JP5620873B2 - Base station, peripheral base station and communication system - Google Patents

Description

  The present invention relates to a technique for communicating using a plurality of antennas.

  Conventionally, various techniques relating to wireless communication have been proposed. For example, Patent Document 1 discloses a technique related to LTE (Long Term Evolution). LTE is also referred to as “E-UTRA”.

JP 2008-099079 A

  In a communication system such as LTE, an adaptive array antenna system that adaptively controls the directivity of an array antenna including a plurality of antennas may be employed. When transmitting a signal to a communication terminal using the adaptive array antenna system, the base station controls transmission directivities at a plurality of antennas based on known signals from the communication terminal.

  When a base station transmits a signal using a adaptive array antenna method to a communication terminal having a high moving speed, the base station transmits an array based on the known signal after the communication terminal transmits the known signal. There is a possibility that the position of the communication terminal changes greatly before the communication terminal receives a signal to be transmitted by controlling the transmission directivity of the antenna. In such a case, the accuracy in controlling the transmission directivity of the array antenna at the base station is lowered, and the signal from the base station is difficult to reach the communication terminal. As a result, the transmission performance of the base station may be degraded.

  Therefore, the present invention has been made in view of the above points, and an object thereof is to provide a technique capable of improving the transmission performance of a base station.

  In order to solve the above problems, a base station according to the present invention is a base station that communicates with a communication terminal using communication frames in which a plurality of types of frame configurations are defined, and has a plurality of antennas. When transmitting a signal, a communication unit that controls transmission directivity at the plurality of antennas based on a known signal from the communication terminal, a moving speed acquisition unit that acquires a moving speed for the communication terminal, A frame configuration determining unit that determines a frame configuration to be used by the base station for the communication frame based on a moving speed, and for each of the plurality of types of frame configurations, a communication terminal transmits a known signal. An uplink communication period for known signals, and at least one uplink communication period in which data uplink communication is performed and data downlink communication appearing after the known signal uplink communication period are performed. At least one downlink communication period, and when the communication unit transmits data to the communication terminal in the at least one downlink communication period, the communication unit transmits the data from the communication terminal in the known signal uplink communication period. The transmission directivity at the plurality of antennas is controlled based on the received known signals, and the frame configuration determination unit, when there is a communication terminal having the moving speed larger than the first threshold, The base station is configured so that a period between the known signal uplink communication period and the first downlink communication period of the at least one downlink communication period is shorter than a frame configuration currently used by the base station. The frame configuration to be used is changed, and the communication unit performs communication in which the moving speed is greater than the first threshold when the frame configuration used by the base station is changed. For the end, data is transmitted in a downlink communication period prior to the at least one downlink communication period included in the frame configuration before the change among the at least one downlink communication period included in the frame configuration after the change. .

  Further, in one aspect of the base station according to the present invention, the communication unit may be configured to communicate with a communication terminal whose moving speed is greater than the first threshold when the frame configuration used by the base station is changed. Thus, data is transmitted in the first downlink communication period of the at least one downlink communication period included in the changed frame configuration.

  Moreover, in one aspect of the base station according to the present invention, a distance acquisition unit that acquires a distance between the communication terminal and the base station is further provided, and the first speed compared with the moving speed of the communication terminal is provided. The threshold is set smaller as the distance for the communication terminal is larger.

  In the aspect of the base station according to the present invention, the at least one downlink communication period includes a plurality of downlink communication periods, and the communication unit is a communication terminal whose moving speed is smaller than the first threshold value. In the plurality of downlink communication periods, data is transmitted in a downlink communication period later than a downlink communication period in which data is transmitted to a communication terminal whose movement speed is greater than the first threshold value.

  Further, in one aspect of the base station according to the present invention, the communication unit is configured to provide the plurality of communication terminals for the communication terminal whose moving speed is smaller than a second threshold smaller than the first threshold. In a downlink communication period, data is transmitted in a downlink communication period after a downlink communication period in which the moving speed is greater than the second threshold value and smaller than the first threshold value. To do.

  In the aspect of the base station according to the present invention, the frame configuration determination unit may include a communication terminal in which the moving speed is greater than a second threshold value that is greater than the first threshold value. Then, the period between the known signal uplink communication period and the leading downlink communication period of the at least one downlink communication period is shorter than the frame configuration currently used by the base station, The frame configuration used by the base station is changed.

  Also, the peripheral base station according to the present invention is a peripheral base station located in the vicinity of the base station, and notifies the changed frame configuration when the frame configuration used in the base station is changed. Notification information is input to the neighboring base station, and the neighboring base station is currently used by the neighboring base station when the notification information is inputted to the input unit. In the at least one uplink communication period included in the frame configuration, the uplink communication period overlapping with the at least one downlink communication period included in the frame configuration notified by the notification information is not used for uplink communication with the communication terminal. And a determination unit for determining.

  Further, the communication system according to the present invention is a communication system including a plurality of base stations that communicate with a communication terminal using communication frames in which a plurality of types of frame configurations are defined, and each of the plurality of base stations includes: A communication unit that has a plurality of antennas and controls transmission directivity at the plurality of antennas based on a known signal from the communication terminal when transmitting a signal to the communication terminal, and a moving speed of the communication terminal And a frame configuration determining unit that determines a frame configuration used by the base station for the communication frame based on the moving speed, and each of the plurality of types of frame configurations includes: An uplink communication period for a known signal for a communication terminal to transmit a known signal, and an uplink communication of data that appears after the uplink communication period for the known signal is small And at least one downlink communication period in which data downlink communication is performed, and in each of the plurality of base stations, the communication unit communicates in the at least one downlink communication period. When transmitting data to the terminal, the transmission directivity at the plurality of antennas is controlled based on the known signal received from the communication terminal during the known signal uplink communication period, and each of the plurality of base stations The frame configuration determination unit, when there is a communication terminal whose moving speed is larger than a threshold value, the first downlink communication in the known signal uplink communication period and the at least one downlink communication period Change the frame configuration used by the base station so that the period between the frames is shorter than the frame configuration currently used by the base station, In each base station, when the frame configuration used by the base station is changed, the communication unit is included in the changed frame configuration for a communication terminal whose moving speed is larger than the threshold value. Data is transmitted in a downlink communication period before the at least one downlink communication period included in the frame configuration before the change in the at least one downlink communication period.

  Further, a communication system according to the present invention includes a base station that communicates with a communication terminal using a communication frame in which a plurality of types of frame configurations are defined, and a periphery of the base station that communicates with a communication terminal using the communication frame. Each of the plurality of types of frame configurations includes a known signal uplink communication period for transmitting a known signal, and the known signal uplink communication. At least one uplink communication period in which data uplink communication is performed and at least one downlink communication period in which data downlink communication is performed, which appears after the period, and the base station has a plurality of antennas. When transmitting a signal to a communication terminal, a communication unit that controls transmission directivity with the plurality of antennas based on a known signal from the communication terminal, and a communication terminal And a frame configuration determining unit that determines a frame configuration to be used by the base station for the communication frame based on the moving speed, and the communication unit includes the at least When transmitting data to a communication terminal in one downlink communication period, the transmission directivity at the plurality of antennas is controlled based on a known signal received from the communication terminal during the known signal uplink communication period, The frame configuration determination unit, when there is a communication terminal having a moving speed greater than a threshold, the known signal uplink communication period, and the leading downlink communication period of the at least one downlink communication period, The frame configuration used by the base station is changed so that the period between the frames is shorter than the frame configuration currently used by the base station, and the communication When the frame configuration used by the base station is changed, among the at least one downlink communication period included in the changed frame configuration for a communication terminal whose moving speed is greater than the threshold value , Transmitting data in a downlink communication period prior to the at least one downlink communication period included in the frame structure before the change, and notifying the frame structure after the change when the frame structure used in the base station is changed Notification information is input to the neighboring base station, and the neighboring base station is configured to input an input unit to which the notification information is input, and when the notification information is input to the input unit, the neighboring base station In the at least one uplink communication period included in the frame configuration to be used, the at least one downlink included in the frame configuration notified by the notification information The uplink communication period that overlaps with the communication period includes a determination unit that determines not to use for uplink communication with the communication terminal.

  According to the present invention, it is possible to improve the transmission performance of the base station.

It is a figure which shows the structure of the communication system which concerns on embodiment. It is a figure which shows the structure of the base station which concerns on embodiment. It is a figure which shows the basic composition of a TDD frame. It is a figure which shows multiple types of frame structure about a TDD frame. It is a figure which shows the detailed structure of a TDD frame. It is a figure which shows a mode that a SRS transmission band performs frequency hopping. It is a flowchart which shows operation | movement of the base station which concerns on embodiment. It is a figure which shows the moving speed of a communication terminal. It is a figure which shows the example of allocation of the downlink radio | wireless resource with respect to a communication terminal. It is a figure which shows the example of allocation of the downlink radio | wireless resource with respect to a communication terminal. It is a figure which shows the transmission / reception timing of the communication terminal with a small distance with a base station, and the communication terminal with a large distance with a base station. It is a figure which shows the structure of the modification of the base station which concerns on embodiment. It is a figure which shows the modification of the 1st and 2nd threshold value which concerns on embodiment. It is a figure for demonstrating the frame structure used in each base station when the frame structure in a certain base station is changed.

  FIG. 1 is a diagram showing a configuration of a communication system 100 according to the present embodiment. The communication system 100 is, for example, LTE in which a TDD (Time Division Duplexing) method is adopted as a duplex method, and includes a plurality of base stations 1. Each base station 1 communicates with a plurality of communication terminals 2. In LTE, OFDMA (Orthogonal Frequency Division Multiple Access) is used for downlink communication, and SC-FDMA (Single Carrier-Frequency Division Multiple Access) is used for uplink communication. Therefore, the OFDMA scheme is used for transmission from the base station 1 to the communication terminal 2, and the SC-FDMA scheme is used for transmission from the communication terminal 2 to the base station 1. In the OFDMA scheme, an OFDM (Orthogonal Frequency Division Multiplexing) signal in which a plurality of subcarriers orthogonal to each other are combined is used.

