from synchronization controller20for each transmission period Tras shown in following Expression 29. The output of first Doppler shifter101is output from, for example, first transmission antenna102(Tx #1). Here, cp(t) denotes the chirp signal for each transmission period.

Further, for example, second Doppler shifter101in first radar section10gapplies phase rotation Φ2,1(m) to the chirp signal inputted from synchronization controller20, as illustrated in following Expression 30, for each transmission period. The output of second Doppler shifter101is output from, for example, second transmission antenna102(Tx #2).

Similarly, for example, third Doppler shifter101in first radar section10gapplies phase rotation Φ3,1(m) to the chirp signal inputted from synchronization controller20, as illustrated in following Expression (31), for each transmission period. The output of third Doppler shifter101is output from, for example, third transmission antenna102(Tx #3).

Further, for example, when second radar section10gperforms Doppler multiplexing transmission using number Nt of transmission antennas=3, first Doppler shifter101in second radar section10gapplies, for each transmission period Tr, phase rotation Φ1,2(m) to the chirp signal inputted from synchronization controller20, as illustrated in following Expression 32. The output of first Doppler shifter101is output from, for example, first transmission antenna102(Tx #1). Here, cp(t) denotes the chirp signal for each transmission period.

Further, for example, second Doppler shifter101in second radar section10gapplies phase rotation Φ2,2(m) to the chirp signal inputted from synchronization controller20, as illustrated in following Expression 33, for each transmission period. The output of second Doppler shifter101is output from, for example, second transmission antenna102(Tx #2).

Similarly, for example, third Doppler shifter101in second radar section10gapplies phase rotation Φ3,2(m) to the chirp signal inputted from synchronization controller20for each transmission period Tras illustrated in following Expression 34. The output of third Doppler shifter101is output from, for example, third transmission antenna102(Tx #3).

The exemplary setting for Doppler shift amounts has been described above.

Next, an exemplary operation of first CFAR section210, second CFAR section210, first Doppler demultiplexer211, and second Doppler demultiplexer211in qth radar section10gcorresponding to the operation of Doppler shifters101described above will be described.

[Exemplary Operation of First CFAR Section210]

For example, in order to receive the reflected wave signals for the radar transmission signals from radar transmitter100gof qth radar section10g, first CFAR section210of qth radar section10gmay perform the following operation.

For example, when δ1and δ2are set to values that differ from positive integers for Doppler shifters101, first CFAR section210may perform peak detection by, for example, searching, in the power addition values outputted from Doppler analyzers209of first to Na(q)th signal processors206, for a power peak that matches the Doppler shift intervals set for the radar transmission signals of qth radar section10gfor each distance index, and performing adaptive threshold processing (CFAR processing).

On the other hand, for example, when δ1and δ2are set to positive integers for Doppler shifters101, an interval of Δfd(q) or an interval of an integer multiple of Δfd(q) is used as an interval of the Doppler shift amounts. In this case, q may be 1 or 2. Therefore, the Doppler multiplexed signals may be detected as having aliasing at intervals of Δfd(q) in the Doppler frequency domain of the outputs of first to Nt(q)th Doppler analyzers209. By using such characteristics, for example, the operation of first CFAR section210can be simplified as follows.

For example, first CFAR section210of qth radar section10gdetects a Doppler peak by applying a threshold to a power addition value obtained by adding together the reception powers of the reflected wave signals for respective ranges (for example, ranges of Δfd(q)) within the Doppler frequency range to be subjected to the CFAR processing in the output obtained by performing power addition on the outputs of first to Nt(q)th Doppler analyzers209, the ranges corresponding to the intervals of the Doppler shift amounts applied respectively to the radar transmission signals.

For example, first CFAR section210performs the CFAR processing on on outputs PowerFTq(fb, fs) obtained by adding the powers of the outputs of first to Nt(q)th Doppler analyzers209of first to Na(q)th signal processors206, by calculating power addition value PowerDDMq(fb, fsddm) obtained by adding power values PowerqFT(fb, fs) at the intervals of Δfd(q) (for example, corresponding to NΔfd(q)) as illustrated in following Expressions 35 and 36:

In the expressions, fsddm=−Nd/2, . . . , −Nd/2+NΔfd(q)−1 and NΔfd(q)=round(Δfd(q)/(1/(TrNd). In addition, round(x) is an operator that rounds off real number x and outputs an integer value.

The operation in the CFAR processing may be based on the operation disclosed in NPL 3, for example, and detailed explanation of the exemplary operation is omitted.

Accordingly, the range of the Doppler frequencies subjected to the CFAR processing in first CFAR section210can be set (for example, reduced) to 1/(Nt(q)+δq)=1/(NDM(q)+δq) of the entire range (for example, the range of from −Nd/2 to Nd/2−1). It is thus possible to reduce the computational amount of the CFAR processing.

For example, first CFAR section210adaptively sets a threshold, and outputs, to first Doppler demultiplexer211, distance indices fb_cfar, Doppler frequency indices fsddm_cfar, and the reception power information (PowerFT(fb_cfar, fsddm_cfar+(ndm−1)×NΔfd(q))) that provide reception power greater than the threshold. In the expression, ndm is an integer of from 1 to NDM(q)+δq.

[Exemplary Operation of First Doppler Demultiplexer211]

First Doppler demultiplexer211performs the following operations, for example, based on distance indices fb_cfar, Doppler frequency indices fsddm_cfar, and the reception power information (PowerFT(fb_cfar, fsdm_cfar+(ndm−1)×NΔfd(q))) (ndm is an integer of from 1 to NDM(q)+δq)) inputted from first CFAR section210.

For example, assuming that the Doppler velocity of the target object is −1/(2Tr×NDM(q))≤fd<1/(2Tr×NDM(q)), first Doppler demultiplexer211associates the Doppler shift amounts for the transmitted Doppler multiplexed signals with fsddm_cfar+(ndm−1)×NΔfd(q)and outputs resultant demultiplexing index information (for example, fdemul_Tx#1(q), . . . , fdemul_Tx#NDM(q)) of the Doppler multiplexed signals to first direction estimator212.

Here, fdemul_Tx#n(q) indicates the Doppler frequency index of the reflected wave signal for the radar transmission signal transmitted from nth transmission antenna102(Tx #n) of qth radar section10g.

In the present embodiment, for example, transmission antennas102are switched in the time-division manner. From the above, first Doppler demultiplexer211determines, for example, that, among Doppler frequency indices fsddm_cfar+(ndm−1)×NΔfd(q)(ndm is an integer of from 1 to NDM(q)+δq), a signal with highest reception power |VFTn,z,q(fb_cfar, fsddm_cfar+(ndm−1)×NΔfd(q)|2of nth Doppler analyzer209is the reception signal for the radar transmission signal from nth transmission antenna102.

When the difference between the powers of NDM(q) Doppler frequency indices for the higher reception powers is larger than a predetermined value (threshold), first Doppler demultiplexer211may regard (or determine) that signals of the reception signals of the multistatic configuration are highly likely to be mixed, and may add an operation of removing the reception signals without performing an output for subsequent processing (for example, direction estimation processing).

The exemplary operation of first Doppler demultiplexer211has been described above.

[Exemplary Operation of Second CFAR Section210]

For example, second CFAR section210of qth radar section10gmay perform the following operations in order to receive the reflected wave signal for the radar transmission signal from radar transmitter100gof radar section10gthat differs from qth radar section10g.

For example, when δ1and δ2are set to values that differ from positive integers for Doppler shifters101, second CFAR section210may perform peak detection by, for example, searching, in the power addition values outputted from first to Nt(q)th Doppler analyzers209of first to Na(q)th signal processors206, for a power peak that matches the Doppler shift interval set for the radar transmission signal of radar section10gdifferent from qth radar section10gfor each distance index, and performing adaptive threshold processing (CFAR processing).

On the other hand, for example, when δ1and δ2are set to positive integers for Doppler shifters101, an interval of Δfd(q) or an interval of an integer multiple of Δfd(q) is used as an interval of the Doppler shift amounts. In this case, q may be 1 or 2. Therefore, the Doppler multiplexed signals may be detected as having aliasing at intervals of Δfd(q) in the Doppler frequency domain of the outputs of first to Nt(g)th Doppler analyzers209. By using such characteristics, for example, the operation of second CFAR section210can be simplified as follows.

For example, second CFAR section210of qth radar section10gdetects a Doppler peak by applying a threshold to a power addition value obtained by adding together the reception powers of the reflected wave signals for respective ranges (for example, ranges of Δfd(qe)) within the Doppler frequency range to be subjected to the CFAR processing in the output value obtained by performing power addition on the outputs of first to Nt(q)th Doppler analyzers209, the ranges corresponding to the intervals of the Doppler shift amounts applied respectively to the radar transmission signals.

Here, “qe” represents a radar number of radar section10gthat differs from qth radar section10g. For example, in the case of first radar section10g(q=1), qe may be 2, and in the case of second radar section10g(q=2), qe may be 1.

For example, second CFAR section210performs the CFAR processing on the output obtained by adding the powers of the outputs of first to Nt(q)th Doppler analyzers209of first to Na(q)th signal processors206, by calculating power addition value PowerDDMqe(fb, fsddm) obtained by adding power values PowerFTq(fb, fs) at the intervals of Δfd(qe) (for example, corresponding to +NΔfd(qe)) as illustrated in following Expression 37:

In the expression, fsddm=−Nd/2, . . . , −Nd/2+NΔfd(qe)−1. NΔfd(qe)=round(Δfd(qe)/(1/(TrNd)). In addition, round(x) is an operator that rounds off real number x and outputs an integer value.

The operation in the CFAR processing may be based on the operation disclosed in NPL 3, for example, and detailed explanation of the exemplary operation is omitted.

Thus, the Doppler frequency range on which the CFAR processing is performed in second CFAR section210can be set (e.g., reduced) to 1/(Nt(qe)+δqe)=1/(NDM(qe)+δqeof the entire range (e.g., the range of −Nd/2 to Nd/2−1), thereby reducing the computational amount of the CFAR processing.

For example, second CFAR section210adaptively sets a threshold, and outputs to second Doppler demultiplexer211distance indices fb_cfar, Doppler frequency indices fsddm_cfar, and the reception power information (PowerFT(fb_cfar, fsddm_cfar+(ndm−1)×NΔfd(qe))) that provide reception power greater than the threshold. Here, ndm is an integer of from 1 to Nt(qe)+δqe.

[Exemplary Operation of Second Doppler Demultiplexer211]

Second Doppler demultiplexer211performs the following operations based on, for example, distance indices fb_cfar, Doppler frequency indices fsddm_cfar, and the reception power information (PowerFT(fb_cfar, fsddm_cfar+(ndm−1)×NΔfd(qe)))(ndm=1 to NDM(qe)+δqeintegers)) inputted from second CFAR section210.

For example, assuming that the Doppler velocity of the target object is −1/(2Tr×NDM(qe))≤fd<1/(2Tr×NDM(qe)), second Doppler demultiplexer211associates the Doppler shift amounts of the Doppler multiplexed signals to be transmitted with fsddm_cfar+(ndm−1)×NΔfd(qe), and outputs, to second direction estimator212, the resulting demultiplexing index information (fdemul_Tx#1(qe), . . . , and fdemul_Tx#NDM(qe)) of the Doppler multiplexed signals.

Here, fdemul_Tx#n(qe) indicates the Doppler frequency index of the reflected wave signal for the radar transmission signal transmitted from nth transmission antenna102(Tx #n) of qeth radar section10g.

In the present embodiment, for example, transmission antennas102are switched in the time-division manner. From the above, second Doppler demultiplexer211includes determines, for example, that, among Doppler frequency indices fsddm_cfar+(ndm−1)×NΔfd(qe)(ndm is an integer of from 1 to NDM(q)+δq), a signal with highest reception power |VFTn,z,q(fb_cfar, fsddm_cfar+(ndm−1)×NΔfd(q)|2of nth Doppler analyzer209is the reception signal for the radar transmission signal from nth transmission antenna102.

When a difference between the powers for NDM(qe)=Nt(qe) Doppler frequency indices is larger than a predetermined value (for example, a threshold), second Doppler demultiplexer211may regard (or determine) that the reception signals for the monostatic configuration are highly likely to be mixed, and may add an operation of removing a reception signal without outputting the reception signal to subsequent processing (for example, direction estimation processing).

