WO2013145046A1 - Dispositif formant station de base, système de communication mobile, procédé de commande pour un dispositif formant station de base, et support lisible par un ordinateur - Google Patents

Dispositif formant station de base, système de communication mobile, procédé de commande pour un dispositif formant station de base, et support lisible par un ordinateur Download PDF

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Publication number
WO2013145046A1
WO2013145046A1 PCT/JP2012/007340 JP2012007340W WO2013145046A1 WO 2013145046 A1 WO2013145046 A1 WO 2013145046A1 JP 2012007340 W JP2012007340 W JP 2012007340W WO 2013145046 A1 WO2013145046 A1 WO 2013145046A1
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WIPO (PCT)
Prior art keywords
base station
precoding matrix
precoding
radio resource
cell
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PCT/JP2012/007340
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English (en)
Japanese (ja)
Inventor
憲治 小柳
義一 鹿倉
信清　貴宏
石井　直人
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日本電気株式会社
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Publication of WO2013145046A1 publication Critical patent/WO2013145046A1/fr

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H04B7/0456—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
    • H04B7/0617—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal for beam forming
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
    • H04B7/0619—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
    • H04B7/0619—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
    • H04B7/0636—Feedback format
    • H04B7/0639—Using selective indices, e.g. of a codebook, e.g. pre-distortion matrix index [PMI] or for beam selection
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
    • H04W16/24—Cell structures
    • H04W16/28—Cell structures using beam steering

Definitions

  • the present invention relates to a mobile communication system, and more particularly to a technique for reducing inter-cell interference in a mobile communication system.
  • Multiple antenna technologies including MISO (Multiple Input Single Output), SIMO (Single Input Single Output), and MIMO (Multiple Input Multiple Output) are used for antenna diversity, spatial multiplexing, or beamforming, or a combination thereof.
  • MISO Multiple Input Single Output
  • SIMO Single Input Single Output
  • MIMO Multiple Input Multiple Output
  • the Some MISO systems and some MIMO systems use codebook based precoding to implement spatial multiplexing or transmit beamforming.
  • the codebook includes a plurality of quantized precoding matrices. In the case of a single transmission layer (rank 1 transmission), the precoding matrix is a precoding vector (i.e. antenna weight vector).
  • Codebook-based precoding is classified into closed-loop precoding and open-loop precoding depending on the presence or absence of feedback from the receiving station.
  • closed-loop precoding the transmitting station selects a precoding matrix from the codebook in consideration of PMI (Precoding Matrix Indicator) fed back from the receiving station.
  • PMI Precoding Matrix Indicator
  • open loop precoding does not use PMI fed back from a receiving station.
  • open-loop precoding for example, the transmitting station cyclically uses a precoding matrix included in a codebook.
  • a plurality of quantized precoding matrices included in a codebook generally achieve a plurality of quantized directional beams (beam patterns) having different main beam radiation angles.
  • each precoding matrix corresponds to one of a plurality of quantized directional beams.
  • LTE Long Term Term Evolution
  • PDSCH Physical Downlink Shared Channel
  • LTE downlink transmission mode 4 “Closed-loop spatial multiplexing” performs MIMO spatial multiplexing using closed-loop precoding.
  • LTE downlink transmission mode 6 “Closed-loop rank-1 precoding” performs transmission beamforming using closed-loop precoding.
  • Patent Document 1 discloses a technique for suppressing inter-cell interference in a mobile communication system that performs spatial multiplexing or transmission beamforming using codebook-based precoding.
  • the base station described in Patent Literature 1 receives PMI information from neighboring cells.
  • the PMI information from the neighboring cell includes a PMI corresponding to a precoding matrix that the neighboring cell requests to use or restrict usage.
  • the base station generates a basic codebook subset including at least one precoding matrix selected from the basic codebook in consideration of PMI information from neighboring cells. Specifically, for example, a precoding matrix for which use restriction is requested by a neighboring cell is excluded from the basic codebook subset.
  • the base station transmits index information indicating the precoding matrix included in the basic codebook subset to the mobile station.
  • Patent Document 1 performs precoding using a subset selected from a basic codebook, and excludes a precoding matrix that gives large interference to neighboring cells from the subset. Thereby, the interference which the transmission beam of a base station exerts on an adjacent cell is reduced.
  • 3GPP Release 11 (LTE-Advanced) defines several technologies for ICIC (Inter Cell Interference Coordination).
  • 3GPP Release PP11 specifies "ABS (Almost Blank Subframe)" in order to ensure the communication quality of a low-power node especially in a HetNet (Heterogeneous Network) environment. ABS is also called “ProtectedProtectSubframe”. ABS is used for ICIC in the time domain.
