Wireless base stations, methods, and programs

Abstract

The present invention provides a wireless base station, method, and program capable of suppressing the increase in load. [Solution] The wireless base station comprises: a beamweight generation unit that generates a beamweight for each received signal group based on a first channel response information estimated based on a first reference signal included in the received signal; a beamforming unit that generates a beamformed signal for each received signal group based on the generated beamweight and the received signal; a received signal group synthesis weight generation unit that generates a received signal group synthesis weight based on a second channel response information estimated based on a second reference signal included in the generated beamformed signal; and a received signal group synthesis unit that synthesizes the beamformed signals for each received signal group based on the generated received signal group synthesis weight.

Description

[Technical Field]

[0001] This disclosure relates to wireless base stations, methods, and programs. [Background technology]

[0002] In recent years, with the development of mobile communication technologies such as 5G and Massive MIMO (Multi Input Multi Output), there has been an increase in the frequency bandwidth, the number of antennas, and the number of connected terminals at base stations. In connection with this, specifications for fronthaul and base stations in RAN (Radio Access Network) are being discussed. For example, Non-Patent Document 1 describes the functional division between O-DU (O-RAN Distributed Unit) and O-RU (O-RAN Radio Unit) in O-RAN. Note that O-DU is sometimes simply called DU, and O-RU is sometimes simply called RU. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] O-RAN Work Group 4 (Open Fronthaul Interface WG), "7-2x UL Performance Improvement (ULPI) Work Item WG4-2022-01", Technical Report, O-RAN.WG4.TR-ULPI-R003-v01.00, 2023.03.29 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Non-Patent Document 1 describes a configuration of DU and RU for improving the performance of the uplink. However, the technology described in Non-Patent Document 1 may increase the processing load on the RU and other components of the uplink.

[0005] In view of these challenges, one of the objectives of this disclosure is to provide a wireless base station, method, and program that can suppress the increase in load on RUs, etc. [Means for solving the problem]

[0006] A radio base station according to one aspect of the present disclosure includes: a beamweight generation unit that generates a beamweight for each received signal group based on a first channel response information estimated based on a first reference signal included in the received signal; a beamforming unit that generates a beamformed signal for each received signal group based on the generated beamweight and the received signal; a received signal group synthesis weight generation unit that generates a received signal group synthesis weight based on a second channel response information estimated based on a second reference signal included in the generated beamformed signal; and a received signal group synthesis unit that synthesizes the beamformed signals for each received signal group based on the generated received signal group synthesis weight.

[0007] A method according to one aspect of the present disclosure is a method for a radio base station, comprising: generating a beamweight for each received signal group based on first channel response information estimated based on a first reference signal included in the received signal; generating a beamformed signal for each received signal group based on the generated beamweight and the received signal; generating a combined received signal group weight based on a second channel response information estimated based on a second reference signal included in the generated beamformed signal; and combining the beamformed signals for each received signal group based on the generated combined received signal group weight.

[0008] A program according to one aspect of the present disclosure is a program for causing a computer to execute a method for a radio base station, the method comprising: generating beamweights for each received signal group based on first channel response information estimated based on a first reference signal included in the received signal; generating beamformed signals for each received signal group based on the generated beamweights and the received signal; generating combined received signal group weights based on a second channel response information estimated based on a second reference signal included in the generated beamformed signals; and combining the beamformed signals for each received signal group based on the generated combined received signal group weights. [Effects of the Invention]

[0009] According to this disclosure, it is possible to maintain the number of streams transmitted in the fronthaul, suppress degradation of transmission performance, and suppress an increase in load on the RU. [Brief explanation of the drawing]

[0010] [Figure 1] This is a configuration diagram showing an example of the configuration of a wireless communication system according to several embodiments. [Figure 2] This diagram shows the transmission timing for SRS and DMRS. [Figure 3] This diagram shows the transmission timing for SRS and DMRS. [Figure 4] This figure shows an example of SRS placement in the frame configuration of a received signal. [Figure 5] This figure shows an example of DMRS placement in the frame configuration of a received signal. [Figure 6] This is a configuration diagram showing an example of the base station configuration related to Example 1. [Figure 7] This is a configuration diagram showing an example of the base station configuration related to Example 2 of the study. [Figure 8] This is a configuration diagram showing some examples of base station configurations according to several embodiments. [Figure 9] This is a configuration diagram showing some examples of base station configurations according to several embodiments. [Figure 10] This is a configuration diagram showing some examples of base station configurations according to several embodiments. [Figure 11] This flowchart shows examples of base station operation according to several embodiments. [Figure 12] This diagram illustrates some examples of antenna configurations according to several embodiments. [Figure 13] This figure illustrates an example of an antenna group according to several embodiments. [Figure 14] This figure illustrates an example of an antenna group according to several embodiments. [Figure 15] This figure illustrates an example of an antenna group according to several embodiments. [Figure 16] This is a configuration diagram showing some examples of base station configurations according to several embodiments. [Figure 17] This is a configuration diagram showing some examples of base station configurations according to several embodiments. [Figure 18] This is a configuration diagram showing some examples of base station configurations according to several embodiments. [Figure 19] This is a configuration diagram showing some examples of base station configurations according to several embodiments. [Figure 20] This is a configuration diagram showing some examples of base station configurations according to several embodiments. [Figure 21] This is a configuration diagram showing some examples of base station configurations according to several embodiments. [Figure 22] This table illustrates the evaluation results according to several embodiments. [Figure 23] This graph illustrates the evaluation results according to several embodiments. [Figure 24] This is a configuration diagram showing examples of base station hardware configurations according to several embodiments. [Modes for carrying out the invention]

[0011] The embodiments will be described below with reference to the drawings. In each drawing, the same elements are denoted by the same reference numerals, and redundant explanations are omitted where necessary. The arrows shown in each drawing are illustrative for illustrative purposes only and do not limit the type or direction of the signal.

[0012] (Consideration of the issues) First, we will describe the basic wireless communication system for several embodiments. Figure 1 shows an example configuration of the basic wireless communication system 1 for several embodiments. The wireless communication system 1 may be a system defined by standards such as 5G, NR, or LTE (Long Term Evolution), but is not limited to these systems. For example, it may be a system defined by a next-generation standard including Beyond 5G (6G), or a system defined by a standard of another generation.

[0013] In the example shown in Figure 1, the wireless communication system 1 includes a base station 700 and a user terminal UE. Note that the number of base stations 700 and user terminal UEs constituting the wireless communication system 1 is an example and is not limited to this.

[0014] Base station 700 is a network node that constitutes the RAN in the wireless communication system 1. Base station 700 is connected to the core network and provides a cell for wireless communication with user terminals UE. Base station 700 may be, for example, a gNB (next Generation Node B) or an eNB (evolved Node B), or other base stations (NB; Node B, etc.). Base station 700 may be composed of multiple functions. Base station 700 may be functionally divided into CU (Central Unit), DU, RU, etc.

[0015] A base station 700 with multiple functions may be implemented by one device or by multiple devices. The multiple devices constituting the base station 700 may be located in the same location or in different locations. The devices constituting the base station 700 may include physical devices (computers) or virtual machines running on a virtualization infrastructure. The base station 700 may constitute a vRAN (virtual RAN) or O-RAN. Here, as an example, the base station 700 constitutes an O-RAN, but is not limited to an O-RAN.

