JP7741519B2 - Direction of arrival estimation device and direction of arrival estimation method - Google Patents

Description

The present invention relates to a direction of arrival estimation device and a direction of arrival estimation method.

In wireless communications in high-frequency bands, beamforming is an essential function for expanding the coverage area. In existing systems, in order to direct beams from the base station to the terminal, feedback communication from the terminal, such as CSI (Channel State Information) feedback or beam scanning, is required, and improvements are desired from the perspective of realizing an efficient communication method. Therefore, attention is being paid to technology that achieves beamforming without the need for feedback from the terminal by performing DoA (Direction of Arrival) estimation using a Butler matrix (see, for example, Non-Patent Document 1).

In addition, there is technology for estimating the direction of arrival of radio waves in the 2.4 GHz radio frequency band using a beam selector, direct sequence code division multiple access (DS-CDMA), and a neural network (NN) (see, for example, Non-Patent Document 2). The beam selector uses a Butler matrix, which has the function of separating received power according to the angle at which the radio waves arrive. DS-CDMA has the function of multiplexing wireless communications from multiple users using direct sequence codes. The NN has the function of estimating the direction of arrival of propagation using the received power for each direction of arrival (DoA) of the radio waves obtained by the Butler matrix and DS-CDMA as inputs.

F. Muramatsu, K. Nishimori, R. Taniguchi, and T. Hiraguri, "Multi-Beam Massive MIMO with Beam-Selection Using Only Amplitude Information in Uplink Channel," in IEICE Transactions on Communications, Vol.E101-B, No.7, pp.1544-1551, July 2018, doi: 10.1587/transcom.2017CQP0005 K. A. Gotsis, K. Siakavara and J. N. Sahalos, "On the Direction of Arrival (DoA) Estimation for a Switched-Beam Antenna System Using Neural Networks," in IEEE Transactions on Antennas and Propagation, vol. 57, no. 5, pp. 1399-1411, May 2009, doi: 10.1109/TAP.2009.2016721.

The technology described in Non-Patent Document 2 above is a DoA estimation technique limited to the CDMA (Code Division Multiple Access) system. Because the received signals for each DoA used for estimation are acquired by switching switches connected to a Butler matrix, acquiring data for all DoAs requires the time required for the switches to be switched. In addition, the neural network used in the DoA estimation unit requires prior training, and it is expected that retraining will be necessary depending on the environment (location), for example.

In light of the above circumstances, the present invention aims to provide an arrival direction estimation device and arrival direction estimation method that can shorten the time required for estimation and estimate the arrival direction of radio waves regardless of the connection method.

One aspect of the present invention is an arrival direction estimation device that includes an antenna unit with multiple antenna elements; a Butler matrix circuit that receives signals wirelessly from each of the multiple antenna elements of the antenna unit, separates the received signals for each arrival direction, and outputs the signals from multiple output ports corresponding to each arrival direction; a power measurement unit that measures the received power of the signals output from each of the multiple output ports of the Butler matrix circuit; and an estimation unit that estimates the arrival direction of the radio waves of the signals based on a comparison between the received power of each of the multiple output ports measured by the power measurement unit and each of the power patterns indicating the received power of each of the multiple output ports.

One aspect of the present invention is a direction-of-arrival estimation method comprising: a receiving step in which a Butler matrix circuit receives signals wirelessly from each of a plurality of antenna elements, separates the received signals for each direction of arrival, and outputs the signals from a plurality of output ports corresponding to each direction of arrival; a power measurement step in which the received power of the signals output from each of the plurality of output ports of the Butler matrix circuit is measured; and an estimation step in which the received power of each of the plurality of output ports measured in the power measurement step is compared with a power pattern indicating the received power of each of the plurality of output ports, and the estimation step estimates the direction of arrival of the radio wave of the signal based on a comparison with each of the power patterns for each direction of arrival.

This invention shortens the time required for estimation and makes it possible to estimate the direction of arrival of radio waves regardless of the connection method.

1 is a block diagram showing the configuration of a communication system according to an embodiment of the present invention. FIG. 10 is a diagram showing an example of power pattern information according to the embodiment. FIG. 10 is a flowchart showing a terminal DoA estimation process of the base station according to the embodiment. FIG. 10 is a block diagram showing another configuration of the base station according to the embodiment.