  • a normal subframe that is not ABS or Protected Subframe is referred to as “non-ABS” or “Unprotected Subframe”.
  • the macro base station not only stops user data transmission (PDSCH (Physical Downlink Shared Channel) transmission) but also stops transmission of most control signals in the ABS.
  • Control signals transmitted by the ABS include, for example, PDCCH (Physical Downlink Control Channel) for granting uplink scheduling, PHICH (Physical Hybrid-ARQ Indicator Channel) for HARQ ACK / NACK, broadcast channel (PBCH (Physical Broadcast). Channel), cell-specific RS (Reference Signal), and Primary and Secondary Synchronization Signals (PSS and CSS).
  • PDCCH Physical Downlink Control Channel
  • PHICH Physical Hybrid-ARQ Indicator Channel
  • PBCH Physical Broadcast
  • Cell-specific RS Reference Signal
  • PSS and CSS Primary and Secondary Synchronization Signals
  • the macro base station notifies the adjacent pico base station of the ABS setting information through the inter-base station interface (i.e. X2 interface).
  • the ABS setting information is called an ABS pattern or a Protected Subframe pattern.
  • the macro base station stops user data transmission (PDSCH transmission) in the ABS. Therefore, when the ABS is used, the capacity of the macro base station is lower than when the ABS is not used.
  • ABS is an ICIC technique in the time domain, but an ICIC technique in the frequency domain and an ICIC technique in the frequency and time domains may be used.
  • radio resource usage restrictions based on resource blocks based on RNTP (Relative Narrowband Transmit Power) notification are known.
  • RNTP Relative Narrowband Transmit Power
  • the macro base station and the pico base station use different subcarrier groups for user data transmission. Even when the ICIC technology in the frequency domain or the ICIC technology in the frequency and time domain is performed, the macro base station stops user data transmission in some radio resources, so that the macro base station Capacity may be reduced.
  • Patent Document 1 describes that the use of some precoding matrices included in the basic codebook is always stopped in consideration of PMI information notified from neighboring cells in order to reduce inter-cell interference. .
  • the base station always stops using a part of the precoding matrix, there is a possibility that the downlink throughput in the cell managed by the base station is reduced.
  • one of the objects of the present invention is to provide a base station, a mobile communication system, a control method, and a program capable of suppressing deterioration of cell capacity due to use of ICIC technology such as ABS.
  • the first aspect of the present invention includes a base station apparatus.
  • the base station apparatus includes a signal processing unit and a control unit.
  • the signal processing unit is configured to generate a plurality of time domain signals supplied to a plurality of transmission antennas by performing signal processing including precoding.
  • the control unit can use a plurality of precoding matrices in a first radio resource defined by at least one of time and frequency, and in a second radio resource different from the first radio resource, The precoding matrix subset corresponding to a part of the plurality of precoding matrices is configured to be restricted.
  • the second aspect of the present invention includes a mobile communication system.
  • the mobile communication system includes first and second base stations that operate the first and second cells, respectively.
  • the first base station is configured to generate a plurality of time domain signals supplied to a plurality of transmission antennas by performing signal processing including precoding.
  • the first base station can use a plurality of precoding matrices in a first radio resource defined by at least one of time and frequency, and a second radio different from the first radio resource.
  • the resource is configured to restrict use of a precoding matrix subset corresponding to a part of the plurality of precoding matrices.
  • a third aspect of the present invention includes a control method for a base station apparatus configured to generate a plurality of time domain signals supplied to a plurality of transmission antennas by performing signal processing including precoding.
  • the control method is (A) enabling a plurality of precoding matrices in a first radio resource defined by at least one of time and frequency; and (b) in a second radio resource different from the first radio resource. Restricting the use of a precoding matrix subset corresponding to a portion of the plurality of precoding matrices; including.
  • the fourth aspect of the present invention includes a program for causing a computer to perform the method according to the third aspect described above.
  • the mobile communication system of this embodiment includes a macro base station 1 and a pico base station 2.
  • the macro base station 1 operates the macro cell 100
  • the pico base station 2 operates the pico cell 200.
  • the macro cell 100 and the pico cell 200 are adjacent to each other.
  • the pico cell 200 has a smaller coverage than the macro cell 100 and is arranged in the macro cell 100.
  • the macro cell 100 and / or the pico cell 200 may be sector cells.
  • the macro cell 100 may be a sector cell that covers an angle range of 120 degrees.
  • the macro base station 1 performs MISO or MIMO transmission in downlink communication with at least one mobile station (hereinafter referred to as a macro mobile station) belonging to the macro cell 100.
