JP2010177975A - Radio terminal and wireless communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To sufficiently improve communication quality even if a radio base station receives an interference signal in up-communication. <P>SOLUTION: A radio terminal UE4 includes a transmission unit 312 which transmits a radio signal to the radio base station having a plurality of reception antennas through a plurality of transmission antennas 401 and 402, a transmission directivity control unit 422 which controls directional beams that the plurality of transmission antennas form on the basis of feedback information fed back from the radio base station and used to control the directional beams, and a control information acquisition unit 421 which obtains control information for directing null points of the directional beams to the direction of the other radio base station receiving the radio signal as an interference signal. The transmission directivity control unit 422 directs the directional beams to the direction of the radio base station on the basis of the feedback information and control information, and also directs the null points to the direction of the other radio base station. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wireless terminal and a wireless communication method using multi-antenna technology.

  In recent years, in a wireless communication system, in order to efficiently use a finite frequency band, a multi-antenna technique in which at least one of a transmission side and a reception side of a radio signal uses a plurality of antennas is used. As one of the multi-antenna technologies, a plurality of signal sequences using the same frequency are simultaneously transmitted via a plurality of transmission antennas, and the signal sequences are received via a plurality of reception antennas and separated into signal sequences. Input multiple output (MIMO) communication is known.

  In MIMO communication, there is a method (so-called closed-loop MIMO) in which a reception side estimates propagation path characteristics with a transmission side, and feedback information based on the estimated propagation path characteristics is fed back to the transmission side. The transmission side performs various types of transmission control, for example, weighting for each transmission antenna, based on feedback information from the reception side. According to closed-loop MIMO, transmission quality can be improved because the transmission side can perform transmission control adapted to changes in propagation path characteristics.

Special table 2008-536342 gazette

  In recent years, in order to use the frequency band more efficiently, a wireless communication system using the same communication channel (specifically, the same frequency) between adjacent cells has been realized.

  In uplink communication in such a radio communication system, a radio base station on the radio signal receiving side is connected not only to a desired signal from a radio terminal connected to the own station but also to other radio base stations located in the vicinity. In some cases, an interference signal is received from a wireless terminal.

  However, since the closed-loop MIMO described above performs closed feedback control between the transmission side and the reception side, communication quality can be sufficiently improved when the radio base station receives an interference signal. There was a problem that could not be done.

  Therefore, an object of the present invention is to provide a radio terminal and a radio communication method capable of sufficiently improving communication quality even when a radio base station receives an interference signal in uplink communication.

  In order to solve the above-described problems, the present invention has the following features. First, the first feature of the present invention is that a radio signal is transmitted to a radio base station (radio base station BS2) having a plurality of reception antennas (antennas 301 to 304) via a plurality of transmission antennas (antennas 401 and 402). And a control unit that controls the directional beam based on feedback information that is fed back from the radio base station and used to control the directional beam formed by the plurality of transmission antennas. A radio terminal (radio terminal UE4) having a unit (transmission directivity control unit 422) with respect to the direction of another radio base station (radio base station BS1 or BS1 ′) that receives the radio signal as an interference signal And an acquisition unit (control information acquisition unit 421) for acquiring control information for directing a null point of the directional beam, wherein the control unit includes the radio base Based on the feedback information fed back from the control unit and the control information acquired by the acquisition unit, the directional beam is directed toward the radio base station and the null is directed toward the other radio base station. The point is to turn the point.

  According to such a radio terminal, the communication quality in the radio base station can be kept good by directing the directional beam toward the radio base station to which the radio signal is transmitted. Furthermore, by directing a null point in the direction of another radio base station that receives the radio signal as an interference signal, the other radio base station can be prevented from receiving the interference signal. Communication quality can also be improved.

  A second feature of the present invention relates to the first feature of the present invention, wherein the control information is information for identifying a transmission antenna weight that directs the null point toward the other radio base station, The acquiring unit acquires the control information from the radio base station.

  A third feature of the present invention relates to the first feature of the present invention, wherein the control information is estimated by the other radio base station, and the arrival direction of the radio signal to the other radio base station ( It is information indicating the direction D1), and the acquisition unit acquires the control information from the radio base station.

  A fourth feature of the present invention relates to the first feature of the present invention, wherein the control information is information indicating a position of the other radio base station, and the acquisition unit transmits the control information to the radio base station. The main point is to obtain it from the Bureau.

  A fifth feature of the present invention is that the acquisition unit estimates an arrival direction of the downlink radio signal to the radio terminal when the radio terminal receives the downlink radio signal from the other radio base station. The gist is to obtain information indicating the estimated direction of arrival as the control information.

  A sixth feature of the present invention is that a radio terminal transmits a radio signal to a radio base station having a plurality of reception antennas via a plurality of transmission antennas, and is fed back from the radio base station. A wireless communication method comprising: a step of controlling the directional beam by the wireless terminal based on feedback information used for controlling a directional beam formed by a transmission antenna, wherein the wireless signal is received as an interference signal. The wireless terminal has a step of acquiring control information for directing a null point of the directional beam with respect to the direction of another wireless base station, and the control unit is fed back from the wireless base station. Based on the feedback information and the control information acquired by the acquisition unit, the directivity signal in the direction of the radio base station. Directing the beam, and, and summarized in that directing the null point in the direction of the other radio base station.

  According to the present invention, it is possible to provide a radio terminal and a radio communication method capable of sufficiently improving communication quality even when a radio base station receives an interference signal in uplink communication.