[0016] The User Terminal UE is a wireless terminal device that accesses the RAN, including the base station 700, and communicates with the data network, etc., via the base station 700 and the core network. The User Terminal UE communicates wirelessly with the base station 700 via a wireless channel within the cell provided by the base station 700. For example, the User Terminal UE may be a mobile phone, smartphone, tablet, IoT (Internet of Things) terminal, etc. Furthermore, the User Terminal UE may be mounted on a mobile device such as an automobile, train, robot, or drone.

[0017] In the example shown in Figure 1, the base station 700 is equipped with multiple antennas 701, RU710, and DU720. The RU710 and DU720 are connected via a front-haul (FH) circuit for communication. Note that the base station 700 may also be equipped with multiple RU710s.

[0018] Multiple antennas 701 are antennas that transmit and receive MIMO radio signals to and from the user terminal UE via a radio channel. RU710 performs processing for the radio signals and beams transmitted and received by antennas 701. RU710 includes a beamformer 711 that performs beamforming. RU710 is, for example, an O-RU, but is not limited to an O-RU. DU720 accommodates RU710 and performs control processing of radio signals and beams in RU710, as well as protocol processing higher than RU710. DU720 is, for example, an O-DU, but is not limited to an O-DU.

[0019] We will examine uplink reception at a base station as shown in Figure 1. In uplink reception in O-RAN, three aspects are important: fronthaul (FH) bandwidth, time variation of channel response information, and RU load. The inventor focused on these aspects.

[0020] Because the bandwidth of the fronthaul, which is the link between the RU and DU, is limited, it is difficult to send signals from multiple antennas from the RU to the DU. Therefore, at the RU, a beamformer performs beamforming (BF), which combines the signals from each antenna and reduces the signal dimension. In the example in Figure 1, beamformer 711 converts the received signal from the N antenna into an M stream (N≧M) and outputs it via the fronthaul.

[0021] In beamforming, the channel response is estimated from the antenna's received signal, and the received signal is multiplied by a weight based on the estimated channel response. There are two methods for estimating the channel response: one using a sounding reference signal (SRS) and the other using a demodulation reference signal (DMRS). Figure 2 shows the transmission timing of SRS and DMRS.

[0022] To date, beamforming based on channel response information estimated by SRS has been considered. When estimating channel response with SRS, the same channel estimate is used until the next SRS transmission timing. However, as shown in Figure 2, because SRS has a long transmission period, the actual channel response changes over time from the estimated channel response information, which leads to a problem of degraded transmission performance.

[0023] On the other hand, Non-Patent Document 1 discusses ULPI (Uplink performance improvement), an initiative to improve uplink performance, and proposes beamforming based on channel response information estimated by DMRS. As shown in Figure 2, since DMRS is transmitted together with the data signal, the channel response information estimated by DMRS has a small time difference with the actual channel response. Therefore, by utilizing DMRS, it is possible to suppress the degradation of transmission performance due to time changes in the channel response.

[0024] The inventors, after investigating ULPI, found that channel estimation using DMRS performed at the RU increases the load on the RU and thus increases the circuit size of the RU. This problem is illustrated using Figures 3 to 5.

[0025] Figure 3 shows the transmission timing for SRS and DMRS. Considering the processing load, as shown in Figure 3, when using SRS for channel estimation, it is sufficient to complete the channel estimation within the SRS transmission cycle. In contrast, when using DMRS for channel estimation, it is necessary to perform channel estimation within one slot for each receiving antenna, resulting in a higher processing load.

[0026] Figures 4 and 5 show examples of SRS and DMRS placements in the frame configuration of the received signal. When considering the required memory (circuit size) of the received signal to be beamformed, if channel estimation is performed with SRS, beamforming can be performed if there is enough memory to store the received signal of about one symbol corresponding to the mapped SRS in one slot, as shown in Figure 4.

[0027] In contrast, when performing channel estimation with DMRS, as shown in Figure 5, if DMRS is mapped to, for example, the forward and backward symbols within a single slot, channel estimation cannot be performed until the backward symbol within the slot is reached. Therefore, memory is required to store the received signal equivalent to up to one slot of OFDM symbols, including the forward and backward symbols within the slot, thus increasing the required memory. For this reason, the inventors considered it important to reduce the processing load of channel estimation using DMRS and the beamforming based thereon by reducing the number of streams for which channel estimation is performed using DMRS.

[0028] The above issues will be further explained below with reference to Examples 1 and 2. Examples 1 and 2 are examples in which a receiving antenna receives a two-polarization wireless signal and employs maximum ratio combining as the beamforming method.

[0029] (Example 1) Previously, Weight-based Dynamic Beamforming (WDBF) was being considered, which involves beamforming in the RU based on channel response information estimated by the SRS, and equalization processing in the DU based on channel response information estimated by the DMRS.

[0030] Figure 6 shows an example configuration of base station 800 related to Study Example 1, illustrating an example of a WDBF base station described in Non-Patent Document 1. In the example in Figure 6, base station 800 is equipped with multiple antennas 801, RU810, and DU820. RU810 is equipped with a beamformer 811. DU820 is equipped with an equalizer 821, a channel estimator 822, a beamweight generator 823, a channel-noise covariance matrix estimator 824, and an equalization weight generator 825.

[0031] The received signal y received by multiple antennas 801 is given by the following equation.

number

[0032] The channel estimator 822 estimates the following channel response information H V,S , H H,S based on the SRS included in the received signal y. Note that the channel response information is a matrix indicating the fluctuations in the amplitude and phase of the channel.

Number

[0033] The beam weight generator 823 generates the following beam weight W V,S , H H,S from the estimated channel response information H BF as follows.

Number

[0034] The beamformer 811 multiplies the beam weight W BF generated for the received signal y and generates the following received signal y BF after beamforming as follows.

Number

[0035] Thereby, the N B pieces (number of receiving antennas) of received signals are converted into L streams (number of MIMO layers). The beamformer 811 outputs the received signal y BF after beamforming via the front hole. The channel-noise covariance matrix estimator 824 estimates the channel response information and the noise covariance matrix based on the DMRS included in the received signal y BF after beamforming. The equalization weight generator 825 generates an equalization weight based on the estimated channel response information and the noise covariance matrix. The equalizer 821 multiplies the equalization weight generated for the received signal y BF after beamforming and generates the received signal after equalization.

[0036] In WDBF, beamforming based on channel response information estimated by SRS reduces the number of streams to the number of MIMO layers. As mentioned above, a challenge in this case is the significant temporal degradation of transmission performance due to the temporal changes in channel response.

[0037] (Example 2) As mentioned above, ULPI, an initiative to improve uplink performance, has been proposed in O-RAN. ULPI explores shifting DU processing to RU and synthesizing received signals based on channel response information estimated by DMRS.

[0038] Figure 7 shows an example configuration of base station 900 related to Study Example 2, illustrating an example of a ULPI base station described in Non-Patent Document 1. In the example in Figure 7, base station 900 is equipped with multiple antennas 901, RU910, and DU920. RU910 is equipped with an equalizer 911, a channel-noise covariance matrix estimator 912, and an equalization weight generator 913.

[0039] The received signal y received by antenna 901 is the same as in equation (1) above. The channel-noise covariance matrix estimator 912 calculates the channel response information H based on the DMRS contained in the received signal y as follows. D We estimate the noise covariance matrix R, along with the .

number

[0040] The equalization weight generator 913 generates estimated channel response information H D And from the noise covariance matrix R, the equalization weights W are as follows: EQ Generates.

number

[0041] The equalizer 911 generates an equalization weight W on the received signal y. EQ Multiply by the following, and the equalized received signal yEQ Generates.

number

[0042] This means N B The number of received signals (number of receiving antennas) is converted into L streams (number of MIMO layers). As described above, the channel response information estimated by DMRS has a small time difference from the actual channel response, so there is almost no degradation of transmission performance due to time changes in the channel response. On the other hand, a challenge is the high processing load on the RU due to the fact that the RU performs channel estimation by DMRS on signals of the receiving antenna dimension and also performs equalization processing.