  • the macro base station 1 includes a signal processing unit 10 and an antenna array 15 including a plurality of antennas.
  • the antenna array 15 may be used to cover the macro cell 100 as a sector cell.
  • the signal processing unit 10 generates a plurality of time domain signals supplied to the antenna array 15 by performing signal processing including precoding. That is, the macro base station 1 radiates a directional beam from the antenna array 15 by performing codebook-based precoding on at least some downlink subcarriers. Directional beams are used for spatial multiplexing or simple beamforming, or combinations thereof.
  • the codebook-based precoding performed by the macro base station 1 may be open loop, closed loop, or both.
  • the code book used by the macro base station 1 includes a plurality of quantized precoding matrices.
  • the precoding matrix is a matrix of size N T ⁇ N L.
  • N L means the number of transmission layers.
  • NT means the number of transmission antenna ports.
  • the precoding matrix is a precoding vector (antenna weight vector) of size N T ⁇ 1.
  • the term “precoding matrix” includes precoding vectors.
  • the plurality of quantized precoding matrices included in the codebook correspond to a plurality of quantized (discrete) directional beams having different main beam radiation angles.
  • a directional beam is a beam pattern in which energy is concentrated at a specific radiation angle (radiation direction).
  • a directional beam formed by the use of a precoding matrix can increase interference to neighboring cells.
  • the directional beam B1 is formed by using the first precoding matrix # 1.
  • directional beams B2 to B4 are formed by using the second to fourth precoding matrices # 2 to # 4, respectively.
  • 1A and 1B show only the main beam of the directional beams B1 to B4, the directional beam (beam pattern) formed by precoding is generally other than the main beam (main lobe). Includes sub-beams (side lobes).
  • the pico cell 200 exists in the radiation direction of the directional beam B2. Therefore, every time the directional beam B2 is used, in other words, every time the second precoding matrix # 2 is used, the directional beam B2 exerts downlink interference on the pico cell 200. Thereby, the downlink communication quality of the pico cell 200 may be deteriorated.
  • the downlink interference which the directional beam B2 exerts on the pico cell 200 can be reduced by using the code book subset and excluding the second precoding matrix # 2 from the code book subset. However, as described above, always stopping the use of a part of the precoding matrix may cause a decrease in downlink throughput in the macro cell 100.
  • the angular resolution of the plurality of directional beams corresponding to the plurality of precoding matrices is rough. Therefore, always stopping the use of a part of the precoding matrix in the case shown in FIG. 1A may affect the communication quality such as the system capacity or coverage of the macro cell 100.
  • the present embodiment provides a control method for coordinating ICIC including adjustment of use of radio resources determined by at least one of time and frequency between adjacent cells, and cooperative beamforming based on PMI notification between adjacent cells.
  • the control method can suppress the interference from the macro cell 100 to the pico cell 200 and suppress the deterioration of the cell capacity.
  • the macro base station 1 includes a control unit 16 for the control method according to the present embodiment.
  • the control unit 16 is configured to be able to use a plurality of precoding matrices (i.e. codebook) in the first radio resource (e.g. non-ABS) defined by at least one of time and frequency. Furthermore, the control unit 16 restricts the use of a precoding matrix subset (hereinafter referred to as PM subset) corresponding to a part of a plurality of precoding matrices in a second radio resource (eg, ABS) different from the first radio resource. It is configured as follows. In the present embodiment, the second radio resource is referred to as “protected radio resource”.
  • the PM subset includes at least one precoding matrix.
  • the PM subset may be at least one precoding matrix corresponding to a directional beam having a large interference with neighboring cells including the pico cell 200.
  • the macro base station 1 sets an ABS for ICIC in the time domain. That is, the first radio resource described above is “non-ABS” and the second radio resource (protected radio resource) is “ABS”.
  • the non-ABS the macro base station 1 only needs to be able to use the entire codebook including the precoding matrix subset.
  • the macro base station 1 restricts the use of a part of the code book, that is, the PM subset.
  • other precoding matrices excluding the PM subset can be used in the ABS as well as the non-ABS. Therefore, the macro base station 1 can continue the user data transmission using another precoding matrix excluding the PM subset in the ABS.
  • FIG. 1B shows an example of a directional beam that can be used by the macro base station 1 in the ABS.
  • the precoding matrix corresponding to the directional beam B2 is designated as the PM subset, and the control unit 16 prohibits the use of the PM subset in the ABS. Accordingly, since the directional beam B2 is not used in the ABS, interference from the macro base station 100 to the pico cell 200 can be reduced.
  • the macro base station 1 does not always restrict the use of the PM subset, but selectively restricts the use of the PM subset in the ABS.