1 is an overall configuration diagram of a wireless communication system according to a first embodiment of the present invention. It is a figure for demonstrating the channel used in the radio | wireless communications system which concerns on 1st Embodiment of this invention. It is a figure for demonstrating schematic operation | movement of the radio | wireless communications system which concerns on 1st Embodiment of this invention. It is a figure for demonstrating schematic operation | movement of the radio | wireless communications system which concerns on 1st Embodiment of this invention. It is a functional block diagram which shows the structure of the wireless base station (1st wireless base station) which concerns on 1st Embodiment of this invention. It is a functional block diagram which shows the structure of the control apparatus which concerns on 1st Embodiment of this invention. It is a functional block diagram which shows the structure of the wireless base station (2nd wireless base station) which concerns on 1st Embodiment of this invention. It is a functional block diagram which shows the structure of the radio | wireless terminal which concerns on 1st Embodiment of this invention. It is a figure for demonstrating the detail of the transmission directivity control performed in 1st Embodiment of this invention. It is a figure for demonstrating the detail of the transmission directivity control performed in 1st Embodiment of this invention. It is an operation | movement sequence diagram which shows operation | movement of the radio | wireless communications system which concerns on 1st Embodiment of this invention. It is a whole block diagram of the radio | wireless communications system which concerns on 2nd Embodiment of this invention. It is a functional block diagram which shows the structure of the wireless base station (1st wireless base station) which concerns on 2nd Embodiment of this invention. It is an operation | movement sequence diagram which shows operation | movement of the radio | wireless communications system which concerns on 2nd Embodiment of this invention.

  Next, a first embodiment, a second embodiment, and other embodiments of the present invention will be described with reference to the drawings. In the description of the drawings in the following embodiments, the same or similar parts are denoted by the same or similar reference numerals.

[First Embodiment]
In the first embodiment, (1) an outline of a radio communication system, (2) a detailed configuration of the radio communication system, (3) transmission directivity control in a radio terminal, (4) operation of the radio communication system, and (5) effects explain.

(1) Overview of Radio Communication System First, an overview of the radio communication system according to the first embodiment will be described in the order of (1.1) schematic configuration of radio communication system and (1.2) schematic operation of radio communication system. .

(1.1) Schematic Configuration of Radio Communication System FIG. 1 is an overall configuration diagram of a radio communication system 10A according to the first embodiment.

  As shown in FIG. 1, the radio communication system 10A includes a radio terminal UE1 (first radio terminal), a radio terminal UE2, a radio terminal UE3, a radio terminal UE4 (second radio terminal), a radio terminal UE5, a radio terminal UE6, A base station BS1 (first radio base station), a radio base station BS2 (second radio base station), and a control device 100A are included.

  In FIG. 1, for convenience of explanation, only the radio base station BS1 and the radio base station BS2 are illustrated, but actually, a radio base station is further installed adjacent to each of the radio base station BS1 and the radio base station BS2. ing.

  The wireless communication system 10A has a configuration based on the LTE (Long Term Evolution) standard that is standardized in 3GPP (3rd Generation Partnership Project). In the following, mainly uplink (hereinafter, uplink) communication will be described.

  The radio base station BS1 is a connection destination of the radio terminals UE1 to UE3 located in the cell C1, and performs uplink communication with the radio terminals UE1 to UE3. The radio terminals UE1 to UE3 are movable, and are located at the end of the cell C1 in the example of FIG. Radio terminals other than the radio terminals UE1 to UE3 may be further connected to the radio base station BS1.

  The radio base station BS2 is a connection destination of radio terminals UE4 to UE6 located in the cell C2 adjacent to the cell C1, and performs uplink communication with the radio terminals UE4 to UE6. The radio terminals UE4 to UE6 are movable, and are located at the end of the cell C2 in the example of FIG. Radio terminals other than the radio terminals UE4 to UE6 may be further connected to the radio base station BS2.

  The control device 100A is provided on a backbone network that is a wired communication network, and is wired to the radio base station BS1 and the radio base station BS2. The control device 100A controls the radio base station BS1 and the radio base station BS2. The control device 100A may control radio base stations adjacent to the radio base station BS1 and the radio base station BS2 in addition to the radio base station BS1 and the radio base station BS2. The control device 100A periodically collects information from the radio base station BS1, the radio base station BS2, and other radio base stations, and stores and manages the collected information.

  The radio communication system 10A employs an orthogonal frequency division multiple access (OFDMA) system, which is one of multicarrier communication systems. In the OFDMA scheme, a plurality of subcarriers are used to form a communication channel called a subchannel (hereinafter referred to as a channel), and the channel is assigned from a radio base station to a radio terminal. The radio communication system 10A employs a frequency division duplex (FDD) system as a duplex system.

  The radio base station BS1 assigns the channel A shown in FIG. 2 to the radio terminal UE1, the channel B to the radio terminal UE2, and the channel C to the radio terminal UE3. Hereinafter, the radio signal transmitted from the radio terminals UE1 to UE3 using the channel assigned by the radio base station BS1 is appropriately referred to as a “first radio signal”.

  The radio base station BS2 assigns the channel A shown in FIG. 2 to the radio terminal UE4, the channel B to the radio terminal UE5, and the channel C to the radio terminal UE6. Hereinafter, the radio signal transmitted by the radio terminals UE4 to UE6 using the channel allocated by the radio base station BS2 is appropriately referred to as a “second radio signal”.

  The radio base station BS1 receives a first radio signal using the channel A as a desired signal from the radio terminal UE1, and receives a second radio signal using the channel A from the radio terminal UE4 as an interference signal. The second radio signal using channel A arrives at the radio base station BS1 from the radio terminal UE4 in the direction D1, and arrives at the radio base station BS2 from the radio terminal UE4 in the direction D4.

  Similarly, the radio base station BS1 receives a first radio signal using the channel B as a desired signal from the radio terminal UE2, and receives a second radio signal using the channel B as an interference signal from the radio terminal UE5. Yes. The second radio signal using channel B arrives at the radio base station BS1 from the radio terminal UE5 in the direction D2, and arrives at the radio base station BS2 from the radio terminal UE5 in the direction D5.

  The radio base station BS1 receives a first radio signal using the channel C as a desired signal from the radio terminal UE3, and receives a second radio signal using the channel C from the radio terminal UE6 as an interference signal. The second radio signal using channel C arrives at the radio base station BS1 from the radio terminal UE6 in the direction D3, and arrives at the radio base station BS2 from the radio terminal UE6 in the direction D6.

  The radio base station BS1 and the radio terminals UE1 to UE3 perform uplink communication based on closed loop MIMO. The radio base station BS2 and the radio terminals UE4 to UE6 perform uplink communication based on closed-loop MIMO.

  Specifically, each of the radio terminals UE1 to UE3 transmits the first radio signal to the radio base station BS1 via a plurality of antennas (transmission antennas). The radio base station BS1 receives each first radio signal via a plurality of antennas (receive antennas).

  Each of the radio terminals UE4 to UE6 transmits the second radio signal to the radio base station BS2 via a plurality of antennas (transmission antennas). The radio base station BS2 receives each second radio signal via a plurality of antennas (receive antennas).

  FIG. 1 exemplifies MIMO (so-called 2 × 4 MIMO) having two transmission antennas and four reception antennas in uplink communication.

  The radio base station BS1 analyzes the first radio signals received from the radio terminals UE1 to UE3 and periodically provides feedback information for adaptively controlling multi-antenna transmission in the radio terminals UE1 to UE3. Send to.

  In the LTE standard, feedback information includes “RI (Rank Indicator)”, “PMI (Precoding Matrix Indicator)”, and “CQI (Channel Quality Indicator)”. The RI is information for controlling the number of streams (referred to as layers in the LTE standard) that are signal sequences. PMI is information for controlling transmit antenna weight (referred to as a precoding matrix in the LTE standard). CQI is information for controlling transmission power and modulation scheme.

  The radio base station BS1 determines the number of layers for each of the radio terminals UE1 to UE3, and transmits RI corresponding to the determined number of layers as feedback information. For each of the radio terminals UE1 to UE3, the radio base station BS1 calculates a precoding matrix that maximizes reception quality (for example, SNR) according to the number of layers, and transmits PMI according to the calculation result as feedback information. Also, the radio base station BS1 obtains a CQI corresponding to the reception quality for each of the radio terminals UE1 to UE3, and transmits the CQI as feedback information. Each of the radio terminals UE1 to UE3 controls the number of layers, the directional beam, the transmission power, the modulation scheme, and the like according to feedback information fed back from the radio base station BS1.

  Similarly, the radio base station BS2 analyzes the second radio signals received from the radio terminals UE4 to UE6, and feedback information (RI, PMI, CQI) for adaptively controlling multi-antenna transmission in the radio terminals UE4 to UE6. ) Is periodically transmitted to the radio terminals UE4 to UE6. Each of the radio terminals UE4 to UE6 controls the number of layers, the directional beam, the transmission power, the modulation scheme, and the like according to feedback information fed back from the radio base station BS2.

(1.2) Schematic Operation of Radio Communication System Next, the schematic operation of the radio communication system 10A will be described using FIG. 1, FIG. 3, and FIG.

  When receiving the second radio signal using channel A as an interference signal from the radio terminal UE4, the radio base station BS1 estimates the arrival direction D1 of the second radio signal to the radio base station BS1. As illustrated in FIG. 3, the radio base station BS1 generates interference information based on the arrival direction D1, and transmits the generated interference information to the control device 100A.

  Further, when the radio base station BS1 receives the second radio signal using the channel B as an interference signal from the radio terminal UE5, the radio base station BS1 estimates the arrival direction D2 of the second radio signal to the radio base station BS1. The radio base station BS1 generates interference information based on the arrival direction D2, and transmits the generated interference information to the control device 100A.

  When receiving the second radio signal using channel C as an interference signal from the radio terminal UE6, the radio base station BS1 estimates the arrival direction D3 of the second radio signal to the radio base station BS1. The radio base station BS1 generates interference information based on the arrival direction D3, and transmits the generated interference information to the control device 100A.

  100 A of control apparatuses identify radio base station BS2 based on the information regarding a 2nd radio signal from several radio base stations including radio base station BS2, and transmit interference information with respect to the identified radio base station BS2. To do. The information related to the second radio signal is information included in the second radio signal or information identifying a channel used for the second radio signal.

  When receiving the interference information, the radio base station BS2 transmits control information to the radio terminals UE4 to UE6 based on the received interference information. Specifically, the radio base station BS2 transmits to the radio terminal UE4 control information for directing the null point (dead point) of the directional beam formed by the radio terminal UE4 in the direction D1 of the radio base station BS1. The radio base station BS2 transmits control information for directing the null point of the directional beam formed by the radio terminal UE5 in the direction D2 of the radio base station BS1 to the radio terminal UE5. The radio base station BS2 transmits to the radio terminal UE6 control information for directing the null point of the directional beam formed by the radio terminal UE6 in the direction D3 of the radio base station BS1.

  A communication form in which MIMO communication is performed while forming a directional beam is generally referred to as beam forming MIMO.

  The radio terminal UE4 directs a null point in the direction D1 of the radio base station BS1 based on the control information received from the radio base station BS2 and the PMI fed back from the radio base station BS2, and the radio terminal station BS2 A second radio signal using channel A is transmitted with a directional beam directed in direction D4. By directing the null point in the direction D1 of the radio base station BS1 by the radio terminal UE4, it is possible to prevent the radio base station BS1 from receiving the second radio signal from the radio terminal UE4 as shown in FIG.

  The radio terminal UE5 directs a null point in the direction D2 of the radio base station BS1 based on the control information received from the radio base station BS2 and the PMI fed back from the radio base station BS2, and the radio terminal station BS2 A second radio signal using channel B is transmitted by directing a directional beam in direction D5. By directing the null point in the direction D2 of the radio base station BS1 by the radio terminal UE5, it is possible to prevent the radio base station BS1 from receiving the second radio signal from the radio terminal UE5 as shown in FIG.

  The radio terminal UE6 directs a null point in the direction D3 of the radio base station BS1 based on the control information received from the radio base station BS2 and the PMI fed back from the radio base station BS2, and the radio terminal station BS2 A directional beam is directed in the direction D6, and the second radio signal using the channel C is transmitted. By directing the null point in the direction D3 of the radio base station BS1 by the radio terminal UE6, it is possible to prevent the radio base station BS1 from receiving the second radio signal from the radio terminal UE6 as shown in FIG.

