JP5508973B2 - Radio base station and communication control method - Google Patents

Description

  The present invention relates to a radio base station that transmits and receives radio signals to and from a radio terminal using a plurality of antennas, and a communication control method in the radio base station.

  In 3GPP (Third Generation Partnership Project), in a wireless communication system corresponding to LTE (Long Term Evolution) that is currently under standard development, in wireless communication between a wireless base station eNB and a wireless terminal UE, the wireless base station eNB Radio resources are allocated (for example, see Non-Patent Document 1). Moreover, in the radio | wireless communications system corresponding to LTE, frequency division duplex (FDD: Firequency Division Duplex) and time division duplex (TDD: Time Division Duplex) are used for radio | wireless communication between the radio base station eNB and the radio | wireless terminal UE. ) Is adopted.

  Furthermore, in an LTE (TDD-LTE) radio communication system employing TDD, the radio base station eNB transmits a downlink radio signal in order to ensure communication quality between the radio base station eNB and the moving radio terminal UE. It has been studied to perform control (adaptive array control) in which a beam is adaptively directed to the direction of the radio terminal UE during transmission.

3GPP TS 36.211 V8.7.0 “Physical Channels and Moduration”, MAY 2009

  As a method for calculating the antenna weight, when the radio base station eNB receives a sounding reference signal (SRS) that is an uplink radio signal from the radio terminal UE, an antenna for a downlink RB in the same frequency band as that of the SRS It is assumed that the weight is calculated.

  However, in the TDD-LTE radio communication system, OFDMA (Orthogonal Frequency Division Multiplexing Access) is adopted for downlink radio communication, and SC-FDMA (Single Carrier Frequency Division Multiple Access) is adopted for uplink radio communication. Has been. In these multiplexing schemes, user multiplexing is realized by arranging radio resources (resource blocks: RB) in two dimensions of frequency and time separately for uplink and downlink.

  For this reason, the frequency band of the downlink RB assigned to the radio terminal UE may not be the same as the frequency band of the uplink RB. In such a case, since there is no downlink RB in the same frequency band as the SRS frequency band, the antenna weight for the downlink RB cannot be calculated.

  In view of the above problems, an object of the present invention is to provide a radio base station and a communication control method that can accurately calculate antenna weights for downlink radio resources.

  In order to solve the above-described problems, the present invention has the following features. The first feature of the present invention is that an adaptive array type radio base station (radio base station eNB1-) that applies antenna weights to a plurality of adaptive array antennas 108A, adaptive array antennas 108B, adaptive array antennas 108C, and adaptive array antennas 108D). 1), a reception unit (radio communication unit 106) that receives a reference signal (SRS) to be referred to in the calculation of the antenna weight from the serving radio terminal (radio terminal UE2-1), and before the target subframe An allocation unit (RB allocation unit 112) that preferentially allocates radio resources (downlink resource blocks) having a frequency band used for transmitting a reference signal received at a time close to the target subframe to the serving radio terminal. And the reference signal is the service signal. And gist to be transmitted while switching the frequency band by bridging wireless terminal.

  Such a radio base station is a reference signal transmitted by a serving radio terminal and uses a frequency band used for transmitting a reference signal received at a time close to the target subframe before the target subframe. Preferentially assign the radio resources to the serving radio terminal. Therefore, the radio base station can refer to a reference signal considered to have a propagation environment close to the downlink radio resource allocated to the serving radio terminal in calculating the antenna weight for the downlink radio resource allocated to the serving radio terminal. This makes it possible to accurately calculate the antenna weight.

  A second feature of the present invention is a calculation unit that calculates the antenna weight so that a desired wave direction of a beam having a frequency band used for transmitting a reference signal from the serving wireless terminal is directed to the serving wireless terminal. The gist is to include (antenna weight calculation unit 114).

  The gist of the third feature of the present invention is that the target subframe is a plurality of subframes.

  According to a fourth aspect of the present invention, the reference signal is transmitted from the serving wireless terminal while switching a frequency band for each predetermined switching time width, and the allocating unit is configured to transmit the target signal before the target subframe. The gist is that a radio resource having a frequency band used for transmitting a reference signal received within a predetermined switching time width from a subframe is preferentially allocated to the serving radio terminal.

  According to a fifth feature of the present invention, the reference signal is transmitted at least once by the serving radio terminal within a communication frame time width, and the allocating unit includes the target subframe before the target subframe. The gist is to preferentially allocate a radio resource having a frequency band used for transmitting a reference signal received from a frame within the communication frame time width.

