JP2019176270A - Base station and communication control method by base station - Google Patents

Abstract

To achieve efficient selection of a terminal of a target subjected to MIMO transmission in MU-MIMO.SOLUTION: The base station includes: a transmission circuit which wirelessly transmits signals for a plurality of terminals with a plurality of antennas executing space division multiplex for the signal; a control circuit for selecting some of the plurality of terminals for a terminal candidate for allocating signal reception opportunities on the basis of the information showing at least either one of communication states between the plurality of antennas and the plurality of terminals and states of propagation paths.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a base station and a communication control method by the base station.

  In the UMTS (Universal Mobile Telecommunications System) network, Long Term Evolution (LTE) has been specified for the purpose of higher data rate and lower delay. In order to further increase the bandwidth and speed from LTE, LTE successor systems (for example, LTE-A (LTE-Advanced), FRA (Future Radio Access), 5G (5th generation mobile communication system), 5G + ( 5G plus) and New-RAT (Radio Access Technology) are also being studied.

  In future wireless communication systems (for example, 5G), a large number of antenna elements (for example, 100 elements or more) are used in a high frequency band (for example, 5 GHz or more) in order to further increase the speed of signal transmission and reduce interference. The use of massive MIMO (Multiple Input Multiple Output) is being studied.

  As a technique for controlling a beam or a stream in MIMO, for example, a technique described in Non-Patent Document 2 is known. Multi-user MIMO (MU-MIMO) technology is also known.

T. Obara, S. Suyama, J. Shen, and Y. Okumura, “Joint processing of analog fixed beamforming and CSI-based precoding for super high bit rate Massive MIMO transmission using higher frequency bands,” IEICE Trans. Commun., Vol E98-B, no. 8, pp. 1474-1481, Aug. 2015 Shohei Yoshioka, Tatsuki Okuyama, Satoshi Suyama, Yukihiko Okumura, “Characteristic Evaluation of Massive MIMO Using Digital Beamforming in Low SHF Band for 5G Realization” IEICE Tech. Bulletin, vol. 116, no. 396, RCS2016-238 , pp. 13-18, January 2017

  In MU-MIMO, a target terminal to perform MIMO transmission is selected in consideration of a desired throughput for each of a plurality of user terminals (for example, a radio terminal or a UE (User Equipment), hereinafter referred to as “terminal”). How to do is not fully studied.

  One aspect of the present disclosure is to efficiently select a target terminal for performing MIMO transmission in MU-MIMO.

  A base station according to an aspect of the present disclosure includes a transmission circuit that wirelessly transmits signals addressed to a plurality of terminals using a plurality of antennas and performs wireless transmission, and communication between the plurality of antennas and the plurality of terminals And a control circuit that selects a part of the plurality of terminals as terminal candidates to which the signal reception opportunity is assigned based on information indicating at least one of a situation and a propagation path situation.

  According to one aspect of the present disclosure, it is possible to efficiently select a target terminal for performing MIMO transmission in MU-MIMO.

It is a block diagram which shows the structural example of the wireless base station which performs MU-MIMO. It is a block diagram which shows the other structural example of the wireless base station which performs MU-MIMO. It is a sequence chart which shows an example of the process which selects the terminal of communication object. It is a schematic diagram which shows the operation example which selects the terminal of communication object. It is a figure which shows an example of the hardware constitutions of a base station and a terminal.

  Hereinafter, each embodiment of the present disclosure will be described in detail with reference to the drawings.

  In addition, when distinguishing and explaining the same kind of elements, reference symbols are used such as “base station 10A”, “base station 10B” or “terminal 20-1”, “terminal 20-2”, and the same kind of elements are used. When the description is made without distinguishing the elements, a common number among the reference symbols such as “base station 10” and “terminal 20” may be used.

  Below, the example which performs the MU-MIMO transmission which carries out the space division multiplexing of the signal addressed to a some terminal using a some antenna, and radio-transmits is demonstrated. Hereinafter, a case where the base station 10 performs beamforming (BF) in massive MIMO will be described.

<Base station configuration>
1 and 2 are block diagrams illustrating a configuration example of a base station (for example, a radio base station or gNB) that performs MU-MIMO.

  In the base station 10A shown in FIG. 1, a method of combining digital precoding, analog fixed BF, and channel information (for example, Channel Status Information: CSI) is applied. On the other hand, in the base station 10B shown in FIG. 2, a method of combining digital precoding, digital fixed BF, and channel information (for example, CSI) is applied.

  The base station 10 selects L fixed beams from a plurality (for example, L or more) of fixed beams, selects U terminals (for example, users 1 to U) from the plurality of terminals, and U terminals MIMO transmission. L and U are integers of 1 or more. Each of the plurality of fixed beams has a fixed beam transmission direction (for example, an angle including an azimuth angle or a zenith angle). Hereinafter, the fixed beam may be simply referred to as “beam”.

Further, the base station 10 generates M streams for each terminal. For example, in FIGS. 1 and 2, M _i (any one of i = 1 to U) is an integer of 1 or more. For example, the sum of the total number _(M 1 ~M _U Stream "is less than the fixed number of beams L.

[Configuration Example of Base Station 10A]
In FIG. 1, a base station 10A includes a terminal candidate selection unit 100, a beam selection unit 102, a terminal selection unit 104, a digital precoder 106, a D / A conversion unit 108, a frequency conversion unit 110, and an analog fixed unit. A beam former 112 and a plurality of antennas 116 are provided.

  The terminal candidate selection unit 100 selects some of the plurality of terminals as terminal candidates to which the base station 10 assigns signal reception opportunities (in other words, terminal candidates to be subjected to MIMO transmission with the base station 10). For example, the terminal candidate selection unit 100 is configured based on information indicating at least one of a communication state and a channel (propagation path) state between the plurality of antennas 116 of the base station 10 and the plurality of terminals. Select some as terminal candidates. The terminal candidate selection unit 100 outputs terminal candidate information indicating the selected terminal candidate to the beam selection unit 102 and the terminal selection unit 104. In addition, the terminal candidate selection unit 100 generates a signal (hereinafter, referred to as “terminal candidate notification signal”) for notifying whether or not each terminal is a terminal candidate. The terminal candidate notification signal is transmitted to each terminal (not shown).

  For example, the terminal candidate selection unit 100 calculates a fairness standard parameter. Then, the terminal candidate selection unit 100 selects a terminal candidate from a plurality of terminals based on the fairness standard parameter.

  The fairness standard parameter is a parameter representing a standard for determining the fairness of a communication opportunity (for example, a signal reception opportunity from the base station 10) between a plurality of terminals. In other words, the fairness criterion parameter is a parameter indicating a criterion for selecting a terminal to which the base station 10 assigns a signal reception opportunity. For example, the fairness standard parameter is calculated based on information indicating at least one of a communication status and a channel (propagation path) status between the plurality of antennas 116 and the plurality of terminals of the base station 10.