  The interference information is, for example, information on a coefficient or angle indicating the arrival direction of the interference signal. An existing direction-of-arrival estimation technique can be used for estimating the direction of arrival. In order to reduce the information amount of interference information, coefficient or angle information indicating the arrival direction may be converted into PMI, and the PMI obtained by the conversion may be used as interference information. In this case, the radio base station BS1 or the control device 100A, the PMI corresponding to the precoding matrix that directs the null point in the direction D1, the PMI corresponding to the precoding matrix that directs the null point in the direction D2, and the null point in the direction D3. Is transmitted as interference information to the radio base station BS2.

  When the coefficient or angle information indicating the arrival direction is used as the interference information, the control information transmitted by the radio base station BS2 uses the coefficient or angle information indicating the arrival direction as it is, or uses the information as PMI. Can be used by converting to When PMI is used as interference information, the PMI can be used as it is as control information.

  By using PMI as the interference information and control information, the information amount of the interference information and control information can be reduced, and mounting in the radio communication system 10A can be facilitated.

  In order to respond to changes in the state of the radio terminals UE4 to UE6, each of the radio terminals UE4 to UE6 is provided with a means for detecting an absolute direction (direction) such as a GPS or a direction sensor, and the detected absolute The direction and control information may be used in combination.

(2) Detailed Configuration of Radio Communication System Next, regarding the detailed configuration of the radio communication system 10A, (2.1) configuration of the radio base station BS1, (2.2) configuration of the control device 100A, (2.3) radio The configuration of the base station BS2 and (2.4) the configuration of the radio terminal UE4 will be described in this order. In the following, the configuration related to the present invention will be mainly described.

(2.1) Configuration of Radio Base Station BS1 FIG. 5 is a functional block diagram showing the configuration of the radio base station BS1.

  As illustrated in FIG. 5, the radio base station BS1 includes antennas 201 to 204, a radio communication unit 210, a control unit 220, a storage unit 230, and a wired communication unit 240.

  The wireless communication unit 210 includes a reception unit 211 that receives wireless signals via the antennas 201 to 204 and a transmission unit 212 that transmits wireless signals via the antennas 201 to 204. The reception unit 211 performs channel estimation for each of the radio terminals UE1 to UE3 based on a pilot signal that is a known signal included in the received radio signal, and uses the channel estimation result to feedback information (RI, PMI, CQI). ) Is generated. The transmission unit 212 transmits feedback information to each of the radio terminals UE1 to UE3.

  The control unit 220 is configured by a CPU, for example, and controls various functions provided in the radio base station BS1. The storage unit 230 is configured by a memory, for example, and stores various types of information used for control in the radio base station BS1. The wired communication unit 240 is connected to the control device 100A via a wired communication network.

  The control unit 220 includes an arrival direction estimation unit 221, an interference information generation unit 222, and an identification information acquisition unit 223.

  When the reception unit 211 receives the second radio signal (interference signal), the arrival direction estimation unit 221 estimates the arrival direction of the second radio signal to the radio base station BS1 using the arrival direction estimation technique.

  The interference information generation unit 222 generates interference information based on the arrival direction estimated by the arrival direction estimation unit 221. When PMI is used as the interference information as described above, the storage unit 230 holds in advance the association between the arrival direction and the PMI, and the interference information generation unit 222 generates (acquires) the PMI from the association. .

  The identification information acquisition unit 223 acquires information regarding the second radio signal received by the reception unit 211 as identification information. The identification information is information for identifying a radio terminal as an interference source (hereinafter, an interference source terminal) and a radio base station to which the interference source terminal is connected. The identification information acquisition unit 223 acquires the identification information using any one of the following methods (a1) to (c1) or a combination of the methods.

  Method (a1): The specifying information acquisition unit 223 acquires terminal identification information (terminal ID) included in the second wireless signal received by the receiving unit 211 as specifying information. The terminal identification information is information for identifying the wireless terminal that is the transmission source of the second wireless signal.

  Method (b1): The specifying information acquisition unit 223 acquires channel identification information for identifying a channel used in the second radio signal received by the receiving unit 211 as specifying information.

  Method (c1): The identification information acquisition unit 223 acquires the identification information from the pilot signal included in the second radio signal received by the reception unit 211. Specifically, the pilot signal includes a cell-specific orthogonal sequence, and the specifying information acquisition unit 223 acquires the orthogonal sequence as specifying information.

  The wired communication unit 240 transmits the interference information generated by the interference information generation unit 222 and the specification information acquired by the specification information acquisition unit 223 to the control device 100A. In the first embodiment, the wired communication unit 240 constitutes an interference information transmission unit that transmits interference information.

(2.2) Configuration of Control Device 100A FIG. 6 is a functional block diagram showing the configuration of the control device 100A.

  As illustrated in FIG. 6, the control device 100A includes a wired communication unit 110, a control unit 120, and a storage unit 130.

  The wired communication unit 110 is connected to the radio base stations BS1 and BS2 via a wired communication network. The wired communication unit 110 includes a reception unit 111 that receives a signal and a transmission unit 112 that transmits a signal. The receiving unit 111 receives interference information and identification information from the radio base station BS1.

  The control unit 120 is constituted by a CPU, for example, and controls various functions provided in the control device 100A. The storage unit 130 is configured by a memory, for example, and stores various information used for control and the like in the control device 100A.

  The control unit 120 includes a base station specifying unit 121. Based on the identification information received by the wired communication unit 110, the base station identification unit 121 identifies a radio base station to which the interference source terminal is connected from among a plurality of radio base stations. The base station specifying unit 121 specifies a radio base station to which the interference source terminal is connected using any one of the following methods (a2) to (c2) or a combination of the methods.

