Target extraction system, target extraction method, information processing apparatus, and control method and control program of information processing apparatus

To acquire a beat frequency necessary for target extraction, target speed estimation, and Doppler influence detection by preventing the necessary beat frequency from overlapping unnecessary frequencies in a heterodyne processing result, an apparatus includes a wave receiver that receives a reflected wave of a chirp wave reflected from a target, and outputs a reception wave signal, a dual-sweep signal generator that generates a dual-sweep signal of the chirp wave, having a frequency which does not overlap that of the chirp wave, and a heterodyne processor that generates a beat frequency by multiplying the reception wave signal and the dual-sweep signal as a heterodyne signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage application of International Application No. PCT/JP2014/084613 entitled “Target Extraction System, Target Extraction Method, Information Processing Apparatus, and Control Method and Control Program of Information Processing Apparatus,” filed on Dec. 26, 2014, which claims the benefit of the priority of Japanese Patent Application No. 2014-048144, filed on Mar. 11, 2014, the disclosures of each of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a target extraction system, a target extraction method, an information processing apparatus, and a control method and control program of the information processing apparatus for extracting a target based on the reflected wave of a transmitted chirp wave.

BACKGROUND ART

In the above technical field, patent literatures 1 and 2 disclose techniques of obtaining the distance to a target based on the frequency difference between a transmitted chirp wave and a chirp wave reflected from the target. Furthermore, patent literature3and non-patent literatures 1 and 2 disclose techniques in which a dual-sweep signal that sweeps a frequency band twice the frequency band of a transmitted chirp wave in two cycles of the transmitted chirp wave is used as a heterodyne signal, and the reception wave signal of a chirp wave reflected from a target is multiplied by the heterodyne signal, thereby generating a beat frequency as the frequency difference between the heterodyne signal and the reception wave signal by performing heterodyne processing once regardless of a delay in the reception wave signal of the chirp wave.

CITATION LIST

Patent Literature

Patent literature 1: Japanese Patent Publication No. 59-44593

SUMMARY OF THE INVENTION

Technical Problem

In the techniques described in the above literatures, however, a beat frequency necessary for target extraction, target speed estimation, and Doppler influence detection may overlap unnecessary frequencies in a heterodyne processing result, and thus the target extraction accuracy may be insufficient.

The present invention enables to provide a technique of solving the above-described problem.

Solution to Problem

One aspect of the present invention provides an information processing apparatus comprising:

a wave receiver that receives a reflected wave of a chirp wave reflected from a target, and outputs a reception wave signal;

a dual-sweep signal generator that generates a dual-sweep signal of the chirp wave, having a frequency which does not overlap a frequency band of the chirp wave; and

a heterodyne processor that generates a beat frequency by multiplying the reception wave signal and the dual-sweep signal as a heterodyne signal.

Another aspect of the present invention provides a control method of an information processing apparatus, comprising:

receiving a reflected wave of a chirp wave reflected from a target, and outputting a reception wave signal; and

generating a beat frequency by multiplying the reception wave signal and a dual-sweep signal of the chirp wave as a heterodyne signal, wherein a frequency of the dual-sweep signal does not overlap that of the chirp wave.

Still other aspect of the present invention provides a control program of an information processing apparatus, for causing a computer to execute a method, comprising:

receiving a reflected wave of a chirp wave reflected from a target, and outputting a reception wave signal; and

generating a beat frequency by multiplying the reception wave signal and a dual-sweep signal of the chirp wave as a heterodyne signal, wherein a frequency of the dual-sweep signal does not overlap that of the chirp wave.

Still other aspect of the present invention provides a target extraction system comprising:

a wave transmission apparatus that transmits a chirp wave; and

a wave reception apparatus that receives a reflected wave of the chirp wave reflected from a target, and extracts the target,

said wave reception apparatus comprising:

a wave receiver that receives the reflected wave, and outputs a reception wave signal; and

a heterodyne processor that generates a beat frequency by multiplying the reception wave signal and a dual-sweep signal of the chirp wave as a heterodyne signal, wherein a frequency of the dual-sweep signal does not overlap that of the chirp wave.

Still other aspect of the present invention provides a target extraction method comprising:

transmitting a chirp wave; and

extracting a target based on a frequency spectrum of a beat frequency generated by multiplying a reception wave signal obtained from a reflected wave of the chirp wave reflected from the target and a dual-sweep signal of the chirp wave as a heterodyne signal, wherein a frequency of the dual-sweep signal does not overlap that of the chirp wave.

Advantageous Effects of Invention

According to the present invention, it is possible to improve the target extraction accuracy.

DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will now be described in detail with reference to the drawings. It should be noted that the relative arrangement of the components, the numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present invention unless it is specifically stated otherwise. Note that a “chirp wave” used in this specification indicates a wave whose frequency linearly changes. A wave whose frequency linearly rises will be referred to as an “up chirp wave” hereinafter, and a wave whose frequency linearly lowers will be referred to as a “down chirp wave” hereinafter. A wave obtained by repeating an up chirp wave and a down chirp wave is distinguished from a wave obtained by repeating only an up chirp wave or down chirp wave, and will be referred to as a “serrated chirp wave” hereinafter. A “dual-sweep signal” indicates a signal that linearly changes in a frequency band twice a frequency change in a chirp wave in a cycle twice the cycle of the chirp wave.

In this specification, a signal whose frequency linearly rises will be referred to as an “up dual-sweep signal” hereinafter, and a wave whose frequency linearly lowers will be referred to as a “down dual-sweep signal” hereinafter. Furthermore, a “beat frequency” indicates the frequency of a combined wave whose amplitude slowly, periodically changes when two waves with slightly different frequencies interfere with each other. In this example, the “beat frequency” corresponds to a frequency difference as a calculation result obtained by performing heterodyne processing of integrating a reception wave signal corresponding to a received chirp wave and a heterodyne signal corresponding to a transmitted chirp wave. The “heterodyne signal” includes a “dual-sweep signal”.

First Embodiment

The information processing apparatus100is an apparatus for extracting a target based on the reflected wave of a transmitted chirp wave.

As shown inFIG. 1, the information processing apparatus100includes a wave receiver110, a dual-sweep signal generator120, and a heterodyne processor130. The wave receiver110receives a reflected wave112of a chirp wave111reflected from a target150, and outputs a reception wave signal. The dual-sweep signal generator120generates the dual-sweep signal of the chirp wave111, whose frequency does not overlap that of the chirp wave111. The heterodyne processor130generates a beat frequency by multiplying the reception wave signal by the dual-sweep signal as a heterodyne signal.

According to this embodiment, it is possible to improve the target extraction accuracy by preventing a beat frequency necessary for target extraction, target speed estimation, and Doppler influence detection from overlapping unnecessary frequencies in a heterodyne processing result.

Second Embodiment

An information processing apparatus according to the second embodiment of the present invention will be described next. The information processing apparatus according to this embodiment executes generation and display of a beat frequency, extraction of a target, estimation of the speed of a moving target, correction of the Doppler influence, and the like using, as a heterodyne signal, a dual-sweep signal of a frequency band that does not overlap that of a chirp wave transmitted by a wave transmitter.

<<Overview of Processing of Embodiment>>

FIG. 2Ashows timing charts showing the features of a target extraction method by the information processing apparatus according to this embodiment.

Note thatFIG. 2Ashows frequency changes in a transmission wave and a heterodyne signal to clarify the differences. In the following timing charts respectively showing signals, the signal is illustrated as a frequency change. This embodiment will explain a case in which a center frequency is 40 kHz and a sampling frequency is 160 kHz. The present invention, however, is not limited to this.