  Details of the terminal candidate selection method using the fairness criterion parameter in the terminal candidate selection unit 100 will be described later.

  The beam selection unit 102 and the terminal selection unit 104 perform processing for selecting a target terminal to perform MIMO transmission (for example, selection of a fixed beam or MIMO) with respect to the terminal candidate selected by the terminal candidate selection unit 100. Select the transmission target terminal).

  The beam selection unit 102 selects a beam to be used for transmitting a beam scanning reference signal from a plurality of beams having different transmission directions. The beam selection unit 102 controls the analog fixed beamformer 112 in order to transmit a beam scanning reference signal using the selected beam. For example, the beams used for transmitting the beam scanning reference signal are all the beams that can be formed by the base station 10. However, the beam used for transmitting the beam scanning reference signal is not limited to all the beams that can be formed by the base station 10, but may be a part of the beams.

  Further, the beam selection unit 102 selects a beam to be used for data transmission to the terminal from a plurality of beams. The beam selection unit 102 controls the analog fixed beamformer 112 in order to transmit the data or the channel estimation reference signal using the selected beam. For example, the beam selection unit 102 calculates a beam selection reference parameter based on beam information fed back from each terminal candidate. The beam information indicates, for example, reception power or reception quality of each beam. The beam selection unit 102 selects a beam to be used for data transmission from a plurality of beams based on the beam selection reference parameter. The beam selection unit 102 may select a beam using a fairness criterion parameter in addition to the beam selection criterion parameter.

  Details of the beam selection method using the beam selection reference parameter in the beam selection unit 102 will be described later. Hereinafter, a beam used for transmission of a signal including a beam scanning reference signal, data, and a channel estimation reference signal is referred to as a “used beam”.

  The terminal selection unit 104 selects a target terminal (hereinafter referred to as “target terminal”) that performs MIMO transmission with the base station 10 from the terminal candidates indicated in the terminal candidate information input from the terminal candidate selection unit 100. The terminal selection unit 104 performs control to cause the digital precoder 106 to input data addressed to the selected target terminal.

  For example, the terminal selection unit 104 calculates a terminal selection criterion parameter based on channel information (for example, CSI) fed back from the terminal candidate selected by the terminal candidate selection unit 100. And the terminal selection part 104 selects the object terminal which performs MIMO transmission with the base station 10 based on a terminal selection reference | standard parameter. Further, terminal selection section 104 generates a signal (hereinafter referred to as “selected terminal notification signal”) for notifying whether or not each terminal is a target terminal for MIMO transmission. The selected terminal notification signal is transmitted to each terminal candidate (not shown), for example.

  The details of the method of selecting the target terminal using the terminal selection criterion parameter in the terminal selection unit 104 will be described later.

  In order to improve the reception quality of each terminal, the digital precoder 106 multiplies the signal before transmission by a weight (for example, a precoding matrix) corresponding to the channel between the base station 10A and the terminal. For example, the digital precoder 106 applies the precoding matrix P to the M-sequence baseband signal to generate an L-sequence signal, and outputs the L-sequence signal to the D / A converter 108. Here, L is the number of used beams used for transmitted data. The precoding matrix P has a sequence of L rows and M columns.

  L D converters 108 and frequency converters 110 shown in FIG. 1 are provided corresponding to the L beams.

  Each of the D / A converters 108 converts the signal output from the digital precoder 106 from a digital signal to an analog signal. Each of the frequency converters 110 up-converts the frequency of the signal output from the D / A converter 108 and outputs it to the analog fixed beamformer 112.

Analog fixed beamformer 112, for the signal of L sequence inputted from the frequency conversion unit 110 applies beamforming matrix W _T corresponding to use beam selected in the beam selector 102, N _T sequences of signals Is generated. N _T is the number of transmitting antenna elements. Here, the beamforming matrix W _T has _NT rows and L columns. A plurality of _NT sequence signals are transmitted from a plurality of antennas 116, respectively.

  The analog fixed beamformer 112 performs beamforming corresponding to the used beam selected by the beam selection unit 102 with respect to the beam scanning reference signal or the channel estimation reference signal.

<Configuration example of base station 10B>
In the base station 10B shown in FIG. 2, the same components as those of the base station 10A shown in FIG.

  In the base station 10 </ b> A shown in FIG. 1, the analog fixed beamformer 112 is arranged at the subsequent stage of the frequency conversion unit 110. On the other hand, in the base station 10 </ b> B shown in FIG. 2, the digital fixed beamformer 114 is arranged at the subsequent stage of the digital precoder 106. 1 and 2 differ in this respect.

Further, D / A converter 108 and the frequency converting unit 110 is provided _{to N T} respectively corresponding to the _{N T} transmit antennas 116.

  The beam selection unit 102 controls the digital fixed beamformer 114 to transmit the selected use beam.

Digital fixed beamformer 114, to the L-series of a signal input from the digital pre-coder 106 applies beamforming matrix W _T corresponding to use beam beam selector 102 selects, N _T sequences of signals And outputs an _NT sequence signal to the D / A converter 108.

The _NT sequence signals output from the digital fixed beamformer 114 are each converted from a digital signal to an analog signal by the D / A conversion unit 108, and the frequency is up-converted by the frequency conversion unit 110 and transmitted from the antenna 116. The

<Operation example of base station>
FIG. 3 is a sequence chart illustrating an example of processing for selecting the terminal 20 that communicates with the base station 10. For example, the base station 10 and the terminal 20 perform the process shown in FIG. 3 every time data transmission is performed.

  FIG. 4 is a schematic diagram illustrating an example of the operation of the wireless communication system in the process of selecting a target terminal 20 (not shown) that communicates with the base station 10. In FIG. 4, the beam used is represented by shading.

  As shown in FIG. 3, the base station 10 calculates a fairness standard parameter (ST101). For example, the base station 10 calculates the fairness standard parameter using a parameter (for example, throughput, reception quality, reception power, or the like) indicating the past channel state or communication state of each terminal 20.

For example, the fairness standard parameter is expressed as “ρ _U (u, t)”. Here, u is a terminal number for identifying the terminal 20, and t is a time slot number. In FIG. 4A, the fairness criterion parameter ρ _U (1, t) of the terminal 20-1 (u = 1) is 1.0. Similarly, the fairness criterion parameters of the terminals 20-2, 20-3, 20-4, and 20-5 are ρ _u (2, t) = 2.8, ρ _u (3, t) = 0.2, respectively. ρ _u (4, t) = 0.3 and ρ _u (5, t) = 1.8. Here, the smaller the fairness standard parameter ρ _u (u, t) 20, the fewer reception opportunities assigned to the base station 10 in the past.