  Method (a2): When the terminal identification information is used as identification information, the base station identification unit 121 identifies the radio base station to which the interference source terminal is connected using the connection information stored in the storage unit 130. To do. The connection information is information in which terminal identification information of a wireless terminal currently connected to either the wireless base station BS2 or another wireless base station is associated with a wireless base station to which the wireless terminal is connected. The base station specifying unit 121 specifies the radio base station corresponding to the terminal identification information received by the receiving unit 111 as the radio base station to which the interference source terminal is connected.

  Method (b2): When the channel identification information is used as identification information, the base station identification unit 121 identifies the radio base station to which the interference source terminal is connected using the channel information stored in the storage unit 130. To do. The channel information includes channel identification information of a channel used for uplink communication by a radio terminal connected to either the radio base station BS2 or another radio base station, and a radio base station to which the radio terminal is connected Is information associated with each other. The base station specifying unit 121 specifies the radio base station corresponding to the channel identification information received by the receiving unit 111 as the radio base station to which the interference source terminal is connected.

  Method (c2): When a cell-specific orthogonal sequence is used as identification information, the base station identification unit 121 identifies a radio base station corresponding to the orthogonal sequence as a connection destination radio base station of the interference source terminal. .

  The transmission unit 112 transmits interference information and identification information to the radio base station (in the first embodiment, the radio base station BS2) identified by the base station identification unit 121.

(2.3) Configuration of Radio Base Station BS2 FIG. 7 is a functional block diagram showing the configuration of the radio base station BS2.

  As illustrated in FIG. 7, the radio base station BS2 includes antennas 301 to 304, a radio communication unit 310, a control unit 320, a storage unit 330, and a wired communication unit 340.

  The radio communication unit 310 receives a radio signal from the radio terminals UE4 to UE6 via the antennas 301 to 304, and a transmission unit 312 transmits the radio signal to the radio terminals UE4 to UE6 via the antennas 301 to 304. And have. The receiving unit 311 performs channel estimation for each of the radio terminals UE4 to UE6 based on the pilot signal included in the received radio signal, and generates feedback information (RI, PMI, CQI) using the channel estimation result . The transmission unit 312 transmits feedback information to each of the radio terminals UE4 to UE6.

  The control unit 320 is configured by a CPU, for example, and controls various functions provided in the radio base station BS1. The storage unit 330 is configured by a memory, for example, and stores various types of information used for control and the like in the radio base station BS1. The wired communication unit 340 is connected to the control device 100A via a wired communication network. The wired communication unit 340 receives interference information and identification information from the control device 100A.

  The control unit 320 includes an interference information acquisition unit 321 and a terminal identification unit 322.

  The interference information acquisition unit 321 acquires interference information received by the wired communication unit 340 from the control device 100A. The terminal identifying unit 322 identifies an interference source terminal from among a plurality of wireless terminals connected to the wireless base station BS2, using the identifying information received by the wired communication unit 340 from the control device 100A. The terminal specifying unit 322 specifies the interference source terminal using any one of the following methods (a3) and (b3), or a combination of the methods.

  Method (a3): When the terminal identification information is used as identification information, the terminal identification unit 322 selects the radio terminal indicated by the terminal identification information from the plurality of radio terminals connected to the radio base station BS2. Identify as a terminal.

  Method (b3): When the channel identification information is used as identification information, the terminal identification unit 322 uses the channel indicated by the channel identification information from among a plurality of radio terminals connected to the radio base station BS2 for uplink communication. The wireless terminal being used is identified as the interference source terminal.

  The transmission unit 312 transmits the control information described above to the interference source terminal (in the first embodiment, the radio terminals UE4 to UE6) specified by the terminal specification unit 322.

(2.4) Configuration of Radio Terminal UE4 FIG. 8 is a functional block diagram showing a configuration of the radio terminal UE4. Since the other radio terminals (radio terminals UE1 to UE3, UE5, UE6) are configured in the same manner as the radio terminal UE4, here, the radio terminal UE4 will be described as a representative of each radio terminal.

  As illustrated in FIG. 8, the radio terminal UE4 includes antennas 401 and 402, a radio communication unit 410, a control unit 420, and a storage unit 430.

  The radio communication unit 410 includes a reception unit 411 that receives a radio signal from the radio base station BS2 via the antennas 401 and 402, and a transmission unit 412 that transmits the radio signal to the radio base station BS2 via the antennas 401 and 402. Have. The radio signal received by the receiving unit 411 from the radio base station BS2 includes feedback information and control information.

  The transmission unit 412 controls multi-antenna transmission based on the feedback information received by the reception unit 411. Specifically, the transmission unit 412 distributes the transmission signal to a plurality of layers according to RI, weights the transmission signal of each layer (hereinafter referred to as precoding), and follows the CQI for the transmission signal after precoding. Perform adaptive modulation and transmit power control.

  The control unit 420 is configured by a CPU, for example, and controls various functions provided in the radio terminal UE4. The storage unit 430 is configured by a memory, for example, and stores various types of information used for control and the like in the radio terminal UE4.

  The control unit 420 includes a control information acquisition unit 421 and a transmission directivity control unit 422. The control information acquisition unit 421 acquires acquisition of control information for directing the null point of the directional beam with respect to the direction D1 of the radio base station BS1 that receives the second radio signal transmitted by the transmission unit 412 as an interference signal. Parts.

  The transmission directivity control unit 422 constitutes a control unit that controls the directional beam formed by the antennas 401 and 402 based on the PMI in the feedback information. Specifically, the directional beam formed by the antennas 401 and 402 can be directed in the direction D4 of the radio base station BS2 by precoding using a precoding matrix corresponding to the PMI fed back from the radio base station BS2. .

  Further, the transmission directivity control unit 422 directs a directional beam in the direction D4 of the radio base station BS2 based on the feedback information and the control information acquired by the control information acquisition unit 421, and the radio base station BS1. A null point is directed in the direction D1.

(3) Transmission Directivity Control in Radio Terminal Next, details of transmission directivity control executed by the transmission directivity control unit 422 will be described with reference to FIGS. 9 and 10. Here, a case where a null point is directed in the direction D1 of the radio base station BS1 will be described as an example.