  A sixth feature of the present invention is an adaptive array radio base station that applies antenna weights to a plurality of antennas, and receives a reference signal to be referred to in calculating the antenna weight from a non-serving radio terminal. (Radio communication unit 106) and a null direction of a beam having a frequency band used for transmitting a reference signal received at a time close to the target subframe before the target subframe is directed to the non-serving terminal And a calculation unit (antenna weight calculation unit 114) for calculating the antenna weight, wherein the reference signal is transmitted by the non-serving radio terminal while switching frequency bands.

  A seventh feature of the present invention is a communication control method in an adaptive array radio base station that applies antenna weights to a plurality of antennas, and receives a reference signal to be referred to in the calculation of the antenna weights from a serving radio terminal. And preferentially assigning to the serving radio terminal a radio resource having a frequency band used for transmitting a reference signal received at a time close to the target subframe before the target subframe. The gist of the invention is that the reference signal is transmitted by the serving wireless terminal while switching a frequency band.

  An eighth feature of the present invention is a communication control method in an adaptive array radio base station that applies antenna weights to a plurality of antennas, wherein a reference signal to be referred to in the calculation of the antenna weights is transmitted from a non-serving radio terminal. Receiving, and so that a null direction of a beam having a frequency band used for transmitting a reference signal received at a time close to the target subframe before the target subframe is directed to the non-serving terminal. And a step of calculating an antenna weight, wherein the reference signal is transmitted while the frequency band is switched by the non-serving radio terminal.

  According to the present invention, it is possible to accurately calculate antenna weights for downlink radio resources.

1 is an overall schematic configuration diagram of a wireless communication system according to an embodiment of the present invention. It is a figure which shows the format of a resource block based on embodiment of this invention. It is a figure which shows the format of the flame | frame based on embodiment of this invention. It is a figure which shows the structure of all the frequency bands which can be utilized in the radio | wireless communication between a radio base station and a radio | wireless terminal based on embodiment of this invention. 1 is a configuration diagram of a radio base station according to an embodiment of the present invention. It is a figure which shows the 1st example of a response | compatibility with SRS and allocation downlink RB based on embodiment of this invention. It is a figure which shows the 2nd example of a response | compatibility with SRS and allocation downlink RB based on embodiment of this invention. It is a flowchart which shows the 1st operation | movement of the wireless base station based on embodiment of this invention. It is a flowchart which shows 2nd operation | movement of the wireless base station based on embodiment of this invention.

  Next, an embodiment of the present invention will be described with reference to the drawings. Specifically, (1) the configuration of the radio communication system, (2) the configuration of the radio base station, (3) the operation of the radio base station, (4) operations and effects, and (5) other embodiments will be described. In the description of the drawings in the following embodiments, the same or similar parts are denoted by the same or similar reference numerals.

(1) Configuration of Radio Communication System FIG. 1 is an overall schematic configuration diagram of a radio communication system 10 according to an embodiment of the present invention.

  A wireless communication system 10 illustrated in FIG. 1 is a TDD-LTE wireless communication system. The radio communication system 10 includes a radio base station eNB1-1 and a radio base station eNB1-2, a radio terminal UE2-1, and a radio terminal UE2-2.

  In FIG. 1, a radio base station eNB1-1 and a radio base station eNB1-2 constitute an E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network). The radio terminal UE2-1 exists in the cell 3-1, which is a communicable area provided by the radio base station eNB1-1. The radio terminal UE2-2 exists in a cell 3-2 that is a communicable area provided by the radio base station eNB1-2.

  The radio terminal UE2-1 is a resource block allocation target by the radio base station eNB1-1. On the other hand, the radio terminal UE2-2 is not a resource block allocation target by the radio base station eNB1-1. In this case, on the basis of the radio base station eNB1-1, the radio terminal UE2-1 is a serving radio terminal, and the radio terminal UE2-2 is a non-serving radio terminal.

  Time division duplex is adopted for radio communication between the radio base station eNB1-1 and the radio terminal UE2-1 and radio communication between the radio base station eNB1-2 and the radio terminal UE2-2. In addition, OFDMA (Orthogonal Frequency Division Multiplexing Access) is adopted for downlink wireless communication, and SC-FDMA (Single Carrier Frequency Division Multiple Access) is adopted for uplink wireless communication. Here, downlink means a direction from the radio base station eNB1-1 to the radio terminal UE2-1 and a direction from the radio base station eNB1-2 to the radio terminal UE2-2. Uplink means a direction from the radio terminal UE2-1 to the radio base station eNB1-1 and a direction from the radio terminal UE2-2 to the radio base station eNB1-2.

