Base station device, terminal device, and wireless communication method

Abstract

This base station device comprises: a selection unit which selects a predetermined transmission precoding matrix indicator (TPMI) when a terminal device is present in a line-of-sight environment; and a communication unit which transmits the TPMI selected by the selection unit to the terminal device at each transmission time.

Description

Base station device, terminal device, and wireless communication method

[0001] This application claims priority to Japanese Patent Application No. 2023-163649, filed on September 26, 2023, the contents of which are incorporated herein by reference.

[0002] In the uplink, a base station apparatus selects a transmission precoding matrix indicator (TPMI) index from a codebook based on an uplink reference signal transmitted by a terminal apparatus, and notifies the terminal apparatus of the selected index. The terminal apparatus performs precoding based on the TPMI index notified from the base station apparatus (see, for example, Non-Patent Document 1). The base station apparatus selects a TPMI index from the codebook based on the uplink reference signal transmitted by the terminal apparatus, regardless of the environment in which the terminal apparatus exists.

[0003] Regarding wireless communication systems, there is known a technique for determining whether a system is in a line-of-site (LoS) environment or a non-line-of-sight (NLoS) environment (see, for example, Non-Patent Document 2).

[0004] 3GPP (registered trademark), TS 38.211, NR; Physical channels and modulation, v17.5.0, 6.3.1.5 PrecodingChen Huang, Andreas F. Molisch, Ruisi He, Rui Wang, Pan Tang, Bo Ai, and Zhangdui Zhong, “Machine Learning-Enabled LOS / NLOS Identification for MIMO Systems in Dynamic Environments,” IEEE Transactions on Wireless Communications, vol. 19, NO. 6, pp. 3643-3657, June 2020

[0005] A base station apparatus estimates a propagation channel matrix using an uplink reference signal transmitted by a terminal apparatus, and acquires a left singular matrix and a right singular matrix by performing singular value decomposition on the estimated propagation channel matrix. If the base station apparatus were to feed back the right singular matrix to the terminal apparatus as a precoder, the amount of calculation required for singular value decomposition and the amount of data fed back would increase. An example of an objective of the present disclosure is to provide a base station apparatus, a terminal apparatus, and a wireless communication method that can reduce the overhead of the amount of calculation required for selecting a codebook that the base station apparatus feeds back to the terminal apparatus.

[0006] (1) One aspect of the present disclosure is a base station device including: a selection unit that selects a predetermined transmission precoding matrix indicator (TPMI) when a terminal device is in a line-of-sight environment; and a communication unit that transmits the TPMI selected by the selection unit to the terminal device at each transmission time. (2) One aspect of the present disclosure is the base station device described in (1) above, wherein the communication unit receives a physical uplink control channel transmitted by the terminal device, and the base station device further includes a determination unit that determines whether the physical uplink control channel received by the communication unit includes information indicating a line-of-sight environment and information indicating a transmission time, and the selection unit selects the predetermined TPMI when the determination unit determines that the physical uplink control channel includes the information indicating a line-of-sight environment, and the communication unit transmits the TPMI selected by the selection unit to the terminal device at each transmission time. (3) In one aspect of the present disclosure, the base station apparatus according to (1) above further includes a determination unit that determines whether the terminal apparatus is in a line-of-sight environment based on an uplink reference signal transmitted by the terminal apparatus, and the selection unit selects the predetermined TPMI when the determination unit determines that the terminal apparatus is in a line-of-sight environment. (4) In one aspect of the present disclosure, the base station apparatus according to (1) above further includes a uniform rectangular array antenna, and the communication unit transmits the TPMI from the uniform rectangular array antenna to the terminal apparatus equipped with the uniform rectangular array antenna. (5) In one aspect of the present disclosure, the base station apparatus according to (1) above further includes a uniform circular array antenna, and the communication unit transmits the TPMI from the uniform circular array antenna to the terminal apparatus equipped with the uniform circular array antenna.

[0007] (6) One aspect of the present disclosure is a terminal device including: a determination unit that determines whether a base station device is in a line-of-sight environment based on a downlink reference signal; a signal generation unit that generates, when the determination unit determines that the base station device is in a line-of-sight environment, a feedback signal for the base station device, including information indicating the line-of-sight environment and information indicating a transmission time; and a communication unit that transmits the feedback signal generated by the signal generation unit to the base station device. (7) One aspect of the present disclosure is the terminal device described in (6) above, wherein the signal generation unit generates the feedback signal by including, in uplink control information of a physical uplink control channel, the information indicating the line-of-sight environment and information indicating the transmission time. (8) One aspect of the present disclosure is the terminal device described in (6) above, wherein the signal generation unit generates the feedback signal by including, in uplink control information of a physical uplink control channel, the information indicating the line-of-sight environment and information indicating the transmission time. (9) According to an aspect of the present disclosure, the terminal device according to (6) above further includes a uniform rectangular array antenna, wherein the communication unit receives, via the uniform rectangular array antenna, a transmission precoding matrix indicator (TPMI) transmitted by the base station device equipped with the uniform rectangular array antenna. (10) According to an aspect of the present disclosure, the terminal device according to (6) above further includes a uniform circular array antenna, wherein the communication unit receives, via the uniform circular array antenna, the transmission precoding matrix indicator (TPMI) transmitted by the base station device equipped with the uniform circular array antenna.

[0008] (11) One aspect of the present disclosure is a wireless communication method executed by a base station device, the method including: selecting a transmission precoding matrix indicator (TPMI) that is predetermined when a terminal device is in a line-of-sight environment; and transmitting the TPMI selected in the selecting step to the terminal device for each transmission time. (12) One aspect of the present disclosure is a wireless communication method executed by a terminal device, the method including: determining, based on a downlink reference signal, whether the base station device is in a line-of-sight environment; and, when it is determined in the determining step that the base station device is in a line-of-sight environment, generating a feedback signal for the base station device, the feedback signal including information indicating the line-of-sight environment and information indicating a transmission time; and transmitting the feedback signal generated in the generating step to the base station device.

[0009] According to the present disclosure, as an example, it is possible to provide a base station apparatus, a terminal apparatus, and a wireless communication method that can reduce the overhead of the amount of calculation required for selecting a codebook that the base station apparatus feeds back to the terminal apparatus.

[0010] FIG. 1 is a diagram showing an example of the configuration of a wireless communication system according to the present embodiment. FIG. 2 is a diagram showing a base station device and a terminal device included in the wireless communication system according to the present embodiment. FIG. 3 is a diagram showing an example of antennas provided in the base station device and the terminal device according to the present embodiment. FIG. 4 is a diagram showing an example of operation of the wireless communication system according to the present embodiment. FIG. 5 is a diagram showing another example of antennas provided in the base station device and the terminal device according to the present embodiment. FIG. 6 is a diagram showing a base station device and a terminal device included in a wireless communication system according to a first modification of the embodiment. FIG. 7 is a diagram showing an example of operation of the wireless communication system according to the first modification of the embodiment. FIG. 8 is a diagram showing a base station device and a terminal device included in a wireless communication system according to a second modification of the embodiment. FIG. 9 is a diagram showing an example of operation of the wireless communication system according to the second modification of the embodiment.

[0011] Next, a base station device, a terminal device, and a wireless communication method according to the present embodiment will be described with reference to the drawings. The embodiment described below is merely an example, and the embodiment to which the present disclosure is applied is not limited to the following embodiment. In all drawings used to describe the embodiment, the same reference numerals are used for components having the same functions, and repeated description is omitted. Furthermore, "based on XX" in this application means "based on at least XX," and includes cases where the element is based on XX and other elements. Furthermore, "based on XX" is not limited to cases where XX is directly used, but also includes cases where the element is based on XX after calculation or processing. "XX" is any element (for example, any information).

[0012] (Wireless Communication System Configuration) Fig. 1 is a diagram showing an example of the configuration of a wireless communication system according to this embodiment. An example of the wireless communication system 1 is a cellular communication system (mobile communication network) of a fifth generation mobile communication system (5G). However, the wireless communication system 1 is not limited to this, and may be, for example, a successor cellular communication system after 5G, or a wireless communication system other than a cellular system. The wireless system 1 is configured to include a base station device 100 and a terminal device 200.

[0013] The base station device 100 and the terminal device 200 perform wireless communication. The base station device 100 performs MIMO (Multi-Input Multi-Output) transmission between the base station device 100 and the terminal device 200 using a modulation method such as phase shift keying or quadrature phase amplitude modulation. An example of a phase shift keying method is BPSK (Quadrature phase-shift keying), and an example of quadrature phase amplitude modulation is 16QAM (16 Quadrature Amplitude Modulation). The base station device 100 and the terminal device 200 each have multiple antennas, and transmit signals by multiplexing multiple streams (MIMO layers) according to the number of antennas.

[0014] When the terminal device 200 is in a line-of-sight environment, the base station device 100 selects a transmission precoding matrix indicator (hereinafter referred to as TPMI) index associated with a predetermined precoder. The base station device 100 transmits the selected TPMI index to the terminal device 200 at each transmission time Ts. A line-of-sight environment refers to, for example, an environment in which there are no obstructions between transmission and reception and communication is possible via direct waves, or an environment in which the transmission point is visible to the reception point. Note that in the present disclosure, the phrase "selecting / transmitting / receiving a TPMI index" is used, but this refers to selecting / transmitting / receiving a TPMI.

[0015] (Base Station Device) Fig. 2 is a diagram showing a base station device and a terminal device included in the wireless communication system according to this embodiment. Details of the base station device 100 will be described with reference to Fig. 2. The base station device 100 includes antennas 101-1 to 101-j (j is an integer greater than 1), a communication unit 102, a channel estimation unit 104, a selection unit 106, and a storage unit 110. The antennas 101-1 to 101-j transmit and receive radio signals to and from the terminal device 200. An example of the antennas 101-1 to 101-j is a uniform rectangular array (URA (Uniform Rectangular Array)) antenna.

[0016] 3 is a diagram showing an example of antennas provided in a base station device and a terminal device according to this embodiment. Antennas 101-1 to 101-j are arranged two-dimensionally in a square on a substrate (not shown) to form a URA antenna. For example, in the orthogonal x-axis and y-axis directions, antennas 101-1 to 101-j are arranged at a first distance wTX in the x-axis direction and at a second distance hTX in the y-axis direction. As an example, a case where j is 4 will be described. In this case, antennas 101-1 to 101-4 are arranged two-dimensionally in a square on a substrate (not shown) to form a URA antenna. In the example shown in FIG. 3 , two pairs of antenna elements (antennas 101-1 and 101-2, and antennas 101-3 and 101-4) are arranged in the orthogonal x-axis and y-axis directions, with a first distance wTX between them in the x-axis direction, and two pairs of antenna elements (antennas 101-1 and 101-3, and antennas 101-2 and 101-4) are arranged in the y-axis direction with a second distance hTX between them. FIG. 3 also shows the center 101-C of the URA antenna. The first distance wTX and the second distance hTX are arbitrary and may be different. An example of the first distance wTX and the second distance hTX is half the wavelength λ1 (half wavelength: λ1 / 2), which is the wavelength with the highest intensity among the wavelengths included in the electromagnetic waves transmitted from the terminal device 200. Returning to FIG. 2 , we will continue the explanation.

[0017] The communication unit 102 includes a receiving circuit that receives radio signals (radio waves) from the multiple antennas 101-1 to 101-j and converts them into electrical signals, and a transmitting circuit that converts the electrical signals into radio signals (radio waves) and transmits them from the multiple antennas 101-1 to 101-j. The storage unit 110 is realized by a hard disk drive (HDD), flash memory, random access memory (RAM), read-only memory (ROM), or the like. The storage unit 110 stores a codebook 108. The codebook 108 associates multiple codebooks (precoders) that can be set on the antenna of the terminal device 200 on the base station device 100 side with TPMI indices corresponding to each of the multiple precoders. For example, each of the multiple precoders is represented by a 4x4 matrix and classified into ranks 1 to 4.