Embodiments of the present invention will now be described in detail with reference to the drawings. Figure 1 is a block diagram showing the configuration of a communication system according to one embodiment of the present invention. The communication system has a base station 1 and a terminal 9. The base station 1 communicates with the terminal 9 wirelessly. Although only one terminal 9 is shown in Figure 1, any number of terminals 9 may be used. The terminal 9 is mobile.

Base station 1 is an example of a direction-of-arrival estimation device that estimates the direction of arrival of radio waves from terminal 9. Hereinafter, the direction of arrival of radio waves from terminal 9 will be referred to as terminal DoA. Base station 1 has N antennas 2 (N is an integer greater than or equal to 2), a Butler matrix circuit 3, a power meter 5, and a DoA estimation unit 6. The N antennas 2 will also be referred to as antennas 2-1 to 2-N.

Antenna 2 is an antenna element that transmits and receives wireless radio waves. Antenna 2 receives wireless signals from terminal 9 and outputs them to Butler matrix circuit 3. Butler matrix circuit 3 has N ports 4. These N ports 4 are also referred to as ports 4-1 to 4-N. Ports 4-1 to 4-N correspond to different DoAs, i.e., different reception directions. Butler matrix circuit 3 has the function of forming a beam for each port 4. When Butler matrix circuit 3 receives a signal wirelessly via antenna 2, it separates the power of the received signal by DoA (reception direction) and outputs the separated signal from port 4 corresponding to the signal's DoA. Power meter 5 has the function of deriving the power value of the received signal output from each port 4 of Butler matrix circuit 3. Hereinafter, the power value of the received signal output from port 4 will be referred to as the port 4 power value.

The DoA estimation unit 6 has the function of estimating the terminal DoA. Specifically, the DoA estimation unit 6 receives from the power meter 5 information on the power value of the radio signal separated by the Butler matrix circuit 3 for each port 4 for each DoA. The DoA estimation unit 6 estimates the terminal DoA with a resolution equal to or greater than the number of ports (number of beams) N of the Butler matrix circuit 3 by calculating a correlation coefficient between the received power value information for each port 4 and power pattern information for each DoA that has been prepared in advance. The power pattern information indicates a pattern consisting of the power values of each of ports 4-1 to 4-N. The DoA estimation unit 6 has a memory unit 7. The memory unit 7 stores power pattern information for each of the different types of DoA. The number of DoA types corresponds to the number of DoA measurement resolutions. Note that the memory unit 7 may be provided external to the DoA estimation unit 6.

The antenna unit consisting of antennas 2-1 to 2-N and the Butler matrix circuit 3 may be configured using a reflectarray antenna, a lens antenna with a different beam direction for each feed port, or other beam-selective antennas. The antenna unit consisting of antennas 2-1 to 2-N may also have a subarray configuration. The antenna unit may also be a linear array antenna or a two-dimensional array antenna. An existing two-dimensional Butler matrix can be used for the Butler matrix circuit 3.

The base station 1 may receive radio signals from the terminal 9 using the CDMA method, the TDMA (Time Division Multiple Access) method, or the FDMA (Frequency Division Multiple Access) method. Furthermore, when estimating the terminal DoA, the base station 1 and the terminal 9 may or may not be synchronized.

All or part of the functions of the DoA estimation unit 6 may be realized by a processor such as a CPU (central processing unit) or GPU (graphics processing unit) reading and executing a program from a memory unit included in the base station 1. Furthermore, all or part of the functions of the DoA estimation unit 6 may be realized using hardware such as an ASIC (application specific integrated circuit), a PLD (programmable logic device), or an FPGA (field programmable gate array).

FIG. 2 is a diagram showing an example of power pattern information stored in the storage unit 7. The power pattern information used in advance by the DoA estimation unit 6 for calculating the correlation coefficient indicates the power value patterns of the separated signals when the incoming signals for 180° directions are separated into the ports 4-1 to 4-N of the Butler matrix circuit 3. In the case of the power pattern information shown in FIG. 2, the number of power values in all the power pattern information is the number of ports 4 N times the DoA measurement resolution number. Note that the port number n (n is an integer between 1 and N) is port identification information indicating port 4-n. The DoAs corresponding to each piece of power pattern information may be one-dimensional (horizontal direction) or two-dimensional (horizontal direction + vertical direction). When the DoA measurement resolution number is M and the DoAs corresponding to the power pattern information are one-dimensional, the DoA types are, for example, _a1 , _a2 , ..., _aM in ascending order in the horizontal direction ( _a1 is 0° or more and _aM is 180° or less). When the DoA corresponding to the power pattern information is two-dimensional, the type of DoA is expressed by a combination of horizontal direction b _m and vertical direction c _m (m is an integer greater than or equal to 1 and less than or equal to M, and b _m and c _m are greater than or equal to 0° and less than or equal to 180°).