Referring toFIG. 2A, a heterodyne signal210for a basic method is the same as a frequency change in a chirp wave, and is a heterodyne signal used in patent literatures 1 and 2. A dual-sweep signal220as a heterodyne signal for a dual-sweep method is a frequency change in a frequency band twice the frequency band of the chirp wave in a cycle twice the cycle of the chirp wave, which is obtained by connecting two chirp waves, and is a signal whose frequency band overlaps that of the chirp wave used in patent literature 3 and non-patent literatures 1 and 2.

A dual-sweep signal230of a new heterodyne signal shown inFIG. 2Ais a dual-sweep signal used in this embodiment, and is a signal whose frequency band does not overlap that of the chirp wave. That is, in this embodiment, a heterodyne dual-sweep signal231bis generated so as to satisfy the minimum condition that a frequency band is different from that of a chirp wave231ato be transmitted, and does not overlap that of the chirp wave231a.

(Transmission Wave Signal and Reception Wave Signal)

FIG. 2Bshows timing charts respectively showing a frequency change in a transmission wave signal240and that in a reception wave signal250in a target extraction system including the information processing apparatus according to this embodiment.FIG. 2Bshows the transmission wave signal240which the chirp wave is based on, and the reception wave signal250corresponding to the received chirp wave. In the reception wave signal250, a solid line indicates the reception wave signal of a still object, and a delay time with respect to the transmission wave signal240is constant. On the other hand, in the reception wave signal250, a broken line indicates the reception wave signal of a moving object, and a delay time with respect to the transmission wave signal240changes.FIG. 2Bshows a case in which the distance to the moving object is long.

In a reception wave signal and heterodyne result in each timing chart, a solid line corresponds to a still object, and a broken line corresponds to a moving object.

(Heterodyne Processing Result in Technical Premise)

FIG. 2Cshows timing charts showing a heterodyne processing result270of the reception wave signal250and the dual-sweep signal220according to a technical premise. The reception wave signal250is of the same frequency band as that shown inFIG. 2B.

Referring toFIG. 2C, a dual-sweep signal is generated as the dual-sweep signal220by a signal220athat is the same as the transmission wave signal240and a signal220bof a frequency band continuing to that of the signal220a, thereby executing heterodyne processing of multiplying the reception wave signal250by the generated dual-sweep signal.

In the heterodyne processing result270, beat frequencies271respectively indicating a still object and moving object overlap unnecessary frequencies272during a time period273. Consequently, visual identification is difficult, and separation cannot be performed by a filter. Therefore, during the time period273, that is, while the distance to the target falls within a predetermined range, target extraction, distance estimation, and Doppler correction are difficult.

(Reception Wave Signal and Dual-Sweep Signal of Embodiment)

FIG. 2Dis a timing chart showing frequency changes in the reception wave signal250and the dual-sweep signal230according to this embodiment. The reception wave signal250is of the same frequency band as that shown inFIGS. 2B and 2C.

Referring toFIG. 2D, a dual-sweep signal is generated as the dual-sweep signal230by a signal230aand a signal230bof a frequency band continuing to that of the signal230a, whose frequency bands do not overlap that of the transmission wave signal240, thereby executing heterodyne processing of multiplying the reception wave signal250by the generated dual-sweep signal.

(Heterodyne Processing Result in Embodiment)

FIG. 2Eshows timing charts showing beat frequency changes in the heterodyne processing results in the information processing apparatus according to this embodiment.

In a heterodyne processing result280based on the dual-sweep signal230inFIG. 2D, a heterodyne processing result based on the signal230ais a target beat frequency280a. A heterodyne processing result based on the signal230bis a target beat frequency280b. The beat frequencies280aand280bare connected, resulting in a target heterodyne processing result290.

The frequency band of the target heterodyne processing result290does not overlap unnecessary frequencies292. Thus, visual identification is easy, and separation can be readily performed by a filter. Therefore, target extraction, distance estimation, and Doppler correction are possible regardless of the distance to the target.

<<Functional Arrangement of Target Extraction System Including Information Processing Apparatus>>

FIG. 3is a block diagram showing the functional arrangement of the target extraction system including an information processing apparatus300according to this embodiment.

A transmission wave generation unit350generates a chirp wave of a predetermined frequency band and a predetermined cycle, and transmits it. The chirp wave transmitted from the transmission wave generation unit350propagates through a propagation path360, is reflected from the target, and is detected by a wave receiver310of the information processing apparatus300. The propagation path360is the sea or the water such as a body but is not limited to this. Note that inFIG. 3, the propagation path360is modeled by delays, the Doppler effect, noise generation, and the like. This is merely an example, and the present invention is not limited to this.

The information processing apparatus300includes the wave receiver310, a dual-sweep signal generator320, a heterodyne processor330, and a spectrogram unit340. The wave receiver310receives an acoustic wave which has propagated through the propagation path360and reached the wave receiver310, and includes the chirp wave from the transmission wave generation unit350.

The dual-sweep signal generator320generates, as a heterodyne signal, a dual-sweep signal whose frequency band does not overlap that of the chirp wave transmitted by the transmission wave generation unit350and is twice the frequency band of the transmission wave signal. Note thatFIG. 3shows an example in which the dual-sweep signal generator320acquires the frequency band and cycle of the chirp wave transmitted from the transmission wave generation unit350. However, if the frequency band and cycle of the chirp wave transmitted from the transmission wave generation unit350are already known, a dual-sweep signal can be generated without acquiring the frequency band and cycle of the chirp wave.

The heterodyne processor330multiplies a reception wave signal output from the wave receiver310by the dual-sweep signal whose frequency band does not overlap that of the reception wave signal, thereby generating a beat frequency as the frequency difference between the reception wave signal and the dual-sweep signal. The spectrogram unit340generates, as a processing result of the heterodyne processor330, a spectrogram (to be referred to as a spectrogram of the beat frequency hereinafter) from a frequency change obtained by replacing a frequency along the ordinate by the beat frequency, thereby facilitating identification of a reflected sound from the target in the reception wave signal.

Note that an output from the spectrogram unit340undergoes spectrogram display by an output unit301, and is used by a calculator302for calculation of the distance to the target, estimation of a target speed, correction of the Doppler influence, and the like. The output unit301and the calculator302may be included in the information processing apparatus300.

(Functional Arrangement of Transmission Wave Generation Unit)

FIG. 4Ais a block diagram showing the functional arrangement of the transmission wave generation unit350according to this embodiment. The functional arrangement of the transmission wave generation unit350shown inFIG. 4Ais merely an example, and the present invention is not limited to this as long as a chirp wave is output according to this embodiment.

The transmission wave generation unit350includes a signal generation unit410, a digital-to-analog converter (DAC inFIG. 4A)420, a transmission wave processor430, and a wave transmitter440. The signal generation unit410includes a signal generator411that generates a signal for generating a chirp wave, a chirp wave table412that stores the frequency band and cycle of the chirp wave generated by the signal generator411, and an oscillator413that generates a chirp wave based on the signal from the signal generator411.

The digital-to-analog converter420converts the chirp wave generated by the signal generation unit410into an analog signal. The transmission wave processor430performs processing of, for example, amplifying the analog signal of the chirp wave. The wave transmitter440transmits, to the propagation path360, the chirp wave according to the signal of the transmission wave processor430.

Note thatFIG. 4Ashows the arrangement in which the frequency band and cycle of a chirp wave to be transmitted can be freely set. If the chirp wave is fixed, the chirp wave table412is not necessary.

FIG. 4Bis a table showing the structure of the chirp wave table412according to this embodiment. The chirp wave table412is used to set the frequency band and cycle of a chirp wave generated by the signal generator411.

The chirp wave table412stores a wave type422and a frequency band423and cycle424of the wave in association with a use wave flag421indicating a chirp wave to be used. Referring toFIG. 4B, in the use wave flag421, ο indicates a use wave and x indicates a disuse wave. The wave type422includes an up chirp wave whose frequency linearly rises, a down chirp wave whose frequency linearly lowers, and a serrated chirp wave obtained by alternately repeating an up chirp wave and a down chirp wave.

InFIG. 4B, the down chirp wave shown inFIGS. 2A to 2Eis selected as a use wave.

FIG. 5Ais a block diagram showing the functional arrangement of the dual-sweep signal generator320according to this embodiment. The functional arrangement of the dual-sweep signal generator320shown inFIG. 5Ais merely an example, and the present invention is not limited to this as long as a dual-sweep signal whose frequency band does not overlap that of a chirp wave is output according to this embodiment.

The dual-sweep signal generator320includes a transmitted chirp wave information acquirer510, a dual-sweep signal frequency generator520, an oscillator530on the low-frequency side of a dual-sweep signal, an oscillator540on the high-frequency side of the dual-sweep signal, and a signal combiner550. If a chirp wave to be transmitted changes, the transmitted chirp wave information acquirer510acquires the information (up or down, frequency band, and cycle) of the chirp wave to generate a dual-sweep signal. Note that if the chirp wave to be transmitted is known and fixed, the transmitted chirp wave information acquirer510is not necessary.

The dual-sweep signal frequency generator520includes a dual-sweep signal table521, and generates, based on the transmitted chirp wave, frequency data of the dual-sweep signal whose frequency band does not overlap that of the chirp wave. In accordance with the output of the dual-sweep signal frequency generator520, the oscillators530and540respectively generate signals each of which has the same degree of frequency change as that of the chirp wave and in each of which a frequency change continues without overlapping the frequency band of the transmitted chirp wave. The signal combiner550combines the outputs of the oscillators530and540, and outputs a dual-sweep signal whose frequency band does not overlap that of the transmitted chirp wave.

Note thatFIG. 5Ashows the arrangement in which the frequency band and cycle of the chirp wave to be transmitted can be freely set. However, if the chirp wave is known and fixed, the dual-sweep signal table521is not necessary. A broken line from the transmitted chirp wave information acquirer510to the signal combiner550indicates a case in which a signal corresponding to the transmitted chirp wave is acquired, and used intact.

FIG. 5Bis a table showing the structure of the dual-sweep signal table521according to this embodiment. The dual-sweep signal table521is used to generate a dual-sweep signal corresponding to a transmitted chirp wave.

The dual-sweep signal table521stores a frequency band503and a cycle504, which are set based on a signal type501and a transmitted use chirp wave502. The signal type501includes a low-frequency side and a high-frequency side for one dual-sweep signal.

The use chirp wave502stores the chirp wave information acquired by the transmitted chirp wave information acquirer510.

In the frequency band503, a frequency band which does not overlap that of the chirp wave and is close to that of the chirp wave is set based on the transmitted chirp wave information. The frequency bands503on the low- and high-frequency sides are continuous. Furthermore, the same cycle as that of the chirp wave is set in the cycle504.

FIG. 6Ais a block diagram showing the functional arrangement of the heterodyne processor330according to this embodiment. The functional arrangement of the heterodyne processor330shown inFIG. 6Ais merely an example, and the present invention is not limited to this as long as multiplication processing of a reception wave signal and a dual-sweep signal is performed according to this embodiment.

The heterodyne processor330includes a reception wave signal acquirer610, a dual-sweep signal acquirer620, a multiplier630, and an optional unnecessary signal removal filter640.

The reception wave signal acquirer610acquires the reception wave signal from the wave receiver310. The dual-sweep signal acquirer620acquires the dual-sweep signal from the dual-sweep signal generator320. The multiplier630generates a beat frequency as a difference frequency by multiplying the reception wave signal by the dual-sweep signal.

Based on a filter parameter table641predicted based on the chirp wave and the dual-sweep signal, the unnecessary signal removal filter640removes frequency components unnecessary for target extraction, which are included in the output of the multiplier630. Note that if the chirp signal and the dual-sweep signal are known and fixed, the filter parameter table641is not necessary.

FIG. 6Bis a table showing the structure of the filter parameter table641according to this embodiment. The filter parameter table641stores filter parameters predicted based on the chirp signal and dual-sweep signal.

The filter parameter table641stores a filter frequency band604of each filter type601, which is estimated based on a use chirp wave602and a use dual-sweep signal603. Note that the filter frequency band604may store a plurality of frequency bands including unnecessary frequencies.

FIG. 7is a block diagram showing the functional arrangement of the spectrogram unit340according to this embodiment. The functional arrangement of the spectrogram unit340shown inFIG. 7is merely an example, and the present invention is not limited to this as long as a spectrogram of a beat frequency after heterodyne processing is generated according to this embodiment.

The spectrogram unit340includes a fast Fourier transformer (FFT: Fast Fourier Transform inFIG. 7)710and a spectrogram generator720. The fast Fourier transformer710generates the frequency characteristics of a beat frequency after heterodyne processing. The spectrogram generator720generates, for example, a frequency-vs-level spectrogram (not shown) based on the frequency characteristics of the beat frequency.

<<Hardware Arrangement of Information Processing Apparatus>>

FIG. 8is a block diagram showing the hardware arrangement of the information processing apparatus300according to this embodiment.

Referring toFIG. 8, a CPU810is an arithmetic control processor, and implements the functions of the functional components of the information processing apparatus300shown inFIG. 3by executing programs and modules stored in a storage850using a RAM840. A ROM820stores programs and permanent data such as initial data and programs. Note that the number of CPUs810is not limited to one, and a plurality of CPUs or a GPU for image processing may be included.

The RAM840is a random access memory used by the CPU810as a work area for temporary storage. An area to store data necessary for implementation of the embodiment is allocated to the RAM840. Transmitted chirp wave data841is data of the chirp wave transmitted by the transmission wave generation unit350, which indicates an up or down chirp wave, frequency band, and cycle. Reception wave signal data842is data of the signal received by the wave receiver310. Heterodyne signal data843is data of the dual-sweep signal which has been generated based on the transmitted chirp wave and is used for heterodyne processing. Heterodyne processing data (beat frequency)844is data representing the beat frequency of the heterodyne processing result. Spectrogram data845is data of the spectrogram processing result of the beat frequency. Target distance data846is distance data to the target, which has been calculated based on the spectrogram data845. Target speed data847is data of the moving speed of the target calculated based on the spectrogram data845.

The storage850stores a database and various parameters, or the following data or programs necessary for implementation of the embodiment. The dual-sweep signal table521stores data of a frequency change in the dual-sweep signal, as shown inFIG. 5B.

The filter parameter table641stores the parameters of the unnecessary signal removal filter, as shown inFIG. 6B. A calculation parameter/algorithm851stores parameters and algorithms to be used to optionally calculate a target distance, a target speed, and the like.

The storage850stores the following programs. An information processing apparatus control program852is a control program for controlling the overall information processing apparatus300. A heterodyne signal generation module853is a module for generating a dual-sweep signal, corresponding to the transmitted chirp wave, whose frequency band does not overlap that of the chirp wave. A heterodyne processing module854is a module for performing heterodyne processing using the reception wave signal and the dual-sweep signal.

A spectrogram module855is a module for generating a spectrogram of the beat frequency of the heterodyne processing result. A target distance calculation module856is a module for calculating the distance to the target based on the spectrogram of the beat frequency. A target speed calculation module857is a module for calculating the moving speed of the target based on the spectrogram of the beat frequency.