[0018] The channel estimation unit 104 estimates a propagation channel matrix by performing channel estimation based on the uplink reference signal received by the communication unit 102. The channel estimation unit 104 acquires a left singular matrix and a right singular matrix by singular value decomposition of the estimated result of the propagation channel matrix. In a line-of-sight environment, the channel estimation unit 104 suspends channel estimation for a certain period because channel fluctuations are small. The selection unit 106 acquires the right singular matrix from the channel estimation unit 104, selects a precoder from the codebook 108 based on the acquired right singular matrix, and selects a TPMI index associated with the selected precoder. For example, the selection unit 106 selects a precoder so as to maximize channel capacity. However, when line-of-sight between the terminal device 200 and the base station device 100 is ensured, that is, when the terminal device 200 is in a line-of-sight environment, the selection unit 106 selects a TPMI index associated with a predetermined precoder. For example, the selection unit 106 may determine whether the terminal device 200 is present in a line-of-sight environment based on video data from the base station device 100. Furthermore, the selection unit 106 may select a precoder included in rank 3 or a precoder included in rank 4.

[0019] The signal generation unit 107 generates a downlink signal. Specifically, the signal generation unit 107 acquires the TPMI index selected by the selection unit 106, and generates a feedback signal including the acquired TPMI index. The signal generation unit 107 also generates a downlink reference signal. The communication unit 102 transmits the feedback signal generated by the signal generation unit 107 from the antennas 101-1 to 101-j to the terminal device 200 every transmission time Ts. The transmission time Ts may be set in advance. An example of the transmission time Ts is a time longer than the time interval at which the downlink reference signal is transmitted.

[0020] The channel estimation unit 104, the selection unit 106, and the signal creation unit 107 are realized, for example, by a hardware processor such as a CPU (Central Processing Unit) executing a computer program (software) stored in the storage unit 110. Furthermore, some or all of these functional units may be realized by hardware (circuitry; including circuitry) such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a GPU (Graphics Processing Unit), or may be realized by a combination of software and hardware.

[0021] (Terminal Device) The details of the terminal device 200 will be described with reference to Fig. 2. The terminal device 200 includes antennas 201-1 to 201-k (k is an integer greater than 1), a communication unit 202, a precoding unit 204, a signal creation unit 207, and a storage unit 210. The antennas 201-1 to 201-k transmit and receive radio signals to and from the base station device 100. An example of the antennas 201-1 to 201-k is a uniform rectangular array antenna.

[0022] An example of antennas 201-1 to 201-k will be described with reference to FIG. 3. Antennas 201-1 to 201-k are arranged two-dimensionally in a square on a substrate (not shown) to form a URA antenna. For example, in the orthogonal x-axis and y-axis directions, antennas 201-1 to 201-k are arranged a first distance wRX apart in the x-axis direction and a second distance hRX apart in the y-axis direction. As an example, a case where k is 4 will be described. Antennas 201-1 to 201-4 are arranged two-dimensionally in a square on a substrate (not shown) to form a URA antenna. In the example shown in FIG. 3, two pairs of antenna elements (antennas 201-1 and 201-2, and antennas 201-3 and 201-4) are arranged in the orthogonal x-axis and y-axis directions, with a first distance wRX between them, and two pairs of antenna elements (antennas 201-1 and 201-3, and antennas 201-2 and 201-4) are arranged in the y-axis direction with a second distance hRX between them. FIG. 3 also shows the center 201-C of the URA antenna. The first distance wRX and the second distance hRX are arbitrary and may be different. An example of the first distance wRX and the second distance hRX is half the wavelength λ2 (half wavelength: λ2 / 2), which is the wavelength with the highest intensity among the wavelengths contained in the electromagnetic waves transmitted from the base station device 100. Returning to FIG. 2, the explanation will continue.

[0023] The communication unit 202 includes a receiving circuit that receives wireless signals (radio waves) from the plurality of antennas 201-1 to 201-k and converts them into electrical signals, and a transmitting circuit that converts the electrical signals into wireless signals (radio waves) and transmits them from the plurality of antennas 201-1 to 201-k. The storage unit 210 is realized by a HDD, flash memory, RAM, ROM, etc. The storage unit 210 stores a code book 208. The code book 208 is similar to the code book 108.

[0024] The precoding unit 204 acquires a feedback signal received by the communication unit 202. The precoding unit 204 acquires a precoder associated with the TPMI index included in the acquired feedback signal from the codebook 208 in the storage unit 210. The precoding unit 204 performs precoding for the multiple antennas 201-1 to 201-k based on the acquired precoder. The signal generation unit 207 generates uplink signals. Specifically, the signal generation unit 207 generates an uplink reference signal, a physical uplink control channel, a physical uplink shared channel, and the like. The communication unit 202 transmits the uplink signals generated by the signal generation unit 207 to the base station device 100 from the multiple antennas 201-1 to 201-k.

[0025] The precoding unit 204 and the signal creation unit 207 are realized, for example, by a hardware processor such as a CPU executing a computer program (software) stored in the storage unit 210. Furthermore, some or all of these functional units may be realized by hardware (including circuitry) such as an LSI, ASIC, FPGA, or GPU, or may be realized by a combination of software and hardware.

[0026] (Operation of Wireless Communication System) Fig. 4 is a diagram showing an example of operation of the wireless communication system according to this embodiment. With reference to Fig. 4, the operation when the terminal device 200 is in a line-of-sight environment with respect to the base station device 100 will be described.

[0027] (Step S1-1) In the base station device 100, the selection unit 106 selects a TPMI index associated with a predetermined precoder because the terminal device 200 is in a line-of-sight environment. (Step S2-1) In the base station device 100, the signal creation unit 107 acquires the TPMI index selected by the selection unit 106, and creates a downlink feedback signal. (Step S3-1) In the base station device 100, the communication unit 102 acquires the feedback signal created by the signal creation unit 107, and transmits it to the terminal device 200 from the antennas 101-1 to 101-j.

[0028] (Step S4-1) In the terminal device 200, the communication unit 202 receives a feedback signal transmitted by the base station device 100. The precoding unit 204 acquires the feedback signal received by the communication unit 202, and acquires a precoder associated with the TPMI index included in the acquired feedback signal from the codebook 208 in the storage unit 210. The precoding unit 204 performs precoding on the multiple antennas 201-1 to 201-k based on the acquired precoder.

