JP2020034276A - Arrival direction estimation device - Google Patents

Abstract

To provide a technique capable of improving the estimation accuracy of the direction of arrival while suppressing the memory consumption.SOLUTION: An arrival direction estimation device includes: a plurality of antenna elements; an RF unit that converts a received signal received by each of the plurality of antenna elements into a baseband signal and measures the signal strength of each of the received signals; a threshold output unit that outputs a threshold corresponding to the signal strength; a packet detector for detecting a packet from the baseband signal; a selection unit that selects, after the packet is detected, a timing at which the maximum value of a baseband signal amplitude among antennas exceeds the threshold; a buffer unit that combines the baseband signal at the timing for each antenna element and outputs a combined signal; a phase change unit that changes the phase of the signal after the combination to obtain a signal after the phase change; and an arrival direction estimation unit that estimates an arrival direction of the received signal on the basis of the signal after the phase change.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an arrival direction estimation device.

  In recent years, a technique for estimating the arrival direction of various signals has been known. For example, a technique has been disclosed in which a baseband signal based on a received signal is down-sampled (a part of the signal is thinned out) to reduce the data amount of the baseband signal used for estimating the direction of arrival (for example, see Patent Reference 1).

  In addition, a receiving circuit in DSRC is disclosed (for example, see Patent Document 2). In a receiving circuit that receives an ASK-modulated radio wave, a technique is described in which RSSI is monitored and data is taken in when the RSSI is equal to or larger than a threshold (for example, see Patent Document 3). When storing sampling data, if the data change is small or equal to or less than a predetermined value, a technique is described in which writing of data to the memory is stopped to reduce the memory used (for example, see Patent Document 4). .

JP 2000-241521 A JP 2001-274784 A JP 2008-92136 A JP-A-6-111030

  However, when estimating the direction of arrival using the technique of down-sampling the baseband signal, the amount of memory consumption is reduced, and signals in non-transmission sections are also output to the direction of arrival estimator. Accuracy may be degraded. Even when the baseband signal is output to the arrival direction estimating unit as it is, the estimation accuracy of the arrival direction may be similarly deteriorated. Furthermore, when outputting the baseband signal to the arrival direction estimating unit as it is, it is also difficult to suppress the memory consumption.

  Therefore, it is desired to provide a technique capable of improving the estimation accuracy of the arrival direction while suppressing the memory consumption.

  In order to solve the above problem, according to an aspect of the present invention, a plurality of antenna elements and, while converting a received signal received by each of the plurality of antenna elements into a baseband signal, the signal of each of the received signals An RF unit for measuring the intensity, a threshold output unit for outputting a threshold value according to the signal intensity, a packet detection unit for detecting a packet from the baseband signal, and, after the packet is detected, the baseband signal A selection unit that selects a timing at which the maximum value between the antennas of the amplitudes exceeds the threshold value; a buffer unit that combines the baseband signal at the timing for each antenna element and outputs a combined signal; A phase change unit that obtains a signal after the phase change by changing the phase of the received signal, based on the signal after the phase change, Comprising an arrival direction estimation unit that estimates the arrival direction of the direction of arrival estimation apparatus is provided.

  According to another aspect of the present invention, a plurality of antenna elements, an RF unit that converts a received signal received by each of the plurality of antenna elements into a baseband signal, and detects a packet from the baseband signal A packet detection unit, a selection unit that selects a timing at which the maximum value between the antennas of the amplitude of the baseband signal takes a maximum value at predetermined intervals after the packet is detected, and the baseband signal at the timing Are coupled to each antenna element to output a signal after coupling, a phase change unit that changes the phase of the signal after coupling to obtain a signal after phase change, and a signal after the phase change. An arrival direction estimating unit that estimates an arrival direction of the received signal based on the arrival direction.

  The length of the predetermined cycle may be equal to or longer than the length of a transmission section for one bit by ASK.

  The selection unit may select a timing at which, after the packet is detected, the baseband signal takes the upper n-th amplitude (n is an integer of 2 or more).

