JP3963467B2 - Direct wave arrival direction estimation device - Google Patents

Description

  The present invention relates to a direct wave arrival direction estimation device that estimates the arrival direction of a direct wave of a coherent wave.

  In an environment where radio waves such as indoors and underground shopping streets propagate through multipaths, a plurality of reflected waves arrive from various directions. In this case, the reflected wave and the direct wave are coherent waves having different phases.

As a method of estimating the direction of arrival of reflected waves and direct waves consisting of such coherent waves, the direction of the beam radiated from the antenna is changed to receive the radio wave, and the direction in which the received radio wave intensity of the received radio wave is maximum is determined. A method for estimating the arrival direction of a direct wave is known (Non-Patent Document 1).
Tomoshige Furudate, Masaya Hashiguchi, Takashi Ohira, Toshio Asada, Toshimi Okada, “Snow Experiments on Microwave Beacons and Portable Radio Direction-of-arrival Detectors”, Science Theory (B), Vol. 186-B, no. 2, pp 219-225, Feb. 2003.

  However, in the direction-of-arrival estimation method described in Non-Patent Document 1, since the radio wave has a single carrier frequency, there is a region where the received radio wave intensity of the direct wave is weaker than the received radio wave intensity of the reflected wave. There is a problem that it is difficult to accurately estimate the direction of arrival of waves.

  FIG. 15 is a distribution diagram showing the distribution of the received power of the direct wave and the reflected wave when the carrier frequency is one. In FIG. 15, the vertical axis represents received power, and the horizontal axis represents the distance between the transmission source and the arrival direction estimation device. The thick line represents the distribution of the received power of the direct wave, and the dotted line represents the distribution of the received power of the reflected wave. Furthermore, the broken line represents the distribution of received power when there is no reflected wave.

  As is apparent from FIG. 15, at 2.4 m, 3.5 m, and 3.7 to 3.8 m, the reception power of the direct wave is significantly lower than the reception power of the reflected wave. This is because in a multipath environment, a plurality of reflected waves interfere with each other and may be stronger than direct waves.

  Thus, when the radio wave carrier frequency is set to one, there is a region where the received power of the reflected wave is stronger than the received power of the direct wave, and it is difficult to accurately estimate the arrival direction of the direct wave. It is.

  Therefore, the present invention has been made to solve such a problem, and an object of the present invention is to provide a direct wave arrival direction estimation device capable of accurately estimating the arrival direction of a direct wave even in a multipath environment. is there.

  According to the present invention, the direct wave arrival direction estimation device is a direct wave arrival direction estimation device that estimates the arrival direction of a direct wave coming from a transmission source in a multipath environment in which radio waves are reflected and / or diffracted. An antenna device and direction estimating means are provided. The antenna device switches the directivity to n (n is an integer of 2 or more) directions in a horizontal plane substantially parallel to the installation surface of the transmission source, and the carrier frequency from the transmission source differs in each direction m (m is Receive an integer of 2 or more radio waves. The direction estimation means suppresses the influence of reflection and / or diffraction based on m received radio wave intensities corresponding to m radio waves received by the antenna device when the directivity is set in one direction. By detecting the received radio field strength in one direction, n received radio field strengths in n directions are detected, and the direction in which the received radio wave intensity is the maximum among the detected n received radio field strengths is the arrival of a direct wave. Estimated direction.

  Preferably, the direction estimating means detects the maximum received radio wave intensity among the m received radio wave intensities as the received radio wave intensity in one direction.

  Preferably, the direction estimating means detects an average value of m received radio wave intensities as a received radio wave intensity in one direction.

  Preferably, the antenna device changes directivity in n directions by changing the capacitance of the feed element, the at least one parasitic element, and the variable capacitance element loaded on the at least one parasitic element. Means.

  The direct wave arrival direction estimation device according to the present invention sequentially switches the directivity of the antenna device in a plurality of directions, and receives a plurality of radio waves having different carrier frequencies from the transmission source in each direction. Then, the direct wave arrival direction estimation device suppresses the influence of the reflection and / or diffraction of the radio waves based on the received radio wave intensities corresponding to the received radio waves having different carrier frequencies, and receives the received radio waves in each direction. The intensity is detected, and the direction in which the maximum received radio wave intensity is obtained among the plurality of received radio wave intensities in the detected directions is estimated as the direct wave arrival direction.

  Therefore, according to the present invention, the arrival direction of a direct wave can be accurately estimated even in a multipath environment.

  The direct wave arrival direction estimation apparatus according to the present invention detects the maximum received radio wave intensity as the received radio wave intensity in each direction among a plurality of received radio wave intensities corresponding to a plurality of radio waves having different carrier frequencies.

  Furthermore, the direct wave arrival direction estimation device according to the present invention detects an average value of a plurality of received radio wave intensities corresponding to a plurality of radio waves having different carrier frequencies as the received radio wave intensity in each direction.

  Therefore, according to the present invention, it is possible to accurately estimate the arrival direction of a direct wave while suppressing the influence of radio wave reflection and / or diffraction with a simple configuration.

  Embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

  FIG. 1 is a schematic diagram of an arrival direction estimating apparatus according to an embodiment of the present invention. Referring to FIG. 1, arrival direction estimation apparatus 100 according to the embodiment of the present invention includes an array antenna 10, directivity switching means 20, radio wave intensity detection means 30, and direction estimation means 40. The arrival direction estimation apparatus 100 is an apparatus that estimates the arrival direction of a direct wave from a transmission source in a multipath environment where radio waves are reflected and / or diffracted.

  Array antenna 10 includes antenna elements 1 to 7 and varactor diodes 11 to 16. The antenna elements 1 to 7 are arranged on the xy plane (predetermined plane) along the z axis in the xyz orthogonal coordinates including the x axis, the y axis, and the z axis. In the present invention, a coherent wave having an azimuth indicating a direction in the xy plane shown in FIG. That is, a coherent wave having an azimuth angle in a horizontal plane substantially parallel to the installation surface of the transmission source is used as an object of arrival direction estimation.

  FIG. 2 is a plan layout view of the antenna elements 1 to 7 in the xy plane shown in FIG. Referring to FIG. 2, antenna elements 1 to 6 are arranged in a circle at equal intervals around antenna element 7.

  Referring to FIG. 1 again, antenna elements 1 to 6 are parasitic elements, and antenna element 7 is a feed element. Varactor diodes 11-16 are connected between antenna elements 1-6 and the ground node, respectively. Thereby, the varactor diodes 11 to 16 which are variable capacitance elements are loaded on the antenna elements 1 to 6 which are parasitic elements, respectively.

  As described above, the array antenna 10 has seven antenna elements including one feeding element (antenna element 7) and six parasitic elements (antenna elements 1 to 6) that are circular with the feeding element as the center. It consists of the structure arranged in.

  Directivity switching means 20 supplies control voltage sets CVL 1 to CVL 6 to varactor diodes 11 to 16 to switch the directivity of array antenna 10. The capacitances (reactance values) of the varactor diodes 11 to 16 are changed by the control voltages CVL1 to CVL6, respectively. The directivity switching means 20 determines the voltage values of the control voltages CVL1 to CVL6 so that the reactance values in the varactor diodes 11 to 16 become “hi” or “lo”, and sets the control voltage sets CVL1 to CVL6 to the varactor diodes. To 11-16.

In this case, directivity switching means 20, the reactance value _x m1 _{~x m6} set _{x m} varactor control voltage set CVL1~CVL6 to vary as shown in Table 1 diode in the varactor diode 11 to 16 11 to 16 To supply.

When the reactance value x _m1 is “lo” and the reactance values x _{m2 to} x _m6 are “hi” (i = 1), the array antenna 10 has a direction of 0 degrees (the positive direction of the x axis shown in FIG. 2). Is a beam pattern BP1 having directivity.

Further, when the reactance values x _m1 and x _m2 are “lo” and the reactance values x _{m3 to} x _m6 are “hi” (i = 2), the array antenna 10 has directivity in the direction of 30 degrees. It has a beam pattern BP2.

Furthermore, when the reactance value x _m2 is “lo” and the reactance values x _m1 , x _{m3 to} x _m6 are “hi” (i = 3), the array antenna 10 has directivity in the direction of 60 degrees. It has a beam pattern BP3.

Similarly, when the reactance values x _{m1 to} x _m6 are switched according to Table 1 (i = 4 to 12), the array antenna 10 is 90 degrees, 120 degrees, 150 degrees, 180 degrees, 210 degrees, and 240 degrees. Beam patterns BP4 to BPM12 having directivity in directions of 270 degrees, 300 degrees, and 330 degrees are included (see FIG. 2).

Thus, the directivity switching means 20 switches the directivity of the array antenna 10 by changing the reactance values x _{m1 to} x _m6 of the varactor diodes 11 to 16 loaded on the antenna elements 1 to 6 which are parasitic elements. .

  When arrival direction estimation apparatus 100 estimates the arrival direction of a direct wave from a transmission source (not shown), array antenna 10 sequentially switches its directivity to the 12 directions described above, and the carrier frequency in each direction is 16 different radio waves are received from the source.

  The radio wave intensity detection means 30 receives the radio wave received by the array antenna 10 from the feed element 7 of the array antenna 10, detects the received radio wave intensity RSSI of the received radio wave, and outputs it to the direction estimation means 40.

  More specifically, the radio wave intensity detection means 30 receives 16 radio waves WV1_1 to WV1_16 received by the array antenna 10 from the power feeding element 7 when the directivity is set to a direction of 0 degree, and receives the received 16 Sixteen received radio wave intensities R1_1 to R1_16 corresponding to the individual radio waves WV1_1 to WV1_16 are detected and output to the direction estimating means 40.

  The radio wave intensity detection means 30 receives 16 radio waves WV2_1 to WV2_16 received by the array antenna 10 when the directivity is set in the direction of 30 degrees from the feed element 7, and receives the 16 radio waves WV2_1 received. 16 received radio wave intensities R2_1 to R2_16 corresponding to ˜WV2_16 are detected and output to the direction estimating means 40.

  Hereinafter, in the same manner, the radio wave intensity detection means 30 has a directionality of θ (60 degrees, 90 degrees, 120 degrees, 150 degrees, 180 degrees, 210 degrees, 240 degrees, 270 degrees, 300 degrees and 330 degrees). 16 radio waves WVi_1 to WVi_16 (i = 3 to 12) received by the array antenna 10 when set to 16 from the feeding element 7, and 16 radio waves corresponding to the received 16 radio waves WVi_1 to WVi_16 Received radio wave intensities Ri_1 to Ri_16 are detected and output to direction estimating means 40.

  The direction estimation unit 40 receives the received radio field strengths R1_1 to R1_16,..., R12_1 to R12_16 from the radio field strength detection unit 30. The direction estimating means 40 is known in advance that the directivity of the array antenna 10 is switched in the order of 0 degrees, 30 degrees,..., 330 degrees. , R12_1 to R12_16 are associated with each direction. That is, the direction estimating means 40 creates a received radio wave intensity table shown in Table 2.

  Then, the direction estimating means 40 detects the received radio wave intensity Ri in each direction while suppressing the influence of radio wave reflection and / or diffraction based on the 16 received radio wave intensity Ri_1 to Ri_16 (i = 1 to 12). To do.

  More specifically, the direction estimating means 40 detects the received radio field strength Ri in each direction by calculating an average value of the 16 received radio field strengths Ri_1 to Ri_16.

  Then, the direction estimating means 40 estimates the maximum received radio wave intensity as the direct wave arrival direction among the detected 12 received radio wave intensity R1 to R12.

  If the carrier frequency of the radio wave is different, the phase relationship between the direct wave and the reflected wave changes, so the position where the received radio wave intensity is weak differs depending on the carrier frequency. FIG. 3 shows three received radio wave intensity profiles corresponding to three radio waves having different carrier frequencies. In FIG. 3, the vertical axis represents the received radio wave intensity, and the horizontal axis represents the distance from the transmission source. The profile of the received radio wave intensity shown in FIG. 3 is a profile when the directivity of the array antenna 10 is set in one direction.

  The received radio wave strengths R1 to R3 are the received radio wave strengths corresponding to the three radio waves WV1 to WV3 having different carrier frequencies. The received radio wave strengths R1 to R3 are different from each other in the maximum distance and the minimum distance.

  Thus, if the carrier frequency is different, the distance (position) at which the received radio wave intensity is weakened is different.

  When the average value Rav of the received radio wave strengths R1 to R3 is calculated, the average value Rav does not have a distance (position) where the strength is greatly reduced, unlike the received radio wave strengths R1 to R3.

  This is because the distance (position) where the strength greatly decreases in the received radio wave intensity R1 (or R2 or R3) by adding the received radio wave intensities R1 to R3 whose distance (position) where the intensity greatly decreases is different. This is because the received radio wave intensity R2, R3 (or R3, R1 or R1, R2) is removed.

  Accordingly, by calculating the average value Ri of the received radio wave intensities Ri_1 to Ri_16 corresponding to 16 radio waves WVi_1 to WVi_16 having different carrier frequencies, a large decrease in the received radio wave intensity caused by radio wave reflection and / or diffraction is removed. it can. That is, by calculating the average value Ri of the 16 received radio wave intensities Ri_1 to Ri_16, it is possible to detect the received radio wave intensity in each direction while suppressing the influence of radio wave reflection and / or diffraction.

