Communication device, direction-of-arrival estimation method, control circuit, and storage medium

Abstract

This communication device is characterized by comprising: a reception power measurement unit that measures the reception power of a plurality of signals which have been received by a plurality of array elements (11), respectively, the array elements being receiving antennas; a combination selection unit that selects some of the plurality of signals on the basis of the reception power; a selector that outputs the signals selected by the combination selection unit; and an estimation unit (13) that uses the signals output by the selector to execute direction-of-arrival estimation processing for estimating the direction of arrival of an interference wave.

Description

Communication device, direction of arrival estimation method, control circuit and storage medium

[0001] The present disclosure relates to a communication device, a direction-of-arrival estimation method, a control circuit, and a storage medium that estimate the direction of arrival of an interference wave from signals received by a plurality of receiving antennas.

[0002] In wireless communications, interference waves to communication devices can degrade the transmission quality of the communication system. To address this issue, a method has been proposed to estimate the direction of arrival of the interference waves and spatially suppress the interference waves by nulling in the estimated direction of arrival.

[0003] Patent Literature 1 discloses a technology for estimating the direction of arrival of an interference wave on a satellite. The technology disclosed in Patent Literature 1 uses digital beam forming (DBF) to divide a coverage area into multiple beam areas, assign a beam direction to each beam area, and estimate the direction of arrival by measuring the received power of each beam. First, signals with high received power are identified by coarse estimation, and the beam area corresponding to the identified signal is divided into smaller beam areas than in the coarse estimation, thereby performing two-stage direction of arrival estimation. This type of direction of arrival estimation shortens the time required from receiving an interference wave to estimating the direction of arrival, thereby shortening the time required to deal with the interference wave by nulling.

[0004] U.S. Pat. No. 1,178,218

[0005] However, with the above-mentioned conventional technology, as the number of receiving antennas increases with an expansion of the coverage area and an increase in communication capacity, the amount of calculation required for estimating the direction of arrival increases. For example, in an environment where there are strict restrictions on the size and weight of the device, such as a satellite, it is difficult to increase the size of the device in line with the increase in the amount of calculation, so it is important to reduce the amount of calculation.

[0006] The present disclosure has been made in view of the above, and aims to provide a communication device that can reduce the amount of calculation required for estimating the direction of arrival.

[0007] In order to solve the above-mentioned problems and achieve the objectives, the communication device according to the present disclosure is characterized by comprising a received power measurement unit that measures the received power of multiple signals received by each of multiple receiving antennas, a combination selection unit that selects some of the multiple signals based on the received power, a selector that outputs the signal selected by the combination selection unit, and an estimation unit that performs a direction-of-arrival estimation process to estimate the direction of arrival of an interference wave using the signal output by the selector.

[0008] The present disclosure provides an advantage of being able to provide a communication device that can reduce the amount of calculation required for estimating the direction of arrival.

[0009] 2 is a diagram showing an example of the configuration of a communication system according to the first embodiment; FIG. 2 shows an example of the functional configuration of a direction of arrival estimation unit according to the first embodiment; FIG. 2 shows an example of the functional configuration of an element selection unit according to the first embodiment; FIG. 2 shows an example of the hardware configuration of the direction of arrival estimation unit; FIG. 2 shows dedicated hardware for realizing the function of the direction of arrival estimation unit;

[0010] A communication device, a direction-of-arrival estimation method, a control circuit, and a storage medium according to embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0011] First Embodiment. Fig. 1 is a diagram illustrating an example of the configuration of a communication system 100 according to a first embodiment. In the communication system 100, a transmitting station 1 and a receiving station 3 are wirelessly connected via a relay station 2. The relay station 2 may be a device located in the sky, such as a communication satellite or a mobile object hovering at high altitude, or may be a device fixedly installed on the ground. The relay station 2 is in an environment where it is subject to radio wave interference from an interfering station 5 that does not belong to the communication system 100. The relay station 2 has a function of relaying a signal addressed to the receiving station 3 from the transmitting station 1. The relay station 2 receives control information from a control station 4 and operates in accordance with the control information. In control communication in which control information is transmitted between the relay station 2 and the control station 4, the relay station 2 functions as a receiving station.

[0012] Next, we will explain the direction of arrival estimation at relay station 2. Note that relay station 2 is an example of a communication device that functions as relay station 2 in communication from transmitting station 1 to receiving station 3, and functions as a receiving station in control communication from control station 4 to relay station 2. Therefore, in the following explanation, there will be no discrepancy even if relay station 2 is read as a receiving station.

[0013] 2 is a diagram illustrating an example of the functional configuration of a direction-of-arrival estimator 50 according to the first embodiment. The direction-of-arrival estimator 50 is provided in the relay station 2. The direction-of-arrival estimator 50 includes an array element 11, an element selector 12, and an estimator 13. The estimator 13 includes a coarse estimator 14 and a fine estimator 15. The coarse estimator 14 includes coarse DBFs 16-1 to 16-m, an averaging unit 17, and a maximum value searcher 18. The fine estimator 15 includes a coefficient calculator 19, fine DBFs 20-1 to 20-n, an averaging unit 21, and a center-of-gravity calculator 22.

