Base station device, terminal device, and communication method

Abstract

A base station device according to the present invention comprises: a beam squint estimation unit that estimates a beam squint on the basis of a reference signal for estimating the beam squint or a theoretical formula of an array factor, and that, on the basis of the estimated beam squint, estimates an optimal beam at a frequency other than a specific frequency used for estimating the beam squint; and a data transfer instruction unit that, during data transfer, instructs the data transfer using optimal beams corresponding to the frequencies respectively allocated to terminal devices, on the basis of the optimal beam for each frequency estimated by the beam squint estimation unit.　

Description

Base station equipment, terminal equipment, and communication method

[0001] The present invention relates to a base station device, a terminal device, and a communication method.

[0002] (Beamforming in high-frequency bands) There is a beamforming technique that creates a beam that concentrates power in a specific direction. In particular, in high-frequency bands such as the millimeter wave and terahertz bands, free-space propagation loss is larger compared to low-frequency bands such as the microwave band. Therefore, it is necessary to use beamforming techniques that create a beam that concentrates power in a specific direction in order to compensate for free-space propagation loss.

[0003] In point-to-point (P-P) communication, where the combination of radio stations communicating with each other is always fixed, and where the relative positions of the two radio stations and the propagation environment around them do not change, beamforming can be used to fix a beam that has been pre-formed in a specific direction when the radio stations are installed. However, in point-to-multipoint (P-MP) communication that accommodates multiple radio stations, or when at least one of the radio stations moves, or when at least one of the radio stations communicating with each other moves, the appropriate beam formation direction changes, making it impossible to use a beam formed in a specific direction in a fixed manner.

[0004] In such cases, it is necessary to control the beam formation direction to adaptively change in accordance with the relative positions of the two radio stations and changes in the propagation environment around them. This type of beamforming, which adaptively controls the beam formation direction, is called adaptive beamforming. Generally, adaptive beamforming does not require a mechanical drive to change the beam formation direction. Adaptive beamforming creates a directional beam by adjusting the phase relationship of the radio waves emitted from multiple antenna elements.

[0005] However, in order to properly adjust this phase relationship, it is necessary to understand the phase relationship for each combination of multiple antenna elements of the transmitting radio station and multiple antenna elements of the receiving radio station, and to derive the optimal phase relationship from among these multiple phase relationships. In other words, it is necessary to understand the state of the propagation path for every combination of antenna elements of the transmitting and receiving stations.

[0006] Understanding the state of the propagation path for all the above combinations is possible, for example, by having a known signal sent and received between the transmitting and receiving radio station. However, this method increases communication overhead because other communications cannot take place while the known signal is being sent and received, and because it is necessary to accurately convey the state of the propagation path.

[0007] Therefore, in typical adaptive beamforming, multiple discretely configured beams are set up in advance. Each of these beams is associated with a beam ID (Identifier) ​​that uniquely identifies it. For example, in adaptive beamforming, beam identification signals, including the beam ID, are transmitted and received between the two radio stations by the beams associated with that beam ID. Based on the results of the transmission and reception of beam identification signals by each beam, the optimal beam and the beam ID associated with that beam are identified between the two radio stations. Adaptive beamforming can suppress the increase in overhead through this beam selection.

[0008] The beam selection described above is defined in 3GPP (registered trademark) 5G (5th Generation) and IEEE (Institute of Electrical and Electronics Engineers) 802.11ad, and has been implemented in wireless communication systems that are being increasingly put into practical use in recent years.

[0009] (Beam Selection Procedure) Generally, beam selection is performed using the following procedure. Here, we will explain beam selection by the transmitting radio station (see, for example, Non-Patent Document 1). First, one radio station (the transmitting radio station) transmits a beam identification signal to the other radio station (the receiving radio station). The beam identification signal here is a signal that enables the other radio station to identify the beam used to transmit the beam identification signal transmitted by the other radio station. Here, the one radio station controls the transmission so that the beam identification signals transmitted by each beam do not interfere with each other. Specifically, the one radio station transmits the beam identification signals for each beam sequentially with staggered transmission timings. Hereafter, the process by which the radio stations transmit the beam identification signals for each beam sequentially with staggered transmission timings is sometimes called "sweeping".

[0010] Next, the other radio station measures the reception quality of each beam-specific signal transmitted sequentially from the first radio station by each beam. The other radio station then selects, for example, the beam-specific signal with the best reception quality. The other radio station then transmits a signal containing information based on the selected beam-specific signal (hereinafter referred to as the "feedback signal") to the first radio station. With this configuration, adaptive beamforming allows one radio station to recognize which beam is optimal to use when transmitting data to the other radio station.

[0011] Furthermore, as a beam identification signal, for example, a beam search signal including a beam ID (Identifier) ​​that identifies the beam used by one of the radio stations can be used. The beam search signal referred to here is, for example, a signal defined in IEEE 802.11ay (see, for example, Non-Patent Document 6), or a signal defined in 5G, such as SS / PBCH (Synchronization Signal / Physical Broadcast Channel). In the following explanation, a beam search signal will be used as an example of a beam identification signal.

[0012] In the following description, the reception quality measured at the radio station may be any of the following: received power, RSSI (Received Signal Strength Indicator), SNR (Signal to Noise Ratio), RSRP (Reference Signal Received Power), RSRQ (Reference Signal Received Quality), SIR (Signal to Interference Ratio), or SINR (Signal to Interference plus Noise Ratio).

[0013] Regarding beam selection at the receiving radio station, in systems like TDD (Time Division Duplex) which use the same frequency for transmission and reception, it is possible to select the same beam used by the transmitting radio station. In contrast, in systems like FDD (Frequency Division Duplex) which use different frequencies for transmission and reception, beam selection must be performed at the receiving radio station, just as it is performed at the transmitting radio station.

[0014] When a receiving radio station performs beam selection, it sends a signal to the transmitting radio station requesting a receive beam search procedure. This receive beam search procedure request is a signal that asks the transmitting radio station to transmit a signal in order to select the beam to be used to receive the signal at the receiving radio station. The receiving radio station receives the signal by switching the receiving direction of the beam in time according to the signal transmitted by the transmitting radio station, and measures the reception quality of the received signal. This allows the receiving radio station to select the beam to be used by the receiving radio station by identifying the beam with the best reception quality.

[0015] Adaptive beamforming using array antennas results in beam squint (see, for example, Non-Patent Document 2). Beam squint is a phenomenon in which the beam direction shifts proportionally to the frequency difference relative to a beam direction set at a certain frequency.

[0016] (Beam squint in the high frequency band) Here, beam direction shift will be explained using a one-dimensional array as an example. Figure 22 is a diagram for explaining beam direction shift. Assume that a one-dimensional array is arranged horizontally as shown in Figure 22. Under the conditions shown in Figure 22, θ ０ The phase difference Ψ between adjacent elements when setting the beam direction can be expressed as shown in equation (1) below.

[0017]

[0018] k in equation (1) ０ The design frequency f ０ This represents the corresponding wavenumber, and d represents the spacing between elements. In contrast, the beam direction θ at a certain frequency f can be expressed as shown in equation (2) below.

[0019]

[0020] In equation (2), Ψ represents the phase difference between adjacent elements at a certain frequency f, and k represents the wavenumber corresponding to a certain frequency f. Here, the design frequency f ０ And, the ratio of a certain frequency f is r = f / f ０ If we define it as such, equation (2) can be expressed as equation (3).

[0021]

[0022] Based on equation (3), the beam shift Δθ can be expressed as shown in equation (4) below.

[0023]

[0024] M. Giordani, M. Polese, A. Roy, D. Castor and M. Zorzi, “A Tutorial on Beam Management for 3GPP NR at mmWave Frequencies”, in IEEE Communications Surveys & Tutorials, vol. 21, no. 1, pp. 173-196, Firstquarter 2019.N. T. Nguyen, J. Kokkoniemi and M. Juntti, “Beam Squint Effects in THz Communications with UPA and ULA: Comparison and Hybrid Beamforming Design”, 2022 IEEE Globecom Workshops (GC Wkshps), Rio de Janeiro, Brazil, 2022, pp. 1754-1759.

[0025] In a wireless communication system having a wideband signal bandwidth, it is conceivable to perform beam search at some frequencies in order to reduce beam search resources. However, when resources are allocated to other frequencies during data transmission, the beam direction shifts due to the influence of beam squint. For example, for frequency f １ a beam search is performed, and when other frequencies f ２ , f ３ that are not used for the beam search are used during data transmission, the beams for the terminal devices assigned to frequencies f ２ , f ３ shift in beam direction due to the influence of beam squint. As a result, there is a problem that the reception quality deteriorates.

[0026] In view of the above circumstances, an object of the present invention is to provide a technique capable of suppressing deterioration of reception quality due to the influence of beam squint.

[0027] One aspect of the present invention is a base station device including: a beam squint estimation unit that estimates a beam squint based on a reference signal for estimating the beam squint or a theoretical formula of an array factor, and estimates an optimal beam at a frequency other than a specific frequency used for the estimation of the beam squint based on the estimated beam squint; and a data transmission instruction unit that, at the time of data transmission, instructs data transmission using an optimal beam corresponding to the frequency assigned to each terminal device based on the optimal beam for each frequency estimated by the beam squint estimation unit.

[0028] One aspect of the present invention is a terminal device including: a beam squint estimation unit that estimates a beam squint based on a reference signal for estimating the beam squint or a theoretical formula of an array factor, and estimates an optimal beam at a frequency other than a specific frequency used for the estimation of the beam squint based on the estimated beam squint; and a data transmission instruction unit that, at the time of data transmission, instructs data transmission using an optimal beam corresponding to the assigned frequency based on the optimal beam for each frequency estimated by the beam squint estimation unit.

[0029] One aspect of the present invention is a communication method in which the base station device that performs wireless communication with a plurality of terminal devices estimates a beam squint based on a reference signal for estimating the beam squint or a theoretical formula of an array factor, estimates an optimal beam at a frequency other than a specific frequency used for the estimation of the beam squint based on the estimated beam squint, and at the time of data transmission, instructs data transmission using an optimal beam corresponding to the frequency assigned to each terminal device based on the optimal beam for each estimated frequency.

[0030] One aspect of the present invention is a communication method in which a terminal device that performs wireless communication between a base station device and a plurality of terminal devices estimates a beam squint based on a reference signal for estimating the beam squint or a theoretical formula for an array factor, estimates an optimal beam at frequencies other than the specific frequency used to estimate the beam squint based on the estimated beam squint, and during data transmission, instructs data transmission to be performed with the optimal beam corresponding to the assigned frequency based on the estimated optimal beam for each frequency.

[0031] This invention makes it possible to suppress the deterioration of reception quality caused by beam squint.