As shown in FIG. 3, base station 10 (for example, terminal candidate selection section 100) selects terminal candidates using the fairness standard parameters calculated in ST101 (ST102). For example, in FIG. 4B, the base station 10 selects a terminal 20 whose fairness criterion parameter ρ _u (u, t) is equal to or less than a threshold as a terminal candidate. FIG. 4B shows a case where the threshold is 1.5 as an example. In this case, as shown in FIG. 4B, the base station 10 uses the terminals 20-1, 20-3, and 20-4 whose fairness standard parameters ρ _u (u, t) are not more than a threshold value 1.5 as terminal candidates. select. In other words, as shown in FIG. 4B, the base station 10 transmits the terminals 20-2 and 20-5 having the fairness criterion parameter ρ _u (u, t) larger than the threshold value 1.5 from the base station 10. Are excluded from candidates to be assigned a signal reception opportunity.

  As shown in FIG. 3, base station 10 transmits to each terminal 20 a terminal candidate notification signal for notifying whether or not it is a terminal candidate selected in ST102 (ST103). The terminal 20 can recognize whether or not an opportunity to receive a signal from the base station 10 is assigned based on the terminal candidate notification signal.

  The terminal candidate notification signal may be associated (or related) with other parameters transmitted from the base station 10 to each terminal 20, for example. In this case, each terminal 20 can recognize the contents of the terminal candidate notification signal based on the other parameters. By this processing, the terminal candidate notification signal is notified implicitly, so that the amount of signaling can be reduced.

  The base station 10 controls the analog fixed beamformer 112 (refer to FIG. 1) or the digital fixed beamformer 114 (refer to FIG. 2), and uses the beams having different transmission directions (angles) to perform the beam scanning reference signal. Is transmitted (ST104). For example, in FIG. 4B, the base station 10 transmits a beam scanning reference signal using all the beams 30 that can be formed by the base station 10.

  Note that the base station 10 may transmit the terminal candidate notification signal in ST103 and the beam scanning reference signal in ST104 separately, or may transmit them together or in association with each other.

  As shown in FIG. 3, each terminal 20 measures the received power of each beam 30, for example, using the received beam scanning reference signal when the received terminal candidate notification signal indicates that it is a terminal candidate. (ST105).

  Terminal 20 which is a terminal candidate feeds back beam information including the received power of each beam 30 measured in ST105 to base station 10 (ST106). The received power included in the beam information may be, for example, the received power of all the beams that can be formed in the base station 10, may be the received power of a predetermined number of beams in descending order, or the received power of beams that are equal to or greater than a predetermined threshold value. But you can.

  In FIG. 4B, the terminals 20-1, 20-3 and 20-4 selected as terminal candidates measure the received power using the beam scanning reference signals corresponding to the beams 30, Information including the received power of the beam 30 is fed back to the base station 10.

  As illustrated in FIG. 3, the base station 10 (for example, the beam selection unit 102) calculates a beam selection reference parameter based on the received power included in the received beam information. Then, base station 10 selects a beam to be used for data transmission from a plurality of beams 30 based on the calculated beam selection reference parameter (ST107). In FIG.4 (c), the base station 10 is based on the received power of each beam 30 fed back from the terminals 20-1, 20-3, and 20-4 selected as the terminal candidates, for example. , 20-3 and 20-4 are selected.

  As shown in FIG. 3, base station 10 transmits a channel estimation reference signal using the used beam selected in ST107 (ST108). For example, the channel estimation reference signal is multiplied by a beamforming weight corresponding to the used beam.

  The terminal 20 selected as the terminal candidate estimates a channel (an equivalent channel including a beamforming weight) to which the used beam is applied between the base station 10 and the terminal 20 using the received channel estimation reference signal. (ST109). Terminal 20 feeds back channel information including the estimated equivalent channel to base station 10 (ST110).

  Based on the channel information fed back from terminal 20, base station 10 (for example, terminal selection section 104) selects a target terminal that performs MIMO transmission with base station 10 from the terminal candidates selected in ST102 ( ST111). In FIG.4 (d), the base station 10 selects the terminal 20-1 and 20-3 to an object terminal among the terminals 20-1, 20-3, and 20-4 selected as the terminal candidate, for example. In other words, the base station 10 excludes the terminal 20-4 among the terminals 20-1, 20-3, and 20-4 from the candidates for assigning reception opportunities for signals transmitted from the base station 10.

  As shown in FIG. 3, base station 10 transmits to each terminal candidate a selected terminal notification signal indicating whether or not the target terminal is selected in ST111 (ST112). When each terminal candidate indicates that it is a target terminal in the received selection terminal notification signal, reception processing for receiving data transmitted by MIMO from the base station 10 (for example, setting of various parameters related to MIMO transmission, etc.) (Not shown).

  Base station 10 transmits data by MIMO transmission to the target terminal selected in ST111 using the used beam selected in ST107 (ST113).

<Selecting terminal candidates>
Next, a method for selecting terminal candidates using the fairness standard parameters (for example, the processing of ST101 and ST102 shown in FIG. 3) will be described.

The fairness criterion parameter ρ _u (u, t) is, for example, a moving average throughput calculated according to the equation (1).

In equation (1), u represents a terminal number and t represents a time slot number. R (u, t) indicates the throughput of the u-th terminal in the t-th time slot. T _s indicates the throughput averaging time. R ⁻ (u, t) represents the average throughput of the u th terminal in the t th time slot.

For example, when the reception opportunity of the signal transmitted by the base station 10 at the u-th terminal is small, the average throughput is low, and the fairness criterion parameter ρ _u (u, t) shown in Equation (1) is small.

Alternatively, the fairness criterion parameter ρ _u (u, t) is, for example, a PF (Proportional Fairness) metric calculated according to the equation (2).

In equation (2), u indicates a terminal number, and t indicates a time slot number. In addition, the molecular component R (u, t) on the right side of Equation (2) indicates the instantaneous throughput in the t-th time slot of the u-th terminal. Also, the denominator component R ⁻ (u, t) on the right side of Equation (2) indicates the average throughput in the past time slots from the t-th time slot of the u-th terminal.

The fairness criterion parameter ρ _u (u, t) shown in Equation (2) indicates the ratio of the instantaneous throughput to the past average throughput in the u-th terminal.

For example, from the viewpoint of system throughput, it is assumed that the terminal 20 whose instantaneous throughput R (u, t) is higher than the average throughput R ⁻ (u, t) has more reception opportunities. In other words, it is assumed that the terminal 20 whose instantaneous throughput R (u, t) is lower than the average throughput R ⁻ (u, t) has fewer reception opportunities. Therefore, for example, when the reception opportunity of the signal transmitted from the base station 10 at the u-th terminal is small, the fairness criterion parameter ρ _u (u, t) shown in Expression (2) is small.