The power value of port 4 is expected to be higher for ports 4 corresponding to a DoA closer to the terminal DoA, which is the direction of arrival of the radio signal from terminal 9. For example, suppose a DoA (hereinafter referred to as DoA#n) corresponding to port 4-n (n is an integer between 1 and N) is adjacent to a DoA (hereinafter referred to as DoA#i) corresponding to port 4-i (i ≠ n, i is an integer between 1 and N). If the terminal DoA is between DoA#n and DoA#i, the power values of port 4-n and port 4-i are expected to be higher than the power values of other ports 4. Furthermore, if DoA#n is closer to the terminal DoA than DoA#i, the power value of port 4-n is expected to be higher than the power value of port 4-i. For simplicity, we have explained an example in which the terminal DoA is between the DoAs corresponding to two ports 4, but the same applies when the terminal DoA is between the DoAs corresponding to three or more ports 4. In this way, by taking advantage of the fact that the power value of ports 4 corresponding to DoAs closer to the terminal DoA is higher, the DoA measurement resolution number can be made larger than the number N of ports 4.

Figure 3 is a flow diagram showing the terminal DoA estimation process of the base station 1. The base station 1 repeatedly executes the terminal DoA estimation process shown in Figure 3. For example, the base station 1 may set the start trigger for the terminal DoA estimation process to a regular periodic interval, or may synchronize with the movement speed of the terminal 9.

The antenna 2 receives the radio signal and outputs it to the Butler matrix circuit 3 (step S1). The Butler matrix circuit 3 inputs the radio signal received by each antenna 2 and separates and outputs the input radio signal to each port 4 for each DoA (step S2). The power meter 5 measures the power value of the signal output from each port 4 of the Butler matrix circuit 3 (step S3). The power meter 5 outputs measurement result information that associates the port number with the power value of the signal output from the port 4 of that port number to the DoA estimation unit 6. The power meter 5 may also set the measurement time in the measurement result information.

After acquiring the power values of each port 4 from the measurement result information, the DoA estimation unit 6 calculates a correlation coefficient between the information arranging the power values of each port 4 and each piece of power pattern information stored in the memory unit 7 (step S4). The DoA estimation unit 6 estimates the terminal DoA based on the calculated correlation coefficient (step S5). For example, the DoA estimation unit 6 obtains the DoA corresponding to the power pattern information whose correlation coefficient value is equal to or greater than a threshold value as the terminal DoA estimation result. Furthermore, if the number of simultaneous connections of the terminal 9 is known, the DoA estimation unit 6 may select the same number of power pattern information as the number of simultaneous connections in descending order of correlation coefficient value, and obtain the DoA corresponding to each selected power pattern information as the terminal DoA estimation result. The DoA estimation unit 6 may write information associating the time at which the estimation result was obtained or the measurement time set in the measurement result information with the terminal DoA estimation result to the memory unit 7.

When the base station 1 and multiple terminals 9 are asynchronous and the multiple terminals 9 do not emit radio waves at the same time and in the same frequency band, the DoA estimation unit 6 can estimate the terminal DoAs of the multiple terminals 9. Examples of this include transmission using TDMA or FDMA. In this case, the terminal 9 identification does not need to be set in the wireless signal. In the case of FDMA, each terminal 9 transmits a wireless signal using a different frequency within the same frequency band. The power meter 5 measures the power value of the signal in that frequency band. As a result of the measurement, a peak appears in the power value of port 4 corresponding to a DoA close to the terminal DoA of each terminal 9. Therefore, power pattern information with a high correlation coefficient is obtained for each terminal 9. In addition, in the case of FDMA, the power meter 5 may measure the signal power value for each frequency used by each terminal 9. The DoA estimation unit 6 obtains the terminal DoA based on the results of calculating the correlation coefficient between the information arranging the power values of each port 4 for each frequency and each power pattern information.