[0032] This is a diagram showing the configuration of an antenna system, which is an example of a general antenna system. This is a diagram showing the configuration of a distributed antenna system, which is an example of a high-frequency band distributed antenna system. This is a diagram showing an example configuration of a distributed antenna system in the first embodiment of the present invention. This shows an example configuration of a base station device in the first embodiment of the present invention. This is a diagram showing an example configuration of a terminal device in the first embodiment of the present invention. This is a diagram for explaining the beam quint estimation process in the first embodiment of the present invention. This is a diagram for explaining the beam quint estimation process in the first embodiment of the present invention. This is a flowchart showing the processing flow of a base station device in the first embodiment. This is a flowchart showing the processing flow of a terminal device in the first embodiment. This is a sequence diagram showing the processing flow of a distributed antenna system in the first embodiment. This shows an example configuration of a base station device in the second embodiment of the present invention. This is a diagram showing an example configuration of a terminal device in the second embodiment of the present invention. This is a flowchart showing the processing flow of a base station device in the second embodiment. This is a flowchart showing the processing flow of a terminal device in the second embodiment. This is a sequence diagram showing the processing flow of a distributed antenna system in the second embodiment. This shows an example configuration of a base station device in the third embodiment of the present invention. This is a diagram showing an example configuration of a terminal device in the third embodiment of the present invention. This is a flowchart showing the processing flow of a base station device in the third embodiment. This is a flowchart showing the processing flow of a terminal device in the third embodiment. This is a sequence diagram showing the processing flow of a distributed antenna system in the third embodiment. This figure shows an example of beam searching at different frequencies for each distributed antenna device. It is a diagram illustrating beam direction shift.

[0033] One embodiment of the present invention will be described below with reference to the drawings.

[0034] (Distributed Antenna System) Before describing the specific details of the present invention, a possible antenna system to which the present invention can be applied will be described using Figures 1 and 2. Figure 1 is a diagram showing the configuration of an antenna system 500, which is an example of a general antenna system. The antenna system 500 comprises an antenna device 200 and a digital signal processing device 210. In Figure 1, as an example, an example is shown in which the antenna system 500 comprises five antenna devices 200-1 to 200-5 and five digital signal processing devices 210-1 to 210-5.

[0035] As shown in Figure 1, the digital signal processing device 210, which transmits and receives signals, and the antenna device 200 are connected to each other on a one-to-one basis. In other words, in this case, one cell 100 is formed for each antenna device 200. In this configuration, one terminal device is connected to the single antenna device 200 that exists only within the cell.

[0036] In the case of cell 100-1, the antenna device 200-1 and the digital signal processing device 210-1 constitute the so-called base station equipment. If, for example, one terminal device is located in cell 100-1, that terminal device will be connected to one antenna device 200-1 by radio waves.

[0037] As mentioned earlier, in high-frequency bands such as the millimeter wave and terahertz bands, beamforming technology is used, which reduces the effects of reflected and diffracted waves. Therefore, in high-frequency bands, there is a high possibility of communication interruption if the beam is shielded, and line-of-sight communication is the norm. Incidentally, there is a promising spatial multiplexing technology called MIMO (Multiple Input Multiple Output). MIMO is a technology that uses multiple antennas for transmission and reception, thereby increasing the transmission speed by up to several times the number of antennas through spatial multiplexing with the same time and frequency resources. However, since line-of-sight communication is the norm in high-frequency bands, the spatial correlation between the multiple antennas for transmission and reception becomes high when MIMO technology is applied, making spatial multiplexing difficult.

[0038] Therefore, in wireless communication using high-frequency bands, distributed antenna systems using distributed antennas that have the effect of improving shielding resistance are being considered. Figure 2 shows the configuration of a distributed antenna system 500a, which is an example of a high-frequency band distributed antenna system. As shown in Figure 2, in the distributed antenna system 500a, a digital signal processing device 210a that transmits and receives signals and a plurality of distributed antenna devices 200a are connected to each other in a one-to-many relationship. That is, in the distributed antenna system 500a, a single cell 100 is formed by a plurality of distributed antenna devices 200a. In this configuration, a single terminal device is connected to one of the plurality of distributed antenna devices 200a present in the cell.

[0039] In cell 100-1, multiple distributed antenna devices 200a-1-1 to 200a-1-4 are installed in a distributed manner, and one digital signal processing device 210a-1 is connected to each of the multiple distributed antenna devices 200a-1-1 to 200a-1-4. In the distributed antenna system 500a, the multiple distributed antenna devices 200a-1-1 to 200a-1-4 and the digital signal processing device 210a-1 constitute a so-called base station device, and the other cells 100-2 to 100-5 have a similar configuration. In the distributed antenna system 500a, if a terminal device is located in cell 100-1, for example, the terminal device will be connected to the multiple distributed antenna devices 200a-1-1 to 200a-1-4 by radio waves.

[0040] (First Embodiment) Figure 3 shows an example of the configuration of a distributed antenna system 1 in the first embodiment of the present invention. The distributed antenna system 1 comprises a digital-analog signal processing device 20, distributed antenna devices 30-1 to 30-4, and a plurality of terminal devices 40. In the distributed antenna system 1, one or more distributed antenna devices 30 are arranged for one cell 100, and communication is performed using a high-frequency band. Thus, the distributed antenna system 1 is a communication system equipped with one or more distributed antenna devices on the receiving station side. However, the configuration is not limited to this, and it is also possible for both opposing radio stations to be distributed antenna systems equipped with multiple distributed antennas. The digital-analog signal processing device 20 and the distributed antenna devices 30-1 to 30-4 constitute a so-called base station device.

[0041] The distributed antenna system 1 shown in Figure 3 is illustrated as an example where four distributed antenna devices 30-1 to 30-4 are arranged for one cell 100, but the number of distributed antenna devices 30 is not particularly limited. For example, the distributed antenna system 1 may be configured such that one distributed antenna device 30 is arranged for one cell 100, as shown in Figure 1. The technology of the present invention can be applied to any of the following cases: when one terminal device 40 communicates with one distributed antenna device 30, when one terminal device 40 communicates with multiple distributed antenna devices 30, when multiple terminal devices 40 communicate with one distributed antenna device 30, or when multiple terminal devices 40 communicate with multiple distributed antenna devices 30. In the following description, the case where the technology is applied to a configuration where multiple terminal devices 40 communicate with multiple distributed antenna devices 30 will be described as an example, but an example where the technology is applied to a configuration where one terminal device 40 communicates with multiple distributed antenna devices 30 may also be described. Furthermore, the explanation will be supplemented to include cases where communication occurs between one terminal device 40 and one distributed antenna device 30. In the following explanation, a configuration in which communication occurs between one terminal device 40 and one distributed antenna device 30 may be simply referred to as one-to-one communication, and a configuration in which communication occurs between multiple terminal devices 40 and one distributed antenna device 30 may be simply referred to as many-to-one communication.

[0042] As shown in Figure 3, the digital-analog signal processing unit 20 is connected to the distributed antenna devices 30-1 to 30-4. Hereafter, unless it is necessary to distinguish between the distributed antenna devices 30-1 to 30-4, they will simply be referred to as "distributed antenna device 30". In the following description, the direction from the distributed antenna device 30 to the terminal device 40 will be described as the downdirection, and the direction from the terminal device 40 to the distributed antenna device 30 will be described as the updirection.

[0043] Note that in Figure 3, only one cell 100 is shown for the sake of simplicity, but the distributed antenna system 1 may be configured to include multiple cells 100. In this case, the distributed antenna system 1 is equipped with a number of digital-analog signal processing devices 20 corresponding to the number of cells 100, and each digital-analog signal processing device 20 is connected to the distributed antenna devices 30-1 to 30-4 in the corresponding cell 100.

[0044] Each of the distributed antenna devices 30-1 to 30-4 comprises one distributed antenna 31-1 to 31-4 and one main unit device 32-1 to 32-4. Each of the distributed antennas 31-1 to 31-4 is pre-assigned a distributed antenna ID that uniquely identifies it.

[0045] Each of the main units 32-1 to 32-4 transmits and receives analog signals at radio frequencies through the distributed antennas 31-1 to 31-4 connected to it. That is, each of the main units 32-1 to 32-4 transmits the analog signal of the transmission data output by the digital-to-analog signal processing unit 20 via radio waves from the distributed antennas 31-1 to 31-4.

[0046] Each of the main units 32-1 to 32-4 outputs the analog signals received and output by the distributed antennas 31-1 to 31-4 connected to each unit to the digital-to-analog signal processing unit 20.

[0047] The distributed antenna device 30 is an antenna capable of adaptive beamforming. The distributed antenna device 30 can select one of several types of beams to communicate with the terminal device 40. Here, several types of beams are beams having different directivity in the direction of radiation.

[0048] The digital-analog signal processing device 20 is composed of, for example, an information processing device such as a general-purpose computer. The digital-analog signal processing device 20 performs communication control related to beam selection, which involves selecting the beam used in wireless communication between the distributed antenna devices 30-1 to 30-4 and each terminal device 40 from among a plurality of types of beams. Furthermore, the digital-analog signal processing device 20 uses the distributed antenna devices 30-1 to 30-4 to transmit and receive wireless signals with each terminal device 40.

[0049] When the present invention is applied to one-to-one and many-to-one communication, the digital-analog signal processing device 20 performs communication control related to beam selection, selecting the beam used in wireless communication between one distributed antenna device 30 and each terminal device 40 from among a plurality of types of beams. Furthermore, the digital-analog signal processing device 20 uses one distributed antenna device 30 to transmit and receive wireless signals between it and each terminal device 40.

[0050] In the first embodiment, a configuration in which beamforming is performed in the distributed antenna device 30 and beamforming is not performed in the terminal device 40 will be described. In this case, the base station device requests the terminal device 40 to transmit a reference signal at a certain reference frequency in order to estimate the beam squint. Hereinafter, the reference signal used to estimate the beam squint will be referred to as the beam squint estimation reference signal. The terminal device 40 transmits the beam squint estimation reference signal in response to a request from the distributed antenna device 30. The base station device estimates the beam squint based on the beam squint estimation reference signal transmitted from the terminal device 40. Then, the base station device corrects the optimal beam ID at other frequencies based on the estimated beam squint. The base station device performs beam squint estimation for each optimal beam ID that maximizes reception quality at a certain reference frequency, and by performing this for all beam IDs, it maintains information that associates the optimal beam ID for each frequency. Then, during data transmission, the base station device selects the optimal beam ID according to the frequency used for data transmission and performs data transmission. This makes it possible to suppress the effect of beam squint. The following describes the specific configuration required to perform the above process.

[0051] [Configuration of the base station device] The configuration of the base station device will be described below. Figure 4 shows an example of the configuration of base station device B in the first embodiment of the present invention. As shown in Figure 4, base station device B comprises a digital-analog signal processing device 20 and P (P is an integer of 2 or more) distributed antenna devices 30-1 to 30-P.

[0052] The digital-to-analog signal processing device 20 comprises a base station communication control unit 21, a digital signal processing unit 22, and an analog signal unit 23. The base station communication control unit 21 performs communication control related to beam selection as described above. The digital signal processing unit 22 performs digital signal processing. The analog signal unit 23 converts the digital signals processed by the digital signal processing unit 22 into analog signals and transmits them from each distributed antenna device 30. The analog signal unit 23 converts the signals received by each distributed antenna device 30 (e.g., feedback signals) into digital signals and outputs them to the digital signal processing unit 22.

[0053] The base station communication control unit 21 includes a request transmission unit 211, a reference signal receiving unit 212, a beam quint estimation unit 213, a beam search signal transmission unit 214, a feedback signal receiving unit 215, and a data transmission instruction unit 216.