[0029] (Step S5-1) After a transmission time Ts has elapsed since step S1-1, in the base station device 100, the selection unit 106 selects a TPMI index associated with a predetermined precoder when the terminal device 200 is in a line-of-sight environment. (Step S6-1) In the base station device 100, the signal creation unit 107 acquires the TPMI index selected by the selection unit 106, and creates a downlink feedback signal. (Step S7-1) In the base station device 100, the communication unit 102 acquires the feedback signal created by the signal creation unit 107, and transmits it to the terminal device 200 from the antennas 101-1 to 101-j.

[0030] (Step S8-1) In the terminal device 200, the communication unit 202 receives a feedback signal transmitted by the base station device 100. The precoding unit 204 acquires the feedback signal received by the communication unit 202 and acquires a precoder associated with the TPMI index included in the acquired feedback signal from the codebook 208 in the storage unit 210. The precoding unit 204 performs precoding on the multiple antennas 201-1 to 201-k based on the acquired precoder. Thereafter, the base station device 100 continues to transmit the predetermined TPMI index until the terminal device 200 is in a non-line-of-sight environment.

[0031] In the above-described embodiment, a case has been described in which the antennas 101-1 to 101-j are arranged in a two-dimensional square to form a URA antenna, as an example of the antennas provided in the base station device 100. However, the present invention is not limited to this example. For example, the antennas 101-1 to 101-j may form a Uniform Circular Array (UCA) antenna.

[0032] FIG. 5 is a diagram showing another example of antennas provided in the base station device and terminal device according to this embodiment. Antennas 101-1 to 101-j are arranged two-dimensionally in a circular ring shape at equal intervals on a substrate (not shown) to form a UCA antenna. For example, in the orthogonal x-axis and y-axis directions, antennas 101-1 to 101-j are arranged along a circumference of radius rTX at intervals of rTX × θm [degrees]. As an example, a case where j is 12 will be described. In this case, antenna elements (antennas 101-1 to 101-j) are arranged along a circumference of radius rTX at intervals of rTX × 30 degrees. FIG. 5 also shows the center 101-C of the UCA antenna. The radius rTX is arbitrary.

[0033] In the above-described embodiment, a case has been described in which antennas 201-1 to 201-k are arranged two-dimensionally in a square to form a URA antenna as an example of antennas provided in terminal device 200, but this is not limiting. For example, antennas 201-1 to 201-k may form a UCA antenna.

[0034] The following description will be given with reference to FIG. 5. Antennas 201-1 to 201-k are arranged two-dimensionally in a circular ring shape at equal intervals on a substrate (not shown) to form a UCA antenna. For example, in the orthogonal x-axis and y-axis directions, antennas 201-1 to 201-k are arranged along a circumference of radius rRX at intervals of rRX × θm [degrees]. As an example, a case where k is 12 will be described. In this case, antenna elements (antennas 201-1 to 201-k) are arranged along a circumference of radius rRX at intervals of rRX × 30 degrees. FIG. 5 also shows the center 201-C of the UCA antenna. The radius rRX is arbitrary.

[0035] In the above-described embodiment, the antennas provided in the base station device 100 and the terminal device 200 may be antennas other than a URA antenna or a UCA antenna. In the above-described embodiment, the transmission time Ts may be varied. For example, the transmission time Ts may be varied based on the number of times a feedback signal is transmitted. In the above-described embodiment, the base station device 100 may perform wireless communication with a plurality of terminal devices 100.

[0036] The base station device 100 according to this embodiment includes a selection unit 106 that selects a predetermined TPMI index when the terminal device 200 is in a line-of-sight environment, and a communication unit 102 that transmits the TPMI index selected by the selection unit 106 to the terminal device 200 at every transmission time Ts.

[0037] With this configuration, the base station device 100 can select a predetermined TPMI index when the terminal device 200 is in a line-of-sight environment and transmit the TPMI index to the terminal device 200 at every transmission interval. This reduces the computational overhead required for precoder selection compared to when the base station device 100 selects a TPMI index based on an uplink reference signal transmitted by the terminal device 200. Furthermore, because the TPMI index is transmitted at every transmission time Ts, the number of transmissions can be reduced compared to when the TPMI index is transmitted every time a downlink reference signal is transmitted. This can improve the overall quality of service in wireless networks, for example, and contribute to Goal 9 of the United Nations' Sustainable Development Goals (SDGs), which states, "Build resilient infrastructure, promote sustainable industrialization, and foster innovation."

[0038] Base station device 100 further includes a uniform rectangular array antenna, and communication unit 102 transmits the TPMI index from the uniform rectangular array antenna to terminal device 200 equipped with the uniform rectangular array antenna. Base station device 100 further includes a uniform circular array antenna, and communication unit 102 transmits the TPMI index from the uniform circular array antenna to terminal device 200 equipped with the uniform circular array antenna.

[0039] With this configuration, the derived channel matrix becomes a circulant matrix, and therefore the optimal precoder becomes a unitary matrix in the base station apparatus 100. Therefore, the base station apparatus 100 can ensure communication quality even if it selects a TPMI index associated with the determined precoder and transmits it to the terminal apparatus 200 without selecting a TPMI index based on the uplink reference signal.

[0040] (First Modification of the Embodiment) Fig. 6 is a diagram showing a base station device and a terminal device included in a wireless communication system according to a first modification of the embodiment. A wireless communication system 2 according to the first modification of the embodiment includes a base station device 300 and a terminal device 400. The wireless communication system 2 differs from the wireless communication system 1 in the following respects. The terminal device 400 determines whether the base station device 300 is in a line-of-sight environment based on a downlink reference signal. When the terminal device 400 determines that the base station device 200 is in a line-of-sight environment, it creates an uplink signal including information indicating that the base station device 200 is in a line-of-sight environment and information indicating a transmission time Ts, and transmits the uplink signal to the base station device 300.