The input/output interface860is connected to the wave receiver310, a display unit861, an operation unit862such as a keyboard, touch panel, and pointing device, a GPS position determiner863, and the like.

Note that programs and data which are associated with the general-purpose functions of the information processing apparatus300and other feasible functions are not shown in the RAM840or the storage850ofFIG. 8. Calculation of the target distance and target speed shown inFIG. 8is optional.

<<Processing Procedure of Information Processing Apparatus>>

FIG. 9is a flowchart illustrating the processing procedure of the information processing apparatus300according to this embodiment. This flowchart is executed by the CPU810ofFIG. 8using the RAM840, thereby implementing the functional components ofFIG. 3.

In step S901, the information processing apparatus300acquires a transmitted chirp wave or its parameters. Note that if the transmitted chirp wave is known and fixed, step S901can be skipped. In step S903, the information processing apparatus300generates a dual-sweep signal whose frequency band does not overlap that of the chirp wave. In step S905, the information processing apparatus300receives the chirp wave transmitted and reflected by the target. In step S907, the information processing apparatus300executes heterodyne processing using the received chirp wave and the dual-sweep signal. In step S909, the information processing apparatus300generates a spectrogram of a beat frequency of a heterodyne processing result, and outputs it. Note that in step S911, the information processing apparatus300optionally calculates a target distance and target speed based on the spectrogram of the beat frequency.

FIG. 10Ais a flowchart illustrating the procedure of the dual-sweep signal generation processing (S903) according to this embodiment.

In step S1011, the information processing apparatus300generates the first copy signal whose frequency band does not overlap that of the transmitted chirp wave. Note that the copy signal indicates that it has the same degree of frequency change, as shown inFIGS. 2A to 2E, and does not indicate that it has the same frequency. Assume that the frequency band of the first copy signal is close to the frequency band of the chirp wave. In step S1013, the information processing apparatus300generates the second copy signal whose frequency band does not overlap that of the transmitted chirp wave and continues to that of the first copy signal. In step S1015, the information processing apparatus300generates a dual-sweep signal whose frequency band does not overlap that of the transmitted chirp wave by adding the first and second copy signals. In step S1017, the information processing apparatus300outputs the generated dual-sweep signal to the heterodyne processor330.

FIG. 10Bis a flowchart illustrating the procedure of the heterodyne processing (S907) and spectrogram processing (S909) according to this embodiment.

In step S1021, the information processing apparatus300acquires the reception wave signal. In step S1023, the information processing apparatus300acquires the dual-sweep signal.

In step S1025, the information processing apparatus300generates a beat frequency by multiplying the reception signal by the dual-sweep signal. Note that in step S1027, the information processing apparatus300optionally removes unnecessary frequencies using a filter.

In step S1029, the information processing apparatus300performs fast Fourier transform processing for the beat frequency, thereby generating a frequency spectrum. In step S1031, the information processing apparatus300generates a spectrogram based on the frequency spectrum.

In step S1033, the information processing apparatus300outputs the generated spectrogram.

According to this embodiment, it is possible to separate a signal necessary for target extraction and an unnecessary signal from a heterodyne result, thereby effectively extracting the target.

Third Embodiment

An information processing apparatus according to the third embodiment of the present invention will be described next. The information processing apparatus according to this embodiment is different from that according to the second embodiment in that a plurality of chirp waves are transmitted. The remaining components and operations are the same as those in the second embodiment. Hence, the same reference numerals denote the same components and operations, and a detailed description thereof will be omitted.

<<Overview of Processing of Embodiment>>

(Transmission Wave Signal and Reception Wave Signal)

FIG. 11Ashows timing charts respectively showing a frequency change in a transmission wave signal1110and that in a reception wave signal1120in a target extraction system including the information processing apparatus according to this embodiment.

FIG. 11Ashows the transmission wave signal1110formed from a plurality of chirp waves whose frequencies change in an inverted “V”-shaped pattern, and its reception wave signal1120. In the reception wave signal1120, a solid line indicates the reception wave signal of a still object, and a broken line indicates the reception wave signal of a moving object.FIG. 11Ashows a case in which the distance to the moving object becomes longer with time. Note that this embodiment will exemplify the transmission wave signal1110formed from the plurality of chirp waves whose frequencies change in an inverted “V”-shaped pattern. However, any transmission wave signal formed from a plurality of chirp waves may be used. For example, a combination of up or down chirp waves or a combination with a serrated chirp wave may be used.

In this embodiment, it is possible to separate a signal necessary for target extraction and an unnecessary signal from a heterodyne result by preventing the frequency band of a heterodyne dual-sweep signal from overlapping those of the plurality of transmitted chirp waves.

(Reception Wave Signal and Up Heterodyne Signal)

FIG. 11Bis a timing chart showing frequency changes in the reception wave signal1120and an up heterodyne signal1130according to this embodiment. Note that the up heterodyne signal1130is set in a high-frequency band which does not overlap the frequency band of the reception wave signal1120but may be set in a low-frequency band. The frequency band is selected so as to prevent the use band of the frequency from becoming wide as much as possible.

FIG. 11Cis a timing chart showing a beat frequency change in an up heterodyne processing result1140according to this embodiment. As shown inFIG. 11C, two sets of beat frequencies1141and1142of a still object and moving object corresponding to two reception wave signals are generated to be separated from unnecessary frequencies1143. Since a shift in the beat frequency is different between the still object and the moving object in each of the two sets of beat frequencies1141and1142depending on the influence of the Doppler effect, it is possible to calculate the correct position and speed of a moving target by correcting the Doppler influence based on the output data.

(Reception Wave Signal and Down Heterodyne Signal)

FIG. 11Dis a timing chart showing frequency changes in the reception wave signal1120and a down heterodyne signal1150according to this embodiment. Note that the down heterodyne signal1150is sets in a low-frequency band which does not overlap the frequency band of the reception wave signal1120but may be set in a high-frequency band. The frequency band is selected so as to prevent the use band of the frequency from becoming wide as much as possible.

FIG. 11Eis a timing chart showing a beat frequency change in a down heterodyne processing result1160according to this embodiment. As shown inFIG. 11E, two sets of beat frequencies1161and1162of a still object and moving object corresponding to two reception wave signals are generated to be separated from unnecessary frequencies1163. Since a shift in the beat frequency is different between the still object and the moving object in each of the two sets of beat frequencies1161and1162depending on the influence of the Doppler effect, it is possible to calculate the correct position and speed of the moving target by correcting the Doppler influence based on the output data.

Note that it is understood from the heterodyne processing results shown inFIGS. 11C and 11Ethat a heterodyne dual-sweep signal is more desirably set in a frequency band as low as possible since the frequency band becomes narrow.

<<Functional Arrangement of Target Extraction System Including Information Processing Apparatus>>

FIG. 12is a block diagram showing the functional arrangement of the target extraction system including an information processing apparatus1200according to this embodiment. Note that inFIG. 12, the same reference numerals as inFIG. 3denote the same functional components and a description thereof will be omitted.

A transmission wave generation unit1250generates a plurality of chirp waves of predetermined frequency bands and predetermined cycles, and transmits them. This example will explain an example in which two chirp waves whose frequencies change in an inverted “V”-shaped pattern are transmitted. The present invention, however, is not limited to this.