[0054] The request transmission unit 211 generates a transmission request instruction for a beam quint estimation reference signal. Here, the transmission request instruction for a beam quint estimation reference signal generated by the request transmission unit 211 is an instruction to request the base station device B to transmit a reference signal for estimating beam quints. The request transmission unit 211 outputs the generated beam quint estimation reference signal transmission request instruction to the digital signal processing unit 22.

[0055] The channel transmitted by the request transmission unit 211 may be a PDCCH (Physical Downlink Control channel) or a PDSCH (Physical Downlink Shared Channel). Furthermore, the request information may be stored in DCI (Downlink Control Information) or UCI (Uplink Control Information), in MAC CE (MAC Control Element), in RRC (Radio Resource Control) parameters, or in a NAS message.

[0056] The digital signal processing unit 22 acquires a transmission request instruction for the beam quint estimation reference signal output from the request transmission unit 211. In response to the acquired transmission request instruction for the beam quint estimation reference signal, the digital signal processing unit 22 causes the distributed antenna devices 30-1 to 30-P to transmit the transmission request instruction for the beam quint estimation reference signal. When applied to one-to-one and many-to-one communication in the distributed antenna system 1, the digital signal processing unit 22 only needs to cause one distributed antenna device 30 to transmit the transmission request instruction for the beam quint estimation reference signal in response to the acquired transmission request instruction for the beam quint estimation reference signal.

[0057] The reference signal receiving unit 212 acquires the reference frequency beam quint estimation reference signal transmitted from the terminal device 40 as a response to the digital signal processing unit 22's instruction to transmit the beam quint estimation reference signal. The reference signal receiving unit 212 acquires the reference frequency beam quint estimation reference signal for each distributed antenna device 30. The reference signal receiving unit 212 outputs the acquired beam quint estimation reference signal for each distributed antenna device 30 to the beam quint estimation unit 213.

[0058] The beam squint estimation unit 213 estimates a beam squint for each distributed antenna device 30 based on a beam squint estimation reference signal for each distributed antenna device 30 acquired by the reference signal receiving unit 212. The specific method by which the beam squint estimation unit 213 estimates the beam squint will be described later. The beam squint estimation unit 213 also estimates the optimal beam ID at other frequencies based on the reception results of the beam squint estimation reference signal. Based on the estimation results, the beam squint estimation unit 213 generates and maintains a beam selection table that associates frequencies with the optimal beam ID. Note that a beam selection table may be generated for each distributed antenna device 30, or the same beam selection table may be used for each distributed antenna device 30.

[0059] Furthermore, the beam squint estimation unit 213 selects the optimal beam for each terminal device 40 during data transmission, based on the optimal beam ID selected for each terminal device 40 based on a beam search signal transmitted at a certain frequency, the frequency assigned to each terminal device 40, and the beam selection table it holds.

[0060] The beam search signal transmitting unit 214 assigns a beam ID to each beam, which is an identifier for uniquely identifying all beams used in the distributed antenna devices 30-1 to 30-P. The beam assignment information, which indicates the beam ID assigned by the beam search signal transmitting unit 214, may be in tabular format, where the combination of the distributed antenna device 30 and the beam corresponds to the beam ID. The beam assignment information is stored, for example, in the beam search signal transmitting unit 214.

[0061] The beam search signal transmission unit 214 outputs a beam search signal transmission instruction to the digital signal processing unit 22, which is an instruction for each of the distributed antenna devices 30-1 to 30-P to transmit a beam search signal. The beam search signal transmission instruction includes information indicating the beam ID assigned to each beam.

[0062] In response to a beam search signal transmission instruction, the digital signal processing unit 22 causes the distributed antenna devices 30-1 to 30-P to transmit a beam search signal sequentially in the time domain for each beam to which a beam ID has been assigned. Depending on the location where the distributed antenna devices 30-1 to 30-P are arranged, there may be an error in the timing at which the instruction from the digital signal processing unit 22 arrives at the distributed antenna devices 30-1 to 30-P. Therefore, the digital signal processing unit 22 may notify time information indicating the timing for transmitting the beam search signal for each beam ID, or the distributed antenna devices 30-1 to 30-P may synchronize their time in advance. The beam search signal transmitted from each distributed antenna device 30 includes information indicating each distributed antenna device 30 used to transmit the beam search signal and information indicating the beam ID associated with the beam. The beam search signal may be transmitted at different times for each distributed antenna device 30-1 to 30-P, or at different frequencies, or at different codes.

[0063] When beam search signals are transmitted at different times for each distributed antenna device 30-1 to 30-P, the distributed antenna devices 30-1 to 30-P transmit beam search signals using the same frequency and the same code. When beam search signals are transmitted at different frequencies for each distributed antenna device 30-1 to 30-P, the distributed antenna devices 30-1 to 30-P transmit beam search signals at the same time using the same code. When beam search signals are transmitted at different codes for each distributed antenna device 30-1 to 30-P, the distributed antenna devices 30-1 to 30-P transmit beam search signals at the same time using the same frequency.

[0064] When applied to one-to-one and many-to-one communication in the distributed antenna system 1, the digital signal processing unit 22 should, in response to a beam search signal transmission instruction, sequentially transmit beam search signals to one distributed antenna device 30 for each different beam.

[0065] The feedback signal receiving unit 215 obtains information from the digital signal processing unit 22 indicating the optimal beam ID for each distributed antenna ID included in the feedback signal and their reception quality. The feedback signal is transmitted from the terminal device 40, received by each distributed antenna device 30, and then decoded by the digital signal processing unit 22. The optimal beam ID for each distributed antenna ID is the beam ID included in the beam search signal with the best reception quality among the multiple beam search signals received by the terminal device 40, for example, the beam search signal for each distributed antenna ID.

[0066] When applied to one-to-one and many-to-one communication, the optimal beam ID for each distributed antenna ID is the beam ID included in the beam search signal with the best reception quality among the multiple beam search signals received by each terminal device 40 for the distributed antenna ID corresponding to each distributed antenna device 30.

[0067] The feedback signal receiving unit 215 outputs information to the beam squint estimation unit 213 indicating the combination of the beam (optimal beam) associated with the acquired optimal beam ID and the distributed antenna ID.

[0068] The data transmission instruction unit 216, in response to instructions from the beam quint estimation unit 213, instructs each terminal device 40 to transmit data after correcting it to the optimal beam ID corresponding to the frequency assigned to it. For terminal devices 40 assigned the same frequency as the one used during beam search, the data transmission instruction unit 216 instructs them to transmit data using the optimal beam ID notified by the terminal device 40. In this case, the distributed antenna devices 30 used may be assigned to each terminal device 40 in order of highest received power across the entire distributed antenna system 1, or they may be assigned to each terminal device 40 in order of highest received signal-to-interference and noise power ratio. Thus, the distributed antenna devices 30 used for communication with each terminal device 40 do not need to be a single unit; multiple units may be used.

[0069] [Configuration of the terminal device] Figure 5 is a diagram showing an example of the configuration of a terminal device 40 in the first embodiment of the present invention. As shown in Figure 5, the terminal device 40 comprises a terminal communication control unit 41, a digital signal processing unit 42, an analog signal unit 43, and Q (where Q is an integer of 2 or more) antenna units 44-1 to 44-Q. Hereinafter, unless it is necessary to distinguish between the antenna units 44-1 to 44-Q, they will simply be referred to as "antenna unit 44".

[0070] The terminal communication control unit 41 performs communication control related to beam selection, which involves selecting the beam used in wireless communication between each antenna unit 44-1 to 44-Q and the base station device B from among multiple types of beams. The terminal communication control unit 41 also uses the antenna units 44-1 to 44-Q to transmit and receive wireless signals with the base station device B.

[0071] The digital signal processing unit 42 acquires the wireless signal output from the antenna unit 44. The digital signal processing unit 42 also measures the reception quality of the beam search signal for each beam ID included in the beam search signal received by the antenna unit 44. The digital signal processing unit 42 outputs information indicating the measurement result of the reception quality of the beam search signal for each beam ID to the terminal communication control unit 41.

[0072] Furthermore, the digital signal processing unit 42 outputs a transmission request instruction for the beam quint estimation reference signal received by the antenna unit 44 to the terminal communication control unit 41. The digital signal processing unit 42 also acquires the transmission instruction for the beam quint estimation reference signal output from the terminal communication control unit 41. Upon acquiring the transmission instruction for the beam quint estimation reference signal, the digital signal processing unit 42 generates the beam quint estimation reference signal. The digital signal processing unit 42 outputs the generated beam quint estimation reference signal to the analog signal unit 43.

[0073] Furthermore, the digital signal processing unit 42 acquires a feedback signal transmission instruction output from the terminal communication control unit 41. Upon acquiring the feedback signal transmission instruction, the digital signal processing unit 42 generates a feedback signal that includes the distributed antenna ID, the optimal beam ID of the distributed antenna ID, and information indicating its reception quality. The digital signal processing unit 42 outputs the generated feedback signal to the analog signal unit 43.

[0074] The feedback signal may be any of the 3GPP standard PRACH (Physical Random Access Channel), PUCCH (physical uplink control channel), or PUSCH (physical uplink shared channel), or it may be an IEEE 802.11ad or IEEE 802.11ay SSW frame, Sector sweep feedback (SSW-Feedback) frame, or BRP frame.

[0075] The analog signal unit 43 converts the feedback signal or beam quint estimation reference signal output from the digital signal processing unit 42 into an analog signal and transmits it from each antenna unit 44. The analog signal unit 43 converts the signal received by each antenna unit 44 (for example, a beam search signal) into a digital signal and outputs it to the digital signal processing unit 42.

[0076] The antenna unit 44 receives radio signals transmitted from the distributed antenna device 30. For example, the antenna unit 44 receives a transmission request instruction for a beam search signal or a beam squint estimation reference signal transmitted from the distributed antenna device 30. The antenna unit 44 outputs the received radio signals to the analog signal unit 43.

[0077] Furthermore, the antenna unit 44 acquires the feedback signal or beam quint estimation reference signal, which will be described later, output from the analog signal unit 43. The antenna unit 44 transmits the acquired feedback signal or beam quint estimation reference signal to the base station device B.

[0078] The terminal communication control unit 41 includes a request receiving unit 411, a reference signal transmitting unit 412, a beam search signal receiving unit 413, a feedback signal transmitting unit 414, and a data transmission instruction unit 415.

[0079] The request receiving unit 411 receives a transmission request instruction for a beam quint estimation reference signal from the digital signal processing unit 42. The request receiving unit 411 outputs the acquired transmission request instruction for a beam quint estimation reference signal to the reference signal transmitting unit 412.

[0080] The reference signal transmission unit 412 receives a transmission request instruction for a beam quint estimation reference signal from the request reception unit 411. The reference signal transmission unit 412 generates a transmission instruction for a beam quint estimation reference signal in response to the acquired transmission request instruction for a beam quint estimation reference signal. The reference signal transmission unit 412 outputs the generated transmission instruction for a beam quint estimation reference signal to the digital signal processing unit 42.

[0081] The channel transmitted by the reference signal transmission unit 412 may be an SRS (Sounding Reference Signal). Furthermore, it may be a channel with a different time and frequency resource arrangement than the above-mentioned channel. It may be arranged on a single subcarrier in the frequency direction, multiplexed on subcarriers, continuously, or discretely. It may also be arranged as a single symbol in the time direction, multiplexed, continuously, or discretely.

