JP2015142285A - Radio communication method, radio communication system and control station device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cancel a difference in reception timing of each of spatial multiplexed signals which are generated by a plurality of transmission stations in the case of multistream transmission from the plurality of transmission stations to a plurality of reception stations, in each reception station and characteristic deterioration caused by different frequency errors of the transmission stations.SOLUTION: In a radio communication method by which a control station performs MIMO transmission with a plurality of reception stations via a plurality of transmission stations, the control station generates a beam forming matrix from channel information from the plurality of transmission stations to the plurality of reception stations, calculates a power allocation matrix on the basis of the beam forming matrix, generates a precoding matrix that is obtained by multiplying the beam forming matrix and the power allocation matrix, and outputs results of multiplying transmission data to the plurality of reception stations with the precoding matrix as transmission signals to be transmitted from the plurality of transmission stations. The plurality of reception stations receive a plurality of signals coming from different transmission stations as input signals and output the plurality of input signals while separating them into individual signals.

Description

  The present invention relates to a radio communication method, a radio communication system, and a control station apparatus including a plurality of multi-beam transmission stations and a plurality of reception stations that can communicate with all the transmission stations.

  In multi-user MIMO transmission, a transmitting station performs multi-beam transmission using a plurality of antennas, and performs parallel transmission to a plurality of receiving stations. In this multi-user MIMO transmission, the communication quality when performing multi-stream transmission to a single receiving station having multiple antennas is greatly influenced by the channel correlation between the transmitting and receiving stations. Especially in environments with small direct wave components such as Rayleigh fading, different fading fluctuations occur between the transmitting and receiving antennas on the receiver side, so that the channel correlation becomes small, and simultaneously transmitted information sequences are separated and detected. Can do. This enables multi-stream transmission to a single receiving station.

  However, if the channel has a large direct wave component, such as the line-of-sight environment, it is difficult to obtain a sufficiently low correlation with only the antenna spacing of the transmitting station, making it difficult to separate and detect multiple signals. There is a limit to the improvement of communication capacity by multi-stream transmission to a station.

  Non-Patent Documents 1 and 2 disclose that, in satellite communication, which is an example of wireless communication in a line-of-sight environment, as shown in FIG. 2, a control station (base station) with respect to one receiving station (earth station) having a plurality of antennas. This is a technique that enables multi-stream transmission by lowering the correlation of each channel by performing single-user MIMO transmission through a plurality of transmission stations (satellite relay stations) under the control of the (station) station.

  In Non-Patent Document 3, as shown in FIG. 3, a single transmitting station (satellite repeater) using a plurality of antennas is controlled by a control station (base station) with respect to a plurality of receiving stations (earth stations). In this technique, a frequency-repetitive multi-beam is formed and interference is reduced by precoding the base station.

  Non-Patent Document 4, as shown in FIG. 4, is an inter-base station cooperative MIMO technique mainly in a cellular system in a terrestrial radio communication system, and is a cell edge receiving station of a plurality of transmitting stations (base stations) that form a multi-beam. On the other hand, the characteristics of the entire system are improved by performing MIMO transmission in cooperation with a plurality of transmitting stations under the control of the control station.

Yamashita, Fumihiro, et al. "Broadband multiple satellite MIMO system." Vehicular Technology Conference, 2005. VTC-2005-Fall. 2005 IEEE 62nd. Vol.4. IEEE, 2005. Liolis, Konstantinos P., Athanasios D. Panagopoulos, and Panayotis G. Cottis. "Multi-satellite MIMO communications at ku-band and above: investigations on spatial multiplexing for capacity improvement and selection diversity for interference mitigation." EURASIP Journal on Wireless Communications and Networking 2007.2 (2007): 16-16. Cottatellucci, L., et al. "Interference mitigation techniques for broadband satellite systems." 24th AIAA International Communications Satellite Systems Conference (ICSSC 2006). 2006. Zhang, Hongyuan, and Huaiyu Dai. "Cochannel interference mitigation and cooperative processing in downlink multicell multiuser MIMO networks." EURASIP Journal on Wireless Communications and Networking 2004.2 (2004): 222-235. Ryunosuke Hebei, Shinsuke Kinu, Seiichi Sampei. "A study on efficient resource management in multi-user MIMO environment [in Japanese] IEICE technical report. RCS, Wireless communication systems 107.192 (2007): 57-62.

