JP7051990B1 - Mobile communication system and inter-base station cooperation control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To greatly improve the cell boundary throughput without deteriorating the total throughput of all terminals located in a plurality of cells formed by a plurality of base stations performing codebook type beamforming control, and to improve the throughput. Reduce the amount of calculation. SOLUTION: An inter-base station cooperation control device acquires, from a base station, a plurality of reception quality feedback information measured by a plurality of terminals and fed back to the base station for each of the plurality of base stations, and the plurality of base stations. For each of the multiple combinations of and multiple beams, calculate multiple throughputs for multiple terminals based on multiple receive quality feedback information and one of multiple combinations based on the results of multiple throughput calculations. One combination is selected, information about the selected combination is transmitted to each of the plurality of base stations, and the number of candidate beams that can be selected based on the result of the immediately preceding selection process in the second and subsequent selection processes is limited. .. [Selection diagram] Fig. 2

Description

Application of Article 30, Paragraph 2 of the Patent Act (1) Proceedings of the 2020 Society Conference of the Institute of Electronics, Information and Communication Engineers, B-1-5 (published on DVD and WEB), B-1-5 (General Incorporated Association) Published at the Institute of Electronics, Information and Communication Engineers) (2) Announced at the EiC Institute of Electronics, Information and Communication Engineers 2020 Society Conference, WEB held (Zoom) on September 17, 2nd year.

The present invention relates to beamforming control linked between base stations.

Conventionally, multiple (8) users (8 units) located in the cell boundary area have realized coordinated beamforming between two adjacent base stations having multi-element (128 elements in total) antennas by digital signal processing. A mobile communication system that controls beamforming in cooperation with each other so as to reduce interference in a terminal) is known (see, for example, Non-Patent Document 1).

Nippon Electric Co., Ltd., NTT DoCoMo, Inc., "(Notice) Realization of 5G wireless communication to multiple mobile stations by reducing interference using coordinated beamforming between base stations-Reduction of interference using beam control by digital signal processing-" , [Online], Press release material, May 23, 2018, [Search on August 21, 2020], Internet <https://www.nttdocomo.co.jp/info/news_release/2018/05/23_00. html>

In the above-mentioned conventional beamforming cooperation control, since a multi-element antenna having a high gain in the beam formed by each base station is used, there is a possibility that interference may occur between base stations that are not adjacent to each other. Considering such interference between non-adjacent base stations, the problem is to greatly improve the cell boundary throughput without degrading the total throughput of all terminals located in multiple cells in a wide target area. There is.

The mobile communication system according to one aspect of the present invention is arranged so as to form a plurality of cells in a target area, and a plurality of beams are defined in advance for each of the plurality of mobile terminals in the cell. It is a mobile communication system including a plurality of base stations having a multi-element antenna for performing a codebook type beamforming control to be used, and an inter-base station cooperation control device for controlling the plurality of base stations. The inter-base station cooperation control device of this mobile communication system has a plurality of reception qualities measured by a plurality of terminals corresponding to a plurality of beams in the cell and fed back to the base station for each of the plurality of base stations. For each of the information acquisition means for acquiring the feedback information from the base station and the plurality of combinations consisting of the combination of the plurality of base stations and the plurality of beams, the plurality of reception qualities fed back from the plurality of terminals. Based on the throughput calculation means for calculating the plurality of throughputs for the plurality of terminals based on the feedback information of the above, and the calculation result of the plurality of throughputs for the plurality of terminals calculated for each of the plurality of combinations. A selection means for selecting any one combination of the above combinations, an information transmission means for transmitting information regarding the selected combination to each of the plurality of base stations, and the beam combination based on the calculation result of the throughput. When the selection process to be selected is repeatedly executed at a predetermined time interval Δt, the second and subsequent beams after the selection process of the first beam combination that does not limit the number of candidate beams that can be selected for each of the plurality of base stations. In the combination selection process, a candidate beam control means for limiting the number of selectable candidate beams based on the result of the selection process of the immediately preceding beam combination is provided. Each of the plurality of base stations controls a plurality of beams of its own station based on the information regarding the selected combination. In the inter-base station cooperation control device, for each of the plurality of base stations, the combination of the plurality of terminals for which the feedback information is acquired in the second and subsequent beam combination selection processes is the beam combination selection process immediately before. If it is different from the combination of the plurality of terminals for which the feedback information has been acquired, the beam combination selection process is performed without limiting the number of selectable candidate beams.

In the mobile communication system, the inter-base station cooperation control device may increase the number of selectable candidate beams after a certain period of time has elapsed in the second and subsequent beam combination selection processes.

In the mobile communication system, in the inter-base station cooperation control device, for each of the plurality of base stations, the throughput in the beam combination selection process for the second and subsequent times is relative to the throughput in the beam combination selection process immediately before. When it drops below a predetermined threshold, the number of selectable candidate beams may be increased.

In the mobile communication system, the inter-base station cooperation control device can be selected according to the magnitude of the difference in the throughput in the second and subsequent beam combination selection processes with respect to the throughput in the immediately preceding beam combination selection process. The number of candidate beams may be changed.

In the mobile communication system, the inter-base station cooperation control device has a movement direction of the terminal with respect to the base station, a distance between the base station and the terminal, and a cell of the base station for each of the plurality of base stations. The number of selectable candidate beams may be changed based on at least one of the environmental information including the density of terminals located in the area.

In the mobile communication system, the inter-base station cooperation control device selects a combination from the plurality of combinations that maximizes the minimum throughput in the plurality of throughputs for the plurality of terminals calculated for each of the plurality of combinations. You may choose.

In the mobile communication system, the inter-base station cooperation control device is a combination in which the minimum throughput in the plurality of throughputs for the plurality of terminals calculated for each of the plurality of combinations is maximized from the plurality of combinations. , The minimum throughput is tentatively selected from one or a plurality of combinations having a lower allowable lower limit throughput which is lower than the maximum value by a predetermined value, and the plurality of throughputs to the plurality of terminals are tentatively selected from the plurality of tentatively selected combinations. You may select the combination that maximizes the total of.

In the mobile communication system, the inter-base station cooperation control device has the minimum throughput in the plurality of throughputs and the plurality of throughputs for the plurality of terminals calculated for each of the plurality of combinations from the plurality of combinations. You may select the combination that maximizes the product with the total.

The inter-base station cooperation control device according to another aspect of the present invention is arranged so as to form a plurality of cells in the target area, and a plurality of beams are previously applied to each of the plurality of movable terminals in the cells. It is an inter-base station cooperation control device that controls a plurality of base stations having a multi-element antenna that performs codebook type beamforming control to be defined and used. The inter-base station cooperation control device receives feedback information of a plurality of reception qualities measured by a plurality of terminals corresponding to a plurality of beams in the cell and fed back to the base station for each of the plurality of base stations. Based on the feedback information of the plurality of reception qualities fed back from the plurality of terminals for each of the information acquisition means acquired from the base station and the plurality of combinations including the combination of the plurality of base stations and the plurality of beams. Then, one of the plurality of combinations based on the throughput calculation means for calculating the plurality of throughputs for the plurality of terminals and the calculation result of the plurality of throughputs for the plurality of terminals calculated for each of the plurality of combinations. A selection means for selecting one combination, an information transmission means for transmitting information about the selected combination to each of the plurality of base stations, and a selection process for selecting the beam combination based on the calculation result of the throughput. When the execution is repeated at a predetermined time interval Δt, in the second and subsequent beam combination selection processes after the first beam combination selection process that does not limit the number of selectable candidate beams for each of the plurality of base stations. A candidate beam control means that limits the number of candidate beams that can be selected based on the result of the selection process of the immediately preceding beam combination. In the inter-base station cooperation control device, for each of the plurality of base stations, the combination of the plurality of terminals that have acquired the feedback information in the second and subsequent beam combination selection processes is the beam combination selection process immediately before. If it is different from the combination of the plurality of terminals for which the feedback information has been acquired, the beam combination selection process is performed without limiting the number of selectable candidate beams.