  • the macro base station 1 can suppress a decrease in downlink throughput in the macro cell 100 as compared to a method in which the use of a part of the precoding matrix is always stopped. Furthermore, the macro base station 1 can continue transmission of user data using other directional beams B1, B3, and B4 in the ABS. Therefore, compared with the case where user data transmission is completely stopped in the ABS, it is possible to suppress a decrease in capacity of the macro cell 100.
  • FIG. 2 is a conceptual diagram showing how user data transmission is continued using another precoding matrix, although the use of the PM subset is restricted in ABS.
  • the example of FIG. 2 shows subframes of the macro cell 100 and the pico cell 200.
  • one of the four subframes of the macro cell 100 is designated as the ABS.
  • subframes # 0 and # 4 hatched with diagonal lines are ABS, and the other subframes # 1, # 2, and # 3 are non-ABS.
  • the macro base station 1 prohibits the use of the directional beam B2 in the ABS (subframes # 0 and # 4) and transmits the three directional beams B1, B3, and B4. use.
  • the macro base station 1 uses all four directional beams B1 to B4 in the non-ABS (subframes # 1, # 2, and # 3).
  • the pico base station 2 may perform scheduling in consideration of the ABS of the macro cell 100. For example, the pico base station 2 may schedule downlink transmission to the pico mobile station located in an edge region where interference from the macro cell 100 is large in the ABS (subframes # 0 and # 4).
  • a pico mobile station means a mobile station belonging to the pico cell 200.
  • the use restriction of the PM subset is not limited to use prohibition.
  • the usage restriction of the PM subset in the ABS may be achieved by reducing the downlink transmission power of the macro base station 1 when the PM subset is used compared to when other precoding matrices are used. Good.
  • the macro base station 1 can use the PM subset for user data transmission to a macro mobile station located near the macro base station 1, for example. Thereby, it is possible to further suppress the deterioration of the capacity of the macro cell 100 when the ABS is introduced.
  • the transmission power when using the PM subset in the ABS is reduced within a range in which the downlink communication quality (eg throughput or SINR (Signal toInterference plus Noise ration)) of the macro cell 100 satisfies a predetermined standard. Also good.
  • the macro base station 1 determines the transmission power when using the PM subset in the ABS, on the condition that the degradation of the downlink communication quality of the macro cell 100 in the ABS from the non-ABS is suppressed within the reference range. May be. Thereby, it is possible to prevent the downlink communication quality of the macro cell 100 from being significantly deteriorated by introducing the ABS for the purpose of suppressing interference with the pico cell 200.
  • FIG. 1B and 2 show an example in which an ABS is introduced to suppress interference from the macro cell 100 to the pico cell 200.
  • ICIC technology in the frequency domain or ICIC technology in the frequency and time domains may be used instead of or in combination with ABS.
  • FIG. 3A shows the ICIC technology in the frequency and time domain.
  • the macro base station 1 restricts the use of the PM subset in the resource block groups # 0 and # 4 of the frequency F2 hatched with diagonal lines.
  • FIG. 3B shows ICIC technology in the frequency domain.
  • the MAC base station 1 uses two downlink component carriers CC1 and CC2 by carrier aggregation.
  • the macro base station 1 may restrict the use of the PM subset in some subcarrier groups of the component carrier CC2 hatched with diagonal lines.
  • FIG. 4 is a flowchart showing a specific example of the control method.
  • the control unit 16 of the macro base station 1 determines a radio resource (e.g. ABS) to be protected.
  • a radio resource e.g. ABS
  • an ABS repetition pattern protected for the pico cell 200, a protected resource block, or a protected subcarrier is determined.
  • the determination of the radio resource to be protected in step S11 may be performed based on signaling with the pico base station 2 (eg, request from the pico base station 2) or based on an instruction from the operator. May be.
  • the control unit 16 determines a PM subset that is restricted from being used in the protected radio resource (e.g. ABS). Specifically, the control unit 16 may determine a precoding matrix corresponding to a directional beam that has a relatively large interference with the pico cell 200, and include this in the PM subset.
  • the PM subset determination may be performed based on signaling with the pico base station 2 or the pico mobile station. In this case, the pico base station 2 or the pico mobile station may perform channel estimation similar to that performed by the macro mobile station for closed-loop precoding.
  • the pico base station 2 or the pico mobile station receives the downlink signal (eg reference signal) from the macro base station 1, performs channel estimation with the macro base station 1, and receives the downlink signal from the macro base station 1.
  • the precoding matrix that maximizes the received power eg RSRS (Reference Signal Received Power) or PMI (Precoding Matrix Index) corresponding thereto may be determined.