The exemplary operation of second Doppler demultiplexer211has been described above.

InFIG.21, first direction estimator212of qth radar section10gperforms the direction estimation processing on the target object based on, for example, the information (for example, distance indices fb_cfarand demultiplexing index information (fdemul_Tx#1(q), fdemul_Tx#2(q), . . . , and fdemul_Tx#Nt(q)) on the Doppler multiplexed signal) inputted from first Doppler demultiplexer211. Since the operation of first direction estimator212according to the present embodiment is the same as the operation of first direction estimator212according to Embodiment 1, the description thereof will be omitted.

InFIG.21, second direction estimator212of qth radar section10gperforms the direction estimation processing on the target object based on, for example, the information (for example, distance indices fb_cfarand demultiplexing index information (fdemul_Tx#1(qe), fdemul_Tx#2(qe), . . . , and fdemul_Tx#NDM(qe)) on the Doppler multiplexed signal) inputted from second Doppler demultiplexer211. Since the operation of second direction estimator212according to the present embodiment is the same as the operation of second direction estimator212according to Embodiment 1, the description thereof will be omitted.

Positioning output integrator30integrates the positioning outputs of first direction estimator212and second direction estimator212from first radar section10gand the positioning outputs of first direction estimator212and second direction estimator212from second radar section10g, and performs positioning of the target object. Since the operation of positioning output integrator30according to the present embodiment is the same as the operation of positioning output integrator30in Embodiment 1, the description thereof will be omitted.

As described above, in the present embodiment, radar apparatus1gincludes first radar section10gthat transmits radar transmission signals from a plurality of transmission antennas102, and second radar section10gthat transmits radar transmission signals from a plurality of transmission antennas102. Here, the Doppler multiplexing interval between the Doppler shift amounts applied respectively to the radar transmission signals transmitted from the plurality of transmission antennas102of first radar section10gis different from the Doppler multiplexing interval between the Doppler shift amounts applied respectively to the radar transmission signals transmitted from the plurality of transmission antennas102of second radar section10g.

Accordingly, radar apparatus1gcan demultiplex the reflected wave signals corresponding to the radar transmission signals of radar sections10gfrom the reception signals, for example, based on the Doppler multiplexing intervals set in radar sections10g.

Therefore, radar apparatus1gcan simultaneously perform radar positioning by the monostatic configuration of each of first radar section10gand second radar section10gusing time-division multiplexing transmission, and radar positioning by the multistatic configuration from first radar section10gto second radar section10gand the multistatic configuration from second radar section10gto first radar section10gby using Doppler multiplexing transmission.

Therefore, according to the present embodiment, even when time-division multiplexing is applied in the monostatic MIMO radar, the radar positioning time can be reduced as compared with the case where inter-multistatic time-division transmission is used, and the same advantages as those in Embodiment 1 can be obtained.

Further, for example, radar apparatus1gcan expand the observable Doppler range (for example, can set the observable Doppler range to +1/(2NtTr)) by performing Doppler aliasing determination using unequal-interval Doppler multiplexing, and can suppress reduction of the maximum Doppler observable by the inter-multistatic multiplexing transmission. For example, radar apparatus1gcan maintain the same observation range as the maximum Doppler in the case of time-division multiplexing transmission in which Nt transmission antennas are used.

Also in the present embodiment, for example, at least one of Variations 1 to 7 of Embodiment 1 may be applied, and the same effect can be obtained.

Embodiment 1 has been described in which the Doppler multiplexing is applied to the transmission multiplexing in the monostatic MIMO radar, but the present disclosure is not limited thereto, and the code multiplexing may be applied. In the present embodiment, an exemplary operation when Doppler multiplexing is applied to a multistatic MIMO radar and code multiplexing is applied to a monostatic MIMO radar will be described.

FIG.25is a block diagram illustrating an exemplary configuration of radar apparatus1haccording to the present embodiment. InFIG.25, components that perform the same operations as those inFIG.3are denoted by the same reference numerals. Hereinafter, operations different from those of Embodiment 1 will be mainly described.

Radar apparatus1hillustrated inFIG.25may include, for example, a plurality of radar sections10h, synchronization controller20, and positioning output integrator30(not illustrated inFIG.25).FIG.25illustrates an exemplary configuration of one radar section10h.

InFIG.25, synchronization controller20includes, for example, radar transmission signal generator301including modulation signal generator302and Voltage-Controlled Oscillator (VCO)303, and signal controller304. Radar transmission signal generator301generates a radar transmission signal (for example, a predetermined frequency-modulated wave (chirp signal)) based on, for example, control by signal controller304, and outputs the generated radar transmission signal to a plurality of radar sections10h(for example, radar transmitters100h) constituting the multistatic configuration. The chirp signal outputted by synchronization controller20is also inputted to radar receiver200h(each mixer204). The operation of synchronization controller20may be the same as that of Embodiment 1.

In addition, each of the plurality of radar sections10hillustrated inFIG.25may transmit radar transmission signals by code multiplexing, for example, for each Doppler shift amount. By way of example,FIG.25illustrates an example in which code multiplexers108are provided to code-multiplex a signal to be transmitted from two transmission antennas102for each output of one Doppler shifter101(for example, each signal to which one Doppler shift amount is applied). However, the present disclosure is not limited thereto, and the longer the code length of code multiplexing, the more the signals transmitted from transmission antennas102can be code-multiplexed.

[Exemplary Configuration of Radar Transmitter100h]

To apply Doppler shift amount DOPn(q) to the chirp signal inputted from VCO303, each of Doppler shifters101of qth radar section10happlies phase rotation Φn,q(m) to the chirp signal for each transmission period Trof the chirp signal, and outputs the Doppler-shifted signal to code multiplexers108.

For example, qth radar section10hmay apply a predetermined phase rotation Φn,q(m) to apply Doppler shifts that provide Doppler multiplexing intervals different between radar section10hthat perform multistatic radar multiplexing transmission (an exemplary operation will be described later). Here, n is an integer of from 1 to NDM(q), and q is 1 or 2.

For example, code multiplexing controller107controls code multiplexers108such that one or more codes with code length Ncolenare superimposed on the output of each of Doppler shifters101(an exemplary operation will be described later). In addition, code multiplexing controller107outputs information on the code multiplexing control to radar receiver200h(output switcher214).

Note that same code length Ncolenis used for both first radar section10hand second radar section10h. This makes it easy to distinguish Doppler multiplexed signals used in both first radar section10hand second radar section10h.

For example, one or more (two inFIG.25) code multiplexers108are connected to each Doppler shifter101. Code multiplexers108superimpose codes having code length Ncolenon the outputs of Doppler shifters101under the control of code multiplexing controller107(an exemplary operation will be described later).

The signals outputted from code multiplexers108are amplified to a predetermined transmission power, and are emitted from transmission antennas102(Tx #1 to Tx #Nt(q) into space.

Here, in the present embodiment, for example, the numbers of transmission antennas102(or the numbers of transmission antennas102used) included in respective qth radar sections10h(q=1 or 2) may be the same or different. In the following description, the number of transmission antennas in qth radar section10his referred to as Nt(q) (or simply “Nt”). Here, Nt(q)>1.

[Exemplary Configuration of Radar Receiver200h]

InFIG.25, radar receiver200hincludes Na reception antennas202(for example, Rx #1 to Rx #Na), and serves as a component of an array antenna. Further, radar receiver200hincludes Na antenna system processors201, CFAR sections210, Doppler demultiplexers211, code separators215, and direction estimators212.

For example, the number of reception antennas202may be the same or different between qth radar sections10h(e.g., q=1 or 2). Hereinafter, the number of reception antennas in qth radar section10hwill be referred to as “Na(q).” Here, Na(q)≥1.

The operation of reception radio203of antenna system processor201is the same as that of Embodiment 1, and the description thereof is omitted.

The operations of A/D converter207and beat frequency analyzer208in signal processor206hof the antenna system processor201are the same as those in Embodiment 1, and the explanation thereof is omitted.

Output switcher214performs, for example, an operation associated with the operation of code multiplexing controller107based on the control by code multiplexing controller107of radar transmitter100h, and selectively switches a destination of an output of beat frequency analyzer208to one of NcolenDoppler analyzers209(for example, also represented by Doppler analyzers209-1to209-Ncolen) for each transmission period Tr.

For example, when code multiplexing controller107performs control to add a first code element to an output signal of Doppler shifters101, output switcher214outputs an output signal from beat frequency analyzer208to first Doppler analyzer209, but does not output the output signal to other Doppler analyzers209.

Similarly, for example, when code multiplexing controller107performs control to add a second code element to the output signal of Doppler shifters101, output switcher214outputs the output signal from beat frequency analyzer208to second Doppler analyzer209, but does not output the output signal to other Doppler analyzers209.

Similarly, for example, when code multiplexing controller107performs control to add a nclth code element to the output signal of Doppler shifters101, output switcher214outputs the output signal from beat frequency analyzer208to nclth Doppler analyzer209but does not output the output signal to other Doppler analyzers209. Here, ncl is an index indicating each element of the code with code length Ncolen, and is represented by an integer of ncl=1 to Ncolen.

Here, for example, code multiplexing controller107may perform control to apply the Ncolenth code element to the output signal of Doppler shifters101, and then may perform control to apply the first code element to the output signal of Doppler shifters101at subsequent transmission period Tr. Thereafter, code multiplexing controller107cyclically repeatedly adds a code element to an output signal of Doppler shifters101for each transmission period Tr. Output switcher214switches the output destination of the output signal from beat frequency analyzer208in accordance with the operation of control of code multiplexing controller107.

The nclth Doppler analyzer209(or Doppler analyzer209-ncl) of zth signal processor206hperforms Doppler analysis for each distance index fbbased on a beat frequency response for transmission period Trin which a signal is transmitted with the nclth code element being superimposed thereon, among beat frequency responses RFTz(fb, 1), RFTz(fb, 2), . . . , and RFTz(fb, NC) obtained by NCchirp pulse transmissions of the chirp signals.

For example, when the control for applying codes composed of Ncolencode elements to the output signals of Doppler shifters101in an order from the first code element to the Ncolenth code element for each transmission period Tris cyclically repeated based the control of code multiplexing controller107, Doppler analyzers209may apply Fast Fourier Transform (FFT) processing as illustrated in following Expression 38, and output VFTncl,z,q(fb, fs) as the output of nclth Doppler analyzer209in zth signal processor206h. Note that Nsis an integer multiple of Ncolen, and may be set to Ns=Nc/Ncolen, for example. Note that RFTz,q(fb, m) represents the beat frequency response outputted from beat frequency analyzer208in qth radar section10.

Here, the FFT size is Ns, and the maximum Doppler frequency at which no aliasing occurs and which is derived from the sampling theorem is +1/(2TrNs). Further, the Doppler frequency interval of Doppler frequency index fsis 1/(Ns×Tr), and the range of Doppler frequency index fsis fs=−Ns/2, . . . , 0, . . . , and Ns/2−1.

In the following, a case where Nsis a power of 2 will be described. When Nsis not a power of 2, zero-padded data is included, for example, to obtain the data size of a power of 2 and the FFT processing can thus be performed. In the FFT processing, Doppler analyzer209may perform multiplication by a window function coefficient such as the Han window or the Hamming window. It is possible to suppress sidelobes generated around the beat frequency peak by applying a window function.

InFIG.25, for example, first CFAR section210selectively extracts local peaks of reflected wave signals for radar transmission signals of qth radar section10h(corresponding radar), which has the monostatic configuration, using outputs VFTncl,z,q(fb, fs) of first to Ncolenth Doppler analyzers209of first to Na(q)th signal processors206h. For example, first CFAR section210may perform the CFAR processing of performing the adaptive threshold determination after power addition at intervals matching the Doppler multiplexing intervals set for the radar transmission signals transmitted from qth radar section10h, extract distance indices fb_cfarand Doppler frequency indices fsddm_cfarthat provide local peak signals, and output extracted distance indices fb_cfarand Doppler frequency indices fsddm_cfarto first Doppler demultiplexer211(an exemplary operation will be described later).