The information processing apparatus1200includes a wave receiver310, a dual-sweep signal generator1220, a heterodyne processor1230, and a spectrogram unit340. The dual-sweep signal generator1220generates, as a heterodyne signal, a dual-sweep signal whose frequency band does not overlap those of the plurality of chirp waves transmitted by the transmission wave generation unit1250and is twice that of each transmission wave signal. Note thatFIG. 12shows an example in which the dual-sweep signal generator1220acquires the frequency bands and cycles of the chirp waves transmitted from the transmission wave generation unit1250. However, if the frequency bands and cycles of the plurality of chirp waves transmitted from the transmission wave generation unit1250are already known, a dual-sweep signal can be generated without acquiring the frequency bands and cycles of the chirp waves.

The heterodyne processor1230multiplies a plurality of reception wave signals output from the wave receiver310by the dual-sweep signal whose frequency band does not overlap those of the plurality of reception wave signals, thereby generating beat frequencies as the frequency differences between the reception wave signals and the dual-sweep signal.

(Functional Arrangement of Transmission Wave Generation Unit)

FIG. 13Ais a block diagram showing the functional arrangement of the transmission wave generation unit1250according to this embodiment. Note that inFIG. 13A, the same reference numerals as inFIG. 4Adenote the same functional components and a description thereof will be omitted. The functional arrangement of the transmission wave generation unit1250shown inFIG. 13Ais merely an example, and the present invention is not limited to this as long as a plurality of chirp waves are output according to this embodiment.

The transmission wave generation unit1250includes a signal generation unit1310, a digital-to-analog converter (DAC inFIG. 13A)420, a transmission wave processor430, and a wave transmitter440. The signal generation unit1310includes a signal generator1311that generates signals for generating chirp waves, and a chirp wave table1312that stores the frequency bands and cycles of the chirp waves generated by the signal generator1311. The signal generation unit1310includes oscillators1313and1314that generate a plurality of chirp waves based on the signals from the signal generator1311, and a combiner1315that combines the plurality of chirp waves.

Note thatFIG. 13Ashows the arrangement in which the frequency bands and cycles of the chirp waves to be transmitted can be freely set. However, if the plurality of chirp waves are fixed, the chirp wave table1312is not necessary.

FIG. 13Bis a table showing the structure of the chirp wave table1312according to this embodiment. The chirp wave table1312is used to set the frequency bands and cycles of the plurality of chirp waves generated by the signal generator1311.

The chirp wave table1312stores a wave type1322and a frequency band1323and cycle1324of the wave in association with a use wave flag1321indicating a chirp wave to be used.

In the use wave flag1321, ο indicates a use wave and x indicates a disuse wave. The wave type1322includes an up chirp wave whose frequency linearly rises, a down chirp wave whose frequency linearly lowers, and a serrated chirp wave obtained by alternately repeating an up chirp wave and a down chirp wave. In this example, a plurality of chirp waves to be used are stored in association with each use wave flag1321.

InFIG. 13B, up and down chirp waves which have an inverted “V” shape, as shown inFIG. 11A, are selected as use waves.

FIG. 14Ais a block diagram showing the functional arrangement of the dual-sweep signal generator1220according to this embodiment. Note that the functional arrangement of the dual-sweep signal generator1220shown inFIG. 14Ais merely an example, and the present invention is not limited to this as long as dual-sweep signals whose frequency bands do not overlap those of a plurality of chirp waves are output according to this embodiment. In the dual-sweep signal generator1220ofFIG. 14A, an arrangement of generating both an up dual-sweep signal and a down dual-sweep signal is shown. However, as shown inFIG. 11B or 11D, one of the up and down dual-sweep signals may be generated. Alternatively, one of the two signals may be selected.

The dual-sweep signal generator1220includes a transmitted up chirp wave information acquirer1410, a dual-sweep signal frequency generator1420, an oscillator1430on the low-frequency side of the dual-sweep signal, an oscillator1440on the high-frequency side of the dual-sweep signal, and a signal combiner1450. The dual-sweep signal generator1220also includes a transmitted down chirp wave information acquirer1460, an oscillator1470on the low-frequency side of the dual-sweep signal, an oscillator1480on the high-frequency side of the dual-sweep signal, and a signal combiner1490.

Note that the transmitted up chirp wave information acquirer1410and the transmitted down chirp wave information acquirer1460may be integrated into one chirp wave information acquirer. If the chirp waves to be transmitted are known and fixed, the chirp wave information acquirers are not necessary.

The dual-sweep signal frequency generator1420includes a dual-sweep signal table1421, and generates, based on the plurality of transmitted chirp waves, frequency data of dual-sweep signals whose frequency bands do not overlap those of the plurality of chirp waves. In accordance with the output of the dual-sweep signal frequency generator1420, the oscillators1430and1440respectively generate signals each of which has the same degree of frequency change as that of the up chirp wave and in each of which a frequency change continues without overlapping the frequency bands of the plurality of transmitted chirp waves. The signal combiner1450combines the outputs of the oscillators1430and1440, and outputs an up dual-sweep signal whose frequency band does not overlap those of the plurality of transmitted chirp waves. On the other hand, in accordance with the output of the dual-sweep signal frequency generator1420, the oscillators1470and1480respectively generate signals each of which has the same degree of frequency change as that of the down chirp wave and in each of which a frequency change continues without overlapping the frequency bands of the plurality of transmitted chirp waves. The signal combiner1490combines the outputs of the oscillators1470and1480, and outputs a down dual-sweep signal whose frequency band does not overlap those of the plurality of transmitted chirp waves.

Note thatFIG. 14Ashows the arrangement in which the frequency bands and cycles of the plurality of chirp waves to be transmitted can be freely set. However, if the plurality of chirp waves are known and fixed, the dual-sweep signal table1421is not necessary.

FIG. 14Bis a table showing the structure of the dual-sweep signal table1421according to this embodiment. The dual-sweep signal table1421is used to generate dual-sweep signals corresponding to the plurality of transmitted chirp waves.

The dual-sweep signal table1421stores a frequency band1404and a cycle1405, which are set based on a signal type1401, a transmitted use chirp wave1402, and another chirp wave1403. Note that the other chirp wave1403is not limited to one chirp wave. The signal type1401includes a low-frequency side and a high-frequency side for one dual-sweep signal. The use chirp wave1402and the other chirp wave1403store the pieces of chirp wave information acquired by the transmitted up chirp wave information acquirer1410and transmitted down chirp wave information acquirer1460.

In the frequency band1404, frequency bands which do not overlap those of the plurality of chirp waves and are close to those of the plurality of chirp waves are set based on the information of the transmitted use chirp wave1402. The frequency bands1404on the low-frequency and high-frequency sides are continuous. Furthermore, the same cycle as that of the use chirp wave is set in the cycle1405.

FIG. 15Ais a block diagram showing the functional arrangement of the heterodyne processor1230according to this embodiment. Note that the functional arrangement of the heterodyne processor1230shown inFIG. 15Ais merely an example, and the present invention is not limited to this as long as multiplication processing of a reception wave signal and a dual-sweep signal is performed according to this embodiment. In the heterodyne processor1230ofFIG. 15A, the arrangement of executing both heterodyne processing based on the up dual-sweep signal and that based on the down dual-sweep signal is shown. However, as shown inFIG. 11B or 11D, one of the heterodyne processes may be executed. Alternatively, one of the two processes may be selected.

The heterodyne processor1230includes a reception wave signal acquirer1510, an up dual-sweep signal acquirer1520, a multiplier1530, and an optional unnecessary signal removal filter1540. The heterodyne processor1230also includes a down dual-sweep signal acquirer1550, a multiplier1560, and an optional unnecessary signal removal filter1570.