[0043] Specifically, the processing load on RUs when performing channel estimation using DMRS is as follows. RUs may not be able to tolerate this processing load. • Processing load for channel estimation (number of antenna streams): N B • Required memory size (number of signals per slot and per RB (Resource block)): 168N B • Equalization load (number of real multiplications per RE (Resource element)): 4N B 3 +4N B 2 L+4N B 2 +4N B L Here, RB is a unit that groups 12 subcarriers on the frequency axis, and 1 slot / 1 RB refers to a unit enclosed by 14 OFDM symbols on the time axis and 12 subcarriers on the frequency axis. RE refers to one of the 12 subcarriers that make up the RB.

[0044] As described above, related technologies such as those in Examples 1 and 2 have the problem of not being able to suppress the degradation of transmission performance due to temporal changes in channel response while suppressing the increase in processing load at the RU. Therefore, the embodiment provides a means to achieve both a reduction in processing load at the RU and suppression of degradation of transmission performance due to temporal changes in channel response without increasing the number of streams transmitted in the fronthaul.

[0045] (Embodiment 1) Next, Embodiment 1 will be described.

[0046] Figures 8 and 9 show examples of the configuration of a base station 10 according to several embodiments. In the example of Figure 8, the base station 10 includes a plurality of antennas 101, a plurality of beamformers 110, a first channel estimator 121, a beamweight generator 122, a received signal group combiner 130, a second channel estimator 141, and a received signal group combiner weight generator 142.

[0047] Furthermore, as shown in Figure 9, the base station 10 may include at least a beamformer 110, a beamweight generation unit 120, a received signal group combiner 130, and a received signal group combined weight generation unit 140. For example, the beamweight generation unit 120 includes a first channel estimator 121 and a beamweight generator 122. The received signal group combined weight generation unit 140 includes a second channel estimator 141 and a received signal group combined weight generator 142.

[0048] Multiple antennas 101 receive wireless signals from the user terminal UE, as in Figure 1. The received signals from the multiple antennas 101 are grouped into any number of groups. A beamformer 110 is placed for each group that is set up. In this example, the received signals are grouped into groups 1 to K. Antennas with a high correlation of the time-direction phase change of the received signals may also be grouped together. For example, if the multiple antennas 101 include antennas that receive two polarizations, they may be grouped by polarization. Two polarizations include not only horizontal and vertical polarizations, but all polarizations that intersect perpendicularly to each other.

[0049] The beamweight generation unit 120 generates beamweights for each received signal group based on first channel response information estimated based on a first reference signal included in the received signal received by the antenna 101. For example, the first reference signal is SRS, but it may also be other reference signals that have a lower processing load for channel estimation and beamforming compared to the second reference signal.

[0050] For example, the first channel estimator 121 takes the received signals of base stations included in the received signal group set for each beamformer 110 as input and estimates first channel response information based on a first reference signal. The beamweight generator 122 generates beamweights for each received signal group based on the first channel response information estimated by the first channel estimator 121.

[0051] Multiple beamformers (beamforming units) 110 generate a beamformed received signal for each received signal group based on the beamweight generated by the beamweight generator 122 and the received received signal. Each of the multiple beamformers 110 corresponds to a received signal group 1 to K, and includes, for example, beamformers 110-1 to 110-K. Each beamformer 110 takes the generated beamweight and the received signal of the antenna 101 included in the received signal group as input, multiplies the received signal by the beamweight, and outputs a beamformed received signal. For example, the number of streams (beamformed received signals) generated by each beamformer 110 is L (number of MIMO layers), and a KL stream is generated by all beamformers 110. For example, L is less than or equal to the number of received signals (antennas).

[0052] The beamforming method of the beamformer 110 is, for example, a method using maximum ratio synthesis, but any other beamforming method may be applied. For example, beamforming may be performed using zero forcing, Minimum Mean Square Error (MMSE), etc. Furthermore, the beamformer 110 may perform beamforming based on a channel response information matrix including a precoding matrix. It is not limited to this, but beamforming may also be performed based on a channel response information matrix between the base station and the user terminal. When beamforming is performed based on a channel response information matrix between the base station and the user terminal, an improvement in transmission performance can be expected, but the number of streams may increase, which may increase the load on channel estimation and whitening processing using DMRS.

[0053] The received signal group synthesis weight generation unit 140 generates a received signal group synthesis weight based on a second channel response information estimated based on a second reference signal included in the beamformed received signal generated by the multiple beamformers 110. For example, the second reference signal is DMRS, but it may be any other reference signal.

[0054] For example, the second channel estimator 141 takes all of the beamformed received signals output by all beamformers 110 as input and estimates the second channel response information based on the second reference signal. The received signal group synthesis weight generator 142 generates received signal group synthesis weights based on the estimated second channel response information.

[0055] The received signal group combiner (received signal group combining unit) 130 combines the beamformed received signals for each received signal group based on the received signal group combining weights generated by the received signal group combining weight generator 142. The received signal group combiner 130 takes the generated received signal group combining weights and the beamformed received signals output by all beamformers 110 as input, multiplies the beamformed received signals by the received signal group combining weights, and outputs the received signal after receiving signal group combining. For example, the received signal group combiner 130 combines the beamformed KL stream into an L stream.

[0056] Figure 10 shows an example configuration of a base station 10 equipped with RU100 and DU200, including the configuration shown in Figure 8. Specifically, RU100, like in Figure 8, includes multiple beamformers 110, a first channel estimator 121, a beamweight generator 122, a received signal group combiner 130, a second channel estimator 141, and a received signal group combiner weight generator 142.

[0057] The received signals after group synthesis of the received signals are output from RU100 and input to DU200 via the fronthaul. DU200 includes an equalizer 210, a channel-noise covariance matrix estimator 221, and an equalization weight generator 222.

[0058] The channel-noise covariance matrix estimator 221 takes the received signal after the received signal group synthesis as input and estimates the third channel response information and noise covariance matrix based on a second reference signal (e.g., DMRS). The equalization weight generator 222 generates equalization weights based on the estimated third channel response information and noise covariance matrix.

[0059] The equalizer 210 performs equalization on the received signal after the received signal group synthesis based on the equalization weights generated by the equalization weight generator 222. The equalizer 210 takes the generated equalization weights and the received signal after the received signal group synthesis as inputs, multiplies the received signal after the received signal group synthesis by the equalization weights, and outputs the equalized received signal.

[0060] Figure 11 shows an example of the operation of a base station 10 according to several embodiments. In the example in Figure 11, the first channel estimator 121 performs a first channel estimation for each received signal group based on a first reference signal included in the received signal and generates first channel response information (S101). The first channel estimator 121 performs the first channel estimation at the timing of reception of the first reference signal. That is, the first channel estimator 121 extracts a first reference signal from the received signal and estimates the first channel response information based on the extracted first reference signal. The first channel estimator 121 estimates the first channel response information for received signal groups 1 to K based on the first reference signals included in the received signals of received signal groups 1 to K.