The radar transmitter having the monostatic configuration in first radar section10his radar transmitter100hof first radar section10h. Similarly, the radar transmitter having the monostatic configuration in second radar section10his radar transmitter100hof second radar section10h.

Further, for example, second CFAR section210selectively extracts local peaks of the reflected wave signals for the radar transmission signals of another radar section10hdifferent from qth radar section10h(the corresponding radar), which has the multistatic configuration, using outputs VFTncl,z,q(fb, fs) of first to Ncolenth Doppler analyzers209of first to Na(q)th signal processors206h. For example, second CFAR section210may perform the CFAR processing of performing the adaptive threshold determination after the power addition at intervals matching the Doppler multiplexing intervals set for the radar transmission signals transmitted from radar section10hother than qth radar section10h, extract distance indices fb_cfarand Doppler frequency indices fsddm_cfarthat provide local peak signals, and output the extracted distance indices fb_cfarand Doppler frequency indices fsdm_cfarto second Doppler demultiplexer211(an exemplary operation will be described later).

The radar transmitter having the multistatic configuration in first radar section10his radar transmitter100hof second radar section10h. Similarly, radar transmitter100hhaving the multistatic configuration in second radar section10his radar transmitter100hof first radar section10.

Next, the operation of qth Doppler demultiplexer211will be described together with the exemplary operation of Doppler shifters101and qth CFAR section210. For example, q=1 or 2 may hold true.

Doppler demultiplexers211of qth radar section10hmay include, for example, first Doppler demultiplexer211that performs Doppler demultiplexing on the reflected wave signals for the radar transmission signals from qth radar section10h(corresponding radar), which has the monostatic configuration, using the outputs of first CFAR section210and second Doppler demultiplexer that performs Doppler demultiplexing on the reflected wave signals for the radar transmission signals from another radar section10hdifferent from qth radar section10h, which has the multistatic configuration, using the outputs of second CFAR section210.

The operation of qth Doppler demultiplexer211is related to the operation of Doppler shifters101, code multiplexing controller107, and code multiplexers108of radar transmitter100h. Similarly, the operation of qth CFAR section210is related to the operation of Doppler shifters101of radar transmitter100h.

Hereinafter, an exemplary operation of Doppler shifters101, code multiplexing controller107, and code multiplexers108will be described, and thereafter, an exemplary operation of qth CFAR section210and an exemplary operation of qth Doppler demultiplexer211will be described.

To begin with, exemplary operations of Doppler shifters101, code multiplexing controller107, and code multiplexer108in radar transmitter100hwill be described.

For example, number NDM(q) of Doppler multiplexing and number Ncodeof code multiplexing may be preset to satisfy NDM×Ncode≥Nt(q) for first to Nt(q)th transmission antennas102in qth radar section10h.

In addition, for example, an orthogonal code such as a Walsh Hadamard code or a pseudo-orthogonal code may be applied to the code multiplexing. By using same code length Ncolenfor both first radar section10hand second radar section10h, it becomes easier for radar apparatus1hto distinguish the Doppler multiplexed signals used in each of first radar section10hand second radar section10h.

In addition, in the present embodiment, first to NDM(q)th Doppler shifters101of qth radar section10hperform Doppler multiplexing transmission by applying respective different Doppler shift amounts DOPn(q) of predetermined Doppler multiplexing intervals Δfd(q) to the chirp signals inputted from synchronization controller20. Here, n is an integer of from 1 to NDM(q). At this time, Doppler multiplexing intervals Δfd(q) may satisfy the following setting conditions (1) and (2).(1) The Doppler multiplexing intervals between the plurality of radar sections10hmay be set to different intervals. For example, the intervals for respective Doppler shift amounts applied to the radar transmission signals transmitted from the plurality of transmission antennas102of first radar section10hand the intervals for respective Doppler shift amounts applied to the radar transmission signals transmitted from the plurality of transmission antennas102of second radar section10hmay be different from each other (for example, Δfd(1) #Δfd(2)).(2) For example, the ratio between Δfd(1) and Δfd(2) may be set so as not to match an integer. For example, of Δfd(1) and Δfd(2), the ratio of the Doppler multiplexing interval having the larger value to the Doppler multiplexing interval having the smaller value may be different from the integer. For example, Δfd(1)/Δfd(2) or Δfd(2)/Δfd(1) may be set so as not to match the integer (so as to be different from the integer).

Hereinafter, an example of setting Doppler multiplexing interval Δfd(q) will be described.

For example, Doppler shifters101apply the same phase rotation within a period (for example, a transmission period of Ncolen×Tr) of a code length in code multiplexing. For example, Doppler shifter101may apply a predetermined phase rotation (e.g., ranging from 0 to 2π) to the chirp signal at every Ncolen×Trperiod.

Here, in Doppler analyzers209, the range of Doppler frequency fdin which no aliasing is generated and which is derived from the sampling theorem is from −1/(2Tr×Ncolen(q))≤fd<1/(2Tr×Ncolen(q)). For example, even when the Doppler frequency exceeds the range of Doppler frequency fdin which no aliasing occurs, the range of Doppler frequency fdobserved in Doppler analyzers209is −1/(2Tr×Ncolen(q))≤fd<1/(2Tr×Ncolen(q)).

Therefore, for example, when Doppler shifters101apply a Doppler shift within −1/(2Tr×Ncolen(q))≤fd<1/(2Tr×Ncolen(q)), maximum Doppler shift interval Δfdmax for NDM(q) Doppler multiplexed signals is Δfdmax=1/(TrNcolenNDM(q)). For example, Doppler shifters101may set Δfd(1) and Δfd(2) to different intervals within the range up to Δfdmax. Accordingly, Doppler shifters101can set the Doppler shift within the range of 0 to 2π that is the phase rotation providing the Doppler shift.

For example, the Doppler multiplexing intervals of each of first radar section10hand second radar section10hmay be set to Δfd(1)=1/(Tr×Ncolen×(NDM(1)+δ1)) and Δfd(2)=1/(Tr×Ncolen×(NDM(2)+δ2)), respectively.

Here, δ1, δ2≥0 and satisfies NDM(1)+δ1≠NDM(2)+δ2. Further, δ1and δ2may be set so that the ratio between NDM(1)+δ1and NDM(2)+δ2does not match an integer. With this setting, the Doppler multiplexing interval between the plurality of radar sections10h(for example, between first radar section10hand second radar section10h) is different (Δfd(1) #Δfd(2)), and the ratio between Δfd(1) and Δfd(2) does not match an integer.

Note that each of δ1and δ2may be a positive integer or a positive real number. For example, by setting δ1and δ2to be positive integers, the processes in first CFAR section210and second CFAR section210, which will be described later, can be simplified. Descriptions are given below of a case where δ1and δ2are each set to zero or a positive integer. However, the present disclosure is not limited thereto, and positive real numbers may be set.

In addition, a configuration may be adopted in which parameters (for example, values such as Doppler multiplexing intervals Δfd(q) or δq) which, for example, cause the Doppler shift amounts to match each other between first radar section10hand second radar section10hare excluded in advance. For example, for all of n1and n2, the parameters may be set so as to satisfy following Expression 39:

By this setting, for example, Doppler shift amount DOPn1(1) applied to the radar transmission signal of first radar section10hand Doppler shift amount DOPn2(2) applied to the radar transmission signal of second radar section10hare set to values different from each other.

The parameter setting satisfying Expression 39 may be applied, for example, to situations in which both radar apparatus1hand the target are supposed to be mostly stationary. For example, when radar apparatus1hand the target are both stationary, a Doppler component is zero. Therefore, for example, even when the reflected wave signal for the radar transmission signal of first radar section10hand the reflected wave signal for the radar transmission signal of second radar section10hare included in the same distance index, Doppler shift amount DOPn(q) for each MIMO multiplexed transmission signal is different. Thus, radar apparatus1hcan demultiplex and receive both the reflected wave signals by utilizing the difference in detected Doppler components.

A description is given below of exemplary setting of Doppler shift amounts.

Setting Example 1

For example, when NDM(1)≠NDM(2) and the ratio of NDM(1) to NDM(2) does not match an integer multiple, then Δfd(1)=1/(Tr×Ncolen×NDM(1)) and Δfd(2)=1/(Tr×Ncolen×NDM(2)) may be set. In this case, the above-described setting conditions of the Doppler multiplexing intervals are satisfied.

In this case, the Doppler multiplexing interval can be maximized within the range of −1/(2Tr×Ncolen)≤fd<1/(2Tr×Ncolen) of Doppler frequencies fdobserved by Doppler analyzers209. Therefore, for example, even in a case where the Doppler spectrum has a spread, such as a case where the moving speed of the target is not constant and has a component such as acceleration, the interference effect between the Doppler multiplexed signals can be reduced. For example, when the Doppler velocity observable by using the non-uniformity of the Doppler multiplexing intervals as disclosed in PTL 1 does not increase, the Doppler velocity is −1/(2Tr×Ncolen×NDM(1))≤fd<1/(2Tr×Ncolen×NDM(1)) or −1/(2Tr×Ncolen×NDM(2))≤fd<1/(2Tr×Ncolen×NDM(2)).

By way of example,FIG.26illustrates an example of Doppler shift setting of first radar section10h(upper part ofFIG.26) and an example of Doppler shift setting of second radar section10h(lower part ofFIG.26) in a case of NDM(1)=Nt(1)=3 and NDM(2)=Nt(2)=4. InFIG.26, Δfd(1)=1/(3Tr×Ncolen) (e.g., δ1=0) is set and Δfd(2)=1/(4Tr×Ncolen) (e.g., δ2=0) is set. For example, inFIG.26, Doppler shift amounts DOP1(1) and DOP1(2) assigned to the first Doppler multiplexed signals of each of first radar section10hand second radar section10hare set to values corresponding to Doppler frequency fd=0. For example, inFIG.26, at least one Doppler shift amount is identical between first radar section10hand second radar section10h.

By way of another example,FIG.27illustrates an example of Doppler shift setting of first radar section10h(upper part ofFIG.27) and an example of Doppler shift setting of second radar section10h(lower part ofFIG.27) in the case of NDM(1)=Nt(1)=3 and NDM(2)=Nt(2)=4. InFIG.27as inFIG.26, Δfd(1)=1/(3Tr×Ncolen) (e.g., δ1=0) is set, and Δfd(2)=1/(4Tr×Ncolen) (e.g., δ2=0) is set. Further, inFIG.27, Doppler shift amounts DOPn1(1) and DOPn2(2) of each of first radar section10hand second radar section10hare set so that the Doppler shift amounts do not match each other between first radar section10hand second radar section10h(for example, so as to satisfy Expression 39).

Setting Example 2

For example, the above-described setting condition for Doppler multiplexing intervals are satisfied when NDM(1) #NDM(2) and the ratio of NDM(1) and NDM(2) matches an integer, when Δfd(1)=1/(Tr×Ncolen×(NDM(1)+1)) and Δfd(2)=1/(Tr×Ncolen×(NDM(2)+1)), when Δfd(1)=1/(Tr×Ncolen×NDM(1)) and Δfd(2)=1/(Tr×Ncolen×(NDM(2)+1)), or when Δfd(1)=1/(Tr× Ncolen×(NDM(1)+1)) and Δfd(2)=1/(Tr×Ncolen×NDM(2)).

In this case, the Doppler multiplexing interval can be maximized within the range of −1/(2Tr×Ncolen)≤fd<1/(2Tr×Ncolen) of Doppler frequencies fdobserved by Doppler analyzers209. Therefore, even in a case where the Doppler spectrum has a spread, such as a case where the moving speed of the target is not constant and has a component such as acceleration, the interference effect between the Doppler multiplexed signals can be reduced. Further, for example, when the Doppler multiplexing intervals include a non-uniform part, the Doppler velocity observable by using the non-uniform Doppler intervals is −1/(2Tr×Ncolen)≤fd<1/(2Tr×Ncolen) as disclosed in PTL 1.