According to the present invention, in a mobile communication system including a plurality of base stations arranged so as to form a plurality of cells in a target area and performing codebook type beamforming control for a terminal using a multi-element antenna, a plurality of cells are used. The total throughput of all terminals in the cell can be greatly improved without deteriorating the cell boundary throughput, and the amount of calculation for improving the throughput can be reduced.

Explanatory drawing which shows an example of the whole structure of the mobile communication system which concerns on one Embodiment of this invention. The flowchart which shows an example of the inter-base station cooperation BF control which concerns on this embodiment. The flowchart which shows an example of the beam combination selection process. A flowchart showing another example of the beam combination selection process. The flowchart which shows the further example of the beam combination selection process. Explanatory drawing which shows an example of the relationship between a beam of a base station and a moving terminal. (A) and (b) are explanatory views showing an example of candidate beam control and its effect in the inter-base station cooperation control device which concerns on this embodiment. The flowchart which shows an example of the candidate beam control in the inter-base station cooperation control apparatus which concerns on this embodiment. The flowchart which shows the other example of the candidate beam control in the inter-base station cooperation control apparatus which concerns on this embodiment. The flowchart which shows the further example of the candidate beam control in the inter-base station cooperation control apparatus which concerns on this embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The system according to the embodiment described in this document can reduce the amount of beam selection calculation in the multi-base station cooperation beamforming control technology of a plurality of base stations having a multi-element antenna for performing codebook type beamforming control. It is a mobile communication system that can be used.

FIG. 1 is an explanatory diagram showing an example of a cell configuration in a mobile communication system according to an embodiment of the present invention. In FIG. 1, the mobile communication system of the present embodiment includes a plurality of base stations 20 arranged so as to form a plurality of cells 20A in a target area. Although FIG. 1 shows the case where the number of base stations is 5, the number of base stations may be 2 to 4 or 6 or more.

Each base station 20 has a multi-element antenna 201 in order to improve the throughput which is the communication quality in the cell 20A of its own station, and is relatively relative to each of the plurality of mobile terminals 10 in the cell 20A. Beamforming control can be performed to control so as to direct a plurality of beams 20B having a narrow beam width. Although FIG. 1 shows the case where the number of beams of each base station 20 is 4, the number of beams may be 2 to 3 or 5 or more. Further, the beam 20B shown by the solid line in FIG. 1 is a beam that is actually selected and used for communication with the terminal 10 among a plurality of beam candidates that can be selected and formed by the base station 20. The beam 20B shown by the broken line is a beam that is not used for communication with the terminal 10.

The beamforming control in the present embodiment is a codebook type beamforming control that controls a plurality of beams based on a codebook. The codebook contains information on a plurality of sets of precoding weight matrix candidates for a plurality of sets of beam candidates in which the directivity of each of the plurality of base stations 20 is determined. The precoding weight matrix is a matrix showing the control amount of the phase and amplitude set in the multi-element antenna 201 at the time of transmission or reception of the radio signal.

The base station 20 forms a macrocell. It may be a macrocell base station, or it may be a base station that forms a cell of another size such as a small cell base station. Further, the base station 20 may be a wireless communication device called an eNodeB (evolved Node B: eNB), gNodeB (gNB), en-NodeB (en-gNB), access point, or the like.

The wireless network configuration including the base station 20 of the present embodiment is not limited to a specific configuration. For example, the radio network configuration exemplified in FIG. 1 is a D-RAN (distributed radio access network) configuration, and each base station 20 in the figure includes a multi-element antenna 201, a radio transmission / reception device, and a baseband signal processing device. To prepare for. The baseband signal processing device has, for example, a configuration for performing downlink Massive MIMO transmission to and from a plurality of terminals 10 by a plurality of beams formed by a codebook type beamforming control. For example, the baseband signal processing device includes a series-parallel conversion unit, a precoding unit that performs precoding processing based on the codebook information, a codebook storage unit that stores the codebook information, and a control unit that controls each unit. And so on.

The wireless network configuration may be a C-RAN (centralized wireless access network) configuration. In this case, a plurality of RRHs (remote radio headers) (also referred to as "overhanging base stations" and "optical overhanging devices") having a multi-element antenna and a wireless transmission / reception device are arranged at the positions of the plurality of base stations 20 in the figure. Will be done. A plurality of RRHs are common BBUs that perform baseband signal processing of each base station 20 via a communication line such as a wired communication line such as an optical fiber or an interface between base stations (for example, x2 interface in LTE) or a wireless communication line. It is connected to (baseband unit).

The terminal 10 is a mobile phone, a smartphone, a mobile personal computer having a mobile communication function, or the like, and is also called a user device (UE), a mobile station, a mobile device, or a portable communication terminal. The terminal 10 may be a modular mobile station incorporated in a mobile body such as an automobile or a drone, or may be a terminal device of a device for IoT (Internet of Things).

The terminal 10 is configured by using hardware such as a computer device having a CPU and a memory, a wireless communication unit, and the like, and can perform wireless communication with the base station 20 by executing a predetermined program. can.

When the terminal 10 is located in the cell 20A, the terminal 10 communicates with the mobile communication network side via the base station 20 corresponding to the cell 20A. Further, when the terminal 10 moves to the cell boundary area where the plurality of cells 20A overlap, the terminal 10 communicates with the mobile communication network side via any of the base stations 20 of the plurality of cells 20A.

The terminal 10 is, for example, an antenna for performing downlink MIMO transmission with the base station 20 of the cell 20A in the area, a wireless transmission / reception device, a distributor, a data decoding unit, a parallel series conversion unit, and a propagation path estimation unit. , A feedback information generation unit, a control unit, and the like. The feedback information is, for example, information such as the received power (RSRP) of the radio signal received from the base station 20 by the terminal 10. The feedback information is transmitted from the terminal 10 to the base station 20 of the cell 20A to which the terminal 10 is connected as a measurement report (MR) measured by the terminal 10.

The same wireless transmission method and the same frequency band (for example, a frequency of 6 GHz or less) are used for wireless communication between each base station 20 and the terminal 10. Examples of the wireless transmission method include LTE (Long Term Evolution) and LTE-Advanced communication methods, 4th generation mobile communication system (4G) communication method, 5th generation mobile communication system (5G) communication method, and the like. Subsequent next-generation mobile communication system communication methods can be adopted.

Further, each base station 20 is configured by using hardware such as a computer device having a CPU and a memory, an external communication interface unit for a core network, a wireless communication unit, and the like, and various types are executed by executing a predetermined program. Can communicate. For example, each base station 20 performs wireless communication with the terminal 10 and communication with the core network side. Further, each base station 20 communicates with the inter-base station cooperation beamforming control device (hereinafter referred to as “base station cooperation control device”) 30 described later via a wired or wireless control communication network. Further, each base station 20 communicates with other base stations other than its own station via a wired or wireless inter-base station communication network.