[0014] Although represented as one block in Fig. 2, the direction-of-arrival estimation unit 50 has a plurality of array elements 11. The array elements 11 are receiving antennas, and the plurality of array elements 11 are arranged linearly, planarly, curvedly, or the like. The element selection unit 12 selects, from the plurality of array elements 11, an array element 11 to be used by the subsequent estimation unit 13. The estimation unit 13 estimates the direction of arrival of the interfering signal from the interfering station 5 based on the signal received by the array element 11 selected by the element selection unit 12. The estimation unit 13 outputs an estimated angle indicating the direction of arrival.

[0015] 3 is a diagram illustrating an example of a functional configuration of the element selector 12 according to the first embodiment. The element selector 12 includes a received power measuring unit 121, a combination selecting unit 122, and a selector 123. A plurality of signals received by each of the plurality of array elements 11 are input to the received power measuring unit 121 and the selector 123, respectively. Although the number of signals input to the received power measuring unit 121 and the selector 123 is shown as two for simplicity in FIG. 3, in reality, the number of signals input corresponds to the number of array elements 11. The element selector 12 selects M array elements 11, where M is less than N, from the N array elements 11.

[0016] The received power measurement unit 121 measures the received power of the signal received by each of the multiple array elements 11. Note that the information to be measured may be, for example, a vector or scalar in the complex signal of the received signal, as long as it is information equivalent to the received power. The received power measurement unit 121 outputs the measured received power to the combination selection unit 122.

[0017] The combination selection unit 122 selects some signals from among the multiple signals received by each of the multiple array elements 11, based on the received power output by the received power measurement unit 121. When there is a one-to-one correspondence between the array elements 11 and the signals, selecting an array element 11 is synonymous with selecting a signal. The combination selection unit 122 outputs information indicating the selected signal to the selector 123.

[0018] The selector 123 outputs the signal selected by the combination selection unit 122 from the input signals. The signal output by the selector 123 is input to the rough estimation unit 14 of the estimation unit 13 and used in the direction-of-arrival estimation process.

[0019] Here, a description will be given of the hardware configuration of the direction-of-arrival estimation unit 50. Fig. 4 is a diagram showing an example of the hardware configuration of the direction-of-arrival estimation unit 50. The functions of the direction-of-arrival estimation unit 50 can be realized using a control circuit 90 shown in Fig. 4. The control circuit 90 has a processor 91, a memory 92, and an external interface 93.

[0020] The processor 91 is a CPU (Central Processing Unit) and is also called a central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, or DSP (Digital Signal Processor). The memory 92 is, for example, a non-volatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable ROM), or an EEPROM (Electrically Programmable ROM), a magnetic disk, a flexible disk, an optical disk, a compact disk, a minidisk, or a DVD (Digital Versatile Disk). The external interface 93 is an interface for outputting data generated by the processor 91 to outside the control circuit 90 and inputting data from outside the control circuit 90.

[0021] When the function of the direction-of-arrival estimation unit 50 is realized by the control circuit 90, the processor 91 reads and executes a program corresponding to the processing of each component, which is stored in the memory 92. The memory 92 is also used as a temporary memory for each process executed by the processor 91. The program executed by the processor 91 may be provided in a state stored in a storage medium, or may be provided via a communication path such as the Internet.

[0022] The function of the direction of arrival estimation unit 50 may also be realized using dedicated hardware. Fig. 5 is a diagram showing dedicated hardware for realizing the function of the direction of arrival estimation unit 50. The processing circuit 94 is a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof.

[0023] Fig. 6 is a flowchart for explaining the element selection operation of the element selector 12 shown in Fig. 3. The received power measuring unit 121 of the element selector 12 measures the received power of each array element 11 (step S101).

[0024] The combination selection unit 122 selects the array element 11 with the maximum power (step S102). Subsequently, the combination selection unit 122 selects the array element 11 with the next highest received power from among the array elements 11 adjacent to the selected array element 11 (step S103).

[0025] 7 is an explanatory diagram of the combination selection unit 122 according to the first embodiment. In the example shown in Fig. 7, when the received power of the array element 11 corresponding to x2y1 is the highest, the combination selection unit 122 first selects the array element 11 corresponding to x2y1, and then selects the array element 11 corresponding to x3y1, which has the next highest received power, from among the array elements 11 corresponding to x1y1, x2y2, and x3y1 adjacent to x2y1.

[0026] Returning to the description of Fig. 6, the combination selection unit 122 determines whether the number of selected elements, which is the number of array elements 11 that have been selected, is less than a threshold value (step S104). If the number of selected elements is less than the threshold value (step S104: Yes), the combination selection unit 122 returns to the processing of step S103. If the number of selected elements is not less than the threshold value (step S104: No), that is, if the number of selected elements is equal to or greater than the threshold value, the combination selection unit 122 notifies the selector 123 of the combination of array elements 11 that has been selected, and the selector 123 outputs the signals of the array elements 11 that have been selected by the combination selection unit 122 to the estimation unit 13 (step S105).