  According to another aspect of the present invention, a plurality of antenna elements, an RF unit that converts a received signal received by each of the plurality of antenna elements into a baseband signal, and detects a packet from the baseband signal A packet detection unit, after the packet is detected, a selection unit that selects a timing at which the maximum value between the antennas of the amplitude of the baseband signal exceeds a threshold, and the baseband signal at the timing is set for each of the antenna elements. A buffer unit that combines and outputs a signal after the combination, a phase change unit that changes the phase of the signal after the combination to obtain a signal after the phase change, and the reception signal based on the signal after the phase change. And an arrival direction estimating unit for estimating the arrival direction of the vehicle.

  As described above, according to the present invention, there is provided a technique capable of improving the estimation accuracy of the direction of arrival while suppressing the memory consumption.

It is a figure showing the example of composition of the arrival direction estimating device concerning a 1st embodiment of the present invention. FIG. 4 is a diagram illustrating an example of a temporal change in the amplitude of a baseband signal. FIG. 7 is a diagram illustrating an example of a temporal change in amplitude of a signal after coupling. FIG. 9 is a diagram for describing a specific method of changing a phase. FIG. 9 is a diagram for describing a specific method of changing a phase. It is a figure showing the example of composition of the arrival direction estimating device concerning a 2nd embodiment of the present invention. FIG. 4 is a diagram illustrating an example of a temporal change in the amplitude of a baseband signal. FIG. 7 is a diagram illustrating an example of a temporal change in amplitude of a signal after coupling. FIG. 9 is a diagram for describing a specific method of changing a phase.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

  Further, in this specification and the drawings, a plurality of components having substantially the same function and configuration may be distinguished from each other by the same reference numerals followed by different numbers. However, when it is not necessary to particularly distinguish each of a plurality of components having substantially the same functional configuration, only the same reference numerals are given. Further, similar components in different embodiments may be distinguished by adding different alphabets after the same reference numerals. However, when it is not necessary to particularly distinguish each of similar constituent elements and the like in different embodiments, only the same reference numerals are given.

<0. Overview>
In recent years, a technique for estimating the arrival direction of various signals has been known. For example, there is disclosed a technique of downsampling a baseband signal based on a received signal (decimating a part of the signal) to reduce the amount of data of the baseband signal used for estimating the direction of arrival.

  However, when estimating the direction of arrival using the technique of down-sampling the baseband signal, the amount of memory consumption is reduced, and signals in non-transmission sections are also output to the direction of arrival estimator. Accuracy may be degraded. Even when the baseband signal is output to the arrival direction estimating unit as it is, the estimation accuracy of the arrival direction may be similarly deteriorated. Furthermore, when outputting the baseband signal to the arrival direction estimating unit as it is, it is also difficult to suppress the memory consumption.

  For example, a signal (radio wave) is transmitted from an ETC (Electronic Toll Collection System) vehicle-mounted device by ASK (Amplitude-Shift Keying). When a signal is transmitted by ASK, most of the packet may be a non-transmission section. Therefore, when the direction of arrival is estimated based on the signal from the on-board ETC device, it is assumed that the estimation accuracy of the direction of arrival is likely to deteriorate because many signals in the non-transmission section are output to the direction-of-arrival estimation unit. Is done.

  In view of this, the embodiment of the present invention mainly proposes a technique capable of improving the estimation accuracy of the arrival direction while suppressing the memory consumption.

  The outline of the embodiment of the present invention has been described above.

<1. First Embodiment>
First, a first embodiment of the present invention will be described.

[1-1. Configuration of Arrival Direction Estimation Device]
A configuration example of the direction-of-arrival estimation device according to the first embodiment of the present invention will be described.