[0041] The base station device 300 receives an uplink signal transmitted from the terminal device 400 and determines whether the received uplink signal includes information indicating a line-of-sight environment and information indicating a transmission time Ts. If the base station device 300 determines that the uplink signal includes information indicating a line-of-sight environment, it selects a TPMI index associated with a predetermined precoder. If the base station device 300 determines that the uplink signal includes information indicating the transmission time Ts, it transmits a TPMI index to the terminal device for each transmission time Ts.

[0042] (Base Station Device) The details of the base station device 300 will be described with reference to FIG. 6 . The base station device 300 further includes a beam sweep module 303 and a determination unit 305 in addition to the base station device 100. The beam sweep module 303 causes the transmitter 102 to transmit the same signal while sequentially switching between available beams. This configuration enables coverage of the entire area. In a line-of-sight environment, the beam sweep module 303 stops beam sweeping for a certain period of time because the optimal beam does not change. The determination unit 305 acquires an uplink signal received by the communication unit 102 and determines whether the acquired uplink signal includes information indicating a line-of-sight environment and information indicating a transmission time Ts. If the uplink signal includes information indicating a line-of-sight environment, the determination unit 305 notifies the selection unit 106 that the uplink signal is a line-of-sight environment. If the uplink signal includes information indicating the transmission time Ts, the determination unit 305 notifies the communication unit 102 of the transmission time Ts. The selection unit 106 selects a TPMI index associated with a predetermined precoder when notified by the determination unit 305 that the terminal device is in a line-of-sight environment. The communication unit 102 transmits the TPMI index selected by the selection unit to the terminal device every transmission time Ts when notified by the determination unit 305 of a transmission time Ts.

[0043] (Terminal Device) The terminal device 400 will be described in detail with reference to Fig. 6. The terminal device 400 further includes a determination unit 405 in the terminal device 200. The determination unit 405 acquires a downlink reference signal received by the communication unit 202, and determines whether the base station device 400 is in a line-of-sight environment based on the acquired downlink reference signal.

[0044] Specifically, when the determination unit 405 determines whether the base station device 300 is actually in a line-of-sight environment with respect to the terminal device 400, the determination unit 405 inputs the characteristic parameters of the downlink reference signal received by the communication unit 202 into the learned model 406, which is a downlink reference signal received by the terminal device 400 and stores the characteristic parameters of the downlink reference signal. An example of the characteristic parameter is the Rician K-factor. The Rician K-factor is defined as the ratio between the power of a (possible) dominant multipath component (usually LOS) and the power of the remaining multipath components. Furthermore, as an example of the characteristic parameter, at least one of the maximum power of the received power, kurtosis, skewness, rise time and delay spread, the difference between the radiation angle and the arrival angle, the angular spread between the radiation angle and the arrival angle, and the rate of change of the radiation angle and the arrival angle may be used instead of or in addition to the Rician K-factor. The kurtosis of the received power is defined as the ratio of the fourth moment to the second moment of the amplitude of the received signal. Hereinafter, the characteristic parameters related to the generation of the trained model 406 (the downlink reference signal for which it has been determined whether the base station device 300 is actually in a line-of-sight environment with respect to the terminal device 400, and for which the characteristic parameters of the downlink reference signal have been stored) are referred to as the model target.

[0045] The generation of the trained model 406 will be described. The trained model 406 is generated by a training model generation device (not shown). That is, the training model generation device generates the trained model 406. Note that the terminal device 400 may include the training model generation device, or a device different from the terminal device 400 may be the training model generation device. That is, the terminal device 400 may generate the trained model 406, or a device different from the terminal device 400 may generate the trained model 406.

[0046] The learning model generation device trains a learning model (a model that serves as the basis for the trained model 406) using a learning dataset in which input samples are characteristic parameters of a downlink reference signal to be modeled and output samples are information indicating whether the base station device 300 that transmitted the downlink reference signal is in a line-of-sight environment, thereby generating the trained model 406. For example, a support vector machine (SVC), a random forest (RF), or an artificial neural network (ANN) may be used. The input sample is data input to an input layer when training the learning model. The output sample is data (teaching data) that serves as a correct answer for comparison with an output value output from the output layer when training the learning model. The input sample and the output sample are paired, and the learning dataset is composed of multiple pairs.

[0047] The learning model generation device inputs an input sample into the input layer of the learning model, calculates the error between the output value output from the output layer and the output sample (teacher data) corresponding to the input sample for all pairs, changes the parameters of the learning model (trains the learning model) so as to minimize the error, and generates a learned model 406. The learned model 406 generated as described above is received by the terminal device 400 from the learning model generation device via a network or medium, and is acquired by the determination unit 405.

[0048] The following describes a process for determining whether the base station device 300 is in a line-of-sight environment using the trained model 406. The determination unit 406 derives characteristic parameters and the like from the downlink reference signal to be determined, inputs the derived characteristic parameters to the trained model 406, and obtains an output value from the trained model 406.

[0049] The signal creation unit 207 acquires the result of the determination as to whether the base station device 300 is in a line-of-sight environment from the determination unit 406. When the acquired result of the determination as to whether the base station device 300 is in a line-of-sight environment indicates that the base station device 300 is in a line-of-sight environment, the signal creation unit 207 creates an uplink signal including information indicating that the base station device 300 is in a line-of-sight environment and information indicating the transmission time Ts. Specifically, the signal creation unit 207 introduces a one-bit identifier into uplink control information (UCI) of the physical uplink control channel (PUCCH). The signal creation unit 207 stores "1" in the one bit introduced into the uplink control information. The communication unit 202 transmits the uplink signal (physical uplink control channel) generated by the signal generation unit 207 to the base station apparatus 100 from the antennas 201-1 to 201-k.

[0050] (Operation of Wireless Communication System) FIG. 7 is a diagram showing an example of the operation of the wireless communication system according to the first modification of the embodiment. With reference to FIG. 7, the operation when the base station device 300 is in a line-of-sight environment with respect to the terminal device 400 will be described. (Step S1-2) In the base station device 300, the signal generation unit 107 generates a downlink reference signal. The communication unit 102 transmits the downlink reference signal from the antennas 100-1 to 100-j. An example of the downlink reference signal is a channel state information-reference signal / synchronization signal block (CSI-RS / SSB (Channel State Information-Reference Signal / Synchronization Signal Block)).

