Patent Description:
Conventionally, an antenna for receiving satellite radio waves which suppresses the incidence of radio waves relating to multipath has been known. For example, <CIT> discloses an antenna for receiving a satellite radio wave which does not make a reflected transmission radio wave of a low elevation angle incident thereon.

However, the configuration of above-mentioned patent document cannot completely avoid reception of signals such as multipath. Also, it is not possible to determine whether a signal received by an antenna is a signal based on a direct wave from a satellite or a signal related to multipath or the like.

Accordingly, it is an object of the present invention to provide a GNSS receiver capable of easily determining whether a GNSS signal received by an antenna is based on a direct wave from a satellite or not. From <CIT>, a positioning apparatus is known that can grasp on the basis of a comparison whether a satellite radio wave is different from the original incident direction due to either the azimuth angle or the elevation angle. Specifically, a satellite radio wave whose result of comparison does not match is regarded as a reflected wave reflected from the object after being output from the satellite. <CIT> likewise teaches, inter alia, a multipath determination device in the form of a GPS reception unit including a plurality of antennas for receiving radio waves from a GPS satellite, and the GPS satellites received by the GPS reception unit. Acquisition means are included for acquiring the information, as to the phase difference between the received signals from the GPS satellites received by each of the plurality of antennas for all of the GPS satellites that have received the radio wave. Relative direction estimation means are included for estimating the relative arrival directions of radio waves from the GPS satellites based on the phase difference of the received signals from the GPS satellites, and the GPS acquired by the acquisition means for each GPS satellite. The absolute direction of arrival of radio waves from the GPS satellite is calculated based on the satellite information. Furthermore, <CIT> discloses an apparatus for receiving a signal transmitted from a transmission source by a reference receiver and a calibration target receiver, respectively, and processing the received signal based on carrier phase information of the received signal by the reception calculates a single difference between the receivers, which is a difference in the carrier phase information of the received signal obtained by observation of the reference receiver and the calibration target receiver, and the reception point of the reference receiver and the calibration target receiver and the transmission. Based on the position of the source, a single phase difference between the receivers in the carrier phase between the reference receiver and the calibration target receiver is obtained, and the single difference between the receivers and the observed single difference between the receivers are calculated. And a means for calibrating the error as well as obtaining the difference between the error and the carrier phase information by the observation of the calibration target receiver. The paper by <NPL>, reports on a comparison of power angular spectres at different frequencies in order to understand channel frequency dependence, including both line-of-sight and non-line-of-sight scenarios. <CIT> is concerned with the detection of falsified signals in a satellite navigation system.

The problem to be solved by the present invention is as described above, and it is solved by the subject-matter of the independent claims. Means for solving the problem and the effect thereof will be described with regards to embodiments hereinbelow.

According to a first aspect of the present invention, there is provided a GNSS receiver having the following configuration. That is, the GNSS receiver includes at least two antennas, a satellite direction acquisition module, an estimation module, and a determination module. The satellite direction acquisition module acquires the direction when the satellite corresponding to the GNSS signal received by the antenna is viewed from the antenna based on the satellite orbit information. The estimation module estimates the arrival direction of the GNSS signal on the basis of the difference in timing when the GNSS signal is received by the plurality of antennas. The determination module determines whether the GNSS signal received by the antenna is a direct GNSS signal based on a direct wave from the satellite or a non-line-of-sight (NLOS) GNSS signal by comparing the direction in which the satellite is viewed from the antenna with the arrival direction estimated by the estimation module.

In this configuration, it is possible to determine whether the received signal is a GNSS signal based on a direct wave from the satellite or a NLOS GNSS signal by a simple method of comparing the direction viewed from the antenna with the arrival direction of the estimated GNSS signal.

According to a second aspect of the present invention, there is provided a GNSS receiver having the following configuration. That is, the GNSS receiver includes at least two antennas, an estimation module, and a determination module. The estimation module obtains the angular spectrum of the intensity of the GNSS signal with respect to the estimation of the arrival direction of the GNSS signal on the basis of the difference in timing at which the GNSS signal is received by the plurality of antennas. The determination module determines, based on the angular spectrum obtained by the estimation module, whether the GNSS signal received by the antenna is a direct GNSS signal based on a direct wave from a satellite or an NLOS GNSS signal.

In this configuration, it is possible to determine whether the received signal is a GNSS signal based on a direct wave from the satellite or a NLOS GNSS signal by determining the angular spectrum with respect to the estimation of the arrival direction of the GNSS signal.

The GNSS receiver preferably has the following configuration. That is, the GNSS receiver is provided with a satellite direction acquisition module for acquiring a direction viewed from the antenna of a satellite corresponding to the GNSS signal received by the antenna based on satellite orbit information. The determination module determines whether the GNSS signal received by the antenna is the direct GNSS signal or the NLOS GNSS signal by using the value of the intensity of the GNSS signal corresponding to the direction viewed from the antenna of the satellite based on the angular spectrum.

In most cases, when an NLOS GNSS signal is received, the signal intensity does not increase in the direction of the satellite obtained based on the satellite orbit information. This property can be used to properly distinguish between direct GNSS signals and NLOS GNSS signals.

The GNSS receiver preferably has the following configuration. That is, the GNSS receiver is provided with a satellite direction acquisition module for acquiring a direction viewed from the antenna of a satellite corresponding to the GNSS signal received by the antenna based on satellite orbit information. The determination module determines whether the GNSS signal received by the antenna is the direct GNSS signal or the NLOS GNSS signal by comparing the direction in which the satellite is viewed from the antenna with the direction corresponding to the peak of the angular spectrum.

In most cases, the direction corresponding to the peak of the angular spectrum when receiving the NLOS GNSS signal is deviated from the direction of the satellite obtained based on the satellite orbit information. This property can be used to properly distinguish between direct GNSS signals and NLOS GNSS signals.