  The radio base station eNB1-1 assigns a resource block (RB: Resource Block) as a radio resource to the radio terminal UE2-1 in the cell 3-1. Similarly, the radio base station eNB1-2 assigns a resource block (RB) to the radio terminal UE2-2 in the cell 3-2.

  Resource blocks include a downlink resource block (downlink RB) used for downlink radio communication and an uplink resource block (uplink RB) used for uplink radio communication. The plurality of downlink resource blocks are arranged in the frequency direction and the time direction. Similarly, the plurality of uplink resource blocks are arranged in the frequency direction and the time direction.

  FIG. 2 is a diagram illustrating a format of a resource block. As shown in FIG. 2, the resource block is configured by one subframe having a time length of 1 [ms] in the time direction. The subframe includes time zones S1 to S14. Of these time zones S1 to S14, time zones S1 to S7 constitute the first half time slot (time slot 1), and time zones S8 to S14 consist of the second half time slot (time slot 2). ).

  As shown in FIG. 2, the resource block has a frequency width of 180 [kHz] in the frequency direction. The resource block is composed of 12 symbol carriers F1 to F12 having a frequency width of 15 [kHz].

  In the time direction, one frame is composed of a plurality of subframes. FIG. 3 is a diagram showing a frame format. The frame shown in FIG. 3 is composed of 10 subframes. The frame includes 10 subframes: a subframe of a downlink resource block, a subframe of both a downlink resource block and an uplink resource block (special subframe: SSF), a subframe of an uplink resource block, and a subframe of an uplink resource block , Downlink resource block subframe, downlink resource block subframe, special subframe, uplink resource block subframe, uplink resource block subframe, downlink resource block subframe.

  Further, in the frequency direction, all frequency bands that can be used in radio communication between one radio base station eNB and one radio terminal UE have bands for a plurality of resource blocks. Further, the entire frequency band is divided into frequency bands that are multiples of 4 times the resource block. FIG. 4 is a diagram illustrating a configuration of all frequency bands that can be used in radio communication between one radio base station eNB and one radio terminal UE. As shown in FIG. 4, all frequency bands that can be used in radio communication between one radio base station eNB and one radio terminal UE have a band corresponding to 96 resource blocks. Further, the entire frequency band is divided into frequency bands 1 to 4 having a band corresponding to 24 resource blocks.

  The downlink resource block is divided into a control information channel (PDCCH: Physical Downlink Control CHannel) for downlink control information transmission and a shared data channel (PDSCH: Physical Downlink Shared CHannel) for downlink user data transmission in the time direction. Composed.

  On the other hand, in the uplink resource block, a control information channel (PUCCH: Physical Uplink Control CHannel) for uplink control information transmission is configured at both ends of all frequency bands that can be used for uplink radio communication. A shared data channel (PUSCH: Physical Uplink Shared CHannel) for user data transmission is configured.

(2) Configuration of Radio Base Station FIG. 5 is a configuration diagram of the radio base station eNB1-1. The radio base stations eNB1-2 have the same configuration. As illustrated in FIG. 5, the radio base station eNB1-1 is an adaptive array radio base station that applies antenna weights to a plurality of antennas, and includes a control unit 102, a storage unit 103, an I / F unit 104, and radio communication. Unit 106, modulation / demodulation unit 107, adaptive array antenna 108A, adaptive array antenna 108B, adaptive array antenna 108C, and adaptive array antenna 108D.

  The control unit 102 is configured by a CPU, for example, and controls various functions provided in the radio base station eNB1-1. The control unit 102 includes an RB allocation unit 112 and an antenna weight calculation unit 114. The memory | storage part 103 is comprised by memory, for example, and memorize | stores the various information used for control etc. in the radio base station eNB1-1. The I / F unit 104 can communicate with other radio base stations eNB via the X1 interface. The I / F unit 104 can communicate with an EPC (Evolved Packet Core), specifically, an MME (Mobility Management Entity) / S-GW (Serving Gateway) via the S1 interface.

(2.1) First Process When the serving radio terminal UE2-1 transmits a sounding reference signal (first SRS), the following first process is performed.

  The serving radio terminal UE2-1 uses the frequency hopping method, and transmits the first SRS while switching the frequency band used for transmitting the first SRS. In addition, the serving radio terminal UE2-1 transmits the first SRS at the timing of the special subframe. The first SRS is an uplink radio signal in a radio frequency band.