  The technologies of Non-Patent Documents 1 and 2 shown in FIG. 2 are technologies that consider only transmission to a receiving station at one point, and simultaneous transmission to different receiving stations at a plurality of points is not assumed.

  The technique of Non-Patent Document 3 shown in FIG. 3 is a multi-user MIMO technique on the premise of one transmitting station, and is not assumed to be combined with a plurality of transmitting stations. If the multi-user MIMO technique described in Non-Patent Document 3 is applied to the configuration using a plurality of transmission stations (satellite relay stations) shown in FIG. 5, there are two precoding methods for the transmission stations. Conceivable. The first is a method of performing precoding for each transmitting station and operating a plurality of these. The second is a method of performing precoding in the whole of a plurality of transmitting stations. The former can be realized by adopting the multi-user MIMO technology described in Non-Patent Document 3 as it is, but the precoding of the transmission station is based on the premise of reducing interference in the transmission station alone, and from other transmission stations The same frequency interference is not considered, and there is a problem that the throughput characteristic of the entire system is not maximized. In the latter, the propagation distance from the transmitting station to each receiving station varies greatly depending on the transmitting station, so that the receiving timing of all receiving stations cannot be made coincident with time asynchrony, and each transmitting station uses an independent local oscillator. Therefore, there is a problem that pre-coding that maximizes the throughput characteristics of the entire system cannot be performed due to frequency asynchronization caused by different frequency errors.

  The technique of Non-Patent Document 4 shown in FIG. 4 is a technique for transmitting to a specific receiving station existing at the cell edge in a time-frequency synchronized state, but the transmitting station transmits multi-user MIMO to a plurality of receiving stations. When the inter-transmitting station cooperative MIMO technique is applied when performing transmission, there is a problem that it is difficult to synchronize with a plurality of receiving stations having different transmission distances from each transmitting station.

  The present invention relates to a difference in reception timing at each receiving station of spatially multiplexed signals by a plurality of transmitting stations, which occurs when multistream transmission is performed from a plurality of transmitting stations to a plurality of receiving stations, and characteristics due to different frequency errors of each transmitting station. An object of the present invention is to provide a wireless communication method, a wireless communication system, and a control station apparatus that realize transmission precoding and reception equalization techniques that eliminate degradation.

  The first invention includes a plurality of transmission stations each having a plurality of antennas, a control station that controls the plurality of transmission stations, and a plurality of receptions each having a plurality of antennas and receiving transmission signals from the plurality of transmission stations. In a wireless communication method in which a control station performs MIMO transmission with a plurality of receiving stations via a plurality of transmitting stations, the control station transmits channel information from a plurality of transmitting stations to a plurality of receiving stations. A beam forming step of inputting and generating and outputting a beam forming matrix from the channel information; a power allocation step of calculating a power allocation matrix based on the beam forming matrix output from the beam forming step; a beam forming matrix and a power Precoding that generates and outputs a precoding matrix obtained by multiplying two matrices by using an allocation matrix as an input signal And a result obtained by multiplying the transmission data to the plurality of receiving stations by the transmission data to the plurality of receiving stations is output as a transmission signal transmitted from the plurality of transmitting stations. A signal separation step of separating the plurality of input signals into individual signals and outputting the signals as input signals is provided.

  In the radio communication method according to the first aspect of the present invention, the beamforming step includes the step of multiplying a channel component and a beamforming component when generating a beamforming matrix from channel information from a plurality of transmitting stations to a plurality of receiving stations. Among them, components of different transmitting stations are replaced with zeros, and a beam forming matrix is calculated independently for each transmitting station. In the power allocation step, a plurality of transmitting stations calculate SINR using channel information, and calculate a power allocation weight component based on the SINR and a predetermined guideline.