By way of example,FIG.28illustrates an example of Doppler shift setting of first radar section10h(upper part ofFIG.28) and an example of Doppler shift setting of second radar section10h(lower part ofFIG.28) in a case of NDM(1)=2 and NDM(2)=4. InFIG.28, Δfd(1)=1/(3Tr×Ncolen) (e.g., δ1=1) is set and Δfd(2)=1/(4Tr×Ncolen) (e.g., δ2=0) is set. For example, inFIG.28, Doppler shift amounts DOP1(1) and DOP1(2) assigned to the first Doppler multiplexed signals of each of first radar section10hand second radar section10hare set to values corresponding to Doppler frequency fd=0. For example, inFIG.28, at least one Doppler shift amounts match each other between first radar section10hand second radar section10h.

Further, for example, regarding the Doppler shifts set for first radar section10illustrated inFIG.28, a Doppler shift for providing an interval of Δfd(1) is not assigned on the negative side and thus a non-uniform Doppler multiplexing interval portion is included. For example, the Doppler shift interval set in first radar section10his set to one of intervals obtained by unequally dividing the Doppler frequency range to be subjected to the Doppler analysis.

By way of another example,FIG.29illustrates an example of Doppler shift setting of first radar section10h(upper part ofFIG.29) and an example of Doppler shift setting of second radar section10h(lower part ofFIG.29) in the case of NDM(1)=2 and NDM(2)=4. InFIG.29as inFIG.28, Δfd(1)=1/(3Tr×Ncolen) (e.g., δ1=1) is set, and Δfd(2)=1/(4Tr×Ncolen) (e.g., δ2=0) is set. Further, inFIG.29, Doppler shift amounts DOPn1(1) and DOPn2(2) applied to respective transmission antennas102of first radar section10hand second radar section10hare set so that the Doppler shift amounts do not match each other between first radar section10hand second radar section10h(for example, so as to satisfy Expression 39).

Further, for example, regarding the Doppler shifts set for first radar section10hillustrated inFIG.29, a Doppler shift for providing an interval of Δfd(1) is not assigned on the negative side and thus a non-uniform Doppler multiplexing interval portion is included. For example, the Doppler shift interval set in first radar section10his set to one of intervals obtained by unequally dividing the Doppler frequency range to be subjected to the Doppler analysis.

In the Doppler frequency domain, the position where no Doppler shift is assigned is not limited to the negative-side region as illustrated inFIGS.28and29, and may be a positive-side region.

Setting Example 3

For example, in the case of NDM(1)=NDM(2), the above-described setting conditions for Doppler multiplexing intervals are satisfied when Δfd(1)=1/(Tr×Ncolen×NDM(1)) and Δfd(2)=1/(Tr× Ncolen×(NDM(2)+1)) are set, when Δfd(1)=1/(Tr×Ncolen×(NDM(1)+1)) and Δfd(2)=1/(Tr×Ncolen×NDM(2)) are set, or when Δfd(1)=1/(Tr×Ncolen×(NDM(1)+1)) and Δfd(2)=1/(Tr×Ncolen×(NDM(1)+2)) are set.

In this case, the Doppler multiplexing interval can be maximized within the range of −1/(2Tr×Ncolen)≤fd<1/(2Tr×Ncolen) of Doppler frequencies fdobserved by Doppler analyzers209. Therefore, for example, even in a case where the Doppler spectrum has a spread, such as a case where the moving speed of the target is not constant and has a component such as acceleration, the interference effect between the Doppler multiplexed signals can be reduced. Further, for example, when the Doppler multiplexing intervals include a non-uniform part, the Doppler velocity observable by using the non-uniform Doppler intervals is −1/(2Tr×Ncolen)≤fd<1/(2Tr×Ncolen) as disclosed in PTL 1.

By way of example,FIG.30illustrates an example of Doppler shift setting of first radar section10h(upper part ofFIG.30) and an example of Doppler shift setting of second radar section10h(lower part ofFIG.30) in a case of NDM(1)=2 and NDM(2)=2. InFIG.30, Δfd(1)=1/(3Tr×Ncolen) (e.g., δ1=1) is set and Δfd(2)=1/(4Tr×Ncolen) (e.g., δ2=2) is set. For example, inFIG.30, Doppler shift amounts DOP1(1) and DOP1(2) assigned to the first Doppler multiplexed signals of first radar section10hand second radar section10hare set to values corresponding to Doppler frequency fd=0. For example, inFIG.30, at least one Doppler shift amounts match each other between first radar section10hand second radar section10h.

Further, for example, regarding the Doppler shifts set for first radar section10hillustrated inFIG.30, a Doppler shift for providing an interval of Δfd(1) is not assigned on the negative side and thus a non-uniform Doppler multiplexing interval portion is included. Further, for example, regarding the Doppler shifts set for second radar section10hillustrated inFIG.30, two Doppler shifts for providing an interval of Δfd(2) are not assigned on the negative side and thus a non-uniform Doppler multiplexing interval portion is included. For example, the Doppler shift interval set for each of first radar section10hand second radar section10his set to one of intervals obtained by unequally dividing the Doppler frequency range to be subjected to the Doppler analysis.

By way of another example,FIG.31illustrates an example of Doppler shift setting of first radar section10h(upper part ofFIG.31) and an example of Doppler shift setting of second radar section10h(lower part ofFIG.31) in the case of NDM(1)=2 and NDM(2)=2. InFIG.31as inFIG.30, Δfd(1)=1/(3Tr×Ncolen) (e.g., δ1=1) is set and Δfd(2)=1/(4Tr×Ncolen) (e.g.,82-2) is set. Further, inFIG.31, Doppler shift amounts DOPn1(1) and DOPn2(2) applied to respective transmission antennas102of first radar section10hand second radar section10hare set so that the Doppler shift amounts do not match each other between first radar section10hand second radar section10h(for example, so as to satisfy Expression 39).

Further, for example, regarding the Doppler shifts set for first radar section10hillustrated inFIG.31, a Doppler shift for providing an interval of Δfd(1) is not assigned on the negative side and thus a non-uniform Doppler multiplexing interval portion is included. Further, for example, regarding the Doppler shifts set for second radar section10hillustrated inFIG.31, two Doppler shifts for providing an interval of Δfd(2) are not assigned on the positive side and thus a non-uniform Doppler multiplexing interval portion is included. For example, the Doppler shift interval set for each of first radar section10hand second radar section10his set to one of intervals obtained by unequally dividing the Doppler frequency range to be subjected to the Doppler analysis.

The example of setting the Doppler shift amounts have been described above.

For example, Doppler shifters101may set the Doppler shift amount using the Doppler multiplexing interval set as described above, and apply the phase rotation for applying the Doppler shift amount to the chirp signal at each chirp transmission period.

For example, phase rotations Φn,q(m) for applying Doppler shift amounts DOPn(q) for Doppler shift intervals Δfd(q) to NDM(q) Doppler multiplexed signals are expressed by following Expression 40. Expression 41 represents Doppler shift amounts DOPn(q) for Doppler shift intervals Δfd(q).

In the expression, Φ0is the initial phase and ΔΦ0is a reference Doppler shift phase. Note that α is a coefficient for offsetting the Doppler shift amount for each Doppler multiplexed signal and a real value may be used for the coefficient. For example, when α=1, the Doppler shift amount for the first Doppler multiplexed signal is zero. In addition, floor[x] represents the floor function outputting the minimum integer less than or equal to real number x. As illustrated in Expression 40, Doppler shifters101perform transmission by applying the same phase rotation within a period (e.g., a transmission period of Ncolen×Tr) of code length Ncolenfor code multiplexing.

The exemplary operation of Doppler shifters101has been described above.

[Exemplary Operation of Code Multiplexing Controller107]

Code multiplexing controller107presets number CodeDop(n) of code multiplexing for each of NDM(q) Doppler multiplexed signals, and assigns codes such that the sum of the numbers of code multiplexing matches number Nt of transmission antennas102used for multiplexing transmission. Here, n is an integer of from 1 to NDM(q). In addition, CodeDop(n) is set as an integer value within the range of 1≤CodeDop(n)≤Ncode.

For example, CodeDop(1)=2 and CodeDop(2)=2 are set when the number of code multiplexing is 2 for each Doppler multiplexed signal for which number Nt of transmission antennas used for multiplexing transmission is 4, Ncode is 2, and NDM(q) is 2. In this case, the sum of CodeDop(n) matches Nt of transmission antennas (=4) used for multiplexing transmission.

Further, CodeDop(1)=2, CodeDop(2)=2, and CodeDop(2)=1 are set, for example, when the number of code multiplexing is 2 for each Doppler multiplexed signal for which number Nt of transmission antennas used for multiplexing transmission is 5, Ncodeis 2, and NDM(q) is 3. In this case, the sum of CodeDop(n) corresponds to number Nt of transmission antennas (=5) used for multiplexing transmission.

For example, code multiplexing controller107may use an orthogonal code sequence having code length Ncolen.

In the following, the orthogonal code sequence with code length Ncolenis denoted as Codencm={OCncm(1), OCncm(2), . . . , and OCncm(Ncolen)}. OCncm(noc) represents the nocth code element in ncmth orthogonal code sequence Codencm. Here, noc is the index of the code element and is an integer of noc=1 to Ncolen. Ncmrepresents the number of orthogonal code sequences with code length Ncolen, and the orthogonal codes are used such that Ncode≤ Ncm. The orthogonal code sequences may be, for example, codes that are orthogonal (uncorrelated) to each other. For example, the orthogonal code sequences may be Walsh-Hadamard codes.

For example, when Ncode=2, the Walsh-Hadamard codes with code length Ncolen=2 may be used. In this instance, the orthogonal code sequences are Code1={1, 1} and Code2={1, −1}. Note that, when a code element constituting the orthogonal code sequences is 1, 1=exp(j0) holds true and, thus, the phase thereof is 0. In addition, when a code element constituting the orthogonal code sequences is −1, −1=exp(jπ) holds true and, thus, the phase thereof is π.

For example, when Ncodeis 4, the Walsh-Hadamard-codes with code length Ncolen=4 may be used. In this case, the orthogonal code sequences are Code1={1, 1, 1, 1}, Code2={1−1, 1, −1}, Code3={1, 1−1, −1} and Code4={1−1−1, 1}. For example, when CodeDop(1)=2, code multiplexing controller107may assign Code to the first code and Code2to the second code, for example, to further perform code multiplexing on the Doppler multiplexed signals.

For example, code multiplexer108assigns a code to an output signal of nth Doppler shifter101under the control of code multiplexing controller107. For example, code multiplexer108may apply the phase rotation illustrated in following Expression 42 to the output signal of nth Doppler shifter101:

Here, Ψndopcode(n),n,q(m) represents phase rotations for applying code multiplexing to the output of nth Doppler shifter101in mth transmission period in qth radar section10h. Here, ndopcode(n) is assigned to the output of nth Doppler shifter101under the control of code multiplexing controller107and represents the index of the code, and is an integer of ndopcode(n)=1 to CodeDop(n). For example, when ndopcode(n)=1, a phase rotation by using the code of Code may be applied.

Here, angle[x] is an operator outputting the radian phase of real number x, and for example, angle[1]=0, angle[−1]=π, angle[j]=π/2, and angle[−j]=π/2. In addition, floor[x] is an operator that outputs the largest integer that does not exceed real number x. The character “j” is an imaginary unit. Here, mod(x, y) denotes a modulo operator and is a function that outputs the remainder after x is divided by y. In addition, m is an integer from 1 to Nc. Ncis the number of transmission periods used for radar positioning.

For example, when NDM(1)=NDM(2)=3, ΔΦ0=0, Φ0=0, δ1=1, and δ2=2, it is possible to perform MIMO multiplexing transmission using five transmission antennas102in a case where Ncolen=2, CodeDop(1)=1, CodeDop(2)=2, and CodeDop(3)=2 are set in both first radar section10hand second radar section10h. For example, the Doppler multiplexing intervals are set to Δfd(1)=1/(4TrNcolen) and Δfd(2)=1/(5TrNcolen). Further, for example, when α=1, Doppler shift amount DOPn(q) corresponding to nth transmission antenna102is expressed by following Expression 43:

Further, for example, phase rotations Φn,q(m) for applying, to input mth chirp signals, Doppler shift amounts DOPn(q) different for respective nth Doppler multiplexed signals (n=1, 2, or 3) and phase rotations Ψndopcode(n),n,q(m) applied to the output signal of nth Doppler shifter101of qth radar section10hare expressed by following Expression 44:

For example, when first radar section10hperforms transmission using Doppler multiplexing and code multiplexing using number Nt=5 of transmission antennas, first Doppler shifter101applies phase rotation Φ1,1(m) and first code multiplexer108applies phase rotation Ψ1,1,1(m) to the chirp signal inputted from synchronization controller20at each transmission period in first radar section10has given in following Expression 45. The output of first code multiplexer108is output from, for example, first transmission antenna102(Tx #1). Here, cp(t) denotes the chirp signal for each transmission period.