  Based on the control information, the transmission directivity control unit 422 selects a precoding matrix group that directs the null point in the direction D1 of the radio base station BS1. As shown in FIG. 9, the precoding matrix group is a group composed of a plurality of precoding matrices having null points in the same direction, and is stored in advance in the storage unit 430 of the radio terminal UE4. In the example of FIG. 9, precoding matrix groups 1 to 8 having null points in different directions are illustrated.

  As shown in FIG. 10, the precoding matrix group includes a plurality of precoding matrices each having a directional beam in a different direction. In the example of FIG. 10, each of the precoding matrices 1 to 6 included in the precoding matrix group 1 has directional beams in six directions. The directional beam patterns of the precoding matrices 1 to 6 are different.

  The transmission directivity control unit 422 directs the radio base station BS2 in the direction D4 based on the PMI fed back from the radio base station BS2 from the precoding matrix group having a null point in the direction D1 of the radio base station BS1. A precoding matrix having a beam of directional characteristics is selected. The selected precoding matrix is applied to precoding in the transmission unit 412 of the radio terminal UE4.

(4) Operation of Radio Communication System FIG. 11 is an operation sequence diagram showing the operation of the radio communication system 10A. In FIG. 11, only PMI is illustrated and described among feedback information (RI, PMI, CQI) according to the LTE standard. The operation sequence shown in FIG. 11 is repeatedly executed at predetermined time intervals (for example, in communication frame units).

  In step S101, the radio terminal UE4 transmits a second radio signal using the channel A. In step S104, the radio terminal UE1 transmits a first radio signal using the channel A. The receiving unit 211 of the radio base station BS1 receives the first radio signal using the channel A as a desired signal, and receives the second radio signal using the channel A as an interference signal that interferes with the desired signal.

  In step S102, the radio terminal UE5 transmits a second radio signal using channel B. In step S105, the radio terminal UE2 transmits a first radio signal using the channel B. The receiving unit 211 of the radio base station BS1 receives the first radio signal using the channel B as a desired signal, and receives the second radio signal using the channel B as an interference signal that interferes with the desired signal.

  In step S103, the radio terminal UE6 transmits a second radio signal using the channel C. In step S106, the radio terminal UE3 transmits a first radio signal using the channel C. The receiving unit 211 of the radio base station BS1 receives the first radio signal using the channel C as a desired signal, and receives the second radio signal using the channel C as an interference signal of the desired signal.

  In step S107, the reception unit 211 of the radio base station BS1 performs channel estimation for estimating the channel response of the radio propagation path based on the pilot signal included in the first radio signal for each of the radio terminals UE1 to UE3.

  The identification information acquisition unit 223 of the radio base station BS1 acquires identification information from the second radio signals received by the reception unit 211 from the radio terminals UE1 to UE3 according to the methods (a1) to (c1). .

  In step S108, the reception unit 211 of the radio base station BS1 calculates a precoding matrix based on the estimated channel response, and acquires a PMI corresponding to the calculated precoding matrix.

  In step S109, the arrival direction estimation unit 221 of the radio base station BS1 estimates the arrival direction D1 of the second radio signal to the radio base station BS1. The interference information generation unit 222 of the radio base station BS1 generates interference information based on the arrival direction D1. Similarly, the arrival direction estimation unit 221 estimates the arrival directions D2 and D3 of the second radio signal to the radio base station BS1. The interference information generation unit 222 generates interference information based on the arrival directions D2 and D3.

  In step S110, the receiving unit 211 of the radio base station BS1 equalizes the received signal (channel equalization) based on the estimated channel response, and decodes the equalized received signal. The decoded received signal is input to the control unit 220 of the radio base station BS1.

  In step S111, the transmission unit 212 of the radio base station BS1 transmits PMI as feedback information to the radio terminal UE1. Similarly, the transmission unit 212 transmits PMI to the radio terminal UE2 (step S112), and transmits PMI to the radio terminal UE3 (step S113).

  In step S115a, the radio terminal UE1 selects a precoding matrix corresponding to the PMI received from the radio base station BS1. The radio terminal UE1 performs precoding using the selected precoding matrix when transmitting the first radio signal using the channel A to the radio base station BS1 next time.

  In step S115b, the radio terminal UE2 selects a precoding matrix corresponding to the PMI received from the radio base station BS1. The radio terminal UE2 performs precoding using the selected precoding matrix when transmitting the first radio signal using the channel B to the radio base station BS1 next time.

  In step S115c, the radio terminal UE3 selects a precoding matrix corresponding to the PMI received from the radio base station BS1. The radio terminal UE3 performs precoding using the selected precoding matrix when transmitting the first radio signal using the channel C to the radio base station BS1 next time.

  In step S114, the wired communication unit 240 of the radio base station BS1 transmits the interference information generated by the interference information generation unit 222 and the specification information acquired by the specification information acquisition unit 223 to the control device 100A. The receiving unit 111 of the control device 100A receives interference information and identification information.

  In step S116, the base station specifying unit 121 of the control device 100A uses the specifying information received by the receiving unit 111 according to the methods (a2) to (c2) above, and the radio base station to which the interference source terminal is connected. Specify BS2. The transmission unit 112 of the control device 100A transmits interference information and identification information to the radio base station BS2 identified by the base station identification unit 121. The wired communication unit 340 of the radio base station BS2 receives interference information and identification information.

  On the other hand, the receiving unit 311 of the radio base station BS2 calculates a precoding matrix for each of the radio terminals UE4 to UE6 to which the radio base station BS2 is connected, and acquires a PMI corresponding to the calculated precoding matrix.

  Further, the interference information acquisition unit 321 of the radio base station BS2 acquires the interference information received by the wired communication unit 340 from the control device 100A. The terminal identification unit 322 of the radio base station BS2 uses the identification information received by the wired communication unit 340 from the control device 100A, and is connected to the radio base station BS2 in accordance with the methods (a3) and (b3). The interference source terminal is identified from among the wireless terminals. Here, it is assumed that the radio terminals UE4 to UE6 are specified as interference source terminals.