[0027] The threshold for the number of selected elements may be determined, for example, from the coverage area of ​​the raw beam. A raw beam is a beam pattern received by each array element 11 before being multiplied by an excitation coefficient by DBF. FIG. 8 is a diagram showing an example of the coverage area of ​​a raw beam received using a reflector. FIG. 9 is a diagram showing an example of the coverage area of ​​a raw beam when receiving direct radiation. Referring to FIGS. 8 and 9 , it can be seen that the received power in the area shown by the square grid is measured across nine grids corresponding to nine elements when using a reflector, and across 21 grids when using direct radiation. Therefore, for example, even if relay station 2 has a total of 100 array elements 11 to cover its coverage area, in the cases shown in FIGS. 8 and 9 , the number of elements used for direction-of-arrival estimation is nine when using a reflector and 21 when using direct radiation. Furthermore, the threshold value for the number of selected elements may be determined based on the upper limit of the number of processors 91 , memories 92 , and processing circuits 94 that can be installed, depending on the hardware configuration of the relay station 2 .

[0028] Returning to the description of FIG. 6 , the combination selection unit 122 excludes the array element 11 with the maximum power from the search targets (step S106), and determines whether the number of signals output by the selector 123 is less than the number of estimated simultaneous arrival directions (step S107). If the number is less than the number of estimated simultaneous arrival directions (step S107: Yes), the combination selection unit 122 repeats the process from step S102. If the number is equal to or greater than the number of estimated simultaneous arrival directions (step S107: No), the element selection unit 12 ends the element selection process. The number of estimated simultaneous arrival directions is set to the number that can be processed simultaneously depending on the hardware configuration of the direction of arrival estimation unit 50.

[0029] Although FIG. 6 shows an example in which the received power is calculated for each array element 11, as another example, the signal received by each array element 11 may be divided into frequencies, and the received power may be measured for each array element 11 and for each frequency.

[0030] Fig. 10 is a flowchart for explaining a modification of the element selection operation of the element selector 12 shown in Fig. 3. The difference from the operation shown in Fig. 6 is that the received signal is handled for each array element 11 and for each frequency.

[0031] The received power measuring unit 121 of the element selecting unit 12 measures the received power for each array element 11 and for each frequency (step S201).

[0032] The combination selection unit 122 selects the array element 11 and frequency with the maximum power (step S202). Subsequently, the combination selection unit 122 selects the array element 11 and frequency with the next highest received power among the array elements 11 and the array elements 11 adjacent to the selected element and frequency (step S203).

[0033] The combination selection unit 122 determines whether the number of selected elements, which is the number of selected array elements 11, is less than a threshold value (step S204). If the number of selected elements is less than the threshold value (step S204: Yes), the combination selection unit 122 returns to the process of step S203. If the number of selected elements is not less than the threshold value (step S204: No), that is, if the number of selected elements is equal to or greater than the threshold value, the combination selection unit 122 notifies the selector 123 of the selected combination of array elements 11 and frequencies, and the selector 123 outputs the signal of the array elements 11 and frequencies selected by the combination selection unit 122 to the estimation unit 13 (step S205).

[0034] The combination selection unit 122 excludes the array element 11 and frequency with the maximum power from the search targets (step S206), and determines whether the number of signals output by the selector 123 is less than the estimated number of simultaneous arrival directions (step S207). If the number is less than the estimated number of simultaneous arrival directions (step S207: Yes), the combination selection unit 122 repeats the process from step S202. If the number is equal to or greater than the estimated number of simultaneous arrival directions (step S207: No), the element selection unit 12 ends the element selection process.

[0035] 10, when a frequency-divided signal is used, if an interference wave exists only at a specific frequency, it is possible to form a beam limited to the specific frequency by DBF, thereby further improving the accuracy of estimating the direction of arrival. Also, by outputting a signal that has been frequency-divided in advance using a channelizer or the like to the coarse estimation unit 14, it is possible to reduce the sampling rate, which leads to a reduction in circuit size.

[0036] Figure 11 is an explanatory diagram of the estimation unit 13 shown in Figure 2. The estimation unit 13 estimates the direction of arrival in two stages: coarse estimation and precise estimation. Both coarse estimation and precise estimation have the same function of performing beamforming using DBF, but differ in the granularity of beamforming, i.e., the amount of beam movement using excitation coefficients. While the purpose can be achieved using precise estimation alone, there are problems such as an increase in the amount of memory required to store the DBF excitation coefficients and a long search time required to obtain a correct estimation result. Therefore, a rough search using coarse estimation is performed before precise estimation. The black circles in Figure 11 indicate the positions of interference waves. For example, if the coarse estimation unit 14 divides the target coverage area into nine beam areas x1y1 to x3y3 and identifies the beam area where an interference wave exists as beam area x2y1, the precise estimation unit 15 further divides the identified beam area x2y1 into nine finer beam areas x'1y'1 to x'3y'3, centered on the origin of x2y1, thereby improving the accuracy of estimating the direction of arrival. Note that although Figures 7 and 11 are the same diagram, Figure 7 shows the pattern received by each array element 11, while Figure 11 shows the beam pattern after beamforming of each array element 11 by DBF. For example, if the excitation coefficients of all elements except an arbitrary array element 11 are set to zero, the reception pattern of the array element 11 and the reception pattern of DBF will be the same, and therefore the same diagram is used for convenience.