  • the precoding matrix determined by the pico base station 2 or the pico mobile station is, for example, the macro base station 1 via an interface (eg, X2 interface, radio interface) that can be used between the macro base station 1 and the pico base station 2. May be sent to.
  • the precoding matrix determined by the pico base station 2 or the pico mobile station may be sent to the macro base station 1 via an OAM (Operation Administration and Maintenance) server.
  • the pico mobile station may notify the macro base station 1 of the precoding matrix determined by itself using the control channel provided by the macro base station 1.
  • the PM subset determination in step S12 may be performed using a channel estimation result by a macro mobile station belonging to the macro cell 1.
  • the macro base station 1 forcibly hands over the pico mobile station from the pico cell 200 to the macro cell 100, the channel estimation result by the mobile station (hereinafter referred to as HO mobile station) handed over from the pico cell 200 to the macro cell 100, precoding A matrix or a PMI corresponding to the matrix may be received from the HO mobile station.
  • step S13 the control unit 16 implements the use restriction of the PM subset in the protected radio resource (e.g. ABS).
  • the control unit 16 does not limit the use of other precoding matrices except for the PM subset in the radio resources to be protected.
  • FIG. 5 is a block diagram illustrating a configuration example of the macro base station 1 as an LTE base station.
  • the signal processing unit 10 illustrated in FIG. 5 includes a precoding unit 11, a resource element (RE) mapper 12, an OFDM (Orthogonal Frequency Division Multiplexing) unit 13, and an RF (Radio Frequency) unit 14.
  • the functions and operations of these elements may be the same as the general elements that the LTE base station has.
  • DLSCH Downlink Shared Channel
  • the precoding unit 11 generates a symbol vector X1 by calculating a precoding matrix of size N T ⁇ N L selected from the code book to a symbol vector S.
  • the number of elements of the symbol vector X1 after precoding matches the number of transmission antenna ports NT .
  • the transmission antenna port may not correspond to a physical antenna.
  • a transmission antenna port is associated with transmission of a common reference signal (CRS (cell-specific reference signal or common reference signals)).
  • CRS cell-specific reference signal or common reference signals
  • a plurality of RE mappers 12 provided for each antenna port map the pre-coded symbol vector X1 to resource elements (that is, subcarriers).
  • the symbol vector X2 mapped to the resource element is supplied to the OFDM unit 13 together with the reference symbol vector R.
  • the vector R includes the same number of symbols of the common reference signals CRS # 1 to CRS # NT as the number of antenna ports NT .
  • Reference symbols not subjected to precoding, that is, common reference signals CRS # 1 to CRS # NT are used not only for channel estimation by the mobile station, but also as phase and power (amplitude) references for PDSCH demodulation.
  • a plurality of OFDM units 13 provided for each antenna port perform a plurality of (that is, N T ) signals by performing IFFT (inverse Fast Fourier transform) operations on frequency domain signals, that is, the symbol vector X2 and the reference symbol vector R. Of time domain signal Y (t).
  • IFFT inverse Fast Fourier transform
  • the RF unit 14 performs frequency up-conversion and amplification on the time domain signal Y (t), and supplies the amplified signal to the antenna array 15.
  • the antenna array 15 includes a plurality of antennas 151. Each antenna 151 may be a subarray including a plurality of antenna elements.
  • FIG. 5 shows a specific example of the control unit 16.
  • the control unit 16 includes an ABS control unit 161 and a precoding matrix (PM) selection unit 162.
  • the ABS control unit 161 determines an ABS as an example of a radio resource to be protected. Also, the ABS control unit 161 determines a PM subset that is restricted in use by the ABS. For example, the ABS control unit 161 may determine the ABS and the PM subset according to steps S11 and S12 described with reference to FIG.
  • the ABS control unit 161 communicates with the adjacent pico base station 2 for signaling necessary for determining the ABS and PM subset.
  • the PM selection unit 162 manages a code book 163 including a plurality of quantized precoding matrices.
  • PM selection section 162 can use a plurality of precoding matrices included in codebook 163, and selects a precoding matrix to be used for user data transmission addressed to a macro mobile station from the entire codebook 163.
  • the PM selection unit 162 restricts the use of a part of the code book 163, that is, the PM subset determined by the ABS control unit 161.
  • the macro base station 1 is configured not to always limit the use of the PM subset but to selectively limit the use of the PM subset in the protected radio resource (eg ABS). Has been. For this reason, the macro base station 1 can suppress a decrease in downlink throughput in the macro cell 100 as compared to a method in which the use of a part of the precoding matrix is always stopped.