[0061] Next, the beamweight generator 122 generates beamweights for each received signal group based on the estimated first channel response information (S102). The beamweight generator 122 generates beamweights for received signal groups 1 to K based on the first channel response information for each received signal group 1 to K.

[0062] Next, the beamformer 110 performs beamforming on the received signal for each received signal group based on the generated beamweight (S111). The beamformers 110-1 to 110-K multiply the received signals of each received signal group 1 to K by the beamweight of each group, thereby generating the beamformed received signal for each received signal group 1 to K.

[0063] Next, the second channel estimator 141 performs channel estimation based on the second reference signal included in the beamformed received signal generated for each received signal group, and generates second channel response information (S112). The second channel estimator 141 performs second channel estimation at the reception timing of the second reference signal in the beamformed received signal. That is, the second channel estimator 141 extracts the second reference signal from the beamformed received signal and estimates the second channel response information based on the extracted second reference signal. The second channel estimator 141 estimates the second channel response information for each received signal group 1 to K based on the second reference signal of the beamformed received signal for each received signal group 1 to K.

[0064] Next, the received signal group combining weight generator 142 generates received signal group combining weights based on the estimated second channel response information (S113). The received signal group combining weight generator 142 generates received signal group combining weights based on the second channel response information of received signal groups 1 to K.

[0065] Next, the received signal group combiner 130 combines the beamformed received signals for each received signal group based on the generated received signal group combining weights (S114). The received signal group combiner 130 multiplies the received signal group combining weights by the beamformed received signals for each received signal group 1 to K to generate the received signal after receiving signal group combining. The received signal group combiner 130 outputs the received signal after receiving signal group combining via the fronthaul.

[0066] Next, the channel-noise covariance matrix estimator 221 performs a second channel estimation based on a second reference signal included in the received signal after the received signal group synthesis, and generates a third channel response information and a noise covariance matrix (S115). Subsequently, the equalization weight generator 222 generates equalization weights based on the generated third channel response information and noise covariance matrix (S116). Subsequently, the equalizer 210 performs an equalization process on the received signal after the received signal group synthesis based on the generated equalization weights (S117).

[0067] As described above, in this embodiment, for example, antennas with a high correlation in the temporal phase change of the received signals are grouped together, and beamforming is performed by multiple beamformers corresponding to the group, thereby avoiding phase shifts during the synthesis of received signals. Furthermore, by reducing the number of streams through beamforming, the processing load of channel estimation based on the second reference signal and the amount of memory of the received signals required during polarization synthesis can be reduced. In addition, the number of signal streams transmitted in the fronthaul can be reduced to the smallest possible number by combining the received signal groups.

[0068] (Modification 1 of Embodiment 1) As a modification of Embodiment 1, an example in which the received signal group is an antenna group will be described. That is, the first received signal group may include received signals received by the first antenna, and the second received signal group may include received signals received by the second antenna.

[0069] Figure 12 shows an example configuration of antenna 101 according to several embodiments. Antenna 101 is, for example, a multi-element antenna for Massive MIMO. Antenna 101 includes a plurality of units (antenna units) AU. Each unit AU includes a plurality of antennas (antenna elements).

[0070] For example, each unit AU includes a first polarization antenna for a first polarization and a second polarization antenna for a second polarization. Each unit AU may include both the first and second polarization antennas, or only one of them. As described above, the first and second polarizations do not need to be horizontal or vertical as long as they intersect perpendicularly to each other. Each unit AU is physically separable and may be placed adjacent to each other or spaced apart.

[0071] Figures 13 to 15 show examples of antenna grouping patterns. Figure 13 shows an example of grouping by polarization. In this example, antennas with the same polarization are grouped together. Received signals with different polarizations have low correlation in terms of phase rotation in the time direction. Therefore, beamforming for each polarization group can avoid phase shifts when combining received signals with different polarizations.

[0072] For example, each unit AU includes a first polarization antenna and a second polarization antenna. The first polarization antenna of each unit AU is designated as the first polarization group. The second polarization antenna of each unit AU is designated as the second polarization group.

[0073] Figure 14 shows an example of grouping by unit. In this example, antennas within the same unit are grouped together. It is thought that the received signals of distant antennas have low correlation in terms of phase rotation in the time direction. Therefore, when the units are far apart, beamforming for each unit group can be used to avoid phase shifts when combining received signals from different units. Multiple antennas within the first unit are designated as the first antenna group, and multiple antennas within the second unit are designated as the first antenna group.

[0074] For example, each unit AU includes a first polarization antenna and a second polarization antenna. The first and second polarization antennas of units AU1 to AUn are grouped into groups, from group 1 to group n, for each unit.

[0075] Figure 15 shows an example of grouping by polarization and by unit. In this example, antennas with the same unit and the same polarization are grouped together. This avoids both the phase shift that occurs when combining received signals with different polarizations and those with different units.

[0076] For example, each unit AU includes a first polarization antenna and a second polarization antenna. The first polarization antennas of units AU1 to AUn are grouped into groups from the first polarization unit 1 group to the first polarization unit n group for each unit. Similarly, the second polarization antennas of units AU1 to AUn are grouped into groups from the second polarization unit 1 group to the second polarization unit n group for each unit.

[0077] (Modification 2 of Embodiment 1) As a modification 2 of Embodiment 1, an example in which the received signal group is a beam group will be described.

[0078] Figure 16 shows an example configuration of the base station 10 in the case of a beam group. In the example in Figure 16, the RU100 includes a discrete Fourier transformer 102 in addition to the configuration in Figure 10. The discrete Fourier transformer 102 performs a discrete Fourier transform on the received signal received by the antenna 101 and converts the received signal into a beam domain. In this example, the multiple converted beams are grouped into a beam group. The number of converted beams is the same as the antenna 101, N. B N B The beams are grouped into beam groups 1 through K.

[0079] For example, beams with similar arrival angles of the received signals converted into a beam domain are grouped together as the same received signal group. Received signals with similar arrival angles are likely to have a high correlation in phase rotation in the time direction, while received signals with different arrival angles are likely to have a low correlation in phase rotation in the time direction. By beamforming each beam with similar arrival angles, phase shifts can be avoided when combining received signals with different arrival angles.

[0080] (Embodiment 2) Next, Embodiment 2 will be described. In this embodiment, a specific example of Embodiment 1 will be described.

[0081] Figure 17 shows an example configuration of a base station 10 according to several embodiments. The example in Figure 17 is a specific example of the configuration in Figure 10. That is, in the example in Figure 17, the base station 10 is equipped with multiple antennas 101, RU100, and DU200, similar to Figure 10.

[0082] The multiple antennas 101 include vertically polarized antennas and horizontally polarized antennas. In this example, antennas with the same polarization are grouped together. That is, the multiple antennas 101 are grouped into a vertically polarized antenna group and a horizontally polarized antenna group.

[0083] RU100 is configured as shown in Figure 10, with the receiving signal group consisting of a vertical polarization antenna group and a horizontal polarization antenna group, the first reference signal being SRS, and the second reference signal being DMRS. Specifically, RU100 includes a vertical polarization beamformer 110a, a horizontal polarization beamformer 110b, an SRS channel estimator 121a, a polarization beamweight generator 122a, a polarization combiner 130a, a DMRS channel estimator 141a, and a polarization combining weight generator 142a.

[0084] DU200, like Figure 10, includes an equalizer 210, a channel-noise covariance matrix estimator 221, and an equalization weight generator 222. The configuration and operation of DU200 are the same as in Embodiment 1, so a description is omitted.