In the GNSS receiver, it is preferable that the determination module determines that the GNSS signal received by the antenna is the NLOS GNSS signal when the angular spectrum has a plurality of peaks.

Normally, the angular spectrum when a direct GNSS signal is received shows a distribution with a single peak in a certain direction. This property can be used to properly distinguish between direct GNSS signals and NLOS GNSS signals.

In the GNSS receiver, the determination module determines that the GNSS signal is the NLOS GNSS signal when the arrival directions of the GNSS signals estimated by the estimation module are similar to each other, although the plurality of GNSS signals received by the antenna indicate different source satellites. Note that the case of "The arrival directions of GNSS signals are similar to each other. " includes a case where the angles of the arrival directions are similar and a case where the angle spectra are similar to each other.

The direct GNSS signals typically arrive at different angles for each satellite. On the other hand, since one or a small number of transmission sources installed by a malicious person often transmit GNSS signals by impersonating a plurality of satellites, even if the respective GNSS signals indicate different satellites, their arrival angles tend to be similar to each other. This property can be used to properly distinguish between direct GNSS signals and NLOS GNSS signals (a spoofing signal or an impersonation signal).

Preferably, the GNSS receiver is configured to output the direction of arrival estimated by the estimation module with respect to the GNSS signal determined by the determination module to be the NLOS GNSS signal.

In this configuration, for example, useful information on the multipath situation, the position of the transmission source of the spoofing signal, and the like can be obtained.

In the GNSS receiver, the NLOS GNSS signal preferably includes a multipath signal.

In this configuration, multipath can be dealt with.

The GNSS receiver preferably includes a spoofing signal as the NLOS GNSS signal.

In this configuration, GNSS spoofing can be dealt with.

The GNSS receiver preferably has the following configuration. That is, the GNSS receiver is provided with a plurality of antenna arrays constituted of the plurality of antennas. When there is a GNSS signal determined to be the NLOS GNSS signal, the GNSS receiver estimates the position of the transmission source of the spoofing signal on the basis of the result estimated by the estimation module about the arrival direction of the GNSS signal viewed from each antenna array and the position of each antenna array.

In this configuration, it is possible to know where the transmission source of the spoofing signal is located.

In the GNSS receiving apparatus, the estimation module can be configured to estimate the arrival direction of the GNSS signal from the difference in the timing of the PRN code included in the GNSS signal received by the plurality of antennas.

In this configuration, the direction of arrival of the GNSS signal can be estimated by simple processing.

In the GNSS receiver, the estimation module can also estimate the arrival direction of the GNSS signal from the phase difference of the carrier wave of the GNSS signal received by the plurality of antennas.

In this configuration, the arrival direction of the GNSS signal can be precisely estimated.

In the GNSS receiver, it is preferable that the antennas are fixedly provided so that their positions do not fluctuate with respect to the ground.

In this configuration, since the positional relationship of the plurality of antennas does not change, the arrival direction of the GNSS signal can be stably estimated.

The GNSS receiver preferably includes at least three antennas.

In this configuration, the arrival direction of the GNSS signal can be well estimated.

The GNSS receiver preferably has the following configuration. That is, the GNSS receiver includes a plurality of reception modules. The plurality of antennas are connected to any one of the plurality of reception modules. A clock signal is supplied from a common clock source to a plurality of reception modules.

In this configuration, even if the reception modules are different, the timing at which each antenna receives the GNSS signal can be expressed by using the common clock. Therefore, the arrival direction of the GNSS signal can be estimated by accurately and easily determining the difference in the reception timing of the GNSS signal.

The GNSS receiving apparatus preferably includes an NLOS GNSS signal removal module for removing the NLOS GNSS signal from the received GNSS signal based on the determination result of the determination module.

In this configuration, the accurate operation of the apparatus can be realized by removing the NLOS GNSS signal that degrades the accuracy.

Preferably, the GNSS receiving apparatus includes a notification module for notifying the reception of the NLOS GNSS signal based on the determination result of the determination module.

In this configuration, it is possible to notify the user that the NLOS GNSS signal has been received and to call attention to the user.

According to a third aspect of the present invention, there is provided a GNSS receiver having the following configuration. That is, the GNSS receiver includes at least two antennas, an angular spectrum acquisition module, and a display data generation module. The angular spectrum acquisition module obtains the angular spectrum of the intensity of the GNSS signal on the basis of the difference in timing of receiving the GNSS signal by the plurality of antennas. The display data generation module generates data for displaying the angular spectrum.

In this configuration, the user can concretely grasp the radio wave reception state of the GNSS signal.

The GNSS receiver preferably has the following configuration. That is, the angular spectrum acquisition module obtains the angular spectrum of the intensity of the GNSS signal as a two-dimensional angular spectrum relating to the azimuth angle and the elevation angle. The display data generation module generates data for graphically displaying the angular spectrum in the celestial sphere.

In this configuration, the angular spectrum can be visually and easily understood and displayed.

In the GNSS receiver, the signal intensity in the angular spectrum to be displayed is preferably expressed by a color scale, a shade of a color or an equal intensity line.

In this configuration, it is possible to display the angular spectrum that is easy to see.

The GNSS receiver preferably has the following configuration. That is, the GNSS receiver is provided with a satellite direction acquisition module for acquiring the direction viewed from the antenna of the satellite corresponding to the GNSS signal received by the antenna based on the satellite orbit information. The display data generation module generates data for displaying the direction when the satellite is viewed from the antenna.

In this configuration, the user can understand the angular spectrum of the GNSS signal together with the direction of the satellite corresponding to the GNSS signal.