  • the protected radio resource eg ABS
  • the macro base station 1 can suppress a decrease in the capacity of the macro cell 100 as compared with the case where the user data transmission is completely stopped in the protected radio resource (e.g. ABS).
  • protected radio resources e.g. ABS
  • unprotected radio resources e.g. non-ABS
  • a precoding matrix corresponding to a directional beam that causes relatively large interference on the pico cell 200 is included in the PM subset.
  • the PM subset can be used in the protected radio resource (eg ABS)
  • the throughput of the macro cell 100 is almost the same as when the user data transmission is completely stopped in the protected radio resource. Can be secured.
  • this embodiment can effectively link ICIC including adjustment of use of radio resources between adjacent cells and cooperative beamforming by notification of PMI between adjacent cells.
  • ⁇ Second Embodiment> a specific example of the PM subset determination process (eg, step S12 in FIG. 4) described in the first embodiment will be described.
  • the configuration of the mobile communication system according to this embodiment may be the same as that of the first embodiment shown in FIGS. 1A and 1B.
  • the pico base station 2 feeds back PMI information similar to that of the macro mobile station to the macro base station 1.
  • the macro base station 1 determines the PM subset in consideration of the PMI feedback received from the pico base station 2.
  • FIG. 6 is a sequence diagram showing a specific example of the PMI feedback operation from the pico base station 2 to the macro base station 1.
  • the pico base station 2 receives the reference signal that arrives from the macro base station 100, and performs channel estimation. Then, the pico base station 2 determines a precoding matrix that maximizes the received power (RSRP) of the reference signal of the macro cell 100 (that is, a precoding matrix that is most unfavorable for the pico base station 2) based on the channel estimation result. (Step S22), the PMI corresponding to the determined precoding matrix is fed back to the macro base station 1 (Step S23).
  • RSRP received power
  • the PMI fed back from the pico base station 2 to the macro base station 1 corresponds to a precoding matrix that is most undesirable for the pico cell 200. Therefore, here, the PMI is referred to as “protected PMI”. Protected PMI indicates a precoding matrix for which the pico base station 2 requests the macro base station 1 to stop using it.
  • the macro base station 1 may include the precoding matrix corresponding to the protected PMI in the PM subset in consideration of the protected PMI information received from the pico base station 2.
  • the example of FIG. 6 can also be changed as follows. That is, the pico base station 2 may feed back to the macro base station 1 at least one PMI that is requested to be used by the macro base station 1 (hereinafter referred to as “recommended PMI”). In this case, the macro base station 1 may consider the recommended ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ PMI information received from the pico base station 2 and exclude the precoding matrix corresponding to the recommended PMI from the PM subset.
  • the pico base station 2 performs PMI feedback to the macro base station 1 in response to the downlink interference power from the macro cell 100 exceeding a predetermined reference being measured by the pico base station 2 or the pico mobile station. Good. Thereby, an increase in signaling between the macro base station 1 and the pico base station 2 can be prevented.
  • the macro base station 1 may determine the PM subset by statistically considering the PMI feedback from the plurality of pico base stations 2. For example, the macro base station 1 aggregates protected PMI information notified from the plurality of pico base stations 1, determines a PMI whose frequency notified by the protected MI information exceeds a reference, and a precoding matrix corresponding to the PMI May be included in the PM subset.
  • ⁇ Third Embodiment> another specific example of the PM subset determination process (eg, step S12 in FIG. 4) described in the first embodiment will be described.
  • the configuration of the mobile communication system according to this embodiment may be the same as that of the first embodiment shown in FIGS. 1A and 1B.
  • the pico base station 2 according to the present embodiment feeds back the PMI information to the macro base station 1 as in the second embodiment.
  • the reception of the reference signal that arrives from the macro base station 100 and the channel estimation are performed not by the pico base station 2 but by the pico mobile station.
  • FIG. 7 is a sequence diagram showing a specific example of the PMI feedback operation from the pico base station 2 to the macro base station 1.
  • the pico mobile station receives the reference signal that arrives from the macro base station 100, and performs channel estimation. Then, the pico mobile station determines a precoding matrix that maximizes the received power (RSRP) of the reference signal of the macro cell 100 (that is, a precoding matrix that is most unfavorable for the pico mobile station) based on the channel estimation result, and determines The PMI corresponding to the precoding matrix is notified to the pico base station 2 (step S32). The pico base station 2 determines the PMI received from the pico mobile station as protected PMI (step S33), and feeds back the protected PMI information to the macro base station 1 (step S34).
  • RSRP received power
  • FIG. 7 may be modified so as to feed back the recommended PMI to the macro base station 1 as in FIG. 6 described in the second embodiment.