  FIG. 3 shows how the received radio wave strengths R1 to R3 and the average value Rav thereof change with respect to the distance to the transmission source. For example, the array antenna 10 at a position where the distance to the transmission source is x1. Assume that three radio waves WV1 to WV3 having different carrier frequencies are received from a transmission source.

  In this case, the received radio wave strength R1 is greatly reduced, and the received radio wave strengths R2 and R3 are not greatly reduced. Therefore, the array antenna 10 receives the radio wave WV1 as a radio wave having a weak received radio wave strength, and receives the radio waves WV1 and WV2 as received radio wave strengths. Is received as a strong radio wave. Then, by calculating an average value of the received radio wave strengths R1 to R3 corresponding to the radio waves WV1 to WV3, a large decrease in the received radio wave strength R1 is removed by the received radio wave strengths R2 and R3, and a predetermined distance (position) x1 is obtained. The received radio wave intensity in the direction of can be detected. If this method is applied when the directivity of the array antenna 10 is set in each direction at the distance (position) x1, the received radio wave intensity in each direction at the distance (position) x1 is greatly reduced in the received radio wave intensity R1. It can be detected by removing the received radio wave intensity R2, R3.

  Therefore, calculating the average value of a plurality of received radio wave intensities corresponding to a plurality of radio waves having different carrier frequencies at each position where the array antenna 10 is installed suppresses the influence of radio wave reflection and / or diffraction. This is effective for detecting the received radio wave intensity.

  Therefore, in the present invention, the average value of the 16 received radio wave intensities Ri_1 to Ri_16 received by the array antenna 10 in each direction is calculated to detect the received radio wave intensity Ri in each direction.

  Of the 12 received radio wave intensities in the 12 directions, the direction in which the received radio wave intensity is maximum is estimated as the direct wave arrival direction. The direct wave is the shortest from the source to the array antenna 10. This is because, since the vehicle travels straight through the path, the received radio wave intensity becomes stronger than the reflected wave that is multiple-reflected by the walls, ceiling, floor, etc. and the diffracted wave that is diffracted by the obstacle.

  The received radio field strength in each direction is detected by calculating the average value of the multiple received radio wave strengths corresponding to the multiple radio waves having different carrier frequencies, and the maximum received radio wave strength among the detected multiple received radio wave strengths is A method of estimating the obtained direction as the direct wave arrival direction is called a “frequency smoothing method”.

  In the present invention, the direction estimating means 40 determines the arrival direction of the direct wave based on the received radio wave strengths R1_1 to R1_16,..., R12_1 to R12_16 received from the radio wave strength detecting means 30 by a direction other than the frequency smoothing method. It may be estimated.

  That is, the direction estimation means 40 detects the maximum received radio wave intensity Ri_max among the 16 received radio wave intensity Ri_1 to Ri_16 in each direction as the received radio wave intensity Ri in each direction, and the detected 12 received radio wave intensity. The direction in which the maximum received radio wave intensity is obtained among R1 to R12 is estimated as the direct wave arrival direction. This method is called “frequency selection method”.

  More specifically, the direction estimating means 40 detects the maximum received radio wave strength R1_max among the received radio wave strengths R1_1 to R1_16, detects the maximum received radio wave strength R2_max among the received radio wave strengths R2_1 to R2_16, In the same manner, the maximum received radio wave intensity Ri_max is detected from the received radio wave intensity Ri_1 to Ri_16 (i = 3 to 12). Then, the direction estimating means 40 estimates the direction in which the maximum received radio wave intensity (any one of R1_max to R12_max) is obtained from the 12 received radio wave intensity R1_max to R12_max as the direct wave arrival direction.

  Of the 16 received radio wave strengths Ri_1 to Ri_16 (i = 1 to 12) in each direction, detecting the maximum received radio wave strength Ri_max suppresses the influence of radio wave reflection and / or diffraction and reduces the received radio wave strength. Is equivalent to detecting. The reason is as follows.

  As described above, since the phase relationship between the direct wave and the reflected wave is different if the carrier frequency is different, the received radio wave strengths Ri_1 to Ri_16 are detected as the received radio wave strengths of the radio waves in which the direct wave and the reflected wave overlap in each direction. Even if the received radio wave intensities Ri_1 to Ri_16 are different, they have different intensities. That is, the received radio wave intensities Ri_1 to Ri_16 range from the intensity (minimum intensity) when the phase relationship between the direct wave and the reflected wave is opposite to the intensity (maximum intensity) when the direct wave and the reflected wave are in phase. It is distributed in the range.