According to a fourth aspect of the present invention, the following GNSS receiving method is provided. That is, at least two antennas receive GNSS signals. A direction in which a satellite corresponding to the GNSS signal received by the antenna is viewed from the antenna is acquired based on satellite orbit information. The arrival direction of the GNSS signal is estimated on the basis of a difference in timing when the GNSS signal is received by a plurality of antennas. The direction in which the satellite is viewed from the antenna is compared with the estimated arrival direction of the GNSS signal to determine whether the GNSS signal received by the antenna is a direct GNSS signal based on a direct wave from the satellite or an NLOS GNSS signal.

According to a fifth aspect of the present invention, the following GNSS receiving method is provided. That is, at least two antennas receive GNSS signals. The angular spectrum of the intensity of the GNSS signal is obtained on the basis of the difference of the timing when the GNSS signal is received by the plurality of antennas. Based on the angular spectrum, it is determined whether the GNSS signal received by the antenna is a direct GNSS signal based on a direct wave from a satellite or an NLOS GNSS signal.

According to a sixth aspect of the present invention, the following GNSS receiving method is provided. That is, at least two antennas receive GNSS signals. The angular spectrum of the intensity of the GNSS signal is obtained on the basis of the difference of the timing when the GNSS signal is received by the plurality of antennas. Data for displaying the angular spectrum is generated.

<FIG> is a block diagram showing an electrical configuration of a GNSS receiver <NUM> according to an embodiment of the present invention. <FIG> shows an example of the arrangement of the antennas <NUM> of the GNSS receiver <NUM>.

The GNSS receiver <NUM> outputs a Pulse Per Second (1PPS) signal accurately synchronized with the GNSS time as a timing pulse based on the received GNSS signal, and can be used, for example, in a communication base station or a broadcasting station. The GNSS receiver <NUM> determines whether the received GNSS signal is a direct GNSS signal or a Non-line-of-sight (NLOS) GNSS signal, and performs positioning calculation by excluding the NLOS GNSS signal to output a timing pulse signal with high accuracy. As used herein, a direct GNSS signal means a GNSS signal directly receiving a radio wave transmitted from a GNSS satellite. An NLOS GNSS signal means a GNSS signal other than a direct GNSS signal. An example of the NLOS GNSS signal includes a GNSS signal (hereinafter referred to as a multi-path signal) received after a radio wave transmitted from a GNSS satellite strikes a wall surface of a building or the like and is reflected. The NLOS GNSS signal includes a GNSS signal (hereinafter referred to as a spoofing signal) which receives a radio wave transmitted from a transmission source other than the GNSS satellite by someone for the purpose of spoofing.

The GNSS receiver <NUM> includes an antenna array. The antenna array includes a plurality of antennas <NUM> capable of receiving GNSS signals. Although the configuration of each antenna <NUM> is arbitrary, a patch antenna, for example, is preferable in order to reduce the cost. In the antenna array, each antenna <NUM> is arranged at a prescribed interval and are physically arranged at different positions, therefore, the receiving timing at each antenna <NUM> is different except for a special case even when the same GNSS signal is received. In the present embodiment, the respective antennas <NUM> are fixed so as not to move with respect to the ground.

Although only two antennas <NUM> are shown in <FIG>, as shown in <FIG>, the antenna array may include six antennas <NUM> that are arranged so as to correspond to face center positions of <NUM> faces in a regular hexahedron. As shown in <FIG>, when a first satellite <NUM> existing in a region of a high elevation angle as viewed from the antenna array transmits a GNSS signal, the GNSS signal <NUM> is received by two antennas <NUM> on the upper and lower surfaces of a regular hexahedron, in the order of upper and lower with a time difference. The multipath GNSS signal <NUM> reflected from the GNSS signal after striking from a building or the like, will be described later.

When a second satellite <NUM> located in a region of a low elevation angle region as viewed from the antenna array transmits the GNSS signal, the GNSS signal <NUM> is received by the two antennas <NUM> in the order of upper and lower with a time difference. However, for the second satellite <NUM> having a low elevation angle, the difference in the timing at which the upper and lower two antennas <NUM> receive the GNSS signal <NUM> is smaller than that of the GNSS signal <NUM> of the first satellite <NUM> having a high elevation angle. In the above description, two antennas <NUM> having different heights are focused on, but when four antennas <NUM> having different positions in a horizontal plane are focused on, the precedent and the time difference of the timing at which each antenna <NUM> receives the GNSS signal are different depending on the arrival direction (Azimuth and elevation angles) of the GNSS signal viewed from the antenna array.

Referring back to <FIG>, the GNSS receiver <NUM> is configured to determine whether the received GNSS signal is a direct GNSS signal or an NLOS GNSS signal by using a time difference of reception timings of a plurality of antennas <NUM> arranged at different positions. Furthermore, the GNSS receiver <NUM> can generate a timing pulse signal based on the direct GNSS signal and output the timing pulse signal to the outside after excluding the NLOS GNSS signal.

The GNSS receiver <NUM> includes a satellite direction acquisition module <NUM>, a decision process module <NUM>, a filter module <NUM> (hereinafter also referred to as NLOS GNSS signal removal module <NUM>), a position calculation module <NUM>, and a timing pulse generation module <NUM>. The satellite direction acquisition module <NUM>, the decision process module <NUM>, the filter module <NUM> (hereinafter also referred to as NLOS GNSS signal removal module <NUM>), the position calculation module <NUM>, and the timing pulse generation module <NUM> may also be implemented as "processing circuitry" <NUM>.

The satellite direction acquisition module <NUM> performs signal processing on the received GNSS signal. The satellite direction acquisition module <NUM> includes a clock pulse generation module <NUM> and a reception module <NUM>.