  FIG. 1 is a diagram illustrating a configuration example of an arrival direction estimation device according to the first embodiment of the present invention. As shown in FIG. 1, the direction-of-arrival estimation apparatus 1A according to the first embodiment of the present invention includes an array antenna (antenna elements 10-1 to 10-3) and an RF (Radio Frequency) section 20-1. 20-3, the packet detection unit 30, the threshold value output unit 40, the selection unit 50A, the buffer units 60-1 to 60-3, the phase change units 70-1 to 70-3, and the arrival direction estimation unit 80 And

  RF units 20-1 to 20-3, packet detection unit 30, threshold output unit 40, selection unit 50A, buffer units 60-1 to 60-3, phase change units 70-1 to 70-3, and arrival direction estimation unit 80 Can be realized by a memory and a dedicated circuit. Alternatively, the dedicated circuit may be replaced with an arithmetic processing device that executes a program.

  The antenna element 10 receives a radio wave. Although the transmission source of the radio wave is not limited, it is assumed here that the radio wave is transmitted by the ASK from the vehicle equipped with the on-board ETC device. Hereinafter, a case where there are three antenna elements 10 (antenna elements 10-1 to 10-3) will be mainly described, but the number of antenna elements 10 is not limited as long as it is plural. The antenna element 10 outputs a signal (received signal) obtained by receiving a radio wave to the corresponding RF unit 20. That is, the antenna element 10-1 outputs a reception signal to the corresponding RF unit 20-1, the antenna element 10-2 outputs a reception signal to the corresponding RF unit 20-2, and the antenna element 10-3 outputs , And outputs the received signal to the corresponding RF unit 20-3. The antenna elements 10-1 to 10-3 constitute an array antenna, and are arranged linearly at intervals of, for example, half a wavelength of a radio wave or less.

  The RF unit 20 converts a received signal input from the corresponding antenna element 10 into a baseband signal, and measures a received signal strength (RSSI: Received Signal Strength Indicator / Indication) of the received signal. The number of the RF units 20 may be the same as the number of the antenna elements 10 (here, the RF units 20-1 to 20-3 may be present). The RF units 20-1 to 20-3 output the baseband signal to the packet detection unit 30 and the selection unit 50A, and output the RSSI to the threshold output unit 40.

  The packet detection unit 30 attempts to detect a packet with respect to the baseband signal input from each of the RF units 20-1 to 20-3. Packets may be detected in any manner. As an example, when a packet header is added to the head of the packet, the packet may be detected by detecting the packet header. When detecting a packet from at least one of the baseband signals input from each of the RF units 20-1 to 20-3, the packet detection unit 30 notifies the selection unit 50A that the packet has been detected. Note that the packet detection unit 30 may attempt to detect a packet only from the baseband signal input from any one of the RF units 20-1 to 20-3.

  The threshold output unit 40 outputs a threshold corresponding to the RSSI input from each of the RF units 20-1 to 20-3. Specifically, the threshold output unit 40 has an RSSI-threshold table 45 in which the RSSI is associated with the threshold in advance. The threshold output unit 40 selects an RF unit having the maximum RSSI based on the RSSIs input from the RF units 20-1 to 20-3 (selects an antenna element), and associates the RF unit with the selected RF unit. The threshold value is obtained from the RSSI-threshold table 45. The threshold output unit 40 outputs the obtained threshold to the selection unit 50A. Here, it is assumed that a threshold value corresponding to each of RF units 20-1 to 20-3 is provided by threshold value output unit 40 (a threshold value is provided for each antenna element 10). A common threshold value may be provided for the RF units 20-1 to 20-3.

  The selection unit 50A sets the maximum value (between antennas) of the amplitudes of the baseband signals input from the RF units 20-1 to 20-3 after the input of the detection of the packet from the packet detection unit 30. The selected value is compared with the maximum value of the amplitude of the baseband signal and the threshold value input from the threshold value output unit 40. Then, the selector 50A selects a timing at which the maximum value of the amplitude of the baseband signal exceeds the threshold.