[0085] The SRS channel estimator 121a uses the received signals y of the vertically polarized antenna group and the horizontally polarized antenna group respectively. V , y H Based on the SRS included, channel response information H of the vertical polarization antenna group V,S Channel response information H of the horizontal polarization antenna group H,S Generates.

[0086] The polarization beamweight generator 122a generates channel response information H for the estimated vertically polarized antenna group and horizontally polarized antenna group. V,S H H,S Based on this, beamweight W for each group BF,V , W BF,H Generates.

[0087] For example, the polarization beamweight generator 122a receives channel response information H of the vertical polarization antenna group. V,S Channel response information H of the horizontal polarization antenna group H,S Each matrix is ​​decomposed into its singular value as follows:

number

[0088] The polarization beamweight generator 122a extracts any number of singular vectors from the left singular vector obtained by singular value decomposition according to equation (6), and based on the matrix U' formed by arranging the extracted singular vectors, generates the beamweight W of the vertical polarization antenna group as follows: BF,V , beamweight W of the horizontal polarization antenna group BF,H Generates.

number

[0089] From the left singular vectors obtained by singular value decomposition, any M singular vectors may be extracted, or any M singular vectors with large singular values ​​may be extracted. For example, M singular vectors greater than a predetermined value may be extracted, or the top M singular vectors from the largest may be extracted. For example, M is smaller than the total number of left singular vectors obtained by singular value decomposition. This allows the beamformer to convert the received signal into fewer streams. Beamweights may also be generated from all left singular vectors obtained by singular value decomposition.

[0090] The vertically polarized beamformer 110a and the horizontally polarized beamformer 110b generate the beamweight W BF,V , W BF,H and the received signal y for each polarization antenna group V , y H Using this as input, the beamforming received signal y for each polarization antenna group is processed. BF The vertical polarization beamformer 110a outputs the received signal y of the vertical polarization antenna group. V Beamweight W BF,V Multiply by . The horizontal polarization beamformer 110b receives the signal y from the antenna of the horizontal polarization antenna group. H Beamweight W BF,H Multiply by the generated beamforming received signal y. BF The following applies:

number

[0091] The DMRS channel estimator 141a receives the beamformed received signal y output by the vertical polarization beamformer 110a and the horizontal polarization beamformer 110b. BF All of the above are used as input, and the received signal y after beamforming is used. BF Channel response information H based on DMRS included D The DMRS channel estimator 141a estimates the beamforming received signal y generated by the vertical polarization beamformer 110a. BF Based on the DMRS included, channel response information H of the vertical polarization group V,D The horizontal polarization beamformer 110b generates the beamforming-processed received signal y BF Based on the DMRS included, channel response information H of the horizontal polarization group H,D Generates.

[0092] The polarization synthesis weight generator 142a generates estimated channel response information H V,D HH,D Based on this, the polarization composite weight W is as follows: Comb Generates.

number

[0093] The polarization combiner 130a generates the polarization combine weight W Comb The beamformed received signal y output by the vertical polarization beamformer 110a and the horizontal polarization beamformer 110b BF The input is the received signal y after beamforming. BF Polarization synthesis weight W Comb Multiply by the following, and the received signal y after polarization synthesis is obtained. Comb Outputs.

number

[0094] As described above, in this embodiment, received signals are grouped using antennas with the same polarization, with SRS used as the first reference signal and DMRS as the second reference signal. It is known that received signals from antennas with the same polarization have a high correlation in terms of phase change in the time direction, and even if beamforming for each polarization is based on the channel estimated by SRS, phase shifts during synthesis can be avoided. By accurately synthesizing the signals between polarizations based on the channel response information estimated by DMRS, degradation of transmission performance due to temporal changes in the channel response can be suppressed.

[0095] Furthermore, beamforming reduces the number of streams, thereby reducing the processing load for channel estimation using DMRS and the amount of memory required to store received signals during polarization synthesis based on the channels estimated by DMRS. When singular value decomposition of the channel response information matrix, the fewer left singular vectors there are, the fewer signal streams the beamformer outputs, thus further reducing the processing load for channel estimation using DMRS in the subsequent stage, but this leads to a degradation of transmission performance. This degradation of transmission performance can be mitigated to some extent by selecting vectors with large singular values.

[0096] (Embodiment 3) Next, Embodiment 3 will be described. In this embodiment, an example of whitening, that is, flattening of the power spectral density of noise, will be described. Note that whitening may also be performed in the same manner as in Embodiment 2.

[0097] Figure 18 shows an example configuration of a base station 10 according to several embodiments. In the example in Figure 18, the RU100 includes a vertical polarization whitening processor 150a, a horizontal polarization whitening processor 150b, and a whitening weight generator 160, in addition to the configuration in Figure 17. With this configuration, noise whitening is performed for each polarization after beamforming. The DU200 is the same as in Figures 10 and 17.

[0098] The vertically polarized beamformer 110a and the horizontally polarized beamformer 110b are configured as follows, with beamweight W applied to the received signal y. BF Multiply by the received signal y after beamforming. BF Generates.

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[0099] The whitening weight generator 160 generates a whitening weight W for whitening the received signal. White The whitening weight generator 160 generates the whitening weight W for each received signal group (in this example, for each vertically polarized antenna group and each horizontally polarized antenna group).White The vertical polarization whitening processor 150a and the horizontal polarization whitening processor 150b generate the whitening weight W. White Based on this, the received signal y after beamforming. BF The beamforming of the received signal y is performed by the vertical polarization whitening processor 150a and the horizontal polarization whitening processor 150b for each received signal group (in this example, for each vertical polarization antenna group and each horizontal polarization antenna group). BF This is a whitening processing unit that whitens the signal. The vertical polarization whitening processor 150a and the horizontal polarization whitening processor 150b process the received signal y after beamforming as follows. BF Whitening weight W White Multiply by the whitened received signal y White Generates.

number

[0100] Polarization combiner 130a processes the whitened received signal y as follows: White Polarization synthesis weight W Comb Multiply by the received signal y after polarization synthesis. Comb Outputs.

number

[0101] The following describes specific examples of whitening treatment.

[0102] (Specific example 1) Specific example 1 is an example of calculating whitening weight from beam weight. Figure 19 shows an example of the configuration of a base station 10 according to several embodiments. In the example of Figure 19, similar to Figure 18, it is equipped with a vertical polarization whitening processor 150a, a horizontal polarization whitening processor 150b, and a whitening weight generator 160.

[0103] In the example shown in Figure 19, the SRS channel estimator 121a, similar to Embodiment 2, receives the received signal y for each polarization antenna group. V , y HChannel response information H is estimated based on the SRS included in V,S H H,S .

[0104] The polarization beam weight generator 122a generates beam weights W V,S H H,S based on the estimated channel response information H BF,V W BF,H . In this example, as follows, based on the precoding matrix F and the channel response information H V,S H H,S beam weights W BF,V W BF,H are generated. That is, in this example, different from Embodiment 2, the process of arranging the left singular vectors obtained by singular value decomposition is not performed.

Equation

[0105] The vertical polarization beamformer 110a and the horizontal polarization beamformer 110b multiply the received signals y BF,V W BF,H by the beam weights W V y H and output the received signals y BF after beamforming. The received signals y BF after beamforming are as follows.