In the mobile communication system having the above configuration, since the multi-element antenna 201 having a high gain in the beam 20B formed by each base station 20 is used, there is a possibility that interference may occur between base stations that are not adjacent to each other. Considering such interference between non-adjacent base stations (interference from distant cells), the total throughput of all terminals located in a plurality of cells 20A in a wide target area does not deteriorate and the cell boundary is reached. A technology that can greatly improve the throughput is desired.

Therefore, in the present embodiment, in order to solve the above-mentioned problems, the inter-base station cooperation control device 30 is used for inter-base station cooperation beamforming control in which a plurality of base stations 20 forming a plurality of cells 20A in the target area are cooperated with each other. (Hereinafter, it is also referred to as "base station cooperation BF control").

In the case of the D-RAN (Distributed Radio Access Network) configuration of FIG. 1, the base station inter-base station cooperation control device 30 is connected to each base station 20 via the communication line 40 of the inter-base station network. Further, in the case of a C-RAN (centralized radio access network) configuration, the inter-base station cooperation control device 30 is connected to a BBU common to each base station 20 via, for example, a communication line.

The inter-base station cooperation control device 30 is composed of, for example, a single computer device or a plurality of computer devices, and functions as the following means A to E by executing a predetermined program.
A. For each of the plurality of base stations 20, feedback information of the received power (for example, RSRP) as a plurality of reception qualities measured by the plurality of terminals 10 corresponding to the plurality of beams 20B in the cell 20A and fed back to the base station 20. Information acquisition means for acquiring from the base station 20.
B. For each of the plurality of beam combinations including the combination of the plurality of base stations 20 and the plurality of beams 20B, the feedback information of the received power (for example, RSRP) fed back from the plurality of terminals 10 is used for the plurality of terminals 10. A throughput calculation method that calculates multiple throughputs.
C. A selection means for selecting any one of the plurality of beam combinations based on the calculation result of the plurality of throughputs for the plurality of terminals 10 calculated for each of the plurality of beam combinations.
D. An information transmission means for transmitting information regarding the selected beam combination to each of the plurality of base stations 20.
E. When the selection process of selecting a beam combination based on the calculation result of the throughput is repeatedly executed at a predetermined time interval Δt, the number of candidate beams that can be selected is not limited for each of the plurality of base stations. A candidate beam control means for limiting the number of candidate beams that can be selected based on the result of the selection process of the immediately preceding beam combination in the second and subsequent beam combination selection processes after the selection process.

The information regarding the selected beam combination to be transmitted to each of the plurality of base stations 20 is, for example, the selected beam among the candidates of the plurality of sets of precoding weight matrices included in the codebook stored in the base station 20. Information that specifies a precoding weight matrix for forming a plurality of sets of beams for the base station 20 corresponding to the combination.

FIG. 2 is a flowchart showing an example of inter-base station cooperation BF control according to the present embodiment. In FIG. 2, first, a plurality of base station-to-base station cooperation control devices 30 are measured by a plurality of terminals 10 corresponding to a plurality of beams 20B in the cell 20A and fed back to the base station 20 for each of the plurality of base stations 20. The feedback information of the received power (RSRP) of the above is acquired (S101).

Next, the inter-base station cooperation control device 30 receives feedback (RSRP) from a plurality of terminals 10 for each beam combination for a plurality of beam combinations composed of a combination of the plurality of base stations 20 and the plurality of beams 20B. ), A plurality of received SINRs (signal-to-noise ratio and interference power ratio) for the plurality of terminals 10 are calculated (S102).

Next, the inter-base station cooperation control device 30 calculates a plurality of throughputs (for example, Shannon capacity) for the plurality of terminals 10 based on the calculation results of the plurality of SINRs for the plurality of terminals 10 (S103).

Next, the inter-base station cooperation control device 30 selects any one of the plurality of beam combinations based on the calculation results of the plurality of throughputs (for example, Shannon capacity) for the plurality of terminals 10 (S104). ..

Next, the inter-base station cooperation control device 30 transmits information regarding the selected beam combination (for example, information specifying a precoding weight matrix in a codebook) to each of the plurality of base stations 20 (S105).

First, a beam combination selection process when the cooperation target forms two base stations and each base station forms three beams will be described.

FIG. 3 is a flowchart showing an example of the beam combination selection process (S104 in FIG. 2). FIG. 3 is an example of a beam control algorithm (minimum throughput maximization method) that maximizes the minimum throughput of each terminal 10.

In the example of FIG. 3, two base stations 20 arranged in the target area and adjacent to each other form three beams 20B, respectively, and the terminal 10 is located in the cell 20A of each base station 20. This is an example of the case. The same applies to the examples of FIGS. 4 and 5 described later.

Table 1 shows a numerical example in which the throughput is calculated for the terminal 10 in the beam control algorithm of FIG. 3 and a beam combination selection example. In Table 1 and Tables 2 and 3 described later, a plurality of base stations 20 are referred to as base station # 1 and base station # 2, and beams 20B formed by each base station 20 in three different directions are beam #. Notated as 1, beam # 2, and beam # 3. Further, the terminal 10 located in the cell 20A of each base station 20 is referred to as a terminal # 1 and a terminal # 2.

In FIG. 3, the inter-base station cooperation control device 30 calculates the minimum throughput (right end column in Table 1) for each beam combination for all ³³ = 9 beam combinations 1 to 9 for a plurality of base stations 20. (S201).

Next, the inter-base station cooperation control device 30 selects the beam combination having the maximum minimum throughput from all the beam combinations 1 to 9 (S202). In the example of Table 1, the beam combination 6 having the maximum minimum throughput (14) is selected as surrounded by a thick frame line. That is, the beam # 2 is selected for the base station # 1, and the beam # 3 is selected for the base station # 2.

FIG. 4 is a flowchart showing another example of the beam combination selection process (S104 in FIG. 2). FIG. 4 is an example of a beam control algorithm (modified minimum throughput maximization method) that allows a slight decrease in throughput in the above-mentioned minimum throughput maximization method and also maximizes the total throughput of the entire mobile communication system. ..

Table 2 shows a numerical example and a beam combination selection example for which the throughput was calculated for the terminal 10 in the beam control algorithm of FIG.

In FIG. 4, the inter-base station cooperation control device 30 has a minimum throughput (second from the right in Table 2) for each beam combination for all ³³ = 9 beam combinations 1 to 9 for a plurality of base stations 20. Column) and the total throughput (rightmost column in Table 2), which is the sum of the plurality of throughputs for the plurality of terminals 10 (S301).

Next, as shown by the thick frame in Table 2, the inter-base station cooperation control device 30 has the beam combination 6 having the maximum lowest throughput and the maximum throughput among all beam combinations 1 to 9. Temporarily select beam combinations 2 and 9 having a lower permissible lower limit throughput (13 in the example of Table 2) that is lower by a predetermined value ε (1 in the example shown in the figure) from a value (14 in the example of Table 2) (S302). ).

Next, the inter-base station cooperation control device 30 selects the beam combination that maximizes the total throughput (right end column of Table 2) from the plurality of tentatively selected beam combinations 2, 6 and 9 (S303). In the example of Table 2, the beam combination 2 having the maximum total throughput (31) is selected. That is, the beam # 1 is selected for the base station # 1, and the beam # 2 is selected for the base station # 2.