[0051] (Step S2-2) In the terminal device 400, the communication unit 202 receives the downlink reference signal transmitted by the base station device 300. The determination unit 405 acquires the downlink reference signal received by the communication unit 202 and determines whether the base station device 400 is in a line-of-sight environment based on the acquired downlink reference signal. Here, the explanation will continue for the case where the terminal device 400 determines that the base station device 400 is in a line-of-sight environment. (Step S3-2) In the terminal device 400, the signal creation unit 207 creates an uplink signal including information indicating that the base station device 400 is in a line-of-sight environment and information indicating the transmission time Ts. (Step S4-2) In the terminal device 400, the communication unit 202 transmits the uplink signal created by the signal creation unit 207 to the base station device 100 from the antennas 201-1 to 201-k.

[0052] (Step S5-2) In the base station device 300, the communication unit 102 receives an uplink signal transmitted by the terminal device 200. The determination unit 305 acquires the uplink signal received by the communication unit 102 and determines whether the uplink signal includes information indicating a line-of-sight environment and information indicating a transmission time Ts. Since the uplink signal includes information indicating a line-of-sight environment, the determination unit 305 notifies the selection unit 106 that the uplink signal includes a line-of-sight environment. Since the uplink signal includes information indicating the transmission time Ts, the determination unit 305 notifies the communication unit 102 of the transmission time Ts. When the determination unit 305 notifies the selection unit 106 that the terminal device 200 is in a line-of-sight environment, the selection unit 106 selects a TPMI index associated with a predetermined precoder. Steps S2-1 to S8-1 in FIG. 4 can be applied to steps S6-2 to S12-2, and therefore description thereof will be omitted.

[0053] In the first modification of the above-described embodiment, the signal generation unit 207 sets one bit introduced into the uplink control information of the physical uplink control channel to "1" when the acquired result of determining whether the base station device 300 is in a line-of-sight environment indicates that the base station device 300 is in a line-of-sight environment. However, this is not limiting. For example, a duration bit may be provided in the PUCCH. When the acquired result of determining whether the base station device 300 is in a line-of-sight environment indicates that the base station device 300 is in a line-of-sight environment, the signal generation unit 207 may generate information for notifying that the number of PUCCH bits will be reduced by "line-of-sight - notification of non-line-of-sight determination result + notification of duration" for a certain period of time. The number of bits exchanged on the PUCCH is determined by the contents of the RRC (Radio Resource Control) configuration. Increasing or decreasing the number of bits requires RRC signaling, and changing the number of bits depending on whether or not the line-of-sight / non-line-of-sight determination result is notified is difficult to track over time with RRC. For this reason, when the base station device 300 indicates that it is in a line-of-sight environment, the signal generation unit 207 generates information for notifying that the number of PUCCH bits will be reduced by the amount of "line-of-sight / non-line-of-sight determination result notification + duration notification" for a certain period of time. In the first modification of the above-described embodiment, the terminal device 400 may vary the transmission time Ts. For example, based on the reception quality of the downlink reference signal, the terminal device 400 may lengthen the transmission time Ts when the reception quality is good and shorten the transmission time Ts when the reception quality is poor.

[0054] According to the wireless communication system 2 relating to the first modification of the embodiment, in the base station device 300, the communication unit 102 receives the physical uplink control channel transmitted by the terminal device 400, and the base station device 300 further includes a determination unit 305 that determines whether or not the physical uplink control channel received by the communication unit 102 includes information indicating a line-of-sight environment and information indicating a transmission time Ts, and the selection unit 306 selects a predetermined TPMI index when the determination unit 305 determines that the physical uplink control channel includes the information indicating a line-of-sight environment, and the communication unit 102 transmits the TPMI index selected by the selection unit 306 to the terminal device 400 for each transmission time Ts when the determination unit 305 determines that the physical uplink control channel includes the information indicating the transmission time Ts.

[0055] With this configuration, when the physical uplink control channel transmitted by the terminal device 400 includes information indicating a line-of-sight environment and information indicating a transmission time Ts, the base station device 300 can select a TPMI index associated with a predetermined precoder and transmit the TPMI index to the terminal device 200 at every transmission time Ts. Therefore, compared to when the base station device 100 selects a TPMI index based on an uplink reference signal transmitted by the terminal device 200, the overhead of the computation required for selecting a precoder can be reduced. Furthermore, because the TPMI index is transmitted at every transmission time Ts, the number of transmissions can be reduced compared to when the TPMI index is transmitted every time a downlink reference signal is transmitted.

[0056] According to the wireless communication system 2 relating to the modified embodiment, the terminal device 400 includes a determination unit 405 that determines whether the base station device 300 is in a line-of-sight environment based on the downlink reference signal, a signal creation unit 207 that, when the determination unit 405 determines that the base station device 300 is in a line-of-sight environment, creates a feedback signal for the base station device 300 that includes information indicating that the environment is line-of-sight and information indicating the transmission time Ts, and a communication unit 200 that transmits the feedback signal created by the signal creation unit 207 to the base station device 300.

[0057] With this configuration, when the base station device 300 is in a line-of-sight environment, the terminal device 400 can notify the base station device 300 that it is in a line-of-sight environment and of the transmission time Ts. Therefore, the base station device 300 can select a predetermined TPMI index based on the notified information and transmit it to the terminal device 400 for each transmission time Ts.

[0058] Furthermore, in the terminal device 400, the signal generation unit 207 generates a feedback signal by including information indicating a line-of-sight environment and information indicating the transmission time Ts in the uplink control information of the physical uplink control channel. Furthermore, in the terminal device 400, the signal generation unit 207 may generate a feedback signal by including information indicating a line-of-sight environment and information indicating the transmission time Ts in the channel quality signal of the uplink control information of the physical uplink control channel. With this configuration, the terminal device 400 can notify the base station device 300 that it is in a line-of-sight environment and the transmission time Ts via the physical uplink control channel. Therefore, notification can be made using an existing signal without providing a new signal for notifying that it is in a line-of-sight environment.