  Of the received radio wave strengths Ri_1 to Ri_16, the maximum received radio wave strength Ri_max is when the direct wave and the reflected wave are overlapped so as to increase the received radio wave strength of the direct wave, or the received radio wave strength of the direct wave is weakened. In this way, even when the direct wave and the reflected wave overlap, it is detected when the degree of weakening the received radio wave intensity is the smallest.

  Therefore, detecting the maximum received radio wave intensity Ri_max among the 16 received radio wave intensity Ri_1 to Ri_16 corresponds to detecting the received radio wave intensity while suppressing the influence of radio wave reflection and / or diffraction.

  FIG. 4 is a flowchart for explaining the operation of estimating the arrival direction of the direct wave by the frequency smoothing method. When a series of operations is started, the directivity switching means 20 of the arrival direction estimating apparatus 100 sets i = 1 (step S1), and changes the directivity of the array antenna 10 to the direction Di (i = 1, that is, 0). (Direction of degrees) is set (step S2).

  Then, the direction estimating means 40 sets j = 1 (step S3). Thereafter, the transmission source radiates the radio wave WVi_j having the carrier frequency fj in an omni pattern in the xy plane. The array antenna 10 receives the radio wave WVi_j from the transmission source (step S4), and the radio wave intensity detection means 30 receives the radio wave WVi_j from the feeding element 7 of the array antenna 10 and receives the received radio wave intensity of the received radio wave WVi_j. Ri_j is detected (step S5), and the detected received radio wave intensity Ri_j is output to the direction estimating means 40.

  The direction estimation unit 40 holds the received radio field intensity Ri_j received from the radio field intensity detection unit 30, and determines whether j = 16 (step S6). If j = 16 is not true, the direction estimating means 40 sets j = j + 1 (step S7). Thereafter, the above-described steps S4 to S7 are repeatedly executed until it is determined in step S6 that j = 16.

  If it is determined in step S6 that j = 16, 16 received radio wave intensities Ri_1 to Ri_16 in one direction are detected (step S8), and the direction estimating means 40 is in one direction ( 16 received radio wave intensities Ri_1 to Ri_16 are stored in association with the direction of 0 degree.

  Thereafter, the directivity switching means 20 determines whether i = 12 (step S9), and when i = 12, i = i + 1 is set (step S10). In step S9, steps S2 to S10 described above are repeatedly executed until it is determined that i = 12.

  If it is determined in step S10 that i = 12, 16 received radio wave intensities R1_1 to R1_16,..., R12_1 to R12_16 are detected corresponding to 12 directions (step S10). S11).

  Then, the direction estimation means 40 calculates an average value Ri_ave in each direction based on the received radio wave strengths R1_1 to R1_16,..., R12_1 to R12_16 (step S12), and the calculated 12 average values R1_ave˜ Of R12_ave, the direction in which the maximum received radio wave intensity is obtained is estimated as the direct wave arrival direction (step S13). Thereby, a series of operation | movement is complete | finished.

  FIG. 5 is a flowchart for explaining the operation of estimating the arrival direction of the direct wave by the frequency selection method. The flowchart shown in FIG. 5 is the same as the flowchart shown in FIG. 4 except that steps S12 and S13 in the flowchart shown in FIG. 4 are replaced with steps S12A and S13A, respectively.

  When 16 received radio wave strengths R1_1 to R1_16,..., R12_1 to R12_16 are detected corresponding to 12 directions (step S11), the direction estimating means 40 receives the received radio wave strength Ri_1 in each direction. The maximum received radio wave intensity Ri_max is detected among -Ri_16 (step S12A).

  That is, the direction estimating means 40 detects the maximum received radio wave strength R1_max among the received radio wave strengths R1_1 to R1_16 in the direction of 0 degrees, and the maximum of the received radio wave strengths R2_1 to R2_16 in the direction of 30 degrees. In the direction of θ (60 degrees, 90 degrees, 120 degrees, 150 degrees, 180 degrees, 210 degrees, 240 degrees, 270 degrees, 300 degrees and 330 degrees), the received radio wave intensity R2_max is detected in the same manner. Among the received radio wave intensities Ri_1 to Ri_16 (i = 3 to 12), the maximum received radio wave intensity Ri_max (i = 3 to 12) is detected.