  As described above, the fairness standard parameter shown in the equation (1) or the equation (2) is set according to, for example, the allocation situation of the reception opportunity of the signal transmitted by the base station 10. Note that the fairness standard parameter is not limited to a value (for example, a value representing a communication status) shown in the formula (1) or the formula (2). The fairness standard parameter may be set in accordance with, for example, the allocation situation of reception opportunities for signals transmitted from the base station 10. For example, the fairness standard parameter may be calculated on the basis of reception quality (for example, reception SINR (Signal to Interference and Noise Ratio)) or reception power indicating a channel condition in each terminal 20. For example, it is assumed that a terminal 20 with lower reception quality or reception power is less likely to be assigned a reception opportunity in communication with the base station 10. Therefore, the value of the fairness standard parameter of the terminal 20 with low reception quality or reception power is set smaller.

The base station 10 (for example, the terminal candidate selection unit 100) performs MIMO transmission with the base station 10 based on, for example, the fairness standard parameter ρ _u (u, t) shown in the equation (1) or the equation (2). Select terminal candidates.

For example, the base station 10 selects some of the plurality of terminals 20 as terminal candidates based on the comparison result between the fairness standard parameter and the threshold value. As an example, a terminal candidate selection criterion using the fairness criterion parameter ρ _u (u, t) is expressed by Equation (3).

In Equation (3), u represents a terminal number, U represents a set of selected terminal candidates (for example, terminal numbers), and ρ _{U, TH} corresponds to a fairness criterion parameter ρ _u (u, t). Indicates the threshold value.

When the selection criterion shown in Expression (3) is used, the base station 10 includes, in the terminal candidate U, the u-th terminal whose fairness criterion parameter ρ _u (u, t) is equal to or less than the threshold ρ _{U, TH} . Note that the base station 10 may select all the terminals 20 that satisfy Equation (3) as terminal candidates, and select a predetermined number of terminals 20 among the terminals 20 that satisfy Equation (3) as terminal candidates. Also good.

Alternatively, as another example, the base station 10 preferentially selects a terminal 20 having a low reception opportunity allocation among a plurality of terminals 20 as a terminal candidate based on the fairness criterion parameter. As an example, a terminal candidate selection criterion using the fairness criterion parameter ρ _u (u, t) is expressed by Equation (4).

  In Expression (4), u indicates a terminal number, U indicates a set of selected terminal candidates (for example, terminal numbers), and u ′ indicates a terminal number that is not included in the terminal candidate set U.

When the selection criterion shown in Expression (4) is used, the base station 10 includes the terminal 20 with the terminal number u having the smallest fairness reference parameter ρ _u (u, t) in the terminal candidate U. For example, the base station 10 selects terminal candidates based on the selection rule shown in Expression (4) until the number of terminals included in the terminal candidate U reaches a predetermined number.

  By using the selection criteria shown in Formula (3) or Formula (4), the base station 10 can easily select the terminal 20 with few reception opportunities as a terminal candidate. In other words, the terminal 20 with many reception opportunities is less likely to be selected as a terminal candidate.

  By this process, the base station 10 selects a target terminal for performing MIMO transmission from terminals having a small reception opportunity, so that the reception opportunity of the terminal can be increased. In other words, since the base station 10 excludes the terminals 20 with many reception opportunities from the target terminals that perform MIMO transmission, the reception opportunities of the terminals 20 can be reduced. Therefore, in the plurality of terminals 20 that can communicate with the base station 10, the frequency selected for the target terminal that performs MIMO transmission with the base station 10 can be made closer, and the fairness of reception opportunities between the terminals 20 can be improved. . In other words, it is possible to prevent the terminal 20 selected as a target terminal that performs MIMO transmission with the base station 10 from being biased toward a specific terminal 20.

Further, for example, in the selection criterion shown in Equation (3), the smaller the threshold ρ _{U, TH} value, the smaller the fairness standard parameter of the terminal 20 selected as the terminal candidate, and the terminal 20 with many reception opportunities. The possibility of being selected as a terminal candidate is reduced. On the other hand, in the selection criterion shown in Expression (3), as the value of the threshold ρ _{U, TH} is larger, the fairness standard parameter of the terminal 20 selected as the terminal candidate is larger, and the terminal 20 with relatively many reception opportunities is the terminal. The possibility of being selected as a candidate increases. Therefore, in the selection criterion shown in Expression (3), as the value of the threshold ρ _{U, TH} is smaller, the fairness of the reception opportunity among the plurality of terminals 20 can be further improved, whereas the value of the threshold ρ _{U, TH} is The larger the system throughput, the more the system throughput (the total throughput in the plurality of terminals 20) can be improved. In other words, the base station 10 can adjust the fairness and the system throughput in a trade-off relationship according to the setting of the threshold values ρ _{U and TH} . By this processing, fairness of reception opportunities of the plurality of terminals 20 is maintained, and high system throughput can be obtained.

Equation (3) shows a case where the value of the threshold ρ _{U, TH} is constant regardless of the terminal. However, the threshold values ρ _{U, TH} may not be the same between the terminals 20. For example, the threshold value ρ _{U, TH} may be set for each terminal 20 according to the desired throughput for each terminal 20. For example, the threshold value ρ _{U, TH of the} terminal 20 having a high desired throughput is set higher. For example, fairness reference parameter ρ _{u (u,} t) if there is the same terminal, as compared to the desired low throughput terminal 20, fairness criteria parameters desired high throughput terminal 20 [rho _u (u, t ) Is likely to be less than or equal to the threshold value ρ _{U, TH} . With this process, the base station 10 can select terminal candidates according to the desired throughput for each terminal 20.

  Further, before the terminal candidate selection process (for example, ST102) shown in FIG. 3, each terminal 20 determines the reception quality (for example, reception SINR or reception power) between the base station 10 and the terminal 20 to the base station. 10 may be fed back. In ST102, the base station 10 may select a candidate terminal using at least one of the received reception quality and fairness criterion parameter.

  In addition, in the formulas (1) and (2), as an example, the case has been described in which the fairness criterion parameter indicates a smaller value as the terminal 20 has a smaller allocation of signal reception opportunities. However, the fairness criterion parameter may indicate a larger value as the terminal 20 has less allocation of signal reception opportunities. When the fairness criterion parameter shows a larger value as the terminal 20 with less allocation of signal reception opportunities, the fairness criterion parameter is greater than or equal to the threshold value among the plurality of terminals 20 instead of the selection criterion shown in Equation (3). The terminal 20 may be selected as a terminal candidate. In addition, when the fairness criterion parameter shows a larger value for a terminal 20 with less allocation of signal reception opportunities, the fairness criterion parameter is more of the plurality of terminals 20 instead of the selection criterion shown in Equation (4). A large predetermined number of terminals 20 may be selected as terminal candidates.