FIG. 5 is a flowchart showing still another example of the beam combination selection process (S104 in FIG. 2). FIG. 5 shows a beam control algorithm (evaluation value (minimum throughput and total) that can obtain the same effect as the modified minimum throughput maximization method of FIG. 4 by maximizing the evaluation value obtained by multiplying the minimum throughput and the total throughput. This is an example of (product of throughput) maximization method).

Table 3 shows a numerical example and a beam combination selection example for which the throughput was calculated for the terminal 10 in the beam control algorithm of FIG.

In FIG. 5, the inter-base station cooperation control device 30 has a minimum throughput (third from the right in Table ³ ) for each beam combination for all 33 = 9 beam combinations 1 to 9 for a plurality of base stations 20. Column) and the total throughput (second column from the right in Table 3), which is the sum of the plurality of throughputs for the plurality of terminals 10 (S401).

Next, the inter-base station cooperation control device 30 calculates an evaluation value (the rightmost column in Table 3) obtained by multiplying the minimum throughput and the total throughput for each beam combination for all beam combinations 1 to 9 (S402). ..

Next, the inter-base station cooperation control device 30 selects the beam combination having the maximum evaluation value (rightmost column in Table 3) from all the beam combinations 1 to 9 (S403). In the example of Table 3, the beam combination 9 having the maximum evaluation value (411.75) is selected. That is, the beam # 3 is selected for the base station # 1, and the beam # 3 is selected for the base station # 2.

According to the example of the beam combination selection process of FIGS. 3 to 5, when two base stations 20 to be linked with each other adjacent to each other are arranged in the target area, they are located in the cells 20A of the plurality of base stations 20. The total throughput of the plurality of terminals 10 can be greatly improved without degrading the cell boundary throughput.

Next, the beam combination selection process when the cooperation target is 5 base stations and each base station forms 5 beams will be described. When the number of base stations is 5 and the number of beams of each base station is ⁵ , the total number of beam combinations N is 3125 (= 55). Hereinafter, the five base stations are referred to as base stations # 1 to # 5, the five beams formed by each base station are referred to as beams # 1 to # 5, and are located in each cell of the base stations # 1 to # 5. Terminals are referred to as terminals # 1 to # 5.

As shown in S101 to S103 of FIG. 2 described above, as a pre-processing of the beam combination selection process, the inter-base station cooperation control device 30 acquires feedback information of received power (RSRP) and SINR (signal-to-noise ratio and interference). The power ratio) and the throughput (Shannon capacity) are calculated.

First, the inter-base station cooperation control device 30 measures each of the base stations # 1 to # 5 by the terminals # 1 to # 5 corresponding to the beams # 1 to # 5 and feeds them back to the base stations # 1 to # 5. Acquire feedback information of multiple received powers (RSRP).

Table 4 shows the received power (RSRP) [dBm) measured by the terminals # 1 to # 5 and reported to the base stations # 1 to # 5 for each beam # 1 to # 5 of the base stations # 1 to # 5. ] Is a numerical example that summarizes the feedback information.

Next, the inter-base station cooperation control device 30 relates to all beam combinations # 1 to # N (N = 3125) including a combination of a plurality of base stations # 1 to # 5 and a plurality of beams # 1 to # 5. Based on the feedback information of the received power (RSRP) fed back from the terminals # 1 to # 5, the SINR (signal-to-noise and interference power ratio) for the terminals # 1 to # 5 is calculated. Table 5 is a numerical example that summarizes the calculation results for calculating the SINR (signal-to-noise and interference power ratio) of each terminal # 1 to # 5 for all beam combinations # 1 to # N (N = 3125). be.

Next, the inter-base station cooperation control device 30 calculates a plurality of throughputs (Shannon capacity) for a plurality of terminals 10 based on the calculation results of a plurality of SINRs for the plurality of terminals 10. Table 6 is a numerical example in which the throughput (Shannon capacity) [bps] of each terminal # 1 to # 5 is calculated for each beam combination for all beam combinations # 1 to # N (N = 3125).

Next, as shown in S104 of FIG. 2 described above, the base station-to-base station cooperation control device 30 has all beam combinations # 1 to # 1 based on the calculation results of a plurality of throughputs (Shannon capacity) for terminals # 1 to # 5. Select any one beam combination from # N (N = 3125). As the beam combination selection process, the beam control algorithms shown in FIGS. 3 to 5 described above can be used.

Table 7 shows a numerical example when the beam combination is selected by the beam control algorithm (minimum throughput maximization method) of FIG. 3 described above. In this example, the inter-base station cooperation control device 30 calculates the minimum throughput (right end column in Table 7) for each beam combination for all beam combinations # 1 to # N (N = 3125) (S201 in FIG. 3). ), Select the beam combination # k having the maximum minimum throughput (2.4 bps) as surrounded by the thick frame line from all the beam combinations # 1 to # N (S202 in FIG. 3).

Table 8 shows a numerical example in the case of selecting a beam combination by the beam control algorithm (modified minimum throughput maximization method) of FIG. 4 described above. In this example, the inter-base station cooperation control device 30 has a minimum throughput (second column from the right in Table 8) and a plurality of all beam combinations # 1 to # N (N = 3125) for each beam combination. Calculate the total throughput (rightmost column in Table 8), which is the sum of the plurality of throughputs for terminals # 1 to # 5 (S301 in FIG. 4). Next, as shown by the thick frame line in Table 8, the inter-base station cooperation control device 30 has the beam combination # that maximizes the minimum throughput among all beam combinations # 1 to # N (N = 3125). k and the lower permissible lower limit throughput (1.9 bps in the example of Table 8) whose minimum throughput is lower than the maximum value (2.4 bps in the example of Table 8) by a predetermined value ε (0.5 bps in the example of the figure). Temporarily select the above beam combinations # 1, # 2, # l, # m, and #n (S302 in FIG. 4). Then, the inter-base station cooperation control device 30 has the maximum total throughput (right end column in Table 8) from among the plurality of tentatively selected beam combinations # 1, # 2, # k, # l, # m, #n. Select the beam combination # l to be (18.9 bps) (S303 in FIG. 4).

Table 9 shows numerical examples when the beam combination is selected by the beam control algorithm of FIG. 5 described above. In this example, the inter-base station cooperation control device 30 has the minimum throughput (third column from the right in Table 9) and the terminal # for each beam combination for all beam combinations # 1 to # N (N = 3125). Calculate the total throughput (second column from the right in Table 9), which is the sum of the plurality of throughputs from 1 to # 5 (S401 in FIG. 5). Further, the inter-base station cooperation control device 30 evaluates all beam combinations # 1 to # N (N = 3125) by multiplying the minimum throughput and the total throughput for each beam combination (the rightmost column in Table 9). Is calculated (S402 in FIG. 5). Then, the inter-base station cooperation control device 30 has a beam combination # m in which the evaluation value (right end column of Table 9) becomes the maximum (41.1 bps) from all the beam combinations # 1 to # N (N = 3125). Is selected (S403 in FIG. 5).

According to the example of the beam combination selection process in Tables 4 to 9, when the base stations # 1 to # 5 to be linked are arranged in the target area, they are located in the cells of the base stations # 1 to # 5. The total throughput of terminals # 1 to # 5 can be greatly improved without degrading the cell boundary throughput.