Note that if multiple terminals 9 emit radio waves at the same time in the same frequency band, some of the radio signals may cancel each other out due to frequency amplitude, making it impossible to estimate the terminal DoA. This is because power values are measured based on frequency amplitude, but phase information is not used. Furthermore, if synchronization between the base station 1 and multiple terminals 9 is established, a code identifying each terminal 9 may be included in the wireless frame. In this case, the DoA estimation unit 6 may write information in the memory unit 7 that associates the terminal 9 code obtained from the received wireless frame with the estimated terminal DoA of that terminal 9 and the time.

The base station 1 may further include a speed estimation unit. The speed estimation unit is a functional unit that estimates the moving speed of the terminal 9 based on the results of multiple terminal DoA estimations by the DoA estimation unit 6. For example, the speed estimation unit estimates the moving speed of the terminal 9 based on the difference in the time at which the terminal DoA was estimated and the difference in the angle of the estimated terminal DoA. Note that if the received signal contains the code of the terminal 9, the speed estimation unit estimates the moving speed using the terminal DoA estimated by the DoA estimation unit 6 at a different time for the terminal 9 with the same code. For example, the speed estimation unit reads information on the terminal DoA of the terminal 9 with the same code and information on the time at which the estimation was performed from the memory unit 7 and uses this information to estimate the moving speed.

The base station 1 may adjust the start trigger period of the DoA estimation process shown in Figure 2 to match the speed of the terminal 9 estimated by the speed estimation unit.

The port 4 for measuring power may also be switched over time. Figure 4 shows the configuration of the base station 1a. In Figure 4, parts identical to those in the base station 1 shown in Figure 1 are designated by the same reference numerals, and their description will be omitted. The base station 1a shown in Figure 4 differs from the base station 1 shown in Figure 1 in that it further includes a beam selector 8. The beam selector 8 switches between the ports 4 of the Butler matrix circuit 3 one port at a time and sends the received signal output from the port 4 to the power meter 5. Alternatively, the beam selector 8 may switch the received signal sent to the power meter 5 in units of multiple ports 4. In this way, the number of signals for which the power meter 5 simultaneously measures the power value can be reduced. In this case, additional switching time is required before the power values of all ports 4 are measured. The beam selector 8 may also arbitrarily select a portion of the ports 4 of the Butler matrix circuit 3 and send only the received signal output from the arbitrarily selected port 4 to the power meter 5. By storing power pattern information in the memory unit 7 corresponding to the case where the received power from a port 4 of the Butler matrix circuit 3 selected arbitrarily by the beam selector 8 is used instead of power pattern information corresponding to the case where the received power from all ports 4 is used, the amount of calculation required by the DoA estimator 6 to estimate the terminal DoA can be reduced. For example, when the terminal 9 is moving at high speed and it is acceptable to perform terminal DoA estimation with reduced resolution, the base station 1a equipped with the beam selector 8 is used. Note that it may be possible to switch between operating the beam selector 8 and not operating the beam selector 8 and sending the output from all ports 4 to the power meter 5. Other operations of the base station 1a are the same as those of the base station 1.

The base station of this embodiment described above has the following features. Specifically, the base station can estimate terminal DoA regardless of the multiple access method, such as CDMA, TDMA, or FDMA. Furthermore, the base station can simultaneously acquire received signals from all ports of the Butler matrix circuit without delay and use all or some of them to estimate terminal DoA. This eliminates the need for Butler matrix circuit switching, thereby speeding up the estimation process. Furthermore, terminal DoA can be estimated accurately even when the terminal is moving. Additionally, the base station can estimate DoA with a resolution equal to or greater than the number of ports (beams) of the Butler matrix circuit, without the need for pre-training for each environment, as in machine learning. Furthermore, unlike neural networks, there is no need to optimize settings for each different wireless propagation environment, making it easy to apply to practical operations.

According to the embodiment described above, the direction of arrival estimation device includes an antenna unit, a Butler matrix circuit, a power measurement unit, and an estimation unit. The direction of arrival estimation device corresponds, for example, to base stations 1 and 1a in the embodiments. The antenna unit includes multiple antenna elements. The Butler matrix circuit receives signals wirelessly from each of the multiple antenna elements of the antenna unit, separates the input signals for each direction of arrival (reception direction), and outputs them from multiple output ports corresponding to each direction of arrival. The output port corresponds, for example, to port 4 in the embodiments. The power measurement unit measures the received power of the signals output from each of the multiple output ports of the Butler matrix circuit. The power measurement unit corresponds, for example, to power meter 5 in the embodiments. The estimation unit estimates the direction of arrival of the radio wave of the signal based on a comparison between the received power of each of the multiple output ports measured by the power measurement unit and the power pattern for each direction of arrival. The power pattern indicates the received power of each of the multiple output ports. The estimation unit corresponds, for example, to DoA estimation unit 6 in the embodiments.