The clock pulse generation module <NUM> outputs a clock signal having a predetermined frequency (clock frequency) to the reception module <NUM>. The clock pulse generation module <NUM> functions as a clock source for supplying a clock signal to the reception module <NUM>.

The clock pulse generation module <NUM> includes an oscillator <NUM> and a synthesizer <NUM>.

The oscillator <NUM> generates a signal of a predetermined frequency by oscillating an oscillator made of, for example, crystal. The oscillator <NUM> outputs the generated signal to the synthesizer <NUM>.

The synthesizer <NUM> generates a clock signal of a predetermined frequency (clock frequency) based on the signal output from the oscillator <NUM>. The synthesizer <NUM> outputs the generated clock signal to the reception module <NUM>.

The reception module <NUM> performs signal processing. In this embodiment, a reception module <NUM> is arranged corresponding to each antenna <NUM>. Each reception module <NUM> is connected to a corresponding antenna <NUM>. Accordingly, the GNSS signals received at each antenna <NUM> are processed individually by corresponding reception module <NUM>.

Each reception module <NUM> includes a signal input interface <NUM>, a Radio Frequency/Intermediate Frequency (IF) down-conversion module <NUM>, and a baseband processing module <NUM>.

The signal input interface <NUM> receives the GNSS signal received by the antenna <NUM>. The signal input interface <NUM>, for example, may be a connector. A signal line electrically connecting the antenna <NUM> and the reception module <NUM> is connected to the connector.

The RF/IF down-conversion module <NUM> converts the GNSS signal acquired by the signal input interface <NUM> into signal data that can be processed by the baseband processing module <NUM>, which will be described later.

The RF/IF down-conversion module <NUM> includes a Voltage controlled oscillator (VCO) and a mixer. The RF/IF down-conversion module <NUM> mixes the GNSS signal acquired by the signal input interface <NUM> and the output from the VCO to match the phase of the clock frequency with the mixer. Thus, the RF/IF down-conversion module <NUM> can convert the frequency of the GNSS signal to an intermediate frequency that is a frequency division ratio multiple of the clock frequency.

The RF/IF down-conversion module <NUM> may further include an amplifier and an Analog to Digital (A/D) converter. The amplifier amplifies the GNSS signal whose frequency is converted to the intermediate frequency. The A/D converter converts the amplified GNSS signal into digital data. The RF/IF down-conversion module <NUM> outputs data relating to the GNSS signal to the baseband processing module <NUM>.

The baseband processing module <NUM> is configured as a known computer and includes a Central Processing Unit (CPU), a Read only Memory (ROM), a correlator, and the like. The ROM stores a program for processing the GNSS signal, and the baseband processing module <NUM> operates based on the program.

The correlator of the baseband processing module <NUM> receives data relating to the GNSS signal output from the RF/IF down-conversion module <NUM> and a clock signal from the synthesizer <NUM>. The correlator obtains the correlation between a plurality of kinds of Pseudonoise (PRN) codes, and GNSS signals while shifting the timing of the PRN codes little by little. Thus, the baseband processing module <NUM> specifies the PRN code number on which the GNSS signal is modulated, and specifies the reception timing of the PRN code.

Although the GNSS system is constructed by many GNSS satellites, the PRN code is unique to each GNSS satellite. Thus, identifying the PRN code number is synonymous with identifying the GNSS satellite corresponding to the received GNSS signal.

By specifying the reception timing of the PRN code, the reception timing of the GNSS signal can be obtained. To specify the reception timing of the PRN code, the clock signal input from the clock pulse generation module <NUM> to the correlator is used as a reference.

The baseband processing module <NUM> performs arithmetic processing by the CPU to data inputted to the correlator. Thus, the GNSS signal modulated based on the PRN code can be demodulated.

The baseband processing module <NUM> calculates the position information of the satellite by using the navigation message included in the demodulated data. The position information of the satellites can be obtained by using a known calculation formula based on the orbit information (satellite orbit information) of each GNSS satellite included in the navigation message and the GNSS time. The GNSS time can be obtained by performing positioning calculation by a normal method.

The baseband processing module <NUM> calculates information of a direction (Specifically, azimuth angle and elevation angle) in which a GNSS satellite corresponding to the received GNSS signal is viewed from an antenna array on the basis of the position of the GNSS satellite corresponding to the GNSS signal and the position of the antenna <NUM> obtained by positioning calculation. More specifically, referring to the example shown in <FIG>, the baseband processing module <NUM> can calculate, for example, that the first satellite <NUM> is located in a direction having an azimuth angle of <NUM>° and an elevation angle of <NUM>°, when viewed from the antenna array.

Referring back to <FIG>, the baseband processing module <NUM> outputs data regarding the azimuth and elevation angles of the first and second satellites <NUM> and <NUM> as viewed from the antenna array and data acquired regarding the reception timing of the GNSS signal to the decision process module <NUM> and the determination module <NUM>. The baseband processing module <NUM> outputs the obtained GNSS signal to the filter module <NUM>.

The decision process module <NUM> determines whether the received GNSS signal is a direct GNSS signal or an NLOS GNSS signal based on data inputted from the reception module <NUM>. The decision process module <NUM> includes an estimation module <NUM> and a determination module <NUM>.

The estimation module <NUM> estimates the arrival direction of the received GNSS signal based on the reception timing of the PRN code acquired by the reception module <NUM> corresponding to the six antennas <NUM> and the positional relation of the six antennas <NUM>.

Referring back to <FIG>, six antennas <NUM> are arranged in three pairs so as to form a pair with each other across the center of a regular hexahedron. As described above, when the pair of two antennas <NUM> receive the same GNSS signal, a time difference in reception timing occurs, and the time difference is different depending on the arrival direction of the GNSS signal.

To briefly describe the method of estimating the arrival direction, it is assumed that the angle formed by the arrival direction of the GNSS signal with respect to the plane perpendicular to the virtual straight line connecting the pair of two antennas <NUM> is θ, the path difference of the GNSS signal can be expressed as dsin θ, where d is the interval between the two antennas <NUM>. Therefore, the difference Δt of the reception timing of the GNSS signal can be expressed by Δt = dsinθ/c, where c is the speed of light. This equation shows that the angle θ can be obtained from the difference Δt of the reception timing.

As shown in <FIG>, the three pairs of antennas <NUM> are arranged in different directions represented by the virtual straight line connecting the paired antennas <NUM>. In the example of <FIG>, the three pairs are shown to be orthogonal to each other. Therefore, the directions of arrival of the GNSS signals can be specified three-dimensionally by determining the angles θ of the remaining two pairs of antennas <NUM>.

An example of the arrival direction of the GNSS signal estimated by the estimation module <NUM> is explained with reference to <FIG> and <FIG>. In the example of <FIG>, the estimation module <NUM> estimates that the GNSS signal <NUM> arrived from a direction in which the azimuth angle is <NUM>°, and the elevation angle is <NUM>°. The GNSS signal <NUM> is estimated to have arrived from a direction having an azimuth angle of <NUM>° and an elevation angle of <NUM>°. The GNSS signal <NUM> is estimated to have arrived from a direction having an azimuth angle of <NUM>° and an elevation angle of <NUM>°. The estimation module <NUM> outputs data relating to the arrival direction of the estimated GNSS signal to the determination module <NUM>.

For each GNSS signal, the determination module <NUM> compares the azimuth angle and elevation angle indicating the arrival direction of the GNSS signal estimated by the estimation module <NUM> with the azimuth angle and elevation angle obtained from the navigation message by the baseband processing module <NUM> for the satellite corresponding to the GNSS signal, and determines whether or not they match.

Thus, the determination module <NUM> can determine whether the received GNSS signal is a direct GNSS signal based on a direct wave from the satellite or an NLOS GNSS signal.

Specifically, the determination module <NUM> compares the azimuth angle and elevation angle indicating the arrival direction of the GNSS signal acquired from the estimation module <NUM> with the azimuth angle and elevation angle based on the position of the satellite acquired from the navigation message. When both the difference in azimuth angle and the difference in elevation angle are within a predetermined range, the determination module <NUM> determines that the received GNSS signal is a direct GNSS signal. When at least one of the azimuth angle difference and the elevation angle difference is out of a predetermined range, the determination module <NUM> determines that the received GNSS signal is an NLOS GNSS signal.

As shown in <FIG>, when the GNSS signal <NUM> transmitted by the satellite <NUM> is directly received by the antenna array, the arrival direction of the GNSS signal <NUM> coincides with the azimuth angle and the elevation angle of the first satellite <NUM>. On the other hand, since the GNSS signal <NUM> based on the multipath changes its direction by reflection, the direction of arrival of the GNSS signal is in most cases substantially different from the azimuth angle and the elevation angle of the first satellite <NUM>. Therefore, by comparing the directions, the determination module <NUM> can determine that the GNSS signal <NUM> is a direct GNSS signal and the GNSS signal <NUM> is an NLOS GNSS signal.

Although spoofed GNSS signals are omitted in <FIG>, the location of the source transmitting the spoofed GNSS signals is usually different from the location of the satellite intended to spoofed. Therefore, the determination module <NUM> can determine that the GNSS signal received from such a transmitting device is an NLOS GNSS signal by comparing directions in exactly the same manner as described above. The decision process module <NUM> outputs the determination result of the determination module <NUM> to the filter module <NUM>.

The filter module <NUM> receives GNSS signals from the baseband processing module <NUM> of one reception module <NUM>, and also receives a determination result from the decision process module <NUM>. The filter module <NUM> selectively removesa signal determined as an NLOS GNSS signal by the determination module <NUM> from the GNSS signal input from the reception module <NUM>. The GNSS signal generated after the filter processing becomes only the direct GNSS signal. The filter module <NUM> outputs the GNSS signal after the filter processing to the position calculation module <NUM>.

The position calculation module <NUM> performs a known positioning calculation based on the GNSS signal input from the filter module <NUM>. As a result, GNSS time is obtained. The position calculation module <NUM> outputs the obtained GNSS time to a timing pulse generation module <NUM>.

The timing pulse generation module <NUM> generates a pulse signal of <NUM> time per second (<NUM> PPS signal) synchronized with the GNSS time based on the GNSS time inputted from the position calculation module <NUM>. The timing pulse signal generated by the timing pulse generation module <NUM> is output from the GNSS receiver <NUM> and input to an external device such as a reference frequency generator.

The GNSS receiver <NUM> determines whether a received GNSS signal is a direct GNSS signal or an NLOS GNSS signal, performs positioning calculation excluding an NLOS GNSS signal reducing positioning accuracy, and generates a timing pulse. Therefore, the effect of the multipath and the spoofing signal can be avoided, and the accurate timing pulse can be stably outputted.

The reception timing of the GNSS signal is specified in the plurality of reception modules <NUM>, and the plurality of reception modules <NUM> are supplied with a common clock signal from a single clock pulse generation module <NUM>. Therefore, since the plurality of reception modules <NUM> can represent the reception timing with a common reference, the estimation module <NUM> can accurately and easily obtain the time difference of the reception timing.

The GNSS receiving device <NUM> is not limited to the application for generating a timing pulse. For example, it can be suitably used not only for navigation using a positioning result outputted from the GNSS receiver <NUM> but also for various other purposes.

The number and arrangement of the antennas <NUM> constituting the antenna array can be variously changed. In the antenna array of <FIG>, the antenna <NUM> may be further disposed at a body center position of a regular hexahedron. Alternatively, instead of arranging the antennas <NUM> three-dimensionally at different heights, an appropriate number of antennas can be arranged side by side so as to form a polygon in a horizontal plane.