[0082] The digital signal processing unit 42 acquires a transmission instruction for the beam quint estimation reference signal output from the reference signal transmission unit 412. In response to the acquired transmission instruction for the beam quint estimation reference signal, the digital signal processing unit 42 causes the antenna unit 44 to transmit the beam quint estimation reference signal at a specified reference frequency.

[0083] The beam search signal receiving unit 413 acquires information indicating the measurement results of the reception quality of the beam search signal for each distributed antenna ID and beam ID output from the digital signal processing unit 42. The beam search signal receiving unit 413 identifies, for example, the optimal beam ID included in the beam search signal with the best reception quality for each distributed antenna ID. The beam search signal receiving unit 413 outputs the identified optimal beam ID for each distributed antenna ID and information indicating its reception quality to the feedback signal transmitting unit 414.

[0084] The feedback signal transmission unit 414 acquires the optimal beam ID for each distributed antenna ID output from the beam search signal receiving unit 413, along with information indicating its reception quality. The feedback signal transmission unit 414 outputs a feedback signal transmission instruction to the digital signal processing unit 42, which is an instruction to transmit a feedback signal containing the optimal beam ID for each distributed antenna ID and information indicating its reception quality to the base station device B. For example, the feedback signal transmission unit 414 outputs a feedback signal transmission instruction to the digital signal processing unit 42 for each distributed antenna ID, which is an instruction to transmit a feedback signal containing the optimal beam ID for each distributed antenna ID and information indicating their reception quality to the base station device B.

[0085] The digital signal processing unit 42 acquires a feedback signal transmission instruction output from the feedback signal transmission unit 414. The digital signal processing unit 42 then causes the antenna unit 44 to transmit a feedback signal in accordance with the acquired feedback signal transmission instruction.

[0086] The data transmission instruction unit 48 instructs data transmission to and from the base station device B.

[0087] (Details of the beam squint estimation method in the first embodiment) Next, the details of the beam squint estimation method in base station device B will be described. The beam squint estimation unit 213 in base station device B estimates beam squints based on one or more beam squint estimation reference signals transmitted from terminal device 40. This will be explained in detail below.

[0088] (Receiving a reference signal for beam squint estimation using only the optimal beam) Base station equipment B receives a reference signal for beam squint estimation using the optimal beam identified by the beam ID of base station equipment B that is optimal for a certain reference subcarrier or resource block. Figure 6 shows the results of a graph with frequency on the horizontal axis and the optimal beam ID that maximizes reception quality in any of the following units: subcarrier unit, resource block unit, multiple subcarrier unit, or multiple resource block unit, on the vertical axis. From equation (5) shown below, it can be seen that the beam direction θ corresponding to the optimal beam ID shifts continuously in the frequency direction due to beam squint.

[0089]

[0090] Note that equation (5) is a simplified version of equation (3) above, so equation (3) will be used for explanation as needed. In equation (3), θ represents the beam direction at the target frequency f, and θ ０ The reference frequency is f ０ This represents the beam direction, where r is the reference frequency f. ０ This represents the ratio of the target frequency f to the given frequency.

[0091] Figure 6 shows three data points with different optimal beam IDs for a reference subcarrier (reference frequency). Three different data points are obtained when the terminal device 40 is located at a different position and the optimal beam ID changes. In reality, it is not a straight line but ideally an arcsin function. This makes it possible to associate the optimal beam ID for a given subcarrier with the optimal beam ID for a different subcarrier. For example, the beam squint estimation unit 213 estimates the optimal beam ID for each other subcarrier from equation (3) based on the optimal beam ID for the reference subcarrier. By obtaining data with different optimal beam IDs for the reference subcarrier for each beam ID, the beam squint estimation unit 213 stores the estimated optimal beam IDs for each subcarrier as a beam selection table, associated with frequencies.

[0092] Furthermore, although the above method describes how to acquire data for each beam ID that is optimal for the reference subcarrier, the interval between these optimal beam IDs may be estimated by interpolation. In this case, linear interpolation may be used, polynomial interpolation may be used, spline interpolation may be used, or interpolation may be performed while considering the angular spacing of the discrete beams.

[0093] In the example described above, a configuration was shown in which a reference signal for beam squint estimation is transmitted on the reference subcarrier, and the optimal beam ID for each other subcarrier is estimated based on equation (3). In contrast, the beam squint estimation unit 213 may estimate the beam squint by having the terminal device 40 transmit a reference signal for beam squint estimation on some subcarriers, including the reference subcarrier, or on all subcarriers, and then estimate the optimal beam ID for each subcarrier based on the beam squint estimation result. When all subcarriers transmit a reference signal for beam squint estimation, the base station device B directly measures the beam squint, and when estimating on some subcarriers, it interpolates the optimal beam ID at other frequencies. At this time, linear interpolation may be used, polynomial interpolation may be used, spline interpolation may be used, or a method of fitting to the arcsin function of equation (3) may be used. However, since the beam ID is a discrete value, interpolation may be performed considering the angular spacing of the discrete beams. Furthermore, while the above method describes how to acquire data for each beam ID that is optimal for the reference subcarrier, the intervals between these optimal beam IDs may be estimated by interpolation, similar to the method described above.

[0094] (Receiving reference signals for beam squint estimation on multiple beams) Base station device B receives a reference signal for beam squint estimation for each of the multiple beams identified by multiple beam IDs. Based on this, base station device B estimates the beam squint based on three-dimensional data of beam ID, frequency, and reception quality. The beam squint estimation unit 213 creates three-dimensional data shown in Figure 7 for each optimal beam ID in the reference subcarrier and estimates the beam ID that yields the maximum reception quality for each frequency for each optimal beam ID in the reference subcarrier. The estimation is plotted for each optimal beam ID in the reference subcarrier, and this is obtained when multiple terminal devices 40 are located in different positions and the optimal beam ID in the reference subcarrier changes.

[0095] Base station device B may transmit a reference signal for beam squint estimation on all subcarriers, measure the beam squint, and output the optimal beam ID at each frequency. Alternatively, it may transmit a reference signal for beam squint estimation on some subcarriers, including the reference subcarrier, and interpolate the optimal beam ID at other frequencies. For beam squint estimation, linear interpolation may be used, polynomial interpolation may be used, spline interpolation may be used, or a method of fitting to a theoretical formula for the ratio of array factors may be used. Alternatively, base station device B may transmit a reference signal for beam squint estimation on one subcarrier and estimate based on equation (3). The reference signal may be transmitted and received for all beam IDs, or for the adjacent beam IDs of the optimal beam ID on the reference subcarrier, or for the top N beam IDs on the reference subcarrier.

[0096] If there are multiple data points for the optimal beam ID on the same reference subcarrier, the average reception quality may be used, the data may not be updated, or the latest data may be used. Also, if the transmission timing of the reference signal differs between multiple beam pairs, and the terminal moves at high speed, the beam direction shift due to the terminal's movement may be affected. Therefore, the reliability may be changed according to the terminal's movement speed to obtain more reliable information, or if the terminal device 40 is moving at a high speed, the method shown in the second embodiment (transmitting the reference signal only with the optimal beam) may be used. A method for acquiring data for each beam ID that is optimal on the reference subcarrier has been described, but the data between optimal beam IDs may be estimated by interpolation as described above.

[0097] [Operation of Base Station Device B] The operation example of base station device B will be described below. Figure 8 is a flowchart showing the processing flow of base station device B in the first embodiment. The request transmission unit 211 instructs all distributed antenna devices 30 to transmit a request instruction for the transmission of a beam quint estimation reference signal. Specifically, first the request transmission unit 211 generates a request instruction for the transmission of a beam quint estimation reference signal. Next, the request transmission unit 211 outputs the generated request instruction for the transmission of a beam quint estimation reference signal to the digital signal processing unit 22. The digital signal processing unit 22 outputs the request instruction for the transmission of a beam quint estimation reference signal output from the request transmission unit 211 to all distributed antenna devices 30 via the analog signal unit 23. Each distributed antenna device 30 transmits the request instruction for the transmission of a beam quint estimation reference signal output from the digital signal processing unit 22 to the terminal device 40 (step S101).

[0098] After sending a transmission request instruction for the beam quint estimation reference signal, base station device B waits for a response to the transmission request instruction for the beam quint estimation reference signal to be transmitted from terminal device 40. Let's assume that base station device B receives the beam quint estimation reference signal from terminal device 40 as a response to the transmission request instruction for the beam quint estimation reference signal. For example, let's assume that one distributed antenna device 30-1 installed in base station device B receives the beam quint estimation reference signal from terminal device 40 as a response to the transmission request instruction for the beam quint estimation reference signal. Distributed antenna device 30-1 outputs the received beam quint estimation reference signal to the digital-analog signal processing device 20. Distributed antenna device 30-1 will be used as an example in this explanation.

[0099] In this case, the reference signal receiving unit 212 acquires a reference signal for beam quint estimation from the digital signal processing unit 22 (step S102). For example, the reference signal receiving unit 212 acquires a reference signal for beam quint estimation received by the distributed antenna device 30-1 from the digital signal processing unit 22. The reference signal receiving unit 212 outputs the acquired reference signal for beam quint estimation to the beam quint estimation unit 213.

[0100] The beam squint estimation unit 213 estimates the beam squint using one of the methods described above, based on the beam squint estimation reference signal output from the reference signal receiving unit 212 (step S103). Based on the beam squint estimation result, the beam squint estimation unit 213 generates a beam selection table that associates the frequency with the optimal beam ID.

[0101] The beam search signal transmission unit 214 initializes the beam search period counter (step S104). Then, the beam search signal transmission unit 214 instructs all distributed antenna devices 30 to transmit beam search signals sequentially in the time domain (step S105). For example, the beam search signal transmission unit 214 instructs each distributed antenna device 30 to transmit beam search signals separately for time, frequency, or code. As a result, each distributed antenna device 30 transmits beam search signals separately for time, frequency, or code. Here, we will explain using the case where each distributed antenna device 30 transmits beam search signals separately for time as an example.

[0102] A more detailed explanation of the processing flow in step S105 follows. The beam search signal transmission unit 214 determines the value of P, which is the number of distributed antenna devices 30 that perform beam selection, and the value of n, which is the number of beams used by each distributed antenna device 30. The beam search signal transmission unit 214 assigns a beam ID to each beam used by the multiple distributed antenna devices 30 for transmitting the beam search signal, so that the beam can be uniquely identified. For example, the beam search signal transmission unit 214 assigns beam IDs such as beam ID #1, beam ID #2, and beam ID #3 so that three beams can be uniquely identified.

[0103] Next, the beam search signal transmitting unit 214 initializes the value of counter i, which counts the beams to which the beam search signal is transmitted, to i = 0. The beam search signal transmitting unit 214 also initializes the value of counter j, which counts the distributed antenna devices 30 that transmit the beam search signal, to j = 0. Next, in order to transmit the beam search signal with the next beam (i.e., to sweep the beam), the beam search signal transmitting unit 214 increments the value of counter i by 1, to i ← i + 1. The beam search signal transmitting unit 214 also increments the value of counter j by 1, to j ← j + 1, in order to identify the distributed antenna device 30 that transmits the beam search signal.