  For example, as shown in FIG. 4, when the entire frequency band is divided into frequency band 1 to frequency band 4, the serving radio terminal UE2-1 switches frequency band 1 to frequency band 4 in a predetermined order. The first SRS is transmitted. When the frame format is as shown in FIG. 3, the serving radio terminal UE2-1 transmits the first SRS twice within the time of one frame. In addition, the radio base station eNB1-1 transmits instruction information for instructing the serving radio terminal UE2-1 about the transmission timing of the first SRS in advance. The serving radio terminal UE2-1 sets the transmission timing of the first SRS based on the received instruction information. Thus, the transmission timing of the first SRS is determined in advance. Therefore, the radio base station eNB1-1 can discriminate between the first SRS and another radio signal (for example, a second SRS described later) based on the reception timing.

(2-1) Processing at the time of receiving the first SRS In the first processing, the following processing is performed at the time of receiving the first SRS. That is, the radio communication unit 106 receives the first SRS transmitted from the serving radio terminal UE2-1 via the adaptive array antenna 108A to the adaptive array antenna 108D. Radio communication section 106 detects the frequency band used for transmission of the received first SRS, and outputs information on the frequency band (first SRS frequency band information) to RB allocation section 112 in control section 102.

  The wireless communication unit 106 includes a low noise amplifier (LNA) and a mixer (not shown). The wireless communication unit 106 amplifies the received first SRS and converts (down-converts) it into a baseband signal. Further, the wireless communication unit 106 outputs the baseband signal to the modulation / demodulation unit 107.

  An RB allocation unit 112 in the control unit 102 generates an allocation value (uplink RB allocation value) of an uplink resource block obtained by processing in a medium access control (MAC) layer. This uplink RB allocation value includes a resource block number that is information for uniquely identifying the time band and frequency band of the uplink resource block already allocated to the serving radio terminal UE2-1. The RB allocation unit 112 outputs the uplink RB allocation value to the modulation / demodulation unit 107.

  Modulation / demodulation section 107 removes CP (Cyclic Prefix) from the input baseband signal. The CP is a copy of the end portion of the OFDM symbol and is included in a guard interval period provided to suppress intersymbol interference caused by multipath. Modulation / demodulation section 107 performs fast Fourier transform on the baseband signal from which CP has been removed, to obtain a frequency domain signal. The frequency domain signal is output to the antenna weight calculation unit 114 in the control unit 102.

  When the frequency domain signal from the modulation / demodulation unit 107 is input to the antenna weight calculation unit 114, the antenna weight calculation unit 114 performs the serving radio terminal UE2- for each adaptive array antenna 108A to adaptive array antenna 108D based on the frequency domain signal. An antenna weight (reception weight) that maximizes the signal-to-interference and noise ratio (SINR) when receiving an uplink radio signal from 1 is calculated.

  Specifically, the antenna weight calculation unit 114 identifies the time band and frequency band of the uplink resource block allocated to the serving radio terminal UE2-1 based on the uplink RB allocation value generated by the RB allocation unit 112. . Further, the antenna weight calculation unit 114 corresponds to the PUSCH frequency band in the uplink resource block allocated to the serving radio terminal UE2-1 based on the frequency domain signal corresponding to the identified frequency band of the uplink resource block. The reception weight of each adaptive array antenna 108A to adaptive array antenna 108D is calculated. Further, the antenna weight calculation unit 114 stores the calculated reception weight in the storage unit 103 together with the corresponding frequency band information and current time information (time stamp information).

  The modulation / demodulation unit 107 performs channel equalization processing on the acquired frequency domain signal. Next, the modulation / demodulation unit 107 performs inverse discrete Fourier transform on the signal subjected to channel equalization processing. Next, the modulation / demodulation unit 107 performs demodulation and decoding processing on the signal that has been subjected to inverse discrete Fourier transform. Thereby, data included in the first SRS transmitted by the radio terminal UE2-1 is obtained. Data is output to the control unit 102.

  The RB allocation unit 112 in the control unit 102 allocates downlink resource blocks to the serving radio terminal UE2-1.

  Specifically, the RB allocation unit 112 adopts a PF (Propotional Fair) method and determines a frequency band (allocation candidate frequency band) of a downlink resource block that can be allocated to the serving radio terminal UE2-1.

  Next, the RB allocation unit 112 determines the timing for allocating downlink resources to the serving radio terminal UE2-1. Specifically, the RB allocating unit 112 determines the timing of at least one of the subframes of the downlink resource block from the latest received first SRS timing to the last part of the frame including the first SRS timing. To decide. Alternatively, the RB allocating unit 112 may perform downlink from the latest received first SRS timing to the timing in which the first SRS is assumed to be received in the same frequency band as that of the first SRS. The timing of at least one of the subframes of the resource block is determined.