  A second invention includes a plurality of transmission stations each having a plurality of antennas, a control station that controls the plurality of transmission stations, and a plurality of receptions each having a plurality of antennas and receiving transmission signals from the plurality of transmission stations. In a wireless communication system in which a control station performs MIMO transmission with a plurality of receiving stations via a plurality of transmitting stations, the control station transmits channel information from a plurality of transmitting stations to a plurality of receiving stations. Beam forming matrix generating means for inputting and generating a beam forming matrix from the channel information and outputting; and power allocation matrix generating means for calculating a power allocation matrix based on the beam forming matrix output from the beam forming matrix generating means; Using the beamforming matrix and power allocation matrix as input signals, a precoding matrix obtained by multiplying two matrices is generated and output. And a precoding matrix generation means for outputting a transmission signal to be transmitted from a plurality of transmitting stations as a result of multiplying the transmission data to the plurality of receiving stations by a precoding matrix. A signal separation output unit is provided that uses a plurality of signals coming from a station as input signals and separates the plurality of input signals into individual signals for output.

  In the radio communication system of the second invention, the beamforming matrix generation means multiplies the channel component and the beamforming component when generating the beamforming matrix from channel information from a plurality of transmitting stations to a plurality of receiving stations. Of the components, components of different transmitting stations are replaced with zeros, and a beam forming matrix is calculated independently for each transmitting station. Also, the power allocation matrix generation means calculates SINR using a plurality of transmission stations using channel information, and calculates a power allocation weight component based on the SINR and a predetermined guideline.

  A third invention provides a plurality of transmission stations each having a plurality of antennas, a control station for controlling the plurality of transmission stations, and a plurality of receptions each having a plurality of antennas and receiving transmission signals from the plurality of transmission stations. A control station device of a wireless communication system in which a control station performs MIMO transmission with a plurality of receiving stations via a plurality of transmitting stations, channel information from a plurality of transmitting stations to a plurality of receiving stations. Beam forming matrix generating means for inputting and generating a beam forming matrix from the channel information and outputting; and power allocation matrix generating means for calculating a power allocation matrix based on the beam forming matrix output from the beam forming matrix generating means; Generates and outputs a precoding matrix obtained by multiplying two matrices by using a beamforming matrix and a power allocation matrix as input signals That a pre-coding matrix generation means, is configured to output as a transmission signal to transmit the result of multiplying the transmission data of a precoding matrix to a plurality of receiving stations from a plurality of transmitting stations.

  In the present invention, the control station performs beamforming transmission by transmission precoding using a plurality of transmission stations using the same frequency, but forms the beamforming by a single transmission station in consideration of channel information between the transmission and reception stations. By doing so, multi-stream transmission is performed to each receiving station. On the other hand, the receiving station implements multi-user transmission that separates a plurality of desired signals received at different timings by applying an equalization technique that separates a plurality of signals arriving at different timings from different transmitting stations.

  At this time, when generating a beamforming matrix from channel information between a plurality of transmitting and receiving stations, the control station replaces components of different transmitting stations among components multiplied by the channel component and the beamforming component with zero. By combining the precoding technique for each transmitting station using a precoding matrix obtained by multiplying the beam forming matrix and the power allocation matrix, and the separation technique for multiple signals using equalization technique in the receiving station, the transmitting station and the receiving station are combined. It is possible to eliminate the difference in reception timing caused by the difference in path length and the degradation of the desired signal due to the different frequency errors generated from the respective transmission stations, thereby realizing improvement in system throughput characteristics by a plurality of transmission stations.

  Further, when parallel transmission is performed by a plurality of transmission stations having different locations, it is possible to expect an improvement in frequency utilization efficiency as compared with the conventional parallel transmission technique of one transmission station.

It is a figure which shows the Example structure of the radio | wireless communications system of this invention. It is a figure which shows the 1st structural example of the conventional radio | wireless communications system. It is a figure which shows the 2nd structural example of the conventional radio | wireless communications system. It is a figure which shows the 3rd structural example of the conventional radio | wireless communications system. It is a figure which shows the 4th structural example of the conventional radio | wireless communications system.

FIG. 1 shows an embodiment of a radio communication system according to the present invention.
In FIG. 1, a wireless communication system according to the present embodiment includes a control station (base station) CS and b transmission stations TX that are connected to the control station CS via a wired line or a wireless line and each have a number of antennas. And d receiving stations RX each having c antennas, and MIMO transmission is performed between the transmitting station TX and the receiving station RX. Here, for the sake of simplicity, a configuration in the case of a = b = c = d = 2 is shown, and is expressed as transmitting stations TX <1> and TX <2> and receiving stations RX (1) and RX (2). In addition, this structure is an example and the application structure of this invention is not restrict | limited to these values.