<Selection method of beam used>
Next, a method of selecting a beam to be used using the beam selection reference parameter (for example, the process of ST107 shown in FIG. 3) will be described.

The beam selection reference parameter ρ _B (l) is, for example, the total received power at each terminal 20 calculated according to Equation (5).

In Equation (5), l represents a beam number, U represents a set of terminal candidates (for example, terminal numbers), and P _{r, u} (l) represents received power in the l-th beam of the u-th terminal. The received power P _{r, u} (l) of each terminal 20 is fed back from each terminal 20 to the base station 10 in ST106 of FIG. 3, for example. As shown in Expression (5), the beam selection criterion parameter ρ _B (l) is the total received power of a plurality of terminals 20 (for example, terminals 20 included in the set U) in the l-th beam.

  Alternatively, the beam selection reference parameter is, for example, the sum of received SIR (Signal to Interference Ratio) at each terminal 20 calculated according to the following equation (6).

For example, the base station 10 uses the received power P _{r, u} (l) fed back from each terminal 20 to calculate the beam selection reference parameter for the l-th beam.

  Note that the beam selection reference parameter is not limited to the values shown in Expression (5) or Expression (6).

The base station 10 (for example, the beam selection unit 102) selects a beam to be used for data transmission based on, for example, the beam selection reference parameter ρ _B (l) shown in Expression (5) or Expression (6).

As an example, the beam selection criterion using the beam selection criterion parameter ρ _B (l) is expressed by Equation (7).

  For example, when the beam selection criterion parameter shown in Equation (5) is used, the base station 10 selects the beam l having the maximum total received power at each terminal 20 as the used beam. Further, for example, when the beam selection criterion parameter shown in Expression (6) is used, the base station 10 selects the beam l having the maximum total received SIR at each terminal 20 as the used beam. For example, the base station 10 selects a predetermined number of used beams according to Equation (6) or Equation (7).

  Note that the terminal 20 may feed back past throughput information to the base station 10 in addition to the beam information (for example, received power), for example, in the process of ST106 shown in FIG. In this case, the base station 10 (for example, the beam selection unit 102) may use the beam information and the throughput information to calculate a beam selection reference parameter based on the Proportional Fairness norm and select a beam to be used. With this process, the base station 10 can select a beam to be used by comparing past throughputs among a plurality of terminals 20, thereby improving system throughput.

  Further, when using OFDM (Orthogonal Frequency Division Multiplexing) transmission, the base station 10 does not have to calculate the beam selection reference parameter in all subcarriers. For example, the base station 10 may calculate a beam selection reference parameter by paying attention to one or a plurality of subcarriers, and may select a use beam based on the calculated beam selection reference parameter.

Further, when selecting the beam to be used, the base station 10 may use the fairness criterion parameter used for selecting the terminal candidate in addition to the beam selection criterion parameter. For example, the base station 10 determines the u-th received beam power P _{r, u} (l) of the u-th terminal when calculating the beam selection reference parameter (for example, the equation (5) or the equation (6)). Weighting is performed using the fairness criterion parameter ρ _u (u, t) of the terminal. By this processing, the influence of the reception power of the terminal 20 having a smaller fairness criterion parameter (for example, the terminal 20 having a relatively small reception opportunity) on the beam selection criterion parameter is larger than that in the case of using the actual reception power. Become. For this reason, in the base station 10, it becomes easy to select a beam suitable for the terminal 20 having a smaller fairness criterion parameter among the terminal candidates.

<How to select a terminal>
Next, a terminal selection method using the terminal selection criterion parameter (for example, the processing of ST111 shown in FIG. 3) will be described.

  The terminal selection criterion parameter is calculated based on, for example, channel information fed back from each terminal candidate to base station 10 in ST110 shown in FIG.

  The channel information may be, for example, reception power, reception SIR or reception SINR measured using a channel estimation reference signal received by each terminal 20 or an inter-beam interference coefficient at each terminal 20.

  Further, the selection criterion of the terminal 20 using the terminal selection criterion parameter is, for example, the criterion for selecting the terminal 20 having the above-described reception power, reception SIR or reception SINR, or the terminal 20 having the small inter-beam interference coefficient described above. Is the norm to be selected. In addition, the selection criterion of the terminal 20 using the terminal selection criterion parameter may be, for example, the Max-C / I criterion, the Proportional Fairness criterion, or the Chordal Distance maximum criterion.

  Note that, for example, the terminal 20 may feed back past throughput information to the base station 10 in addition to the channel information in the process of ST110 shown in FIG. In this case, the base station 10 (for example, the terminal selection unit 104) may use the channel information and the throughput information to calculate the terminal selection criterion parameter based on the Proportional Fairness norm and select the target terminal. With this process, the base station 10 can select a beam to be used by comparing past throughputs among a plurality of terminals 20, thereby improving system throughput.

  Further, when using OFDM transmission, the base station 10 does not have to calculate the terminal selection criterion parameter in all subcarriers. For example, the base station 10 may calculate a terminal selection criterion parameter by paying attention to one or a plurality of subcarriers, and may select a target terminal based on the calculated terminal selection criterion parameter.

Further, when selecting the target terminal, the base station 10 may use the fairness standard parameter used for selecting the terminal candidate in addition to the terminal selection standard parameter. For example, when calculating the terminal selection criterion parameter, the base station 10 weights the value indicated in the channel information of each terminal 20 using the fairness criterion parameter ρ _u (u, t) of the terminal. As a result of this processing, the influence of the channel information of the terminal 20 having a smaller fairness criterion parameter (for example, the terminal 20 having a relatively small reception opportunity) on the terminal selection criterion parameter is larger than when actual channel information is used. Become. For this reason, in the base station 10, it becomes easy to select the terminal 20 with a smaller fairness standard parameter among terminal candidates.

  In FIG. 3, the cycle in which the terminal candidate selection process based on the fairness standard parameter in ST102 and the cycle in which the target terminal selection process based on the channel information in ST111 is performed may be the same or different. Good. For example, the terminal candidate selection period may be shorter than the target terminal selection period. By this processing, the base station 10 can improve the fairness of reception opportunities between the terminals 20 according to the communication status or communication environment of each terminal. Alternatively, the cycle of selecting terminal candidates in ST102 may be longer than the cycle of selecting target terminals in ST111. This processing can reduce the amount of computation of terminal candidate selection processing in the base station 10.