  Then, the direction estimating means 40 sets the 12 received radio wave strengths R1_max to R12_max as the received radio wave strengths in 12 directions, and the direction in which the maximum received radio wave strength is obtained among the 12 received radio wave strengths R1_max to R12_max. Is estimated as the direct wave arrival direction (step S13A). Thereby, a series of operation | movement is complete | finished.

  As described above, in this invention, the arrival direction estimating apparatus 100 sequentially switches the directivity of the array antenna 10 to 12 directions, and sets the directivity in each direction, so that a plurality of carrier frequencies differ from the transmission source. A radio wave is received, and the received radio wave intensity in each direction is detected while suppressing the influence of reflection and / or diffraction of the radio wave based on a plurality of received radio wave intensities corresponding to a plurality of radio waves having different carrier frequencies. Then, arrival direction estimation apparatus 100 estimates the direction in which the maximum received radio wave intensity is obtained among the plurality of received radio wave intensities in a plurality of directions as the direct wave arrival direction.

  The result of simulating the estimation of the direction of arrival by the frequency smoothing method and the frequency selection method described above will be described.

  FIG. 6 is a schematic diagram showing a radio wave space used for the simulation. One corner A of a rectangular parallelepiped room 50 of 10 m × 10 m × 3 m was used as the origin of the xyz coordinates. The array antenna 10 was installed at coordinates [x, y, 1 m], and the transmission source 60 was fixed at coordinates [5 m, 5 m, 1 m]. The room 50 is surrounded by a concrete wall.

  Then, the array antenna 10 was sequentially moved in the xy plane while maintaining the height of the array antenna 10 at 1 m, and the arrival direction of the direct wave from the transmission source 60 was estimated.

  Table 3 shows the simulation conditions.

  The radio wave was reflected by the concrete wall of the room 50 eight times, and the amplitude of each reflected wave was weighted with the Fresnel coefficient.

  In addition, the frequency band of the radio wave radiated from the transmission source 60 is in the range from 2404 MHz to 2484 MHz, and the number of carrier frequencies has been changed to 1, 2, 4, 8, 16, and 32. . When there are two or more carrier frequencies, the intervals between the carrier frequencies are set at equal intervals.

  Furthermore, the transmission source 60 radiates radio waves of non-directional horizontal polarization and vertical polarization.

  FIG. 7 is a diagram showing a beam pattern of array antenna 10 shown in FIG. 1 in directions of 150 degrees and 180 degrees. When the directivity of the array antenna 10 is set to a direction of 150 degrees, the capacitances of the varactor diodes 11 to 16 are 13.4 [pF], 13.4 [pF], 0.645 [pF], 0. 645 [pF], 13.4 [pF], and 13.4 [pF]. When the directivity of the array antenna 10 is set to a direction of 180 degrees, the capacitances of the varactor diodes 11 to 16 are 13.4 [pF], 13.4 [pF], 13.4 [pF], It is set to 0.59 [pF], 13.4 [pF], and 13.4 [pF].

  As shown in FIG. 7, the beam pattern is almost the same even when the carrier frequency is changed in the range of 2404 MHz to 2484 MHz in the directions of 150 degrees and 180 degrees. That is, the array antenna 10 can receive radio waves having a carrier frequency in the range of 2404 MHz to 2484 MHz with substantially the same antenna characteristics.

  Table 4 shows the 3 dB beam width, F / B ratio, and adjacent beam discrimination.

  From the results of Table 4, it can be seen that the beam patterns are substantially the same in the entire frequency band of 2404 MHz to 2484 MHz.

  FIG. 8 is a relationship diagram between received power and distance when the carrier frequency is 16. In FIG. 8, the vertical axis represents the received power, that is, the received radio wave intensity, and the horizontal axis represents the distance between the array antenna 10 and the transmission source 60.

  A solid line and a plurality of dotted lines in FIG. 8 indicate 12 directions. Each of the solid line and the plurality of dotted lines is obtained from the received radio wave intensity by the frequency smoothing method described above.

  As a result, in the range where the distance between the array antenna 10 and the transmission source 60 is 2 m to 4 m, the received radio wave intensity represented by the solid line is equal to or higher than the received radio wave intensity represented by the dotted line. Therefore, the direction in which the received radio wave intensity represented by the solid line is obtained is the direct wave arrival direction.