Further, for example, second Doppler shifter101applies phase rotation Φ2,1(m) and first code multiplexer108applies phase rotation Ψ1,2,1(m) to the chirp signal inputted from synchronization controller20at each transmission period in first radar section10has given by following Expression 46. The output of first code multiplexer108is output from second transmission antenna102(Tx #2).

Further, for example, second Doppler shifter101applies phase rotation Φ2,1(m) and second code multiplexer108applies phase rotation Ψ2,2,1(m) to the chirp signal inputted from synchronization controller20in first radar section10hfor each transmission period as given by following Expression 47. The output of second code multiplexer108is output from third transmission antenna102(Tx #3).

Further, for example, third Doppler shifter101applies phase rotation Φ3,1(m) and first code multiplexer108applies phase rotation Ψ1,3,1(m) to the chirp signal inputted from synchronization controller20at each transmission period in first radar section10has given by following Expression 48. The output of first code multiplexer108is output from fourth transmission antenna102(Tx #4).

Further, for example, third Doppler shifter101applies phase rotation Φ3,1(m) and second code multiplexer108applies phase rotation Ψ2,3,1(m) to the chirp signal inputted from synchronization controller20at each transmission period in first radar section10has given by following Expression 49. The output of second code multiplexer108is output from fifth transmission antenna102(Tx #5).

Further, for example, when second radar section10hperforms transmission using Doppler multiplexing and code multiplexing using number Nt=5 of transmission antennas, first Doppler shifter101applies phase rotation Φ1,2(m) and first code multiplexer108applies phase rotation Ψ1,1,2(m) to the chirp signal inputted from synchronization controller20at each transmission period in second radar section10has given in following Expression 50. The output of first code multiplexer108is output from, for example, first transmission antenna102(Tx #1). Here, cp(t) denotes the chirp signal for each transmission period.

Further, for example, second Doppler shifter101applies phase rotation Φ2,2(m) and first code multiplexer108applies phase rotation Ψ1,2,2(m) to the chirp signal inputted from synchronization controller20at each transmission period in second radar section10has given by following Expression 51. The output of first code multiplexer108is output from second transmission antenna102(Tx #2).

Further, for example, second Doppler shifter101applies phase rotation Φ2,2(m) and second code multiplexer108applies phase rotation Ψ2,2,2(m) to the chirp signal inputted from synchronization controller20at each transmission period in second radar section10has given by following Expression 52. The output of second code multiplexer108is output from third transmission antenna102(Tx #3).

Further, for example, third Doppler shifter101applies phase rotation Φ3,2(m) and first code multiplexer108applies phase rotation Ψ1,3,2(m) to the chirp signal inputted from synchronization controller20at each transmission period in second radar section10has given by following Expression 53. The output of first code multiplexer108is output from fourth transmission antenna102(Tx #4).

Further, for example, third Doppler shifter101applies phase rotation Φ3,2(m) and second code multiplexer108applies phase rotation Ψ2,3,2(m) to the chirp signal inputted from synchronization controller20at each transmission period in second radar section10has given by following Expression 54. The output of second code multiplexer108is output from fifth transmission antenna102(Tx #5).

As described above, setting the Doppler multiplexing intervals and application of code multiplexing for each of first radar section10hand second radar section10hare performed such that the above-described setting conditions for Doppler multiplexing intervals are satisfied. It is thus possible for radar sections10hto perform multiplexing transmission using a larger number of transmission antennas.

Further, since the number of Doppler multiplexing is less than the number of transmission antennas, the Doppler components corresponding to the reflected wave signals for the radar transmission signals from first radar section10hand second radar section10hare more likely to appear at different positions within the range of −1/(2Tr×Ncolen)≤fd<1/(2Tr×Ncolen) of Doppler frequencies fdobserved in Doppler analyzers209. Thus, it becomes easier to separate the radar reflected waves (reception signals) corresponding to first radar section10hand second radar section10hfrom each other.

By way of example,FIG.32illustrates an example of a case where all the powers of outputs (for example, received Doppler frequencies) of first to Ncolenth Doppler analyzers209are added in a case where the reflected wave signals for the radar transmission signals from first radar section10hand second radar section10hare received. InFIG.32, the vertical axis represents the distance axis, and the horizontal axis represents the Doppler frequency axis. Further, inFIG.32, Doppler components having high power are represented by arrows.

Doppler-multiplexed and code-multiplexed radar transmission signals are transmitted from a plurality of transmission antennas102. Since different Doppler shifts are applied respectively to the radar transmission signals, the reception quality (e.g., Signal to Noise Ratio (SNR)) can be improved and the accuracy of distinguishing (or detecting) the Doppler multiplexing intervals Δfd(1) and Δfd(2) can be enhanced by adding all the powers of the outputs of first to Ncolenth Doppler analyzers209. Further, since the radar transmission signals are transmitted using different Doppler multiplexing intervals for each of first radar section10hand second radar section10h, radar apparatus1hcan distinguish, based on the Doppler multiplexing intervals, whether the reflected wave signals for the radar transmission signals are reflected wave signals for the radar transmission signals of first radar section10hor of second radar section10h.

When the Doppler components corresponding to the intervals of Δfd(1) (1/(3Tr×Ncolen) in the example ofFIG.32) or the Doppler components corresponding to an integer multiple of intervals Δfd(1) are observed at distance index fb1 or fb2 illustrated inFIG.32, radar apparatus1hcan distinguish (or detect) that these Doppler components are reflected wave signals for the radar transmission signals transmitted from first radar section10h.

Further, when the Doppler components corresponding to the intervals of Δfd(2) (1/(4Tr×Ncolen) in the example ofFIG.32) or the Doppler components corresponding to an integer multiple of intervals Δfd(2) are observed at distance index fb3 or fb4 illustrated inFIG.32, radar apparatus1hcan distinguish that these Doppler components are reflected wave signals for the radar transmission signals transmitted from second radar section10h.

Further, when a Doppler component that matches interval Δfd(1) (or an integer multiple of Δfd(1)) and a Doppler component that matches the interval of Δfd(2) (or an integer multiple of Δfd(2)) are observed in a mixed manner at distance index fb5 illustrated inFIG.32, radar apparatus1hcan distinguish the reflected wave signals for the radar transmission signals transmitted from first radar section10and the reflected wave signals for the radar transmission signals transmitted from second radar section10, for example, based on the intervals of the Doppler components.

As described above, radar apparatus1hcan distinguish whether the observed Doppler components are the reflected wave signals for the radar transmission signals transmitted from the radar section of first radar section10hor from second radar section10h, based on the difference between the Doppler multiplexing intervals of the Doppler multiplexing transmissions in first radar section10hand the Doppler multiplexing intervals of the Doppler multiplexing transmissions in second radar section10h.

The exemplary operation of Doppler shifters101, code multiplexing controller107, and code multiplexers108have been described above.

Next, an exemplary operation of first CFAR section210, second CFAR section210, first Doppler demultiplexer211, and second Doppler demultiplexer211in qth radar section10hcorresponding to the operation of Doppler shifters101will be described.

[Exemplary Operation of First CFAR Section210]

For example, first first CFAR section210of qth radar section10hmay perform the following operations in order to receive radar reflected waves for radar transmission signals from radar transmitter100hof qth radar section10h.

For example, when δ1and δ2are set in Doppler shifters101to values that differ from positive integers, first CFAR section210may perform peak detection, for example, by searching for a power peak that matches the Doppler shift interval set for the radar transmission signals of qth radar section10h, and by performing adaptive threshold processing (CFAR processing), the search being performed for each distance index on an output value obtained by adding all the powers of the outputs from first to Ncolenth Doppler analyzers209of first to Na(q)th signal processors206.

On the other hand, for example, when δ1and δ2are set to positive integers for Doppler shifters101, an interval of Δfd(q) or an interval of an integer multiple of Δfd(q) is used as an interval of the Doppler shift amounts. In this case, q may be 1 or 2. Therefore, the reception quality (e.g., SNR) of the output value obtained by adding all the powers f the outputs of first to Ncolenth Doppler analyzers209can be enhanced. Further, Doppler multiplexed signals can be detected as aliasing at an interval of Δfd(q) in the Doppler frequency domain of the outputs of Doppler analyzers209. By using such characteristics, for example, the operation of first CFAR section210can be simplified as follows.

For example, first CFAR section210of qth radar section10hdetects a Doppler peak by applying a threshold to a power addition value obtained by adding together the reception powers of the reflected wave signals for respective ranges (for example, ranges of Δfd(q)) within the Doppler frequency range to be subjected to the CFAR processing in the output value obtained by performing power addition on all the outputs of first to Ncolenth Doppler analyzers209, the ranges corresponding to the intervals of the Doppler shift amounts applied respectively to the radar transmission signals.

For example, first CFAR section210performs the CFAR processing on the output obtained by power addition of all the outputs from first to Ncolenth Doppler analyzers209of first to Na(q)th signal processors206, by calculating power addition value PowerDDMq(fb, fsddm) obtained by adding power values PowerFTq(fb, fs) at the intervals of Δfd(q) (for example, corresponding to NΔfd(q)) as illustrated in following Expressions 55 and 56:

In the expressions, fsddm=−Ns/2, . . . , and −Ns/2+NΔfd(q)−1 holds true and NΔfd(q)=round(Δfd(q)/(1/(TrNs) also holds true. In addition, round(x) is an operator that rounds off real number x and outputs an integer value.

The operation in the CFAR processing may be based on the operation disclosed in NPL 3, for example, and detailed explanation of the exemplary operation is omitted.

Accordingly, the range of the Doppler frequencies subjected to the CFAR processing in first CFAR section210can be set (for example, reduced) to 1/(NDM(q)+δq) of the entire range (for example, the range of from −Ns/2 to Ns/2−1). It is thus possible to reduce the computational amount of the CFAR processing.

For example, first CFAR section210adaptively sets a threshold, and outputs, to first Doppler demultiplexer211, distance indices fb_cfar, Doppler frequency indices fsddm_cfar, and the reception power information (PowerFT(fb_cfar, fsddm_cfar+(ndm−1)×NΔfd(q))) that provide reception power greater than the threshold. In the expression, ndm is an integer of from 1 to NDM(q)+δq.

[Exemplary Operation of First Doppler Demultiplexer211]

First Doppler demultiplexer211performs the following operations, for example, based on distance indices fb_cfar, Doppler frequency indices fsddm_cfar, and the reception power information (PowerFT(fb_cfar, fsddm_cfar+(ndm−1)×NΔfd(q))) (ndm is an integer of from 1 to NDM(q)+δq)) inputted from first CFAR section210.

<(1) Case of δq=0>

For example, assuming that the Doppler velocity of the target object is −1/(2Tr×Ncolen×NDM(q))≤fd<1/(2Tr×Ncolen×NDM(q)), first Doppler demultiplexer211associates the Doppler shift amounts of the Doppler multiplexed signals to be transmitted with fsddm_cfar+(ndm−1)×NΔfd(q), and outputs, to first code separator215, the resulting demultiplexing index information (fdemul#1(q), . . . , and fdemul_#NDM(q)) of the Doppler multiplexed signals.

Here, fdemul_#n(q)indicates the Doppler frequency index of the reflected wave signal corresponding to the nth Doppler multiplexed signal of qth radar10h.

By way of example, a Doppler shift setting example illustrated inFIG.26in which NDM(1)=Nt(1)=3 and NDM(2)=Nt(2)=4 will be described. In this case, Δfd(1)=1/(3Tr×Ncolen) and Δfd(2)=1/(4Tr×Ncolen).