  FIG. 2 is a diagram illustrating an example of a temporal change in the amplitude Sa of the baseband signal. Referring to FIG. 2, a graph is shown in which the horizontal axis is time t and the vertical axis is the amplitude Sa (t) of the baseband signal corresponding to time t. T1 is a transmission section of the bit “1” after the detection of the packet is input. T2 is a transmission section of bit “0”. T3 is a transmission section of bit “1”. The transmission section after T3 is omitted due to space limitations. Sam indicates the average value of the amplitude Sa (t) of the baseband signal. The threshold value is set at an intermediate value between the amplitude of the transmission section of bit “0” and the amplitude of the transmission section of bit “1”.

The selection unit 50A notifies the buffer unit 60 of the timing at which the maximum value of the amplitude of the baseband signal exceeds the threshold. That is, the selection unit 50 </ b> A sets the timing at which the maximum value (between antennas) of the baseband signals input from the RF units 20-1 to 20-3 exceeds the threshold output from the threshold output unit 40. The buffer units 60-1 to 60-3 are notified.

  The buffer unit 60 combines the baseband signals at the timing notified from the selection unit 50A for each antenna element 10, and outputs the combined signals. For example, the number of the buffer units 60 may be the same as the number of the antenna elements 10. More specifically, buffer section 60-1 combines the baseband signal corresponding to antenna element 10-1 at the timing notified from selection section 50A, and outputs the combined signal to phase changing section 70-1. . The buffer unit 60-2 combines the baseband signal corresponding to the antenna element 10-2 at the timing notified from the selection unit 50A, and outputs the combined signal to the phase change unit 70-2. Further, buffer section 60-3 combines the baseband signal corresponding to antenna element 10-3 at the timing notified from selection section 50A, and outputs the combined signal to phase changing section 70-3.

  FIG. 3 is a diagram illustrating an example of a temporal change in the amplitude Sb of the signal after the combination. Referring to FIG. 3, there is shown a graph in which the horizontal axis is time t and the vertical axis is the amplitude Sb (t) of the combined signal corresponding to time t. Referring to FIG. 3, the baseband signal in section T2 corresponding to the non-transmission section is removed as a baseband signal whose amplitude is equal to or smaller than the threshold, and the baseband signals in sections T1 and T3 whose amplitude is larger than the threshold are combined. ing. By removing the signal in the non-transmission section, the amount of memory consumption is reduced, and the signal in the non-transmission section does not need to be output to the arrival direction estimation unit 80.

  Sbm indicates the average value of the amplitude Sb (t) of the combined signal. Here, the arrival direction may be estimated by directly using the combined signal. However, after the non-transmission section is removed, the difference between the average value Sbm and the amplitude Sb (t) becomes small, so that the covariance matrix calculated based on the combined signal becomes small. Here, the covariance matrix can be used for estimating the direction of arrival. For example, in a MUSIC (Multiple Signal Classification) method, an arrival direction is estimated based on an evaluation function defined based on a covariance matrix. For example, details of processing by the MUSIC method are described in JP-A-2014-137241.

  Note that the covariance matrix can be calculated as follows. That is, assuming that k (= 1 to N) is the number of times of sampling and ΔT is a sampling interval, the sampling time is represented as kΔT, and the signal after coupling corresponding to each of the antenna elements 10-1 to 10-m at the sampling time kΔT. Is defined as X1 (k) to Xm (k), the covariance matrix R of the combined signal can be calculated as in the following equations (1) and (2). Here, T indicates transpose, and H indicates complex conjugate transpose.

  As described above, by eliminating the signal in the non-transmission section, the amount of memory consumption is reduced, and the signal in the non-transmission section does not need to be output to the arrival direction estimation unit 80. However, when the covariance matrix is reduced as described above, the direction of arrival of the signal received by the antenna element 10 cannot be estimated with high accuracy by the direction-of-arrival estimating unit 80. Therefore, the phase changing section 70 changes the phase of the signal after coupling for each antenna element 10 to obtain a signal after the phase change. Then, phase change section 70 outputs the signal after the phase change for each antenna element 10 to arrival direction estimation section 80.