Equation

[0106] The whitening weight generator 160 generates whitening weights W BF,V W BF,H based on the beam weights W WhiteThis generates the following. In this example, the noise covariance matrix is ​​estimated using the beam weights based on the channel response information estimated from the SRS, and whitening weights are generated based on the estimated noise covariance matrix. The whitening weight generator 160 generates the beam weight W as follows: BF,V , W BF,H From this, the noise covariance matrix R V , R H Calculate the value raised to the power of -1 / 2.

number

[0107] The whitening weight generator 160 calculates the noise covariance matrix R V , R H The whitening weight W is calculated by raising the value of -1 / 2 to the power of the following: White,V , W White,H Let's assume that.

number

[0108] The vertical polarization whitening processor 150a and the horizontal polarization whitening processor 150b process the received signal y after beamforming as follows: BF Whitening weight W generated White,V , W White,H Multiply by the whitened received signal y White Outputs.

number

[0109] The DMRS channel estimator 141a processes the whitened received signal y output by the vertical polarization whitening processor 150a and the horizontal polarization whitening processor 150b. White Based on the DMRS included, DMRS channel response information H V,D H H,D The polarization synthesis weight generator 142a estimates the channel response information H as follows, similar to Embodiment 2. V,D H H,D Based on this, polarization synthesis weight WComb Generates.

number

[0110] The polarization combiner 130a generates the polarization combine weight W Comb The whitened received signal y output by the vertical polarization whitening processor 150a and the horizontal polarization whitening processor 150b White Based on this, the received signal y after polarization synthesis is as follows: Comb Outputs.

number

[0111] As described above, in specific example 1, a whitening weight generator is added that generates whitening weights based on the beamweights generated by the beamweight generator, and multiple whitening processors are added that take the output signals of each polarization beamformer as inputs and input the output signals to a polarization combiner. This makes it possible to accurately whiten only the noise components that have been colored (correlated with the channel) by beamforming.

[0112] (Specific example 2) Specific example 2 is an example of calculating whitening weights from the noise covariance matrix estimated by DMRS. Figure 20 shows an example configuration of a base station 10 according to several embodiments. In the example of Figure 20, compared to the configuration in Figure 19, RU100 is equipped with a DMRS channel-noise covariance matrix estimator 161 instead of a DMRS channel estimator 141a. Otherwise, it is the same as in Figure 19.

[0113] Similar to equation (15) in specific example 1, the SRS channel estimator 121a calculates the channel response information H V,S H H,S The polarization beamweight generator 122a estimates the beamweight W BF,V , W BF,H The vertical polarization beamformer 110a and the horizontal polarization beamformer 110b generate the beamformed received signal y BFGenerates.

[0114] The DMRS channel-noise covariance matrix estimator 161 uses the beamforming received signal y output by the vertical polarization beamformer 110a and the horizontal polarization beamformer 110b. BF Channel response information H based on DMRS included V,D H H,D , Noise covariance matrix R V , R H We estimate this.

[0115] The whitening weight generator 160 generates the noise covariance matrix R generated by the DMRS channel noise covariance matrix estimator 161. V , R H Based on this, whitening weight W White This generates the whitening weights based on the noise covariance matrix estimated from the DMRS. In this example, similar to equation (17) in specific example 1, the estimated noise covariance matrix R V , R H The whitening weight W is the -1 / 2 power of White,V , W White,H Let's assume that.

[0116] The vertical polarization whitening processor 150a and the horizontal polarization whitening processor 150b, similar to equation (18) in Specific Example 1, process the received signal y after beamforming. BF Whitening weight W generated White,V , W White,H Multiply by the whitened received signal y White Outputs.

[0117] Polarization combining weight generator 142a generates whitening weight W generated by whitening weight generator 160. White,V , W White,H And channel response information H estimated from DMRS by DMRS channel-noise covariance matrix estimator 161 V,D H H,D Based on this, the polarization synthesis weight Wcomb is generated. Channel response information H V,D H H,D The noise covariance matrix R V , RH Multiply by the -1 / 2 power and obtain the polarization synthesis weight W Comb Generates.

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[0118] The polarization combiner 130a generates the polarization combine weight W, similar to the example in Specific Example 1. Comb The whitened received signal y output by the vertical polarization whitening processor 150a and the horizontal polarization whitening processor 150b White Based on this, the received signal y after polarization synthesis is as follows: Comb Outputs.

number

[0119] As described above, in specific example 2, a whitening weight generator is added that generates whitening weights based on the noise covariance matrix estimated by DMRS, and multiple whitening processors are added that take the output signals of each polarization beamformer as inputs and input the output signals to a polarization combiner. In addition, the whitening weights are calculated using the noise covariance matrix raised to the power of -1 / 2, and polarization synthesis is performed based on the whitened equivalent channel obtained by multiplying the equivalent channel after beamforming by the whitening weights.

[0120] This allows interference noise components, including interference from other cells and noise, to be whitened. Whitening of noise components that have been colorized by beamforming is less accurate compared to Specific Example 1. Furthermore, as in Embodiment 2, it is also possible to generate beam weights based on the left singular vector obtained when the channel response information matrix is ​​decomposed by singular value decomposition. In this case, the fewer left singular vectors that are arranged when singular value decomposition is performed, the fewer signal streams the beamformer outputs, thus further reducing the load on whitening weight generation and channel estimation by DMRS. However, this results in a degradation of transmission performance.

[0121] (Specific example 3) Specific Example 3 is an example in which the calculation of the equivalent channel for polarization synthesis in Specific Example 2 is omitted.

[0122] Figure 21 shows an example configuration of a base station 10 according to several embodiments. In the example in Figure 21, the configuration is the same as in Figure 20, and the RU100 includes a DMRS channel-noise covariance matrix estimator 161.

[0123] In the example in Figure 21, the whitening weight generator 160 generates the noise covariance matrix R estimated from the DMRS by the DMRS channel-noise covariance matrix estimator 161. V , R H Based on this, whitening weight W White This generates the noise covariance matrix R. Specifically, the noise covariance matrix R is generated as follows: V , R H The whitening weight W is the -1 power of White,V , W White,H Let's assume that.

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[0124] The vertical polarization whitening processor 150a and the horizontal polarization whitening processor 150b, as in Specific Example 2, process the received signal y after beamforming. BF Whitening weight W generated White,V , W White,H Multiply by the whitened received signal y White Outputs the whitened received signal y. White The following applies:

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[0125] The polarization synthesis weight generator 142a uses channel response information H estimated from the DMRS by the DMRS channel-noise covariance matrix estimator 161. V,D H H,DBased on this, polarization synthesis weights are generated. In this example, whitening weights are not used, and polarization synthesis weights are generated only from channel response information estimated from DMRS. As described above, by using the -1 power of the noise covariance matrix as the whitening weight, it is not necessary to use whitening weights in the polarization synthesis weights. That is, the polarization synthesis weight generator 142a generates polarization synthesis weights W as follows, similar to Specific Example 1. comb Generates.

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[0126] The polarization combiner 130a generates the polarization combine weight W, similar to the example in Specific Example 2. Comb The whitened received signal y output by the vertical polarization whitening processor 150a and the horizontal polarization whitening processor 150b White Based on this, the received signal y after polarization synthesis is as follows: Comb Outputs.

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[0127] As described above, in specific example 3, a whitening weight generator is added that generates whitening weights based on the noise covariance matrix estimated by DMRS, and multiple whitening processors are added that take the output signals of each polarization beamformer as inputs and input the output signals to a polarization combiner. In addition, the whitening weights are calculated using the noise covariance matrix raised to the power of -1, and polarization combining is performed based on the equivalent channel after beamforming.