[0037] The operation of the estimation unit 13 will be described using the example shown in FIG. 11 . The coarse estimation unit 14 inputs the signal output by the element selection unit 12 to the coarse DBFs 16-1 to 16-m. Each of the coarse DBFs 16-1 to 16-m calculates the received power of a beam directed toward each of the nine beam areas x1y1 to x3y3, which are obtained by dividing the target coverage area. The coarse DBFs 16-1 to 16-m output the calculated received power to the averaging unit 17. The averaging unit 17 averages the received power output by the coarse DBFs 16-1 to 16-m and outputs the averaged received power to the maximum value search unit 18. The maximum value search unit 18 searches for the maximum received power among the received powers of the beam areas output by the averaging unit 17. The maximum value search unit 18 outputs information indicating the beam area with the maximum received power to the coefficient calculation unit 19 of the precise estimation unit 15.

[0038] The coefficient calculation unit 19 calculates DBF excitation coefficients for the fine DBFs 20-1 to 20-n. Each of the fine DBFs 20-1 to 20-n calculates the received power of a beam directed toward each of the beam areas x'1y'1 to x'3y'3, which are obtained by further dividing the beam area with the maximum received power estimated by the rough estimation unit 14 within the target coverage area. The fine DBFs 20-1 to 20-n output the calculated received power to the averaging unit 21. The averaging unit 21 averages the received powers output by the fine DBFs 20-1 to 20-n and outputs the averaged received power to the center of gravity calculation unit 22. The center of gravity calculation unit 22 calculates an estimated angle indicating the center of gravity corresponding to the source position of the interference wave, based on the received power corresponding to each beam area output by the averaging unit 21. The fine estimation unit 15 outputs an estimated angle, which is the estimated result of the direction of arrival.

[0039] As described above, according to the first embodiment, it is possible to provide relay station 2, which is a communication device comprising: received power measurement unit 121 that measures the received power of a plurality of signals received by array elements 11, which are a plurality of receiving antennas; combination selection unit 122 that selects some of the plurality of signals based on the received power; selector 123 that outputs the signal selected by combination selection unit 122; and estimation unit 13 that performs direction-of-arrival estimation processing to estimate the direction of arrival of an interference wave using the signal output by selector 123.

[0040] The received power measuring unit 121 may measure the received power of the frequency-divided signal for each array element 11, which is a receiving antenna, and for each frequency, and the combination selecting unit 122 may select a signal for each array element 11, which is a receiving antenna, and for each frequency, based on the received power.

[0041] The combination selection unit 122 can sequentially select the signal with the highest received power and select the signal with the next highest received power from among the signals received by the array elements 11 adjacent to the array element 11 corresponding to the selected signal, until the number of selected signals reaches a threshold value. Note that "adjacent array elements 11" means that the beam areas corresponding to the array elements 11 are adjacent to each other.

[0042] Furthermore, the combination selection unit 122 can sequentially select the signal with the highest received power from among the signals for each array element 11 and each frequency, and select the signal with the next highest received power from among the signals received by the receiving antenna adjacent to the array element 11 corresponding to the selected signal and having the same frequency as the selected signal, until the number of selected signals reaches a threshold value.

[0043] The threshold value for the number of selected signals may be determined in advance based on the coverage area of ​​the elementary beam, which is the beam pattern received by each array element 11.

[0044] The communication device including the direction-of-arrival estimation unit 50 may be a relay station 2 that functions as a receiving station that receives a signal transmitted from a control station 4, or may be a relay station 2 that relays a signal transmitted from a transmitting station 1 to a receiving station 3. The relay station 2 may also be mounted on a satellite. When mounted on a satellite such as a communication satellite, there are restrictions on the size of the device compared to devices installed on the ground, so application of the technology of this embodiment is particularly effective. However, the communication device to which the technology of this embodiment is applied is not limited to one mounted on a satellite.

[0045] Furthermore, according to the first embodiment, it is possible to provide an arrival direction estimation method including a received power measurement step of measuring the received power of a plurality of signals received by each of array elements 11, which are a plurality of receiving antennas; a combination selection step of selecting some of the plurality of signals based on the received power; and an estimation step of estimating the arrival direction of an interference wave using the signal selected in the combination selection step.

[0046] In the received power measurement step, the received power of the frequency-divided signal is measured for each receiving antenna and for each frequency, and in the combination selection step, a signal can be selected for each receiving antenna and for each frequency based on the received power.

[0047] Furthermore, in the combination selection step, the process of selecting the signal with the highest received power and selecting the signal with the next highest received power from among the signals received by the array element 11 adjacent to the array element 11 corresponding to the selected signal can be executed sequentially until the number of selected signals reaches a threshold value.

[0048] In the combination selection step, the signal with the highest received power is selected from among the signals for each array element 11 and each frequency, and the signal with the next highest received power is selected from among the signals received by an array element 11 adjacent to the array element 11 corresponding to the selected signal and having the same frequency as the selected signal. This process can be performed sequentially until the number of selected signals reaches a threshold value.