  As shown in FIG. 1, the service area 10 of each base station 1 partially overlaps with the service area 10 of the neighboring base station 1 located in the vicinity thereof. In FIG. 1, only four base stations 1 are shown, so there are only two or three neighboring base stations 1 for one base station 1, but in reality one base station 1 For example, there may be six neighboring base stations 1 for the station 1.

  The plurality of base stations 1 are connected to a network (not shown) and can communicate with each other through the network. Further, a server device (not shown) is connected to the network, and each base station 1 can communicate with the server device through the network.

  FIG. 2 is a diagram showing the configuration of each base station 1. The base station 1 can simultaneously communicate with the plurality of communication terminals 2 by individually allocating radio resources specified in two dimensions including a time axis and a frequency axis to each of the plurality of communication terminals 2. It has become. The base station 1 has an array antenna as a transmission / reception antenna, and can control the directivity of the array antenna using an adaptive array antenna system.

  As shown in FIG. 2, the base station 1 includes a wireless processing unit 11, a control unit 12 that controls the wireless processing unit 11, and a network communication unit 13 connected to a network. The wireless processing unit 11 includes an array antenna 110 including a plurality of antennas 110a.

  The network communication unit 13 is connected to the network by, for example, an optical fiber. The network communication unit 13 transmits data input from the control unit 12 to the network, and outputs data input from the network to the control unit 12.

  The radio processing unit 11 performs amplification processing, down-conversion, A / D conversion processing, and the like on each of the plurality of reception signals received by the array antenna 110, and generates and outputs a plurality of baseband reception signals. To do. Further, the radio processing unit 11 performs D / A conversion processing, up-conversion, amplification processing, and the like on each of the plurality of baseband transmission signals generated by the control unit 12 to transmit a plurality of transmissions in the carrier band. Generate a signal. Then, the wireless processing unit 11 inputs the generated plurality of transmission signals in the carrier band to the plurality of antennas 110a configuring the array antenna 110, respectively. Thereby, a transmission signal is wirelessly transmitted from each antenna 110a.

  The control unit 12 includes a CPU (Central Processing Unit), a DSP (Digital Signal Processor), a memory, and the like. The control unit 12 includes, as functional blocks, a transmission signal generation unit 120, a reception data acquisition unit 121, a radio resource allocation unit 122, a transmission weight processing unit 123, a reception weight processing unit 124, a moving speed acquisition unit 125, and a frame configuration determination unit 126. It has.

  The transmission signal generation unit 120 generates transmission data including data to be transmitted to the communication terminal 2 to be communicated that is output from the network communication unit 13. The transmission data includes user data and control data. Then, the transmission signal generation unit 120 generates a baseband transmission signal including the generated transmission data. This transmission signal is generated by the number of the plurality of antennas 110a constituting the array antenna 110.

  The transmission weight processing unit 123 sets a plurality of transmission weights for controlling the transmission directivity at the array antenna 110 for the plurality of transmission signals generated by the transmission signal generation unit 120, respectively. Then, the transmission weight processing unit 123 performs inverse discrete Fourier transform (IDFT) or the like on the plurality of transmission signals in which the plurality of transmission weights are set, and then wirelessly transmits the plurality of transmission signals. Output to the processing unit 11.

  The reception weight processing unit 124 performs discrete Fourier transform (DFT: Discrete Fourier Transform) on a plurality of reception signals input from the wireless processing unit 11 and then controls reception directivity at the array antenna 110. A plurality of reception weights are respectively set. Then, the reception weight processing unit 124 generates a new reception signal by combining a plurality of reception signals each having a plurality of reception weights.

  The reception data acquisition unit 121 performs inverse discrete Fourier transform, demodulation processing, or the like on the new reception signal generated by the reception weight processing unit 124, and acquires control data and user data included in the reception signal. . The reception data acquisition unit 121 inputs data to be transmitted to the network among the acquired data to the network communication unit 13.

  In base station 1 according to the present embodiment, radio processing unit 11, transmission weight processing unit 123, and reception weight processing unit 124 communicate with a plurality of communication terminals 2 while adaptively controlling the directivity of array antenna 110. A communication unit 14 is configured. The communication unit 14 controls each of the reception directivity and transmission directivity of the array antenna 110 when communicating with the communication terminal 2. Specifically, the communication unit 14 sets the reception directivity beam and null at the array antenna 110 in various directions by adjusting the reception weight multiplied by the reception signal in the reception weight processing unit 124. Can do. Further, the communication unit 14 can set the transmission directivity beam and the null in the array antenna 110 in various directions by adjusting the transmission weight to be multiplied by the transmission signal in the transmission weight processing unit 123. The transmission weight can be obtained from the reception weight, and the reception weight can be obtained based on a known signal from the communication terminal 2. Hereinafter, the control of the reception directivity of the array antenna 110 may be referred to as “array reception control”, and the control of the transmission directivity of the array antenna 110 may be referred to as “array transmission control”.

  The radio resource allocation unit 122 allocates downlink radio resources (transmission frequency and transmission time zone) used for signal transmission to the communication terminal 2 to each communication terminal 2 to be communicated. The transmission signal generation unit 120 generates a transmission signal to be transmitted to the communication terminal 2 based on the downlink radio resource allocated to the communication terminal 2 by the radio resource allocation unit 122, and at a timing based on the downlink radio resource. The transmission signal is input to the transmission weight processing unit 123. Thereby, a transmission signal to be transmitted to the communication terminal 2 is transmitted from the communication unit 14 using the downlink radio resource assigned to the communication terminal 2. The transmission signal generation unit 120 generates and outputs a transmission signal including control data for notifying the communication terminal 2 of the downlink radio resource allocated to the communication terminal 2 by the radio resource allocation unit 122. Thereby, the communication terminal 2 can know the downlink radio resource used in the transmission of the signal addressed to the own device, and can appropriately receive the signal addressed to the own device from the base station 1.

  The radio resource allocation unit 122 allocates, to each communication terminal 2 to be communicated, an uplink radio resource that is used when the communication terminal 2 transmits a signal to the base station 1. The transmission signal generation unit 120 generates and outputs a transmission signal including control data for notifying the communication terminal 2 of the uplink radio resource allocated to the communication terminal 2 by the radio resource allocation unit 122. Thereby, the communication terminal 2 can know the uplink radio resource used for transmission of the signal to the base station 1, and wirelessly transmits the signal to the base station 1 using the uplink radio resource.

  The moving speed acquisition unit 125 acquires the moving speed for each communication terminal 2 to be communicated with in the base station 1. In the present embodiment, each communication terminal 2 periodically notifies the base station 1 of the position of its own device. Each communication terminal 2 is equipped with a GPS (Global Positioning System) receiver, for example, and the position of the communication terminal 2 is obtained in the GPS receiver. The moving speed acquisition unit 125 obtains the moving speed for the communication terminal 2 based on the position of the communication terminal 2 periodically notified from the communication terminal 2 to the base station 1.

  Note that the communication terminal 2 may obtain the position of the own device using a means other than the GPS receiver. Moreover, the movement speed acquisition part 125 may acquire the movement speed of the communication terminal 2 by another method. For example, the communication terminal 2 obtains the movement speed of the own device and notifies the obtained movement speed to the base station 1 so that the movement speed acquisition unit 125 can obtain the movement speed of the communication terminal 2. good.

  The frame configuration determination unit 126 determines a frame configuration for a communication frame that the base station 1 uses for communication with the communication terminal 2. In this embodiment, as will be described later, a plurality of types of frame configurations are defined for the communication frame, and the frame configuration determination unit 126 uses the base station 1 from the plurality of types of frame configurations. Determine the frame configuration. The operation of the frame configuration determination unit 126 will be described in detail later.

<Configuration of TDD frame>
Next, a TDD frame 300 that is a communication frame used by the base station 1 for communication with the communication terminal 2 will be described. The TDD frame 300 is specified in two dimensions including a time axis and a frequency axis. The frequency bandwidth (system bandwidth) of the TDD frame 300 is 10 MHz, for example, and the time length of the TDD frame 300 is 10 ms. The base station 1 determines an uplink radio resource and a downlink radio resource to be allocated to each communication terminal 2 from the TDD frame 300.

  FIG. 3 is a diagram showing a basic configuration of the TDD frame 300. As shown in FIG. 3, the TDD frame 300 is composed of two half frames 301. Each half frame 301 is composed of five subframes 302. That is, the TDD frame 300 is composed of ten subframes 302. The time length of the subframe 302 is 1 ms. Hereinafter, the ten subframes 302 constituting the TDD frame 300 may be referred to as the 0th to 9th subframes 302 in order from the top.

  Each subframe 302 includes two slots 303 in the time direction. Each slot 303 is composed of seven symbol periods 304. Therefore, each subframe 302 includes 14 symbol periods 304 in the time direction. This symbol period 304 is one symbol period of OFDM symbols in OFDMA downlink communication, and one symbol period of DFTS (Discrete Fourier Transform Spread) -OFDM symbols in SC-FDMA uplink communication.

  The TDD frame 300 configured as described above includes a subframe 302 dedicated for uplink communication and a subframe 302 dedicated for downlink communication. Hereinafter, the subframe 302 dedicated to uplink communication is referred to as “uplink subframe 302”, and the subframe 302 dedicated to downlink communication is referred to as “downlink subframe 302”. The communication terminal 2 transmits control data and user data to the base station 1 in the uplink subframe 302, and the base station 1 transmits control data and user data to the communication terminal 2 in the downlink subframe 302.

  In LTE, in the TDD frame 300, a region (radio resource) including a frequency bandwidth of 180 kHz in the frequency direction and including seven symbol periods 304 (one slot 303) in the time direction is referred to as a “resource block (RB)”. Yes. The resource block includes 12 subcarriers. The radio resource allocation unit 122 assigns downlink radio resources used when the communication terminal 2 allocates uplink radio resources used for data transmission to the communication terminal 2 or when data is transmitted to the communication terminal 2. In the case of allocation to the communication terminal 2, uplink radio resources or downlinks are made in units of two resource blocks that are continuous in the time direction, that is, one subframe 302 unit and one resource block unit in the frequency direction. Allocate radio resources. Since the SC-FDMA scheme is used in uplink communication, when a plurality of resource blocks are allocated in a frequency direction to a certain communication terminal 2 in one slot 303 of the uplink subframe 302, the frequency A plurality of resource blocks continuous in the direction are allocated to the communication terminal 2.

  In LTE, for the TDD frame 300, seven types of frame configurations with different combinations of the uplink subframe 302 and the downlink subframe 302 are defined. FIG. 4 is a diagram showing the seven types of frame configurations.

  As shown in FIG. 4, in LTE, frame configurations from No. 0 to No. 6 are defined. When the base station 1 communicates with the communication terminal 2, one of these seven types of frame configurations is used. In FIG. 4, the subframe 302 indicated by “D” means the downlink subframe 302, and the subframe 302 indicated by “U” means the uplink subframe 302. Further, a subframe 302 indicated by “S” means a subframe 302 in which switching from downlink communication to uplink communication is performed in the communication system 100. This subframe 302 is referred to as a “special subframe 302”.

  For example, in the TDD frame 300 having the frame configuration 0, the 0th and 5th subframes 302 are downlink subframes 302, and the 2nd to 4th subframes 302 and the 7th to 9th subframes 302 are uplink subframes. 302, and the first and sixth subframes 302 are special subframes 302. In the TDD frame 300 having the frame configuration 4, the 0th subframe 302 and the fourth to ninth subframes 302 are downlink subframes 302, and the second and third subframes 302 are uplink subframes 302. The first subframe 302 is a special subframe 302.

  FIG. 5 is a diagram showing in detail the TDD frame 300 of the frame configuration 1. As shown in FIG. 5, the special subframe 302 includes a downlink pilot time slot (DwPTS) 351, a guard time (GP) 350, and an uplink pilot time slot (UpPTS) 352 in the time direction. The guard time 350 is a no-signal period necessary for switching from downlink communication to uplink communication, and is not used for communication.

  In LTE, a plurality of types of combinations are defined for combinations of time lengths of the downlink pilot time slot 351, the guard time 350, and the uplink pilot time slot 352. In the example of FIG. 5, the time length of the downlink pilot time slot 351 is set to 11 symbol periods 304, and the time length of the uplink pilot time slot 352 is set to 2 symbol periods 304.

  In communication system 100 according to the present embodiment, each communication terminal 2 transmits a known signal called a sounding reference signal (SRS) in one of two symbol periods 304 of uplink pilot time slot 352. The SRS is composed of a plurality of complex symbols that modulate a plurality of subcarriers. In the present embodiment, SRS transmitted in uplink pilot time slot 352 is used to calculate a transmission weight. That is, the communication unit 14 of the base station 1 can perform array transmission control based on the SRS that the communication terminal 2 transmits in the uplink pilot time slot 352.

  Note that the reception weight set for the signal including data transmitted by the communication terminal 2 in the uplink subframe 302 is not SRS, but a demodulation reference signal (DRS: transmitted from the communication terminal 2 in the uplink subframe 302). It is calculated based on a known signal called Demodulation Reference Signal.

  In addition, the base station 1 can transmit data to the communication terminal 2 not only in the downlink subframe 302 but also in the downlink pilot time slot 351 of the special subframe 302. The pilot time slot 351 is not used for downlink communication.

  The SRS can also be transmitted in the last symbol period 304 of the uplink subframe 302. That is, in the uplink subframe 302, the communication terminal 2 can transmit data in each symbol period 304 except for the last symbol period 304, and can transmit SRS in the last symbol period 304. For array transmission control, it is possible to use the SRS transmitted in the last symbol period 304 of the uplink subframe 302, but in this embodiment, the SRS transmitted in the uplink pilot time slot 352 is used. Shall. Hereinafter, unless otherwise specified, SRS refers to SRS transmitted using uplink pilot time slot 352.

  Thus, in communication system 100 according to the present embodiment, uplink radio resources that can be used when communication terminal 2 transmits data (portion of uplink subframe 302 excluding the last symbol period 304). Separately, uplink radio resources (a part including the uplink pilot time slot 352 of the special subframe 302 and a part including the last symbol period 304 of the uplink subframe 302) capable of transmitting the SRS are determined. ing.

  Hereinafter, each symbol period 304 included in the uplink pilot time slot 352 is referred to as an “SRS uplink communication period 370”. Also, the 14 symbol periods 304 included in the uplink subframe 302 are collectively referred to as “uplink communication period 380”, and the 14 symbol periods 304 included in the downlink subframe 302 are collectively referred to as “downlink communication period 390”. Call.

  The SRS is a signal transmitted periodically, and the length of the transmission cycle (transmission interval) can be changed. Hereinafter, the SRS transmission cycle is referred to as “SRS transmission cycle 360”. In the example of FIG. 5, the length (transmission interval) of the SRS transmission period 360 is set to 5 ms, and the SRS is transmitted for each uplink pilot time slot 352 of the uplink special subframe 302.

<SRS transmission frequency band>
In the communication system 100, the frequency band 400 that can be used for SRS transmission (hereinafter referred to as “SRS transmittable band 400”) alternates between the high frequency side and the low frequency side of the system band every SRS transmission period 360. It is arranged. In FIG. 5, the SRS transmittable band 400 is indicated by hatching.

  Further, in communication system 100 according to the present embodiment, a frequency band (hereinafter referred to as “SRS transmission band”) used by one communication terminal 2 for SRS transmission is within the entire range of SRS transmittable band 400 or Within a certain range, it is possible to change every SRS transmission period 360. This control is called “frequency hopping”. Further, in the communication system 100, the bandwidth of the SRS transmission band 450 (hereinafter referred to as “SRS transmission bandwidth”) can be changed.

  FIG. 6 is a diagram illustrating an example of a state in which an SRS transmission band 450 used by a certain communication terminal 2 performs frequency hopping within the entire range of the SRS transmittable band 400. In the example of FIG. 6, the length of the SRS transmission cycle 360 is set to 5 ms, and the SRS transmittable band 400 is divided into first to fourth frequency bands. Then, the SRS transmission band 450 having a quarter of the bandwidth of the SRS transmittable band 400 has a first frequency band, a third frequency band, a second frequency band, a fourth frequency for each SRS transmission period 360. It changes in the order of frequency band.

  Note that the SRS transmission band 450 can be fixed to a certain frequency band without frequency hopping. That is, the communication terminal 2 can also periodically transmit SRS having a constant transmission frequency band.

  In the base station 1, the radio resource allocation unit 122 determines the transmission mode of SRS for each communication terminal 2 to be communicated. Specifically, the radio resource assignment unit 122 determines the SRS transmission bandwidth, the head position of the SRS transmission band 450, and the SRS transmission cycle 360 for each communication terminal 2. When the head position of the SRS transmission band 450 changes every SRS transmission cycle 360, the SRS transmission band 450 comes to be frequency hopped. The radio resource allocation unit 122 determines the SRS transmission bandwidth 450 for the communication terminal 2 by determining the SRS transmission bandwidth for the communication terminal 2 and the head position of the SRS transmission band 450.

  The transmission signal generation unit 120 is control data for notifying the communication terminal 2 of the transmission mode of the SRS transmitted by the communication terminal 2 determined by the radio resource allocation unit 122 (hereinafter referred to as “SRS control data”). Is generated. This transmission signal is transmitted from the communication unit 14 to the communication terminal 2 using the downlink subframe 302. Thereby, SRS control data is transmitted to each communication terminal 2, and each communication terminal 2 can know the transmission mode of SRS transmitted by itself. That is, each communication terminal 2 can recognize the SRS transmission bandwidth for the SRS that it transmits, the head position of the SRS transmission band 450, and the SRS transmission cycle 360. Each communication terminal 2 periodically transmits SRS based on the transmission mode determined by the base station 1. The SRS control data is called “RRCConnectionReconfiguration message” in LTE.

<About array transmission control>
In the base station 1 according to the present embodiment, for example, both null steering and beam forming are performed simultaneously as array transmission control. When the communication unit 14 of the base station 1 transmits a signal to the communication terminal 2 in the downlink subframe 302, based on the SRS transmitted by the communication terminal 2, the null steering and the beam are transmitted with respect to the transmission directivity of the array antenna 110. Perform forming. In the communication unit 14, for example, using a sequential update algorithm such as an RLS (Recursive Least-Squares) algorithm, the reception weight is updated a plurality of times based on a plurality of complex symbols included in the SRS, and the reception weight after the update is completed. Both null steering and beamforming are performed by obtaining a transmission weight based on the above.

  Further, in the base station 1 according to the present embodiment, the transmission weight transmitted to the communication terminal 2 in a certain SRS transmission cycle 360 is determined based on the SRS transmitted by the communication terminal 2 in the SRS transmission cycle 360. Is calculated (more precisely, based on the reception weight calculated based on the SRS), and the transmission weight is set in the transmission signal. That is, in the base station 1, the array transmission control when transmitting data to the communication terminal 2 in the downlink subframe 302 in a certain SRS transmission cycle 360 is performed by the SRS received from the communication terminal 2 in the SRS transmission cycle 360. Based on.

  Furthermore, in base station 1 according to the present embodiment, a transmission weight is obtained for each frequency band of one resource block, for example. Hereinafter, the frequency band of one resource block is referred to as “allocation unit band”. For example, assuming that the frequency band of the transmission signal transmitted to the communication terminal 2 in the downlink subframe 302 is composed of four allocation unit bands, transmission weights are obtained for each of the four allocation unit bands. A transmission weight applied to a signal transmitted to the communication terminal 2 using a certain allocation unit band uses the certain allocation unit band among a plurality of complex symbols constituting the SRS received from the communication terminal 2. It is determined based on the 12 complex symbols transmitted. Since 12 subcarriers are included in one resource block, 12 complex symbols can be transmitted using one allocation unit band.

  Thus, in the present embodiment, when transmitting a transmission signal to communication terminal 2 in downlink subframe 302, the same frequency as the frequency band of the transmission signal in SRS received from communication terminal 2 Array transmission control is performed using the portion transmitted in the band. Thereby, the accuracy of array transmission control is improved, and the beam can be directed to the communication terminal 2 appropriately.

<Method for determining frame configuration>
When the base station 1 performs downlink communication with the communication terminal 2 having a high moving speed, the communication terminal 2 transmits the SRS, and then the base station 1 performs array transmission control based on the SRS and transmits the SRS. In the period until the communication terminal 2 receives the signal (hereinafter referred to as “array transmission control period”), the position of the communication terminal 2 may change significantly. In such a case, the accuracy of array transmission control for the communication terminal 2 in the base station 1 is reduced, and a signal from the base station 1 is difficult to reach the communication terminal 2. As a result, the transmission performance of the base station 1 may be degraded.

  Therefore, in the present embodiment, when there is a communication target communication terminal 2 whose transfer speed is higher than the threshold, the base station 1 has a timing close to the SRS reception timing from the communication terminal 2. Thus, the frame configuration of the TDD frame 300 is changed so that a signal can be transmitted to the communication terminal 2. Thereby, the array transmission control period for the communication terminal 2 having a high moving speed can be shortened, and the position of the communication terminal 2 can be prevented from changing greatly in the array transmission control period. As a result, the accuracy of array transmission control for the communication terminal 2 in the base station 1 is improved, and the signal from the base station 1 can be reliably delivered to the communication terminal 2. Therefore, the transmission performance of the base station 1 is improved. Below, this operation | movement in the base station 1 is demonstrated in detail.

  In base station 1 according to the present embodiment, frame configuration 1 and frame configuration 2 are used, for example, among the seven types of frame configurations for TDD frame 300 shown in FIG. In the base station 1, the frame configuration 1 is used in the initial state after the power is turned on. In the base station 1, when there is a communication terminal 2 whose moving speed is higher than the threshold value in the communication terminal 2 to be communicated, the frame structure 2 is used instead of the frame structure 1. . In the frame configuration 1, the fourth subframe 302 is the first downlink subframe 302 among the plurality of downlink subframes 302 behind the front special subframe 302 (first subframe 302). In the frame configuration 2, the third subframe 302 is the first downlink subframe 302 of the plurality of downlink subframes 302 behind the front special subframe 302. Therefore, when the frame configuration is changed from the frame configuration 1 to the frame configuration 2, in the TDD frame 300, the SRS uplink communication period 370 for the communication terminal 2 to transmit the SRS, and the base station 2 performs data downlink communication. Of the plurality of downlink communication periods 390, the period between the leading downlink communication period 390 is shortened.

  FIG. 7 is a flowchart illustrating the operation of the base station 1 when the base station 1 determines the frame configuration and allocates radio resources to the communication terminal 2 for the TDD frame 300 having the determined frame configuration. A series of processing from steps s 1 to s 5 shown in FIG. 7 is executed in each TDD frame 300. Also, in the base station 1, the uplink and downlink radio resources are assigned to the communication terminal 2 in units of SRS transmission cycles 360. That is, in the base station 1, radio resource allocation to the communication terminal 2 for the uplink subframe 302 and the downlink subframe 302 included in the SRS transmission cycle 360 is performed independently in each SRS transmission cycle 360.

  As shown in FIG. 7, in the base station 1, in step s1, the moving speed acquisition unit 125 acquires the moving speed for each communication terminal 2 to be communicated with the base station 1 as described above.

  Next, in step s2, the frame configuration determination unit 126 determines the latest usable subframe for each communication terminal 2 to be communicated based on the moving speed of the communication terminal 2. Here, the latest available subframe for the communication terminal 2 means the slowest subframe 302 that can be used by the base station 1 as a downlink radio resource for the communication terminal 2 in the SRS transmission period 360. ing. In other words, the latest available subframe for the communication terminal 2 is a subframe 302 that the base station 1 should execute downlink communication with the communication terminal 2 in the subframe 302 at the latest in the SRS transmission period 360. Means.

  As described above, when the moving speed of the communication terminal 2 is high, the position of the communication terminal 2 is highly likely to change greatly during the array transmission control period. Therefore, the accuracy of the array transmission control for the communication terminal 2 is high. Is likely to deteriorate. Therefore, it is preferable for the communication terminal 2 having a high moving speed to shorten the array transmission control period by speeding up the downlink communication with the communication terminal 2. Therefore, in the present embodiment, the latest usable subframe for the communication terminal 2 is earlier as the moving speed for the communication terminal 2 is higher. A method for determining the latest available subframe for the communication terminal 2 will be described below.

  As described above, in this embodiment, the frame configuration 1 and the frame configuration 2 are used as the frame configuration of the TDD frame 300. Therefore, in the SRS transmission cycle 360, the maximum number of subframes 302 in which downlink communication is possible is greater than the subframe 302 immediately before the downlink pilot time slot 351 included in the SRS transmission cycle 360 and the subframe 302 immediately preceding the subframe 302. There are three subframes 302, ie, the previous subframe 302 and the subframe 302 two before the previous subframe 302. Specifically, in the SRS transmission period 360 including the uplink pilot time slot 352 of the special subframe 302 (first subframe 302) in front of the TDD frame 300, the subframe 302 capable of downlink communication is the There are three subframes 302, a fourth subframe 302 and a fifth subframe 302. Further, in the SRS transmission period 360 including the upstream pilot time slot 352 of the special subframe 302 (sixth subframe 302) behind the TDD frame 300, the subframe 302 capable of downlink communication is the maximum in the TDD frame 300. The eighth sub-frame 302 and the ninth sub-frame 302 and the first sub-frame 302 of the next TDD frame 300 become three.

  Therefore, the frame configuration determination unit 126 according to the present embodiment determines the latest usable subframe for the communication terminal 2 from the above three subframes 302 based on the moving speed of the communication terminal 2. To do. Hereinafter, the three subframes 302 will be referred to as “front subframe 302”, “intermediate subframe 302”, and “rear subframe 302” in order from the top.

  In step s2, the frame configuration determining unit 126 compares the moving speed of the communication terminal 2 with each of the first and second threshold values. The first threshold value is set larger than the second threshold value. The frame configuration determination unit 126 sets the latest usable subframe 302 for the communication terminal 2 (hereinafter, sometimes referred to as “high-speed mobile terminal 2”) whose moving speed is higher than the first threshold to the front subframe. 302 is determined. That is, for the high-speed mobile terminal 2, the frame configuration determination unit 126 determines that the base station 1 should execute downlink communication with the communication terminal 2 in the forward subframe 302 at the latest in the SRS transmission cycle 360.

  The frame configuration determining unit 126 uses the latest speed for the communication terminal 2 (hereinafter referred to as “medium-speed mobile terminal 2”) whose moving speed is equal to or lower than the first threshold value and higher than the second threshold value. The possible subframe 302 is determined as the intermediate subframe 302. Then, the frame configuration determination unit 126 sets the latest usable subframe 302 for the communication terminal 2 whose movement speed is equal to or lower than the second threshold (hereinafter, sometimes referred to as “low-speed mobile terminal 2”) to the rear subframe 302. Frame 302 is determined. In this way, the frame configuration determination unit 126 determines the latest usable subframe 302 for each communication terminal 2 to be communicated.

  Next, in step s3, the frame configuration determination unit 126 determines whether to use the frame configuration 1 or the frame configuration 2 based on the latest available subframe 302 for each communication terminal 2 to be communicated. Specifically, the frame configuration determination unit 126 determines to use the frame configuration 2 when there is a communication terminal 2 whose latest usable subframe 302 is the front subframe 302 in the communication terminal 2 to be communicated. When there is no communication terminal 2 whose latest usable subframe 302 is the front subframe 302, it is determined that the frame configuration 1 is used. Since the latest available subframe 302 for the high speed mobile terminal 2 is the front subframe 302, the frame configuration determination unit 126 determines the frame configuration when the high speed mobile terminal 2 exists in the communication terminal 2 to be communicated. 2 is used. When the high-speed mobile terminal 2 does not exist, it is determined that the frame configuration 1 is used.

  In the frame configuration 1, the third or eighth subframe 302 corresponding to the front subframe 302 is the uplink subframe 302, and therefore there is a communication terminal 2 in which the latest usable subframe 302 is the front subframe 302. In some cases, if the frame configuration 1 is adopted, downlink communication cannot be performed with the communication terminal 2 in the front subframe 302. On the other hand, in the frame configuration 2, the third or eighth subframe 302 corresponding to the forward subframe 302 is the downlink subframe 302, and thus the communication terminal 2 in which the latest usable subframe 302 is the forward subframe 302. When the frame configuration 2 is adopted, downlink communication can be performed with the communication terminal 2 in the front subframe 302. Therefore, the frame configuration determination unit 126 determines to use the frame configuration 2 when there is a communication terminal 2 (high-speed mobile terminal 2) whose latest usable subframe 302 is the front subframe 302.

  When the frame configuration used by the base station 1 is determined by the frame configuration determination unit 126, the communication unit 14 communicates with the communication terminal 2 using the determined frame configuration in the next TDD frame 300.

  When step s3 is executed, in step s4, the radio resource allocation unit 122 determines the uplink pilot time of the next TDD frame 300, that is, the special subframe 302 in front of the TDD frame 300 having the frame configuration determined in step s3. An SRS transmission period 360 including a slot 352 (hereinafter, also referred to as “forward SRS transmission period 360”) and an SRS transmission period 360 including an upstream pilot time slot 352 of the special subframe 302 behind the TDD frame 300 (see FIG. Thereafter, allocation of uplink and downlink radio resources to the communication terminal 2 is executed for each of “rear SRS transmission cycle 360”.

  In step s4, when allocating downlink radio resources to the communication terminal 2, the radio resource allocation unit 122 considers the latest usable subframe 302 for the communication terminal 2. That is, when the radio resource allocation unit 122 allocates downlink radio resources for the SRS transmission cycle 360 to the communication terminal 2, the SRS transmission cycle corresponding to the latest available subframe 302 of the communication terminal 2 At least a part of the downlink subframe 302 included in 360 or the downlink subframe 302 before that included in the SRS transmission cycle 360 is allocated to the communication terminal 2 as a downlink radio resource.

  For example, when the frame configuration of the next TDD frame 300 is the frame configuration 2, the front subframe 302 is forwarded with respect to the communication terminal 2 (high-speed mobile terminal 2) determined as the latest usable subframe 302. When downlink radio resources are assigned for the SRS transmission period 360, at least a part of the third subframe 302 corresponding to the forward subframe 302 is assigned as downlink radio resources to the communication terminal 2. .

  Further, in the case where the frame configuration of the next TDD frame 300 is the frame configuration 2, for the communication terminal 2 (medium-speed mobile terminal 2) in which the intermediate subframe 302 is determined as the slowest usable subframe 302, When the downlink radio resource is assigned for the forward SRS transmission period 360, the communication terminal 2 is assigned with at least a part of the fourth subframe 302 corresponding to the intermediate subframe 302 or the fourth subframe. At least a part of the third subframe 302 before the frame 302 is allocated as a downlink radio resource.

  Further, when the frame configuration of the next TDD frame 300 is the frame configuration 2, the communication terminal 2 (low-speed mobile terminal 2) in which the rear subframe 302 is determined as the latest usable subframe 302 is forward When downlink radio resources are assigned for the SRS transmission period 360, at least a part of the fifth subframe 302 corresponding to the rear subframe 302 or the fifth subframe is assigned to the communication terminal 2. At least a part of the fourth subframe 302 before 302 or at least a part of the third subframe 302 before the fourth subframe 302 is allocated as a downlink radio resource.

  Further, when the frame configuration of the next TDD frame 300 is the frame configuration 1, for the communication terminal 2 (medium-speed mobile terminal 2) in which the intermediate subframe 302 is determined as the latest usable subframe 302, When downlink radio resources are assigned for the forward SRS transmission period 360, at least a part of the fourth subframe 302 corresponding to the intermediate subframe 302 is assigned to the communication terminal 2 as downlink radio resources. It is done.

  Further, when the frame configuration of the next TDD frame 300 is the frame configuration 1, the communication terminal 2 (low-speed mobile terminal 2) in which the rear subframe 302 is determined as the latest usable subframe 302 is forward When downlink radio resources are assigned for the SRS transmission period 360, at least a part of the fifth subframe 302 corresponding to the rear subframe 302 or the fifth subframe is assigned to the communication terminal 2. At least a part of the fourth subframe 302 before 302 is allocated as a downlink radio resource.

  Note that, as described above, the downlink radio resources are allocated to the communication terminal 2 in units of one subframe 302 in the time direction, and thus the downlink radio of the same subframe 302 is assigned to a plurality of communication terminals 2. When resources are allocated, downlink radio resources are allocated so as not to overlap in the frequency direction.

  In step s4, when uplink and downlink radio resources are allocated to each communication terminal 2 to be communicated, in step s5, the communication unit 14 determines that the radio resource allocation unit 122 The uplink and downlink radio resources allocated to the communication terminal 2 are notified.

  In base station 1 according to the present embodiment, a series of processes from steps s1 to s5 described above are performed in each TDD frame 300.

  As described above, in base station 1 according to the present embodiment, frame configuration 2 is used when high-speed mobile terminal 2 exists, and frame configuration 1 is used when high-speed mobile terminal 2 does not exist. It is like that. Therefore, in the base station 1, when the high-speed mobile terminal 2 exists from the situation where the high-speed mobile terminal 2 does not exist, the frame configuration to be used is changed from the frame configuration 1 to the frame configuration 2. That is, in the base station 1, when the high-speed communication terminal 2 is present, the frame configuration is such that the period between the SRS uplink communication period 370 and the first downlink communication period 390 that appears thereafter in the TDD frame 300 is shortened. Will be changed. Then, in the base station 1, when the frame configuration to be used is changed from the frame configuration 1 to the frame configuration 2, the communication terminal 2 in which the latest usable subframe 302 is determined to be the front subframe 302 (high-speed movement) For the terminal 2), the downlink radio resource of the downlink subframe 302 corresponding to the forward subframe 302 included in the frame configuration 2 is allocated. That is, in the base station 1, when the frame configuration 1 is changed to the frame configuration 2, the high-speed mobile terminal 2 is included in the frame configuration 1 among the plurality of downlink communication periods 390 included in the frame configuration 2. The data is transmitted in the downlink communication period 390 before the plurality of downlink communication periods 390. Therefore, the array transmission control period for the high-speed mobile terminal 2 can be shortened. Therefore, it is possible to suppress the position of the high-speed mobile terminal 2 from largely moving during the array transmission control period, and it is possible to improve the accuracy of array transmission control for the high-speed mobile terminal 2. As a result, data can be reliably delivered to the high-speed mobile terminal 2.

  In the above example, the communication terminal 2 whose moving speed is higher than the first threshold is the high-speed mobile terminal 2, but the communication terminal 2 whose moving speed is the first threshold or higher is the high-speed mobile terminal 2. It is also good. In this case, the frame configuration to be used is changed from the frame configuration 1 to the frame configuration 2 even when there is a communication target communication terminal 2 having the same moving speed as the first threshold value. Become so. When the communication terminal 2 whose moving speed is equal to or higher than the first threshold value is the high-speed mobile terminal 2, the communication terminal 2 whose moving speed is smaller than the first threshold value and larger than the second threshold value, Alternatively, the communication terminal 2 whose moving speed is smaller than the first threshold value and equal to or higher than the second threshold value is set as the medium speed mobile terminal 2. Further, the communication terminal 2 having a moving speed equal to or lower than the first threshold and equal to or higher than the second threshold may be used as the medium speed mobile terminal 2. The communication terminal 2 in which the moving speed is smaller than the first threshold and is equal to or higher than the second threshold, or the communication terminal 2 whose moving speed is equal to or lower than the first threshold and is equal to or higher than the second threshold is medium speed. When the communication terminal 2 is used, the low-speed mobile terminal 2 is the communication terminal 2 whose moving speed is lower than the second threshold value.

  FIG. 8 is a diagram illustrating an example of the moving speeds of the communication terminals 2a, 2b, and 2c in the (N-2) th and (N-1) th TDD frames 300. As shown in FIG. 8, the moving speed 470a of the communication terminal 2a is constant, and the communication terminal 2a is the medium speed mobile terminal 2 in each of the (N-2) th and (N-1) th TDD frames 300. It has become. Further, the moving speed 470b of the communication terminal 2b is small, and in the (N-2) th TDD frame 300, the communication terminal 2b is the medium speed mobile terminal 2, but the (N-1) th TDD frame. In 300, the communication terminal 2b is the low-speed mobile terminal 2. The moving speed 470c of the communication terminal 2c is increased. In the (N-2) th TDD frame 300, the communication terminal 2c is the medium speed mobile terminal 2, but the (N-1) th TDD frame. In 300, the communication terminal 2c is the high-speed mobile terminal 2.

  9 and 10 are diagrams illustrating examples of allocation of downlink radio resources to the communication terminals 2a, 2b, and 2c having the moving speed illustrated in FIG. FIG. 9 shows an example of downlink radio resource allocation in the forward SRS transmission period 360 included in the (N−1) th TDD frame 300, and FIG. 10 shows the forward SRS transmission period included in the Nth TDD frame 300. An example of downlink radio resource allocation at 360 is shown.

  In the example of FIG. 8, since the high-speed mobile terminal 2 does not exist in the (N-2) th TDD frame 300, the frame configuration of the next (N-1) th TDD frame 300 is shown in FIG. Thus, the frame configuration 1 is established. Then, since the high-speed mobile terminal 2 is present in the (N−1) th TDD frame 300, the frame configuration is changed from the frame configuration 1 to the frame configuration in the Nth TDD frame 300, as shown in FIG. Changed to configuration 2.

  9 and 10, for each of the communication terminals 2a, 2b, and 2c, a part of the downlink subframe 302 corresponding to the latest available subframe 302 determined for the communication terminal 2 is a downlink radio resource. Assigned as.

  Specifically, in the forward SRS transmission cycle 360 included in the (N-1) th TDD frame 300, as shown in FIG. 9, the latest available for the communication terminal 2a (medium speed). A part of the fourth subframe 302 corresponding to the subframe 302 is allocated as a downlink radio resource 480a used in downlink communication with the communication terminal 2a. For the communication terminal 2b (medium speed), a part of the fourth subframe 302 corresponding to the latest available subframe 302 is a downlink radio resource 480b used for downlink communication with the communication terminal 2b. Assigned as. For the communication terminal 2c (low speed), a part of the fifth subframe 302 corresponding to the latest available subframe 302 is a downlink radio resource 480c used for downlink communication with the communication terminal 2c. Assigned.

  In the forward SRS transmission period 360 included in the Nth TDD frame 300, as shown in FIG. 10, the communication terminal 2a (medium speed) has a fourth sub corresponding to the latest usable subframe 302. A part of the frame 302 is allocated as the downlink radio resource 480a. Further, a part of the fifth subframe 302 corresponding to the latest available subframe 302 is allocated to the communication terminal 2b (low speed) as the downlink radio resource 480b. A part of the third subframe 302 corresponding to the latest available subframe 302 is allocated to the communication terminal 2c (high speed) as the downlink radio resource 480c.

  As shown in FIGS. 9 and 10, in the base station 1, when the high-speed mobile terminal 2 is present, the frame configuration to be used is changed from the frame configuration 1 to the frame configuration 2. Then, in the base station 1, when the frame configuration to be used is changed from the frame configuration 1 to the frame configuration 2, the high-speed mobile terminal 2 is out of the plurality of downlink subframes 302 included in the frame configuration 2. Downlink radio resources of downlink subframes 302 (third downlink subframe 302 in the example of FIG. 10) prior to the plurality of downlink subframes 302 included in frame configuration 1 are allocated. Therefore, the array transmission control period for the high-speed mobile terminal 2 can be shortened, and the accuracy of the array transmission control for the high-speed mobile terminal 2 can be improved.

  In addition, as shown in FIG. 10, communication is performed by assigning a downlink subframe 302 after the downlink subframe 302 assigned to the high-speed mobile terminal 2 c to the medium-speed mobile terminal 2 a and the low-speed mobile terminal 2 b. The degree of freedom of allocation of downlink radio resources to the terminals 2a to 2c is improved. That is, communication is performed for the medium speed mobile terminal 2a and the low speed mobile terminal 2b by transmitting data in the downlink communication period 390 after the downlink communication period 390 for transmitting data to the high speed mobile terminal 2a. The degree of freedom of allocation of downlink radio resources to the terminals 2a to 2c is improved.

  For example, the communication terminal 2c transmits SRS in the symbol period 304 (SRS uplink communication period 370) ahead of the uplink pilot time slot 352 included in the special subframe 302, and the symbol behind the uplink pilot time slot 352 is transmitted. If the communication terminal 2a transmits SRS in the period 304 (SRS uplink communication period 370), that is, the communication terminal 2c and the communication terminal 2a are different from each other in the uplink pilot time slot 352 of the special subframe 302. If the SRS is transmitted in the same time zone, the SRS transmission frequency band from the communication terminal 2c and the SRS transmission frequency band from the communication terminal 2a can be overlapped. Therefore, it is possible to allocate downlink radio resources having frequency bands that overlap each other to the communication terminal 2c and the communication terminal 2a. Similarly, if the communication terminal 2c and the communication terminal 2b transmit SRS in different time zones in the uplink pilot time slot 352, the frequency band for the communication terminal 2c and the communication terminal 2b is It is possible to allocate downlink radio resources that overlap each other. Therefore, the degree of freedom of allocation of downlink radio resources to the communication terminals 2a to 2c is improved.

  In LTE, eight types of code patterns composed of a plurality of complex symbols constituting the SRS are defined, and eight types of code sequences orthogonal to each other are adopted for the eight types of code patterns. Therefore, in LTE, a maximum of eight communication terminals 2 can transmit SRS using the same SRS transmission band in the same symbol period 304. That is, SRS from up to eight communication terminals 2 can be multiplexed in the same transmission frequency band. Downlink radio with frequency bands overlapping each other for communication terminal 2a and communication terminal 2c, or for communication terminal 2b and communication terminal 2c by multiplexing SRS from communication terminals 2a to 2c in the same transmission frequency band Resources can be allocated. Therefore, the degree of freedom of allocation of downlink radio resources to the communication terminals 2a to 2c is improved.

  Further, as shown in FIG. 10, by assigning a downlink subframe 302 after the downlink subframe 302 assigned to the medium speed mobile terminal 2a to the low speed mobile terminal 2b, for the same reason as above, The degree of freedom of allocation of downlink radio resources to the communication terminals 2a and 2b is further improved.

  In the example of FIG. 10, the downlink radio resource of the fifth subframe 302 is allocated to the communication terminal 2 b in the Nth TDD frame 300. For the communication terminal 2b whose latest usable subframe 302 is the fifth subframe 302, it is possible to allocate downlink radio resources of the downlink subframe 302 before the fifth subframe 302. The same downlink radio resource as the downlink radio resource assigned to the communication terminal 2 b in the (N−1) th TDD frame 300 can be assigned in the Nth TDD frame 300.

  As described above, when assigning the downlink radio resource in the Nth TDD frame 300 to the communication terminal 2, the downlink radio resource in the immediately preceding (N-1) th TDD frame 300 is as much as possible. By assigning the same downlink radio resource to the communication terminal 2, the assignment process of the downlink radio resource for the communication terminal 2 is simplified.

<Various modifications>
Hereinafter, various modifications of the communication system according to the present embodiment will be described.

<First Modification>
In the above example, the first and second threshold values are provided as threshold values to be compared with the moving speed of the communication terminal 2, but only one type of threshold value may be provided. In this case, the frame configuration 2 is used when there is a communication terminal 2 larger than the threshold, and the frame configuration 1 is used when the communication terminal 2 does not exist. Then, the latest usable subframe 302 for the communication terminal 2 whose movement speed is equal to or lower than the threshold value becomes the rear subframe 302, and the latest usable subframe 302 for the communication terminal 2 whose movement speed is larger than the threshold value. Becomes the front subframe 302.

  When one type of threshold value is provided as a threshold value to be compared with the moving speed of the communication terminal 2, the rear subframe 302 is set for both of the two communication terminals 2 whose moving speed is equal to or less than the threshold value. Since the latest usable subframe 302 is used, the rear subframe 302 may be assigned as a downlink radio resource to the communication terminal 2 having the higher moving speed among the two communication terminals 2. In this case, data is transmitted to the communication terminal 2 with the higher moving speed at the same timing as the communication terminal 2 with the lower moving speed.

  On the other hand, when two types of threshold values are provided as threshold values to be compared with the moving speed of the communication terminal 2, for the two communication terminals 2 whose moving speed is equal to or lower than the first threshold value, If the movement speed of the communication terminal 2 with the higher movement speed among them is larger than the second threshold value, the latest usable subframe 302 for the communication terminal 2 becomes the intermediate subframe 302. Therefore, the intermediate subframe 302 before the rear subframe 302 is assigned to the communication terminal 2 as a downlink radio resource. Therefore, in the two communication terminals 2 whose movement speed is equal to or less than the first threshold value, data is transmitted to the communication terminal 2 with the higher movement speed faster than the communication terminal 2 with the lower movement speed. It becomes possible. As a result, by transmitting data to the communication terminal 2 faster as the communication terminal 2 has a higher moving speed, the communication terminal 2 having a higher moving speed shortens the array transmission control period and improves the accuracy of array transmission control. The control can be performed more finely.

<Second Modification>
In the above example, the combination of the frame configuration 1 and the frame configuration 2 is adopted as the two types of frame configurations that can be used for communication between the base station 1 and the communication terminal 2, but other combinations may be adopted. For example, a combination of frame configuration 0 and frame configuration 1 may be employed, or a combination of frame configuration 0 and frame configuration 2 may be employed.

  When the combination of the frame configuration 0 and the frame configuration 1 is adopted, the threshold value to be compared with the moving speed of the communication terminal 2 is one type, and if there is a communication terminal 2 larger than the threshold value, the frame When the configuration 1 is used and the communication terminal 2 does not exist, the frame configuration 0 is used. Then, the latest usable subframe 302 for the communication terminal 2 whose movement speed is equal to or lower than the threshold value becomes the rear subframe 302, and the latest usable subframe 302 for the communication terminal 2 whose movement speed is larger than the threshold value. Becomes the intermediate subframe 302.

  Further, when the combination of the frame configuration 0 and the frame configuration 2 is adopted, one type of threshold value may be provided as a threshold value to be compared with the moving speed of the communication terminal 2, or the first and first threshold values may be provided. Two threshold values (first threshold value> second threshold value) may be provided. When one kind of threshold value is provided, the frame configuration 2 is used when there is a communication terminal 2 larger than the threshold value, and the frame configuration 0 is used when there is no communication terminal 2. Then, the latest usable subframe 302 for the communication terminal 2 whose movement speed is equal to or lower than the threshold value becomes the rear subframe 302, and the latest usable subframe 302 for the communication terminal 2 whose movement speed is larger than the threshold value. Becomes the intermediate subframe 302. On the other hand, when the first and second threshold values are provided, the frame configuration 2 is used when there is a communication terminal 2 larger than the lower second threshold value, and the communication terminal 2 exists. If not, frame structure 0 is used. Then, the latest usable subframe 302 for the communication terminal 2 whose moving speed is equal to or lower than the second threshold value is the rear subframe 302, and the moving speed is larger than the second threshold value and the first threshold value. The latest available subframe 302 for the following communication terminal 2 becomes the intermediate subframe 302, and the latest available subframe 302 for the communication terminal 2 whose moving speed is larger than the first threshold is the forward frame 302. Become.

<Third Modification>
In the above example, two types of frame configurations can be used for communication between the base station 1 and the communication terminal 2, but three or more types of frame configurations may be used. For example, frame configurations 0 to 2 may be used. In this case, when there is a communication terminal 2 that is larger than the first threshold, among the frame configurations 0 to 2, the SRS uplink communication period 370 and the downlink communication period 390 that appears first thereafter The frame configuration 2 having the shortest period is used. Further, when there is no communication terminal 2 larger than the first threshold value and there is a communication terminal 2 smaller than the first threshold value and larger than the second threshold value, the frame configuration Among frames 0 to 2, the frame configuration 1 in which the period between the uplink communication period 370 for SRS and the downlink communication period 390 that appears first thereafter is the next shortest is used. Then, when there is no communication terminal 2 larger than the second threshold value, the period between the SRS uplink communication period 370 and the first downlink communication period 390 appearing after that in the frame configurations 0 to 2 Uses frame structure 0 with the longest. Thereby, when there is no communication terminal 2 larger than the first threshold and there is a communication terminal 2 that is equal to or lower than the first threshold and larger than the second threshold, the frame configuration is changed. Frame configuration 0 is changed to frame configuration 1. That is, the frame configuration is changed so that the period between the SRS uplink communication period 370 and the leading downlink communication period 390 appearing thereafter in the TDD frame 300 is shortened. Further, when there is a communication terminal 2 larger than the first threshold, the frame configuration is changed from the frame configuration 0 or the frame configuration 1 to the frame configuration 2. That is, the frame configuration is changed so that the period between the SRS uplink communication period 370 and the leading downlink communication period 390 appearing thereafter in the TDD frame 300 is shortened.

  When frame configurations 0 to 2 are used, the latest available subframe 302 for the communication terminal 2 whose moving speed is equal to or lower than the second threshold is the rear subframe 302, and the moving speed is the second The latest available subframe 302 for the communication terminal 2 that is greater than the threshold value and less than or equal to the first threshold value is the intermediate subframe 302, and for the communication terminal 2 that has a moving speed greater than the first threshold value. The latest usable subframe 302 becomes the front subframe 302.

<Fourth Modification>
When the distance between the base station 1 and the communication terminal 2 is large, it takes time until the data reaches the communication terminal 2 after transmitting data from the base station 1 to the communication terminal 2. The array transmission control period for the communication terminal 2 becomes longer.

  Further, the base station 1 according to the present embodiment controls the transmission timing of each communication terminal 2 so that the signal from each communication terminal 2 can be received at the frame timing of the own device. When the distance between the base station 1 and the communication terminal 2 is large, it takes time until the SRS reaches the base station 1 after the communication terminal 2 transmits the SRS. The SRS is transmitted to the communication terminal 2 earlier than the communication terminal 2 having a small distance to the communication device 2 so that the SRS from the communication device 2 having a large distance to the communication device 2 can be received at the frame timing of the communication device 2. Notify you. As a result, the array transmission control period for the communication terminal 2 having a large distance from the base station 1 becomes long.

  FIG. 11 is a diagram illustrating transmission / reception timings of the communication terminal 2 having a small distance to the base station 1 and the communication terminal 2 having a large distance to the base station 1. As shown in FIG. 11, the timing 501 u at which the communication terminal 2 having a large distance to the base station 1 transmits the SRS by the control of the transmission timing of the communication terminal 2 by the base station 1 has a small distance to the base station 1. It is earlier than the timing 500u at which the communication terminal 2 transmits the SRS. The timing 501d at which the communication terminal 2 having a large distance to the base station 1 receives data from the base station 1 is the timing 500d at which the communication terminal 2 having a small distance to the base station 1 receives data from the base station 1. Is slower than Therefore, the array transmission control period 511 for the communication terminal 2 having a large distance to the base station 1 is longer than the array transmission control period 510 for the communication terminal 2 having a small distance to the base station 1.

  As described above, the communication terminal 2 having a large distance from the base station 1 has a long array transmission control period. Therefore, when the moving speed of the communication terminal 2 is high, the position of the communication terminal 2 is controlled by the array transmission control. Can vary significantly over time. As a result, the accuracy of the array transmission control for the communication terminal 2 may deteriorate, and the data of the base station 1 may not reach the communication terminal 2.

  Therefore, in the base station 1 according to this modification, the threshold value to be compared with the moving speed of the communication terminal 2 is set to be smaller as the distance from the base station 1 for the communication terminal 2 is larger. As a result, for the communication terminal 2 having a large distance from the base station 1, the frame configuration is changed from the frame configuration 1 to the frame configuration 2 even if the moving speed is relatively small, and the position of the communication terminal 2 is It is possible to suppress a large change in the array transmission control period. Therefore, the accuracy of array transmission control for the communication terminal 2 can be improved. The base station 1 according to this modification will be described in detail below.

  FIG. 12 is a block diagram showing a configuration of the base station 1 according to this modification. As shown in FIG. 12, the base station 1 according to the present modification is further provided with a distance acquisition unit 127 as compared with the base station 1 shown in FIG.

  The distance acquisition unit 127 acquires the distance between the communication terminal 2 and the base station 1 for each communication terminal 2 to be communicated with the base station 1. The distance acquisition unit 127 calculates the distance between the communication terminal 2 and the base station 1 based on the position of the communication terminal 2 notified from the communication terminal 2 and the position of the base station 1 stored in advance. To do. In step s1 described above, the distance acquisition unit 127 calculates the distance from the base station 1 for each communication terminal 2 to be communicated.

  In the base station 1 according to the present modification, the first and second threshold values common to the communication terminals 2 are not set as in the above example, but the individual first 1 And a second threshold is set. Specifically, each of the first and second threshold values compared with the transfer speed of a certain communication terminal 2 is set to be smaller as the distance between the communication terminal 2 and the base station 1 is larger.

  FIG. 13 is a diagram showing an example of the first threshold th1 and the second threshold th2 according to the present modification. The vertical axis and the horizontal axis in FIG. 13 indicate the moving speed and the distance to the base station for the communication terminal 2, respectively.

  As shown in FIG. 13, the first threshold th1 compared with the moving distance of the communication terminal 2 is set to be smaller as the distance between the communication terminal 2 and the base station 1 is larger. Similarly, the second threshold th2 compared with the moving distance of the communication terminal 2 is set to be smaller as the distance between the communication terminal 2 and the base station 1 is larger. In the example of FIG. 13, each of the first threshold value th1 and the second threshold value th2 compared with the moving distance of the communication terminal 2 increases as the distance between the communication terminal 2 and the base station 1 increases. However, it may be set so as to be reduced linearly.

  As shown in FIG. 13, the frame configuration determining unit 126 determines the correspondence between the distance between the communication terminal 2 and the base station 1 and the first threshold th1 and the second threshold th2 in advance. I remember it. When the frame configuration determination unit 126 compares the moving speed of the communication terminal 2 with each of the first threshold value th1 and the second threshold value th2 in step s2, the step s1 is performed. The first speed to be compared with the moving speed of the communication terminal 2 based on the distance between the communication terminal 2 and the base station 1 obtained by the distance acquisition unit 127 and the correspondence relationship stored in advance. The threshold value th1 and the second threshold value th2 are determined. Subsequent operations at the base station 1 are the same as those described with reference to FIG.

  In FIG. 13, in addition to the first threshold th1 and the second threshold th2, the communication terminals 2a, 2b, 2c in the (N-2) th and (N-1) th TDD frames 300 are shown. An example of the moving speed and the distance to the base station is also shown. In FIG. 13, “2a” surrounded by a wavy circle indicates the moving speed and the distance to the base station for the communication terminal 2a in the (N−2) th TDD frame 300. “2a” surrounded by a circle indicates the moving speed of the communication terminal 2a in the (N−1) th TDD frame 300 and the distance to the base station. The same applies to “2b” surrounded by a wavy circle and a solid circle, and “2c” surrounded by a wavy circle and a solid circle.

  In the example of FIG. 13, the moving speed of the communication terminal 2a is constant. And the distance between the communication terminal 2a and the base station 1 is small. Therefore, each of the first threshold th1 and the second threshold th2 compared with the moving speed of the communication terminal 2a is greater than the value used in the (N−1) th TDD frame 300 ( The value used in the (N-2) th TDD frame 300 is larger.

  In the example of FIG. 13, the moving speed of the communication terminal 2b is small. And the distance between the communication terminal 2b and the base station 1 is small. Therefore, each of the first threshold th1 and the second threshold th2 compared with the moving speed of the communication terminal 2b is greater than the value used in the (N−1) th TDD frame 300 ( The value used in the (N-2) th TDD frame 300 is larger.

  In the example of FIG. 13, the moving speed of the communication terminal 2c is high. And the distance between the communication terminal 2c and the base station 1 is large. Therefore, each of the first threshold value th1 and the second threshold value th2 compared with the moving speed of the communication terminal 2c is greater than the value used in the (N−1) th TDD frame 300 ( The value used in the (N-2) th TDD frame 300 is smaller. Since the moving speed of the communication terminal 2c in the (N-1) th TDD frame 300 is larger than the first threshold th1, the frame configuration is changed from the frame configuration 1 to the frame in the next Nth TDD frame 300. Change to configuration 2. Therefore, although the array transmission control period becomes longer due to an increase in the distance between the communication terminal 2c and the base station 1, the array configuration is caused by changing the frame configuration from the frame configuration 1 to the frame configuration 2. The transmission control period can be shortened. Therefore, it is possible to suppress an increase in the array transmission control period due to an increase in the distance between the communication terminal 2c and the base station 1. As a result, it is possible to prevent the position of the communication terminal 2c from changing greatly during the array transmission control period.

  On the other hand, the first threshold th1 compared with the moving speed of the communication terminal 2c is always set to a value when the distance between the communication terminal 2c and the base station 1 is zero, and changes. If not, the moving speed of the communication terminal 2c in the (N-1) th TDD frame 300 is smaller than the first threshold th1. Therefore, in the next Nth TDD frame 300, the frame configuration is not changed from the frame configuration 1 to the frame configuration 2. Therefore, in this case, the effect of shortening the array transmission control period by changing the frame configuration cannot be obtained. Therefore, there is a possibility that the array transmission control period for the communication terminal 2c becomes longer and the position of the communication terminal 2c changes greatly in the array transmission control period.

  As described above, in this modification, the first threshold th1 to be compared with the moving speed of the communication terminal 2c is set to be smaller as the distance from the base station 1 with respect to the communication terminal 2c is larger. Therefore, when the distance between the communication terminal 2c and the base station 1 increases, the frame configuration can be changed from the frame configuration 1 to the frame configuration 2. Therefore, it can suppress that the position of the communication terminal 2c changes largely in an array transmission control period, and the precision of the array transmission control with respect to the communication terminal 2c can further be improved. As a result, the transmission performance of the base station 1 is further improved.

  Note that the downlink radio resource allocation to the communication terminals 2a to 2c in the example of FIG. 13 can be performed, for example, as shown in FIGS.

<Fifth Modification>
As described above, when the base station 1 changes the frame configuration, the downlink subframe 302 included in the changed frame configuration and the frame configuration used by the peripheral base station 1 located around the base station 1 May overlap with the uplink subframe 302 included in. In other words, when the base station 1 changes the frame configuration, it is included in the downlink communication period 390 included in the changed frame configuration and the frame configuration used by the peripheral base station 1 located around the base station 1. The uplink communication period 380 may overlap.

  Specifically, when the neighboring base station 1 uses the default frame configuration 1, the third and eighth subframes 302 are uplink subframes 302 in the neighboring base station 1. When the base station 1 changes the frame configuration from the frame configuration 1 to the frame configuration 2, the base station 1 changes the third and eighth subframes 302 from the uplink subframe 302 to the downlink subframe 302. In the third and eighth subframes 302, the uplink subframe 302 of the neighboring base station 1 and the downlink subframe 302 of the base station 1 overlap each other.

  When the uplink subframe 302 of the neighboring base station 1 and the downlink subframe 302 of the base station 1 overlap, the neighboring base station 1 receives a signal from the communication terminal 2 with which the neighboring base station 1 communicates. In addition, there is a possibility of receiving a signal transmitted by the base station 1, and the signal from the base station 1 is subject to interference. Therefore, there is a possibility that the peripheral base station 1 cannot properly receive a signal from the communication terminal 2 to be communicated.

  Therefore, in the communication system 100 according to the present modification, when each base station 1 changes the frame configuration used by itself, notification information for notifying the changed frame configuration is transmitted to the periphery of the base station 1. Each neighboring base station 1 is notified. Then, in the neighboring base station 1, the downlink subframe 302 (downlink communication period) included in the frame configuration of the base station 1 notified by the notification information in the uplink subframe 302 included in the currently used frame configuration. 390) and the uplink subframe 302 (uplink communication period 380) are not used for uplink communication with the communication terminal 2. Hereinafter, the operation of the communication system 100 according to this modification will be described in detail.

  In each base station 1, when the frame configuration is changed in step s3, the frame configuration determination unit 126 generates notification information for notifying the changed frame configuration and inputs the notification information to the network communication unit 13. The network communication unit 13 transmits notification information to a server device (not shown) connected to the network through the network.

  In the server device, the arrangement status of the plurality of base stations 1 in the communication system 100 is stored. When the server device receives the notification information from the base station 1, the server device transmits the notification information to each peripheral base station 1 located around the base station 1 through the network. Thereby, when the frame configuration is changed in the base station 1, notification information for notifying the frame configuration after the change is notified to each neighboring base station 1.

  On the other hand, in each base station 1, when the network communication unit 13 receives the notification information from the server device, the control unit 12 includes the frame configuration currently used by the base station 1 and the frame configuration indicated by the notification information. Compare Then, the control unit 12 includes, in the uplink subframe 302 included in the frame configuration currently used by the base station 1, the frame configuration indicated by the notification information, that is, the downlink subframe included in the frame configuration used by the neighboring base station 1. It is determined that the uplink subframe 302 that overlaps with the frame is not used for uplink communication with the communication terminal 2. Thereafter, the control unit 12 performs wireless communication in an uplink subframe 302 that overlaps with a downlink subframe included in the frame configuration indicated by the notification information among the uplink subframes 302 included in the frame configuration currently used by the base station 1. When the signal from the communication terminal 2 is received by the processing unit 11, the received signal is discarded without performing reception processing such as discrete Fourier transform on the received signal. Alternatively, the control unit 12 performs reception processing on the received signal, but discards the data obtained thereby.

  When each base station 1 operates as described above and the base station 1 changes the frame configuration used by itself, the notification information for notifying the changed frame configuration is displayed around the base station 1. To each neighboring base station 1 located in the base station 1 in the upstream subframe 302 included in the currently used frame configuration. The uplink subframe 302 that overlaps the included downlink subframe 302 is not used for uplink communication with the communication terminal 2. As a result, the neighboring base station 1 is restrained from operating based on the signal transmitted from the communication terminal 2 and subjected to the interference of the signal from the base station 1, and as a result, the neighboring base station 1 malfunctions. It is suppressed.

  FIG. 14 is a diagram for explaining the frame configuration in each base station 1 when the frame configuration of a certain base station 1 is changed from the frame configuration 1 to the frame configuration 2. When the frame configuration 1 is used in each of the plurality of base stations 1 shown in FIG. 14, the central base station 1 (the base station 1 in which the service area 10 is indicated by hatching of sand (multiple points)) When the frame configuration is changed from the frame configuration 1 to the frame configuration 2 in FIG. 6, each of the six peripheral base stations 1 located in the vicinity of the central base station 1 in each of the upstream subframes included in the currently used frame configuration In 302, the uplink subframe 302 that overlaps with the downlink subframe 302 included in the frame configuration of the central base station 1 that is notified by the notification information is not used for uplink communication with the communication terminal 2. In FIG. 14, the service area 10 of the base station 1 in which the frame configuration 1 is used is indicated by hatching with hatching other than the six neighboring base stations 1.

<Other variations>
In the above example, the case where the present invention is applied to LTE has been described. However, the present invention can also be applied to other communication systems.

DESCRIPTION OF SYMBOLS 1 Base station 2 Communication terminal 12 Control part 13 Network communication part 14 Communication part 100 Communication system 125 Movement speed acquisition part 126 Frame structure determination part 127 Distance acquisition part 380 Uplink communication period 390 Downlink communication period 470a-470c

Claims (9)

A base station that communicates with a communication terminal using a communication frame in which a plurality of types of frame configurations are defined,
A communication unit that has a plurality of antennas and controls transmission directivity at the plurality of antennas based on a known signal from the communication terminal when transmitting a signal to the communication terminal;
A moving speed acquisition unit that acquires the moving speed of the communication terminal;
A frame configuration determining unit that determines a frame configuration to be used by the base station for the communication frame based on the moving speed;
Each of the plurality of types of frame configurations includes at least one known signal uplink communication period for transmitting a known signal by the communication terminal, and at least one data uplink communication that appears after the known signal uplink communication period. An uplink communication period and at least one downlink communication period during which data downlink communication is performed,
When the communication unit transmits data to the communication terminal in the at least one downlink communication period, the communication unit transmits the data using the plurality of antennas based on the known signal received from the communication terminal in the known signal uplink communication period. Control the directivity,
The frame configuration determination unit, when there is a communication terminal whose moving speed is higher than a first threshold, includes the upstream communication period for the known signal and the head of the at least one downstream communication period. Change the frame configuration used by the base station so that the period between the downlink communication period is shorter than the frame configuration currently used by the base station,
When the frame configuration used by the base station is changed, the communication unit is configured to change the at least one included in the changed frame configuration to a communication terminal whose moving speed is greater than the first threshold value. A base station that transmits data in a downlink communication period prior to the at least one downlink communication period included in the frame configuration before the change among the two downlink communication periods. The base station according to claim 1, wherein
When the frame configuration used by the base station is changed, the communication unit is configured to change the at least one included in the changed frame configuration to a communication terminal whose moving speed is greater than the first threshold value. A base station that transmits data in the first downlink communication period of the two downlink communication periods. A base station according to any one of claims 1 and 2,
A distance acquisition unit for acquiring a distance between the communication terminal and the base station;
The base station, wherein the first threshold value to be compared with the moving speed for a communication terminal is set to be smaller as the distance for the communication terminal is larger. A base station according to any one of claims 1 to 3,
The at least one downlink communication period includes a plurality of downlink communication periods;
For the communication terminal having the moving speed smaller than the first threshold, the communication unit transmits data to the communication terminal having the moving speed larger than the first threshold in the plurality of downlink communication periods. A base station that transmits data in a downlink communication period after a downlink communication period in which is transmitted. The base station according to claim 4, wherein
In the communication unit, the communication speed of the communication terminal is smaller than the second threshold value smaller than the first threshold value, and the movement speed is equal to the second threshold value in the plurality of downlink communication periods. A base station that transmits data in a downlink communication period after a downlink communication period in which data is transmitted to a communication terminal that is larger than a threshold value and smaller than the first threshold value. A base station according to any one of claims 1 to 4,
The frame configuration determination unit, when there is a communication terminal whose moving speed is greater than a second threshold value that is greater than the first threshold value, the known signal uplink communication period, and Changing the frame configuration used by the base station so that a period between the first downlink communication period of at least one downlink communication period is shorter than the frame configuration currently used by the base station, Bureau. A neighboring base station located around the base station according to any one of claims 1 to 6,
When the frame configuration used in the base station is changed, notification information for notifying the changed frame configuration is input to the neighboring base station,
The surrounding base station is
An input unit for inputting the notification information;
When the notification information is input to the input unit, the at least one included in the frame configuration notified by the notification information in the at least one uplink communication period included in the frame configuration currently used by the neighboring base station. A neighboring base station comprising: a determination unit that determines that an uplink communication period overlapping with one downlink communication period is not used for uplink communication with a communication terminal. A communication system comprising a plurality of base stations that communicate with a communication terminal using communication frames in which a plurality of types of frame configurations are defined,
Each of the plurality of base stations is
A communication unit that has a plurality of antennas and controls transmission directivity at the plurality of antennas based on a known signal from the communication terminal when transmitting a signal to the communication terminal;
A moving speed acquisition unit that acquires the moving speed of the communication terminal;
A frame configuration determining unit that determines a frame configuration used by the base station for the communication frame based on the moving speed;
Each of the plurality of types of frame configurations includes at least one known signal uplink communication period for transmitting a known signal by the communication terminal, and at least one data uplink communication that appears after the known signal uplink communication period. An uplink communication period and at least one downlink communication period during which data downlink communication is performed,
In each of the plurality of base stations, when transmitting data to a communication terminal in the at least one downlink communication period, the communication unit converts the known signal received from the communication terminal in the known signal uplink communication period. Based on the transmission directivity of the plurality of antennas,
In each of the plurality of base stations, when there is a communication terminal whose moving speed is greater than a threshold value, the frame configuration determination unit, the uplink communication period for the known signal, and the at least one downlink communication Change the frame configuration used by the base station so that the period between the first downlink communication period of the period is shorter than the frame configuration currently used by the base station,
In each of the plurality of base stations, when the frame configuration used by the base station is changed, the communication unit changes the frame configuration for the communication terminal whose moving speed is greater than the threshold value. A communication system that transmits data in a downlink communication period before the at least one downlink communication period included in the frame configuration before the change in the at least one downlink communication period included in the frame. Communication comprising a base station that communicates with a communication terminal using a communication frame in which a plurality of types of frame configurations are defined, and a peripheral base station that is located around the base station and communicates with the communication terminal using the communication frame A system,
Each of the plurality of types of frame configurations includes at least one known signal uplink communication period for transmitting a known signal by the communication terminal, and at least one data uplink communication that appears after the known signal uplink communication period. An uplink communication period and at least one downlink communication period during which data downlink communication is performed,
The base station
A communication unit that has a plurality of antennas and controls transmission directivity at the plurality of antennas based on a known signal from the communication terminal when transmitting a signal to the communication terminal;
A moving speed acquisition unit that acquires the moving speed of the communication terminal;
A frame configuration determining unit that determines a frame configuration to be used by the base station for the communication frame based on the moving speed;
When the communication unit transmits data to the communication terminal in the at least one downlink communication period, the communication unit transmits the data using the plurality of antennas based on the known signal received from the communication terminal in the known signal uplink communication period. Control the directivity,
When there is a communication terminal whose moving speed is greater than a threshold value, the frame configuration determination unit is configured to use the known signal uplink communication period and a leading downlink communication period of the at least one downlink communication period. The frame configuration used by the base station is changed so that the period between and the base station is shorter than the frame configuration currently used by the base station,
When the frame configuration used by the base station is changed, the communication unit transmits the at least one downlink communication included in the changed frame configuration to a communication terminal whose moving speed is greater than the threshold value. Transmitting data in a downlink communication period prior to the at least one downlink communication period included in the frame configuration before the change in the period,
When the frame configuration used in the base station is changed, notification information for notifying the changed frame configuration is input to the neighboring base station,
The surrounding base station is
An input unit for inputting the notification information;
When the notification information is input to the input unit, the at least one included in the frame configuration notified by the notification information in the at least one uplink communication period included in the frame configuration currently used by the neighboring base station. A communication system comprising: a determination unit that determines that an uplink communication period overlapping with one downlink communication period is not used for uplink communication with a communication terminal.

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