と定義する。また、各基地局で利用可能なビーム数をＬとし、選択可能なビームの組み合わせ数を

とし、ビームの全組み合わせの集合を

と定義する。 Next, the inter-base station cooperation BF control of the present embodiment can be described by a generalized model as follows. Here, the number of base stations is set to _NVS , and the set of base stations (cooperation base stations) to be linked is set as

Is defined as. Further, the number of beams that can be used in each base station is L, and the number of combinations of beams that can be selected is set.

And the set of all combinations of beams

Is defined as.

Assuming that the terminals located at each base station can ideally measure the received power of all the beams from the cooperative base station, the received SINR of the i-th terminal # i in the k-th beam combination is the following equation ( It can be calculated in 1).

は、ｋ番目のビーム組み合わせを選択した場合の基地局＃ｊからの端末＃ｉの受信電力であり、ｎ_ｉは、端末＃ｉにおける雑音電力である。 Here, in equation (1)

Is the received power of the terminal # i from the base station # j when the k-th beam combination is selected, and n _i is the noise power of the terminal # i.

は、次式（２）を用いて推定（計算）することができる。

Based on the above received SINR, the throughput (Shannon capacity) of the i-th terminal # i in the k-th beam combination.

Can be estimated (calculated) using the following equation (2).

Here, the throughput of each terminal varies greatly depending on the combination of beams. As the beam combination selection algorithm, the beam control algorithm (minimum throughput maximization method) that maximizes the minimum throughput of each terminal mentioned above, and the minimum throughput maximization method allow a slight decrease in the overall system throughput. A beam control algorithm (modified minimum throughput maximization method) that increases the beam control algorithm and a beam control algorithm (evaluation value maximization method) that maximizes the evaluation value obtained by multiplying the minimum throughput and the total throughput can be used.

For example, the minimum throughput maximization method can be realized in step 1 shown below.

Step 1: For the set S, select the beam combination k _Final having the maximum estimated throughput among the terminals in the cell of the base station to be linked by the following equations (3) and (4). The throughput C _maxmin after maximizing the minimum throughput at that time is given by the following equation (5).

Further, the modified minimum throughput maximization method can be realized by the equations (3) and (4) of the above step 1 and the next step 2.

Step 2: In order to allow a slight decrease in throughput, set the throughput _C'maxmin which is ε lower than the throughput C _maxmin after maximizing the minimum throughput. The beam combination S'that has the lowest throughput higher than the set minimum throughput is determined, and the beam combination k _Final that maximizes the total throughput of the terminal is determined from the beam combinations S'.

The beam combination k _Final can be obtained by the following equations (6) to (8).

Further, in the above evaluation value maximization method, the optimum beam combination k _Final can be determined by the following equation (9).

In the inter-base station cooperation BF control of the inter-base station cooperation control device 30 having the above configuration, when the number of base stations 20 to be coordinated control and the number of candidate beams selectable for each base station increase, the beam for each base station 20 The amount of calculation required for selection increases. For example, if the number of base stations 20 to be linked and controlled is N and the number of candidate beams that can be selected for each base station is M, the number of beam combinations for the entire plurality of base stations 20 becomes an ^MN pattern. In the case of the beam combination selection process of FIG. 3 described above, it is necessary to calculate the throughput of each terminal 10 and the minimum throughput of each terminal 10 for all the ^MN patterns. Therefore, the amount of calculation required for beam selection for each base station 20 increases exponentially.

On the other hand, in the mobile communication system having the above configuration, as illustrated in FIG. 6 below, switching of the beam used by the base station 20 for communication with the terminal 10 is unlikely to occur even if the terminal 10 moves at a relatively high speed. ..

FIG. 6 is an explanatory diagram showing an example of the relationship between the beam 20B of the base station 20 and the moving terminal 10. In FIG. 6, the beam width θ _half = 10 ° of the beam 20B of the base station 20, and the terminal 10 is at a point in the middle of the cell radius (R = 1000 m) (position of 500 m from the base station 20) at a speed of 40 km / h (about 10 m). Consider the case of moving at / s). The displacement width Δθ (θ1-θ2) of the depression angle θ1 when the terminal 10 before the movement (immediately before the movement) is seen from the antenna 201 of the base station 20 and the depression angle θ2 when the terminal 10 is seen from the base station 20 one second later is about 0. It is 1 ° (in the illustrated example, the depression angle before movement θ1 = 5.7 °, and the depression angle after movement θ2 = 5.6 °). Since Δθ << θ _half , the communication between the base station 20 and the terminal 10 can be performed even if the same beam as the beam used before (immediately before) the movement is used again, that is, without switching the beam. The characteristics are likely to remain the same.

Therefore, in the present embodiment, when the selection process for selecting the beam combination is repeatedly executed at a predetermined time interval Δt, the beam selected immediately before or the beam thereof is used in the second and subsequent beam combination selection processes. Considering that there is a high possibility that adjacent beams are selected, candidate beam control is performed to limit the number of candidate beams that can be selected in the beam combination selection process. By this control, the number of searches for the beam combination at the time of the base station cooperation BF control in the base station cooperation control device 30 is reduced, and the calculation amount is reduced.

Here, the time interval Δt for repeatedly executing the second and subsequent beam combination selection processes may be constant or may be changed based on various conditions. For example, the beam combination selection process may be executed at each timing when the terminal 10 moves a predetermined distance.

7 (a) and 7 (b) are explanatory views showing an example of candidate beam control and its effect in the inter-base station cooperation control device 30 according to the present embodiment. Here, the number of base stations 20 to be linked and controlled is N (2 in the illustrated example), and the number of candidate beams that can be selected for each base station 20 in the initial beam combination selection process is M.

In the initial beam combination selection process shown in FIG. 7A, any of the beam combination selection processes exemplified in FIGS. 3 to 5 described above is executed for the combination of ^MN patterns. As shown in FIG. 7A, when the number ^M of the candidate beams is 5, one of the three types of beam combination selection processes exemplified in FIGS. 3 to 5 described above is performed for the combination of 5N patterns. To execute.

In the second beam combination selection process shown in FIG. 7B, the beam selected in the first beam combination selection process and a beam close thereto (for example, in the illustrated example, the first selected beam and two adjacent beams are used. The beam combination selection process exemplified in FIGS. 3 to 5 above is applied to the combination of ^M'N patterns for the limited number of M'(<M) candidate beams limited to three candidate beams including the beam). Do one of the above. When the number ^M of the candidate beams shown in FIG. 7A is 5, one of the three types of beam combination selection processes exemplified in FIGS. 3 to 5 described above is executed for the combination of 5N patterns. do.

By limiting the number of candidate beams from M to M'(<M), the target for beam combination selection processing is the ^{M'N pattern with respect to the MN pattern, so (M'/ M) N times .} It is possible to reduce the amount of calculation. For example, by limiting the number of candidate beams from 5 (= M) to 3 (<M), the target for beam combination selection processing changes from 5 ^N patterns to 3 ^N patterns, so (3/5) ^N times. It is possible to reduce the amount of calculation (about 8/100 times when the number N of base stations to be linked is 5) (reduction effect of about 92%).

FIG. 8 is a flowchart showing an example of a control algorithm for candidate beam control in the inter-base station cooperation control device 30 according to the present embodiment. In FIG. 8 and FIGS. 9 and 10 described later, the i-th terminal 10 is described as "MS # i", and the j-th base station 20 is described as "BS # j" (j = 1 to N). Then, the set of candidate beams of the _j -th base station 20 and the maximum number of selectable candidate beams are described as "Mj" and "L", respectively.