When considering a combination of arbitrarily selecting two antennas <NUM> from the antennas <NUM> constituting the antenna array, it is preferable that three or more virtual straight lines connecting the two antennas <NUM> can be defined so that their directions are different from each other. Thus, the arrival direction of the GNSS signal can be easily specified three-dimensionally. The antenna array described in <FIG> also satisfies this condition, but as the simplest antenna array satisfying this condition, a configuration in which three antennas <NUM> are arranged so as to form a triangle is conceivable.

The antenna array may be composed of two antennas <NUM>. In this case, the arrival direction of the GNSS signal cannot be estimated at a pin point, but the arrival direction should be a bus bar of a conical surface having the position of the antenna array as a vertex and a virtual straight line connecting the <NUM> antennas <NUM> as an axis. The angle formed by the bus of the conical surface with the imaginary straight line (axis) is equal to <NUM>° minus the angle θ described above. In this manner, the estimation module <NUM> may estimate the arrival direction of the GNSS signal so as to narrow it to a certain range. The determination module <NUM> can be configured to determine that the GNSS signal is an NLOS GNSS signal when the direction in which the GNSS satellite corresponding to the GNSS signal is viewed from the antenna array is deviated from the conical surface by a predetermined distance or more.

It is also possible to determine whether the GNSS signal is a direct GNSS signal or an NLOS GNSS signal based on the order of reception by the antennas <NUM> without evaluating the time difference of reception timing by the plurality of antennas <NUM>. For example, using the antenna array of <FIG>, if the southern antenna <NUM> receives the GNSS signal earlier than the northern antenna, the estimation module <NUM> estimates that the direction of arrival of the GNSS signal is generally south. When the direction in which the GNSS satellite corresponding to the GNSS signal is viewed from the antenna array is north contrary to the estimation result of the estimation module <NUM>, the determination module <NUM> determines that the GNSS signal is an NLOS GNSS signal.

Referring back to <FIG>, the GNSS receiver <NUM> estimates the arrival direction of the GNSS signal by using the reception time difference of the PRN code when the GNSS signal is received by the two antennas <NUM>. However, instead of the time difference of the PRN code, the carrier wave phase difference of the GNSS signal can be used to estimate the arrival direction of the GNSS signal. In this case, the direction of arrival of the GNSS signal can be precisely estimated. Since, the phase is an angular representation of time, the carrier phase difference is a kind of difference in the reception timing of the GNSS signal.

As described above, the GNSS receiver <NUM> includes at least two antennas <NUM>, the baseband processing module <NUM>, the estimation module <NUM>, and the determination module <NUM>. The baseband processing module <NUM> acquires the direction in which the satellite <NUM>, <NUM> corresponding to the GNSS signal received by the antenna <NUM> is viewed from the antenna <NUM> based on the satellite orbit information. The estimation module <NUM> estimates the arrival direction of the GNSS signal <NUM>, <NUM> and <NUM> on the basis of the difference Δt between the timings at which the GNSS signal is received by the plurality of antennas <NUM>. The determination module <NUM> compares the direction in which the satellite <NUM>,<NUM> is viewed from the antenna with the arrival direction estimated by the estimation module <NUM>, and determines whether the GNSS signal (<NUM>,<NUM>,<NUM>) received by the antenna <NUM> is a direct GNSS signal based on a direct wave from the satellite (<NUM>,<NUM>) or an NLOS GNSS signal.

Thus, it is possible to determine whether the received GNSS signal is a direct GNSS signal or an NLOS GNSS signal based on a simple method for comparing the estimated arrival direction of the GNSS signal <NUM>,<NUM>,<NUM> with the direction of the satellite <NUM>, <NUM> as viewed from the antenna <NUM>.

The estimation module <NUM> may be configured to determine the angular spectrum of the intensity of the GNSS signal based on the difference Δt between the reception timings of the GNSS signal at the plurality of antennas <NUM>. The angular spectrum can be calculated using known methods such as the minimum norm method, the linear prediction method, the Multiple Signal Classification (MUSIC) method, and the like. The angular spectrum may be obtained based on the difference in the timing of the PRN code included in the GNSS signal, or may be obtained from the phase difference of the carrier wave of the GNSS signal. However, it is preferable to use the phase difference of the carrier wave because a highly accurate angular spectrum can be obtained.

Normally, the closer a certain direction is to the arrival direction of the GNSS signal, the stronger the signal strength in that direction should be. Thus, determining the angular spectrum of the intensity of the GNSS signal is substantially the same as determining the distribution of correctness when a direction is assumed to be the arrival direction of the GNSS signal.

The angular spectrum may be a one-dimensional spectrum relating to either the azimuth angle or the elevation angle, but preferably a two-dimensional spectrum relating to both.

<FIG> show examples of the angular spectrum determined by the estimation module <NUM> of <FIG>. In <FIG>, a two-dimensional angular spectrum is arranged on the inner surface of a virtual sphere (celestial sphere) centered on the antenna array, and the celestial sphere is looked up from the point of the antenna array. The angle from the center of the circle corresponds to the azimuth angle in the direction of arrival of the GNSS signal. The outermost circle corresponds to an elevation angle of <NUM>° in the arrival direction, and the center of the circle corresponds to an elevation angle of <NUM>° in the arrival direction. For convenience of illustration, in the angular spectrum of <FIG>, the signal intensity is represented by the spacing of the hatches. The narrow hatched areas indicate high signal strength, wide hatched areas indicate low signal strength, and unhatched areas indicate substantially zero signal strength.

By determining the angular spectrum as described above, the determination module <NUM> can determine the direct GNSS signal and the NLOS GNSS signal, for example, as follows. A plurality of the following four determination methods may be combined. Further, the determination method may be switched according to the accuracy required in the positioning operation or the like.

First, the signal intensity corresponding to the direction of the satellite calculated by the baseband processing module <NUM> is obtained by using the angular spectrum, and if the signal intensity is not less than a predetermined intensity, the determination module <NUM> determines that the signal is a direct GNSS signal, and otherwise determines that the signal is an NLOS GNSS signal.

In <FIG>, the direction of the satellite calculated by the baseband processing module <NUM> is indicated by an X. In the case of <FIG>, the signal intensity at the position corresponding to the mark X is large, and in the case of <FIG>, the signal intensity at the position corresponding to the mark X is zero. Therefore, the determination module <NUM> determines that the GNSS signal of <FIG> is a direct GNSS signal, and determines that the GNSS signal of <FIG> is an NLOS GNSS signal.

Second, the direction corresponding to the peak of the signal intensity in the angular spectrum is determined, and this direction is compared with the direction of the satellite calculated by the baseband processing module <NUM>, and if the difference in direction is within a predetermined range, the determination module <NUM> determines that the signal is a direct GNSS signal, and if not, it determines that the signal is an NLOS GNSS signal.

In the case of <FIG>, the direction in which the signal intensity is the largest in the angular spectrum is slightly different from the direction of the satellite (cross) calculated by the baseband processing module <NUM>. Therefore, the determination module <NUM> determines that the GNSS signal shown in <FIG> is an NLOS GNSS signal.

Third, when there are a plurality of peaks of signal intensity in the angular spectrum, the possibility that there are a plurality of transmission sources and the possibility of multipath is suspected, so that the determination module <NUM> determines that the signal is an NLOS GNSS signal.

In <FIG>, peaks appear in both the south and north directions in the angular spectrum. Therefore, the determination module <NUM> determines that the GNSS signal shown in <FIG> is an NLOS GNSS signal.

Fourth, the angle spectra of the GNSS signals representing a plurality of satellites (In other words, the GNSS signals that are spread coded with different PRN codes) are compared, and if they are similar to each other, the determination module <NUM> determines that they are NLOS GNSS signals. That is, when a malicious person transmits a spoofing signal in order to mislead the current position of the mobile body to a specific position, it is necessary to transmit the GNSS signal to the mobile body by spoofing a plurality of different satellites. On the other hand, since most of the facilities for transmitting the spoofing signal are one or a few, the spoofing signal is transmitted from a small number of places. Therefore, even if the spoofing signal is a GNSS signal indicating a plurality of different satellites, the angular spectra thereof tend to be similar to each other. Thus, it is possible to appropriately determine whether or not the received GNSS signal is an NLOS GNSS signal (In particular, whether it is a spoofing signal or not).

One countermeasure for spoofing signals is the need to locate the source of such signals. In this regard, for example, if a plurality of antenna arrays having the configuration shown in <FIG> are provided, the antenna arrays are arranged at a distance from each other, and the arrival direction of the spoofing signals received in the respective antenna arrays is estimated, the position of the transmission source can be known by a known geometric calculation.

<FIG> shows a conceptual diagram for obtaining the position of a GNSS spoofer <NUM>, in accordance with an embodiment of the present disclosure. The GNSS spoofer <NUM> is hereinafter referred to as a spoofing attacker or a malicious transmitter <NUM>, which is the transmission source of the spoofing signal, by using a plurality of antenna arrays. The estimation of the arrival direction of the spoofing signal can be realized, for example, by obtaining a direction corresponding to the peak of the angular spectrum calculated in each antenna array.

In <FIG>, it can be estimated that the GNSS spoofer <NUM> exists at a point where a straight line extending in the opposite direction of the arrival direction of the spoofing signal intersects. Although a plurality of antenna arrays may be provided, the number of antenna arrays is preferably large in order to obtain the position of the transmission source with high accuracy.

Referring back to <FIG>, in the GNSS receiver <NUM>, the estimation module <NUM> can be configured to obtain the angular spectrum of the intensity of the GNSS signal with respect to the estimation of the arrival direction of the GNSS signal, based on the difference in the timing at which the GNSS signal is received by the plurality of antennas <NUM>. The determination module <NUM> determines whether the GNSS signal received by the antenna <NUM> is a direct GNSS signal or an NLOS GNSS signal on the basis of the angular spectrum determined by the estimation module <NUM>.

Thus, by determining the distribution of the certainty of the estimation of the arrival direction of the GNSS signal as the angular spectrum, it is possible to determine whether the received GNSS signal is a GNSS signal based on a direct wave from the satellite or not.

The angular spectrum is not limited to the use of estimating the direction of arrival of the GNSS received signal, but may be calculated for the purpose of simply displaying the signal for monitoring, for example.

<FIG> illustrates the GNSS receiver 1x, in accordance with another embodiment of the present disclosure. In the GNSS receiver 1x, a decision process module <NUM>, the filter module <NUM>, the position calculation module <NUM>, and the timing pulse generation module <NUM> are omitted.

The GNSS receiver 1x includes an angular spectrum acquisition module <NUM> and a display data generation module <NUM>. The satellite direction acquisition module <NUM>, the angular spectrum acquisition module <NUM> and the display data generation module <NUM> may also be implemented as "processing circuitry" <NUM>.

The angular spectrum acquisition module <NUM> calculates and acquires the angular spectrum of the intensity of the GNSS signal for each satellite number (In other words, for each PRN code number) based on the phase difference of the carrier wave of the GNSS signal of each satellite obtained from the baseband processing module <NUM>. Since, the operation of the angular spectrum acquisition module <NUM> is exactly the same as that of the estimation module <NUM> of <FIG> for calculating the angular spectrum, a detailed description thereof is omitted.