  Next, the RB allocation unit 112 recognizes the frequency band used for transmission of the latest received first SRS based on the first SRS frequency band information. Next, the RB allocation unit 112 determines whether or not the frequency band used for transmission of the latest received first SRS and the allocation candidate frequency band overlap. When the frequency band used for the transmission of the latest received first SRS and the allocation candidate frequency band overlap, the RB allocation unit 112 corresponds to the determined timing of the subframe and receives the latest received In order to allocate the downlink resource block having the overlapping frequency band of the frequency band used for the transmission of the first SRS and the allocation candidate frequency band to the serving radio terminal UE2-1 that is the latest transmission source of the first SRS, An RB allocation value (downlink RB allocation value) is generated. The downlink RB allocation value is obtained by processing in the medium access control (MAC) layer, similarly to the above-described uplink RB allocation value. Also, the downlink RB allocation value includes a resource block number that is information for uniquely identifying the time band and the frequency band of the downlink resource block allocated to the serving radio terminal UE2-1.

  The RB allocation unit 112 outputs the downlink RB allocation value to the modulation / demodulation unit 107. Further, the RB assigning unit 112 assigns the resource block number of the downlink resource block assigned to the serving radio terminal UE2-1 through the modulation / demodulation unit 107, the radio communication unit 106, and the adaptive array antenna 108A to the adaptive array antenna 108D. To the serving radio terminal UE2-1.

  6 and 7 are diagrams illustrating examples of correspondence between SRSs and allocated downlink resource blocks.

  In FIG. 6, the radio terminal UE2-1 transmits the first SRS while switching the frequency band at the time of transmission to each of the frequency band 1 to the frequency band 4. The radio base station eNB1-1 is a downlink having a frequency band used for transmission of the first SRS in a frame including the reception timing of the first SRS and in the subframe timing of the downlink resource block after the reception timing. The resource block is assigned to the radio terminal UE2-1 in preference to the downlink resource block having another frequency band.

  In FIG. 7, the radio terminal UE2-1 transmits the first SRS while switching the frequency band at the time of transmission to each of the frequency band 1 to the frequency band 4. The radio base station eNB1-1 is a sub-resource block of the downlink resource block from the reception timing of the first SRS to the timing at which reception of the first SRS next to the first SRS is assumed in the same frequency band as the first SRS. At the frame timing, the downlink resource block having the frequency band used for transmission of the first SRS is assigned to the radio terminal UE2-1 in preference to the downlink resource block having another frequency band.

(2.1.2) Processing during transmission of downlink radio signal to serving radio terminal UE2-1 Thereafter, transmission of a downlink radio signal to serving radio terminal UE2-1 is performed. That is, when data from the control unit 102 is input, the modulation / demodulation unit 107 encodes and modulates the data to obtain a frequency domain signal.

  The antenna weight calculation unit 114 transmits, for each adaptive array antenna 108A to adaptive array antenna 108D, a downlink radio signal for the serving radio terminal UE2-1 using a downlink resource block assigned to the serving radio terminal UE2-1. The antenna weight (transmission weight) at the time of performing is calculated.

  Specifically, the antenna weight calculation unit 114 specifies the time band and the frequency band of the downlink resource block to be allocated to the serving radio terminal UE2-1 based on the downlink RB allocation value from the RB allocation unit 112. The PDSCH in the identified downlink resource block is a PDSCH for which a transmission weight is set.

  Next, the antenna weight calculation unit 114 has the latest time among the reception weights corresponding to each adaptive array antenna 108A to adaptive array antenna 108D, and the corresponding frequency band is serving radio. The reception weight including the frequency band of the downlink resource block to be allocated to the terminal UE2-1 is specified. Furthermore, the antenna weight calculation unit 114 sets the reception weight for each specified adaptive array antenna 108A to adaptive array antenna 108D to each adaptive array antenna 108A to adaptive response corresponding to the frequency band of the downlink resource block for which transmission weights are set. The transmission weight of the array antenna 108D is assumed.

  The specified reception weight for each adaptive array antenna 108A to adaptive array antenna 108D is an antenna weight that maximizes the SINR when an uplink radio signal is received from the serving radio terminal UE2-1. Therefore, when the reception weight is set as the transmission weight, the transmission weight becomes an antenna weight in which the desired wave direction of the beam is directed to the serving radio terminal UE2-1.

  The modulation / demodulation unit 107 performs weighting processing for combining the transmission weight calculated by the antenna weight calculation unit 114 and the frequency domain signal. The modulation / demodulation unit 107 performs inverse fast Fourier transform on the weighted frequency domain signal to obtain a baseband signal. Further, modulation / demodulation section 107 adds a CP to the baseband signal and outputs the result to radio communication section 106.

  The radio communication unit 106 converts (up-converts) the baseband signal to which the CP is added into a downlink radio signal in the radio frequency band. Further, the radio communication unit 106 amplifies the downlink radio signal in the radio frequency band, and transmits the amplified downlink radio signal in the radio frequency band via the adaptive array antenna 108A to the adaptive array antenna 108D.

(2.2) Second Process When the non-serving radio terminal UE2-2 transmits a sounding reference signal (second SRS) and the radio base station eNB1-1 receives the second SRS, the following second Is performed.

(2.2.1) Processing at the time of receiving the second SRS The non-serving radio terminal UE2-2 uses the frequency hopping method, and transmits the frequency band used for transmission of the second SRS while switching.

  The radio communication unit 106 receives the first SRS transmitted from the serving radio terminal UE2-1 and the second SRS transmitted from the non-serving radio terminal UE2-2 via the adaptive array antenna 108A to the adaptive array antenna 108D. Receive.

  Further, the wireless communication unit 106 amplifies the received first SRS and converts (downconverts) it into a baseband signal. Further, the wireless communication unit 106 outputs the baseband signal to the modulation / demodulation unit 107. Similarly, the wireless communication unit 106 amplifies the received second SRS and converts (downconverts) it into a baseband signal. Further, the wireless communication unit 106 outputs the baseband signal to the modulation / demodulation unit 107.

  Modulation / demodulation section 107 and antenna weight calculation section 114 perform the same processing as the processing at the time of reception of the first SRS in the first processing described above on each of the first SRS and the second SRS. However, the antenna weight calculation unit 114 has the maximum SINR when receiving the uplink radio signal from the serving radio terminal UE2-1, and the minimum SINR when receiving the uplink radio signal from the non-serving radio terminal UE2-2. An antenna weight (reception weight) is calculated.

  Data included in the first SRS from the modulation / demodulation unit 107 is input to the control unit 102. Further, the data included in the second SRS from the modulation / demodulation unit 107 is input to the control unit 102.

(2.2.2) Processing during transmission of downlink radio signal to serving radio terminal UE2-1 Thereafter, the modulation / demodulation unit 107 and the antenna weight calculation unit 114 perform the same processing as the first processing. That is, when data from the control unit 102 is input, the modulation / demodulation unit 107 encodes and modulates the data to obtain a frequency domain signal.

  The antenna weight calculation unit 114 transmits, for each adaptive array antenna 108A to adaptive array antenna 108D, a downlink radio signal for the serving radio terminal UE2-1 using a downlink resource block assigned to the serving radio terminal UE2-1. The antenna weight (transmission weight) at the time of performing is calculated.

  Specifically, as in the first process, the antenna weight calculation unit 114, based on the downlink RB allocation value from the RB allocation unit 112, and the time zone of the downlink resource block to be allocated to the serving radio terminal UE2-1 and Specify the frequency band. The PDSCH in the identified downlink resource block is a PDSCH for which a transmission weight is set.

  Next, the antenna weight calculation unit 114 has the latest time among the reception weights corresponding to each adaptive array antenna 108A to adaptive array antenna 108D, and the corresponding frequency band is serving radio. The reception weight including the frequency band of the downlink resource block to be allocated to the terminal UE2-1 is specified. Furthermore, the antenna weight calculation unit 114 sets the reception weight for each specified adaptive array antenna 108A to adaptive array antenna 108D to each adaptive array antenna 108A to adaptive response corresponding to the frequency band of the downlink resource block for which transmission weights are set. The transmission weight of the array antenna 108D is assumed.

  The reception weight for each of the specified adaptive array antenna 108A to adaptive array antenna 108D has the maximum SINR when receiving the uplink radio signal from the serving radio terminal UE2-1, and the reception weight from the non-serving radio terminal UE2-2. This is an antenna weight that minimizes the SINR when an uplink radio signal is received. Therefore, when the reception weight is set as the transmission weight, the transmission weight is such that the desired wave direction of the beam is directed to the serving radio terminal UE2-1 and the null direction of the beam is to the non-serving radio terminal UE2-2. Antenna weight to face.

  The modulation / demodulation unit 107 performs weighting processing for combining the transmission weight calculated by the antenna weight calculation unit 114 and the frequency domain signal. The modulation / demodulation unit 107 performs inverse fast Fourier transform on the weighted frequency domain signal to obtain a baseband signal. Further, modulation / demodulation section 107 adds a CP to the baseband signal and outputs the result to radio communication section 106.