[0104] Next, the beam search signal transmission unit 214 outputs a beam search signal transmission instruction to the digital signal processing unit 22, which is an instruction for the j-th distributed antenna device 30 to transmit a beam search signal containing information indicating the beam ID associated with the i-th beam using the i-th beam. As a result, the beam search signal is transmitted from the j-th distributed antenna device 30 using the i-th beam.

[0105] The beam search signal transmission unit 214 repeatedly outputs a beam search signal transmission instruction to the digital signal processing unit 22 until the j-th distributed antenna device 30 transmits a beam search signal using n types of beams (i.e., until i = n). As a result, a beam search signal is transmitted from one distributed antenna device 30 using n types of beams.

[0106] Furthermore, the beam search signal transmission unit 214 repeats the above process until all P-unit distributed antenna devices 30 transmit beam search signals using n types of beams (i.e., until j = P). As a result, beam search signals are transmitted at different timings using n types of beams from each distributed antenna device 30.

[0107] Next, the feedback signal receiving unit 215 waits for the distributed antenna devices 30 to receive the feedback signal transmitted from the terminal device 40 in response to the transmitted beam search signal (step S106). Each distributed antenna device 30 receives a feedback signal as a response to the beam search signal transmitted by each distributed antenna device 30, and the feedback signal receiving unit 215 performs the following processing each time a feedback signal is received. Here, the feedback signal includes the distributed antenna ID, the optimal beam ID for the distributed antenna ID, and information indicating their reception quality.

[0108] The feedback signal receiving unit 215 obtains from the digital signal processing unit 22 information indicating the distributed antenna ID, the optimal beam ID of the distributed antenna ID, and their reception quality included in the feedback signal received by each distributed antenna device 30. For example, the feedback signal receiving unit 215 obtains the distributed antenna ID, the optimal beam ID of the distributed antenna ID, and information indicating the reception quality included in the feedback signal received by distributed antenna device 30-1, and obtains feedback information indicating the distributed antenna ID, the optimal beam ID of the distributed antenna ID, and the reception quality included in the feedback signal received by distributed antenna device 30-P. The feedback signal receiving unit 215 outputs the acquired feedback information to the beam quint estimation unit 213. For example, if there are three terminal devices 40 (for example, terminal devices 40-1 to 40-3), the feedback signal receiving unit 215 outputs the feedback information transmitted from each of the terminal devices 40-1 to 40-3 to the beam quint estimation unit 213.

[0109] The beam quint estimation unit 213 acquires feedback information for each terminal device 40 output from the feedback signal receiving unit 215. Furthermore, the beam quint estimation unit 213 acquires information indicating the frequency assigned to each terminal device 40. The frequency assignment to each terminal device 40 may be performed by the feedback signal receiving unit 215. Based on the information indicating the frequency assigned to each terminal device 40, the feedback information for each terminal device 40, and the beam selection table, the beam quint estimation unit 213 determines the optimal beam for each terminal device 40.

[0110] Specifically, the beam squint estimation unit 213 determines the optimal beam included in the feedback information as the optimal beam for the terminal device 40 to which the frequency used during beam search was assigned. Here, as an example, the frequency used during beam search is f ２ The optimal beam IDs responded from each of the terminal devices 40-1 to 40-3 are designated as "Beam ID #2", and the frequency f is set in terminal device 40-1. ３ Assign a frequency f to terminal device 40-2. ２Assign a frequency f to terminal device 40-3. １ Let's assume that a beam squint is assigned. In this case, the beam squint estimation unit 213 assigns "beam ID #2" to the terminal device 40-2.

[0111] Furthermore, for terminal devices 40 to which a frequency other than the frequency used during beam search has been assigned, the beam squint estimation unit 213 refers to the beam selection table and determines the beam identified by the optimal beam ID associated with the assigned frequency as the optimal beam for the terminal device 40. For example, in the above example, the beam squint estimation unit 213 assigns the optimal beam ID "beam ID #2" to terminal device 40-1, and the frequency f １ The optimal beam ID associated with the frequency f is corrected and assigned. Similarly, the beam squint estimation unit 213 assigns the optimal beam ID "beam ID #2" to the terminal device 40-3, with frequency f ３ The optimal beam ID is corrected and assigned to the associated beam. The beam squint estimation unit 213 outputs information indicating the optimal beam for each terminal device 40 and information indicating the combination with the optimal antenna ID to the data transmission instruction unit 216.

[0112] Based on the information output from the beam quint estimation unit 213, the data transmission instruction unit 216 selects a combination of the distributed antenna device 30 and beam ID for each terminal device 40 and instructs data transmission (step S107). For example, for a terminal device 40 (e.g., terminal device 40-2) to which the frequency used during beam search was assigned, the data transmission instruction unit 216 selects a combination of the optimal beam and optimal antenna ID included in the feedback information and instructs data transmission. In the above example, the data transmission instruction unit 216 assigns "beam ID #2" as the optimal beam ID for the terminal device 40 to which the frequency used during beam search was assigned.

[0113] Furthermore, the data transmission instruction unit 216, for terminal devices 40 (for example, terminal devices 40-1 and 40-3) that have been assigned frequencies other than those used during beam search, selects a combination of the optimal beam and optimal antenna ID instructed by the beam squint estimation unit 213 and instructs them to transmit data.

[0114] Subsequently, base station device B determines whether the beam search period has elapsed (step S108). If base station device B determines that the beam search period has elapsed (step S108-YES), base station device B executes the processes from step S104 onwards. On the other hand, if base station device B determines that the beam search period has not elapsed (step S108-NO), base station device B executes the processes from step S107 onwards.

[0115] [Operation of Terminal Device 40] The operation of the terminal device 40 will be described below. Figure 9 is a flowchart showing the processing flow of the terminal device 40 in the first embodiment. The request receiving unit 411 receives a transmission request instruction for the beam quint estimation reference signal transmitted from the base station device B from the digital signal processing unit 42 (step S201). The request receiving unit 411 outputs the acquired transmission request instruction for the beam quint estimation reference signal to the reference signal transmitting unit 412. The reference signal transmitting unit 412 generates a transmission instruction for the beam quint estimation reference signal in response to the transmission request instruction for the beam quint estimation reference signal output from the request receiving unit 411. The reference signal transmitting unit 412 outputs the generated transmission instruction for the beam quint estimation reference signal to the digital signal processing unit 42.

[0116] The digital signal processing unit 42 transmits the beam quint estimation reference signal to the base station device B via the analog signal unit 43 and the antenna unit 44 in response to the transmission instruction for the beam quint estimation reference signal output from the reference signal transmission unit 412 (step S202).

[0117] The digital signal processing unit 42 waits for the antenna unit 44 to receive beam search signals for each beam ID transmitted from each distributed antenna device 30 (step S203). The beam search signals for each beam ID transmitted from the distributed antenna device 30 are received sequentially by the antenna unit 44 using, for example, omnidirectional or low-directional beams.

[0118] When the beam search signal for each beam ID transmitted from each distributed antenna device 30 is received by the antenna unit 44, the digital signal processing unit 42 measures the reception quality of the beam search signal for each beam ID included in the beam search signal received by the antenna unit 44. The beam search signal receiving unit 413 selects the optimal beam ID for each distributed antenna ID based on the reception quality of the beam search signal for each beam ID measured by the digital signal processing unit 42. For example, the beam search signal receiving unit 413 selects the beam ID included in the beam search signal with the best reception quality as the optimal beam ID. The beam search signal receiving unit 413 outputs information indicating the identified optimal beam ID, information indicating the distributed antenna ID, and information indicating the reception quality corresponding to the optimal beam ID to the feedback signal transmitting unit 414.

[0119] Next, the feedback signal transmission unit 414 outputs a feedback signal transmission instruction to the digital signal processing unit 42, which is an instruction to transmit a feedback signal to the base station device B that includes the distributed antenna ID, information indicating the optimal beam ID of the distributed antenna ID, and information indicating the reception quality corresponding to the optimal beam ID. The digital signal processing unit 42 generates a feedback signal that includes the distributed antenna ID, information indicating the optimal beam ID of the distributed antenna ID, and information indicating the reception quality corresponding to the optimal beam ID. The antenna unit 44 transmits the generated feedback signal to the base station device B (step S204). After that, the data transmission instruction unit 415 obtains information from the digital signal processing unit 42 indicating the time-frequency resource allocated from the base station device B (step S205).

[0120] Subsequently, the data transmission instruction unit 415 instructs data transmission using the allocated time-frequency resources (step S206). Then, the terminal device 40 determines whether or not it has received the beam search signal again (step S207). If the terminal device 40 determines that it has received the beam search signal again (step S207-YES), the terminal device 40 executes the processes from step S203 onwards. On the other hand, if the terminal device 40 determines that it has not received the beam search signal again (step S207-NO), the terminal device 40 executes the processes from step S206 onwards.

[0121] [Operation of Distributed Antenna System 1] The following describes an example of the operation of the entire distributed antenna system 1. Figure 10 is a sequence diagram showing the processing flow of the distributed antenna system 1 in the first embodiment. The base station device B sends a request to the terminal device 40 to transmit a beam quint estimation reference signal (step S301). In response to the request to transmit a beam quint estimation reference signal sent from the base station device B, the terminal device 40 transmits a beam quint estimation reference signal at a reference frequency (step S302).

[0122] Base station device B receives a beam quint estimation reference signal transmitted from terminal device 40. Based on the received beam quint estimation reference signal, base station device B instructs the beam quint estimation unit 213 to estimate the beam quint (step S303). As a result, the beam quint estimation unit 213 estimates the beam quint. Subsequently, base station device B transmits beam search signals sequentially in the time domain for each distributed antenna device 30 (step S304). Base station device B performs this process for each distributed antenna device 30 for the number of beam IDs in total.

[0123] The terminal device 40 receives beam search signals corresponding to the beam IDs transmitted from the base station device B. The terminal device 40 generates a feedback signal based on the beam search signals corresponding to the received beam IDs. The terminal device 40 transmits the generated feedback signal to the base station device B (step S305). The base station device B receives the feedback signal transmitted from the terminal device 40. Based on the received feedback signal, the base station device B detects the combination of the assigned distributed antenna ID and its optimal beam ID and outputs it to the beam quint estimation unit 213.

[0124] Base station device B allocates time-frequency resources to be used for data transmission to terminal devices 40 (step S306). Base station device B outputs information indicating the frequency allocated to each terminal device 40, and information indicating the allocated distributed antenna ID and its optimal beam ID included in the feedback signal, to the beam quint estimation unit 213 (step S307). Based on the beam quint estimation results, the beam quint estimation unit 213 outputs information indicating the beam direction (optimal beam ID) at the frequency allocated to each terminal device 40 to the data transmission instruction unit 216 (step S308).

[0125] Base station device B instructs data transmission based on the information obtained. When base station device B transmits data, it transmits the data instructed by the data transmission instruction unit 216 using one or more distributed antenna devices 30 (step S309). When terminal device 40 transmits data, terminal device 40 transmits data to base station device B using its allocated resources (step S310).