  Further, the base station 10 calculates, for example, the total terminal throughput that can be achieved when the terminal 20 is selected by changing the number of terminals, and determines the number and combination of terminals that can achieve the highest terminal total throughput. You may decide. The base station 10 can improve system throughput by performing MIMO transmission for the determined combination of terminals 20.

  Further, after selecting the target terminal in ST111 shown in FIG. 3, the base station 10 may perform the same processing as ST107 and reselect the beam to be used for the selected target terminal, for example. At the time of reselecting the beam to be used, base station 10 excludes beam information fed back from terminal 20 that is not selected as a target terminal in ST111 from terminal candidates selected in ST102 shown in FIG. With this process, the base station 10 can select a beam to be used that is suitable for the selected target terminal. In other words, by not considering the beam information of the terminal 20 that is not selected as the target terminal, the base station 10 can prevent useless use of the beam for the target terminal and reduce power consumption.

  The operation example of the base station 10 has been described above.

<Effect>
In the present embodiment, the base station 10 determines a part of the plurality of terminals 20 based on information indicating at least one of a communication state and a channel state between the plurality of antennas 116 and the plurality of terminals 20. A plurality of antennas 116 are used to select terminal candidates to be assigned reception opportunities for signals addressed to a plurality of terminals.

  For example, the base station 10 excludes the terminal 20 with a high reception opportunity from the target terminals that perform MIMO transmission, and selects the terminal 20 with a low reception opportunity. Therefore, the throughput of the terminal 20 with few reception opportunities can be improved. In other words, the base station 10 makes the reception opportunities assigned to the plurality of terminals 20 evenly between the terminals 20 (reducing the bias of reception opportunities), so that the fairness of the reception opportunities among the plurality of terminals 20 can be improved.

  Therefore, according to the present embodiment, base station 10 can efficiently select a communication target terminal 20 in consideration of a desired throughput for each of a plurality of terminals 20 in MU-MIMO.

  Further, according to the present embodiment, the base station 10 performs a process including a use beam selection process or a target terminal selection process on a terminal candidate selected from the plurality of terminals 20. In other words, the base station 10 does not perform a process including a use beam selection process or a target terminal selection process on the terminals 20 other than the terminal candidates among the plurality of terminals 20. Therefore, the base station 10 can reduce the amount of calculation compared to the case where the processing including the beam selection process or the target terminal selection process is performed on the plurality of terminals 20.

  Moreover, the base station 10 can select a terminal candidate based on a selection rule using the fairness standard parameter regardless of the selection rule applied in the selection process of the target terminal based on the channel information. For example, the base station 10 can use both terminal candidate selection processing based on the fairness criterion parameter and low-calculation target terminal selection processing such as Chordal Distance maximum norm.

  The embodiments have been described above.

  In the above embodiment, a case has been described where channel estimation is performed by transmitting a reference signal from a base station. However, in the channel estimation, the reference signal may be transmitted from the terminal 20 to perform the channel estimation, or the channel estimation value (channel information) may be acquired without using the reference signal. That is, in channel estimation, channel information indicating an equivalent channel matrix (HW) including a BF weight may be acquired.

(Hardware configuration)
In addition, the block diagram used for description of the said embodiment has shown the block of the functional unit. These functional blocks (components) are realized by any combination of hardware and / or software. Further, the means for realizing each functional block is not particularly limited. That is, each functional block may be realized by one device physically and / or logically coupled, and two or more devices physically and / or logically separated may be directly and / or indirectly. (For example, wired and / or wireless) and may be realized by these plural devices.

  For example, a base station, a terminal, or the like according to an embodiment of the present disclosure may function as a computer that performs processing of the wireless communication method of the present disclosure. FIG. 5 is a diagram illustrating an example of a hardware configuration of a base station and a terminal according to an embodiment of the present disclosure. The base station 10 and the terminal 20 described above may be physically configured as a computer device including a processor 1001, a memory 1002, a storage 1003, a communication device 1004, an input device 1005, an output device 1006, a bus 1007, and the like.

  In the following description, the term “apparatus” can be read as a circuit, a device, a unit, or the like. The hardware configuration of the base station 10 and the terminal 20 may be configured to include one or a plurality of devices illustrated in the figure, or may be configured not to include some devices.

  For example, although only one processor 1001 is shown, there may be a plurality of processors. Further, the processing may be executed by one processor, or the processing may be executed by one or more processors simultaneously, sequentially, or in another manner. Note that the processor 1001 may be implemented by one or more chips.

  Each function in the base station 10 and the terminal 20 is obtained by reading predetermined software (program) on hardware such as the processor 1001 and the memory 1002, so that the processor 1001 performs computation and communication by the communication device 1004 or memory This is realized by controlling data reading and / or writing in the storage 1003 and the storage 1003.

  For example, the processor 1001 controls the entire computer by operating an operating system. The processor 1001 may be configured by a central processing unit (CPU) including an interface with peripheral devices, a control device, an arithmetic device, a register, and the like. For example, the above-described terminal candidate selection unit 100, beam selection unit 102, terminal selection unit 104, digital precoder 106, digital fixed beamformer 114, and the like may be realized by the processor 1001.

  In addition, the processor 1001 reads a program (program code), software module, or data from the storage 1003 and / or the communication device 1004 to the memory 1002, and executes various processes according to these. As the program, a program that causes a computer to execute at least a part of the operations described in the above embodiments is used. For example, at least some of the functional blocks constituting the base station 10 and the terminal 20 may be realized by a control program stored in the memory 1002 and operated by the processor 1001, and other functional blocks may be similarly realized. Also good. Although the above-described various processes have been described as being executed by one processor 1001, they may be executed simultaneously or sequentially by two or more processors 1001. The processor 1001 may be implemented by one or more chips. Note that the program may be transmitted from a network via a telecommunication line.

  The memory 1002 is a computer-readable recording medium and includes, for example, at least one of ROM (Read Only Memory), EPROM (Erasable Programmable ROM), EEPROM (Electrically Erasable Programmable ROM), RAM (Random Access Memory), and the like. May be. The memory 1002 may be called a register, a cache, a main memory (main storage device), or the like. The memory 1002 can store a program (program code), a software module, and the like that can be executed to implement the communication control method according to an embodiment of the present disclosure.

  The storage 1003 is a computer-readable recording medium, such as an optical disc such as a CD-ROM (Compact Disc ROM), a hard disc drive, a flexible disc, a magneto-optical disc (eg, a compact disc, a digital versatile disc, a Blu-ray). (Registered trademark) disk, smart card, flash memory (for example, card, stick, key drive), floppy (registered trademark) disk, magnetic strip, and the like. The storage 1003 may be referred to as an auxiliary storage device. The storage medium described above may be, for example, a database, server, or other suitable medium including the memory 1002 and / or the storage 1003.