  The radio communication unit 106 converts (up-converts) the baseband signal to which the CP is added into a downlink radio signal in the radio frequency band. Further, the radio communication unit 106 amplifies the downlink radio signal in the radio frequency band, and transmits the amplified downlink radio signal in the radio frequency band via the adaptive array antenna 108A to the adaptive array antenna 108D.

(3) Operation of Radio Base Station FIG. 8 is a flowchart showing a first operation of the radio base station eNB1-1. The flowchart shown in FIG. 8 corresponds to the case where the first process described above is performed.

  In step S101, the radio base station eNB1-1 receives the first SRS from the serving radio terminal UE2-1.

  In step S102, the radio base station eNB1-1 allocates a downlink resource block having a frequency band used for transmission of the first SRS to the serving radio terminal UE2-1 that is the latest SRS transmission source. .

  In step S104, the radio base station eNB1-1 uses the downlink resource block allocated to the serving radio terminal UE2-1 that is the transmission source of the most recently received first SRS, based on the most recently received first SRS. Sets the transmission weight when transmitting a signal.

  In step S105, the radio base station eNB1-1 transmits a downlink radio signal to the serving radio terminal UE2-1 using the downlink resource block allocated to the serving radio terminal UE2-1 that is the latest SRS transmission source. Send.

  FIG. 9 is a flowchart showing a second operation of the radio base station eNB1-1. The flowchart shown in FIG. 9 corresponds to the case where the second process described above is performed.

  In step S201, the radio base station eNB1-1 receives the first SRS from the serving radio terminal UE2-1.

  In step S202, the radio base station eNB1-1 assigns a downlink resource block having a frequency band used for transmission of the first SRS to the serving radio terminal UE2-1 that is the latest SRS transmission source. .

  In step S203, the radio base station eNB1-1 receives the second SRS from the non-serving radio terminal UE2-2.

  In step S204, the radio base station eNB1-1 assigns the downlink resource block assigned to the serving radio terminal UE2-1 that is the latest transmission source of the first SRS, based on the latest received first SRS and the received second SRS. Is used to set a transmission weight when transmitting a downlink radio signal.

  In step S205, the radio base station eNB1-1 transmits a downlink radio signal to the serving radio terminal UE2-1 using the downlink resource block allocated to the serving radio terminal UE2-1 that is the latest SRS transmission source. Send.

(4) Operation and Effect As described above, according to the present embodiment, the radio base station eNB1-1 receives the first SRS transmitted by the serving radio terminal UE2-1. Further, the radio base station eNB1-1 is the latest in the subframe timing of the downlink resource block at the time point that is after the latest received first SRS timing and close to the latest received first SRS timing. A downlink resource block having a frequency band used for transmission of the received first SRS is allocated to the serving radio terminal UE2-1. As a result, the radio base station eNB1-1 corresponds to the downlink resource block allocated to the serving radio terminal UE2-1 with the first SRS considered to have a propagation environment close to the downlink resource block allocated to the serving radio terminal UE2-1. By referring to the calculation of the antenna weight, the antenna weight in which the desired wave direction of the beam is directed to the serving radio terminal UE2-1 can be calculated, and the antenna weight can be calculated accurately.

  Moreover, when the radio base station eNB1-1 receives the second SRS transmitted by the non-serving radio terminal UE2-2, the radio base station eNB1-1 corresponds to the downlink resource block assigned to the serving radio terminal UE2-1. By referring to the calculation of the antenna weight, it is possible to calculate the antenna weight in which the desired wave direction of the beam is directed to the serving radio terminal UE2-1 and the null direction of the beam is directed to the non-serving radio terminal UE2-2. The antenna weight can be calculated more accurately.

  In addition, the radio base station eNB1-1 has the frequency band used for transmitting the most recently received first SRS at the subframe timing of the downlink resource block in the frame including the most recently received first SRS timing. A downlink resource block is allocated to the serving radio terminal UE2-1. Accordingly, the time from the most recently received first SRS timing to the assigned downlink resource block timing can be within one frame time. For this reason, by shortening the time from the timing of the first SRS to the timing of the downlink resource block allocated to the serving radio terminal UE2-1, the propagation environment in the first SRS and the downlink resource block allocated to the serving radio terminal UE2-1 are reduced. It can be guaranteed that the propagation environment is close.