[0049] Furthermore, according to the first embodiment, it is possible to provide a control circuit 90 that controls a communication device having a plurality of array elements 11, and causes the communication device to execute a received power measurement step of measuring the received power of a plurality of signals received by each of the plurality of array elements 11, a combination selection step of selecting some of the plurality of signals based on the received power, and an estimation step of estimating the direction of arrival of an interference wave using the signal selected in the combination selection step.

[0050] Furthermore, according to the first embodiment, it is possible to provide a storage medium that stores a program for controlling a communication device having a plurality of array elements 11, wherein the program causes the communication device to execute a received power measurement step of measuring received power of a plurality of signals received by each of the plurality of array elements 11, a combination selection step of selecting some of the plurality of signals based on the received power, and an estimation step of estimating the direction of arrival of an interference wave using the signal selected in the combination selection step.

[0051] Here, the effect of the direction of arrival estimation unit 50 will be described using a comparative example. Fig. 12 is a diagram showing an example configuration of a communication system according to a first comparative example. The first comparative example is an example of Time Difference of Arrival (TDOA) and Frequency Difference of Arrival (FDOA), which is a method of estimating the direction of arrival using the frequency difference and time difference between two signals by receiving a signal transmitted from an interfering station at a receiving station via two relay stations.

[0052] The method of the first comparative example requires two or more relay stations, whereas the method of the arrival direction estimation unit 50 has the advantage of not having such a restriction. Also, in the method of the first comparative example, the arrival angle estimation process is performed at a terrestrial receiving station, which results in a large time lag between receiving an interference wave and dealing with it by nulling, whereas the method of the arrival direction estimation unit 50 can perform the arrival angle estimation process at relay station 2, which has the advantage of being able to shorten the time between receiving an interference wave and dealing with it by nulling compared to the first comparative example.

[0053] FIG. 13 is a diagram illustrating a configuration example of a direction-of-arrival estimation unit 55 according to a second comparative example. The direction-of-arrival estimation unit 55 has a configuration in which the element selection unit 12 is omitted from the direction-of-arrival estimation unit 50 according to the first embodiment. In this case, the estimation unit 13 processes all of the signals received by the multiple array elements 11 of the relay station 2. In this case, as the number of array elements 11 increases with an expansion of the coverage area, the amount of calculation increases, which poses a problem in that the processing power required to realize the function of the direction-of-arrival estimation unit 55 increases. In contrast, the direction-of-arrival estimation unit 50 has an element selection unit 12 between the array elements 11 and the estimation unit 13, which can limit the number of signals to be processed by the estimation unit 13. This makes it possible to reduce the amount of calculation and memory required for direction-of-arrival estimation.

[0054] In the second comparative example, when an interference wave and a desired wave are close to each other at the same time and frequency, there is a problem that the accuracy of estimating the direction of arrival may decrease. FIG. 14 is an explanatory diagram of the problem that occurs in the second comparative example. In FIG. 14, a black triangle represents a desired wave, and a black circle represents an interference wave. When an interference wave and a desired wave are close to each other at the same time and frequency, as shown in the upper part of FIG. 14, the coarse DBFs 16-1 to 16-m can detect signals in the same area. However, as shown in the lower part of FIG. 14, the fine DBFs 20-1 to 20-n detect the power of both the desired wave located at x'1y'2 and the interference wave located at x'3y'2, resulting in the highest received power at x'2y'2, which is intermediate between the desired wave and the interference wave. In the following second embodiment, a method that can maintain the accuracy of direction of arrival estimation even in an environment where such interference waves and desired waves coexist will be described.

[0055] 15 is a diagram illustrating an example of the functional configuration of an arrival direction estimation unit 51 according to a second embodiment. The arrival direction estimation unit 51 is provided in the relay station 2. The following mainly describes the parts that are different from the first embodiment, and a detailed description of the parts that are the same as those in the first embodiment will be omitted.

[0056] In addition to the configuration of the direction-of-arrival estimation unit 50, the direction-of-arrival estimation unit 51 has a frequency division unit 23 between the array element 11 and the element selection unit 12. The frequency division unit 23 divides the frequency of the signal received by the array element 11 into arbitrary sub-channels and outputs the signals for each frequency to the element selection unit 12.

[0057] Moreover, the direction-of-arrival estimator 51 has a precise estimator 15A instead of the precise estimator 15 of the first embodiment. The precise estimator 15A has a centroid and likelihood calculator 24 instead of the centroid calculator 22.

[0058] Here, the operation related to likelihood calculation in the precise estimation unit 15A will be described. Fig. 16 is a flowchart for explaining the flow of likelihood calculation in embodiment 2. Note that Fig. 16 mainly shows the parts related to likelihood calculation, and therefore omits parts unrelated to likelihood calculation. First, the frequency division unit 23 divides the signals received by each array element 11 into arbitrary sub-channels (step S301). The frequency division unit 23 outputs the divided signals to the element selection unit 12.

[0059] The element selection unit 12 performs element selection processing using the signal output from the frequency division unit 23 (step S302). Specifically, the element selection processing in step S302 is the element selection processing shown in Fig. 10. A detailed description thereof will be omitted here.

[0060] The estimation unit 13 executes a rough estimation process in the rough estimation unit 14 (step S303). Details of the rough estimation process are the same as those in the first embodiment, and therefore will not be described in detail here.