[0128] This allows interference noise components, including interference from other cells and noise, to be whitened. Whitening of noise components that have been colorized by beamforming is less accurate compared to Specific Example 1. Also, unlike Specific Example 2, calculation of the equivalent channel after whitening is unnecessary. As in Embodiment 2, it is also possible to generate beam weights based on the left singular vector obtained when the channel response information matrix is ​​decomposed by singular value decomposition. In that case, the fewer left singular vectors that are lined up when singular value decomposition is performed, the fewer signal streams the beamformer outputs, thus further reducing the load on whitening weight generation and channel estimation by DMRS. However, this results in a degradation of transmission performance.

[0129] Figures 22 and 23 show the evaluation results for Specific Example 1 described above. As shown in Figure 22, Specific Example 1 has a processing load intermediate between WDBF and ULPI. In other words, compared to ULPI, it is possible to reduce the processing load in RU while maintaining the number of signal streams transmitted in the fronthaul.

[0130] Furthermore, as shown in Figure 23, Specific Example 1 exhibits performance intermediate between WDBF and ULPI. In other words, with WDBF, the BER (Bit Error Rate) deteriorates significantly due to the effects of time-dependent changes in channel response information. In contrast, Specific Example 1 can suppress the deterioration of the BER due to the effects of time-dependent changes in channel response information.

[0131] This disclosure is not limited to the embodiments described above, and may be modified as appropriate without departing from its spirit.

[0132] Each configuration in the above-described embodiment may consist of hardware, software, or both, and may consist of one piece of hardware or software, or multiple pieces of hardware or software. Each device and function (process) of the base station, including RUs and DUs, may be realized by a computer 20 having a network interface 21, a processor 22 such as a CPU (Central Processing Unit), and a memory 23 as a storage device, as shown in Figure 24. The network interface 21 may include a network interface card (NIC) for communication between devices. For example, a program for performing the method in the embodiment may be stored in the memory 23, and each function may be realized by executing the program stored in the memory 23 with the processor 22.

[0133] These programs, when loaded into a computer, include a set of instructions (or software code) for causing the computer to perform one or more of the functions described in the embodiments. The programs may be stored on non-temporary computer-readable media or tangible storage media. Examples, but not limited to, include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drives (SSDs), or other memory technologies, CD-ROMs, digital versatile discs (DVDs), Blu-ray® discs, or other optical disc storage, magnetic cassettes, magnetic tapes, magnetic disk storage, or other magnetic storage devices. The programs may be transmitted over temporary computer-readable media or communication media. Examples, but not limited to, include electrical, optical, acoustic, or other forms of propagating signals.

[0134] Although the present disclosure has been described above with reference to embodiments, the present disclosure is not limited to the embodiments described above. Various modifications to the structure and details of the present disclosure can be made as can be understood by those skilled in the art within the scope of the present disclosure. Furthermore, each embodiment can be combined with other embodiments as appropriate.

[0135] Each drawing is merely illustrative to illustrate one or more embodiments. Each drawing may be associated with one or more other embodiments rather than with only one specific embodiment. As those skilled in the art will understand, various features or steps described with reference to any one drawing can be combined with features or steps shown in one or more other drawings, for example, to create embodiments not explicitly shown or described. Not all features or steps shown in any one drawing to illustrate an exemplary embodiment are necessarily required, and some features or steps may be omitted. The order of steps shown in any of the drawings may be changed as appropriate.

[0136] Some or all of the above embodiments may also be described as follows, but are not limited to the following:

[0137] (Note 1) A beamweight generation unit generates a beamweight for each received signal group based on first channel response information estimated based on a first reference signal included in the received signal, For each of the received signal groups, a beamforming unit generates a beamformed signal based on the generated beamweight and the received signal, A received signal group synthesis weight generation unit generates a received signal group synthesis weight based on a second channel response information estimated based on a second reference signal included in the generated beamforming signal, A received signal group combining unit combines the beamforming signals for each of the received signal groups based on the generated received signal group combining weights, A wireless base station equipped with the necessary equipment. (Note 2) Equipped with multiple antennas, The received signal group includes a plurality of received signals received by the plurality of antennas, The wireless base station described in Appendix 1. (Note 3) The plurality of antennas includes a first antenna corresponding to a first polarization and a second antenna corresponding to a second polarization, The first received signal group included in the received signal group includes received signals received by the first antenna, The second group of received signals included in the aforementioned group of received signals includes the received signals received by the second antenna. The wireless base station described in Appendix 2. (Note 4) The aforementioned multiple antennas include separate antennas for each unit. The first received signal group included in the received signal group includes received signals received by antenna elements in the first unit included in the plurality of antennas, The second group of received signals included in the aforementioned group of received signals includes received signals received by antenna elements in the second unit included in the plurality of antennas. The wireless base station described in Appendix 2. (Note 5) The plurality of antennas includes a first antenna corresponding to a first polarization and a second antenna corresponding to a second polarization, The aforementioned multiple antennas include separate antennas for each unit. The first received signal group included in the received signal group includes a received signal received by the first antenna in the first unit included in the plurality of antennas, The second received signal group included in the received signal group includes the received signal received by the second antenna in the first unit included in the plurality of antennas, The third received signal group included in the received signal group includes the received signal received by the first antenna in the second unit included in the plurality of antennas, The fourth received signal group included in the received signal group includes a received signal received by the second antenna in the second unit included in the plurality of antennas. The wireless base station described in Appendix 2. (Note 6) Prior to the beam forming unit, a beam region conversion unit is provided to convert the received signal into a beam region. The received signal group is a beam group based on the received signal converted into the beam region. The wireless base station described in Appendix 1. (Note 7) The beam domain conversion unit is a discrete Fourier transformer. The wireless base station described in Appendix 6. (Note 8) The beam group includes beams of received signals with similar directions of arrival. The wireless base station described in Appendix 6. (Note 9) The first reference signal is a sounding reference signal. A radio base station as described in any one of the items 1 through 8 of the appendix. (Note 10) The aforementioned second reference signal is a demodulated reference signal. A radio base station as described in any one of the items 1 through 9 of the appendix. (Note 11) The first channel response information described above is channel response information including a precoding matrix. A radio base station as described in any one of the items 1 through 10 of the appendix. (Note 12) The first channel response information is channel response information based on a matrix showing the channel response between the wireless base station and the user terminal. A radio base station as described in any one of the items 1 through 11 of the appendix. (Note 13) The beamweight generation unit generates the beamweight based on a plurality of left singular vectors obtained by singular value decomposition of the matrix representing the first channel response information. A radio base station as described in any one of the items 1 through 12 of the appendix. (Note 14) The beamweight generation unit generates the beamweight based on any number of singular vectors selected from the plurality of left singular vectors. The wireless base station described in Appendix 13. (Note 15) The aforementioned arbitrary number is smaller than the number of the plurality of left singular vectors. The wireless base station described in Appendix 14. (Note 16) The aforementioned arbitrary number of singular vectors are singular vectors whose singular values ​​are greater than a predetermined value. The wireless base station described in Appendix 14. (Note 17) The aforementioned arbitrary number of singular vectors are singular vectors ranging from the largest singular value to the aforementioned arbitrary number. The wireless base station described in Appendix 14. (Note 18) The beamforming unit generates a number of beamforming signals that is less than the number of received signals, based on the beamweight and the received signals. A radio base station as described in any one of the items 1 through 17 of the appendix. (Note 19) For each of the received signal groups, a whitening weight generation unit generates a whitening weight to whiten the noise component of the beamforming signal, Each of the received signal groups is provided with a whitening processing unit that performs whitening processing on the beamforming signal based on the generated whitening weight. A radio base station as described in any one of the items 1 through 18 of the appendix. (Note 20) The whitening weight generation unit generates the whitening weight based on the noise covariance matrix calculated based on the generated beam weight. The radio base station described in Supplementary Note 19. (Supplementary Note 21) The whitening weight generation unit generates the whitening weight based on the noise covariance matrix estimated based on the second reference signal. The radio base station described in Supplementary Note 19. (Supplementary Note 22) The whitening weight generation unit generates the whitening weight by taking the -1 / 2 power of the noise covariance matrix obtained for each reception signal group. The reception signal group combining weight generation unit generates the reception signal group combining weight based on the second channel response information estimated based on the second reference signal and the generated whitening weight. The radio base station described in Supplementary Note 21. (Supplementary Note 23) The whitening weight generation unit generates the whitening weight by taking the -1 power of the noise covariance matrix obtained for each reception signal group. The radio base station described in Supplementary Note 21. (Supplementary Note 24) Comprising an RU (Radio Unit) and a DU (Distributed Unit). The RU includes the beam weight generation unit, the beam forming unit, the reception signal group combining weight generation unit, and the reception signal group combining unit. The DU includes an equalization unit that performs equalization processing on the combined signal. The radio base station according to any one of Supplementary Notes 1 to 23. (Supplementary Note 25) A method for a radio base station, For each reception signal group, generating a beam weight based on first channel response information estimated based on a first reference signal included in the reception signal; For each reception signal group, generating a signal after beamforming based on the generated beam weight and the reception signal; Generating a received signal group combining weight based on second channel response information estimated based on a second reference signal included in the signal after the generated beamforming; Combining the signals after the beamforming for each of the received signal groups based on the generated received signal group combining weight; A method comprising the steps of. (Appendix 26) A program for causing a computer to execute a method for a radio base station, wherein the method comprises: For each received signal group, generating a beam weight based on first channel response information estimated based on a first reference signal included in the received signal; For each received signal group, generating a signal after beamforming based on the generated beam weight and the received signal; Generating a received signal group combining weight based on second channel response information estimated based on a second reference signal included in the generated signal after beamforming; Combining the signals after the beamforming for each of the received signal groups based on the generated received signal group combining weight; A program comprising the steps of.

