Wireless communication control device and wireless communication control method

Abstract

To accurately estimate a transmission rate using a small operation amount in a wireless communication system comprising a mobile relay station or a mobile base station that supports spatial multiplexing.SOLUTION: A beam estimation unit estimates a beam associated with each user terminal. A reception power estimation unit estimates reception power of a signal received from the user terminal by a communication device using a beam associated with a target user terminal. A selection probability determination unit determines selection probability representing probability in which the target user terminal is selected, and simultaneous selection probability representing probability in which other each user terminal is simultaneously selected when the target user terminal is selected. An interference power estimation unit estimates average interference power on the basis of the reception power corresponding to each user terminal and the simultaneous selection probability. A transmission rate estimation unit estimates an average transmission rate between the communication device and the target user terminal on the basis of the reception power corresponding to the target user terminal, the average interference power and the selection probability of the target user terminal.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an apparatus and method for estimating a transmission rate in wireless communication. [Background technology]

[0002] As one of the technologies for realizing wideband, high-capacity wireless communication, a communication method using millimeter waves or terahertz waves has been developed. However, communication using millimeter waves or terahertz waves has significant propagation loss and loss due to shielding. Therefore, to improve communication quality, a wireless communication system equipped with a mobile relay device has been proposed. The mobile relay device is placed, for example, in a position where the transmission rate of the wireless communication system is high. In the following description, the mobile relay device includes a mobile base station. Furthermore, a mobile relay device (including a mobile base station) may be referred to as a "relay station" or a "communication device."

[0003] The relay station is implemented, for example, in a UAV (Unmanned Aerial Vehicle) or a vehicle, and relays communications between the base station and user terminals. The location of the relay station is controlled, for example, by the base station. Therefore, the base station can deploy the relay station in an area with a poor radio wave environment or in an area where many user terminals are operating. This ensures a sufficient wireless coverage area.

[0004] On the other hand, spatial multiplexing has been put into practical use as a technology for improving transmission rates. Spatial multiplexing is achieved by forming multiple transmit / receive beams using MIMO (Multi-Input Multi-Output) technology. Spatial multiplexing allows a base station or relay station to communicate with multiple user terminals simultaneously.

[0005] A method for improving the total throughput in a wireless communication system having multiple base stations has been proposed (for example, Patent Document 1). Also, a method for reducing the number of beams used for communication with wireless terminals has been proposed (for example, Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-193288 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-167776 Summary of the Invention [Problem to be solved by the invention]

[0007] It is preferable that a relay station be placed at a location where the average transmission rate or total transmission rate of the wireless communication system is high. Therefore, in the procedure for determining the location of the relay station, the transmission rate at the destination of the relay station is estimated. For example, the transmission rate is estimated for each of a plurality of candidate destinations. Then, the relay station is placed at the destination where the estimated transmission rate is the highest.

[0008] Here, when a relay station supports spatial multiplexing, the relay station can communicate with multiple user terminals simultaneously. Therefore, in this case, the average transmission rate (or total transmission rate) of one or more user terminals connected to the relay station is calculated. However, at the time of estimating the transmission rate, it has not yet been determined which user terminal the relay station will select. Therefore, the average transmission rate of the wireless communication system can be obtained by estimating the transmission rate for each selection pattern of the user terminal and calculating the average.

[0009] In order to obtain a highly accurate average transmission rate using this method, it is preferable to estimate the transmission rate for many selection patterns. However, the amount of calculation required for estimating the transmission rate is large. Therefore, if the number of selection patterns is increased, the amount of calculation required for estimating the transmission rate becomes enormous. Furthermore, if the number of selection patterns is reduced, the accuracy of the transmission rate estimation decreases, which may prevent relay stations from being placed in appropriate locations, resulting in a decrease in communication performance.

[0010] An object according to one aspect of the present invention is to accurately estimate a transmission rate with a small amount of calculation in a wireless communication system including a mobile relay station or a mobile base station that supports spatial multiplexing. [Means for solving the problem]

[0011] A wireless communication control device according to one embodiment of the present invention comprises: a beam estimation unit that estimates beams associated with a plurality of user terminals located within a cell of a communication device that supports spatial multiplexing, using the beams; a received power estimation unit that estimates, for each of the plurality of user terminals, the received power of a signal received from the corresponding user terminal by the communication device using a target beam associated with a target user terminal among the plurality of user terminals; a selection probability determination unit that determines a selection probability representing the probability that the target user terminal will be selected and a simultaneous selection probability representing the probability that each other user terminal among the plurality of user terminals will be selected when the target user terminal is selected, based on a predetermined selection rule for selecting a user terminal in the spatial multiplexing; an interference power estimation unit that estimates an average interference power for a signal transmitted from the target user terminal based on the received power corresponding to each of the other user terminals and the simultaneous selection probability of each of the other user terminals; and a transmission rate estimation unit that estimates an average transmission rate between the communication device and the target user terminal based on the received power corresponding to the target user terminal, the average interference power, and the selection probability of the target user terminal. [Effects of the Invention]