The display data generation module <NUM> generates display data for displaying the angular spectrum obtained by the angular spectrum acquisition module <NUM> on a display device <NUM> connected to the GNSS receiver 1x. The display device <NUM> is configured as a liquid crystal display, for example, and can display various information.

It is conceivable that, for example, contents equivalent to those shown in <FIG> are displayed on the display device <NUM>. Thus, by graphically displaying the angular spectrum arranged on the celestial sphere with the antenna array as the center on the display device <NUM>, the user can intuitively understand the reception state of the GNSS signal.

The display data generated by the display data generation module <NUM> preferably includes, in addition to the angular spectrum, display data for displaying the satellite direction calculated by the baseband processing module <NUM> as a sky plot, as indicated by an X in <FIG>. Thus, the user can understand the angular spectrum together with the direction of the satellite corresponding to the GNSS signal.

As shown in <FIG>, the display device <NUM> can display an angular spectrum focused on <NUM> satellite number corresponding to one PRN code. However, the display device <NUM> can display a list of a large number of angle spectra for each satellite number.

The expression of the angular spectrum is not limited to the expression in the circular region using the celestial sphere as shown in <FIG>, but can be expressed, for example, in a rectangular region with the horizontal axis as the azimuth angle and the vertical axis as the elevation angle. The distribution of the signal intensity in the angular spectrum displayed on the display device <NUM> may be expressed by a color scale such as thermography, may be expressed by a shade of a color, or may be expressed by an equal intensity line.

Although the preferred embodiments and modifications of the present invention have been described above, the above-described configuration can be changed, for example, as follows.

The antenna <NUM> constituting the antenna array need not be fixed to the ground. For example, the antenna array may be provided on a mobile body such as an automobile and a ship.

The satellite orbit information may not be acquired from the GNSS signal transmitted from the satellite. For example, the GNSS receivers <NUM> and 1x may be configured to be connected to the Internet, and the reception module <NUM> may acquire satellite orbit information from GNSS assist data distributed through the Internet.

When the baseband processing module <NUM> obtains an azimuth angle and an elevation angle when the satellite is viewed from the antenna array, information on the position of the antenna array including the location of the antennas <NUM>, is required as a premise. When the antenna array is fixed to the ground, the position of the antenna array can be determined in advance. Therefore, the baseband processing module <NUM> can use a position set by the user in advance without determining the position of the antenna array by positioning calculation.

The reception module <NUM> capable of connecting two or more antennas <NUM> per piece may be used. In this case, the GNSS receiver <NUM> may include, for example, six antennas <NUM> and three reception modules <NUM>, and it is preferable that clock signals are supplied to the three reception modules <NUM> from the ecommon clock pulse generation module <NUM>. All the antennas <NUM> constituting the array antenna may be connected to one reception module <NUM>.

The GNSS receiver <NUM> may be provided with a notification module that notifies reception of an NLOS GNSS signal instead of or in addition to the filter module <NUM>. In this case, it is possible to notify the user that the NLOS GNSS signal has been received and to call attention to the user. The configuration of the notification module is not particularly limited. The notification module can be, for example, a buzzer for notifying by utilizing sound. The notification module can be a display device for displaying a warning.

As shown in <FIG>, the arrival directions of GNSS signals representing a plurality of different satellites are estimated by pinpoints, and when the difference in the angle of the estimated arrival directions is not more than a predetermined value. In other words, when the directions of arrival are similar to each other, the determination module <NUM> determines that the GNSS signals are NLOS GNSS signals (spoofing signal).

With respect to the GNSS signal determined by the determination module <NUM> to be an NLOS GNSS signal, the GNSS receiver <NUM> may output the arrival direction of the GNSS signal estimated by the estimation module <NUM> to an appropriate display device. In this case, it is possible to obtain useful information such as how multipath occurs and from which direction the spoofing signal is transmitted.

The GNSS receiver <NUM> of <FIG> may include the display data generation module <NUM> of <FIG>, and may have a function of displaying the angular spectrum on the display device <NUM>.

The GNSS receivers <NUM> and 1x may be integrally provided with the display device <NUM>.

Claim 1:
A Global Navigation Satellite System, GNSS, receiver (<NUM>, 1x) comprising:
at least two antennas (<NUM>);
a satellite direction acquisition module (<NUM>) configured to acquire, based on satellite orbit information, a direction viewed from the at least two antennas (<NUM>), of a satellite (<NUM>, <NUM>) corresponding to a GNSS signal (<NUM>, <NUM>, <NUM>) received by the at least two antennas (<NUM>);
an estimation module (<NUM>) configured to estimate an arrival direction of the GNSS signal (<NUM>, <NUM>, <NUM>) on the basis of a difference in timings at which the GNSS signal (<NUM>, <NUM>, <NUM>) is received by the at least two antennas (<NUM>); and
a determination module (<NUM>) configured to determine whether the GNSS signal (<NUM>, <NUM>, <NUM>) received by the at least two antennas (<NUM>) is a direct GNSS signal based on a direct wave from the satellite (<NUM>, <NUM>) or a non-line-of-sight, NLOS, GNSS signal by comparing the direction in which the satellite (<NUM>, <NUM>) is viewed from the at least two antennas (<NUM>) with the arrival direction estimated by the estimation module (<NUM>), characterized in that:
the determination module (<NUM>) determines that the GNSS signal is the NLOS GNSS signal when the arrival directions of a plurality of GNSS signals (<NUM>, <NUM>, <NUM>) estimated by the estimation module (<NUM>) are similar to each other although the plurality of GNSS signals received by the at least two antennas (<NUM>) indicate different source satellites (<NUM>, <NUM>), wherein the arrival directions are similar when the angles of the arrival directions are similar.