The estimation unit may calculate an estimated moving speed of the device that transmitted the signal based on the direction of arrival estimated at different times. In this case, the estimation unit corresponds to, for example, the speed estimation unit of the embodiment.

The direction-of-arrival estimation device may further include a selection unit. The selection unit corresponds, for example, to the beam selection unit 8 in the embodiment. The selection unit selects some of the multiple output ports of the Butler matrix circuit and outputs the signals output from the selected output ports to the power measurement unit while switching between the selected output ports.

The antenna unit receives wireless signals transmitted from multiple terminals using code division multiple access, time division multiple access, or frequency division multiple access. The antenna unit may also be a linear array antenna or a two-dimensional array antenna.

The functions of the estimation unit of the direction of arrival estimation device described above may be implemented by a computer. In this case, a program for implementing the functions of the estimation unit may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be read and executed by a computer system. The computer system may include hardware such as a processor, an OS, and peripheral devices. The program of the estimation unit may be recorded on a computer-readable recording medium. Examples of computer-readable recording media include portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, and storage devices such as hard disks built into a computer system. The program of the estimation unit of the direction of arrival estimation device may be transmitted via a telecommunications line.

The above describes an embodiment of the present invention with reference to the drawings, but it is clear that the above embodiment is merely an example of the present invention and that the present invention is not limited to the above embodiment. Therefore, components may be added, omitted, substituted, or otherwise modified without departing from the technical spirit and scope of the present invention.

1, 1a Base Station 2-1 to 2-N Antenna 3 Butler Matrix Circuit 4-1 to 4-N Port 5 Power Meter 6 DoA Estimation Unit 7 Memory Unit 8 Beam Selection Unit 9 Terminal

Claims (6)

an antenna unit including a plurality of antenna elements;
a Butler matrix circuit that receives signals wirelessly from each of a plurality of antenna elements of the antenna unit, separates the received signals for each direction of arrival, and outputs the separated signals from a plurality of output ports corresponding to the respective directions of arrival;
a selection unit that switches between outputting the signals from some of the plurality of output ports of the Butler matrix circuit or outputting the signals from all of the output ports;
a power measurement unit that measures the received power of the signal output from the selection unit among the signals output from each of the plurality of output ports of the Butler matrix circuit;
an estimation unit that estimates the direction of arrival of radio waves of the signal based on a comparison between the received power of each of some or all of the plurality of output ports measured by the power measurement unit and a power pattern indicating the received power of each of some or all of the plurality of output ports, and each of the power patterns for each direction of arrival;
An arrival direction estimation device comprising: the estimation unit calculates an estimated moving speed of the device that transmitted the signal based on a difference between angles of the arrival directions estimated at different times and the difference between the different times .
The direction of arrival estimation device according to claim 1 . a selection unit that selects some of the plurality of output ports of the Butler matrix circuit, and outputs the signal output from the selected output port to the power measurement unit while switching the selected output port;
The direction of arrival estimation device according to claim 1 . the antenna unit receives wireless signals transmitted from a plurality of terminals by a code division multiple access method, a time division multiple access method, or a frequency division multiple access method;
The direction-of-arrival estimation device according to any one of claims 1 to 3. The antenna unit is a linear array antenna or a two-dimensional array antenna.
The direction-of-arrival estimation device according to any one of claims 1 to 3. a receiving step in which a Butler matrix circuit receives signals wirelessly received by each of a plurality of antenna elements, separates the received signals for each direction of arrival, and outputs the separated signals from a plurality of output ports corresponding to the respective directions of arrival;
a selection step of switching between outputting the signals from some of the plurality of output ports of the Butler matrix circuit or outputting the signals from all of the output ports;
a power measurement step of measuring the received power of the signal output in the selection step among the signals output from each of the plurality of output ports of the Butler matrix circuit;
an estimation step of estimating the direction of arrival of radio waves of the signal based on a comparison between the received power of each of some or all of the plurality of output ports measured in the power measurement step and a power pattern indicating the received power of each of some or all of the plurality of output ports, the power pattern being for each direction of arrival;
A direction of arrival estimation method comprising: