JP2016167776A - Beam control method, base station, and communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow for reducing the number of beams used for communication with a radio terminal.SOLUTION: A beam control method comprises: steps S12 and S16 of estimating communication quality of a transmission path between a plurality of radio terminals and a base station; a first determining step S14 of determining a first beam weight required by a first radio terminal whose communication quality is not higher than a prescribed label in association with the first radio terminal; a determining step S17 of determining whether a second radio terminal whose communication quality is higher than the prescribed level can receive a first beam generated using any of first beam weights; a second determining step S19 of determining a second beam weight required by the second radio terminal which cannot receive the first beam to receive a beam in association with the second radio terminal; and a selecting step S21 of selecting a plurality of beam weights from the first and second beam weights.SELECTED DRAWING: Figure 10

Description

  The present invention relates to a method for controlling a beam transmitted by a base station, a base station that transmits the beam, and a communication system including the base station and a radio terminal.

  Conventionally, a method is known in which a base station having a plurality of antennas controls the directivity of a beam transmitted to a wireless terminal by adjusting the amplitude and phase of a transmission signal transmitted from each of the plurality of antennas. Patent Document 1 discloses a method for determining the number of beams used for communication with a wireless terminal based on signal-to-interference and noise ratios reported from all wireless terminals capable of communicating with a base station.

JP 2007-336547 A

  In the conventional method, the system capacity is maximized after preferentially selecting a beam having a large signal-to-interference noise ratio based on the result of transmitting a plurality of beams having predetermined characteristics to the wireless terminal. The number of beams was determined. The objective function used in this technology is system capacity, and it is not intended to ensure an environment where communication can be performed with a wireless terminal having a weak electric field.

  As a method for ensuring an environment in which communication is possible with a wireless terminal having a weak electric field, there is a conventional technique in which directivity is directed toward the terminal or randomly. By using a beam having high directivity and radio field intensity, communication quality during communication with individual wireless terminals is improved. However, when communicating with individual wireless terminals while sequentially switching a plurality of beams with high directivity and radio field strength, compared with the case of communicating simultaneously with many wireless terminals using beams with low directivity and radio field intensity, Terminal communication opportunities are reduced. As a result, there is a problem that the throughput of the entire system is lowered.

  Therefore, the present invention has been made in view of these points, and an object thereof is to reduce the number of beams used for communication with a wireless terminal.

  According to a first aspect of the present invention, there is provided a beam control method for controlling a beam weight for determining directivity of a beam transmitted from a base station to a plurality of radio terminals using a plurality of antennas, Estimating a communication quality of a transmission path between each and the base station, and one or more first wireless terminals required for the communication quality to be received by the one or more first wireless terminals having a communication quality equal to or lower than a predetermined level. A first determination step of determining one beam weight in association with each of the one or more first wireless terminals; and a wireless terminal having a communication quality higher than the predetermined level, wherein any one of the one or more first beam weights A determination step of determining whether or not the first beam generated using the beam weight can be received, and one or more second wireless terminals that cannot receive the first beam receive the beam A second determination step of determining one or more second beam weights necessary for the determination in association with the one or more second wireless terminals, and the one or more first beam weights and the one or more second beam weights. And a selection step of selecting a plurality of beam weights.

  The selecting step includes, for example, identifying communication quality when the plurality of wireless terminals receive the beam corresponding to each of the one or more first beam weights and the one or more second beam weights; The one of the plurality of wireless terminals is configured to receive at least one of the one or more first beam weights and the one or more second beam weights with a communication quality of the predetermined level or higher. Selecting a plurality of beam weights from the first beam weight and the one or more second beam weights.

  The selecting step includes: generating a plurality of combinations including a part of the plurality of beam weights; and a plurality of radio terminals receiving the beam generated using each of the plurality of beam weights. There may be included a step of specifying communication quality and a step of selecting one combination from the plurality of combinations based on a result of calculating a sum of the plurality of communication qualities.

  In the step of selecting the one combination, the sum of the plurality of communication qualities is calculated by excluding the communication qualities of the plurality of wireless terminals whose types are equal to or lower than a predetermined threshold. Also good.

  The beam control method may further include a step of transmitting the plurality of beams generated using the plurality of beam weights by time division multiplexing or frequency multiplexing.

  In the step of selecting the one combination, the number of opportunities that the plurality of wireless terminals can communicate may be used as the communication quality. In the step of generating the plurality of combinations, the plurality of combinations may be generated by assigning different weights to the plurality of beam weights. At this time, the ratio of resources allocated to each beam weight in the time division multiplexing or frequency multiplexing may be determined at the same ratio as the weighting ratio given to each of the plurality of beam weights.

  In the second determining step, a provisional beam weight necessary for each of the one or more second wireless terminals to receive the beam having a predetermined intensity is assigned to each of the one or more second wireless terminals. Determining in association with and determining the one or more second beam weights by averaging one or more provisional beam weights associated with each of the one or more second wireless terminals; You may have.

  In the step of determining the one or more second beam weights, a phase rotation is applied to one of the one or more temporary beam weights associated with each of the one or more second wireless terminals and then averaged with the other Accordingly, the one or more second beam weights may be determined.

  In the step of determining the one or more second beam weights, communication quality of the second radio terminal is set to a predetermined level using channel information between each of the one or more second radio terminals and the base station. As described above, the one or more second beam weights may be determined by searching for a second beam weight used in the base station. In the search, after obtaining an optimum beam weight for one of the second wireless terminals, a part of the beam weight is phase rotated so that the communication quality of the other second wireless terminal is equal to or higher than the specified value. The search may be performed. Moreover, you may use the search method generally used.

  The second determining step includes estimating an arrival direction of radio waves transmitted by the one or more second wireless terminals, and determining the one or more second beam weights based on the arrival direction. May be.

  According to a second aspect of the present invention, there is provided a base station capable of controlling a beam weight for determining directivity of a beam transmitted to a plurality of radio terminals using a plurality of antennas, An estimation unit that estimates communication quality of a transmission path with a base station, and one or more first wireless terminals whose communication quality estimated by the estimation unit is equal to or lower than a predetermined level are necessary for receiving the beam A first determination unit that determines one or more first beam weights in association with each of the one or more first wireless terminals, and a wireless terminal whose communication quality is higher than the predetermined level include the one or more first beam weights. A determination unit that determines whether or not a first beam using any one of the beam weights can be received, and one or more second wireless terminals that cannot receive the first beam are necessary for receiving the beam. One or more A second determining unit that determines a second beam weight in association with the one or more second wireless terminals, and a plurality of beam weights are selected from the one or more first beam weights and the one or more second beam weights. And a selection unit.

  In a third aspect of the present invention, a communication system comprising: a plurality of radio terminals; and a base station capable of controlling a beam weight that determines the directivity of a beam transmitted to the plurality of radio terminals using a plurality of antennas. The base station estimates the communication quality of a transmission path between each of the plurality of wireless terminals and the base station, and the communication quality estimated by the estimation unit is below a predetermined level. A first determining unit that determines one or more first beam weights necessary for one or more first wireless terminals to receive the beam in association with each of the one or more first wireless terminals; and the communication A determination unit that determines whether or not a wireless terminal having a quality higher than the predetermined level can receive a first beam using any one of the one or more first beam weights; and Can receive A second determination unit that determines one or more second beam weights necessary for one or more second wireless terminals to receive a beam in association with the one or more second wireless terminals; and the one or more second wireless terminals; A selection unit that selects a plurality of beam weights from one beam weight and the one or more second beam weights, wherein the plurality of radio terminals receive the beam from the base station; A wireless terminal transmission unit that transmits a response signal including information on the amplitude and phase of the signal included in the beam received by the wireless terminal reception unit in response to the reception of the beam by the wireless terminal reception unit; A communication system is provided.

  According to the present invention, it is possible to reduce the number of beams used for communication with a wireless terminal.

It is a figure for demonstrating the outline | summary of a communication system. It is a block diagram which shows the structure of a base station. It is a figure which shows the structure of a transmission / reception part. It is a table | surface which shows the relationship between several beam weight memorize | stored in the memory | storage part, and SN ratio of each radio | wireless terminal. It is a figure which shows the example of arrangement | positioning of a radio | wireless terminal. It is a table | surface which shows the relationship between beam weight Wa, Wb, Wc memorize | stored in the memory | storage part, and the SN ratio of each radio | wireless terminal. It is a figure which shows typically the relationship between the radio | wireless terminal and the range which the beam based on beam weight Wa, Wb, Wc reaches. It is a table | surface which shows the relationship between beam weight Wa, Wc, Wd, We memorize | stored in the memory | storage part, and the SN ratio of each radio | wireless terminal. It is a figure which shows typically the relationship between the radio | wireless terminal and the range which the beam based on beam weight Wa, Wc, Wd, We reaches. It is a flowchart of the beam control process in a base station.

[Overview of base station 1]
First, the outline of the communication system S of the present invention will be described with reference to FIG. The communication system S includes a base station 1 and a plurality of wireless terminals 2 (UE1 to UE4 in FIG. 1). The base station 1 transmits a beam that is a directional radio wave. The base station 1 includes a plurality of antennas, and controls the directivity of the beam to be transmitted by controlling the beam weight that determines the amplitude and phase of signals transmitted from the plurality of antennas.

  FIG. 1A shows a case where the base station 1 uses four beams suitable for each of the four wireless terminals 2. In this case, the base station 1 communicates with the four wireless terminals 2 by transmitting, for example, four beams using a time division multiplex channel or a frequency division multiplex channel. Therefore, the communication opportunity of each wireless terminal 2 is ¼ that when only one wireless terminal 2 communicates with the base station 1. Note that the area surrounded by the broken line in FIG. 1A is an area where the beam reaches, and the beam is transmitted to the wireless terminal 2 when the tip of the antenna of the wireless terminal 2 is included in the area surrounded by the broken line. Shall arrive.

  FIG. 1B shows that the base station 1 is relatively weak in directivity and can be received by all three radio terminals 2 (UE1, UE2, UE3) included in the shaded area in FIG. 1B. The case where a beam is used is shown. In this case, the base station 1 uses a beam B1 used for communication with the three radio terminals 2 relatively close to the base station 1, and a beam B2 used for communication with the radio terminal 2 (UE4) relatively far from the base station 1. Are sequentially switched to communicate with the four wireless terminals 2. Accordingly, the communication opportunity of each wireless terminal 2 is ½ that when only one wireless terminal 2 communicates with the base station 1, and is twice the communication opportunity in the case shown in FIG.

As described above, the base station 1 shares one beam based on the communication quality such as the propagation loss of the transmission path or the SN ratio determined by the distance between the base station 1 and the wireless terminal 2 and the presence or absence of an obstacle. For a plurality of wireless terminals 2 that can be used, it is possible to control so as to reduce the number of beams necessary for communication with all the wireless terminals 2 capable of communication by not using dedicated beams. .
Hereinafter, the details of the configuration and operation of the base station 1 will be described.

[Configuration and operation of base station 1]
FIG. 2 is a block diagram showing the configuration of the base station 1 of the present invention. As shown in FIG. 2, the base station 1 includes a transmission / reception unit 11, a storage unit 12, and a control unit 13, and adjusts the amplitude and phase of a signal transmitted from the transmission / reception unit 11. Control the transmission pattern of radio waves to be transmitted. Note that the communication method of the base station 1 may be any communication method, and the multiplexing method with the wireless terminal 2 may be time division multiplexing (TDD) or frequency division multiplexing (TDD). FDD (Frequency-Division-Duplex) may be used.

  The transmission / reception unit 11 includes an antenna capable of controlling the directivity of radio waves to be transmitted or received, and can concentrate radio wave radiation or increase reception sensitivity in a specific direction. FIG. 3 is a diagram illustrating a configuration of the transmission / reception unit 11. The example shown in FIG. 3 is merely an example, and the directivity may be controlled by other configurations.

  As shown in FIG. 3, the transmission / reception unit 11 includes, for example, a modulation unit 111, a signal generation unit 112, and a plurality of antenna elements 113. The modulation unit 111 modulates the input transmission data using a predetermined modulation method, generates a high frequency signal, and supplies the high frequency signal to the signal generation unit 112.

  The signal generation unit 112 multiplies the high-frequency signal input from the modulation unit 111 by a weight value corresponding to each antenna element 113 selected according to the directivity of the beam to be transmitted. A signal adjusted to an amplitude and a phase corresponding to 113 is generated. The signal generation unit 112 outputs the generated high frequency signal to the antenna element 113 and radiates the high frequency signal from the antenna element 113.

  As described above, the signal generation unit 112 adjusts the weight value of the high-frequency signal radiated from each antenna element 113, so that the transmission / reception unit 11 can control the directivity of the transmission antenna. It should be noted that the transmission antenna and the reception antenna need only have a large gain in the reception antenna at least in the direction in which the gain of the transmission antenna is large (that is, the direction in which radio waves are radiated to the wireless terminal 2). The sex patterns may be different.

  Returning to FIG. 2, the storage unit 12 is a memory such as a ROM and a RAM, or a storage medium such as a hard disk. The storage unit 12 stores a program for operating the control unit 13 and data generated when the control unit 13 operates. The storage unit 12 stores beam weights used by the transmission / reception unit 11. The beam weight is composed of a weight value corresponding to each of the plurality of antenna elements 113 included in the transmission / reception unit 11.

  The control unit 13 is, for example, a CPU, and executes a program stored in the storage unit 12 to execute a weight control unit 131, a search unit 132, an estimation unit 133, a first determination unit 134, a determination unit 135, and a second determination. Functions as a unit 136 and a selection unit 137.

  The weight control unit 131 controls the beam directivity by setting the beam weight read from the storage unit 12 in the transmission / reception unit 11. Specifically, the weight control unit 131 reads the beam weight stored in the storage unit 12 and sets the weight value included in the read beam weight to each of the plurality of antenna elements. The directivity of the beam is controlled by adjusting the amplitude and phase of the high-frequency signal transmitted from the antenna element.

  The search unit 132 searches for the wireless terminal 2. Specifically, the search unit 132 transmits a search beam including a pilot signal set to a predetermined amplitude and phase in a plurality of directions, and receives response signals from the plurality of wireless terminals 2 that have received the search beam. By doing so, a plurality of wireless terminals 2 are searched. For example, the search unit 132 acquires the beam weight for search stored in the storage unit 12, and switches the beam weight at predetermined time intervals via the weight control unit 131, thereby piloting in a 360 ° direction. A search beam including a signal is transmitted. The search unit 132 stores the identification information of the wireless terminal 2 that has received the response signal to the pilot signal in the storage unit 12 in association with the channel information included in the response signal. Here, the channel information is information related to the amplitude and phase of the pilot signal received by the wireless terminal 2.

  Note that the search unit 132 may determine the length of time for transmitting the search beam in the direction in which each wireless terminal 2 can receive based on the position of the wireless terminal 2. For example, the search unit 132 transmits a search beam to the radio terminal 2 located far from the base station 1 for a longer time than the radio terminal 2 located near the base station 1, thereby estimating the estimation unit 133 makes it possible to correctly estimate the communication quality of the transmission path.

  The estimation unit 133 estimates the communication quality of the transmission path between each of the plurality of wireless terminals and the base station 1 based on the response signal. For example, the estimation unit 133 calculates a channel matrix indicating a transfer function of a transmission path between the base station 1 and the wireless terminal 2 based on channel information included in a response signal transmitted by the wireless terminal 2. The estimation unit 133 may calculate a channel matrix by receiving a predetermined signal having a known amplitude and phase from the wireless terminal 2 instead of using the response signal.

  Subsequently, the estimation unit 133 estimates the propagation loss of the transmission path between the base station 1 and the wireless terminal 2 based on the calculated channel matrix. The estimation unit 133 classifies the plurality of wireless terminals 2 into a plurality of groups based on the estimated propagation loss. Specifically, the estimation unit 133 identifies the wireless terminal 2 whose estimated propagation loss is larger than a predetermined threshold as the wireless terminal 2 whose communication quality is equal to or lower than a predetermined level (hereinafter referred to as the first wireless terminal 2a). . In addition, the estimation unit 133 identifies one or more wireless terminals 2 whose estimated propagation loss is smaller than a predetermined threshold as wireless terminals 2 whose communication quality is higher than a predetermined level (hereinafter referred to as second wireless terminal 2b). .

  The first determination unit 134 determines and determines the first beam weight necessary for the first wireless terminal 2a to receive the beam in the descending order of the estimated propagation loss in association with each first wireless terminal 2a. The first beam weight is stored in the storage unit 12 in association with the first wireless terminal 2a. Further, the first determination unit 134 calculates an estimated value of the SN ratio when the first wireless terminal 2a receives a beam transmitted using the first beam weight, and stores the calculated estimated value in the storage unit 12. Remember. For example, the first determination unit 134 calculates the estimated value of the SN ratio by estimating the received power of the beam received by the first wireless terminal 2 a based on the propagation loss estimated by the estimation unit 133.

  The first determination unit 134 sets the respective phases of the high-frequency signals transmitted from the plurality of antenna elements to the same phase, so that the communication quality of the beam received by the first radio terminal 2a from the base station 1 is a predetermined level. A first beam weight that is larger is determined. Here, the first determination unit 134 may set the amplitude of the high-frequency signal transmitted from each antenna element so as to be proportional to the channel coefficient corresponding to each antenna element in the channel matrix, for example. By doing so, the SN ratio can be increased. Note that the first determination unit 134 may set the amplitude of the high-frequency signal transmitted from all antenna elements to 1.

  The determination unit 135 includes one or more second wireless terminals 2b whose communication quality is higher than a predetermined level (for example, the wireless terminal 2 closer to the base station 1 than the first wireless terminal 2a) determined by the first determination unit 134. It is determined whether or not the transmitted beam can be received using any one of the first beam weights. Specifically, the determination unit 135 determines whether or not the communication quality (for example, the estimated value of received power or the SN ratio) when the second radio terminal 2b receives the first beam is greater than a predetermined level. To do. The determination unit 135 causes the storage unit 12 to store information indicating that the beam transmitted using the first beam weight can be received in association with the second wireless terminal 2b that has determined that the communication quality is greater than a predetermined level. Further, the determination unit 135 calculates an estimated value of the SN ratio when the second wireless terminal 2b receives a beam transmitted using the first beam weight, and causes the storage unit 12 to store the calculated estimated value. .

  The second determination unit 136 sets one or more second beam weights necessary for one or more second wireless terminals 2b that cannot receive a beam transmitted using the first beam weight to receive a beam to one or more The determination is made in association with each of the second wireless terminals 2b. The second determination unit 136 stores the determined second beam weight in the storage unit 12 in association with the second wireless terminal 2b.

  Here, for example, the second wireless terminal 2b is considered to be closer to the base station 1 than the first wireless terminal 2a, and the second wireless terminal 2b does not use a beam having a dedicated directivity for the plurality of second wireless terminals 2b. There is a possibility that even a beam having directivity that can be received by the terminal 2b can be received. Therefore, the second determination unit 136 calculates a second beam weight that can generate a beam that can be received by the plurality of second wireless terminals 2b.

  The second determination unit 136 uses the channel information between each of the one or more second wireless terminals 2b and the base station 1 so that the communication quality of the second wireless terminal 2b is equal to or higher than a predetermined level. One or more second beam weights may be determined by searching for a second beam weight used for multiplication in the signal generator 112 of the station 1. In the search, the second determination unit 136 obtains the optimum beam weight for one of the second radio terminals 2b, and then the communication quality of the other second radio terminal 2b becomes equal to or higher than the specified value. The search may be performed by rotating a part of the beam weight. The second determination unit 136 may use other commonly used search methods.

  The second determination unit 136 calculates an estimated value of the SN ratio when the second wireless terminal 2b receives a beam transmitted using the second beam weight, and stores the calculated estimated value in the storage unit 12. . Details of the second beam weight calculation method will be described later.

  The selection unit 137 selects a plurality of beam weights from one or more first beam weights and one or more second beam weights stored in the storage unit 12. Specifically, the selection unit 137 includes the first beam weight stored in the storage unit 12 and the first beam weight so that all of the plurality of wireless terminals 2 can receive at least one of the beams with a communication quality equal to or higher than a predetermined level. A plurality of beam weights are selected from the second beam weights. In addition, the selection unit 137 specifies communication quality when a plurality of wireless terminals 2 receive beams corresponding to the first beam weight and the second beam weight.

  For example, the selection unit 137 specifies the communication quality based on the estimated value of the S / N ratio when each wireless terminal 2 receives a beam transmitted using each beam weight stored in the storage unit 12. The selection unit 137 specifies a combination of usable beam weights from among the plurality of first beam weights and second beam weights based on the specified communication quality. The selection unit 137 transmits a plurality of beams generated by using a plurality of beam weights included in the specified combination, so that the S / N ratio when all the wireless terminals 2 receive any one of the plurality of beams. A combination of a plurality of beam weights is specified so that the estimated value of becomes equal to or more than 0 dB. The transmission / reception unit 11 transmits the beam generated using the plurality of beam weights selected by the selection unit 137 so that all the radio terminals 2 can receive the beam by either time division multiplexing or frequency division multiplexing.

  FIG. 4 is a table showing a relationship between a plurality of beam weights stored in the storage unit 12 and the SN ratio of each wireless terminal 2. FIG. 5 is a diagram showing an arrangement example of the wireless terminals 2 corresponding to the table shown in FIG. UE1 in FIG.4 and FIG.5 is the 1st radio | wireless terminal 2a. UE2 to UE7 are second radio terminals 2b.

  A circle in the “first check” column in FIG. 4 indicates the first wireless terminal 2a. A circle in the “second check” column indicates that each wireless terminal 2 can communicate with one of the beam weights.

  Wa to We in FIG. 4 indicate beam weights. The broken lines with Wa to We in FIG. 5 indicate the ranges where beams corresponding to the respective beam weights reach. Wa is the first beam weight determined by the first determination unit 134 and is necessary for UE1 to receive the beam. The SN ratio when UE1 receives the beam transmitted using the beam weight Wa is 3 dB. Since the S / N ratio when UE2 to UE7 receive a beam transmitted using the beam weight Wa is less than 0 dB, an X mark is given.

  Wb to We are second beam weights determined by the second determination unit 136 and necessary for the plurality of second wireless terminals 2b to receive beams. The beam transmitted using Wb can be received by UE2, UE5 and UE7. The beam transmitted using Wc can be received by UE3, UE4, and UE6. The beam transmitted using Wd can be received by UE2, UE4, UE6, and UE7. The beam transmitted using We can be received by UE5 and UE7.

When the following beam weights are combined among Wa to We, all the radio terminals 2 of UE1 to UE7 can receive any one of the beams.
(1) Wa, Wb, Wc
(2) Wa, Wc, Wd, We

  In this way, when there are a plurality of combinations for all the terminals to receive the beam, the selection unit 137 generates a plurality of combinations including a part of the plurality of beam weights. Specifically, the selection unit 137 identifies the communication quality (for example, the SN ratio or the throughput) of each of the plurality of wireless terminals 2 that have received the beam generated using each of the plurality of beam weights, and performs each communication. Based on the result of calculating the sum of quality, one combination is selected from a plurality of combinations.

  FIG. 6 is a table showing the relationship between the beam weights Wa, Wb, Wc stored in the storage unit 12 and the SN ratio of each wireless terminal 2. FIG. 7 is a diagram schematically illustrating a relationship between the wireless terminal 2 and a range in which a beam based on the beam weights Wa, Wb, and Wc reaches. As shown in FIG. 7, UE1 is farthest from base station 1 and receives a beam corresponding to beam weight Wa dedicated to UE1. UE2, UE5, and UE7 receive a beam corresponding to the beam weight Wb, and UE3, UE4, and UE6 receive a beam corresponding to the beam weight Wc. In this case, as shown in FIG. 6, in the combination of Wa, Wb, and Wc, the SN ratio of UE1 is 3 dB, the SN ratio of UE2 is 5 dB, the SN ratio of UE3 is 5 dB, the SN ratio of UE4 is 7 dB, and the SN ratio of UE5 The ratio is 3 dB, the SN ratio of UE6 is 2 dB, the SN ratio of UE7 is 3 dB, and the sum of the SN ratios is 28 dB.

  FIG. 8 is a table showing the relationship between the beam weights Wa, Wc, Wd, We stored in the storage unit 12 and the SN ratio of each wireless terminal 2. FIG. 9 is a diagram schematically illustrating a relationship between the wireless terminal 2 and a range in which a beam based on the beam weights Wa, Wc, Wd, and We reaches. In FIG. 9, UE3, UE4 and UE6 receive a beam corresponding to the beam weight Wc, UE2, UE4, UE6 and UE7 receive a beam corresponding to the beam weight Wd, and UE5 and UE7 receive the beam weight We. The beam corresponding to is received. In this case, as shown in FIG. 8, in the combination of Wa, Wc, Wd, and We, the SN ratio of UE1 is 3 dB, the SN ratio of UE2 is 3 dB, the SN ratio of UE3 is 5 dB, the SN ratio of UE4 is 7 dB, UE5 The SN ratio of UE6 is 2 dB, the SN ratio of UE6 is 7 dB, the SN ratio of UE7 is 4 dB, and the sum of the SN ratios is 31 dB.

  As described above, in the case of the examples shown in FIGS. 4 to 9, the sum of SN ratios when using a combination of Wa, Wb, and Wc is 28 dB, and when using a combination of Wa, Wc, Wd, and We The sum of the S / N ratios is 31 dB. Therefore, the selection unit 137 selects a combination of Wa, Wc, Wd, and We having a large sum of SN ratios.

  In the above calculation of the sum of the S / N ratios, when there is a plurality of beam weights with which a single wireless terminal 2 can receive a beam, the S / N ratio at the beam weight that can obtain the maximum S / N ratio is calculated. However, the S / N ratio in a plurality of beam weights capable of receiving a beam may be used for calculating the sum.

Further, the selection unit 137 may set an upper limit on the maximum value of the SN ratio corresponding to each wireless terminal 2 when calculating the sum of the SN ratios in each combination of beam weights. For example, even when the estimated value of the SN ratio of UE1 becomes a high value such as 40 dB, the actual communication speed is determined by the value of modulation and coding, and the communication speed when the SN ratio is 40 dB is the SN ratio. Is considered to be the same as the communication speed in the case of 30 dB. In such a case, when the SN ratio used for calculating the sum of the SN ratios exceeds 30 dB, the selection unit 137 calculates the sum of the SN ratios assuming that the SN ratio is 30 dB.
The selection unit 137 may use an estimated value of throughput instead of the SN ratio as a determination criterion. The estimated value of the throughput can be held in the storage unit 12 as a function or a reference table as one-to-one correspondence with the SN ratio.

  When selecting one combination from a plurality of combinations, the selection unit 137 excludes the communication quality of the plurality of wireless terminals 2 from the wireless terminals 2 of a type whose communication rate is equal to or lower than a predetermined threshold, and performs a plurality of communication You may calculate the sum of quality. For example, when the wireless terminal 2 includes a terminal that requires a low communication rate and does not require a large S / N ratio, such as a sensor module, when calculating the sum of a plurality of S / N ratios, The SN ratio corresponding to such a type of wireless terminal 2 may not be included in the sum.

  When the selection unit 137 selects one combination from a plurality of combinations, the selection unit 137 may use, as the communication quality, the number of opportunities that the plurality of wireless terminals 2 can communicate. When the number of beam weights included in the combination of beam weights increases, the opportunity (time or frequency width) at which each wireless terminal 2 can communicate is reduced compared to the case where there is only one beam weight. Therefore, a combination of beam weights may be selected based on a value obtained by dividing the sum of the SN ratios by the number of beam weights included in the combination.

  In the case of the above example shown in FIG. 4, the sum of the SN ratios when using a combination of three beam weights Wa, Wb, and Wc is 28 dB, and the SN ratio per one beam weight is 28 ÷ 3. = 9.33. On the other hand, when four combinations of Wa, Wc, Wd, and We are used, the sum of the SN ratios is 31 dB, and the SN ratio per beam weight is 31 ÷ 4 = 7.75. Therefore, the selection unit 137 selects a combination of Wa, Wb, and Wc when giving priority to increasing the communication opportunity of the wireless terminal 2.

  The selection unit 137 may generate a plurality of combinations by assigning different weights to the plurality of beam weights. In this case, the selection unit 137 determines the ratio of resources to be allocated to each beam weight in time division multiplexing or frequency multiplexing at the same ratio as the weighting ratio given to each of the plurality of beam weights. For example, the selection unit 137 may calculate the sum of the SN ratios by weighting based on the use frequency of each beam weight in each combination, and may select the combination that maximizes the calculated sum. For example, in the combination of three beam weights Wa, Wb, and Wc, the usage ratios (for example, time or frequency allocation ratios) of Wa, Wb, and Wc are αa, αb, and αc, respectively. When the sum of the SN ratios for each beam weight is Sa, Sb, and Sc, the selection unit 137 selects a combination of beam weights that maximizes αa · Sa + αb · Sb + αc · Sc.

[Second Beam Weight Calculation Method]
The second determination unit 136 can calculate beam weights that can be received by the plurality of second wireless terminals 2b by, for example, the following method 1 or method 2.

(Method 1)
When the SN ratio of the second radio terminal 2b is within 3 dB from the lowest level at which a beam can be received, the second determination unit 136 calculates a dedicated beam weight for the second radio terminal 2b, and the beam weight Is determined as the second beam weight.

  When the SN ratio of the second wireless terminal 2b is within the range of 3 dB to 4.7 dB from the lowest level at which the beam can be received, the second determining unit 136 transmits the second wireless terminal 2b to the second wireless terminal 2b. Are selected two by two, and the optimum beam weight is provisionally calculated for each. The second determination unit 136 calculates the average value of the two provisional beam weights, thereby obtaining beam weights that can generate beams that can be received by the two second radio terminals 2b as the second beam. Decide on weight. Since the determined second beam weight is an average value of the two beam weights, the reception power at the two second wireless terminals 2b is reduced by about 3 dB. However, since the S / N ratio of the two second wireless terminals 2b is within the range of 3 dB to 4.7 dB from the lowest level at which the beam can be received, the two second wireless terminals 2b use the second beam weight. The generated beam can be received.

  When there are n second wireless terminals 2b whose S / N ratio is within the range of 3 dB to 4.7 dB from the lowest level at which a beam can be received, there are n (n−1) / 2 combinations. The second determination unit 136 calculates a second beam weight for each combination.

  When the S / N ratio of the second wireless terminal 2b is within the range of 4.7 dB to 6.0 dB from the lowest level at which the beam can be received, the second determining unit 136 includes three units from the second wireless terminal 2b. The second radio terminal 2b is selected, and the optimum beam weight for each is tentatively calculated. The second determination unit 136 calculates the average value of the calculated three provisional beam weights to obtain beam weights that can generate beams that can be received by the three second wireless terminals 2b as the second beam. Decide on weight.

In calculating the average value of the provisional beam weight, one of the one or more provisional beam weights associated with each of the one or more second wireless terminals 2b is subjected to phase rotation and then averaged with the other. Thus, one or more second beam weights may be determined. Specifically, when the weight matrix W ₁ = [w _1a , w _1b , w _1c , w _1d ] and W ₂ = [w _2a , w _2b , w _2c , w _2d ] are averaged, the weight is , W _{1 + 2} = [(w _1a ^* e ^jθ + w _2a ) / 2, (w _1b ^* e ^jθ + w _2b ) / 2, (w _1c ^* e ^jθ + w _2c ) / 2, (w _1d ^* e ^jθ + w _2d ) / 2], and θ is the amount of phase rotation. When performing simple averaging, θ = 0.

Depending on the phase relationship between W ₁ and W ₂ , when a simple average is performed, there is a possibility that the phase is reversed at the location of the wireless terminal 2 and the signals are weakened. In order to prevent this, it is preferable to change the phase difference. Regarding how to give the phase difference, for example, a pattern from 0 ° to 360 ° in 10 ° steps may be created as candidates. The second determination unit 136 selects a phase rotation amount that improves the communication quality of the plurality of wireless terminals 2. Note that the second determination unit 136 may directly calculate θ that maximizes the reception power of the wireless terminal 2 based on channel information of the communication path with the wireless terminal 2.

(Method 2)
The second determination unit 136 estimates the arrival direction of the radio wave transmitted by the second wireless terminal 2b, and determines the second beam weight based on the estimated arrival direction. Specifically, the second determination unit 136 can use a known Directionally Constrained Minimization of Power (DCMP) adaptive array technique.

[Beam control method executed by base station 1]
FIG. 10 is a flowchart of the beam control process in the base station 1. Hereinafter, with reference to FIG. 10, the procedure of the beam control process in the base station 1 will be described.

  First, the search unit 132 searches for the wireless terminal 2 by sequentially transmitting beams having predetermined directivities in a plurality of directions, and receives a response signal from the wireless terminal 2 (S11). The estimating unit 133 estimates the communication quality of the transmission path between the base station 1 and the wireless terminal 2 based on the received response signal (S12).

  Subsequently, the first determination unit 134 identifies the first wireless terminal 2a whose communication quality estimated in S12 is equal to or lower than a predetermined level, and associates the first wireless terminal 2a with the identification information of the first wireless terminal 2a stored in the storage unit 12. A first check flag is assigned (S13). The first determination unit 134 determines a first beam weight necessary for the first wireless terminal 2a to receive a beam for each of the first wireless terminals 2a to which the first check flag is assigned (S14). When the first determination unit 134 determines the first beam weight, the first determination unit 134 assigns a second check flag in association with the identification information of the first wireless terminal 2a that can receive the beam generated using the first beam weight (S15). .

  Subsequently, the determination unit 135 estimates the communication quality when each of the second wireless terminals 2b not assigned with the first check flag receives a beam generated using the first beam weight (S16). . The determination unit 135 determines whether or not the estimated communication quality is equal to or higher than a predetermined level (S17). When the estimated communication quality is equal to or higher than the predetermined level (Yes in S17) and the second wireless terminal 2b can receive the beam generated using the first beam weight, the determination unit 135 stores the beam in the storage unit 12. A second check flag is assigned in association with the identification information of the second wireless terminal 2b that has been set (S18). If the estimated communication quality is lower than the predetermined level (No in S17), the determination unit 135 proceeds to S19 without proceeding to S18.

  Subsequently, the second determination unit 136 extracts the second wireless terminal 2b to which the second check flag is not assigned, and determines a second beam weight for the extracted second wireless terminal 2b to receive a beam ( S19). By using either the first beam weight or the second beam weight determined by the above procedure, all the radio terminals 2 can receive the beam.

  Subsequently, in order to determine which beam weight is preferable to be used among the determined plurality of beam weights, the selection unit 137 transmits the beam generated using each beam weight to each wireless terminal 2. Is estimated (S20). Specifically, the selection unit 137 estimates the communication quality by calculating the S / N ratio or the throughput when each wireless terminal 2 receives a beam generated using each beam weight. The selection unit 137 selects a beam weight for enabling all the wireless terminals 2 to receive a beam based on the estimated communication quality (S21).

  Here, when there are a plurality of beam weight combinations for enabling all the wireless terminals 2 to receive the beam (Yes in S22), the optimum combination is selected using any of the various methods described above. (S23).

  In the above description, in S19, the second determination unit 136 determines the second beam weight for the second wireless terminal 2b not assigned with the second check flag to receive the beam. The second determination unit 136 may further determine an optimum beam weight for the second wireless terminal 2b to which the second check flag is assigned.

[Effect in this embodiment]
As described above, the base station 1 in the present embodiment first determines the first beam weight necessary for the first wireless terminal 2a having low communication quality to receive the beam, and then the communication quality is the first. A second beam weight that can be received by the second wireless terminal 2b higher than the wireless terminal 2a is determined. At this time, the base station 1 sets a beam weight that allows the plurality of second radio terminals 2b to receive the beam as the second beam weight. In this way, for example, for the second radio terminal 2b that is relatively close to the base station 1, a beam weight with a low directivity in which the reception power at each second radio terminal 2b is suppressed to be small is used. Thus, a plurality of second wireless terminals 2b can share one second beam weight. Therefore, since the number of beam weights to be used can be reduced, the communication opportunity of the wireless terminal 2 can be increased.

  In addition, when there are a plurality of beam weight combinations that allow all the radio terminals 2 to receive beams, the base station 1 can select an optimal combination based on the communication quality. In this way, the base station 1 can reduce the number of beam weights and ensure good communication quality.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above embodiment. In particular, the specific embodiments of the distribution / integration of the devices are not limited to those illustrated above, and all or a part thereof may be added in arbitrary units according to various additions or according to functional loads. It can be configured functionally or physically distributed and integrated.

DESCRIPTION OF SYMBOLS 1 Base station 2 Wireless terminal 11 Transmission / reception part 12 Storage part 13 Control part 111 Modulation part 112 Signal generation part 113 Antenna element 131 Weight control part 132 Search part 133 Estimation part 134 First determination part 135 Determination part 136 Second determination part 137 Selection S Communication system

Claims (14)

A beam control method for controlling a beam weight for determining directivity of a beam transmitted from a base station to a plurality of wireless terminals using a plurality of antennas,
Estimating communication quality of a transmission path between each of the plurality of wireless terminals and the base station;
One or more first beam weights required for one or more first wireless terminals having the communication quality equal to or lower than a predetermined level to receive the beam are determined in association with each of the one or more first wireless terminals. A first determination step;
A determination step of determining whether a wireless terminal having a communication quality higher than the predetermined level can receive a first beam generated using any one of the one or more first beam weights;
A second determining step of determining, in association with the one or more second wireless terminals, one or more second beam weights necessary for one or more second wireless terminals that cannot receive the first beam to receive the beam; ,
A selection step of selecting a plurality of beam weights from the one or more first beam weights and the one or more second beam weights;
A beam control method. The selection step includes
Identifying communication quality when the plurality of wireless terminals receive the beam corresponding to each of the one or more first beam weights and the one or more second beam weights;
The one of the plurality of wireless terminals is configured to receive at least one of the one or more first beam weights and the one or more second beam weights with a communication quality of the predetermined level or higher. Selecting a plurality of beam weights from the first beam weight and the one or more second beam weights;
Having
The beam control method according to claim 1. The selection step includes
Generating a plurality of combinations including a portion of the plurality of beam weights;
Identifying a plurality of communication qualities of the plurality of wireless terminals that have received the beam generated using each of the plurality of beam weights;
Selecting one combination from the plurality of combinations based on the result of calculating the sum of the plurality of communication qualities;
The beam control method according to claim 2. In the step of selecting the one combination, calculating the sum of the plurality of communication qualities by excluding the communication qualities in the types of wireless terminals whose communication rate is equal to or lower than a predetermined threshold among the plurality of wireless terminals.
The beam control method according to claim 3. Further comprising transmitting the plurality of beams generated using the plurality of beam weights by time division multiplexing or frequency multiplexing.
The beam control method according to claim 3 or 4. In the step of selecting the one combination, the number of opportunities that the plurality of wireless terminals can communicate is used as the communication quality.
The beam control method according to claim 5. In the step of generating the plurality of combinations, the plurality of combinations are generated by weighting each of the plurality of beam weights differently.
The beam control method according to claim 5 or 6. Determining a ratio of resources to be allocated to each beam weight in the time division multiplexing or frequency multiplexing in the same ratio as the weighting ratio given to each of the plurality of beam weights;
The beam control method according to claim 7. The second determining step includes
Determining a provisional beam weight necessary for each of the one or more second wireless terminals to receive the beam of a predetermined intensity in association with each of the one or more second wireless terminals;
Determining the one or more second beam weights by averaging one or more provisional beam weights associated with each of the one or more second wireless terminals;
Having
The beam control method according to any one of claims 1 to 8. In the step of determining the one or more second beam weights, a phase rotation is applied to one of the one or more temporary beam weights associated with each of the one or more second wireless terminals and then averaged with the other Determining the one or more second beam weights;
The beam control method according to claim 9. In the step of determining the one or more second beam weights, communication quality of the second radio terminal is set to a predetermined level using channel information between each of the one or more second radio terminals and the base station. As described above, the one or more second beam weights are determined by searching for the second beam weights used in the base station.
The beam control method according to claim 9. The second determining step includes
Estimating an arrival direction of radio waves transmitted by the one or more second wireless terminals;
Determining the one or more second beam weights based on the direction of arrival;
Having
The beam control method according to any one of claims 1 to 8. A base station capable of controlling a beam weight that determines the directivity of a beam transmitted to a plurality of wireless terminals using a plurality of antennas,
An estimation unit that estimates communication quality of a transmission path between each of the plurality of wireless terminals and the base station;
The one or more first radio terminals whose communication quality estimated by the estimation unit is equal to or lower than a predetermined level are set to one or more first beam weights necessary for the beam to be received by the one or more first radio terminals. A first deciding unit for deciding in association with each;
A determination unit that determines whether or not a wireless terminal having the communication quality higher than the predetermined level can receive a first beam using any one of the one or more first beam weights;
A second determination unit that determines one or more second beam weights necessary for one or more second wireless terminals that cannot receive the first beam to receive a beam in association with the one or more second wireless terminals; ,
A selector for selecting a plurality of beam weights from the one or more first beam weights and the one or more second beam weights;
Base station with A communication system comprising: a plurality of wireless terminals; and a base station capable of controlling a beam weight that determines the directivity of a beam transmitted to the plurality of wireless terminals using a plurality of antennas,
The base station
An estimation unit that estimates communication quality of a transmission path between each of the plurality of wireless terminals and the base station;
The one or more first radio terminals whose communication quality estimated by the estimation unit is equal to or lower than a predetermined level are set to one or more first beam weights necessary for the beam to be received by the one or more first radio terminals. A first deciding unit for deciding in association with each;
A determination unit that determines whether or not a wireless terminal having the communication quality higher than the predetermined level can receive a first beam using any one of the one or more first beam weights;
A second determination unit that determines one or more second beam weights necessary for one or more second wireless terminals that cannot receive the first beam to receive a beam in association with the one or more second wireless terminals; ,
A selector for selecting a plurality of beam weights from the one or more first beam weights and the one or more second beam weights;
Have
The plurality of wireless terminals are:
A wireless terminal receiver for receiving the beam from the base station;
A wireless terminal transmitter that transmits a response signal including information on the amplitude and phase of the signal included in the beam received by the wireless terminal receiver in response to the reception of the beam by the wireless terminal receiver;
A communication system.

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