(4) Other Embodiments As described above, the present invention has been described according to the embodiment. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  In the embodiment described above, the radio base station eNB1-1 sets the time from the most recently received first SRS timing to the assigned downlink resource block timing within the time of one frame. However, the radio base station eNB1-1 sets the time from the most recently received first SRS timing to the assigned downlink resource block timing within the period of the period in which the frequency band used for transmission of the first SRS is switched, You may make it be in the time of the transmission period of 1st SRS. Also in this case, the time from the timing of the first SRS to the timing of the downlink resource block allocated to the serving radio terminal UE2-1 is shortened, and the propagation environment in the first SRS and the downlink resource allocated to the serving radio terminal UE2-1 are reduced. It can be guaranteed that the propagation environment of the block is close.

  In the above-described embodiment, the serving radio terminal UE2-1 transmits the first SRS at the timing of the special subframe. However, the transmission timing of the first SRS is not limited to this, and may be a timing agreed in advance between the radio base station eNB1-1 and the serving radio terminal UE2-1. However, it is preferable that the transmission timing of the first SRS exists once within the time of at least one frame.

  In the above-described embodiment, the radio base station eNB1-1 uses the reception weight as the transmission weight. However, the radio base station eNB1-1 may calculate the transmission weight regardless of the reception weight.

  In the above-described embodiments, the TDD-LTE radio communication system has been described. However, radio communication employing up / down asymmetric communication in which the frequency band of the uplink radio signal allocated to the radio terminal is different from the frequency band of the downlink radio signal. The present invention can be similarly applied to any system.

  Thus, it should be understood that the present invention includes various embodiments and the like not described herein. Therefore, the present invention is limited only by the invention specifying matters in the scope of claims reasonable from this disclosure.

  eNB1-1, eNB1-2 ... wireless base station, UE2-1, UE2-2 ... wireless terminal, 3-1, 3-2 ... cell, 10 ... wireless communication system, 102 ... control unit, 103 ... storage unit, 104 ... I / F unit, 106 ... radio communication unit, 107 ... modulation / demodulation unit, 108A, 108B, 108C, 108D ... adaptive array antenna, 112 ... RB allocation unit, 114 ... antenna weight calculation unit

Claims (8)

An adaptive array radio base station that applies antenna weights to a plurality of antennas,
A receiver that receives a reference signal to be referred to in the calculation of the antenna weight from a serving wireless terminal;
An allocating unit that preferentially allocates a radio resource having a frequency band used for transmitting a reference signal received at a time close to the target subframe before the target subframe to the serving radio terminal;
The reference signal is a radio base station that is transmitted while switching frequency bands by the serving radio terminal.   The radio | wireless of Claim 1 provided with the setting part which sets the said antenna weight so that the desired wave direction of the beam which has the frequency band used for transmission of the reference signal from the said serving radio | wireless terminal may face the said serving radio | wireless terminal. base station.   The radio base station according to claim 1, wherein the target subframe is a plurality of subframes. The reference signal is transmitted from the serving wireless terminal while switching the frequency band for each predetermined switching time width,
The allocating unit preferentially uses a radio resource having a frequency band used for transmitting a reference signal received from the target subframe within the predetermined switching time width before the target subframe. The radio base station according to claim 1, which is assigned to. The reference signal is transmitted at least once by the serving wireless terminal within a communication frame time width;
2. The allocation unit preferentially allocates radio resources having a frequency band used for transmitting a reference signal received from the target subframe within the communication frame time width before the target subframe. The radio base station described in 1. An adaptive array radio base station that applies antenna weights to a plurality of antennas,
A receiver that receives a reference signal to be referred to in the calculation of the antenna weight from a non-serving wireless terminal;
The antenna weight is set so that a null direction of a beam having a frequency band used for transmitting a reference signal received at a time close to the target subframe before the target subframe is directed to the non-serving terminal. A setting unit,
The reference signal is a radio base station that is transmitted while the frequency band is switched by the non-serving radio terminal. A communication control method in an adaptive array radio base station that applies antenna weights to a plurality of antennas,
Receiving a reference signal to be referred to in the calculation of the antenna weight from a serving wireless terminal;
Preferentially assigning a radio resource having a frequency band used for transmission of a reference signal received at a time close to the target subframe before the target subframe to the serving radio terminal;
The communication control method, wherein the reference signal is transmitted while the frequency band is switched by the serving wireless terminal. A communication control method in an adaptive array radio base station that applies antenna weights to a plurality of antennas,
Receiving a reference signal to be referred to in calculating the antenna weight from a non-serving wireless terminal;
The antenna weight is calculated so that a null direction of a beam having a frequency band used for transmitting a reference signal received at a time close to the target subframe before the target subframe is directed to the non-serving terminal. With steps,
The communication control method, wherein the reference signal is transmitted while switching a frequency band by the non-serving wireless terminal.

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