  In step S119a, the transmission unit 312 of the radio base station BS2 transmits PMI as feedback information and control information to the radio terminal UE4. In step S119b, the transmission unit 312 transmits PMI as feedback information and control information to the radio terminal UE5. In step S119c, the transmission unit 312 transmits PMI as feedback information and control information to the radio terminal UE6. The receiving unit 411 of each of the radio terminals UE4 to UE6 receives PMI and control information.

  In step S120a, the transmission directivity control unit 422 of the radio terminal UE4 directs a directional beam in the direction D4 of the radio base station BS2 based on the PMI and control information received by the reception unit 411, and the radio base station BS1. The transmission unit 412 is controlled so that the null point is directed in the direction D1. Specifically, the transmission directivity control unit 422 of the radio terminal UE4 directs the directional beam in the direction D4 of the radio base station BS2 from the precoding matrix group that directs the null point in the direction D1 of the radio base station BS1. Select a precoding matrix. The transmitter 412 of the radio terminal UE4 performs precoding using the selected precoding matrix when transmitting the second radio signal using the channel A next time.

  Similarly, in step S120b, the transmission directivity control unit 422 of the radio terminal UE5, based on the PMI and control information received by the reception unit 411, a precoding matrix group that directs the null point in the direction D2 of the radio base station BS1 The precoding matrix for directing the directional beam in the direction D5 of the radio base station BS2 is selected from the above. The transmitter 412 of the radio terminal UE5 performs precoding using the selected precoding matrix when transmitting the second radio signal using the channel B next time.

  In step S120b, the transmission directivity control unit 422 of the radio terminal UE6, based on the PMI and control information received by the reception unit 411, from the precoding matrix group that directs the null point in the direction D3 of the radio base station BS1, A precoding matrix for directing a directional beam in the direction D6 of the radio base station BS2 is selected. The transmitter 412 of the radio terminal UE6 performs precoding using the selected precoding matrix when transmitting the second radio signal using the channel C next time.

(5) Effect According to the radio communication system 10A according to the first embodiment, when the radio base station BS1 receives the second radio signal from the radio terminals UE4 to UE6 as an interference signal, the radio terminals UE4 to UE6 perform radio communication. A null point is directed in the direction D1 to D3 of the base station BS1. For this reason, it can avoid that radio base station BS1 receives a 2nd radio signal (interference signal), and the communication quality in radio base station BS1 can fully be improved. Thus, by preventing the generation of interference signals from the beginning, cell throughput increases and high-speed uplink communication can be provided to each wireless terminal.

  In the first embodiment, the transmission directivity control unit 422 of the radio terminals UE4 to UE6 directs a null point in the directions D1 to D3 of the radio base station BS1 based on the PMI and control information received from the radio base station BS2. In addition, a directional beam is directed in the directions D4 to D6 of the radio base station BS2. Therefore, the communication quality in the radio base station BS2 can be kept good while sufficiently improving the communication quality in the radio base station BS1.

  In the first embodiment, the base station specifying unit 121 of the control device 100A specifies the radio base station BS2 to which the interference source terminal is connected according to the methods (a2) to (c2). As a result, even when there are a plurality of candidates for the connection destination radio base station of the interference source terminal, the connection destination radio base station of the interference source terminal can be easily identified, and the interference information can be transmitted to the appropriate radio base station. Can be sent.

  In the first embodiment, the terminal specifying unit 322 of the radio base station BS2 specifies the interference source terminal according to the methods (a3) and (b3). As a result, even when there are a plurality of interference source terminal candidates, the interference source terminal can be easily identified, and the control information can be transmitted to an appropriate wireless terminal.

[First Modification of First Embodiment]
In the first embodiment described above, the control information acquisition unit 421 of the radio terminals UE4 to UE6 has acquired coefficient or angle information indicating the arrival direction or PMI from the radio base station BS2 as interference information and control information. It was.

  However, since the rough direction of the radio base station BS1 can be identified from the position of the radio base station BS1, information indicating the position of the radio base station BS1 may be used as interference information and control information. Since the installation position of the radio base station BS1 is fixed, the position information of the radio base station BS1 can be held in advance in the radio base station BS1 or the control device 100A.

  When the location information of the radio base station BS1 is used as interference information and control information, the transmission directivity control unit 422 of the radio terminals UE4 to UE6 can identify the direction of the radio base station BS1 from the location of the radio base station BS1. Good.

  In order to more accurately identify the direction of the radio base station BS1, the control information acquisition unit 421 uses the GPS provided in each of the radio terminals UE4 to UE6 to obtain the position information of each of the radio terminals UE4 to UE6. Furthermore, you may acquire. The detailed direction of the radio base station BS1 can be specified from the position of each of the radio terminals UE4 to UE6 and the position of the radio base station BS1.

[Modification 2 of the first embodiment]
In the first embodiment described above, the control information acquisition unit 421 of the radio terminals UE4 to UE6 has acquired coefficient or angle information indicating the arrival direction or PMI from the radio base station BS2 as interference information and control information. However, the control information may be acquired by other methods.

  Specifically, when the radio terminals UE4 to UE6 receive the downlink radio signal from the radio base station BS1, the control information acquisition unit 421 estimates the arrival direction of the downlink radio signal and indicates the estimated arrival direction. Information may be acquired as control information. In this case, the transmission directivity control unit 422 of the radio terminals UE4 to UE6 may specify the direction of the radio base station BS1 from the arrival direction of the downlink radio signal.

[Second Embodiment]
In the first embodiment described above, the control device 100A is provided separately for the radio base station BS1 and the radio base station BS2. In the second embodiment, a mode in which the control device 100A is included in the radio base station BS1 will be described.

  In the second embodiment, (1) the configuration of the radio communication system, (2) the operation of the radio communication system, and (3) the effects will be described.

(1) Configuration of Radio Communication System FIG. 12 is an overall configuration diagram of a radio communication system 10B according to the second embodiment.