  The communication device 1004 is hardware (transmission / reception device) for performing communication between computers via a wired and / or wireless network, and is also referred to as a network device, a network controller, a network card, a communication module, or the like. For example, the D / A conversion unit 108, the frequency conversion unit 110, the analog fixed beamformer 112, the antenna 116, and the like described above may be realized by the communication device 1004.

  The input device 1005 is an input device (for example, a keyboard, a mouse, a microphone, a switch, a button, a sensor, or the like) that accepts an external input. The output device 1006 is an output device (for example, a display, a speaker, an LED lamp, etc.) that performs output to the outside. The input device 1005 and the output device 1006 may have an integrated configuration (for example, a touch panel).

  Each device such as the processor 1001 and the memory 1002 is connected by a bus 1007 for communicating information. The bus 1007 may be configured with a single bus or may be configured with different buses between apparatuses.

  The base station 10 and the terminal 20 include hardware such as a microprocessor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a programmable logic device (PLD), and a field programmable gate array (FPGA). And a part or all of each functional block may be realized by the hardware. For example, the processor 1001 may be implemented by at least one of these hardware.

(Information notification, signaling)
The notification of information is not limited to the aspect / embodiment described in the present specification, and may be performed by other methods. For example, information notification includes physical layer signaling (for example, DCI (Downlink Control Information), UCI (Uplink Control Information)), upper layer signaling (for example, RRC (Radio Resource Control) signaling, MAC (Medium Access Control) signaling), It may be implemented by broadcast information (MIB (Master Information Block), SIB (System Information Block))), other signals, or a combination thereof. The RRC signaling may be referred to as an RRC message, and may be, for example, an RRC connection setup message, an RRC connection reconfiguration message, or the like.

(Adaptive system)
Each aspect / embodiment described herein includes LTE (Long Term Evolution), LTE-A (LTE-Advanced), SUPER 3G, IMT-Advanced, 4G, 5G, FRA (Future Radio Access), W-CDMA. (Registered trademark), GSM (registered trademark), CDMA2000, UMB (Ultra Mobile Broadband), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, UWB (Ultra-WideBand), Bluetooth (Registered trademark), a system using another appropriate system, and / or a next generation system extended based on the system may be applied.

(Processing procedure etc.)
As long as there is no contradiction, the order of the processing procedures, sequences, flowcharts, and the like of each aspect / embodiment described in this specification may be changed. For example, the methods described herein present the elements of the various steps in an exemplary order and are not limited to the specific order presented.

(Operation of base station)
The specific operation assumed to be performed by the base station (radio base station) in this specification may be performed by the upper node in some cases. In a network composed of one or more network nodes having a base station, various operations performed for communication with a terminal may be performed by the base station and / or other network nodes other than the base station (e.g., It is obvious that this can be performed by MME (Mobility Management Entity) or S-GW (Serving Gateway), but not limited thereto. Although the case where there is one network node other than the base station in the above is illustrated, a combination of a plurality of other network nodes (for example, MME and S-GW) may be used.

(I / O direction)
Information, signals, and the like can be output from the upper layer (or lower layer) to the lower layer (or upper layer). Input / output may be performed via a plurality of network nodes.

(Handling of input / output information, etc.)
Input / output information and the like may be stored in a specific location (for example, a memory) or may be managed by a management table. Input / output information and the like can be overwritten, updated, or additionally written. The output information or the like may be deleted. The input information or the like may be transmitted to another device.

(Judgment method)
The determination may be performed by a value represented by 1 bit (0 or 1), may be performed by a true / false value (Boolean: true or false), or may be performed by comparing numerical values (for example, a predetermined value) Comparison with the value).

(software)
Software, whether it is called software, firmware, middleware, microcode, hardware description language, or other names, instructions, instruction sets, code, code segments, program codes, programs, subprograms, software modules , Applications, software applications, software packages, routines, subroutines, objects, executable files, execution threads, procedures, functions, etc. should be interpreted broadly.

  Also, software, instructions, etc. may be transmitted / received via a transmission medium. For example, software may use websites, servers, or other devices using wired technology such as coaxial cable, fiber optic cable, twisted pair and digital subscriber line (DSL) and / or wireless technology such as infrared, wireless and microwave. When transmitted from a remote source, these wired and / or wireless technologies are included within the definition of transmission media.

(Information, signal)
Information, signals, etc. described herein may be represented using any of a variety of different technologies. For example, data, commands, commands, information, signals, bits, symbols, chips, etc. that may be referred to throughout the above description are voltages, currents, electromagnetic waves, magnetic fields or magnetic particles, light fields or photons, or any of these May be represented by a combination of

  Note that the terms described in this specification and / or terms necessary for understanding this specification may be replaced with terms having the same or similar meaning. For example, the channel and / or symbol may be a signal. The signal may be a message. Further, the component carrier (CC) may be called a carrier frequency, a cell, or the like.

("System", "Network")
As used herein, the terms “system” and “network” are used interchangeably.

(Parameter, channel name)
In addition, information, parameters, and the like described in this specification may be represented by absolute values, may be represented by relative values from a predetermined value, or may be represented by other corresponding information. . For example, the radio resource may be indicated by an index.

  The names used for the parameters described above are not limiting in any way. Further, mathematical formulas and the like that use these parameters may differ from those explicitly disclosed herein. Since various channels (eg, PUCCH (Physical Uplink Control Channel), PDCCH (Physical Downlink Control Channel), etc.) and information elements (eg, TPC, etc.) can be identified by any suitable name, these various channels and information The various names assigned to the elements are not limiting in any way.

(base station)
A base station (radio base station) can accommodate one or more (eg, three) cells (also referred to as sectors). When the base station accommodates multiple cells, the entire coverage area of the base station can be partitioned into multiple smaller areas, each smaller area being a base station subsystem (eg, indoor small base station RRH: Remote Radio Head) can also provide communication services. The term “cell” or “sector” refers to part or all of the coverage area of a base station and / or base station subsystem that provides communication services in this coverage. Further, the terms “base station”, “eNB”, “gNB”, “cell”, and “sector” may be used interchangeably herein. A base station may also be referred to in terms such as a fixed station, NodeB, eNodeB (eNB), gNodeB (gNB), access point, femtocell, small cell, and the like.

(Terminal)
A user terminal is a mobile station, subscriber station, mobile unit, subscriber unit, wireless unit, remote unit, mobile device, wireless device, wireless communication device, remote device, mobile subscriber station, access terminal, mobile by a person skilled in the art It may also be referred to as a terminal, wireless terminal, remote terminal, handset, user agent, mobile client, client, UE (User Equipment), or some other appropriate terminology.