The reception wave signal acquirer1510acquires a reception wave signal including a plurality of chirp waves from the wave receiver310. The up dual-sweep signal acquirer1520acquires the up dual-sweep signal from the dual-sweep signal generator1220. On the other hand, the down dual-sweep signal acquirer1550acquires the down dual-sweep signal from the dual-sweep signal generator1220. The multiplier1530multiplies the reception wave signal by the up dual-sweep signal to generate a beat frequency as a difference frequency. On the other hand, the multiplier1560multiplies the reception wave signal by the down dual-sweep signal to generate a beat frequency as a difference frequency.

Based on a filter parameter table1541predicted based on the plurality of chirp waves and the up dual-sweep signal, the unnecessary signal removal filter1540removes frequency components unnecessary for target extraction, which are included in the output of the multiplier1530. On the other hand, based on a filter parameter table1571predicted based on the plurality of chirp waves and the down dual-sweep signal, the unnecessary signal removal filter1570removes frequency components unnecessary for target extraction, which are included in the output of the multiplier1560. Note that the filter parameter tables1541and1571may be integrated into one table capable of identifying each parameter. If the plurality of chirp waves and the dual-sweep signals are known and fixed, the filter parameter tables1541and1571are not necessary.

FIG. 15Bis a table showing the structures of the filter parameter tables1541and1571according to this embodiment. Each of the filter parameter tables1541and1571stores filter parameters predicted based on the plurality of chirp waves and the up or down dual-sweep signal.

Each of the filter parameter tables1541and1571stores a filter frequency band1504of each filter type1501, which is estimated based on a use chirp wave1502and a use dual-sweep signal1503. Note that the filter frequency band1504may store a plurality of frequency bands including unnecessary frequencies.

<<Processing Procedure of Transmission Wave Generation Unit>>

FIG. 16Ais a flowchart illustrating the processing procedure of the transmission wave generation unit1250according to this embodiment.

In step S1601, the transmission wave generation unit1250acquires the parameters (up/down, frequency band, and cycle) of the first chirp wave from the chirp wave table1312. In step S1603, the transmission wave generation unit1250generates the first chirp wave.

In step S1605, in this example, the transmission wave generation unit1250acquires, from the chirp wave table1312, the parameters (up/down, frequency band, and cycle) of the second chirp wave whose frequency band is different from that of the first chirp wave and which has the up/down parameter opposite to that of the first chirp wave. In step S1607, the transmission wave generation unit1250generates the second chirp wave.

In step S1609, the transmission wave generation unit1250transmits the first and second chirp waves. Note that the combination of two chirp waves or the number of chirp waves is not limited to that in this example.

FIG. 16Bis a flowchart illustrating the procedure of the dual-sweep signal generation processing according to this embodiment. This flowchart is executed by a CPU810ofFIG. 8using a RAM840, thereby implementing the dual-sweep signal generator1220ofFIG. 12.

In step S1611, the information processing apparatus1200acquires the transmitted first and second chirp waves or their parameters. In step S1613, the information processing apparatus1200generates the first copy signal of the first chirp wave and the second copy signal of the second chirp wave, whose frequency bands do not overlap those of the first and second chirp waves. Note that each copy signal indicates that it has the same degree of frequency change, as shown inFIGS. 11A, 11B, and 11D, and does not indicate that it has the same frequency. The frequency band of the first or second copy signal is close to those of the plurality of chirp waves.

In step S1615, the information processing apparatus1200generates the third and fourth copy signals whose frequency bands do not overlap those of the plurality of transmitted chirp waves and continue to that of the first or second copy signal. In step S1617, the information processing apparatus1200generates the first dual-sweep signal whose frequency band does not overlap those of the plurality of transmitted chirp waves by adding the first and third copy signals. In step S1618, the information processing apparatus1200generates the second dual-sweep signal whose frequency band does not overlap those of the plurality of transmitted chirp waves by adding the second and fourth copy signals. In step S1619, the information processing apparatus1200outputs the generated first and second dual-sweep signals to the heterodyne processor1230.

FIG. 17shows timing charts for explaining transmission wave generation conditions according to this embodiment.FIG. 17shows conditions of reducing an unnecessary frequency spectrum of the beat frequency when using the chirp waves whose frequencies change in an inverted “V”-shaped pattern in this example. However, the conditions can be applied when using a plurality of other chirp waves.

The first condition is that a chirp wave does not enter a region to which a frequency change in heterodyne signal is translated (see a frequency change1710). Conversely, a heterodyne signal does not enter a region to which a frequency change in a chirp wave is translated.

The second condition is that two chirp waves are combined by shifting their cycles by a half to reduce a wasted use band to half, as compared with the inverted “V” shape obtained when the cycles of the chirp waves coincide with each other (see frequency changes1720and1730).

By separating a plurality of chirp waves to have predetermined frequency intervals by a band filter before transmission, it is possible to generate a plurality of chirp waves for which an unnecessary frequency spectrum of the beat frequency is reduced with a simple arrangement (see a frequency change1740).

<<Target Object Speed Estimation and Doppler Influence Correction>>

FIG. 18shows timing charts for explaining target object speed estimation and Doppler influence correction according to this embodiment.

A frequency change1810shown inFIG. 18explains target speed estimation when the up and down chirp waves having the inverted “V” shape are used. In this example, a frequency Fc is set as the center frequency of the up and down chirp waves.

In this case, Fsu represents the frequency of the transmitted up chirp wave, Fsd represents the frequency of transmitted down chirp wave, Fru represents the frequency of the received up chirp wave, Frd represents the frequency of the received down chirp wave, and D represents a Doppler deviation ratio. All of these pieces of information can be acquired from, for example,FIG. 11D or 11E.

Therefore, transmitting a plurality of chirp waves makes it possible to perform target speed calculation (estimation) by executing processing once.

A frequency change1820shown inFIG. 18explains Doppler influence correction when the up and down chirp waves having the inverted “V” shape are used.

The Doppler deviation ratio D can be calculated by D=(Fru+Frd)/(Fsu+Fsd)=(Fru+Frd)/2Fc. Therefore, transmitting a plurality of chirp waves makes it possible to correct the influence of the Doppler effect by performing processing once.

Note that a case in which two chirp waves are used has been described above. However, it is apparent that not two but three or more chirp waves may be used. Obtaining a plurality of heterodyne results allows statistical processing such as averaging, and can also improve the measurement accuracy.

According to this embodiment, it is possible to separate a signal necessary for target extraction and an unnecessary signal from heterodyne results, and obtain different results of the Doppler influence at once, thereby effectively performing target extraction, target speed estimation, and Doppler influence correction.

Fourth Embodiment

An information processing apparatus according to the fourth embodiment of the present invention will be described next. The information processing apparatus according to this embodiment is different from that according to the third embodiment in that a reception wave signal of a plurality of chirp waves is separated to perform heterodyne processing. That is, in this embodiment, a reception wave is separated by a band separation filter to perform different heterodyne processes for respective chirps. Beat frequencies obtained by the heterodyne processes are combined using a band filter and the like so as not to overlap each other. A beat frequency change image is obtained for each heterodyne result, and these two beat frequency change images are combined. The remaining components and operations are the same as those in the second and third embodiments. Hence, the same reference numerals denote the same components and operations, and a detailed description thereof will be omitted.

<<Overview of Processing of Embodiment>>

(Separation of Reception Wave Signal)

FIG. 19Ashows timing charts showing the features of a target extraction method by the information processing apparatus according to this embodiment.