[0012] According to the above-described aspect, in a wireless communication system including a mobile relay station or a mobile base station that supports spatial multiplexing, it is possible to accurately estimate a transmission rate with a small amount of calculation. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram illustrating an example of a wireless communication system according to an embodiment of the present invention. [Figure 2]FIG. 10 is a diagram illustrating an example of a method for calculating a transmission rate. [Figure 3] FIG. 1 is a diagram illustrating an overview of a transmission rate estimation method according to an embodiment of the present invention. [Figure 4] FIG. 1 is a diagram illustrating an example of a wireless communication control device according to an embodiment of the present invention. [Figure 5] 10 is a flowchart illustrating an example of processing by the wireless communication control device. [Figure 6] FIG. 1 illustrates an example method for estimating a beam associated with a user terminal. [Figure 7] FIG. 10 is a diagram illustrating an example of a method for estimating received power. [Figure 8] FIG. 10 is a diagram illustrating a method for determining the selection probability of a user terminal. [Figure 9] FIG. 10 is a diagram illustrating a method for determining the probability that another user terminal will be simultaneously selected when a target user terminal is selected. [Figure 10] 10 is a flowchart illustrating an example of a process for estimating an average transmission rate. [Figure 11] FIG. 10 is a diagram showing the results of a simulation comparing an embodiment of the present invention with an all-pattern selection method. DETAILED DESCRIPTION OF THE INVENTION

[0014] 1 shows an example of a wireless communication system according to an embodiment of the present invention. In this example, the wireless communication system 100 includes a base station (BS) 1, a relay station (RS) 2, and a user equipment (UE) 3. Note that the wireless communication system 100 may include multiple relay stations 2 and / or multiple user equipments 3.

[0015] The base station 1 can accommodate one or more user terminals 3. The base station 1 can also accommodate one or more relay stations 2. The base station 1 is not particularly limited, but may be, for example, an eNodeB that supports 4G or a gNodeB (NR base station) that supports 5G. The relay station 2 relays communications between the base station 1 and the user terminals 3. The relay station 2 can also be mobile. For example, the relay station 2 is implemented on a UAV (a so-called drone). The position of the relay station 2 is controlled by the base station 1. That is, the base station 1 includes a wireless communication control device 10 that controls the position of the relay station 2. Therefore, the base station 1 can deploy the relay station 2 in, for example, an area with a poor radio wave environment or an area where a large number of user terminals 3 are operating. This ensures a sufficient wireless coverage area. The base station 1 may also control the direction of the transmit / receive beam of the relay station 2.

[0016] Base station 1 and relay station 2 each periodically output a reference signal. The transmission power of the reference signal is predetermined. User terminal 3 measures the received power (RSRP: Reference Signal Received Power) of the reference signal transmitted from base station 1 and relay station 2. The RSRP measurement result is notified to base station 1. Then, based on this measurement result, it is determined whether user terminal 3 will connect to base station 1 or relay station 2. In the following description, it is assumed that user terminal 3 will connect to relay station 2.

[0017] The radio communication control device 10 controls the position of the relay station 2. Specifically, the radio communication control device 10 determines the position of the relay station 2 so that the transmission rate between the relay station 2 and the user terminal 3 is high. Then, the radio communication control device 10 moves the relay station 2 to the determined position. As a result, the average transmission rate or the total transmission rate of the radio communication system 100 increases.

[0018] In this embodiment, the relay station 2 is located at position P0. P1 to P4 represent candidate destinations for the relay station 2. P1, P2, P3, and P4 represent positions obtained by moving a predetermined distance north, east, south, and west from position P0, for example. The radio communication control device 10 estimates the transmission rate when the relay station 2 moves to each of positions P1 to P4. The transmission rate represents the average or sum of the transmission rates between the relay station 2 and each user terminal 3 (#1 to #3). The radio communication control device 10 then moves the relay station 2 to the position among positions P1 to P4 where the highest transmission rate can be obtained. Note that if the transmission rates estimated for each of positions P1 to P4 are all lower than the transmission rate obtained at the current position P0, there is no need to move the relay station 2.

[0019] FIG. 2 shows an example of a method for calculating a transmission rate. Relay station 2 supports spatial multiplexing. In this example, the multiplexing level is "2." That is, relay station 2 can communicate with two user terminals 3 simultaneously. Three user terminals 3 (#1 to #3) are located within the cell of relay station 2. Therefore, relay station 2 selects two of the three user terminals 3 to communicate with. In the following description, user terminal 3 (#i) may be referred to as "UE#i."

[0020] 2(a), relay station 2 communicates with UE#1 and UE#2. In this case, radio communication control device 10 estimates a transmission rate R1 between relay station 2 and UE#1 and a transmission rate R2 between relay station 2 and UE#2. Then, by calculating the average of transmission rates R1 and R2, the transmission rate when relay station 2 communicates with UE#1 and UE#2 is obtained.

[0021] Similarly, in the case shown in Fig. 2(b), the transmission rate when relay station 2 communicates with UE #1 and UE #3 is estimated. In the case shown in Fig. 2(c), the transmission rate when relay station 2 communicates with UE #2 and UE #3 is estimated. Then, by calculating the average of the transmission rates obtained in the three cases shown in Fig. 2, the average transmission rate for one destination candidate is obtained. Note that in the wireless communication system 100 shown in Fig. 1, this calculation is performed for each of positions P1 to P4.

[0022] 2, transmission rates are estimated for all selection patterns of relay station 2 and user terminal 3, and their average is calculated. Therefore, when the number of multiplexed relay stations 2 is large and / or when there are many user terminals 3 located within the cell of relay station 2, the amount of calculation required to calculate the average transmission rate becomes enormous. For example, when the number of multiplexed relay stations 2 is four and ten user terminals 3 are located within the cell of relay station 2, there are 210 selection patterns (i.e., the number of combinations in which four terminals are selected from ten terminals). Then, transmission rates corresponding to each selection pattern are estimated for each terminal. Therefore, 840 transmission rate estimations are required.

[0023] 3 shows an overview of a transmission rate estimation method according to an embodiment of the present invention. In this example, the multiplexing level of relay station 2 is also "2." Three user terminals 3 (#1 to #3) are located within the cell of relay station 2.

[0024] In a method according to an embodiment of the present invention, the radio communication control device 10 calculates a transmission rate for each user terminal 3. At this time, the radio communication control device 10 determines the selection probability for each user terminal and the probability that when a certain user terminal is selected, another user terminal will be selected at the same time, based on a selection rule prepared in advance. The radio communication control device 10 then estimates the transmission rate taking these probabilities into consideration.

[0025] The relay station 2 can simultaneously communicate with two user terminals 3. Therefore, in estimating the transmission rate, two user terminals 3 are selected from among UE#1 to UE#3 located within the cell of the relay station 2.

[0026] In the case shown in FIG. 3(a), UE#1 is selected. Furthermore, based on a predetermined selection rule, the probability that each user terminal other than UE#1 will be selected when UE#1 is selected is determined. In this example, the selection rule is "fair" or "equal." That is, each user terminal (UE#2 to UE#3) other than UE#1 has the same probability of being selected. Specifically, the probability that UE#2 will be selected is 50 percent, and the probability that UE#3 will be selected is also 50 percent.

[0027] The radio communication control device 10 estimates the transmission rate between the relay station 2 and UE #1. This transmission rate depends on the interference power caused by signals transmitted from other user terminals (UE #2, UE #3). However, when UE #1 is selected, the probability that UE #2 and UE #3 will be selected is 50 percent for each. Therefore, when calculating the transmission rate of UE #1, the radio communication control device 10 multiplies the interference power caused by signals transmitted from UE #2 and UE #3 by "0.5" for each. As a result, a transmission rate that takes into account the probability that other user terminals will be selected is obtained. Furthermore, the radio communication control device 10 multiplies this transmission rate by the probability that UE #1 will be selected (100 percent in this example). This results in the transmission rate between the relay station 2 and UE #1.

[0028] In the case shown in Figure 3(b), UE #2 is selected. In this case, according to the above-mentioned selection rule, the probability that UE #1 will be selected is 50 percent, and the probability that UE #3 will be selected is also 50 percent. Therefore, when calculating the transmission rate of UE #2, the radio communication control device 10 multiplies the interference power caused by the signals transmitted from UE #1 and UE #3 by "0.5" respectively. Furthermore, the radio communication control device 10 multiplies this transmission rate by the probability that UE #2 will be selected (100 percent in this example). This gives the transmission rate between relay station 2 and UE #2.

[0029] In the case shown in Figure 3(c), UE #3 is selected. In this case, according to the above-mentioned selection rule, the probability that UE #1 will be selected is 50 percent, and the probability that UE #2 will be selected is also 50 percent. Therefore, when calculating the transmission rate of UE #3, the radio communication control device 10 multiplies the interference power caused by the signals transmitted from UE #1 and UE #2 by "0.5" respectively. Furthermore, the radio communication control device 10 multiplies this transmission rate by the probability that UE #3 will be selected (100 percent in this example). This gives the transmission rate between the relay station 2 and UE #3.

[0030] Thereafter, the radio communication control apparatus 10 calculates the average transmission rate by averaging the transmission rates estimated for each user terminal (UE#1 to UE#3). In this way, in the method according to the embodiment of the present invention, the radio communication control apparatus 10 estimates the transmission rate for each user terminal 3 and calculates the average of these to obtain the average transmission rate. That is, the average transmission rate can be obtained by performing the same number of calculations as the number of user terminals 3 located within the cell of the relay station 2. Therefore, compared to the method shown in FIG. 2, the amount of calculation required for calculating the average transmission rate is significantly reduced. For example, when 10 user terminals 3 are located within the cell of the relay station 2, the average transmission rate of the relay station 2 can be obtained by estimating the transmission rate for each of the 10 selection patterns, regardless of the number of multiplexed relay stations 2.

[0031] In estimating the transmission rate, the transmitting / receiving beam may be formed by taking into consideration only the weight for the target user terminal. Also, it is preferable to multiply the estimated interference power by a coefficient according to the interference suppression performance of relay station 2.

[0032] 4 shows an example of a radio communication control device 10 according to an embodiment of the present invention. The radio communication control device 10 is implemented in a base station 1, for example, as shown in FIG. 1. However, the embodiment of the present invention is not limited to this configuration. In other words, the radio communication control device 10 may be provided independently of the base station 1.

[0033] The radio communication control device 10 includes a location information acquisition unit 11, a candidate destination management unit 12, an estimation unit 13, a destination determination unit 14, and a relay station control unit 15. The radio communication control device 10 may include other functions or circuits not shown in FIG.

[0034] The location information acquisition unit 11 acquires location information indicating the location of each user terminal 3 within the cell of the relay station 2. The location of each user terminal 3 is detected, for example, by using a Global Positioning System (GPS). The location information acquisition unit 11 may also acquire location information indicating the location of the relay station 2. However, in this embodiment, the location of the relay station 2 is controlled by the wireless communication control device 10. Therefore, the location information acquisition unit 11 does not need to acquire the location information of the relay station 2.

[0035] The destination candidate management unit 12 manages candidate destinations for the relay station 2. For example, in the case shown in Fig. 1, when the current position of the relay station 2 is P0, P1 to P4 are set as candidate destinations. P1, P2, P3, and P4 represent positions that are a predetermined distance north, east, south, and west from the position P0, for example.

[0036] The estimation unit 13 estimates the average transmission rate between the relay station 2 and the user terminal 3 for each destination candidate set by the destination candidate management unit 12. The method for estimating the average transmission rate will be described in detail later.

[0037] The destination determination unit 14 determines the destination of the relay station 2 based on the average transmission rate estimated by the estimation unit 13. Specifically, the destination determination unit 14 selects, as the destination of the relay station 2, the destination candidate with the highest average transmission rate from among the destination candidates set by the destination candidate management unit 12.

[0038] The relay station control unit 15 generates an instruction to move the relay station 2 to the destination determined by the destination determination unit 14. For example, if the relay station 2 is implemented in a UAV, the relay station control unit 15 issues a movement instruction to the UAV. As a result, the relay station 2 is placed in a position where a high transmission rate is expected. Therefore, the performance of the wireless communication system is improved. Note that the relay station control unit 15 is an example of a position control unit that controls the position of the communication device.

[0039] 5 is a flowchart showing an example of the processing of the radio communication control device 10. The processing of this flowchart is executed, for example, periodically. In this case, the radio communication control device 10 may execute the processing of this flowchart at intervals of several seconds.

[0040] In S1, the location information acquisition unit 11 acquires location information indicating the location of each user terminal 3. In S2, the estimation unit 13 estimates the average transmission rate between the relay station 2 and the user terminal 3 for each candidate destination of the relay station 2. In S3, the destination determination unit 14 determines the destination of the relay station 2 by selecting the candidate destination that has the highest average transmission rate. In S4, the relay station control unit 15 generates an instruction to move the relay station 2 to the destination determined in S3. This movement instruction is transmitted to the relay station 2 or a mobile object (e.g., a UAV) that carries the relay station 2. As a result, the relay station 2 is placed at a position where the transmission rate is high.

[0041] Next, we will explain a method for estimating the average transmission rate between the relay station 2 and the user terminal 3. The average transmission rate between the relay station 2 and the user terminal 3 is estimated by the estimation unit 13 shown in FIG.

[0042] 4, the estimation unit 13 includes a beam estimation unit 21, a received power estimation unit 22, a selection probability determination unit 23, an interference power estimation unit 24, and a transmission rate estimation unit 25. Note that the estimation unit 13 may include other functions not shown in FIG.

[0043] The beam estimation unit 21 estimates a beam associated with each user terminal 3 by the relay station 2 based on the position of the relay station 2 and the position of each user terminal 3. Here, the relay station 2 selects and uses one or more beams from a plurality of predetermined beams.

[0044] As shown in Fig. 6, relay station 2 is capable of forming a plurality of beams B1 to BN. The beams correspond to transmission beams for transmitting radio signals and / or reception beams for receiving radio signals. Relay station 2 is also equipped with a plurality of antenna elements to achieve MIMO communication. Relay station 2 can form transmission beams by controlling the weights by which signals transmitted via each antenna element are multiplied, and can form reception beams by controlling the weights by which signals received via each antenna element are multiplied. It is preferable that the plurality of beams B1 to BN are set uniformly.

[0045] The beam estimation unit 21 estimates a beam to be associated with the user terminal 3 from among the multiple beams B1 to BN, based on the relative position of the user terminal 3 with respect to the relay station 2. In the example shown in FIG. 6, the beam estimation unit 21 estimates that beam B3, beam B4, and beam B4 are associated with UE#1, UE#2, and UE#3, respectively. In this way, one beam is associated with each user terminal 3. At this time, the same beam may be associated with multiple user terminals 3.

[0046] The received power estimation unit 22 estimates, for each user terminal 3, the received power of a signal received by the relay station 2 from the user terminal served by the relay station 2, using the beam associated with the target user terminal. The target user terminal refers to any one of the user terminals located within the cell of the relay station 2. For example, in the embodiment shown in FIG. 6, it is assumed that UE#1 is the target user terminal. Here, beam B3 is associated with UE#1. Therefore, in this case, the received power of signals received by the relay station 2 from UE#1 to UE#3 is estimated using beam B3.

[0047] The received power depends on the distance between relay station 2 and user terminal 3 and the relative direction of user terminal 3 with respect to relay station 2. For example, in the case shown in FIG. 7, UE #1 is the target user terminal. Then, the power of signals received by relay station 2 from UE #1 to UE #3 using beam B3 is estimated. In this case, the received power corresponding to UE #1 is calculated based on the distance between relay station 2 and UE #1 and the angle θ(B3_#1) between beam B3 and the relative direction of UE #1 with respect to relay station 2. The received power corresponding to UE #2 is calculated based on the distance between relay station 2 and UE #2 and the angle θ(B3_#2) between beam B3 and the relative direction of UE #2 with respect to relay station 2. The received power corresponding to UE #3 is calculated based on the distance between relay station 2 and UE #3 and the angle θ(B3_#3) between beam B3 and the relative direction of UE #3 with respect to relay station 2.

[0048] The received power estimation unit 22 estimates the received power while selecting the target user terminals one by one in turn. That is, in the case shown in Fig. 6, the received power corresponding to UE#1 to UE#3 when UE#1 is the target user terminal, the received power corresponding to UE#1 to UE#3 when UE#2 is the target user terminal, and the received power corresponding to UE#1 to UE#3 when UE#3 is the target user terminal are estimated.

[0049] The selection probability determination unit 23 determines a selection probability representing the probability that each user terminal will be selected, and a simultaneous selection probability representing the probability that other user terminals will be selected at the same time when a target user terminal is selected. At this time, the selection probability determination unit 23 determines the selection probability and simultaneous selection probability based on a selection rule for selecting user terminals in spatial multiplexing. The selection rule is, for example, "fair" or "equal."

[0050] An example will be described. Here, as shown in FIG. 8(a), relay station 2 can set three beams B1 to B3. Relay station 2 can communicate with two user terminals 3 simultaneously through spatial multiplexing. In other words, the multiplexing level of relay station 2 is 2. Five user terminals (UE#1 to RE#5) are located within the cell of relay station 2. Specifically, UE#1 to UE#2 are located in the direction of beam B1, UE#3 is located in the direction of beam B2, and UE#4 to UE#5 are located in the direction of beam B3. However, relay station 2 can only communicate with one user terminal using one beam.

[0051] The selection probability of each user terminal is calculated by equally allocating resources corresponding to the multiplexing number of relay station 2 to each user terminal. That is, when relay station 2 is configured to be able to communicate with N user terminals simultaneously, the selection probability of each user terminal is determined by equally allocating "N x 100 percent" to the multiple user terminals. In this embodiment, the multiplexing number of relay station 2 is 2. Therefore, "200 percent" is equally allocated to five user terminals. Specifically, "200 percent" is equally allocated to UE#1 to UE#5. That is, the selection probability of each of UE#1 to UE#5 is "40 percent."

[0052] In the case shown in FIG. 8(b), UE #1 to UE #4 are associated with beam B1, and UE #5 is associated with beam B2. In this case, if "200 percent" is evenly allocated to UE #1 to UE #5, the sum of the selection probabilities of the user terminals (UE #1 to UE #4) associated with beam B1 is 160 percent, which exceeds 100 percent. However, in this embodiment, the number of user terminals with which relay station 2 can communicate using one beam is "1." Here, a state in which the sum of the selection probabilities of user terminals associated with one beam exceeds 100 percent corresponds to a state in which multiple user terminals connect to relay station 2 using one beam. Therefore, selection probability determination unit 23 sets the selection probability of each user terminal so that the sum of the selection probabilities of user terminals associated with one beam does not exceed "100 percent."

[0053] In this example, four user terminals (i.e., UE#1 to UE#4) are associated with beam B1, so the selection probability of each of UE#1 to UE#4 is determined by equally allocating "100 percent" to UE#1 to UE#4. Therefore, the selection probability of each of UE#1 to UE#4 is "25 percent." Furthermore, the remaining resources are allocated to another user terminal (i.e., UE#5). In other words, "100 percent" is allocated to UE#5. Therefore, the selection probability of UE#5 is "100 percent."

[0054] Next, the selection probability determination unit 23 determines the simultaneous selection probability of each user terminal 3. That is, the probability that other user terminals will be selected simultaneously when the target user terminal is selected is determined. Here, as an example, the simultaneous selection probability of each user terminal is calculated for the case shown in FIG. 8(a). The calculation result is as shown in FIG. 9(a).

[0055] In the case shown in Figure 8(a), when relay station 2 selects UE#1 (i.e., when UE#1 is the target user terminal), beam B1 is occupied by UE#1. Therefore, when UE#1 is selected, the probability that another user terminal associated with beam B1 will be selected is zero. Specifically, when UE#1 is selected, the probability that UE#2 will be selected at the same time is zero.

[0056] When relay station 2 selects UE #1, the probability that user terminals associated with other beams (i.e., beams B2 and B3) (hereinafter, "other beam UEs") will be simultaneously selected is calculated by allocating the remaining resources to the other beam UEs according to the selection probability of the other beam UEs. Here, if relay station 2 is configured to be able to communicate with N user terminals simultaneously, the resources remaining after selecting the target user terminals correspond to "(N-1) x 100 percent." Therefore, the simultaneous selection probability of other beam UEs is determined by allocating "(N-1) x 100 percent" to the other beam UEs according to the selection probability of the other beam UEs. In this example, the multiplexing number is 2. Therefore, "100 percent" is allocated to the other beam UEs. Also, in this example, the user terminals associated with other beams (i.e., beams B2 and B3) are UE #3 to UE #5. Furthermore, the selection probabilities of UE #3 to UE #5 are the same as each other, as shown in FIG. 8(a). Therefore, the probability that UE#3 to UE#5 will be simultaneously selected when UE#1 is selected is obtained by equally allocating "100 percent" to UE#3 to UE#5. In other words, the simultaneous selection probability of UE#3 to UE#5 is 33 percent for each. Note that the probability that other user terminals will be simultaneously selected when UE#2, UE#4, or UE#5 is selected can be considered to be the same as when UE#1 is selected.

[0057] When relay station 2 selects UE #3 (i.e., when UE #3 is the target user terminal), the remaining resources (i.e., 100 percent) are allocated to other beam UEs (i.e., UE #1, UE #2, UE #4, and UE #5). Here, the selection probabilities of UE #1, UE #2, UE #4, and UE #5 are the same, as shown in FIG. 8(a). Therefore, the probability that UE #1, UE #2, UE #4, and UE #5 are simultaneously selected when UE #3 is selected is obtained by equally allocating "100 percent" to UE #1, UE #2, UE #4, and UE #5. In other words, the simultaneous selection probabilities of UE #1, UE #2, UE #4, and UE #5 are each 25 percent.

[0058] Furthermore, in the case shown in Figure 8(b), when a target user terminal is selected, the probability that other user terminals will be selected at the same time is as shown in Figure 9(b). Specifically, when relay station 2 selects UE#1 (i.e., when UE#1 is the target user terminal), beam B1 is occupied by UE#1. Therefore, when UE#1 is selected, the probability that UE#2 to UE#4 will be selected at the same time is zero.

[0059] When relay station 2 selects UE #1, the only user terminal (i.e., other beam UE) associated with another beam (i.e., beams B2 and B3) is UE #5. In this case, all resources remaining after selecting the target user terminal are allocated to UE #5. Therefore, when relay station 2 selects UE #1, the probability that UE #5 will be simultaneously selected is 100 percent. Note that the probability that other user terminals will be simultaneously selected when UE #2, UE #3, or UE #4 are selected can be considered the same as when UE #1 is selected.

[0060] When relay station 2 selects UE #5 (i.e., when UE #5 is the target user terminal), the remaining resources are allocated to other beam UEs (i.e., UE #1 to UE #4). Here, the selection probabilities of UE #1 to UE #4 are the same, as shown in FIG. 8(b). Therefore, the probability that UE #1, UE #2, UE #3, and UE #4 will be simultaneously selected when UE #5 is selected is obtained by equally allocating "100 percent" to UE #1, UE #2, UE #3, and UE #4. In other words, the simultaneous selection probabilities of UE #1, UE #2, UE #3, and UE #4 are each 25 percent.

[0061] The interference power estimation unit 24 estimates the average interference power for the signal transmitted from the target user terminal, based on the received power corresponding to each user terminal other than the target user terminal and the simultaneous selection probability of each user terminal other than the target user terminal.

[0062] For example, the average interference power Iu for a signal transmitted from UE#u is expressed by equation (1).

number

[0063] The interference power estimation unit 24 estimates the average interference power for the signal transmitted from each user terminal using equation (1). Here, the average interference power is estimated in the cases shown in Fig. 8(b) and Fig. 9(b).

[0064] For example, the average interference power for a signal transmitted from UE#1 is expressed by equation (2). Here, P1,5 represents the power of the signal received from UE#5 by relay station 2 using the beam associated with UE#1 (beam B1 in this embodiment). Note that, since the probability that UE#2 to UE#4 are simultaneously selected when UE#1 is selected is zero, it is not necessary to consider the received power corresponding to UE#2 to UE#4.

number

[0065] The average interference power for the signal transmitted from UE#5 is expressed by equation (3). In equation (3), P5,1, P5,2, P5,3, and P5,4 represent the power of the signals received from UE#1, UE#2, UE#3, and UE#4 by relay station 2 using the beam associated with UE#5 (beam B2 in this embodiment), respectively.

number

[0066] The transmission rate estimation unit 25 estimates the average transmission rate between the relay station 2 and the target user terminal based on the received power corresponding to the target user terminal, the average interference power for the signal transmitted from the target user terminal, and the selection probability of the target user terminal. Specifically, the transmission rate estimation unit 25 first calculates the average SINR (Signal to Interference plus Noise Ratio) of the signal transmitted from the target user terminal based on the received power corresponding to the target user terminal and the average interference power for the signal transmitted from the target user terminal. Here, the average SINR is expressed by equation (4).

number

[0067] Pu,u represents the received power corresponding to the target user terminal. In other words, Pu,u represents the power of the signal received by relay station 2 from UE#u using the beam associated with UE#u. The square of σ represents the noise power. Note that the noise power is assumed to be obtained in advance through simulation, measurement, or the like. β represents the interference suppression coefficient, which is a real number greater than zero and less than 1. Here, relay station 2 is assumed to have an interference suppression function that suppresses interference components in order to extract the target signal from the signal received using the reception beam. The interference suppression coefficient β is set in advance through simulation or the like based on the performance of relay station 2. In this case, the performance of relay station 2 depends on the hardware performance of relay station 2 and the interference suppression calculation algorithm used by relay station 2.

[0068] Next, the transmission rate estimation unit 25 estimates the average transmission rate between the relay station 2 and the target user terminal based on the average SINR and the selection probability of the target user terminal. Specifically, the average transmission rate Ru between the relay station 2 and UE#u is expressed by equation (5), where αu represents the probability that UE#u (i.e., the target user terminal) will be selected.

number

[0069] The transmission rate estimation unit 25 estimates the average transmission rate between the relay station 2 and each user terminal. In the example shown in Figs. 8 and 9, the average transmission rate is estimated for each of UE #1 to UE #5. The transmission rate estimation unit 25 then calculates the average of the average transmission rates of each user terminal. As a result, the average transmission rate between the relay station 2 and the user terminal for one destination candidate is obtained. Furthermore, the transmission rate estimation unit 25 calculates the average transmission rate for each of multiple destination candidates.

[0070] Thereafter, the destination determination unit 14 shown in Fig. 4 identifies the destination candidate that will result in the highest average transmission rate from among the multiple destination candidates. That is, the destination of the relay station 2 is determined. Then, the relay station control unit 15 generates an instruction to move the relay station 2 to the destination determined by the destination determination unit 14. As a result, the relay station 2 is placed in a position where the average transmission rate is expected to be high. Therefore, the performance of the wireless communication system 100 is improved.

[0071] 10 is a flowchart showing an example of processing for estimating an average transmission rate, which corresponds to S2 in the flowchart shown in FIG.

[0072] In S11, the estimation unit 13 selects a destination candidate for which the average transmission rate is to be estimated from among a plurality of destination candidates. After that, the estimation unit 13 performs the processes of S12 to S19 assuming that the relay station 2 is located in the selected destination candidate.

[0073] In S12, the beam estimation unit 21 estimates beams associated by the relay station 2 with each of a plurality of user terminals located within the cell of the relay station 2. In S13, the estimation unit 13 selects a target user terminal from among the plurality of user terminals located within the cell of the relay station 2. Thereafter, the estimation unit 13 executes the processes of S14 to S17 for the target user terminal. At S14, the received power estimation unit 22 estimates the received power of a signal received by the relay station 2 from a user terminal corresponding to the target user terminal, using a target beam associated with the target user terminal. At S15, the selection probability determination unit 23 determines, based on a predetermined selection rule, the probability that the target user terminal will be selected and the probability that other user terminals will be simultaneously selected when the target user terminal is selected. At S16, the interference power estimation unit 24 estimates the average interference power for signals transmitted from the target user terminal, based on the received power corresponding to each user terminal and the simultaneous selection probability of each user terminal. At S17, the transmission rate estimation unit 25 estimates the average transmission rate between the relay station 2 and the target user terminal, based on the received power corresponding to the target user terminal, the average interference power for signals transmitted from the target user terminal, and the selection probability of the target user terminal. That is, a weighted average is calculated based on the selection probability of each user terminal.

[0074] In S18, the estimation unit 13 determines whether or not the average transmission rates have been estimated for all user terminals. If there are any user terminals whose average transmission rates have not been estimated, the processing of the estimation unit 13 returns to S13. If the average transmission rates have been estimated for all user terminals, the transmission rate estimation unit 25 calculates the average transmission rate of the destination candidate by calculating the average of the average transmission rates of each user terminal.

[0075] In S20, the estimation unit 13 determines whether or not the average transmission rates have been estimated for all destination candidates. If there are any remaining destination candidates for which the average transmission rates have not been estimated, the processing of the estimation unit 13 returns to S11. Then, when the average transmission rates have been estimated for all destination candidates, the processing of the estimation unit 13 ends. In this way, the estimation unit 13 executes the processing of S14 to S17 for each destination candidate the same number of times as the number of user terminals located within the cell of the relay station 2.

[0076] The radio communication control device 10 is realized by, for example, a computer including a processor and a memory. In this case, a control program describing the processing of the flowchart shown in Fig. 5 is stored in the memory. Then, when the processor executes this control program, the functions of the location information acquisition unit 11, the destination candidate management unit 12, the estimation unit 13, the destination determination unit 14, and the relay station control unit 15 shown in Fig. 4 are provided. Alternatively, a transmission rate estimation program describing the processing of the flowchart shown in Fig. 10 is stored in the memory. Then, when the processor executes this transmission rate estimation program, the functions of the beam estimation unit 21, the received power estimation unit 22, the selection probability determination unit 23, the interference power estimation unit 24, and the transmission rate estimation unit 25 shown in Fig. 4 are provided.

[0077] <Simulation> In order to confirm the effectiveness of the transmission rate estimation method according to the embodiment of the present invention, a method in which transmission rates are estimated for all user terminal selection patterns and then their average is calculated (hereinafter referred to as the all-pattern selection method) is compared with the embodiment of the present invention. Note that the all-pattern selection method provides high transmission rate estimation accuracy, but requires a huge amount of calculation. For example, when the number of multiplexed relay stations 2 is four and ten user terminals 3 are located within the cell of the relay station 2, 840 transmission rate estimations are required. In contrast, in the embodiment of the present invention, the transmission rate is estimated by performing the same number of calculations as the number of user terminals 3 located within the cell of the relay station 2.

[0078] The simulation conditions are as follows: (1) The number of relay stations is 3 (2) The relay station can communicate with four user terminals simultaneously through spatial multiplexing (multiplexing number = 4). (3) Frequency: 28 GHz, Bandwidth: 400 MHz (4) The relay station antenna configuration is 8 elements x 8 elements (0.5λ spacing). (5) The coverage area of ​​the relay station is -60 degrees to +60 degrees, 60 to 100 meters. (6) 18 user terminals are uniformly distributed within the relay station cell. (7) The relay station is placed at a height of 30 m, and the user terminal is placed at a height of 1.5 m. (8) The maximum transmission power of the user terminal is 23 dBm, and TPC is performed with a target SNR of 30 dB. (9) Path loss model is 3GPP UMi Street Canyon (LOS) (10) Calculate throughput based on Shannon channel capacity (11) Digital beamforming with MMSE

[0079] Fig. 11 shows the results of a simulation comparing an embodiment of the present invention with the all-pattern selection method. In Fig. 11, the dashed line represents the reference level. The reference level represents the state in which the transmission rate is estimated using the all-pattern selection method. The solid line represents the state in which the transmission rate is estimated using an embodiment of the present invention. The vertical axis represents the correlation between the reference level and an embodiment of the present invention. The horizontal axis corresponds to the interference suppression coefficient β used in an embodiment of the present invention.