[0061] Next, the estimation unit 13 calculates the received power before and after the reference index in the precision estimation unit 15A (step S304). Here, the reference index is the direction-of-arrival estimated position in the rough estimation unit 14, and corresponds to x2y1 in the example of FIG. 11, for example. The precision estimation unit 15A changes the beam positions of the fine DBFs 20-1 to 20-n with finer accuracy based on the center position of the reference index x2y1, and calculates the received power from x'1y'1 to x'3y'3.

[0062] Thereafter, the precise estimation unit 15A calculates the center of gravity from the determined center position of each DBF and the calculated received power (step S305). The calculated center of gravity is reflected in the calculation of the excitation coefficient.

[0063] Furthermore, the received signals of each beam output from the fine DBFs 20-1 to 20-n of the precise estimation unit 15A are used to calculate the SIR (Signal-to-Interference Ratio) for each beam and frequency to generate likelihood information (step S306). Here, likelihood refers to the accuracy of the estimation result of the direction of arrival. Here, the SIR is calculated, and the lower the SIR, the higher the likelihood. For example, the likelihood level can be classified into "low," "medium," and "high" for each range of SIR values, and this classification can be used as likelihood information.

[0064] FIG. 17 is an explanatory diagram of likelihood information obtained in the second embodiment. Here, among the six subchannels with subchannel IDs #1 to #6, interference waves can be detected in subchannels #2 to #6, and desired waves can be detected in subchannels #4 and #5. In this case, the likelihood information for subchannels #4 and #5, where both desired waves and interference waves are detected, is "medium." The likelihood information for subchannels #2, #3, and #6, where only interference waves are detected, is "high." The likelihood information for subchannel #1, where neither desired waves nor interference waves are detected, is "low." Note that, while the likelihood information is shown here as indicating the level of likelihood in three levels, "low," "medium," and "high," the likelihood information is not limited to this example. The likelihood information may indicate the level of likelihood in two levels, or four or more levels. Alternatively, the likelihood information may be a numerical value indicating the likelihood.

[0065] The likelihood information may be a value averaged over an arbitrary time period, or the reliability of the likelihood information may be included as additional information using the variance in the time direction, i.e., the amount of fluctuation. Also, a method may be adopted in which the likelihood information and the estimated result of the direction of arrival are treated as multidimensional information of time and frequency, and the most likely result is estimated.

[0066] In the second embodiment, the hardware configuration of the arrival direction estimation unit 51 is the same as that in the first embodiment, and therefore a description thereof will be omitted here.

[0067] As described above, according to the second embodiment, in addition to the configuration of the relay station 2 that is the communication device according to the first embodiment, it is possible to provide a relay station 2 that includes a frequency dividing unit 23 that divides the frequency of a received signal, a received power measuring unit 121 that measures the received power of the frequency-divided signal for each array element 11 and for each frequency, a combination selecting unit 122 that selects a signal for each array element 11 and for each frequency based on the received power, and an estimating unit 13 that uses the signal to calculate the likelihood of the estimation result of the direction of arrival.

[0068] The estimation unit 13 can calculate the likelihood based on the signal-to-interference ratio of the signal for each array element 11 and each frequency.

[0069] Furthermore, according to the second embodiment, it is possible to provide a direction-of-arrival estimation method having the following features in addition to the features of the direction-of-arrival estimation method according to the first embodiment: The direction-of-arrival estimation method according to the second embodiment further includes a frequency division step of frequency-dividing a received signal, in which the received power of the frequency-divided signals is measured for each array element 11 and for each frequency in the received power measurement step, a signal is selected for each array element 11 and for each frequency based on the received power in the combination selection step, and the likelihood of the direction of arrival can be calculated using the signals in the estimation step.

[0070] In the estimation step, the likelihood can be calculated based on the signal-to-interference ratio of the signal for each array element 11 and each frequency.

[0071] The configurations shown in the above embodiments are examples of the contents of the present disclosure, and may be combined with other known technologies, and parts of the configurations may be omitted or modified within the scope of the gist of the present disclosure.

[0072] Various aspects of the present disclosure are summarized below as appendices.

[0073] (Supplementary Note 1) A communication device comprising: a received power measurement unit that measures received power of a plurality of signals received by each of a plurality of receiving antennas; a combination selection unit that selects a portion of the plurality of signals based on the received power; a selector that outputs the signals selected by the combination selection unit; and an estimation unit that performs a direction-of-arrival estimation process that estimates a direction of arrival of an interference wave using the signals output by the selector. (Supplementary Note 2) The communication device according to Supplementary Note 1, wherein the received power measurement unit measures the received power of the frequency-divided signals for each of the receiving antennas and for each frequency, and the combination selection unit selects a signal for each of the receiving antennas and for each frequency based on the received power. (Supplementary Note 3) The communication device according to Supplementary Note 1, comprising: a frequency division unit that divides the frequency of the received signals, wherein the received power measurement unit measures the received power of the frequency-divided signals for each of the receiving antennas and for each frequency, and the combination selection unit selects a signal for each of the receiving antennas and for each frequency based on the received power, and the estimation unit calculates a likelihood of the direction of arrival using the signals. (Supplementary Note 4) The communication device according to Supplementary Note 3, wherein the estimation unit calculates the likelihood based on a signal-to-interference ratio of the signal for each receiving antenna and for each frequency. (Supplementary Note 5) The communication device according to Supplementary Note 1, wherein the combination selection unit selects the signal with the highest received power and sequentially executes a process of selecting the signal with the next highest received power from among signals received by a receiving antenna adjacent to the receiving antenna corresponding to the selected signal, until the number of selected signals reaches a threshold. (Supplementary Note 6) The communication device according to any one of Supplementary Notes 2 to 4, wherein the combination selection unit selects the signal with the highest received power from among signals received by a receiving antenna adjacent to the receiving antenna corresponding to the selected signal and sequentially executes a process of selecting the signal with the next highest received power from among signals having the same frequency as the selected signal, until the number of selected signals reaches a threshold.(Supplementary Note 7) The communication device according to Supplementary Note 5 or 6, wherein the threshold value is determined in advance based on a coverage area of ​​a raw beam, which is a beam pattern received by each receiving antenna. (Supplementary Note 8) The communication device according to any one of Supplements 1 to 7, wherein the communication device is a receiving station that receives a signal transmitted from a transmitting station. (Supplementary Note 9) The communication device according to any one of Supplements 1 to 7, wherein the communication device is a relay station that relays a signal transmitted from a transmitting station to a receiving station. (Supplementary Note 10) The communication device according to any one of Supplements 1 to 9, wherein the communication device is mounted on a satellite. (Supplementary Note 11) An arrival direction estimation method comprising: a received power measurement step of measuring received power of a plurality of signals received by each of a plurality of receiving antennas; a combination selection step of selecting some of the plurality of signals based on the received power; and an estimation step of estimating an arrival direction of an interference wave using the signals selected by the combination selection step. (Supplementary Note 12) The arrival direction estimation method according to Supplementary Note 11, characterized in that in the received power measurement step, the received power of the frequency-divided signal is measured for each of the receiving antennas and for each frequency, and in the combination selection step, a signal is selected for each of the receiving antennas and for each frequency based on the received power. (Supplementary Note 13) The arrival direction estimation method according to Supplementary Note 11, characterized in that it further includes a frequency division step of frequency-dividing the received signal, wherein in the received power measurement step, the received power of the frequency-divided signal is measured for each of the receiving antennas and for each frequency, and in the combination selection step, a signal is selected for each of the receiving antennas and for each frequency based on the received power, and in the estimation step, a likelihood of the arrival direction is calculated using the signals. (Supplementary Note 14) The arrival direction estimation method according to Supplementary Note 13, characterized in that in the estimation step, the likelihood is calculated based on a signal-to-interference ratio of the signal for each of the receiving antennas and for each frequency.(Supplementary Note 15) The direction-of-arrival estimation method according to Supplementary Note 11, wherein in the combination selection step, a process of selecting the signal with the highest received power and selecting the signal with the next highest received power from among signals received by a receiving antenna adjacent to the receiving antenna corresponding to the selected signal is sequentially performed until the number of selected signals reaches a threshold. (Supplementary Note 16) The direction-of-arrival estimation method according to any one of Supplementary Notes 12 to 14, wherein in the combination selection step, a process of selecting the signal with the highest received power from among signals received by a receiving antenna adjacent to the receiving antenna corresponding to the selected signal and having the same frequency as the selected signal is sequentially performed until the number of selected signals reaches a threshold. (Supplementary Note 17) The direction-of-arrival estimation method according to Supplementary Note 15 or 16, wherein the threshold is predetermined based on a coverage area of ​​a raw beam, which is a beam pattern received by each receiving antenna. (Supplementary Note 18) A control circuit for controlling a communication device having a plurality of receiving antennas, the control circuit causing the communication device to execute the following steps: a received power measurement step of measuring received power of a plurality of signals received by each of the plurality of receiving antennas, a combination selection step of selecting a portion of the plurality of signals based on the received power, and an estimation step of estimating an arrival direction of an interference wave using the signals selected by the combination selection step. (Supplementary Note 19) A storage medium for storing a program for controlling a communication device having a plurality of receiving antennas, the program causing the communication device to execute the following steps: a received power measurement step of measuring received power of a plurality of signals received by each of the plurality of receiving antennas, a combination selection step of selecting a portion of the plurality of signals based on the received power, and an estimation step of estimating an arrival direction of an interference wave using the signals selected by the combination selection step.

[0074] 1 transmitting station, 2 relay station, 3 receiving station, 4 control station, 5 interfering station, 11 array element, 12 element selection unit, 13 estimation unit, 14 coarse estimation unit, 15, 15A precision estimation unit, 16-1 to 16-m coarse DBF, 17, 21 averaging unit, 18 maximum value search unit, 19 coefficient calculation unit, 20-1 to 20-n precision DBF, 22 centroid calculation unit, 23 frequency division unit, 24 centroid / likelihood calculation unit, 50, 51, 55 arrival direction estimation unit, 90 control circuit, 91 processor, 92 memory, 93 external interface, 94 processing circuit, 100 communication system, 121 received power measurement unit, 122 combination selection unit, 123 selector.