[0138] Some or all of the elements (e.g., configurations and functions) described in Appendices 2 to 24 that are subordinate to Appendix 1 (radio base station) may be subordinate to Appendices 25 (method) and 26 (program) in the same subordinate relationship as Appendices 2 to 24. Some or all of the elements described in any appendix may be applied to various hardware, software, recording means for recording software, systems, and methods.

Explanation of Reference Numerals

[0139] 1 Wireless communication system 10 Base station 20 Computer 21 Network interface 22 processors 23 memory 100 RU 101 Antenna 102 Discrete Fourier Transformer 110 Beamformer 110a Vertical Polarization Beamformer 110b Horizontal Polarization Beamformer 120 Beamweight generation unit 121 First channel estimator 121a SRS channel estimator 122 Beamweight Generator 122a Polarization beamweight generator 130 Received Signal Group Combiner 130a Polarization combiner 140 Received signal group synthesis weight generation unit 141 Second channel estimator 141a DMRS channel estimator 142 Received Signal Group Synthesis Weight Generator 142a Polarization Synthesizing Weight Generator 150a Vertical Polarization Whitening Treatment Unit 150b horizontal polarization whitening processor 160 Whitening Weight Generator 161 DMRS Channel-Noise Covariance Matrix Estimator 200 DU 210 Equalizer 221-Channel Noise Covariance Matrix Estimator 222 Equalization Weight Generator 700 base stations 701 Antenna 710 RU 711 Beamformer 720 DU 800 base stations 801 Antenna 810 RU 811 Beamformer 820 DU 821 Equalizer 822 Channel Estimator 823 Beam Weight Generator 824 Channel Noise Covariance Matrix Estimator 825 Equalization Weight Generator 900 Base Station 910 RU 901 Antenna 911 Equalizer 912 Channel Noise Covariance Matrix Estimator 913 Equalization Weight Generator 920 DU

Claims

1. A beamweight generation unit generates a beamweight for each received signal group based on first channel response information estimated based on a first reference signal included in the received signal, For each of the received signal groups, a beamforming unit generates a beamformed signal based on the generated beamweight and the received signal, A received signal group synthesis weight generation unit generates a received signal group synthesis weight based on a second channel response information estimated based on a second reference signal included in the generated beamforming signal, A received signal group combining unit combines the beamforming signals for each of the received signal groups based on the generated received signal group combining weights, A wireless base station equipped with the necessary equipment.

2. Equipped with multiple antennas, The received signal group includes a plurality of received signals received by the plurality of antennas, The wireless base station according to claim 1.

3. The plurality of antennas includes a first antenna corresponding to a first polarization and a second antenna corresponding to a second polarization. The first received signal group included in the received signal group includes received signals received by the first antenna, The second group of received signals included in the aforementioned group of received signals includes the received signals received by the second antenna. The wireless base station according to claim 2.

4. The aforementioned multiple antennas include separate antennas for each unit. The first received signal group included in the received signal group includes received signals received by antenna elements in the first unit included in the plurality of antennas, The second group of received signals included in the aforementioned group of received signals includes received signals received by antenna elements in the second unit included in the plurality of antennas. The wireless base station according to claim 2.

5. The plurality of antennas includes a first antenna corresponding to a first polarization and a second antenna corresponding to a second polarization. The aforementioned multiple antennas include separate antennas for each unit. The first received signal group included in the received signal group includes a received signal received by the first antenna in the first unit included in the plurality of antennas, The second received signal group included in the received signal group includes the received signal received by the second antenna in the first unit included in the plurality of antennas, The third received signal group included in the received signal group includes the received signal received by the first antenna in the second unit included in the plurality of antennas, The fourth received signal group included in the received signal group includes a received signal received by the second antenna in the second unit included in the plurality of antennas. The wireless base station according to claim 2.

6. Prior to the beam forming unit, a beam region conversion unit is provided to convert the received signal into a beam region. The received signal group is a beam group based on the received signal converted into the beam region. The wireless base station according to claim 1.

7. The beam domain conversion unit is a discrete Fourier transformer. The wireless base station according to claim 6.

8. The beam group includes beams of received signals with similar directions of arrival. The wireless base station according to claim 6.

9. A method for a wireless base station, For each received signal group, a beamweight is generated based on first channel response information estimated based on a first reference signal included in the received signal, For each of the received signal groups, a beamforming signal is generated based on the generated beamweight and the received signal. Based on the second channel response information estimated based on the second reference signal included in the generated beamforming signal, a received signal group synthesis weight is generated. Based on the generated received signal group synthesis weights, the beamforming signals for each received signal group are synthesized. A method that includes this.

10. A program that causes a computer to execute a method for a wireless base station, The aforementioned method, For each received signal group, a beamweight is generated based on first channel response information estimated based on a first reference signal included in the received signal, For each of the received signal groups, a beamforming signal is generated based on the generated beamweight and the received signal. Based on the second channel response information estimated based on the second reference signal included in the generated beamforming signal, a received signal group synthesis weight is generated. Based on the generated received signal group synthesis weights, the beamforming signals for each received signal group are synthesized. A program that includes this.

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