Further, the candidate beams that can be selected in each base station 20 are given beam identification numbers (1 to L) as continuous indexes in the spatial arrangement order, and the beam identification of each of the candidate beam and the selected beam of the jth base station 20. The numbers are described as "l _j " and "l' _j ".

Further, the search range specification parameter for defining the search range of the candidate beam that limits the number of candidate beams based on the selected beam l' _j selected in the immediately preceding candidate beam control is described as "Δl". For example, when this range specification parameter Δl is 1, three beams including the selection beam l' _j and one beam before and after it (l' _j -1, l' _j +1) are candidates for the next beam combination selection process. It becomes a beam.

In FIG. 8, first, the inter-base station cooperation control device 30 receives and aggregates the received power information for each beam and each base station of each terminal 10 (S501).

Next, the inter-base station cooperation control device 30 determines whether or not it is the first candidate beam control (S502), and in the case of the first candidate beam control (Yes in S502), of each base station 20 (BS # j). The candidate beam Mj is set as shown by the following equation (10) (S503). This setting is a setting for performing a full search lj ( ₌ 0 to L) for executing beam combination control for all selectable candidate beams.

On the other hand, in the case of the second and subsequent candidate beam control instead of the first candidate beam control (No in S502), the inter-base station cooperation control device 30 is further located in the cell 20A of the base station 20 for each base station 20. It is determined whether or not the combination of the terminals 10 is the same as the combination of the terminals 10 in the immediately preceding candidate beam control (S504).

Here, when the combination of terminals 10 is not the same (No in S504), the beam combination in the base station 20 for greatly improving the cell boundary throughput without degrading the total throughput of all terminals 10 has changed. Since there is a high possibility, the candidate beam Mj of each base station 20 (BS # j) is set in the equation (10) for full search as in the above-mentioned S503. As a result, when the combination of terminals 10 changes, the total throughput of all terminals can be greatly improved without deteriorating the cell boundary throughput.

On the other hand, in the case of the same combination of terminals 10 (Yes in S504), there is a possibility that the beam combination in the base station 20 for greatly improving the cell boundary throughput without deteriorating the total throughput of all terminals 10 has changed. Is low, the inter-base station cooperation control device 30 sets the candidate beam Mj of each base station 20 (BS # j) by limiting the number of candidate beams as shown in the following equation (11) (S505). .. As a result, it is possible to avoid calculation due to unnecessary throughput and reduce the amount of calculation for improving the throughput.

Next, the inter-base station cooperation control device 30 is used for each terminal 10 for all combinations of beams 20B considering the candidate beam (Mj) of cell 20A of each base station 20 set in S503 or S505 described above. SINR and throughput are calculated (S506).

Next, the inter-base station cooperation control device 30 selects a beam for the cell 20A of each base station 20 by any one of the three types of beam combination selection processes exemplified in FIGS. 3 to 5 described above, and BS # j L' _j is set as the beam of (S507).

The above control including the candidate beam control and the beam combination selection process is repeatedly executed at a predetermined time interval Δt (S501 to S507).

FIG. 9 is a flowchart showing another example of the control algorithm of the candidate beam control in the inter-base station cooperation control device 30 according to the present embodiment. The example of FIG. 9 is an example of a control algorithm in which the search range of the candidate beam is increased periodically at regular intervals.

In FIG. 9, the inter-base station cooperation control device 30 first initially sets a timer (t = 0), and receives and aggregates received power information for each beam and each base station of each terminal 10 (S601).

Next, the inter-base station cooperation control device 30 determines whether or not it is the first candidate beam control (S602), and in the case of the first candidate beam control (Yes in S602), each base station 20 (BS # j) The candidate beam Mj is set in the above-mentioned equation (10) for full search (S603), and the timer of the elapsed time t after expanding the range of the candidate beam to the full search range is initialized (t = 0). (S604).

On the other hand, in the case of the second and subsequent candidate beam control instead of the first candidate beam control (No in S602), the inter-base station cooperation control device 30 is further located in the cell 20A of the base station 20 for each base station 20. It is determined whether or not the combination of the terminals 10 is the same as the combination of the terminals 10 in the immediately preceding candidate beam control (S605).

Here, when the combination of terminals 10 is not the same (No in S605), the candidate beam Mj of each base station 20 (BS # j) is set in the equation (10) for total search as in S603 described above. ..

On the other hand, in the case of the same combination of terminals 10 (Yes in S605), the inter-base station cooperation control device 30 determines whether or not ΔT has elapsed for a certain period of time from the start of the timer (S606), and ΔT has elapsed for a certain period of time. If not (No in S606), the search range designation parameter Δl that defines the search range of the candidate beam is set to a predetermined first range designation value Δl ₁ that limits the search range (S607).

The value of ΔT for a certain period of time used in the determination of S606 may be set to a different value for each base station 20 (for each cell 20A).

In the above-mentioned S606, when ΔT has elapsed for a certain period of time (Yes in S606), in order to widen the range of the candidate beam, the search range specification parameter Δl is set to the second range specification value larger than the first range specification value Δl ₁ . It is set to Δl ₂ (S608), and the timer of the elapsed time t after expanding the range of the candidate beam is initialized (t = 0) (S609). Here, when the second range specified value Δl ₂ = L is set, it corresponds to the case of performing a full search.

By expanding the range of the candidate beam when ΔT has elapsed for a certain period of time in this way, it is possible to prevent the selected beam selected by the beam combination selection process from falling into a local solution.

Next, the inter-base station cooperation control device 30 sets the candidate beam Mj of each base station 20 (BS # j) into the above-mentioned equation (11) based on the search range designation parameter Δl set in the above-mentioned S607 or S608. ), The number of candidate beams is set (S610).

Since the control algorithms of S611 and S612 of FIG. 9 are the same as the control algorithms of S506 and S507 of FIG. 8 described above, their description will be omitted.

The above control including the candidate beam control and the beam combination selection process is repeatedly executed at a predetermined time interval Δt (S601 to S612).

FIG. 10 is a flowchart showing still another example of the control algorithm of the candidate beam control in the inter-base station cooperation control device 30 according to the present embodiment. In the example of FIG. 10, when the throughput C of any of the terminals in the immediately preceding beam combination selection process deteriorates by the specified threshold value Cth or more for each of the plurality of base stations 20, the full search lj ( ₌ 0 to L) is performed again. ) Is an example of a control algorithm.

In FIG. 10, the inter-base station cooperation control device 30 first receives and aggregates the received power information for each beam and each base station of each terminal 10 (S701).

Next, the inter-base station cooperation control device 30 determines whether or not it is the first candidate beam control (S702), and in the case of the first candidate beam control (Yes in S702), of each base station 20 (BS # j). The candidate beam Mj is set in the above-mentioned equation (10) for full search (S703).

On the other hand, in the case of the second and subsequent candidate beam control instead of the first candidate beam control (No in S702), the inter-base station cooperation control device 30 is further located in the cell 20A of the base station 20 for each base station 20. It is determined whether or not the combination of the terminals 10 is the same as the combination of the terminals 10 in the immediately preceding candidate beam control (S704).

Here, when the combination of the same terminals 10 is not the same (No in S704), the candidate beam Mj of each base station 20 (BS # j) is set in the equation (10) for total search as in the above-mentioned S703. ..

On the other hand, in the case of the same combination of terminals 10 (Yes in S704), the inter-base station cooperation control device 30 sets the search range designation parameter Δl that defines the search range of the candidate beam described above as a predetermined first search range. The range specification value Δl ₁ is set.

Since the control algorithms of S706 and S707 of FIG. 10 are the same as the control algorithms of S505 and S506 of FIG. 8 described above, their description will be omitted.

Next, the inter-base station cooperation control device 30 selects a beam for the cell 20A of each base station 20 by any one of the three types of beam combination selection processes exemplified in FIGS. 3 to 5 described above, and each terminal MS. The throughput C _i ⁽ⁿ⁾ of #i is calculated (S708).

Next, when the throughput of each terminal MS # _i in the immediately preceding (previous) control loop is Ci ^(n-1) , the inter-base station cooperation control device 30 is the inter-base station cooperation control device 30. Is the difference (degree of decrease in throughput) of the current throughput Ci ⁽ⁿ⁾ _from the throughput immediately before (one time before) any of the terminals 10 to Ci ( _n ^-1) is a predetermined threshold C _th or more. That is, it is determined whether or not the throughput of any of the terminals 10 has dropped to a predetermined threshold _Cth or more (S709).

Here, when the throughput of any of the terminals 10 has not dropped to a predetermined threshold value _Cth or more (No in S709), the base station-to-base station cooperation control device 30 is of the three types illustrated in FIGS. 3 to 5 described above. A beam is selected for the cell 20A of each base station 20 by any of the beam combination selection processes of the above, and l' _j is set as the beam of BS # j (S710).

On the other hand, when the throughput of any of the terminals 10 drops to a predetermined threshold value _Cth or more (Yes in S709), the inter-base station cooperation control device 30 uses a search range designation parameter to widen the range of the candidate beam. Δl is set to the second range designation value Δl ₂ which is larger than the first range designation value Δl ₁ (S711). Here, when the second range specified value Δl ₂ = L is set, it corresponds to the case of performing a full search.

The second range specified value Δl ₂ corresponding to the number of selectable candidate beams is changed according to the magnitude of the difference in throughput (C _i ^(n-1) -C _i ⁽ⁿ⁾ ). May be good. For example, the larger the difference in the above throughput (C _i ^(n-1) -C _i ⁽ⁿ⁾ ), that is, the larger the degree of decrease in the throughput of any one of the terminals 10, the larger the second range specified value Δl ₂ . You may set it large.

The above control including the candidate beam control and the beam combination selection process is repeatedly executed at a predetermined time interval Δt (S701 to S711).

According to the control algorithm of the candidate beam control of FIG. 10, in each base station, the throughput of all the terminals 10 in the cell 20A of the plurality of base stations 20 to be linked is not lowered to a predetermined threshold _Cth or more. You can choose the beam combination.

In S709 of the control algorithm for the candidate beam control of FIG. 10, when the difference (degree of decrease in throughput) becomes larger than the predetermined threshold value _Cth , that is, the throughput of any of the terminals 10 is the predetermined threshold value. It may be determined whether or not the decrease is significantly lower than the C _th , and the determination may be used in the control steps of S710 and S711.

Further, in the control algorithm of the candidate beam control of FIGS. 8 to 10 described above, the number of selectable candidate beams, that is, the search range designation parameter is determined according to the length of the time interval Δt for performing the beam combination selection process. The value of (Δl, Δl ₁ ) may be changed.

For example, when the time interval Δt for selecting the beam combination is short, the suitable beam combination in the base station 20 for greatly improving the cell boundary throughput without degrading the total throughput of all terminals 10 changes. Since it is unlikely that the candidate beam is available, the number of selectable candidate beams, that is, the value of the search range specification parameter (Δl, Δl ₁ ) may be reduced. On the contrary, when the time interval Δt for selecting the beam combination is long, it is highly possible that the suitable beam combination has changed, so that the number of candidate beams that can be selected, that is, the search range specification parameter (Δl, Δl). The value of ₁ ) may be increased.

Further, in the control algorithm for the candidate beam control of FIGS. 8 to 10 described above, the number of selectable candidate beams, that is, the search range designation parameters (Δl, Δl ₁ ) for each of the plurality of base stations 20 to be linked and controlled. The value of is based on at least one of environmental information including the direction of movement of the terminal 10 with respect to the base station 20, the distance between the base station 20 and the terminal 10, and the density of the terminal 10 located in the cell 20A of the base station 20. May be changed.

For example, when the terminal 10 is moving in the circumferential direction in the cell 20A centered on the base station 20, or when the distance between the base station 20 and the terminal 10 is short, the cell does not deteriorate the total throughput of the terminal 10. Since the suitable beam combination in the base station 20 for greatly improving the boundary throughput is likely to change, the number of selectable candidate beams, that is, the value of the search range specification parameter (Δl, Δl ₁ ) is increased. May be good. Conversely, if the terminal 10 is moving in the radial direction of the cell centered on the base station 20, or if the distance between the base station 20 and the terminal 10 is long, the cell boundary without degrading the total throughput of the terminal 10. Since it is unlikely that the suitable beam combination in the base station 20 for greatly improving the throughput of the above will change, the number of selectable candidate beams, that is, the value of the search range specification parameter (Δl, Δl ₁ ) is reduced and calculated. The amount reduction effect may be enhanced.

Further, in an urban environment where the density of the terminals 10 in the cell 20A of the base station 20 is high, the base station 20 is suitable for greatly improving the cell boundary throughput without deteriorating the total throughput of the terminals 10. Since there is a high possibility that the beam combination will change, the number of selectable candidate beams, that is, the value of the search range specification parameter (Δl, Δl ₁ ) may be increased. On the contrary, in an environment such as a suburb or a depopulated area where the density of the terminal 10 in the cell 20A of the base station 20 is low, the base for greatly improving the cell boundary throughput without degrading the total throughput of the terminal 10. Since it is unlikely that the suitable beam combination in the station 20 will change, the number of selectable candidate beams, that is, the value of the search range specification parameter (Δl, Δl ₁ ) may be reduced to increase the effect of reducing the calculation amount. ..

As described above, according to the present embodiment, not only the interference between adjacent base stations but also the interference between non-adjacent base stations (interference from a distant cell) is taken into consideration in a plurality of cells 20A in a wide target area. The total throughput of all terminals in the area can be greatly improved without deteriorating the cell boundary throughput, and the amount of calculation for improving the throughput can be reduced.

The processing process described herein and the components of the communication system, wireless device, base station and terminal (user device, mobile station, mobile device) can be implemented by various means. For example, these processing steps and components may be implemented in hardware, firmware, software, or a combination thereof.

Regarding hardware implementation, in order to realize the above steps and components in an entity (for example, various wireless communication devices, wireless relay devices, NodeBs, servers, gateways, exchanges, computers, hard disk drive devices, or optical disk drive devices). The means such as the processing unit used in the above are one or more application-specific ICs (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), fields. Programmable gate array (FPGA), processor, controller, microprocessor, microprocessor, electronic device, other electronic unit, computer, or combination thereof designed to perform the functions described herein. It may be implemented in.