Here, it may be assumed that the Doppler frequency of the reflected wave signal for the radar transmission signal transmitted from first radar section10h, which is received by first radar section10h, is −1/(2Tr×Ncolen×NDM(1))≤fd<1/(2Tr×Ncolen×NDM(1)). Therefore, inFIG.26, the demultiplexing index information (fdemul_#1(1), fdemul_#2(1), and fdemul_#3(1)) of the Doppler multiplexed signals for fsddm_cfar+(ndm−1)×NΔfd(1)has a correspondence relation of fdemul_#3(1)<fdemul_#1(1)<fdemul#2(1). First Doppler demultiplexer211may, for example, output each of fsddm_cfar+(ndm−1)×NΔfd(1)(ndm is an integer of from 1 to 3) as fdemul_#3(1), fdemul_#1(1), and fdemul_#2(1).

Similarly, it may be assumed that the Doppler frequency of the reflected wave signal for the radar transmission signal transmitted from second radar section10h, which is received by second radar section10h, is −1/(2Tr×Ncolen×NDM(2))≤fd<1/(2Tr×Ncolen×NDM(2)). Therefore, the demultiplexing index information (fdemul_#1(2), fdemul_#2(2), fdemul_#3(2), and fdemul_#4(2)) of the Doppler multiplexed signals for fsddm_cfar+(ndm−1)×NΔfd(2) has a correspondence relation of fdemul_#3(2)<fdemul_#4(2)<fdemul_#1(2)<fdemul_#2(2) when 0≤fd<1/(2Tr×Ncolen×NDM(1)). When −1/(2Tr×Ncolen×NDM(1))≤fd<0), the correspondence relation of fdemul_#4(2)<fdemul_#1(2)<fdemul_#2(2)<fdemul_#3(2) is obtained. First Doppler demultiplexer211may, for example, output each of fsddm_cfar+(ndm−1)×NΔfd(2)(ndm is an integer of from 1 to 4) as fdemul_#3(2), fdemul_#4(2), fdemul_#1(2), and fdemul_#2(2).

When a difference between the powers for NDM(q) Doppler frequency indices is larger than a predetermined value (for example, a threshold), first Doppler demultiplexer211may regard (or determine) that the components of the reception signal for the multistatic configuration are highly likely to be mixed, and may add an operation of removing a reception signal without outputting the reception signal to subsequent processing (for example, direction estimation processing).

<(2) Case of δq>0>

For example, it may be assumed that the Doppler velocity of the target object is −1/(2Tr×Ncolen)≤fd<1/(2Tr×Ncolen). Further, a large difference between, on one hand, the reception levels for top NDM(q) Doppler frequency indices of reception power and, on the other hand, the reception levels for δqDoppler frequency indices different from the top NDMDoppler frequency indices of reception power (for example, the difference being equal to or greater than the threshold) may be used. For example, first Doppler demultiplexer211compares the reception power information inputted from first CFAR section210and determines the Doppler frequency in the range of −1/(2Tr×Ncolen)≤fd<1/(2Tr×Ncolen). Note that an exemplary operation of first Doppler demultiplexer211is disclosed in, for example, PTL 1, and therefore description of the exemplary operation is omitted here.

For example, first Doppler demultiplexer211associates the Doppler shift amounts of the transmitted Doppler multiplexed signals with fsddm_cfar+(ndm−1)×NΔfd(q)based on the relation between δqDoppler frequency indices of a lower reception level and top NDMDoppler frequency indices of a higher reception power, and performs an output to first code separator215as demultiplexing index information (fdemul_#1(q), . . . , and fdemul_#NDM(q)) of the Doppler multiplexed signals.

Here, fdemul_#n(q)represents the Doppler frequency index of the reflected wave signal corresponding to nth Doppler multiplexed signal of qth radar section10h.

By way of example,FIG.33illustrates an example of an output (for example, a reception Doppler frequency) of Doppler analyzer209in a case where a reflected wave signal with respect to a radar transmission signal from first radar section10his received. InFIG.33, the vertical axis represents the distance axis, and the horizontal axis represents the Doppler frequency axis.

For example, when the Doppler components corresponding to interval Δfd(1) or the Doppler components corresponding to an integer multiple of interval Δfd(1) are observed at distance index fb1 illustrated inFIG.33, first Doppler demultiplexer211can distinguish (for example, detect) that these Doppler components are reflected wave signals for radar transmission signals transmitted from first radar section10h.

Further, for example, inFIG.33, δq(=1) Doppler frequency index for a lower reception level is indicated by mark “o,” and top NDM(=2) Doppler frequency indices of reception power are indicated by marks “x” and “Δ.” For example, since the Doppler components (mark “o” inFIG.33) that do not match the interval of Δfd(1) is uniquely determined in the range of −1/(2Tr×Ncolen)≤fd<1/(2Tr×Ncolen), first Doppler demultiplexer211can uniquely determine the Doppler velocity of the target object in the range of −1/(2Tr×Ncolen)≤fd<1/(2Tr×Ncolen).

Further, first Doppler demultiplexer211can determine the association between the Doppler frequencies and the Doppler multiplexed signals, for example, based on the magnitude relationship between the Doppler frequency indices (mark “o” inFIG.33) that do not match the interval of Δfd(1) and other Doppler frequency indices (marks “x” and “Δ” inFIG.33) that match the interval of Δfd(1).

By way of example, a description will be given in which at distance index fb1 ofFIG.33, NDM(1)=2, the first Doppler multiplexed signal is assigned to the Doppler frequency (mark “x” inFIG.33) higher by Δfd(1) than the detected Doppler frequency index (mark “o” inFIG.33), and the second Doppler multiplexed signal is assigned to the Doppler frequency (mark “Δ” inFIG.33) lower by Δfd(1) than the detected Doppler frequency index (mark “o” inFIG.33).

In this case, at distance index fb1 ofFIG.33, first Doppler demultiplexer211, for example, detects δq(=1) Doppler frequency index for a lower reception level (“o” inFIG.33), and can thus determine that the Doppler frequency (mark “x” inFIG.33) higher by Δfd(1) than the detected Doppler frequency corresponds to the first Doppler multiplexed signal and the Doppler frequency (mark “Δ” inFIG.33) lower by Δfd(1) than the detected Doppler frequency corresponds to the second Doppler multiplexed signal.

Further, it is, for example, assumed that at distance index fb2 ofFIG.33, the same assignment of the Doppler multiplexed signals as at distance index fb1 is performed. In this case, for example, as is seen at distance index fb2 ofFIG.33, there may be a case where δq(=1) Doppler frequency index for a lower reception level (“o” inFIG.33) is lower by Δfd(1) or 2Δfd(1) than top NDM(=2) Doppler frequency indices of reception power. In this case, the Doppler frequency range that can be observed by Doppler analyzers209is a range of −1/(2Tr×Ncolen)≤fd<1/(2Tr×Ncolen), and the Doppler frequency (mark “Δ” inFIG.33) that is lower by Δfd(1) than δq(=1) Doppler frequency index (mark “o” inFIG.33) for a lower reception level can be observed with aliasing on the higher-frequency side. Since first Doppler demultiplexer211can assume the occurrence of such aliasing in advance, first Doppler demultiplexer211can, for example, detect δq(=1) Doppler frequency index (mark “o” inFIG.33) for a lower reception level, and can thus determine that the Doppler frequency (mark “x” inFIG.33) higher by Δfd(1) than the detected Doppler frequency for the lower reception level corresponds to the first Doppler multiplexed signal and the Doppler frequency (mark “\” inFIG.33) even higher by Δfd(1) than the detected Doppler frequency for the lower reception level corresponds to the second Doppler multiplexed signal.

Likewise, it is, for example, assumed that also at distance index fb3 ofFIG.33, the same assignment of the Doppler multiplexed signals as at distance index fb1 is performed. In this case, for example, as is seen at distance index fb3 ofFIG.33, there may be a case where δq(=1) Doppler frequency index for a lower reception level (“o” inFIG.33) is higher by Δfd(1) or 2Δfd(1) than top NDM(=2) Doppler frequency indices of reception power. In this case, the Doppler frequency range that can be observed by Doppler analyzers209is a range of −1/(2Tr×Ncolen)≤fd<1/(2Tr×Ncolen), and the Doppler frequency (mark “x” inFIG.33) that is higher by Δfd(1) than δq(=1) Doppler frequency index (mark “o” inFIG.33) for the lower reception level can be observed with aliasing on the lower-frequency side. Since first Doppler demultiplexer211can assume the occurrence of such aliasing in advance, first Doppler demultiplexer211can, for example, determine that the Doppler frequency (mark “Δ” inFIG.33) lower by Δfd(1) than δq(=1) Doppler frequency index (mark “o” inFIG.33) for a lower reception level corresponds to the second Doppler multiplexed signal and the Doppler frequency (mark “x” inFIG.33) even lower by Δfd(1) corresponds to the first Doppler multiplexed signal.

When the difference between the powers of NDM(q) Doppler frequency indices for the higher reception powers is larger than a predetermined value (threshold), first Doppler demultiplexer211may regard (or determine) that signals of the reception signals of the multistatic configuration are highly likely to be mixed, and may add an operation of removing the reception signals without performing an output for subsequent processing (for example, direction estimation processing).

The exemplary operation of first Doppler demultiplexer211has been described above.

[Exemplary Operation of First Code Separator215]

First code separator215(also referred to as code separator215-1) performs a process of separating codes multiplexed in code multiplexers108of radar transmitter100husing, for example, the distance index information and the demultiplexing index information (fdemul_#1(q), . . . , and fdemul_#NDM(q)) of the Doppler multiplexed signal inputted from first Doppler demultiplexer211.

For example, since qth radar section10hknows the doppler indices of the first to NDM(q)th Doppler multiplexed signals of qth radar section10h, first code separator215calculates the Doppler frequencies based on the demultiplexing index information (fdemul_#1(q), . . . , and fdemul_#NDM(q)) of the Doppler multiplexed signals outputted from first Doppler demultiplexer211. Further, first code separator215may demultiplex the signals code-multiplexed into the Doppler multiplexed signals, by performing code separation processing using calculated Doppler frequencies fdop as illustrated in following Expression 57:

In the expression, Yz,q(fb_cfar, ncm, ndop) represents the reception signal multiplexed and transmitted from qth radar section10husing the nemth code of the ndopth Doppler multiplexed signal at distance index fb_cfarin zth signal processor206h. Further, the number of Doppler multiplexing in qth radar section10his NDM(q), and ndop represents the indices of the Doppler multiplexed signals and is an integer of ndop=1 to NDM(q). In addition, the number of code multiplexing for the ndopth Doppler multiplexed signal is CodeDop(ndop), and ncm represents an index of a code, and is an integer of ncm=1 to CodeDop(ndop).

Since transmission antenna102used for multiplexing transmission using the ndopth code for the nemth Doppler multiplexed signal in qth radar section10his known, first code separator215can specify, for example, the reception signal from transmission antenna102of qth radar section10h. Thus, for example, first code separator215in zth signal processor206hmay associate the code separated signal calculated using Expression 57 with the reception signal corresponding to the multiplexed signal from each of first to Nt(q)th transmission antennas102. For example, first code separator215outputs, to first direction estimator212, code separated signals YOz=(Yz,Tx#1, Yz,Tx#2, . . . , and Yz,Tx#Nt(q)) rearranged in the order of first to Nt(q)th transmission antennas102.

Here, YOzis an Nt(q)th-order vector, and is composed of reception signals (complex numbers) obtained by code separation in the order from first transmission antenna102(Tx #1) to Nt(q)th transmission antenna102(Tx #Nt(q)). In addition, z is an integer of from 1 to Na(q).

In Expression 57, the term

is a term that cancels out a phase variation caused by the Doppler frequency in the period (Tr×Ncolen) in which the code is transmitted.

[Exemplary Operation of Second CFAR Section210]

For example, second CFAR section210of qth radar section10hmay perform the following operations in order to receive the reflected wave signal for the radar transmission signal from radar transmitter100hof radar section10hthat differs from qth radar section10h.

For example, when δ1and δ2are set to values that differ from positive integers for Doppler shifters101, second CFAR section210may perform peak detection by, for example, searching, in the power addition values outputted from Doppler analyzers209of first to Na(q)th signal processors206h, for a power peak that matches the Doppler shift interval set for the radar transmission signal of radar section10hdifferent from qth radar section10hfor each distance index, and performing adaptive threshold processing (CFAR processing).