  As shown in FIG. 12, in the radio communication system 10B, the radio base station BS1 'has the function of the control device 100B. Specifically, as illustrated in FIG. 13, the control unit 220 of the radio base station BS1 'includes a base station specifying unit 224 that specifies a radio base station to which the interference source terminal is connected. The function of the base station specifying unit 224 is the same as the function of the base station specifying unit 121 described in the first embodiment.

(2) Operation of Radio Communication System FIG. 14 is an operation sequence diagram showing the operation of the radio communication system 10B. In FIG. 14, each process up to step S213 and each process after step S218 are the same as those in the first embodiment, and therefore the processes in steps S214 and S217 will be described.

  In step S214, the base station specifying unit 224 of the radio base station BS1 ′ specifies the radio base station BS2 to which the interference source terminal is connected according to the methods (a2) to (c2) using the specifying information. .

  In step S217, the wired communication unit 240 of the radio base station BS1 'transmits interference information and identification information to the radio base station BS2 identified by the base station identification unit 224. The wired communication unit 340 of the radio base station BS2 receives interference information and identification information.

(3) Effects According to the wireless communication system 10B according to the second embodiment, the following effects can be obtained in addition to the effects of the first embodiment. That is, since it is not necessary to separately provide the control device 100B, the installation cost of the control device 100B can be reduced.

[Other Embodiments]
As mentioned above, although this invention was described by embodiment, it should not be understood that the description and drawing which form a part of this indication limit this invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  For example, the modified examples 1 and 2 of the first embodiment are applicable not only to the first embodiment but also to the second embodiment.

  In the first and second embodiments described above, when the radio base station BS1 receives the second radio signal, the second radio signal is regarded as an interference signal. However, the second radio signal less than a predetermined reception level is used. May be allowed. In this case, when the radio base station BS1 receives the second radio signal and the reception level of the second radio signal is equal to or higher than a predetermined reception level, the radio base station BS1 regards the second radio signal as an interference signal. Become.

  In the first and second embodiments, the FDD scheme is adopted as the duplex scheme, but a time division duplex (TDD) scheme may be adopted instead of the FDD scheme.

  In the first and second embodiments, the case where there are two transmission antennas and four reception antennas in uplink communication (2 × 4 MIMO) has been described. However, in uplink communication, when there is one reception antenna, that is, a multi-antenna transmission with multiple inputs and one output (MISO) may be implemented.

  In the first and second embodiments, a plurality of radio terminals are connected to each of the radio base stations BS1 and BS2. However, one radio terminal may be connected to each of the radio base stations BS1 and BS2.

  In the first and second embodiments, the wireless communication systems 10A and 10B based on the LTE standard have been described. However, the wireless communication system is not limited to the LTE standard but is standardized in a wireless communication system based on the WiMAX standard (IEEE 802.16) or 3GPP2. The present invention can be applied to the UMB (Ultra Mobile Broadband) standard.

  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.

  BS1, BS2, BS1 '... wireless base station, UE1 to UE6 ... wireless terminals, 10A, 10B ... wireless communication system, 100A, 100B ... control device, 110 ... wired communication unit, 111 ... receiving unit, 112 ... transmitting unit, 120 DESCRIPTION OF SYMBOLS ... Control part 121 ... Base station specific part 130 ... Memory | storage part 201-204 ... Antenna 210 ... Wireless communication part 211 ... Reception part 212 ... Transmission part 220 ... Control part 221 ... Arrival direction estimation part, 222: Interference information generation unit, 223 ... Identification information acquisition unit, 224 ... Base station identification unit, 230 ... Storage unit, 240 ... Wired communication unit, 301-304 ... Antenna, 310 ... Wireless communication unit, 311 ... Reception unit, 312 ... Transmission unit, 320 ... Control unit, 321 ... Interference information acquisition unit, 322 ... Terminal identification unit, 330 ... Storage unit, 340 ... Wired communication unit, 401, 402 ... Antenna, 410 Wireless communication unit, 411 ... receiver, 412 ... transmitting portion, 420 ... controller, 421 ... control information obtaining section, 422 ... transmission directivity control unit, 430 ... storage unit

Claims (6)

For a radio base station having a plurality of reception antennas, a transmission unit that transmits radio signals via a plurality of transmission antennas;
A radio terminal having a control unit for controlling the directional beam based on feedback information used for controlling the directional beam fed back from the radio base station and formed by the plurality of transmission antennas,
An acquisition unit that acquires control information for directing a null point of the directional beam with respect to the direction of another radio base station that receives the radio signal as an interference signal;
The control unit directs the directional beam toward the radio base station based on the feedback information fed back from the radio base station and the control information acquired by the acquisition unit, and the other A wireless terminal that directs the null point toward the wireless base station. The control information is information for identifying a transmission antenna weight that directs the null point toward the other radio base station,
The radio terminal according to claim 1, wherein the acquisition unit acquires the control information from the radio base station. The control information is information indicating an arrival direction of the radio signal to the other radio base station estimated by the other radio base station,
The radio terminal according to claim 1, wherein the acquisition unit acquires the control information from the radio base station. The control information is information indicating the position of the other radio base station,
The radio terminal according to claim 1, wherein the acquisition unit acquires the control information from the radio base station.   The acquisition unit estimates the arrival direction of the downlink radio signal to the radio terminal when the radio terminal receives the downlink radio signal from the other radio base station, and indicates the estimated arrival direction The wireless terminal according to claim 1, which acquires the control information as the control information. A radio terminal transmitting a radio signal via a plurality of transmission antennas to a radio base station having a plurality of reception antennas;
The wireless terminal controlling the directional beam based on feedback information fed back from the wireless base station and used for controlling the directional beam formed by the plurality of transmission antennas. And
The wireless terminal obtains control information for directing a null point of the directional beam with respect to the direction of another wireless base station that receives the wireless signal as an interference signal,
In the step of controlling, based on the feedback information fed back from the radio base station and the control information acquired by the acquisition unit, the directional beam is directed toward the radio base station, and A radio communication method for directing the null point toward the other radio base station.

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