  When the carrier frequency is one, as shown in FIG. 15, the received radio wave intensity of the direct wave is higher than the received radio wave intensity of the reflected wave in the range of 2 m to 4 m between the array antenna 10 and the transmission source 60. There was a weakened region, but when the carrier frequency is 16, the received radio wave intensity of the direct wave in the entire range where the distance between the array antenna 10 and the transmission source 60 is 2 m to 4 m is It is higher than the received radio wave intensity of the reflected wave. Therefore, it was found that the arrival direction of the direct wave can be estimated by using the frequency smoothing method while suppressing the influence of the reflected wave.

  FIG. 9 is an estimated angle error distribution diagram when the carrier frequency is one. FIG. 10 is an estimated angle error distribution diagram when the arrival direction is estimated by the frequency selection method using 16 carrier frequencies. FIG. 11 is an estimated angle error distribution diagram when the arrival direction is estimated by the frequency smoothing method using 16 carrier frequencies.

  In the case shown in FIGS. 9, 10 and 11, the transmission source 60 is fixed at coordinates [5m, 5m, 1m], and the array antenna 10 has an x coordinate and a y coordinate while maintaining a height of 1 m. It was changed every 10 cm. Therefore, the transmission source 60 is installed in the center [50, 50] of the xy plane in FIG. 9, FIG. 10, and FIG. In FIGS. 9, 10, and 11, the white portion indicates that the angle error is 15 degrees or less, and the black portion indicates that the angle error is greater than 15 degrees.

  In the case of a single carrier frequency, a carrier frequency of 2484 MHz was used. When the transmission source 60 radiates a radio wave of 2484 MHz, the area where the angle error is 15 degrees or less occupies most of the distance within 2 m from the transmission source 60, but when the transmission source 60 is 2 m or more, the angular error The area where the angle is 15 degrees or less is reduced, and most of them cannot estimate the correct direction of the transmission source 60 (see FIG. 9).

  When the frequency selection method with 16 carrier frequencies is used, the specific area and the four corners have a large angular error, but the area where the angular error is 15 degrees or less is larger than when the carrier frequency is one. (See FIG. 10).

  Furthermore, when the frequency smoothing method with 16 carrier frequencies is used, as in the frequency selection method, a specific region and four corners have a large angular error, but a region with an angular error of 15 degrees or less has a frequency selection. Compared to the case of using the method (see FIG. 11).

  Thus, by using the frequency selection method and the frequency smoothing method, it is possible to accurately estimate the arrival direction of the direct wave.

  Next, the relationship between the cumulative probability and the angle error will be described. FIG. 12 is a relationship diagram between the cumulative probability and the angle error when the frequency selection method is used. FIG. 13 is a relationship diagram between the cumulative probability and the angle error when the frequency smoothing method is used.

  In FIG. 12 and FIG. 13, the carrier frequency was changed to 1, 2, 4, 8, 16, and 32. 12 and 13, the vertical axis represents the cumulative probability, and the horizontal axis represents the angle error.

  When the frequency selection method is used, the cumulative probability of the estimated angle error within 15 degrees is 30% with one carrier frequency, but the cumulative probability within 15 degrees improves as the carrier frequency increases. Is done. When the carrier frequency is 8 or more, the cumulative probability within 15 degrees is almost saturated, and with 32 carrier frequencies, the cumulative probability within 15 degrees is 42% (see FIG. 12).

  The reason why the cumulative probability within 15 degrees is almost saturated at the carrier frequency of 8 or more is that the drop of the received radio wave intensity is difficult to be reduced because the carrier frequency interval is narrow.

  When the frequency smoothing method is used, the cumulative probability within 15 degrees is improved as the carrier frequency is increased. With 32 carrier frequencies, the cumulative probability within 15 degrees reaches 60%. When the frequency smoothing method is used, the cumulative probability within 15 degrees is improved twice as compared with the case where the carrier frequency is one, and 1.4 times compared with the frequency selection method. The reason why the cumulative probability within 15 degrees is almost saturated at eight or more carrier frequencies is the same as in the frequency selection method.

  Thus, the estimated angle error can be reduced by increasing the carrier frequency.

  FIG. 14 is a relationship diagram between the cumulative probability and the angle error when the carrier interval is changed. In FIG. 14, the vertical axis represents the cumulative probability, and the horizontal axis represents the angle error. Moreover, the carrier frequency was fixed to 8, and the carrier interval was changed in the range from 0.5 MHz to 11.4 MHz.

  With increasing carrier spacing, the cumulative probability improves and shows a tendency to saturate at 5 MHz and above.