On the other hand, for example, when δ1and δ2are set to positive integers for Doppler shifters101, an interval of Δfd(qe) or an interval of an integer multiple of Δfd(qe) is used as an interval of the Doppler shift amounts. Here, qe may be 1 or 2. Therefore, Doppler multiplexed signals can be detected as aliasing at an interval of Δfd(qe) in the Doppler frequency domain of the outputs of Doppler analyzers209. By using such characteristics, for example, the operation of second CFAR section210can be simplified as follows.

For example, second CFAR section210of qth radar section10hdetects a Doppler peak by applying a threshold to a power addition value obtained by adding together the reception powers of the reflected wave signals for respective ranges (for example, ranges of Δfd(qe)) within the Doppler frequency range that is outputted from Doppler analyzers209and subjected to the CFAR processing, the ranges corresponding to the intervals of the Doppler shift amounts applied respectively to the radar transmission signals.

Here, “qe” represents a radar number of radar section10hthat differs from qth radar section10h. For example, “qe” may be 2 in the case of first radar section10h(q=1), or “qe” may be 1 in the case of second radar section10h(q=2).

For example, second CFAR section210performs the CFAR processing on the output obtained by adding all the outputs from the first to Ncolenth Doppler analyzers209of the first to Na(q)th signal processors206, by calculating power addition value PowerDDMqe(fb, fsddm) obtained by adding power values PowerFTq(fb, fs) at the intervals of Δfd(qe) (for example, corresponding to NΔfd(qe)) as illustrated in following Expressions 58 and 59:

In the expressions, fsddm=−Ns/2, . . . , and −Ns/2+NΔfd(qe)−1 holds true and NΔfd(qe)=round(Δfd(qe)/(1/(TrNs) holds true. In addition, round(x) is an operator that rounds off real number x and outputs an integer value.

The operation in the CFAR processing may be based on the operation disclosed in NPL 3, for example, and detailed explanation of the exemplary operation is omitted.

Thus, the Doppler frequency range on which the CFAR processing is performed in second CFAR section210can be set (e.g., reduced) to 1/(NDM(qe)+δqe) of the entire range (e.g., the range of −Ns/2 to Ns/2−1), thereby reducing the computational amount of the CFAR processing.

For example, second CFAR section210adaptively sets a threshold, and outputs to second Doppler demultiplexer211distance indices fb_cfar, Doppler frequency indices fsddm_cfar, and the reception power information (PowerFT(fb_cfar, fsddm_cfar+(ndm−1)×NΔfd(qe))) that provide reception power greater than the threshold. Here, ndm is an integer of from 1 to NDM(qe)+δqe.

[Exemplary Operation of Second Doppler Demultiplexer211]

Second Doppler demultiplexer211performs the following operations based on, for example, distance indices fb_cfar, Doppler frequency indices fsddm_cfar, and the reception power information (PowerFT(fb_cfar, fsddm_cfar+(ndm−1)×NΔfd(qe))) (ndm is an integer of from 1 to NDM(qe)+δqe)) inputted from second CFAR section210.

<(1) Case of δqe=0>

For example, assuming that the Doppler velocity of the target object is −1/(2Tr×Ncolen×NDM(qe))≤fd<1/(2Tr×Ncolen×NDM(qe)), second Doppler demultiplexer211associates the Doppler shift amounts of the Doppler multiplexed signals to be transmitted with fsddm_cfar+(ndm−1)×NΔfd(qe), and outputs, to second code separator215, the resulting demultiplexing index information (for example, fdemul_Tx#1(qe), . . . , and fdemul_Tx#NDM(qe)) of the Doppler multiplexed signals.

Here, fdemul_Tx#n(qe) represents the Doppler frequency index of the reflected wave signal corresponding to nth Doppler multiplexed signal of qeth radar section10.

<(2) Case of δqe>0>

For example, it may be assumed that the Doppler velocity of the target object is −1/(2Tr×Ncolen)≤fd<1/(2Tr×Ncolen). Further, a large difference between, on one hand, the reception levels for top NDM(qe) Doppler frequency indices of reception power and, on the other hand, the reception levels of δqeDoppler frequency indices different from the top NDMDoppler frequency indices of reception power (for example, the difference being equal to or greater than the threshold) may be used. For example, second Doppler demultiplexer211compares the reception power information inputted from second CFAR section210and determines the Doppler frequency in the range of −1/(2Tr×Ncolen)≤fd<1/(2Tr×Ncolen). Note that an exemplary operation of second Doppler demultiplexer211is disclosed in, for example, PTL 1, and therefore description of the exemplary operation is omitted here.

When the difference between the powers of NDM(qe) Doppler frequency indices for the higher reception powers is larger than a predetermined value (threshold), second Doppler demultiplexer211may regard (or determine) that components of the reception signals of the monostatic configuration are highly likely to be mixed, and may add an operation of removing the reception signals without performing an output for subsequent processing (for example, direction estimation processing).

The exemplary operation of second Doppler demultiplexer211has been described above.

[Exemplary Operation of Second Code Separator215]

Second code separator215(also referred to as code separator215-2) performs a process of separating codes multiplexed in code multiplexers108of radar transmitter100husing, for example, the distance index information and the demultiplexing index information (fdemul_#1(qe), . . . , and fdemul_#NDM(qe)) of the Doppler multiplexed signal inputted from second Doppler demultiplexer211.

For example, since qth radar section10hknows the doppler indices of the first to NDM(qe)th Doppler multiplexed signals of qeth radar section10h, second code separator215calculates the Doppler frequencies based on the demultiplexing index information (fdemul #1(qe), . . . , and fdemul_#NDM(qe)) of the Doppler multiplexed signals outputted from second Doppler demultiplexer211. Further, second code separator215may demultiplex the signals code-multiplexed into the Doppler multiplexed signals, by performing code separation processing using calculated Doppler frequencies fdopas illustrated in following Expression 60:

In the expression, Yz(fb_cfar, ncm, ndop) represents the reception signal multiplexed and transmitted from qeth radar section10husing the nemth code of the ndopth Doppler multiplexed signal at distance index fb_cfarin zth signal processor206h. Further, the number of Doppler multiplexing in qeth radar section10his NDM(qe), and ndop represents the indices of the Doppler multiplexed signals and is an integer of ndop=1 to NDM(qe). In addition, the number of code multiplexing for the ndopth Doppler multiplexed signal is CodeDop(ndop), and ncm represents an index of a code, and is an integer of ncm=1 to CodeDop(ndop).

Since transmission antenna102used for multiplexing transmission using the ndopth code for the ncmth Doppler multiplexed signal in qeth radar section10his known, second code separator215can specify, for example, the reception signal from transmission antenna102of qeth radar section10h. Thus, for example, second code separator215in zth signal processor206hmay associate the code separated signal calculated using Expression 60 with the reception signal corresponding to the multiplexed signal from each of first to Nt(qe)th transmission antennas102. For example, second code separator215outputs, to second direction estimator212, code separated signals YOz=(Yz,Tx#1, Yz,Tx#2, . . . , and Yz,Tx#Nt(qe)) rearranged in the order of first to Nt(qe)th transmission antennas102.

Here, YOzis an Nt(qe)th-order vector, and is composed of reception signals (complex numbers) obtained by code separation in the order from first transmission antenna102(Tx #1) to Nt(qe)th transmission antenna102(Tx #Nt(qe)). In addition, z is an integer of from 1 to Nt(qe).

In Expression 60, the term

is a term that cancels out a phase variation caused by the Doppler frequency in the period (Tr×Ncolen) in which the code is transmitted.

The exemplary operation of second code separator215has been described above.

Next, an exemplary operation of first direction estimator212and second direction estimator212illustrated inFIG.25will be described.

[Exemplary Operation of First Direction Estimator212]

First direction estimator212of qth radar section10hperforms the direction estimation processing on the target object based on, for example, information (for example, distance indices fb_cfarand code separated signals YOz=(Yz,Tx#1, Yz,Tx#2, . . . , and Yz,Tx#Nt(q) (z is an integer of from 1 to Nt(q))) inputted from first code separator215. Since the operation of first direction estimator212according to the present embodiment may be the same as the operation of first direction estimator212according to Embodiment 1, the description thereof will be omitted.

First direction estimator212of qth radar section10hmay output, for example, as the positioning outputs, the direction-of-arrival estimation values for distance indices fb_cfar(q) and the demultiplexing index information (fdemul_Tx#1(q), fdemul_Tx#2(q), . . . , and fdemul_Tx#Nt(q)) of the Doppler multiplexed signals. Further, first direction estimator212may further output distance indices fb_cfar(q) and the demultiplexing index information (fdemul_Tx#1(q), fdemul_Tx#2(q), . . . , and fdemul_Tx#Nt(q)) of the Doppler multiplexed signal as the positioning outputs.

Further, distance index fb_cfar(q) may be converted into distance information by using Expression 1 and outputted.

[Exemplary Operation of Second Direction Estimator212]

Second direction estimator212of qth radar section10hperforms the direction estimation processing on the target object based on, for example, information (for example, distance indices fb_cfarand code separated signals YOz=(Yz,Tx#1, Yz,Tx#2, . . . , and Yz,Tx,#Nt(qe)(z is an integer of from 1 to Nt(qe))) inputted from second code separator215. Since the operation of second direction estimator212according to the present embodiment may be the same as the operation of second direction estimator212according to Embodiment 1, the description thereof will be omitted.

Second direction estimator212of qth radar section10hmay output, for example, as the positioning output, the transmission azimuth direction estimation value and reception azimuth direction estimation value at distance index fb_cfar(qe) and the demultiplexing index information (fdemul_Tx#1(qe), fdemul_Tx#2(qe), . . . , and fdemul_Tx#Nt(qe)) of the Doppler multiplexed signals. Further, second direction estimator212may further output distance indices fb_cfar(qe) and the demultiplexing index information (fdemul_Tx#1(qe), fdemul_Tx#2(qe), . . . , and fdemul_Tx#Nt(qe)) of the Doppler multiplexed signal as the positioning outputs.

Further, distance index fb_cfar(qe) may be converted into distance information by using Expression 2 and outputted.

The exemplary operations of first direction estimator212and second direction estimator212have been described above.

InFIG.25, positioning output integrator30integrates the positioning outputs of first direction estimator212and second direction estimator212from first radar section10hand the positioning outputs of first direction estimator212and second direction estimator212from second radar section10h, and performs positioning of the target object. Note that, since the operation of positioning output integrator30according to the present embodiment may be the same as the operation of positioning output integrator30according to Embodiment 1, the description thereof will be omitted.

As described above, in the present embodiment, radar apparatus1hincludes first radar section10hthat transmits radar transmission signals from a plurality of transmission antennas102, and second radar section10hthat transmits radar transmission signals from a plurality of transmission antennas102. Here, the Doppler multiplexing interval between the Doppler shift amounts applied respectively to the radar transmission signals transmitted from the plurality of transmission antennas102of first radar section10his different from the Doppler multiplexing interval between the Doppler shift amounts applied respectively to the radar transmission signals transmitted from the plurality of transmission antennas102of second radar section10h.

Accordingly, radar apparatus1hcan demultiplex the reflected wave signals corresponding to the radar transmission signals of radar sections10hfrom the reception signals, for example, based on the Doppler multiplexing intervals set in radar sections10h. Therefore, radar apparatus1hcan simultaneously perform radar positioning by the monostatic configuration of each of first radar section10hand second radar section10husing code multiplexing transmission, and radar positioning by the multistatic configuration from first radar section10hto second radar section10hand the multistatic configuration from second radar section10hto first radar section10hby using Doppler multiplexing transmission.

Therefore, according to the present embodiment, when code multiplexing is applied in the monostatic MIMO radar, the radar positioning time can be reduced as compared with the case where inter-multistatic time-division transmission is used, and the same advantages as those in Embodiment 1 can be obtained.

Further, for example, radar apparatus1hcan expand the observable Doppler range (for example, can set the observable Doppler range to +1/(2NcolenTr) by performing Doppler aliasing determination using unequal-interval Doppler multiplexing, and can suppress reduction of the maximum Doppler observable by the inter-multistatic multiplexing transmission.