[0126] According to the distributed antenna system 1 configured as described above, the base station device B includes a beam squint estimation unit 213 that estimates beam squints based on a reference signal for estimating beam squints and estimates optimal beams at frequencies other than the specific frequencies used for beam squint estimation based on the estimated beam squints, and a data transmission instruction unit 216 that, during data transmission, instructs data transmission with the optimal beam corresponding to the frequency assigned to each terminal device 40, based on the optimal beam for each frequency estimated by the beam squint estimation unit 213.

[0127] As a result, when transmitting data to a terminal device 40 that is assigned a frequency affected by beam squint, the data is transmitted using a beam that takes the effects of beam squint into account. Therefore, it becomes possible to suppress the deterioration of reception quality due to the effects of beam squint.

[0128] (Modification 1 in the first embodiment) When base station device B receives a reference signal for beam squint estimation, base station device B may use the optimal beam detected in advance for (transmission of the reference signal using only the optimal beam), or it may use multiple beams with high received power detected in advance for (transmission of the reference signal using multiple beams).

[0129] (Modification 2 of the First Embodiment) In the first embodiment, a configuration was described in which a reference signal for beam squint estimation is transmitted uplink from the terminal device 40 and received by the base station device B to estimate the beam squint. In contrast, the base station device B may transmit a reference signal for beam squint estimation to the terminal device 40 using an optimal beam or multiple beams, and the terminal device 40 may receive the reference signal for beam squint estimation. In this case, the terminal device 40 may estimate the beam squint, or the reception result of the reference signal for beam squint estimation may be fed back to the base station device B.

[0130] When estimating beam squints in terminal device 40, terminal device 40 may be equipped with a beam squint estimation unit 213, while base station device B may not be equipped with a beam squint estimation unit 213. When terminal device 40 feeds back the reception results of the beam squint estimation reference signal to base station device B, terminal device 40 may feed back all information to base station device B, or it may feed back information for each discrete frequency interval, or it may feed back only beams whose received power is above a certain threshold.

[0131] (Modification 3 in the First Embodiment) In the first embodiment, the case of a one-dimensional beam was described as an example for the base station device B and the terminal device 40, but the same can be applied when using a two-dimensional beam. In this case, the beam ID that was considered in one dimension is separated and applied in two dimensions. In this case, the beam IDs are made adjacent in the two-dimensional beam direction.

[0132] (Second Embodiment) In the first embodiment, a configuration was described for when beamforming is performed in the base station equipment. In contrast, it is conceivable that beamforming may also be performed in the terminal equipment. In that case, it is necessary to include beam squint in the terminal equipment as well. Therefore, in the second embodiment, a configuration will be described for when beamforming is performed in both the base station equipment and the terminal equipment.

[0133] [Configuration of the Distributed Antenna System] The overall configuration of the distributed antenna system 1 in the second embodiment is basically the same as the overall configuration of the distributed antenna system 1 in the first embodiment shown in Figure 3 above, so the explanation is omitted.

[0134] [Configuration of the base station device] The configuration of the base station device will be described below. Figure 11 shows an example of the configuration of base station device Ba in the second embodiment of the present invention. As shown in Figure 11, base station device Ba comprises a digital-analog signal processing device 20a and P distributed antenna devices 30-1 to 30-P. Base station device Ba differs from base station device B in that it has a digital-analog signal processing device 20a instead of a digital-analog signal processing device 20. The differences from base station device B will be explained below.

[0135] The digital-to-analog signal processing device 20a comprises a base station communication control unit 21a, a digital signal processing unit 22, and an analog signal unit 23. The base station communication control unit 21a comprises a request transmission unit 211, a reference signal receiving unit 212, a beam squint estimation unit 213, a beam search signal transmission unit 214, a feedback signal receiving unit 215, a data transmission instruction unit 216, a request reception unit 217, and a reference signal transmission unit 218.

[0136] The request receiving unit 217 receives a transmission request instruction for the beam quint estimation reference signal from the digital signal processing unit 22. The request receiving unit 217 outputs the acquired transmission request instruction for the beam quint estimation reference signal to the reference signal transmitting unit 218.

[0137] The reference signal transmission unit 218 receives a transmission request instruction for a beam quint estimation reference signal from the request reception unit 217. The reference signal transmission unit 218 generates a transmission instruction for a beam quint estimation reference signal in response to the acquired transmission request instruction for a beam quint estimation reference signal. The reference signal transmission unit 218 outputs the generated transmission instruction for a beam quint estimation reference signal to the digital signal processing unit 22.

[0138] The channel transmitted by the reference signal transmission unit 218 may be CSI-RS or DM-RS (Demodulation Reference Signal). Furthermore, it may be a channel with a different time and frequency resource arrangement than the above-mentioned channel, and may be arranged on a single subcarrier in the frequency direction, multiplexed on subcarriers, continuously, or discretely. It may also be arranged as a single symbol in the time direction, multiplexed, continuously, or discretely.

[0139] The digital signal processing unit 22 acquires a transmission instruction for the beam quint estimation reference signal output from the reference signal transmission unit 218. In response to the acquired transmission instruction for the beam quint estimation reference signal, the digital signal processing unit 22 causes the distributed antenna device 30 to transmit the beam quint estimation reference signal at a reference frequency.

[0140] [Configuration of the terminal device] Figure 12 shows an example configuration of the terminal device 40a in the second embodiment of the present invention. As shown in Figure 12, the terminal device 40a comprises a terminal communication control unit 41a, a digital signal processing unit 42, an analog signal unit 43, and Q antenna units 44-1 to 44-Q. The terminal device 40a differs from the terminal device 40 in that it has a terminal communication control unit 41a instead of a terminal communication control unit 41. The differences from the terminal device 40 will be explained below.

[0141] The terminal communication control unit 41a includes a request receiving unit 411, a reference signal transmitting unit 412, a beam search signal receiving unit 413, a feedback signal transmitting unit 414, a data transmission instruction unit 415, a reference signal request unit 416, a reference signal receiving unit 417, and a beam quint estimation unit 418.

[0142] The reference signal request unit 416 generates a transmission request instruction for a beam quint estimation reference signal. Here, the beam quint estimation reference signal transmission request instruction generated by the reference signal request unit 416 is an instruction to request the terminal device 40a to transmit a reference signal for estimating the beam quint. The reference signal request unit 416 outputs the generated beam quint estimation reference signal transmission request instruction to the digital signal processing unit 42.

[0143] The channel transmitted by the reference signal request unit 416 may be PUCCH or PUSCH (Physical Uplink Shared Channel). The request information may also be stored in DCI or UCI, in MAC CE, in RRC parameters, or in the NAS message.

[0144] The digital signal processing unit 42 receives a transmission request instruction for the beam quint estimation reference signal output from the reference signal request unit 416. In response to the acquired transmission request instruction for the beam quint estimation reference signal, the digital signal processing unit 42 causes the antenna unit 44 to transmit the transmission request instruction for the beam quint estimation reference signal.

[0145] The reference signal receiving unit 417 acquires a reference frequency beam quint estimation reference signal transmitted from the base station device Ba as a response to a transmission request instruction from the digital signal processing unit 42. The reference signal receiving unit 417 outputs the acquired beam quint estimation reference signal to the beam quint estimation unit 418.

[0146] The beam squint estimation unit 418 estimates the beam squint based on the beam squint estimation reference signal acquired by the reference signal receiving unit 417. The specific method by which the beam squint estimation unit 418 estimates the beam squint will be described later. The beam squint estimation unit 418 also estimates the optimal beam ID at other frequencies based on the beam squint estimation result. Based on the estimation result, the beam squint estimation unit 418 generates and maintains a beam selection table that associates frequencies with the optimal beam ID.

[0147] Furthermore, the beam squint estimation unit 418 selects the optimal beam to be used for data transmission based on the assigned frequency and the beam selection table it holds during data transmission.

[0148] (Details of the beam squint estimation method in the second embodiment) Next, the details of the beam squint estimation method in the base station device Ba and the terminal device 40a will be described. The beam squint estimation unit 213 in the base station device B estimates beam squints based on one or more beam squint estimation reference signals transmitted from the terminal device 40a. Similarly, the beam squint estimation unit 418 in the terminal device 40a estimates beam squints based on one or more beam squint estimation reference signals transmitted from the base station device Ba. This will be explained in detail below.

[0149] (Sending and receiving reference signals for beam squint estimation using only the optimal beam) The estimation will be performed in the same manner as described in (receiving reference signals for beam squint estimation using only the optimal beam) in the first embodiment. However, in the second embodiment, since the terminal device 40a also has beamforming, a reference signal for beam squint estimation is sent and received using a beam pair of the beam ID of the base station device Ba and the beam ID of the terminal device 40a that is optimal for a certain reference subcarrier or resource block. As a result, for each optimal beam pair in the reference subcarrier, three-dimensional data of frequency vs. the optimal beam ID of the base station corresponding to each frequency vs. the optimal beam ID of the terminal corresponding to each frequency is created, and the beam pair that can obtain the maximum reception quality for each frequency is estimated for each optimal beam pair in the reference subcarrier.

[0150] Estimation is performed for each optimal beam pair in the reference subcarrier, and this is obtained when the terminal device 40a is located in a different position, or when the orientation of the terminal device 40a changes and the optimal beam ID in the reference subcarrier changes. Similar to the first embodiment, when a reference signal for beam squint estimation is transmitted for all subcarriers, the base station device Ba and the terminal device 40a directly measure the beam squint, and when estimation is performed for some subcarriers, including the reference subcarrier, the optimal beam ID at other frequencies is interpolated. At this time, linear interpolation may be used, polynomial interpolation may be used, spline interpolation may be used, or the beam of the base station device Ba and the beam of the terminal device 40a may be fitted to the arcsin function of equation (3). However, since the beam ID is a discrete value, interpolation may be performed considering the angular spacing of the discrete beams.

[0151] The method described above involves acquiring data for each beam ID that is optimal for the reference subcarrier. However, the data between optimal beam IDs may be estimated by interpolation, similar to the method described above.

[0152] (Transmitting and Receiving Reference Signals for Beam Squint Estimation with Multiple Beams) The estimation will be performed in the same manner as described in (Receiving Reference Signals for Beam Squint Estimation with Multiple Beams) in the first embodiment. However, in the second embodiment, since the terminal device 40a also has beamforming, reference signals for beam squint estimation are transmitted and received using beam pairs of beam IDs from multiple base station devices Ba and beam IDs from the terminal device 40a. This allows estimation to be performed for each optimal beam pair in the reference subcarrier based on four-dimensional data of base station beam ID, terminal device beam ID, frequency, and reception quality. This involves creating four-dimensional data for each optimal beam pair in the reference subcarrier and estimating the beam pair that yields the maximum reception quality for each frequency for each optimal beam pair in the reference subcarrier. Estimation is performed for each optimal beam ID in the reference subcarrier because the optimal beam ID in the reference subcarrier changes if the terminal device 40a is located in a different position or changes orientation.

[0153] Similar to the first embodiment, when a reference signal for beam squint estimation is transmitted on all subcarriers, the base station device Ba and terminal device 40a directly measure the beam squint. When estimation is performed on some subcarriers, the optimal beam IDs at other frequencies are interpolated. In this case, linear interpolation, polynomial interpolation, spline interpolation, or a method of fitting to a theoretical formula for the ratio of array factors may be used for beam squint estimation. The reference signal may be transmitted and received on all beam IDs, on adjacent beam IDs of the optimal beam ID on the reference subcarrier, or on the top N beam IDs on the reference subcarrier.

[0154] If there are multiple data points for the optimal beam ID on the same reference subcarrier, the average reception quality may be used, the data may not be updated, or the latest data may be used. Also, if the transmission timing of the reference signal differs between multiple beam pairs, and the terminal moves at high speed, the beam direction shift due to the terminal's movement may be affected. Therefore, the reliability may be changed according to the terminal's movement speed to obtain more reliable information, or if the terminal device 40 is moving at a high speed, the method shown in the second embodiment (transmitting the reference signal only with the optimal beam) may be used. A method for acquiring data for each beam ID that is optimal on the reference subcarrier has been described, but the data between optimal beam IDs may be estimated by interpolation as described above.

[0155] [Operation of Base Station Device Ba] The operation of base station device Ba will be described below. Figure 13 is a flowchart showing the processing flow of base station device Ba in the second embodiment. In Figure 13, the same reference numerals as in Figure 8 are used for processing similar to that in Figure 8, and their explanation is omitted.

[0156] The request receiving unit 217 receives a transmission request instruction for the beam quint estimation reference signal transmitted from the terminal device 40a from the digital signal processing unit 22 (step S401). The request receiving unit 217 outputs the acquired transmission request instruction for the beam quint estimation reference signal to the reference signal transmitting unit 218. The reference signal transmitting unit 218 generates a transmission instruction for the beam quint estimation reference signal in response to the transmission request instruction for the beam quint estimation reference signal output from the request receiving unit 217. The reference signal transmitting unit 218 outputs the generated transmission instruction for the beam quint estimation reference signal to the digital signal processing unit 22.

[0157] The digital signal processing unit 22 transmits the beam quint estimation reference signal to the terminal device 40 via the analog signal unit 23 and the distributed antenna device 30 in response to the transmission instruction for the beam quint estimation reference signal output from the reference signal transmission unit 218 (step S402). Subsequently, the processing from step S101 onwards is executed. Note that the processing shown in Figure 13 is just one example, and the processing from step S401 to step S402 may be executed after the processing from step S101 to step S103.

[0158] [Operation of Terminal Device 40a] The operation of terminal device 40a will be described below. Figure 14 is a flowchart showing the processing flow of terminal device 40a in the second embodiment. In Figure 14, the same reference numerals as in Figure 9 are used for processing similar to that in Figure 9, and their explanation is omitted.

[0159] The reference signal request unit 416 outputs a transmission request instruction for the beam quint estimation reference signal to the digital signal processing unit 42 (step S501). The digital signal processing unit 42 transmits the transmission request instruction for the beam quint estimation reference signal output from the reference signal request unit 416 to the base station device Ba via the analog signal unit 43 and the antenna unit 44.

[0160] The reference signal receiving unit 417 acquires a reference signal for beam squint estimation from the digital signal processing unit 42 (step S502). The reference signal receiving unit 417 outputs the acquired reference signal for beam squint estimation to the beam squint estimation unit 418. The beam squint estimation unit 418 estimates the beam squint based on the reference signal for beam squint estimation output from the reference signal receiving unit 417 using one of the methods described above (step S503). Subsequently, the processes from steps S201 to S205 are executed.

[0161] The data transmission instruction unit 415 selects a beam ID from among a plurality of beam IDs corresponding to the frequency assigned by the base station device Ba based on the information output from the beam squint estimation unit 418 and instructs data transmission (step S504). Note that the process shown in Figure 14 is just one example, and the processes from steps S501 to S503 may be executed after the processes from steps S201 to S202. However, the terminal device 40a may change its candidate beam and receive beam search signals transmitted from the base station device Ba multiple times to obtain the optimal beam ID for each distributed antenna ID, or it may be equipped with a beam search signal transmission unit similar to the base station device Ba and receive feedback of the optimal beam ID for each distributed antenna ID from the base station device Ba.

[0162] [Operation of Distributed Antenna System 1] The following describes an example of the overall operation of the distributed antenna system 1 in the second embodiment. Figure 15 is a sequence diagram showing the processing flow of the distributed antenna system 1 in the second embodiment. In Figure 15, the same reference numerals as in Figure 10 are used for processing similar to that in Figure 10, and their explanation is omitted.

[0163] The terminal device 40a transmits a request to the base station device Ba to transmit a beam quint estimation reference signal (step S601). In response to the request to transmit a beam quint estimation reference signal transmitted from the terminal device 40a, the base station device Ba transmits a beam quint estimation reference signal at a reference frequency (step S602). At this time, the base station device Ba may transmit the beam quint estimation reference signal with the optimal beam of the base station device Ba at the reference frequency, or it may transmit the beam quint estimation reference signal with multiple beams.

[0164] The terminal device 40a receives a beam quint estimation reference signal transmitted from the base station device Ba. Based on the received beam quint estimation reference signal, the terminal device 40a instructs the beam quint estimation unit 418 to estimate the beam quint (step S603). As a result, the beam quint estimation unit 418 estimates the beam quint. Subsequently, the processes from steps S301 to S306 are executed.

[0165] The terminal device 40a outputs to the beam quint estimation unit 418 information indicating the assigned frequency and the beam ID (terminal beam) of the terminal device 40a to be used for data transmission (step S604). Based on the beam quint estimation result, the beam quint estimation unit 418 outputs to the data transmission instruction unit 415 information indicating the beam direction (optimal beam ID) at the assigned frequency (step S605). Subsequently, the processing of step S309 or step S310 is executed. In the processing of step S310, the terminal device 40a uses the assigned resources to transmit data to the base station device Ba using the beam identified by the optimal beam ID output from the beam quint estimation unit 418.

[0166] According to the distributed antenna system 1 in the second embodiment configured as described above, the same effects as in the first embodiment can be obtained.

[0167] Furthermore, in the distributed antenna system 1 of the second embodiment, beam squint is also estimated in the terminal device 40a, and beam selection is performed taking into account the effect of beam squint. This makes it possible to suppress the deterioration of reception quality due to the effect of beam squint in both the terminal device 40a and the base station device Ba.

[0168] (Modification 1 in the second embodiment) When the base station device Ba and terminal device 40a receive a reference signal for beam squint estimation, the base station device Ba and terminal device 40a may use the optimal beam detected in advance for (transmission of the reference signal using only the optimal beam), or they may use multiple beams detected in advance for (transmission of the reference signal using multiple beams).

[0169] (Modification 2 in the Second Embodiment) In the second embodiment, a configuration was described in which a reference signal for beam squint estimation is transmitted from the base station device Ba and received by the terminal device 40a to estimate the beam squint, and a configuration was described in which a reference signal for beam squint estimation is transmitted from the terminal device 40a and received by the base station device Ba to estimate the beam squint. In contrast, the base station device Ba may transmit a reference signal for beam squint estimation to the terminal device 40a using an optimal beam or multiple beams, and the terminal device 40a may receive the reference signal for beam squint estimation using an optimal beam or multiple beams. In this case, the terminal device 40a may estimate the beam squint, or the reception result of the reference signal for beam squint estimation may be fed back to the base station device Ba. Similarly, the terminal device 40a may transmit a reference signal for beam squint estimation to the base station device Ba using an optimal beam or multiple beams, and the base station device Ba may receive the reference signal for beam squint estimation using an optimal beam or multiple beams. In this case, the base station device Ba may estimate the beam squint, or the result of receiving the beam squint estimation reference signal may be fed back to the terminal device 40a.

[0170] When terminal device 40a feeds back the reception results of the beam squint estimation reference signal to base station device Ba, terminal device 40a may feed back all information to base station device Ba, feed back information for each discrete frequency interval, or feed back only beams with received power above a certain threshold. Also, when base station device Ba feeds back the reception results of the beam squint estimation reference signal to terminal device 40a, base station device Ba may feed back all information to terminal device 40a, feed back information for each discrete frequency interval, or feed back only beams with received power above a certain threshold.

[0171] (Modification 3 in the second embodiment) In the second embodiment, a configuration was shown in which the beam squint is estimated even in the terminal device 40a. However, after the resources of the terminal device 40a are allocated, the beam of the base station device Ba corresponding to the allocated frequency may be fixed, and then the beam search of the terminal device 40a may be performed at the allocated frequency.

[0172] (Third Embodiment) In the first and second embodiments, a configuration for estimating beam squint by transmitting and receiving a reference signal for estimating beam squint was described. In the third embodiment, a configuration for estimating beam squint without using a reference signal will be described. Specifically, in the third embodiment, estimation is performed using only the array factor of multiple antennas provided by the base station equipment (element directivity may also be considered). This will be described in detail below.

[0173] [Configuration of the Distributed Antenna System] The overall configuration of the distributed antenna system 1 in the third embodiment is basically the same as the overall configuration of the distributed antenna system 1 in the first embodiment shown in Figure 3 above, so the explanation is omitted.

[0174] [Configuration of the base station device] The configuration of the base station device will be described below. Figure 16 shows an example of the configuration of base station device Bb in the third embodiment of the present invention. As shown in Figure 16, base station device Bb comprises a digital-analog signal processing device 20b and P distributed antenna devices 30-1 to 30-P. Base station device Bb differs from base station device Ba in that it has a digital-analog signal processing device 20b instead of a digital-analog signal processing device 20a. The differences from base station device Ba will be explained below.

[0175] The digital-to-analog signal processing unit 20b comprises a base station communication control unit 21b, a digital signal processing unit 22, and an analog signal unit 23. The base station communication control unit 21b comprises a beam squint estimation unit 213b, a beam search signal transmission unit 214, a feedback signal reception unit 215, and a data transmission instruction unit 216.

[0176] The beam squint estimation unit 213b determines the direction θ of the optimal beam ID obtained by beam searching at a certain frequency. ０ The optimal beam ID at other frequencies is estimated by correcting it using the frequency ratio r based on equation (3) above. The beam squint estimation unit 213b generates and maintains a beam selection table that associates frequencies with optimal beam IDs based on the estimation results.

[0177] Furthermore, the beam squint estimation unit 213b selects the optimal beam for each terminal device 40b during data transmission, based on the frequency assigned to each terminal device 40b and the beam selection table it holds.

[0178] [Configuration of the terminal device] Next, the configuration of the terminal device will be described. Figure 17 is a diagram showing an example of the configuration of the terminal device 40b in the third embodiment of the present invention. As shown in Figure 17, the terminal device 40b comprises a terminal communication control unit 41b, a digital signal processing unit 42, an analog signal unit 43, and Q antenna units 44-1 to 44-Q. The terminal device 40b differs from the terminal device 40a in that it has a terminal communication control unit 41b instead of a terminal communication control unit 41a. The differences from the terminal device 40a will be explained below.

[0179] The terminal communication control unit 41b includes a beam search signal receiving unit 413b, a feedback signal transmitting unit 414, a data transmission instruction unit 415, and a beam quint estimation unit 418b.

[0180] The beam squint estimation unit 418b determines the direction θ of the optimal beam ID obtained by beam searching at a certain frequency. ０ The optimal beam ID at other frequencies is estimated by correcting it using the frequency ratio r based on equation (3) above. The beam squint estimation unit 418b generates and maintains a beam selection table that associates frequencies with optimal beam IDs based on the estimation results.