[0080] According to this simulation, if the interference suppression coefficient β is set appropriately, the correlation coefficient becomes approximately 1. In other words, if the interference suppression coefficient β is set appropriately, the transmission rate estimated by the method according to the embodiment of the present invention is approximately the same as the transmission rate estimated by the all-pattern selection method. Therefore, according to the embodiment of the present invention, the transmission rate can be estimated accurately with a small amount of calculation. As a result, the relay station 2 is placed in an appropriate position, and the quality of the wireless communication system 100 is improved. [Explanation of symbols]

[0081] 1 Base station (BS) 2. Relay Station (RS) 3 User Equipment (UE) 10. Wireless communication control device 11 Location information acquisition section 12 Destination candidate management department 13 Estimation part 14. Destination determination unit 15. Relay station control section 21 Beam estimation unit 22 Received power estimation unit 23 Selection probability determination unit 24 Interference power estimation unit 25 Transmission rate estimation unit 100 Wireless Communication System

Claims

1. a beam estimator configured to estimate, by a communication device supporting spatial multiplexing, beams associated with a plurality of user terminals located within a cell of the communication device; a received power estimation unit that estimates, for each of the plurality of user terminals, a received power of a signal received by the communication device from a corresponding user terminal by using a target beam that is associated with a target user terminal among the plurality of user terminals; a selection probability determination unit that determines, based on a predetermined selection rule for selecting user terminals in the spatial multiplexing, a selection probability that indicates the probability that the target user terminal will be selected, and a simultaneous selection probability that indicates the probability that each of the other user terminals among the plurality of user terminals will be selected when the target user terminal is selected; an interference power estimation unit that estimates average interference power with respect to a signal transmitted from the target user terminal based on received power corresponding to each of the other user terminals and a simultaneous selection probability of each of the other user terminals; a transmission rate estimation unit that estimates an average transmission rate between the communication device and the target user terminal based on a received power corresponding to the target user terminal, the average interference power, and a selection probability of the target user terminal; A wireless communication control device comprising:

2. The selection probability of each user terminal is determined by equally allocating resources corresponding to the number of user terminals with which the communication device can simultaneously communicate to the plurality of user terminals.

2. The wireless communication control device according to claim 1.

3. When the communication device is configured to be able to communicate with N user terminals simultaneously, the selection probability of each user terminal is determined by equally allocating N×100 percent to the plurality of user terminals.

2. The wireless communication control device according to claim 1.

4. The selection probability of each user terminal is determined so that the sum of the selection probabilities of user terminals associated with one beam does not exceed 100 percent.

4. The wireless communication control device according to claim 3.

5. The simultaneous selection probability of each of the other user terminals is determined by allocating (N-1) x 100 percent according to the selection probability corresponding to the user terminals associated with beams other than the target beam.

4. The wireless communication control device according to claim 3.

6. the transmission rate estimation unit estimates an average transmission rate between the communication device and the target user terminal by multiplying a transmission rate obtained based on the received power corresponding to the target user terminal and the average interference power by a selection probability of the target user terminal.

2. The wireless communication control device according to claim 1.

7. The transmission rate estimation unit calculating a second average interference power by multiplying the average interference power estimated by the interference power estimation unit by an interference suppression coefficient that is greater than zero and smaller than one and that is determined based on interference suppression performance of the communication device; Estimating an average transmission rate between the communication device and the target user terminal based on the received power corresponding to the target user terminal, the second average interference power, and the selection probability of the target user terminal.

2. The wireless communication control device according to claim 1.

8. The received power estimator, the selection probability determiner, the interference power estimator, and the transmission rate estimator are selecting the target user terminals one by one from the plurality of user terminals in turn, and estimating an average transmission rate for each of the target user terminals; A second average transmission rate is obtained by calculating an average of the average transmission rates estimated for each of the plurality of user terminals.

2. The wireless communication control device according to claim 1.

9. a destination determination unit that determines a destination of the communication device from among a plurality of destination candidates; a position control unit that controls the position of the communication device, the reception power estimator, the selection probability determiner, the interference power estimator, and the transmission rate estimator calculate the second average transmission rate for each of the plurality of destination candidates; the destination determination unit selects a destination candidate having the highest second average transmission rate from among the plurality of destination candidates, The location control unit moves the communication device to a location corresponding to the destination candidate selected by the destination determination unit.

9. The wireless communication control device according to claim 8.

10. estimating, by a communication device supporting spatial multiplexing, beams associated with a plurality of user terminals located within a cell of the communication device; For each of the plurality of user terminals, estimating a received power of a signal received by the communication device from the corresponding user terminal using a target beam associated with a target user terminal among the plurality of user terminals; determining a selection probability representing the probability that the target user terminal will be selected and a simultaneous selection probability representing the probability that each of the other user terminals among the plurality of user terminals will be selected when the target user terminal is selected, based on a selection rule that is predetermined for selecting user terminals in the spatial multiplexing; estimating an average interference power for a signal transmitted from the target user terminal based on the received power corresponding to each of the other user terminals and the simultaneous selection probability of each of the other user terminals; estimating an average transmission rate between the communication device and the target user terminal based on the received power corresponding to the target user terminal, the average interference power, and a selection probability of the target user terminal; A wireless communication control method comprising:

11. estimating, by a communication device supporting spatial multiplexing, beams associated with a plurality of user terminals located within a cell of the communication device; For each of the plurality of user terminals, estimating a received power of a signal received by the communication device from the corresponding user terminal using a target beam associated with a target user terminal among the plurality of user terminals; determining a selection probability representing the probability that the target user terminal will be selected and a simultaneous selection probability representing the probability that each of the other user terminals among the plurality of user terminals will be selected when the target user terminal is selected, based on a selection rule that is predetermined for selecting user terminals in the spatial multiplexing; estimating an average interference power for a signal transmitted from the target user terminal based on the received power corresponding to each of the other user terminals and the simultaneous selection probability of each of the other user terminals; estimating an average transmission rate between the communication device and the target user terminal based on the received power corresponding to the target user terminal, the average interference power, and a selection probability of the target user terminal; A transmission rate estimation program that causes a computer to execute processing.

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