Also in the present embodiment, for example, at least one of Variations 1 to 7 of Embodiment 1 may be applied, and the same effect can be obtained.

One exemplary embodiment of the present disclosure has been described above.

Other Embodiments

Regarding Embodiment 1 (for example,FIG.3) of the present embodiment, the configuration and operation for performing positioning by simultaneous multiplexing of the radar having the monostatic configuration and the radar having the multistatic configuration in radar apparatus1have been described. In such a case, the radar transmission signals transmitted from each of a plurality of transmission antennas102of first radar section10and the radar transmission signals transmitted from each of a plurality of transmission antennas102of second radar section10may be transmitted using transmission antennas which emit the same polarized wave. By using the plurality of transmission antennas102of first radar section10and the plurality of transmission antennas102of second radar section10, polarized waves of radio waves being the radar transmission signals transmitted from each of the plurality of transmission antennas102of first radar section10and reflected by the target object and polarized waves of radio waves being the radar transmission signals transmitted from each of the plurality of transmission antennas102of second radar section10and reflected by the target object match each other as long as the target object is identical.

Accordingly, an advantage that the target-object reflected waves of the radar transmission signals transmitted from first radar section10having the multistatic configuration can be received by the monostatic configuration and also by second radar section10. Similarly, an advantage that the target-object reflected waves of the radar transmission signals transmitted from second radar section10having the multistatic configuration can be received by the monostatic configuration and also by first radar section10. As the transmission antennas for emitting the polarized waves, for example, a transmission antenna for emitting any one of a vertically polarized wave, horizontally polarized wave, obliquely 45-degree polarized wave, left-handed circularly polarized wave, and right-handed circularly polarized wave may be used.

In addition, regarding Variation 3 (for example,FIG.17) of Embodiment 1 of the present disclosure, the configuration and operation for performing positioning by simultaneous multiplexing of a plurality of radars having the monostatic configuration in radar apparatus1chave been described. In such a case, the radar transmission signals transmitted from each of a plurality of transmission antennas102of first radar section10cand the radar transmission signals transmitted from each of a plurality of transmission antennas102of second radar section10cmay be transmitted using transmission antennas which emit different polarized waves. By using the plurality of transmission antennas102of first radar section10cand the plurality of transmission antennas102of second radar section10c, polarized waves of radio waves being the radar transmission signals transmitted from each of the plurality of transmission antennas102of first radar section10cand reflected by the target object and polarized waves of radio waves being the radar transmission signals transmitted from each of the plurality of transmission antennas102of second radar section10cand reflected by the target object are polarized waves different from each other as long as the target object is identical.

Thus, an advantage is obtained that the target-object reflected waves for the radar transmission signals transmitted from first radar section10cbrings about reception statuses different between reception in the monostatic configuration and reception in second radar section10c. Here, for example, by using orthogonally related polarized waves as the different polarized waves, an advantage is obtained that the reception at second radar section10cas compared with the reception at the monostatic configuration becomes less likely to be received with increasing cross-polarization discrimination degree between the orthogonal polarized waves.

Likewise, an advantage is obtained that the target-object reflected waves for the radar transmission signals transmitted from second radar section10cbrings about reception statuses different between reception in the monostatic configuration and reception in first radar section10c. Here, for example, by using orthogonally related polarized waves as the different polarized waves, an advantage is obtained that the reception at first radar section10cas compared with the reception at the monostatic configuration becomes less likely to be received with increasing cross-polarization discrimination degree between the orthogonal polarized waves.

By the transmission performed using the polarized waves related to each other as described above, it is possible to further enhance mutual interference cancellation effectiveness between the radar sections, which is more preferable, for example, when a plurality of radar sections10chaving the monostatic configuration using radar transmission waves (e.g., chirp signals) of the same frequency band are disposed close to each other. This enhancement is achieved by transmission performed using transmission antennas providing polarized waves different between the radar sections. For example, when the left-handed circularly polarized waves and right-handed circularly polarized waves are used as the orthogonal polarized waves, reflected waves (reflected waves of the same number of times of reflection) being radar transmission signals transmitted from each of the plurality of transmission antennas102of first radar section10cand reflected by the target object are received as radio waves of polarized waves having a relation of cross polarization. It is thus possible to suppress the reflected wave reception level in the multistatic configuration as compared with the reflected wave reception level in the monostatic configuration, and it is possible to further enhance the interference cancellation effect between the radar sections. As a combination of the orthogonally related polarized waves, for example, a left-handed circularly polarized wave and a right-handed circularly polarized wave, a vertical polarized wave and a horizontal polarized wave, or a right-handed 45-degree polarized wave and a left-handed 45-degree polarized wave may be used.

Further, regarding the above-described embodiments, the configuration has been described in which the chirp signals are used as the radar transmission signals, but the radar transmission signals may be signals differing from the chirp signals. For example, the radar transmission signals may be a pulse compression wave, such as a coded pulse signal. When the coded pulse signal is used for the radar transmission signals, mixer204of reception radio203converts a high-frequency reception signal into a baseband signal, and a correlator (not illustrated) that correlates the high-frequency reception signal with the coded pulse signal transmitted is used instead of beat frequency analyzer208. Accordingly, the subsequent processing can be performed in the same manner as the processing according to each of the above-described embodiments, and the same effects can be obtained.

In the radar apparatuses according to one exemplary embodiment of the present disclosure, the radar transmitter and the radar receiver may be individually arranged in physically separate locations from each other. In the radar receiver according to the exemplary embodiments of the present disclosure, the direction estimator and any other component may be individually arranged in physically separate locations from one another.

Further, in one exemplary embodiment of the present disclosure, the numerical values used for parameters such as the number of transmission antennas, the number of reception antennas, the number of Doppler multiplexing, the number of code multiplexing, the number of radar sections, the Doppler multiplexing interval, the parameter related to the Doppler multiplexing interval (for example, δq), and the number of code multiplexing are examples, and are not limited to these values.

A radar apparatus according to an exemplary embodiment of the present disclosure includes, for example, a central processing unit (CPU), a storage medium such as a read only memory (ROM) that stores a control program, and a work memory such as a random access memory (RAM), which are not illustrated. In this case, the functions of the sections described above are implemented by the CPU executing the control program. However, the hardware configuration of the radar apparatus is not limited to that in this example. For example, the functional sections of the radar apparatus may be implemented as an integrated circuit (IC). Each functional section may be formed as an individual chip, or some or all of them may be formed into a single chip.

Various embodiments have been described with reference to the drawings hereinabove. Obviously, the present disclosure is not limited to these examples. Obviously, a person skilled in the art would arrive variations and modification examples within a scope described in claims, and it is understood that these variations and modifications are within the technical scope of the present disclosure. Each constituent element of the above-mentioned embodiments may be combined optionally without departing from the spirit of the disclosure.

The expression “section” used in the above-described embodiments may be replaced with another expression such as “circuit (circuitry),” “device,” “unit,” or “module.”

The above embodiments have been described with an example of a configuration using hardware, but the present disclosure can be realized by software in cooperation with hardware.

Each functional block used in the description of each embodiment described above is typically realized by an LSI, which is an integrated circuit. The integrated circuit controls each functional block used in the description of the above embodiments and may include an input terminal and an output terminal. The LSI may be individually formed as chips, or one chip may be formed so as to include a part or all of the functional blocks. The LSI herein may be referred to as an IC, a system LSI, a super LSI, or an ultra LSI depending on a difference in the degree of integration.

However, the technique of implementing an integrated circuit is not limited to the LSI and may be realized by using a dedicated circuit or a general-purpose processor and a memory. In addition, a Field Programmable Gate Array (FPGA) that can be programmed after the manufacture of the LSI or a reconfigurable processor in which the connections and the settings of circuit cells disposed inside the LSI can be reconfigured may be used.

If future integrated circuit technology replaces LSIs as a result of the advancement of semiconductor technology or other derivative technology, the functional blocks could be integrated using the future integrated circuit technology. Biotechnology can also be applied.

Summary of Present Disclosure

A radar apparatus according to one non-limiting and exemplary embodiment of the present disclosure includes: first radar circuitry, which, in operation, transmits a first transmission signal from a plurality of first transmission antennas; and second radar circuitry, which, in operation, transmits a second transmission signal from a plurality of second transmission antennas, in which a first interval of each Doppler shift amount applied to the first transmission signal transmitted from each of the plurality of first transmission antennas is different from a second interval of each Doppler shift amount applied to the second transmission signal transmitted from each of the plurality of second transmission antennas.

In one non-limiting and exemplary embodiment of the present disclosure, a ratio of a greater one of the first interval and the second interval to a smaller one of the first interval and the second interval is different from an integer.

In one non-limiting and exemplary embodiment of the present disclosure, the Doppler shift amount applied to the first transmission signal and the Doppler shift amount applied to the second transmission signal are different from each other.

In one non-limiting and exemplary embodiment of the present disclosure, the first radar circuitry and the second radar circuitry demultiplex, from a reception signal, a first reflected wave signal corresponding to the first transmission signal and a second reflected wave signal corresponding to the second transmission signal based on the first interval and the second interval, and perform first direction estimation based on the first reflected wave signal and second direction estimation based on the second reflected wave signal, respectively.

In one non-limiting and exemplary embodiment of the present disclosure, one radar circuitry of the first radar circuitry and the second radar circuitry removes, based on the first interval and the second interval, a reflected wave signal corresponding to a transmission signal transmitted from an other radar circuitry of the first radar circuitry and the second radar circuitry, and performs direction estimation processing using a reflected wave signal corresponding to a transmission signal transmitted from the one radar circuitry.

In one non-limiting and exemplary embodiment of the present disclosure, the first radar circuitry performs time-division transmission of the first transmission signal to which the Doppler shift amount being a different Doppler shift amount is applied, from each of the plurality of first transmission antennas, and the second radar circuitry performs time-division transmission of the second transmission signal to which the Doppler shift amount being a different Doppler shift amount is applied, from each of the plurality of second transmission antennas.

In one non-limiting and exemplary embodiment of the present disclosure, the first radar circuitry transmits the first transmission signal using code multiplexing for each of the Doppler shift amounts, and the second radar circuitry transmits the second transmission signal using code multiplexing for each of the Doppler shift amounts.

in one non-limiting and exemplary embodiment of the present disclosure, control circuitry, which, in operation, outputs a reference signal to the first radar circuitry and the second radar circuitry is further included, and each of the first radar circuitry and the second radar circuitry generates a chirp signal using the reference signal.

In one non-limiting and exemplary embodiment of the present disclosure, the control circuitry is included in one of the first radar circuitry and the second radar circuitry.

In one non-limiting and exemplary embodiment of the present disclosure, a transmission timing of the first transmission signal for the first radar circuitry is different from a transmission timing of the second transmission signal for the second radar circuitry.

In one non-limiting and exemplary embodiment of the present disclosure, at least one of the first interval and the second interval is variably set.

In one non-limiting and exemplary embodiment of the present disclosure, the first radar circuitry and the second radar circuitry switch a multiplexing transmission method between a first multiplexing transmission based on the Doppler shift amount and a second multiplexing transmission different from the first multiplexing transmission.

In one non-limiting and exemplary embodiment of the present disclosure, at least one of the first radar circuitry and the second radar circuitry is configured such that radar transmission circuitry and radar reception circuitry are included in a same housing.

In one non-limiting and exemplary embodiment of the present disclosure, at least one of the first radar circuitry and the second radar circuitry is configured such that radar transmission circuitry and radar reception circuitry are included in different housings.

In one non-limiting and exemplary embodiment of the present disclosure, at least one of the first interval and the second interval is set to one of intervals obtained by unequally dividing a Doppler frequency range to be subjected to Doppler analysis.

A same polarized wave is used for a polarized wave for the plurality of first transmission antennas and a polarized wave for the plurality of second transmission antennas.

Polarized waves orthogonal to each other are used respectively for a polarized wave for the plurality of first transmission antennas and a polarized wave for the plurality of second transmission antennas.

The disclosure of Japanese Patent Application No. 2021-177893, filed on Oct. 29, 2021, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

The present disclosure is suitable as a radar apparatus for wide-angle range sensing.

REFERENCE SIGNS LIST