  More specifically, phase changing section 70-1 obtains a signal after the phase change by changing the phase of the signal after coupling corresponding to antenna element 10-1 input from buffer section 60-1. The phase change may be performed at each sampling interval ΔT (that is, at the sampling time kΔT). An example of a specific method of changing the phase will be described later with reference to FIGS. Phase changing section 70-1 outputs the signal after the phase change to arrival direction estimating section 80 as the signal after the phase change corresponding to antenna element 10-1.

  Similarly, the phase changing unit 70-2 changes the phase of the signal after coupling corresponding to the antenna element 10-2 input from the buffer unit 60-2 to obtain a signal after the phase change. Phase changing section 70-2 outputs the signal after the phase change to arrival direction estimating section 80 as a signal after the phase change corresponding to antenna element 10-2. Further, the phase changing unit 70-3 changes the phase of the signal after coupling corresponding to the antenna element 10-3 input from the buffer unit 60-3 to obtain a signal after the phase change. Phase changing section 70-3 outputs the signal after the phase change to arrival direction estimating section 80 as a signal after the phase change corresponding to antenna element 10-3.

  An example of a specific method of changing the phase will be described with reference to FIGS. 4 and 5 are diagrams for explaining a specific method of changing the phase. As shown in FIG. 4, a position corresponding to the amplitude Sb (t) of the combined signal is a point (A, 0) on a complex plane having a real part as a horizontal axis and an imaginary part as a vertical axis. is there. Here, it is assumed that the phase is changed by ωt from the position corresponding to the amplitude Sb (t) of the combined signal. In such a case, the amplitude Sb (t) is moved to a position represented by the following equation (3) after the phase change.

  Here, it is assumed that the amplitude Sc (t) of the signal after the phase change is represented by the imaginary part of Expression (3). Therefore, the amplitude Sc (t) of the signal after the phase change is expressed by the following equation (4). The amplitude Sc (t) of the signal after the phase change represented by the equation (4) is also shown in FIG. Referring to Equation (4) or FIG. 4, the phase ωt is calculated from a position corresponding to the amplitude Sb (t) of the combined signal on the complex plane by 0, π / 2, π, 3π / 2, 2π,. (Ie, when changed by π / 2), the amplitude Sc (t) of the signal after the phase change changes to 0, A, 0, −A, 0,. It is understood.

  However, the amplitude Sc (t) of the signal after the phase change may be represented by the real part of Expression (3). At this time, the amplitude Sc (t) of the signal after the phase change is expressed by the following equation (5). Referring to equation (5), the phase ωt changes from 0, π / 2, π, 3π / 2, 2π,... From a position corresponding to the amplitude Sb (t) of the combined signal on the complex plane. , The amplitude Sc (t) of the signal after the phase change may change to A, 0, −A, 0, A,... Be grasped.

  FIG. 5 shows a graph in which the horizontal axis represents time t and the vertical axis represents the amplitude Sc (t) of the signal after the phase change corresponding to time t. In the example shown in FIG. 5, it is assumed that the phase changes by π / 2 in accordance with the equation (4), so that the amplitude Sc (t) of the signal after the phase change is 0, A, 0, −A. , 0,... The average value of the amplitude Sc (t) of the signal after the phase change is considered to approach zero. That is, after the phase change, the difference between the average value of the amplitude Sc (t) and the amplitude Sc (t) becomes large, and it is considered that the covariance matrix calculated based on the signal after the phase change becomes large.

  The arrival direction estimating unit 80 estimates the arrival direction of the signal received by the antenna element 10 based on the signal after the phase change. Specifically, the direction-of-arrival estimating unit 80 includes a phase-changed signal input from the phase change unit 70-1, a phase-changed signal input from the phase change unit 70-2, and a phase change unit 70- 3, the arrival direction of the signal received by the antenna elements 10-1 to 10-3 is estimated based on the phase-changed signal input from the third element.