[0181] Furthermore, the beam squint estimation unit 418b selects the optimal beam to be used for data transmission based on the assigned frequency and the beam selection table it holds during data transmission.

[0182] [Operation of Base Station Device Bb] The following describes an example of the operation of base station device Bb. Figure 18 is a flowchart showing the processing flow of base station device Bb in the third embodiment. In Figure 18, processes similar to those in Figure 8 are denoted by the same reference numerals as in Figure 8 and their explanation is omitted.

[0183] The beam squint estimation unit 213b estimates the beam squint (step S701). Specifically, the beam squint estimation unit 213b estimates the direction θ of the optimal beam ID obtained by beam searching at a certain frequency. ０ The optimal beam ID at other frequencies is estimated by correcting it using the frequency ratio r based on equation (3) above. The beam squint estimation unit 213b generates and maintains a beam selection table that associates frequencies with optimal beam IDs based on the estimation results. Subsequently, the processing from step S104 onwards is executed.

[0184] [Operation of Terminal Device 40b] The operation of terminal device 40b will be described below. Figure 19 is a flowchart showing the processing flow of terminal device 40b in the third embodiment. In Figure 19, processes similar to those in Figure 13 are denoted by the same reference numerals as in Figure 13 and their explanation is omitted.

[0185] The beam squint estimation unit 418b estimates the beam squint (step S801). Specifically, the beam squint estimation unit 418b estimates the direction θ of the optimal beam ID obtained by beam searching at a certain frequency. ０ The optimal beam ID at other frequencies is estimated by correcting it using the frequency ratio r based on equation (3) above. The beam squint estimation unit 418b generates and maintains a beam selection table that associates frequencies with optimal beam IDs based on the estimation results. Subsequently, the processing from step S203 onwards is executed.

[0186] [Operation of the Distributed Antenna System 1] The following describes an example of the overall operation of the distributed antenna system 1 in the third embodiment. Figure 20 is a sequence diagram showing the processing flow of the distributed antenna system 1 in the third embodiment. In Figure 20, processes similar to those in Figure 14 are denoted by the same reference numerals as in Figure 14 and their explanation is omitted.

[0187] The base station device Bb instructs the beam squint estimation unit 213b to estimate the beam squint (step S901). The beam squint estimation unit 213b estimates the beam squint according to the instruction. The terminal device 40b instructs the beam squint estimation unit 418b to estimate the beam squint (step S902). The beam squint estimation unit 418b estimates the beam squint according to the instruction. Subsequently, the processing from step S304 onwards is executed.

[0188] In the distributed antenna system 1 of the third embodiment configured as described above, both the terminal device 40b and the base station device Bb estimate beam squint based on the theoretical formula of the array factor. As a result, unlike in the second embodiment, the terminal device 40b and the base station device Bb do not need to transmit a reference signal for beam squint estimation. Therefore, the terminal device 40b and the base station device Bb do not need to have the function of transmitting a reference signal for beam squint estimation and the function of receiving a reference signal for beam squint estimation. Thus, both the terminal device 40a and the base station device Ba can be configured simply, and the deterioration of reception quality due to the effect of beam squint can be suppressed.

[0189] (Modification in the Third Embodiment) In the third embodiment, the case of a one-dimensional beam was described as an example for the base station device Bb and the terminal device 40b, but the same can be applied when using a two-dimensional beam. In this case, the beam ID that was considered in one dimension is separated and applied in two dimensions. In this case, the beam IDs are made adjacent in the two-dimensional beam direction.

[0190] (Modification 1 common to the first to third embodiments) In the embodiments described above, the base station devices B, Ba, and Bb are shown to notify terminal devices 40, 40a, and 40b of the resources they have allocated each time. However, the base station devices B, Ba, and Bb do not have to notify the resources each time. In particular, in the case of downlink transmission (base station devices B, Ba, and Bb → terminal devices 40, 40a, and 40b), a certain frequency may be allocated to the terminal devices 40, 40a, and 40b, and the terminal devices 40, 40a, and 40b may wait until data addressed to them arrives on a beam corresponding to that frequency.

[0191] (Modification 2 common to the first to third embodiments) In the embodiments described above, a configuration was shown in which the relationship of the optimal beam ID is estimated in beam quint estimation. However, the optimal beam at a different frequency may be estimated by angle specification based on the optimal beam ID at a certain frequency. This may make it possible to improve the gain beyond that of discrete beams.

[0192] (Modification 3 common to the first to third embodiments) In the embodiments described above, a configuration applicable to a wireless communication system with a wideband signal bandwidth was described in which base station devices B, Ba, and Bb perform beam search at some frequencies and allocate resources to other frequencies during data transmission. In contrast, the embodiments described above can also be applied to a distributed antenna system when beam search is performed at different frequencies for each distributed antenna device 30. In this case, base station devices B, Ba, and Bb may perform the above processing for each distributed antenna device 30, or they may use a common value estimated based on the results obtained from one distributed antenna device 30.

[0193] Figure 21 shows an example of a case where beam search is performed at different frequencies for each distributed antenna device 30. As shown in Figure 21(A), distributed antenna device 30-1 is at frequency f １ A beam search is performed, and the distributed antenna device 30-2 is set to frequency f ２ A beam search is performed, and the distributed antenna device 30-3 is set to frequency f ３Let's assume that beam search is being performed. In this case, base station devices B, Ba, and Bb perform the beam quint estimation described above for each distributed antenna device 30.

[0194] Then, during data transmission, the estimated result is used to perform data transmission. For example, as shown in Figure 21 (B), the frequency f １ is terminal device 40-1 (UE １ ) and terminal device 40-3 (UE ３ It is assigned to frequency f ２ Terminal device 40-2 (UE ２ ) and terminal device 40-3 (UE ３ It is assigned to frequency f ３ is terminal device 40-1 (UE １ ) and terminal device 40-2 (UE ２ Assume it is assigned to ).

[0195] When base station devices B, Ba, and Bb perform data transmission via distributed antenna device 30-1, the frequency f used during beam search is used. １ For terminal devices 40-2 to which frequencies other than those specified are assigned, data transmission is performed using a beam ID corresponding to the frequency assigned to terminal device 40-2.

[0196] In each of the embodiments described above, the base station devices B and Ba can be read as "Base Station (BS)", "Wireless base station", "Fixed base station", "NodeB", "eNodeB", "gNodeB", "Access Point", "Transmission Point (TP)", "Reception Point (RP)", "Transmission / Reception Point (TRP)", "Distributed Antenna (DA)", "Cell", "Sector", "Macrocell", "Small cell", "Femtocell", and "Picocell".

[0197] Some or all of the digital-analog signal processing devices 20, 20a, 20b and terminal devices 40, 40a, 40b in the first to third embodiments described above may be implemented using a computer. In that case, the program for implementing this function may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be loaded into a computer system and executed. Here, "computer system" includes hardware such as an OS (Operating System) and peripheral devices. Furthermore, "computer-readable recording medium" refers to portable media such as flexible disks, magneto-optical disks, ROMs (Read Only Memory), CD-ROMs, and storage devices such as hard disks built into a computer system.

[0198] Furthermore, "computer-readable recording media" may include those that dynamically hold programs for a short period of time, such as communication lines used when transmitting programs via networks such as the Internet or communication lines such as telephone lines, as well as those that hold programs for a certain period of time, such as volatile memory inside computer systems that act as servers or clients in such cases. In addition, the above-mentioned program may be for the purpose of realizing a part of the aforementioned functions, or it may be a program that can realize the aforementioned functions in combination with a program already recorded in the computer system, or it may be implemented using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0199] While embodiments of this invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and includes designs and the like that do not depart from the spirit of this invention.

[0200] This invention can be applied to distributed antenna systems that perform beam searching.

[0201] 1...Distributed antenna system, 20, 20a, 20b...Digital-analog signal processing unit, 30, 30-1 to 30-P...Distributed antenna device, 40, 40a, 40b...Terminal device, 21, 21a, 21b...Base station communication control unit, 22...Digital signal processing unit, 23...Analog signal unit, 211...Request transmission unit, Reference signal receiving unit, 212...Reference signal receiving unit, 213, 213b...Beam quint estimation unit, 214...Beam search signal transmission unit, 215...Feedback signal receiving unit, 216...Data transmission instruction unit, 217...Request receiving unit, 218...Reference signal transmission unit, 41, 41a, 41b...Terminal communication control unit, 42...Digital signal processing unit, 43...Analog signal unit, 44, 44-1 to 44-Q...Antenna unit, 411...Request receiving unit, 412...Reference signal transmission unit, 413...Beam search signal reception unit, 414...Feedback signal transmission unit, 415...Data transmission instruction unit, 416...Reference signal request unit, 417...Reference signal reception unit, 418, 418b...Beam quint estimation unit, B, Ba, Bb...Base station equipment

Claims

1. A base station device comprising: a beam squint estimation unit that estimates a beam squint based on a reference signal for estimating a beam squint or a theoretical formula for an array factor, and estimates an optimal beam at frequencies other than the specific frequency used to estimate the beam squint based on the estimated beam squint; and a data transmission instruction unit that, during data transmission, instructs data transmission with an optimal beam corresponding to the frequency assigned to each terminal device, based on the optimal beam for each frequency estimated by the beam squint estimation unit.

2. The base station device according to claim 1, wherein the beam squint estimation unit estimates the beam squint using the beam that is optimal at the specific frequency, or the reference signal received by a plurality of beams.

3. A base station device according to claim 1 or 2, further comprising a reference signal transmitting unit that transmits a reference signal for estimating a beam squint in a terminal device, wherein the beam squint estimation unit estimates the beam squint based on a combination of a beam that is optimal at a specific frequency in the base station device and the beam of the terminal device.

4. A terminal device comprising: a beam squint estimation unit that estimates a beam squint based on a reference signal for estimating a beam squint or a theoretical formula for an array factor, and estimates an optimal beam at frequencies other than the specific frequency used to estimate the beam squint based on the estimated beam squint; and a data transmission instruction unit that, during data transmission, instructs data transmission with the optimal beam corresponding to the assigned frequency based on the optimal beam for each frequency estimated by the beam squint estimation unit.

5. The terminal device according to claim 4, wherein the beam squint estimation unit estimates the beam squint based on the combination of the beam that is optimal at the specific frequency in the base station device and the beam of the terminal device.

6. A communication method in which a base station device, which performs wireless communication between the base station device and multiple terminal devices, estimates a beam squint based on a reference signal for estimating the beam squint or a theoretical formula for an array factor, estimates an optimal beam at frequencies other than the specific frequency used to estimate the beam squint based on the estimated beam squint, and during data transmission, instructs each terminal device to transmit data using the optimal beam corresponding to the frequency assigned to it, based on the estimated optimal beam for each frequency.

7. A communication method in which a terminal device that performs wireless communication between a base station device and multiple terminal devices estimates a beam squint based on a reference signal for estimating the beam squint or a theoretical formula for an array factor, estimates an optimal beam at frequencies other than the specific frequency used to estimate the beam squint based on the estimated beam squint, and during data transmission, instructs the terminal device to transmit data with the optimal beam corresponding to the assigned frequency based on the estimated optimal beam for each frequency.

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