(Meaning and interpretation of terms)
As used herein, the terms “determining” and “determining” may encompass a wide variety of actions. “Judgment” and “determination” are, for example, judgment, calculation, calculation, processing, derivation, investigating, looking up (eg, table , Searching in a database or another data structure), considering ascertaining as “determining”, “deciding”, and the like. In addition, “determination” and “determination” include receiving (for example, receiving information), transmitting (for example, transmitting information), input (input), output (output), and access. (accessing) (e.g., accessing data in a memory) may be considered as "determined" or "determined". In addition, “determination” and “decision” means that “resolving”, “selecting”, “choosing”, “establishing”, and “comparing” are regarded as “determining” and “deciding”. May be included. In other words, “determination” and “determination” may include considering some operation as “determination” and “determination”.

  The terms “connected”, “coupled”, or any variation thereof, means any direct or indirect connection or coupling between two or more elements and It can include the presence of one or more intermediate elements between two “connected” or “coupled” elements. The coupling or connection between the elements may be physical, logical, or a combination thereof. As used herein, the two elements are radio frequency by using one or more wires, cables and / or printed electrical connections, and as some non-limiting and non-inclusive examples By using electromagnetic energy, such as electromagnetic energy having a wavelength in the region, microwave region, and light (both visible and invisible) region, it can be considered to be “connected” or “coupled” to each other.

  The reference signal may be abbreviated as RS (Reference Signal), and may be referred to as a pilot depending on an applied standard. Further, the correction RS may be called TRS (Tracking RS), PC-RS (Phase Compensation RS), PTRS (Phase Tracking RS), or Additional RS. Further, the demodulation RS and the correction RS may be called differently corresponding to each. Further, the demodulation RS and the correction RS may be defined by the same name (for example, the demodulation RS).

  As used herein, the phrase “based on” does not mean “based only on,” unless expressly specified otherwise. In other words, the phrase “based on” means both “based only on” and “based at least on.”

  The “unit” in the configuration of each apparatus described above may be replaced with “means”, “circuit”, “device”, and the like.

  As long as “including”, “comprising”, and variations thereof are used in the specification or claims, these terms are inclusive of the term “comprising”. Intended to be Furthermore, the term “or” as used herein or in the claims is not intended to be an exclusive OR.

  A radio frame may be composed of one or more frames in the time domain. One or more frames in the time domain may be referred to as subframes, time units, etc. A subframe may further be composed of one or more slots in the time domain. The slot may be further configured with one or a plurality of symbols (OFDM (Orthogonal Frequency Division Multiplexing) symbols, SC-FDMA (Single Carrier-Frequency Division Multiple Access) symbols, etc.) in the time domain.

  A radio frame, a subframe, a slot, a minislot, and a symbol all represent time units for transmitting a signal. Radio frames, subframes, slots, minislots, and symbols may be called differently corresponding to each.

  For example, in the LTE system, the base station performs scheduling for assigning radio resources (frequency bandwidth, transmission power, etc. that can be used in each mobile station) to each mobile station. The minimum scheduling time unit may be referred to as TTI (Transmission Time Interval), and one minislot may be referred to as TTI.

  For example, one subframe may be called a TTI, a plurality of consecutive subframes may be called a TTI, and one slot may be called a TTI.

  A resource unit is a resource allocation unit in the time domain and the frequency domain, and may include one or a plurality of continuous subcarriers in the frequency domain. In the time domain of the resource unit, it may include one or a plurality of symbols, and may have a length of 1 slot, 1 mini slot, 1 subframe, or 1 TTI. One TTI and one subframe may each be composed of one or a plurality of resource units. Moreover, a resource unit may be called a resource block (RB: Resource Block), a physical resource block (PRB: Physical RB), a PRB pair, an RB pair, a scheduling unit, a frequency unit, and a subband. Further, the resource unit may be composed of one or a plurality of REs. For example, 1 RE may be any resource (for example, the smallest resource unit) smaller than a resource unit serving as a resource allocation unit, and is not limited to the name RE.

  The structure of the radio frame described above is merely an example, and the number of subframes included in the radio frame, the number of slots included in the subframe, the number of minislots included in the subframe, the symbols and resource blocks included in the slots, The number and the number of subcarriers included in the resource block can be variously changed.

  Throughout this disclosure, if articles are added by translation, for example, a, an, and the in English, these articles must be clearly indicated otherwise in context, Including multiple things.

(Aspect variations, etc.)
Each aspect / embodiment described in this specification may be used independently, may be used in combination, or may be switched according to execution. In addition, notification of predetermined information (for example, notification of being “X”) is not limited to explicitly performed, but is performed implicitly (for example, notification of the predetermined information is not performed). Also good.

  Although the present disclosure has been described in detail above, it will be apparent to those skilled in the art that the present disclosure is not limited to the embodiments described herein. The present disclosure can be implemented as modifications and changes without departing from the spirit and scope of the present disclosure as defined by the claims. Therefore, the description of the present specification is for illustrative purposes and does not have any limiting meaning to the present disclosure.

  One aspect of the present disclosure is useful for a mobile communication system.

10A, 10B Base station 20-1 to 20-5 Terminal 30 Beam 100 Terminal candidate selection unit 102 Beam selection unit 104 Terminal selection unit 106 Digital precoder 108 D / A conversion unit 110 Frequency conversion unit 112 Analog fixed beamformer 114 Digital fixed Beamformer 116 Antenna

Claims (6)

A transmission circuit that wirelessly transmits signals addressed to a plurality of terminals using a plurality of antennas and performs space division multiplexing; and
Based on information indicating at least one of a communication status and a propagation path status between the plurality of antennas and the plurality of terminals, a part of the plurality of terminals is set as a terminal candidate to which a reception opportunity of the signal is allocated. A control circuit to select;
A base station comprising: The control circuit includes:
Based on the information, calculate a parameter indicating a selection criterion of a terminal to which the reception opportunity is assigned,
Based on the parameter, a part of the plurality of terminals is selected as the terminal candidate.
The base station according to claim 1. The parameter is set according to the allocation situation of the reception opportunity,
Based on the comparison result between the parameter and the threshold, a part of the plurality of terminals is selected as the terminal candidate.
The base station according to claim 2. The threshold is set for each terminal according to a desired throughput for each of the plurality of terminals.
The base station according to claim 3. The parameter is set according to the allocation situation of the reception opportunity,
Based on the parameter, among the plurality of terminals, a terminal with a low allocation of the reception opportunity is preferentially selected as the terminal candidate.
The base station according to claim 2. A base station that wirelessly transmits signals addressed to a plurality of terminals using a plurality of antennas and performs space division multiplexing,
Based on information indicating at least one of a communication status and a propagation path status between the plurality of antennas and the plurality of terminals, a part of the plurality of terminals is set as a terminal candidate to which a reception opportunity of the signal is allocated. select,
A communication control method by a base station.

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