[0059] Terminal device 400 further includes a uniform rectangular array antenna, and communication unit 202 transmits the TPMI index from the uniform rectangular array antenna to base station device 300 equipped with the uniform rectangular array antenna. Terminal device 400 further includes a uniform circular array antenna, and communication unit 202 transmits the TPMI index from the uniform circular array antenna to base station device 300 equipped with the uniform circular array antenna.

[0060] With this configuration, the derived channel matrix becomes a circulant matrix, and therefore the optimal precoder becomes a unitary matrix in the base station device 300. Therefore, the base station device 300 can ensure communication quality even if it selects a TPMI index associated with the determined precoder and transmits it to the terminal device 200 without selecting a TPMI index based on the uplink reference signal.

[0061] (Second Modification of Embodiment) Fig. 8 is a diagram showing a base station device and a terminal device included in a wireless communication system according to a second modification of the embodiment. A wireless communication system 3 according to the second modification of the embodiment includes a base station device 500 and a terminal device 200. The wireless communication system 3 differs from the wireless communication system 1 in the following respects. The base station device 500 determines whether the terminal device 200 is in a line-of-sight environment based on an uplink reference signal transmitted by the terminal device 200, and selects a predetermined TPMI index when it is determined that the terminal device 200 is in a line-of-sight environment.

[0062] (Base Station Device) Details of the base station device 500 will be described with reference to Fig. 8. The base station device 500 further includes a beam sweep module 303 and a determination unit 505 in addition to the base station device 100. The determination unit 505 acquires an uplink reference signal received by the communication unit 102, and determines whether or not the terminal device 200 is in a line-of-sight environment based on the acquired uplink reference signal.

[0063] Specifically, when determining whether the terminal device 200 is actually present in a line-of-sight environment with respect to the base station device 500, the determination unit 505 inputs the characteristic parameters of the uplink reference signal received by the communication unit 102 to the learned model 506, which is an uplink reference signal received by the base station device 500 and in which characteristic parameters of the uplink reference signal and the like are stored. In this way, the determination unit 505 determines whether the terminal device 200 is present in a line-of-sight environment. An example of the characteristic parameter is the Rice K factor. Furthermore, as an example of the characteristic parameter, instead of or together with the Rice K factor, at least one of the maximum power, kurtosis, skewness, rise time and delay spread of the received power, the difference between the radiation angle and the arrival angle, the angular spread between the radiation angle and the arrival angle, and the rate of change of the radiation angle and the arrival angle may be used. Hereinafter, the characteristic parameters related to the generation of the learned model 506 (the uplink reference signal that has actually determined whether the terminal device 600 is in a line-of-sight environment with respect to the base station device 500, and whose characteristic parameters, etc. have been stored) will be referred to as the model target.

[0064] The generation of the trained model 506 will now be described. The trained model 506 is generated by a training model generation device (not shown). That is, the training model generation device generates the trained model 506. Note that the base station device 500 may include the training model generation device, or a device different from the base station device 500 may be the training model generation device. That is, the base station device 500 may generate the trained model 506, or a device different from the base station device 500 may generate the trained model 506.

[0065] The learning model generation device trains a learning model (a model that serves as the basis for the trained model 506) using a learning dataset in which input samples are characteristic parameters of an uplink reference signal to be modeled, and output samples are information indicating whether the terminal device 200 that transmitted the uplink reference signal is in a line-of-sight environment, thereby generating the trained model 506. For example, a support vector machine, a random forest, or an artificial neural network may be used. The input sample is data input to the input layer when training the learning model. The output sample is data (teaching data) that serves as a correct answer for comparison with the output value output from the output layer when training the learning model. The input sample and the output sample are paired, and the learning dataset is composed of multiple pairs.

[0066] The learning model generation device inputs an input sample into the input layer of the learning model, calculates the error between the output value output from the output layer and the output sample (teacher data) corresponding to the input sample for all pairs, changes the parameters of the learning model (trains the learning model) so as to minimize the error, and generates a learned model 506. The learned model 506 generated as described above is received by the base station device 500 from the learning model generation device via a network or medium, and is acquired by the determination unit 505.

[0067] The process of determining whether or not the terminal device 600 is in a line-of-sight environment using the trained model 506 will be described. The determination unit 505 derives characteristic parameters and the like from the uplink reference signal to be determined, inputs the derived characteristic parameters to the trained model 506, and obtains an output value from the trained model 506. The selection unit 106 acquires the determination result of whether or not the terminal device 600 is in a line-of-sight environment from the determination unit 505. If the determination result of whether or not the terminal device 600 is in a line-of-sight environment from the determination unit 505 indicates that the terminal device 200 is in a line-of-sight environment, the selection unit 106 selects a TPMI index associated with a precoder that has been determined in advance.

[0068] (Operation of Wireless Communication System) Fig. 9 is a diagram showing an example of the operation of the wireless communication system according to the second modification of the embodiment. With reference to Fig. 9, the operation when the terminal device 200 is in a line-of-sight environment with respect to the base station device 500 will be described. (Step S1-3) In the terminal device 200, the signal generation unit 207 generates an uplink reference signal. The communication unit 202 transmits the uplink reference signal from the antennas 201-1 to 201-k. An example of the uplink reference signal is a sounding reference signal.

[0069] (Step S2-3) In the base station device 500, the communication unit 102 receives the uplink reference signal transmitted by the terminal device 200. The determination unit 505 acquires the uplink reference signal received by the communication unit 102 and determines whether or not the terminal device 200 is in a line-of-sight environment based on the acquired uplink reference signal. Here, the description will continue for the case where the base station device 500 determines that the terminal device 400 is in a line-of-sight environment.

[0070] (Step S3-3) In the base station device 500, the selection unit 106 obtains the result of determining whether or not the terminal device 600 is in a line-of-sight environment from the determination unit 505. When the result of determining whether or not the terminal device 600 is in a line-of-sight environment from the determination unit 505 indicates that the terminal device 200 is in a line-of-sight environment, the selection unit 106 selects a TPMI index associated with a precoder that has been determined in advance. Steps S4-3 to S10-3 can be applied to steps S4-1 to S8-1 in FIG. 4, and therefore description thereof will be omitted.