Claims

1. A communication device comprising: a received power measurement unit that measures the received power of multiple signals received by each of multiple receiving antennas; a combination selection unit that selects some of the multiple signals based on the received power; a selector that outputs the signal selected by the combination selection unit; and an estimation unit that performs arrival direction estimation processing to estimate the arrival direction of an interference wave using the signal output by the selector.

2. The communication device according to claim 1, characterized in that the received power measurement unit measures the received power of the frequency-divided signal for each receiving antenna and for each frequency, and the combination selection unit selects a signal for each receiving antenna and for each frequency based on the received power.

3. The communication device according to claim 1, further comprising: a frequency division unit that divides the received signal by frequency; wherein the received power measurement unit measures the received power of the frequency-divided signal for each receiving antenna and for each frequency; the combination selection unit selects a signal for each receiving antenna and for each frequency based on the received power; and the estimation unit calculates the likelihood of the direction of arrival using the signal.

4. The communication device according to claim 3, wherein the estimation unit calculates the likelihood based on a signal-to-interference ratio of the signal for each of the receiving antennas and each of the frequencies.

5. The communication device according to claim 1, characterized in that the combination selection unit sequentially selects the signal with the highest received power and selects the signal with the next highest received power from among the signals received by the receiving antenna adjacent to the receiving antenna corresponding to the selected signal, until the number of selected signals reaches a threshold value.

6. A communication device according to any one of claims 2 to 4, characterized in that the combination selection unit sequentially selects the signal with the highest received power from among the signals for each receiving antenna and each frequency, and selects the signal with the next highest received power from among signals received by a receiving antenna adjacent to the receiving antenna corresponding to the selected signal and having the same frequency as the selected signal, until the number of selected signals reaches a threshold value.

7. A communication device according to claim 5 or 6, characterized in that the threshold value is determined in advance based on the coverage area of ​​a beam, which is a beam pattern received by each receiving antenna.

8. The communication device according to any one of claims 1 to 7, wherein the communication device is a receiving station that receives a signal transmitted from a transmitting station.

9. The communication device according to any one of claims 1 to 7, wherein the communication device is a relay station that relays a signal transmitted from a transmitting station to a receiving station.

10. The communication device according to any one of claims 1 to 9, characterized in that the communication device is mounted on a satellite.

11. A method for estimating direction of arrival, comprising: a received power measurement step of measuring the received power of a plurality of signals received by each of a plurality of receiving antennas; a combination selection step of selecting a portion of the plurality of signals based on the received power; and an estimation step of estimating the direction of arrival of an interference wave using the signals selected by the combination selection step.

12. The method for estimating direction of arrival according to claim 11, characterized in that in the received power measurement step, the received power of the frequency-divided signal is measured for each of the receiving antennas and for each frequency, and in the combination selection step, a signal is selected for each of the receiving antennas and for each frequency based on the received power.

13. The method for estimating direction of arrival according to claim 11, further comprising: a frequency division step of frequency-dividing the received signal; wherein in the received power measurement step, the received power of the frequency-divided signal is measured for each receiving antenna and for each frequency; in the combination selection step, a signal is selected for each receiving antenna and for each frequency based on the received power; and in the estimation step, the likelihood of the direction of arrival is calculated using the signal.

14. The method for estimating direction of arrival according to claim 13, wherein in said estimating step, said likelihood is calculated based on a signal-to-interference ratio of said signal for each of said receiving antennas and each of said frequencies.

15. The method for estimating direction of arrival according to claim 11, characterized in that in the combination selection step, the signal with the highest received power is selected, and the signal with the next highest received power is selected from among the signals received by the receiving antennas adjacent to the receiving antenna corresponding to the selected signal, and this process is performed sequentially until the number of selected signals reaches a threshold value.

16. A method for estimating direction of arrival according to any one of claims 12 to 14, characterized in that in the combination selection step, the signal with the highest received power is selected from among the signals for each receiving antenna and each frequency, and the signal with the next highest received power is selected from among signals received by a receiving antenna adjacent to the receiving antenna corresponding to the selected signal and having the same frequency as the selected signal, and this process is performed sequentially until the number of selected signals reaches a threshold value.

17. The method for estimating direction of arrival according to claim 15 or 16, characterized in that the threshold value is determined in advance based on the coverage area of ​​a beam pattern received by each receiving antenna.

18. A control circuit for controlling a communication device having multiple receiving antennas, the control circuit causing the communication device to perform the following steps: a received power measurement step for measuring the received power of multiple signals received by each of the multiple receiving antennas; a combination selection step for selecting a portion of the multiple signals based on the received power; and an estimation step for estimating the direction of arrival of an interference wave using the signal selected by the combination selection step.

19. A storage medium storing a program for controlling a communication device having multiple receiving antennas, the program causing the communication device to execute the following steps: a received power measurement step for measuring the received power of multiple signals received by each of the multiple receiving antennas; a combination selection step for selecting a portion of the multiple signals based on the received power; and an estimation step for estimating the direction of arrival of an interference wave using the signal selected by the combination selection step.

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