  At this time, if the covariance matrix calculated based on the signal after the phase change becomes large as described above, it is considered that the arrival direction of the signal will be estimated with high accuracy. Note that the arrival direction may be estimated by the arrival direction estimation unit 80 in any manner. For example, the direction-of-arrival estimation by the direction-of-arrival estimation unit 80 may be performed by the above-described MUSIC method or may be performed by another method.

  The configuration example of the direction-of-arrival estimation apparatus 1A according to the first embodiment of the present invention has been described above.

[1-2. effect]
According to the first embodiment of the present invention, the threshold output unit 40 that outputs a threshold corresponding to the signal strength of each of the received signals received by each of the plurality of antenna elements, and the maximum of the amplitude of the baseband signal between the antennas A selection unit 50A for selecting a timing at which the value exceeds the threshold value, a buffer unit 60 for combining baseband signals at the timing selected by the selection unit 50A for each antenna element and outputting a combined signal, and a combined signal Direction-of-arrival estimating apparatus, comprising: a phase changing unit 70 that obtains a signal after the phase change by changing the phase of the received signal; and an arrival direction estimating unit 80 that estimates the direction of arrival of the received signal based on the signal after the phase change. 1A is provided.

  According to such a configuration, the baseband signal whose amplitude is equal to or smaller than the threshold is removed, so that the memory consumption is reduced. In addition, since the signal in the non-transmission section does not need to be output to the arrival direction estimation unit 80, deterioration in the estimation accuracy of the arrival direction by the arrival direction estimation unit 80 is suppressed. According to this configuration, the phase of the signal after the combination of the baseband signals whose amplitude exceeds the threshold is changed, so that the covariance matrix can be increased, and the arrival direction of the received signal can be more accurately determined. It can be estimated.

  As above, the first embodiment of the present invention has been described.

<2. Second Embodiment>
Subsequently, a second embodiment of the present invention will be described.

[2-1. Configuration of Arrival Direction Estimation Device]
A configuration example of the DOA estimation apparatus according to the second embodiment of the present invention will be described.

  FIG. 6 is a diagram illustrating a configuration example of the DOA estimation apparatus according to the second embodiment of the present invention. As shown in FIG. 6, the direction-of-arrival estimation device 1B according to the second embodiment of the present invention compares the direction-of-arrival estimation device 1A according to the first embodiment of the present invention with a threshold output unit 40. The difference is that the selection unit 50A is not provided and that the selection unit 50A is replaced with the selection unit 50B. Hereinafter, the selection unit 50B will be mainly described, and detailed description of other configurations will be omitted.

  FIG. 7 is a diagram illustrating an example of a temporal change in the amplitude Sa of the baseband signal. Referring to FIG. 7, similarly to the example shown in FIG. 2, a graph is shown in which the horizontal axis is time t and the vertical axis is the amplitude Sa (t) of the baseband signal corresponding to time t. T1 is a transmission section of the bit “1” after the detection of the packet is input. T2 is a transmission section of bit “0”. T3 is a transmission section of bit “1”. The transmission section after T3 is omitted due to space limitations.

  The selection unit 50B sets the timing at which the amplitude of the baseband signal input from the RF units 20 to 1 to 20-3 takes the maximum value in a predetermined cycle after the input of the detection of the packet from the packet detection unit 30. Select for each. More specifically, the selection unit 50B monitors the maximum value (between antennas) of the amplitude of the baseband signal input from the RF units 20-1 to 20-3, and this maximum value is the maximum value in the time direction. Is selected at predetermined intervals. Here, the length of the predetermined cycle is preferably equal to or longer than the length of a transmission section for one bit by ASK. Then, the maximum value can be obtained from the baseband signal corresponding to one cycle based on the amplitude of at least two bits.

  In the example shown in FIG. 7, the cycle V2 follows the cycle V1, and the cycle V1 and the cycle V2 have the same length, and are set longer than the 1-bit transmission section. Further, in the example shown in FIG. 7, a timing V10 at which the amplitude of the baseband signal takes the maximum value is selected from the cycle V1, and a timing V20 at which the amplitude of the baseband signal takes the maximum value is selected from the cycle V2. Selected.

  The selecting unit 50B notifies the buffer unit 60 of the timing at which the amplitude of the baseband signal takes the maximum value. That is, the selection unit 50B determines the timing at which the maximum value (between antennas) of the amplitude of the baseband signal input from the RF units 20-1 to 20-3 takes the maximum value in the time direction, from the buffer units 60-1 to 60-60. -3.

  As in the first embodiment of the present invention, the buffer unit 60 combines the baseband signal of the timing notified from the selection unit 50A for each antenna element 10, and outputs the combined signal.

  FIG. 8 is a diagram illustrating an example of a temporal change of the amplitude Sb of the signal after the combination. Referring to FIG. 8, similarly to the example shown in FIG. 3, a graph is shown in which the horizontal axis is time t and the vertical axis is the amplitude Sb (t) of the combined signal corresponding to time t. . Referring to FIG. 8, the baseband signals of timing V10 selected from cycle V1 and timing V20 selected from cycle V2 are combined. The baseband signal in the section T2 corresponding to the non-transmission section has been removed as a baseband signal having a value other than the maximum value. By removing the signal in the non-transmission section, the amount of memory consumption is reduced, and the signal in the non-transmission section does not need to be output to the arrival direction estimation unit 80.

  As in the first embodiment of the present invention, the arrival direction may be estimated by directly using the combined signal. However, after the non-transmission section is removed, the covariance matrix becomes small. When the covariance matrix is reduced in this way, the direction of arrival of the signal received by the antenna element 10 cannot be estimated with high accuracy by the direction-of-arrival estimating unit 80. Therefore, the phase changing section 70 changes the phase of the signal after coupling for each antenna element 10 to obtain a signal after the phase change. Then, phase change section 70 outputs the signal after the phase change for each antenna element 10 to arrival direction estimation section 80.

  FIG. 9 is a diagram for explaining a specific method of changing the phase. Referring to FIG. 9, a graph is shown in which the horizontal axis is time t and the vertical axis is the amplitude Sc (t) of the signal after the phase change corresponding to time t. Also in the example shown in FIG. 9, it is assumed that the phase changes by π / 2 in accordance with the equation (4), so that the amplitude Sc (t) of the signal after the phase change is 0, A, 0, −. A, 0,... As in the first embodiment of the present invention, after the phase change, the difference between the average value of the amplitude Sc (t) and the amplitude Sc (t) becomes large, so that the difference is calculated based on the signal after the phase change. It is considered that the covariance matrix increases and the arrival direction of the signal is estimated with high accuracy.

  The example of the configuration of the DOA estimating device 1B according to the second embodiment of the present invention has been described above.

[2-2. effect]
According to the second embodiment of the present invention, the timing at which the maximum value between the antennas of the amplitude of the baseband signal converted from the received signal received by each of the plurality of antenna elements takes the maximum value in the time direction is determined by a predetermined time. A selection unit 50B that selects for each cycle, a buffer unit 60 that combines the baseband signals at the timing selected by the selection unit 50B for each antenna element and outputs a combined signal, and changes the phase of the combined signal A direction-of-arrival estimating device 1B is provided, comprising: a phase changing unit 70 that obtains a signal after the phase change; and an arrival direction estimating unit 80 that estimates the direction of arrival of the received signal based on the signal after the phase change. You.

  According to this configuration, the baseband signal whose amplitude takes a value other than the maximum value is removed, so that the memory consumption can be reduced. In addition, since the signal in the non-transmission section does not need to be output to the arrival direction estimation unit 80, deterioration in the estimation accuracy of the arrival direction by the arrival direction estimation unit 80 is suppressed. According to this configuration, the phase of the signal after the combination of the baseband signals whose amplitude exceeds the threshold is changed, so that the covariance matrix can be increased, and the arrival direction of the received signal can be more accurately determined. It can be estimated.