FIG. 19Ashows a frequency change in a reception wave signal in an example in which the reception wave signal is separated by a band separation filter. A frequency change1900shows up and down reception wave signals obtained by separating the reception wave signal of chirp waves having an inverted “V” shape using a band separation filter. In this embodiment, heterodyne processing is performed for each of the separated up and down reception wave signals using a dual-sweep signal whose frequency band does not overlap that of the reception wave signal, and the thus obtained signals are combined later.

A frequency change1910shows a case in which if a reception wave signal is formed from three chirp waves, it is separated into three reception wave signals by a band separation filter, heterodyne processing is performed for each of the separated reception wave signals using a dual-sweep signal whose frequency band does not overlap that of the reception wave signal, and the thus obtained signals are combined later.

According to this embodiment, it is possible to generate a dual-sweep signal whose frequency band does not overlap that of each reception wave signal, and thus the frequency band can be effectively used.

(Separated Up Reception Wave Signal and Up Heterodyne Signal, and Separated Down Reception Wave Signal and Down Heterodyne Signal)

FIG. 19Bshows timing charts respectively showing frequency changes in a separated up reception wave signal1921and an up heterodyne signal1130, and those a separated down reception wave signal1922and a down heterodyne signal1150according to this embodiment.

Referring toFIG. 19B, the up reception wave signal1921and the down reception wave signal1922are signals obtained by separating, using a band separation filter, in accordance with chirp waves, a signal received by a wave receiver310. Note that a reception wave signal1120shown inFIGS. 11A and 11Bis separated into the up reception wave signal1921and down reception wave signal1922to perform heterodyne processing. Therefore, even if the up heterodyne signal1130is in the low-frequency band of the up reception wave signal1921or the down heterodyne signal1150is in the high-frequency band of the down reception wave signal1922, the reception wave signal and the heterodyne dual-sweep signal do not overlap each other. This allows selection of the frequency band of the dual-sweep signal with ease, and a frequency range to be used can be narrowed.

(Heterodyne Processing Results in Embodiment)

FIG. 19Cis a timing chart showing beat frequency changes in heterodyne processing results in the information processing apparatus according to this embodiment.

Referring toFIG. 19C, a beat frequency1940generated by heterodyne processing using the up reception wave signal1921and the up heterodyne signal1130and a beat frequency1960generated by heterodyne processing using the down reception wave signal1922and the down heterodyne signal1150are combined and output.

<<Functional Arrangement of Target Extraction System Including Information Processing Apparatus>>

FIG. 20is a block diagram showing the functional arrangement of a target extraction system including an information processing apparatus2000according to this embodiment. Note that inFIG. 20, the same reference numerals as inFIGS. 3 and 12denote the same functional components and a description thereof will be omitted. Furthermore,FIG. 20shows an arrangement complying with chirp waves having an inverted “V” shape but the plurality of chirp waves are not limited to those having an inverted “V” shape.

The information processing apparatus2000includes a band separation filter2070, a filter parameter table2011for the band separation filter2070, an up chirp wave dual-sweep signal generator2021, and a down chirp wave dual-sweep signal generator2022.

Furthermore, the information processing apparatus2000includes an up multiplier2031, a down multiplier2032, an up chirp wave bandpass filter2081, a down chirp wave bandpass filter2082, a filter parameter table2012for the bandpass filters, and a heterodyne processing result combiner2090.

The band separation filter2070separates a reception wave signal into an up reception wave signal and a down reception wave signal in accordance with the filter parameter table2011. The up chirp wave dual-sweep signal generator2021generates an up dual-sweep signal whose frequency band does not overlap that of the transmitted up chirp wave in correspondence with the up chirp wave. On the other hand, the down chirp wave dual-sweep signal generator2022generates a down dual-sweep signal whose frequency band does not overlap that of the transmitted down chirp wave in correspondence with the down chirp wave. The up multiplier2031generates a beat frequency by multiplying the up reception wave signal by the up dual-sweep signal. On the other hand, the down multiplier2032generates a beat frequency by multiplying the down reception wave signal by the down dual-sweep signal.

The up chirp wave bandpass filter2081removes unnecessary frequencies from the output of the up multiplier2031in accordance with the filter parameter table2012. On the other hand, the down chirp wave bandpass filter2082removes unnecessary frequencies from the output of the down multiplier2032in accordance with the filter parameter table2012. The heterodyne processing result combiner2090combines the beat frequencies obtained by removing the unnecessary frequencies (seeFIG. 19C).

Note that each of the filter parameter tables2011and2012may be included in the band separation filter2070, or the chirp wave bandpass filter2081or2082. Alternatively, the filter parameter tables may be integrated into one table. If the plurality of chirp waves and the plurality of dual-sweep signals are known and fixed, the filter parameter tables are not necessary.

(Functional Arrangement of Band Separation Filter)

FIG. 21Ais a block diagram showing the functional arrangement of the band separation filter2070according to this embodiment. Note that the functional arrangement of the band separation filter2070is not limited to that shown inFIG. 21A. Any arrangement capable of extracting reception wave signals corresponding to a plurality of transmitted chirp waves from a reception wave signal may be adopted.

The band separation filter2070includes an up chirp wave bandpass filter2171and a down chirp wave bandpass filter2172. The band separation filter2070separates a reception wave signal into reception wave signals corresponding to a plurality of transmitted chirp waves in accordance with the filter parameter table2011.

FIG. 21Bis a table showing the structure of the filter parameter table2011for the band separation filter according to this embodiment. The filter parameter table2011is used to set the frequency band of the band separation filter2070in accordance with a use chirp wave.

The filter parameter table2011stores a separated frequency band2103in association with a filter type2101and a use chirp wave2102.

FIG. 22is a table showing the structure of the filter parameter table2012for the bandpass filters according to this embodiment. The filter parameter table2012is used to set the frequency bands of the bandpass filters after heterodyne processing.

The filter parameter table2012stores a frequency band2204of an unnecessary signal in association with a type2201of unnecessary signal removal filter, a use chirp wave2202, and a use dual-sweep signal2203. Note that the plurality of frequency bands2204may be set depending on the use chirp wave2202and the use dual-sweep signal2203.

<<Processing Procedure of Information Processing Apparatus>>

FIG. 23is a flowchart illustrating the processing procedure of the information processing apparatus2000according to this embodiment. This flowchart is executed by a CPU810ofFIG. 8using a RAM840, thereby implementing the functional components ofFIG. 20. Note that inFIG. 23, the same step numbers as inFIG. 9denote the same steps and a description thereof will be omitted.

In step S2301, the information processing apparatus2000acquires up and down chirp waves or their parameters. Note that if three or more chirp waves are used, data of each chirp wave is acquired. In step S2303, the information processing apparatus2000generates an up dual-sweep signal corresponding to the transmitted up chirp wave.

In step S2304, the information processing apparatus2000generates a down dual-sweep signal corresponding to the transmitted down chirp wave. Note that the processes in steps S2303and S2304are the same as those inFIG. 10Aof the second embodiment and a detailed description thereof will be omitted.

In step S2306, the information processing apparatus2000band-separates the reception wave signal into an up reception wave signal and a down reception wave signal. In step S2307, the information processing apparatus2000executes up heterodyne processing of multiplying the up reception wave signal by the up dual-sweep signal. In step S2308, the information processing apparatus2000executes down heterodyne processing of multiplying the down reception wave signal by the down dual-sweep signal. Note that the processes in steps S2307and S2308are the same as those in steps S1021to S1027inFIG. 10Bof the second embodiment and a detailed description thereof will be omitted. In step S2309, the information processing apparatus2000forms heterodyne results.

According to this embodiment, since a reception wave of a plurality of chirp waves is separated to perform heterodyne processing, the chirp waves and heterodyne signals can be set in narrow frequency bands. Thus, it is possible to effectively perform target extraction, target speed estimation, and Doppler influence correction.