[0071] According to the wireless communication system 3 according to the second modification of the embodiment, the base station device 500 further includes a determination unit 505 in the base station device 100 that determines whether the terminal device 200 is in a line-of-sight environment based on the uplink reference signal transmitted by the terminal device 200. The selection unit selects a predetermined TPMI index when the determination unit 505 determines that the terminal device 200 is in a line-of-sight environment.

[0072] With this configuration, when it is determined that the terminal device 200 is in a line-of-sight environment based on the uplink reference signal transmitted by the terminal device 200, the base station device 500 can select a predetermined TPMI index and transmit it to the terminal device 200. Therefore, compared to the case where the base station device 500 selects a TPMI index based on the uplink reference signal transmitted by the terminal device 200, it is possible to reduce the overhead of the amount of calculation required for selecting a precoder.

[0073] Although the embodiments of the present disclosure have been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and design modifications and the like are also included within the scope of the present disclosure. For example, a computer program for realizing the functions of each of the above-described devices may be recorded on a computer-readable recording medium, and the computer program recorded on this recording medium may be read and executed by a computer system. Note that the "computer system" referred to here may also include hardware such as an OS and peripheral devices.

[0074] Additionally, "computer-readable recording media" refers to writable non-volatile memory such as flexible disks, optical magnetic disks, ROMs, and flash memories, portable media such as DVDs (Digital Versatile Discs), and storage devices such as hard disks built into computer systems. Furthermore, "computer-readable recording media" also includes devices that retain a program for a certain period of time, such as volatile memory (e.g., DRAM (Dynamic Random Access Memory)) within a computer system that serves as a server or client when a computer program is transmitted via a network such as the Internet or a communication line such as a telephone line.

[0075] The program may also be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by transmission waves in the transmission medium. Here, the "transmission medium" that transmits the program refers to a medium that has the function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. The program may also be a program that realizes part of the aforementioned functions. Furthermore, the program may be a so-called differential file (differential program) that can realize the aforementioned functions in combination with a program already stored in the computer system.

[0076] According to the present disclosure, as an example, it is possible to provide a base station apparatus, a terminal apparatus, and a wireless communication method that can reduce the overhead of the amount of calculation required for selecting a codebook that the base station apparatus feeds back to the terminal apparatus.

[0077] 1, 2, 3...wireless communication system, 100, 300, 500...base station device, 101-1 to 101-j...antenna, 102...communication unit, 104...channel estimation unit, 106...selection unit, 107...signal creation unit, 108...codebook, 110...storage unit, 200, 400...base station device, 201-1 to 201-k...antenna, 202...communication unit, 204...precoding unit, 207...signal creation unit, 208...codebook, 210...storage unit, 303...beam sweep module, 305...determination unit, 405...determination unit, 406...trained model, 505...determination unit, 506...trained model

Claims

1. A base station device comprising: a selection unit that selects a predetermined transmission precoding matrix indicator (TPMI) when a terminal device is in a line-of-sight environment; and a communication unit that transmits the TPMI selected by the selection unit to the terminal device at each transmission time.

2. The base station device of claim 1, wherein the communication unit receives a physical uplink control channel transmitted by the terminal device, the base station device further comprises a determination unit that determines whether the physical uplink control channel received by the communication unit includes information indicating a line-of-sight environment and information indicating a transmission time, the selection unit selects the TPMI that has been determined in advance when the determination unit determines that the physical uplink control channel includes information indicating a line-of-sight environment, and the communication unit transmits the TPMI selected by the selection unit to the terminal device for each transmission time when the determination unit determines that the information indicating the transmission time is included.

3. A base station device as described in claim 1, further comprising a judgment unit that judges whether the terminal device is in a line-of-sight environment based on an uplink reference signal transmitted by the terminal device, wherein the selection unit selects the TPMI that has been determined in advance when the judgment unit judges that the terminal device is in a line-of-sight environment.

4. The base station device according to claim 1, further comprising a uniform rectangular array antenna, wherein the communication unit transmits the TPMI from the uniform rectangular array antenna to the terminal device equipped with a uniform rectangular array antenna.

5. The base station device according to claim 1, further comprising a uniform circular array antenna, wherein the communication unit transmits the TPMI from the uniform circular array antenna to the terminal device equipped with a uniform circular array antenna.

6. A terminal device comprising: a determination unit that determines whether a base station device is in a line-of-sight environment based on a downlink reference signal; a signal creation unit that creates a feedback signal to the base station device, when the determination unit determines that the base station device is in a line-of-sight environment, the feedback signal including information indicating that the environment is line-of-sight and information indicating a transmission time; and a communication unit that transmits the feedback signal created by the signal creation unit to the base station device.

7. The terminal device according to claim 6, wherein the signal generation unit generates the feedback signal by including information indicating a line-of-sight environment and information indicating a transmission time in a physical uplink control channel.

8. The terminal device according to claim 6, wherein the signal generation unit generates the feedback signal by including information indicating a line-of-sight environment and information indicating a transmission time in uplink control information of a physical uplink control channel.

9. The terminal device according to claim 6, further comprising a uniform rectangular array antenna, wherein the communication unit receives, via the uniform rectangular array antenna, a Transmission Precoding Matrix Indicator (TPMI) transmitted by the base station device equipped with the uniform rectangular array antenna.

10. The terminal device according to claim 6, further comprising a uniform circular array antenna, wherein the communication unit receives, via the uniform circular array antenna, a Transmission Precoding Matrix Indicator (TPMI) transmitted by the base station device equipped with the uniform circular array antenna.

11. A wireless communication method executed by a base station device, comprising: a step of selecting a transmission precoding matrix indicator (TPMI) that is predetermined when a terminal device is in a line-of-sight environment; and a step of transmitting the TPMI selected in the selection step to the terminal device for each transmission time.

12. A wireless communication method executed by a terminal device, comprising: a step of determining whether a base station device is in a line-of-sight environment based on a downlink reference signal; a step of creating a feedback signal for the base station device when it is determined in the determining step that the base station device is in a line-of-sight environment, the feedback signal including information indicating that the environment is line-of-sight and information indicating a transmission time; and a step of transmitting the feedback signal created in the feedback signal creating step to the base station device.

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