  The control station CS has a function of independently transmitting the transmission signals of the transmission stations TX <1> and TX <2>. The transmitting stations TX <1> and TX <2> can transmit signals independently from the two antennas, respectively, thereby forming two beams, and receiving stations RX (1) existing in each beam. , RX (2) performs parallel transmission at the same frequency. The receiving stations RX (1) and RX (2) have a function of extracting a desired signal from the spatially multiplexed signals transmitted from the transmitting stations TX <1> and TX <2>.

  The control station CS transmits two signals in parallel to the receiving stations RX (1) and RX (2). For this purpose, precoding based on channel information (CSI) up to each antenna between each TX and RX is performed to reduce inter-receiving station interference. There are two methods for obtaining CSI. In the case of time division duplex (TDD), information estimated from a pilot signal from the receiving station RX is used. In the case of frequency division duplex (FDD), the CSI acquired by the receiving station RX is fed back to the control station CS.

  In this wireless communication system, in the case where the control station CS transmits signals to the receiving stations RX (1) and RX (2) of each beam via the transmitting stations TX <1> and TX <2>, Equation (1) shows the relational expression of the reception vector R, the channel matrix H, and the transmission vector X.

r _i ^(k) and n _i ^(k) are the received signal and noise of the i-th receiving antenna, and (k) is the received signal and noise of the receiving antenna of the receiving station RX (k). The channel component h _ij ^<l> is a channel coefficient from the j-th transmitting antenna to the i-th receiving antenna, and <l> is a channel coefficient from the transmitting station TX <l>. x _j ^<l> represents a transmission signal from the j-th transmission antenna, and <l> represents a transmission signal from the transmission station TX <l>. In this system, the transmission signal vector X is generated as shown in Equation (2) using the precoding matrix P and the transmission data vector S.

p _mn ^<l> is a precoding component of the nth transmission data included in the mth transmission signal, and <l> represents a transmission signal from the transmission station TX <l>. s _n ^(k) is the n-th transmission data of this system, and (k) indicates transmission data to the receiving station RX (k).

  The method of generating the precoding matrix P in the present invention is performed by multiplying the beam forming matrix B generated based on the channel matrix H obtained from the channel estimation and the power allocation matrix A as shown in Equation (3).

  The beamforming matrix B is a component that determines beamforming for each receiving station RX, and calculates a weighting matrix that cancels the interference component after selecting the optimum component from the channel components corresponding to the number of antennas owned by each receiving station RX. (Claim 2). The power allocation matrix A is a component that determines the distribution of signal power to each receiving station RX, and a rule determined as a required SINR (for example, whether to maximize the total system throughput or maximize the characteristics of the minimum throughput receiving station RX). Distribution according to whether or not

  When the ZF (Zero Forcing) algorithm is used in generating the beam forming matrix B, each component of the matrix B is generated as shown in equations (4) and (5).

H ⁺ is the Moore-Penrose general inverse matrix H ⁺ = H ^H (HH ^H ) ⁻¹ . h ′ is generated by determining one channel component from the channel component of each antenna of the receiving station RX. As an example, the channel components of each receiving antenna of the receiving station RX from the two transmitting antennas of each transmitting station TX as shown in the equations (6-1), (6-2), (7-1), (7-2) Among these, a method for determining h ′ by selecting the channel component of the antenna having the higher power sum will be described.

Taking the selection method of h ′ ₁₁ ^<1> and h ′ ₁₂ ^<1> in Equation (6-1) as an example, (h ₁₁ ^<1> and h ₁₃ ^<1> ) and (h ₂₁ ^<1> And h ₂₃ ^<1> ), the one with the higher sum of power is selected. That is, the higher combination of | h ₁₁ ^<1> | ² + | h ₁₃ ^<1> | ² and | h ₂₁ ^<1> | ² + | h ₂₃ ^<1> | ² is selected, and h ′ ₁₁ ^<1> and is assigned to h _'12 ^<1>.

In the generation of the beamforming matrix B, components other than the equations (6-1), (6-2), (7-1), and (7-2) are set to zero. This component is a value obtained by multiplying the channel component and the beamforming component by U components such as h _ab ^<x> b _cd ^<y> (x ≠ y) in the matrix HB. However, as described above, since the transmitting stations TX are arranged at distant locations, it is assumed that the transmission distances between the transmitting station TX and the receiving station RX are different. As a result, since the reception timing between different transmission station TX signals is different, an error occurs in a component corresponding to h _ab ^<x> b _cd ^<y> (x ≠ y) in the reception signal of the reception station RX. This error increases as the propagation distance difference increases. In addition, when different local oscillators are used for the transmitting stations, an error occurs in h _ab ^<x> b _cd ^<y> (x ≠ y) even if different frequency errors occur in the signals from the transmitting stations. End up. Therefore, in the present technology, in order to avoid multiplication of h and b with different transmission stations TX, a component that satisfies h _ab ^<x> b _cd ^<y> (x ≠ y) is set to 0, so that the beamforming matrix B Is generated.

  The power allocation matrix A is determined according to a rule defined as a signal-to-noise interference power ratio (SINR) calculated by the channel matrix H (Claim 3). As an example of the rule for determining the components of the power allocation matrix A, when maximizing the total throughput characteristic of the system, the total throughput of four signals is maximized based on the SINR. When maximizing the minimum throughput users, it is not the signal unit but the user unit that is maximized. Therefore, optimization is performed as one user two signals.

  According to Non-Patent Document 3, there is an UpConst algorithm as a method for generating the power allocation matrix A of Expression (8).

sinr _i can be calculated from a matrix M as shown in Equation (9).

(Hb _ij ), k ₁ ≦ i ≦ k ₂ , and k ₃ ≦ j ≦ k ₄ indicate a matrix of k ₁ to k ₂ rows k _{3 to} k ₄ columns of the matrix HB. The matrix W is a weight matrix for each receiving station RX to separate a desired signal from two received signals, and the receiving station RX is calculated from the HB matrix component acquired from the control station CS. Equation (10) is an example calculated by the ZF algorithm. From the diagonal component m _ii of the matrix M, the SINR _i of the i-th received signal can be calculated as shown in Equation (10).

  According to Non-Patent Document 3, this algorithm enables power allocation considering the system throughput and the fairness of the receiving station RX. In this way, by using this precoding technique, flexible power allocation control in a system using different transmission stations TX can be performed, and throughput characteristics can be improved in consideration of the entire system.

  Since each receiving station RX has a function of extracting a desired signal from a plurality of the same frequency signals transmitted from each transmitting station TX, the other 2 × 2 matrix components are obtained from the control station CS and equalized as CSI. A desired signal can be obtained by performing the processing. Equations (11) and (12) represent the received signals of the receiving stations RX (1) and RX (2), respectively.

On the other hand, by multiplying the received signal by each weight matrix as shown in equations (13) and (14), the desired signals s ₁ ⁽¹⁾ ′, s ₂ ⁽¹⁾ ′ and s ₃ ⁽²⁾ ′, s ₄ ⁽²⁾ 'can be obtained.

w _ij ^(k) represents a weight matrix component of i rows and j columns of the receiving station RX (k). Each receiving station RX (1), RX (2) obtains a 2 × 2 matrix portion of the channel information HP from the control station CS and calculates a weight matrix W. When the ZF algorithm is used, each weight matrix is calculated as shown in equations (15) and (16).

Here, as described above, since the reception timing from different transmission stations is different in each reception station RX, the reception timings of the transmission signals x ₁ ^<1> and x ₂ ^<2> are different in the reception station RX (1). In the station RX (2), the reception timings of the transmission signals x ₃ ^<1> and x ₄ ^<2> are different, and there is a possibility that the desired signal cannot be demodulated only by the calculations of the equations (13) and (14). On the other hand, according to Non-Patent Document 5, for multiple signals of the same frequency received asynchronously, frequency domain SC / MMSE (Soft Canceller followed by SC-FDMA (Single Carrier-Frequency Division Multiple Access)) is used. Minimum Mean Square Error) Improves characteristics by turbo equalization. Each receiving station RX uses such an equalization technique to separate two signals that arrive with a delay, and obtain a desired signal.

TX transmitting station RX receiving station CS control station

Claims (7)

A plurality of transmitting stations each having a plurality of antennas, a control station for controlling the plurality of transmitting stations, and a plurality of receiving stations each having a plurality of antennas for receiving transmission signals from the plurality of transmitting stations, and controlling In a wireless communication method in which a station performs MIMO transmission with a plurality of receiving stations via a plurality of transmitting stations,
The control station
Beam forming step of inputting channel information from the plurality of transmitting stations to the plurality of receiving stations, generating a beam forming matrix from the channel information and outputting the beam forming matrix;
A power allocation step of calculating a power allocation matrix based on the beamforming matrix output from the beamforming step;
A precoding step of generating and outputting a precoding matrix obtained by multiplying the beamforming matrix and the power allocation matrix as input signals and multiplying the two matrices, the precoding matrix being the plurality of receiving stations. The result of multiplying the transmission data to output as a transmission signal transmitted from the plurality of transmission stations,
The radio communication method characterized in that the plurality of receiving stations have a signal separation step of taking a plurality of signals arriving from different transmission stations as input signals and separating the plurality of input signals into individual signals and outputting them. The wireless communication method according to claim 1,
In the beam forming step, when generating the beam forming matrix from channel information from the plurality of transmitting stations to the plurality of receiving stations, components of different transmitting stations among the components multiplied by the channel component and the beam forming component A wireless communication method characterized by substituting 0 with zero and calculating a beamforming matrix independently for each transmitting station. The wireless communication method according to claim 1 or 2,
In the power allocation step, the plurality of transmitting stations calculate SINR using the channel information, and calculate a power allocation weight component based on the SINR and a predetermined guideline. A plurality of transmitting stations each having a plurality of antennas, a control station for controlling the plurality of transmitting stations, and a plurality of receiving stations each having a plurality of antennas for receiving transmission signals from the plurality of transmitting stations, and controlling In a wireless communication system in which a station performs MIMO transmission with a plurality of receiving stations via a plurality of transmitting stations,
The control station
Beam forming matrix generating means for inputting channel information from the plurality of transmitting stations to the plurality of receiving stations, generating a beam forming matrix from the channel information, and outputting the beam forming matrix;
Power allocation matrix generation means for calculating a power allocation matrix based on the beamforming matrix output from the beamforming matrix generation means;
Precoding matrix generation means for generating and outputting a precoding matrix obtained by multiplying the beamforming matrix and the power allocation matrix as input signals and multiplying two matrices, and receiving the precoding matrix The configuration is to output the result of multiplying the transmission data to the station as a transmission signal transmitted from the plurality of transmission stations,
The plurality of receiving stations include signal separation output means for receiving a plurality of signals arriving from different transmission stations as input signals and separating the plurality of input signals into individual signals and outputting them. . The wireless communication system according to claim 4, wherein
The beam forming matrix generating means generates different beam transmitting matrix components out of components multiplied by a channel component and a beam forming component when generating the beam forming matrix from channel information from the plurality of transmitting stations to the plurality of receiving stations. A wireless communication system, wherein the component is replaced with zero and a beamforming matrix is calculated independently for each transmitting station. The wireless communication system according to claim 4 or 5,
The power allocation matrix generation means calculates the SINR by the plurality of transmitting stations using the channel information and calculates a power allocation weight component based on the SINR and a predetermined guideline. system. A plurality of transmitting stations each having a plurality of antennas, a control station for controlling the plurality of transmitting stations, and a plurality of receiving stations each having a plurality of antennas for receiving transmission signals from the plurality of transmitting stations, and controlling In a control station apparatus of a wireless communication system in which a station performs MIMO transmission with a plurality of receiving stations via a plurality of transmitting stations,
Beam forming matrix generating means for inputting channel information from the plurality of transmitting stations to the plurality of receiving stations, generating a beam forming matrix from the channel information, and outputting the beam forming matrix;
Power allocation matrix generation means for calculating a power allocation matrix based on the beamforming matrix output from the beamforming matrix generation means;
Precoding matrix generation means for generating and outputting a precoding matrix obtained by multiplying the beamforming matrix and the power allocation matrix as input signals and multiplying two matrices, and receiving the precoding matrix A control station apparatus, characterized in that a result obtained by multiplying transmission data to a station is output as a transmission signal transmitted from the plurality of transmission stations.

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