  As above, the second embodiment of the present invention has been described.

<3. Summary>
As described above, the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that those skilled in the art to which the present invention pertains can conceive various changes or modifications within the scope of the technical idea described in the claims. It is understood that these also belong to the technical scope of the present invention.

  For example, in the second embodiment of the present invention, an example has been described in which the selection unit 50B selects the timing at which the maximum value of the amplitude of the baseband signal between antennas takes the maximum value in the time direction. If only the baseband signal having the maximum value is used for estimating the direction of arrival, the processing speed is considered to be improved. However, there may be cases where it is desired to increase the number of samples used for estimating the direction of arrival. In such a case, the selection unit 50B may select not only the timing at which the amplitude of the baseband signal takes the maximum value, but also the timing at which the amplitude of the baseband signal takes the highest n-th (n is an integer of 2 or more).

  In addition, instead of selecting the timing at which the maximum value of the amplitude of the baseband signal between antennas takes the maximum value in the time direction, the selection unit 50B determines the timing at which the maximum value of the amplitude of the baseband signal exceeds the threshold value. You may choose. At this time, in the first embodiment of the present invention, an example has been described in which the RSSI is measured for each antenna element and a threshold value corresponding to the RSSI is used. However, the selection unit 50B determines in advance without depending on the RSSI. Alternatively, a threshold value may be used.

1A, 1B Arrival direction estimating apparatus 10 Antenna element 20 RF unit 30 Packet detection unit 40 Threshold output unit 45 RSSI-threshold table 50A, 50B selection unit 60 Buffer unit 70 Phase change unit 80 Arrival direction estimation unit

Claims (5)

A plurality of antenna elements,
An RF unit that converts a received signal received by each of the plurality of antenna elements into a baseband signal, and measures a signal strength of each of the received signals.
A threshold output unit that outputs a threshold according to the signal strength;
A packet detection unit that detects a packet from the baseband signal,
After the packet is detected, a selection unit that selects a timing at which the maximum value between the antennas of the amplitude of the baseband signal exceeds the threshold,
A buffer unit that combines the baseband signal at the timing for each antenna element and outputs a combined signal,
A phase change unit that changes the phase of the signal after the combination to obtain a signal after the phase change,
Based on the signal after the phase change, an arrival direction estimation unit that estimates an arrival direction of the received signal,
An arrival direction estimation device comprising: A plurality of antenna elements,
An RF unit that converts a reception signal received by each of the plurality of antenna elements into a baseband signal;
A packet detection unit that detects a packet from the baseband signal,
After the packet is detected, a selection unit that selects a timing at which the maximum value between the antennas of the amplitude of the baseband signal takes the maximum value in the time direction for each predetermined period,
A buffer unit that combines the baseband signal at the timing for each antenna element and outputs a combined signal,
A phase change unit that changes the phase of the signal after the combination to obtain a signal after the phase change,
Based on the signal after the phase change, an arrival direction estimation unit that estimates an arrival direction of the received signal,
An arrival direction estimation device comprising: The length of the predetermined cycle is equal to or longer than a length of a transmission section for one bit by ASK.
An arrival direction estimation device according to claim 2. The selector selects a timing at which the amplitude of the baseband signal reaches the upper nth (n is an integer of 2 or more) after the packet is detected,
An arrival direction estimation device according to claim 2. A plurality of antenna elements,
An RF unit that converts a reception signal received by each of the plurality of antenna elements into a baseband signal;
A packet detection unit that detects a packet from the baseband signal,
After the packet is detected, a selection unit that selects a timing at which the maximum value between the antennas of the amplitude of the baseband signal exceeds a threshold,
A buffer unit that combines the baseband signal at the timing for each antenna element and outputs a combined signal,
A phase change unit that changes the phase of the signal after the combination to obtain a signal after the phase change,
Based on the signal after the phase change, an arrival direction estimation unit that estimates an arrival direction of the received signal,
An arrival direction estimation device comprising:

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