  • the pico mobile station may perform channel estimation for the reference signal that arrives from the macro base station 100 in response to the downlink interference power from the macro cell 100 exceeding a predetermined reference being measured by the pico mobile station.
  • the pico base station 2 may statistically consider the PMI received from the plurality of pico mobile stations in step S32. For example, the pico base station 2 may aggregate PMIs notified from a plurality of pico mobile stations, and determine a PMI whose notification frequency from the pico mobile station exceeds a reference as protected PMI or recommended PMI.
  • ⁇ Fourth Embodiment> another specific example of the PM subset determination process (eg, step S12 in FIG. 4) described in the first embodiment will be described.
  • the configuration of the mobile communication system according to this embodiment may be the same as that of the first embodiment shown in FIGS. 1A and 1B.
  • the pico mobile station is forcibly handed over from the pico cell 200 to the macro cell 100, and the channel estimation result by the HO mobile station handed over from the pico cell 200 to the macro cell 100 is used.
  • FIG. 8 is a sequence diagram showing a specific example of the PM subset determining operation in the present embodiment.
  • the control unit 16 of the macro base station 1 transmits a notification indicating a change in CIO (Cell Individual Offset) to the pico base station 2 in order to forcibly hand over the pico mobile station from the pico cell 200 to the macro cell 100.
  • CIO is a cell-specific power offset value.
  • the CIO is notified from the base station to the mobile station together with or as part of the neighbor cell list (neighbor list).
  • CIO is one of parameters (handover parameters) for controlling handover of a mobile station.
  • CIO is one of parameters for cell edge control called CRE (Cell Range Expansion).
  • the CIO is used as an offset with respect to the received power of the neighboring cell when the mobile station triggers a handover based on the measured value of the received power (RSRP (Reference Signal Received Power)) of the neighboring cell.
  • RSRP Reference Signal Received Power
  • CIO is defined as the threshold for the RSRP M of the neighboring cell (ie macro cell 100) minus the RSRP P of the serving cell (ie pico cell 200). That is, when the following equation (1) is satisfied, the pico mobile station triggers a handover from the pico cell 200 to the macro cell 100.
  • RSRP M -RSRP P > CIO (1)
  • step S42 in response to the CIO change notification from the macro base station 1, the pico base station 2 notifies the pico mobile station of the CIO change for the adjacent macro cell 100.
  • the handover of the pico mobile station from the pico cell 200 to the macro cell 100 is induced by reducing the CIO for the macro cell 100 (for example, by setting it to a minimum value).
  • the macro base station 1 identifies the HO mobile station that has been handed over from the pico cell 200 to the macro cell 100 in accordance with the CIO change in steps S41 and S42. For example, the macro base station 1 may determine that a mobile station that satisfies both the following expressions (2) and (3) is a HO mobile station.
  • CIO BEFORE is the CIO set for the macro cell 100 by the pico base station 2 before steps S41 and S42 are performed.
  • CIO AFTER is a CIO after being updated in steps S41 and S42 for calibration.
  • the macro mobile station that satisfies both the expressions (2) and (3) corresponds to the mobile station that satisfies the handover condition from the pico cell 200 to the macro cell 100 because the CIO is changed along with the calibration.
  • RSRP M -RSRP P > CIO AFTER (3)
  • step S44 the macro base station 1 receives the PMI from the HO mobile station.
  • the operation in step S44 is the same as that of a normal mobile station in closed-loop precoding used in LTE or the like. That is, the HO mobile station receives the reference signal of the macro cell 100 to which the HO mobile station belongs, performs channel estimation, selects RSRP or a PMI that can maximize the throughput, and fordbacks the selected PMI to the macro base station 1.
  • step S45 the control unit 16 of the macro base station 1 determines a PM subset whose use in the protected radio resource (e.g. ABS) is restricted based on the PMI fed back from the HO mobile station.
  • the PMI notified from the HO mobile station is considered to correspond to a precoding matrix that is not preferable (high interference) for the pico mobile stations belonging to the pico cell 200. Therefore, the control unit 16 may include a precoding matrix corresponding to the PMI fed back from the HO mobile station in the PM subset.
  • step S ⁇ b> 46 the control unit 16 transmits a CIO change notification to the pico base station 2 in order to return the CIO related to the macro cell 100 set in the pico base station 2 to the value before calibration (CIO BEFORE ).
  • step S47 the pico base station 2 notifies the pico mobile station of the CIO change for the adjacent macro cell 100 in response to the CIO change notification in step S46.
  • the macro base station 1 may change the CIO regarding the pico cell 200 notified to the macro mobile station.