  From these results, it was found that the estimated angular error can be improved by taking a carrier interval to some extent and using the frequency smoothing method in an environment where the influence of multipath is large.

  As described above, by using the frequency smoothing method or the frequency selection method according to the present invention, the arrival direction of the direct wave from the transmission source 60 can be accurately estimated while suppressing the influence of the reflected wave.

  In the present invention, the array antenna 10 is not limited to the one composed of seven antenna elements, but is composed of two or more antenna elements composed of one feeding element and one or more parasitic elements. It only has to be.

  The carrier frequency is preferably in the direction of many, but the cumulative probability that the estimated angle error is 15 degrees or less is improved when the number of carrier frequencies is two or more as shown in FIG. 12 and FIG. It may be more than one.

  Furthermore, the arrival direction estimating apparatus 100 is not limited to the array antenna 10 and may be equipped with an antenna capable of switching directivity in which a plurality of antenna elements are arranged in a straight line. Any antenna may be mounted.

  Furthermore, array antenna 10 and directivity switching means 20 constitute an “antenna device”.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and is intended to include meanings equivalent to the scope of claims for patent and all modifications within the scope.

  The present invention is applied to a direct wave arrival direction estimation device that can accurately estimate the arrival direction of a direct wave even in a multipath environment.

It is the schematic of the arrival direction estimation apparatus by embodiment of this invention. FIG. 2 is a plan layout view of antenna elements in an xy plane shown in FIG. 1. It is a profile of three received radio wave strengths corresponding to three radio waves having different carrier frequencies. It is a flowchart for demonstrating the operation | movement which estimates the arrival direction of a direct wave by a frequency smoothing method. It is a flowchart for demonstrating the operation | movement which estimates the arrival direction of a direct wave by a frequency selection method. It is a schematic diagram which shows the electromagnetic wave space used for simulation. It is a figure which shows the beam pattern of the array antenna shown in FIG. 1 in the direction of 150 degree | times and 180 degree | times. FIG. 6 is a relationship diagram between received power and distance when the carrier frequency is 16. It is an estimation angle error distribution map in case a carrier frequency is one. It is an estimation angle error distribution map at the time of estimating an arrival direction by the frequency selection method using 16 carrier frequencies. It is an estimated angle error distribution map when the direction of arrival is estimated by the frequency smoothing method using 16 carrier frequencies. FIG. 6 is a relationship diagram between cumulative probability and angle error when using a frequency selection method. FIG. 6 is a relationship diagram between an accumulated probability and an angle error when a frequency smoothing method is used. FIG. 6 is a relationship diagram between cumulative probability and angle error when the carrier interval is changed. It is a distribution map which shows distribution of the received power of a direct wave and a reflected wave in case a carrier frequency is one.

Explanation of symbols

  1 to 7 antenna elements, 10 array antennas, 11 to 16 varactor diodes, 20 directivity switching means, 30 radio wave intensity detection means, 40 direction estimation means, 50 rooms, 60 transmission source, 100 arrival direction estimation device.

Claims (4)

A direct wave arrival direction estimation device for estimating an arrival direction of a direct wave coming from a transmission source in a multipath environment where radio waves are reflected and / or diffracted,
The directivity is switched to n (n is an integer of 2 or more) directions in a horizontal plane substantially parallel to the installation surface of the transmission source, and the carrier frequency from the transmission source differs in each direction m (m is 2 or more). An integer) antenna device for receiving radio waves,
When the directivity is set in one direction, the influence of the reflection and / or diffraction is suppressed based on m received radio wave intensities corresponding to the m radio waves received by the antenna device. N received radio wave intensities in the n directions are detected by detecting received radio wave intensities in one direction, and the direction in which the received radio wave intensity is maximum is detected among the detected n received radio wave intensities. A direct wave arrival direction estimation device comprising a direction estimation means for estimating a direction of arrival of a direct wave.   2. The direct wave arrival direction estimation device according to claim 1, wherein the direction estimation unit detects a maximum received radio wave intensity among the m received radio wave intensities as a received radio wave intensity in the one direction.   The direct wave arrival direction estimation device according to claim 1, wherein the direction estimation means detects an average value of the m received radio wave intensities as a received radio wave intensity in the one direction. The antenna device is
A feeding element;
At least one parasitic element;
The directivity switching means for changing the capacitance of the variable capacitive element loaded on the at least one parasitic element and switching the directivity in the n directions. The direct wave arrival direction estimation apparatus according to the item.