Also, for firmware and / or software implementation, the means used to implement the above components are code for programs (eg, procedures, functions, modules, instructions, etc.) that perform the functions described herein. ) May be implemented. In general, any computer / processor readable medium that clearly embodies the firmware and / or software code is a means such as a processing unit used to implement the steps and components described herein. May be used to implement. For example, firmware and / or software code may be stored in memory and executed by a computer or processor, for example in a control device. The memory may be mounted inside the computer or processor, or it may be mounted outside the processor. The firmware and / or software code may be, for example, a random access memory (RAM), a read-only memory (ROM), a non-volatile random access memory (NVRAM), a programmable read-only memory (PROM), or an electrically erasable PROM (EEPROM). ), Flash memory, floppy (registered trademark) discs, compact discs (CDs), digital versatile discs (DVDs), magnetic or optical data storage devices, etc. good. The code may be executed by one or more computers or processors, or the computers or processors may be made to perform functional embodiments described herein.

Further, the medium may be a non-temporary recording medium. Further, the code of the program may be read and executed by a computer, a processor, or another device or device machine, and the format thereof is not limited to a specific format. For example, the code of the program may be any of source code, object code, and binary code, or may be a mixture of two or more of these codes.

Also, the description of the embodiments disclosed herein is provided to allow one of ordinary skill in the art to manufacture or use the present disclosure. Various amendments to this disclosure will be readily apparent to those of skill in the art and the general principles defined herein are applicable to other variations without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not limited to the examples and designs described herein, but should be recognized in the broadest range consistent with the principles and novel features disclosed herein.

10 terminals (mobile stations)
20 Base station 20A Cell 20B Beam 30 Base station cooperation control device 40 Communication line

Claims (9)

A multi-element that is arranged so as to form a plurality of cells in a target area and performs codebook-type beamforming control in which a plurality of beams are defined in advance for each of a plurality of movable terminals in the cell. A mobile communication system including a plurality of base stations having antennas and an inter-base station cooperation control device for controlling the plurality of base stations.
The inter-base station cooperation control device is
An information acquisition means for acquiring feedback information of a plurality of reception qualities measured by a plurality of terminals corresponding to a plurality of beams in the cell and fed back to the base station for each of the plurality of base stations. ,
For each of the plurality of combinations consisting of the combination of the plurality of base stations and the plurality of beams, a plurality of throughputs to the plurality of terminals based on the feedback information of the plurality of reception qualities fed back from the plurality of terminals. And the throughput calculation method to calculate
A selection means for selecting any one combination of the plurality of combinations based on the calculation result of the plurality of throughputs for the plurality of terminals calculated for each of the plurality of combinations.
An information transmission means for transmitting information regarding the selected combination to each of the plurality of base stations.
When the selection process for selecting the beam combination based on the calculation result of the throughput is repeatedly executed at a predetermined time interval Δt, the first beam that does not limit the number of candidate beams that can be selected for each of the plurality of base stations. In the second and subsequent beam combination selection processes after the combination selection process, a candidate beam control means for limiting the number of selectable candidate beams based on the result of the immediately preceding beam combination selection process is provided.
In the inter-base station cooperation control device, for each of the plurality of base stations, the combination of the plurality of terminals for which the feedback information is acquired in the second and subsequent beam combination selection processes is the beam combination selection process immediately before. If it is different from the combination of the plurality of terminals for which the feedback information has been acquired, the beam combination selection process is performed without limiting the number of selectable candidate beams.
A mobile communication system, wherein each of the plurality of base stations controls a plurality of beams of the own station based on information regarding the selected combination. In the mobile communication system of claim 1,
The inter-base station cooperation control device is characterized in that, for each of the plurality of base stations, the number of selectable candidate beams is increased after a certain period of time has elapsed in the second and subsequent beam combination selection processes. Mobile communication system. In the mobile communication system of claim 1 or 2.
In the inter-base station cooperation control device, for each of the plurality of base stations, the throughput in the beam combination selection process for the second and subsequent times is lowered to a predetermined threshold value or more with respect to the throughput in the beam combination selection process immediately before. A mobile communication system characterized in that the number of selectable candidate beams is increased when the beam is selected. In the mobile communication system according to any one of claims 1 to 3.
The inter-base station cooperation control device determines the number of selectable candidate beams according to the magnitude of the difference in throughput in the second and subsequent beam combination selection processes with respect to the throughput in the immediately preceding beam combination selection process. A mobile communication system characterized by changing. In the mobile communication system according to any one of claims 1 to 4.
In the inter-base station cooperation control device, for each of the plurality of base stations, the movement direction of the terminal with respect to the base station, the distance between the base station and the terminal, and the terminal located in the cell of the base station. A mobile communication system comprising changing the number of selectable candidate beams based on at least one of environmental information including density. In the mobile communication system according to any one of claims 1 to 5.
The inter-base station cooperation control device is characterized in that, from the plurality of combinations, the combination that maximizes the minimum throughput in the plurality of throughputs for the plurality of terminals calculated for each of the plurality of combinations is selected. Mobile communication system. In the mobile communication system according to any one of claims 1 to 5.
The inter-base station cooperation control device has a combination in which the minimum throughput in the plurality of throughputs with respect to the plurality of terminals calculated for each of the plurality of combinations is the maximum among the plurality of combinations, and the minimum throughput is the said. Temporarily select one or a plurality of combinations having a lower permissible lower limit throughput than a predetermined value from the maximum value, and the total of the plurality of throughputs for the plurality of terminals is maximized from the plurality of tentatively selected combinations. A mobile communication system characterized by selecting a combination. In the mobile communication system according to any one of claims 1 to 5.
In the inter-base station cooperation control device, the product of the minimum throughput in the plurality of throughputs calculated for each of the plurality of combinations and the total of the plurality of throughputs for the plurality of terminals is the maximum from the plurality of combinations. A mobile communication system characterized by selecting a combination that becomes. A multi-element that is arranged so as to form a plurality of cells in a target area and performs codebook-type beamforming control in which a plurality of beams are defined in advance for each of a plurality of movable terminals in the cell. An inter-base station cooperation control device that controls multiple base stations with antennas.
An information acquisition means for acquiring feedback information of a plurality of reception qualities measured by a plurality of terminals corresponding to a plurality of beams in the cell and fed back to the base station for each of the plurality of base stations. ,
For each of the plurality of combinations consisting of the combination of the plurality of base stations and the plurality of beams, a plurality of throughputs to the plurality of terminals based on the feedback information of the plurality of reception qualities fed back from the plurality of terminals. And the throughput calculation method to calculate
A selection means for selecting any one combination of the plurality of combinations based on the calculation result of the plurality of throughputs for the plurality of terminals calculated for each of the plurality of combinations.
An information transmission means for transmitting information regarding the selected combination to each of the plurality of base stations.
When the selection process for selecting the beam combination based on the calculation result of the throughput is repeatedly executed at a predetermined time interval Δt, the first beam that does not limit the number of candidate beams that can be selected for each of the plurality of base stations. In the second and subsequent beam combination selection processes after the combination selection process, a candidate beam control means for limiting the number of selectable candidate beams based on the result of the immediately preceding beam combination selection process is provided.
For each of the plurality of base stations, the combination of the plurality of terminals that acquired the feedback information in the second and subsequent beam combination selection processes acquired the feedback information in the immediately preceding beam combination selection process. A base station-to-base station cooperation control device, characterized in that the beam combination selection process is performed without limiting the number of selectable candidate beams when the combination of terminals is different from the above.

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