  • the CIO related to the pico cell 200 may be increased so that handover of the macro mobile station from the macro cell 100 to the pico cell 200 is difficult to occur. Thereby, handover repetition between the macro cell 100 and the pico cell 200 during the execution of the procedure of FIG. 8 is reduced. Therefore, PM subset determination using PMI feedback by the HO mobile station can be performed with high accuracy.
  • step S46 the CIO value related to the pico cell 200 notified to the macro mobile station may be restored.
  • PMI feedback by the HO mobile station that has handed over from the pico cell 200 to the macro cell 100 is used. This makes it possible to reduce the processing to be performed by the pico base station 2 for determining the PM subset by the macro base station 1, as is apparent from the comparison between FIGS. This is because the PMI feedback from the HO mobile station can be acquired by the macro base station 1 itself without going through the pico base station 2.
  • the channel estimation result or PMI feedback by the HO mobile station located in the edge region between the macro cell 100 and the pico cell 200 can be used.
  • the mobile station located in the edge region is considered to be greatly influenced by the directional beam transmitted from the macro base station 1. Therefore, serious inter-cell interference caused by the directional beam from the macro base station 1 can be suppressed by determining the PM subset using the channel estimation result by the mobile station located in the edge region or PMI feedback.
  • the case where the two adjacent cells are the macro cell 100 and the pico cell 200 has been specifically described.
  • the technical ideas described in the first to fourth embodiments can be applied between any adjacent cells such as macro cells, pico cells, femto cells, macro cells and femto cells, or pico cells and femto cells.
  • the technical ideas described in the first to fourth embodiments are particularly effective in a HetNet (Heterogeneous Network) environment including cells having different coverage sizes. For example, considering the environment where the pico cell 200 is arranged in the macro cell 100 shown in the first to fourth embodiments, the coverage of the pico cell 200 is narrower than that of the macro cell 100.
  • HetNet Heterogeneous Network
  • the transmission energy by a directional beam concentrates on the macro mobile station located in the direction of the pico base station 2 (pico cell 200) when viewed from the macro base station 1, the problem becomes significant. That is, since many pico mobile stations continuously receive strong interference from the macro base station 1, the downlink communication quality of the pico mobile station continuously deteriorates, and the pico mobile station throughput deteriorates.
  • the technical ideas described in the first to fourth embodiments can cope with the interference problem that becomes prominent in such a HetNet environment.
  • the processing performed by the control unit 16 described in the first to fourth embodiments may be realized using a semiconductor processing apparatus including Application Specific Integrated Circuit (ASIC).
  • ASIC Application Specific Integrated Circuit
  • These processes may be realized by causing a computer system including at least one processor (e.g. microprocessor, MPU, Digital Signal Processor (DSP)) to execute a program.
  • processor e.g. microprocessor, MPU, Digital Signal Processor (DSP)
  • DSP Digital Signal Processor
  • Non-transitory computer readable media include various types of tangible storage media (tangible storage medium). Examples of non-transitory computer-readable media include magnetic recording media (eg flexible disks, magnetic tapes, hard disk drives), magneto-optical recording media (eg magneto-optical discs), CD-ROMs (Read Only Memory), CD-Rs, CD-R / W, semiconductor memory (for example, mask ROM, PROM (Programmable ROM), EPROM (Erasable ROM), flash ROM, RAM (random access memory)) are included.
  • the program may also be supplied to the computer by various types of temporary computer-readable media. Examples of transitory computer readable media include electrical signals, optical signals, and electromagnetic waves.
  • the temporary computer-readable medium can supply the program to the computer via a wired communication path such as an electric wire and an optical fiber, or a wireless communication path.

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Abstract

Dans l'un de ses modes de réalisation, la présente invention se rapporte à une station de base (1) qui est configurée de façon à exécuter un traitement du signal. Ledit traitement du signal comprend une opération de précodage qui est exécutée afin de générer une pluralité de signaux de fuseaux horaires qui sont fournis à une pluralité d'antennes de transmission. D'autre part, la station de base selon l'invention (1) est configurée de façon à permettre l'utilisation d'une pluralité de matrices de précodage dans une première ressource sans fil qui est définie en fonction du temps et/ou de la fréquence. Par ailleurs, la station de base selon l'invention (1) est configurée de façon à limiter l'utilisation d'un sous-ensemble de matrices de précodage dans une seconde ressource sans fil qui est différente de la première ressource sans fil, ledit sous-ensemble de matrices de précodage correspondant à une partie de la pluralité de matrices de précodage.
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JP2019503094A (ja) * 2016-01-07 2019-01-31 ソニー株式会社 無線通信方法及び無線通信装置
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