Fifth Embodiment

An information processing apparatus according to the fifth embodiment of the present invention will be described next. The information processing apparatus according to this embodiment is different from those according to the second to fourth embodiments in that a transmitted chirp wave is used as a dual-sweep signal. The remaining components and operations are the same as those in the second to fourth embodiments. Hence, the same reference numerals denote the same components and operations, and a detailed description thereof will be omitted.

<<Overview of Processing of Embodiment>>

(Transmission Wave Signal and Reception Wave Signal)

FIG. 24Ashows timing charts showing the frequencies of a transmission wave signal2410and reception wave signal2420in a target extraction system including the information processing apparatus according to this embodiment.

Referring toFIG. 24A, the transmission wave signal2410and the reception wave signal2420are dual-sweep signals. In this embodiment, a plurality of pseudo chirp waves are generated with a simpler arrangement, and a plurality of sets of beat signals can be generated at once.

FIG. 24Bis a timing chart showing frequency changes in the reception wave signal2420and a dual-sweep signal2430according to this embodiment. Note that inFIG. 24B, the dual-sweep signal2430is set on the low-frequency side which does not overlap the reception wave signal2420but may be set on the high-frequency side. The dual-sweep signal2430is desirably set on the low-frequency side to narrow a use frequency range.

(Heterodyne Processing Result in Information Processing Apparatus)

FIG. 24Cis a timing chart showing beat frequency changes in heterodyne processing results2450in the information processing apparatus according to this embodiment.

As shown inFIG. 24C, the plurality of sets of heterodyne processing results2450are output in frequency bands separated from another unnecessary frequency band and close to each other.

<<Functional Arrangement of Transmission Wave Generation Unit>>

FIG. 25Ais a block diagram showing the functional arrangement of a transmission wave generation unit2550according to this embodiment. Note that inFIG. 25A, the same reference numerals as inFIGS. 4A and 13Adenote the same functional components and a description thereof will be omitted. The functional arrangement of the transmission wave generation unit2550shown inFIG. 25Ais merely an example, and the present invention is not limited to this as long as a dual-sweep chirp wave is output according to this embodiment.

The transmission wave generation unit2550includes a signal generation unit2510, a digital-to-analog converter (DAC inFIG. 25A)420, a transmission wave processor430, and a wave transmitter440. The signal generation unit2510includes a signal generator2511that generates a signal of a chirp waveform, and a chirp wave table2512that stores the frequency band and cycle of the chirp waveform generated by the signal generator2511.

Note thatFIG. 25Ashows the arrangement in which the frequency band and cycle of the dual-sweep chirp wave to be transmitted can be freely set. However, if the dual-sweep chirp wave is fixed, the chirp wave table2512is not necessary.

FIG. 25Bis a table showing the structure of the chirp wave table2512according to this embodiment. The chirp wave table2512is used to set the frequency band and cycle of the dual-sweep chirp wave generated by the signal generator2511.

The chirp wave table2512stores a wave type2522and a frequency band2523and cycle2524of the wave in association with a use wave flag2521indicating a chirp wave to be used.

Referring toFIG. 25B, in the use wave flag2521, ◯ indicates a use wave and x indicates a disuse wave. The wave type2522includes a dual-sweep up chirp wave, a dual-sweep down chirp wave, and a serrated chirp wave obtained by alternately repeating a dual-sweep up chirp wave and a dual-sweep down chirp wave. In this example, a plurality of chirp waves to be used, whose frequency bands are continuous, are stored in association with each use wave flag2521.

FIG. 26is a table showing the structure of a dual-sweep signal table2621according to this embodiment. The dual-sweep signal table2621is used to generate a dual-sweep signal for heterodyne processing corresponding to the dual-sweep chirp wave. Note that if the dual-sweep chirp wave is known and fixed, the dual-sweep signal table2621is not necessary.

The dual-sweep signal table2621stores a frequency band2604which does not overlap that of the dual-sweep chirp wave, and a cycle2605in association with a type2601of dual-sweep signal and a low-frequency side2602and high-frequency side2603of the dual-sweep chirp wave to be used.

<<Processing Procedure of Transmission Wave Generation Unit>>

FIG. 27is a flowchart illustrating the processing procedure of the transmission wave generation unit2550according to this embodiment. Note that inFIG. 27, the same step numbers as inFIG. 16denote the same steps and a description thereof will be omitted.

In step S2705, the transmission wave generation unit2550generates parameters of the second chirp wave whose frequency band continues to that of the first chirp wave generated in step S1603and which has the same up/down parameter as that of the first chirp wave. In step S1607, the transmission wave generation unit2550generates the second chirp wave.

According to this embodiment, since a plurality of processing results are output by performing heterodyne processing and spectrogram processing once, it is possible to effectively perform target extraction, target speed estimation, and Doppler influence correction with a simple arrangement.

Sixth Embodiment

An information processing apparatus according to the sixth embodiment of the present invention will be described next. The information processing apparatus according to this embodiment is different from those according to the second to fifth embodiments in that the information processing apparatus includes a wave transmitter. The remaining components and operations are the same as those in the second to fifth embodiments. Hence, the same reference numerals denote the same components and operations, and a detailed description thereof will be omitted.

<<Functional Arrangement of Information Processing Apparatus>>

FIG. 28is a block diagram showing the functional arrangement of an information processing apparatus2800according to this embodiment. Note that inFIG. 28, the same reference numerals as inFIG. 3denote the same functional components and a description thereof will be omitted.

Referring toFIG. 28, a transmission wave generator2850is included in the information processing apparatus2800. The functional arrangement of the transmission wave generator2850is the same as that shown inFIG. 4A, 13A, or25A.

Furthermore, the arrangement can be simplified by integrating the transmission wave generator2850and a dual-sweep signal generator320as a signal generation unit2810. All the components of an output unit301and calculator302can be included in the information processing apparatus2800.

According to this embodiment, since it is possible to correctly adjust a chirp wave to be transmitted and a dual-sweep signal to undergo heterodyne processing, it is possible to perform target extraction, target speed estimation, and Doppler influence correction with higher accuracy.

Other Embodiments

Note that the target extraction method using an acoustic wave or ultrasonic wave, which has been described above, can be used for a technique of making robots pass each other without crashing and a vehicle collision avoidance technique. However, the present invention is not limited to them, and can be used to, for example, monitor an intruder in an office or the like, detect the motion of a person in a gymnasium, and monitor an obstacle in the water. In many cases, an ultrasonic wave cannot be used for monitoring in the water such as a port since it attenuates easily. However, the present invention is applicable to the principles of a target object detection method, distance measurement method, and speed measurement method using an acoustic wave called active sonar. Therefore, by appropriately setting a carrier frequency (center frequency), waveform length, modulated wave frequency, and the like suitable for the water, it is possible to obtain the same effects as those of the present invention. Furthermore, a transmission waveform according to the present invention can also be used for radar using a radio wave.

The present invention is applicable to a system including a plurality of devices or a single apparatus. The present invention is also applicable even when an information processing program for implementing the functions of the embodiments is supplied to the system or apparatus directly or from a remote site. Hence, the present invention also incorporates the program installed in a computer to implement the functions of the present invention by the computer, a medium storing the program, and a WWW (World Wide Web) server that causes a user to download the program. Especially, the present invention incorporates at least a non-transitory computer readable medium storing a program that causes a computer to execute processing steps included in the above-described embodiments.

This application claims the benefit of Japanese Patent Application No. 2014-048144 filed on Mar. 11, 2014, which is hereby incorporated by reference herein in its entirety.