JP5571050B2 - Wireless communication method and wireless communication system - Google Patents

Description

  The present invention relates to a radio communication method and a radio communication system in which each base station performs signal transmission cooperatively in an outdoor radio access system in which a plurality of base stations perform signal transmission using the same frequency channel.

  In order to provide a broadband Internet connection service, an optical line is spreading. However, laying an optical line is very expensive, and it is difficult to lay it unless a certain number of users can be expected. Therefore, in order to provide a broadband Internet connection service with reduced facility costs, a method of using a wireless line at a location closest to the user (last one hop) has been studied.

  As this last one-hop wireless line, it is ideal to use a microwave band in which communication is possible without a line of sight between the base station on the network side and the terminal station on the user's home side. However, in the present situation where frequency resources are being exhausted, it is difficult for a single operator to monopolize many frequency channels in the microwave band. On the other hand, since it is difficult to cover a wide service area with one base station, when expanding the service area in one area, one base station constitutes a service area called a circular cell. It has been dealt with by spreading cells continuously. At this time, if adjacent cells use the same frequency channel, inter-cell interference generally occurs, and the characteristics are greatly deteriorated. Usually, in order to solve such a problem, a plurality of frequency channels are used, and the frequency interval is assigned repeatedly, thereby isolating the cell interval of the same frequency channel.

  As described above, it is possible to suppress mutual interference between cells of the same frequency channel by repeatedly assigning a plurality of frequency channels. However, if there are few available frequency channels, the interference is not necessarily reduced to a sufficient level. It cannot be suppressed. As a method for solving such a problem, a method using an intercell interference canceller for suppressing mutual interference between cells as described in Non-Patent Document 1 has been proposed.

FIG. 6 shows a configuration example of a radio communication system using an inter-cell interference canceller in the prior art.
In FIG. 6, 101 is a control station, 102-1 to 102-5 are remote base stations, 103-1 to 103-5 are terminal stations, 104-1 to 104-5 are cells using the same frequency channel, and 105 is wired. Represents a transmission line. The cells 104-1 to 104-5 using the same frequency are separated from each other by a certain distance due to repeated use of a plurality of frequency channels. That is, although the cells other than the frequency channel cell of interest are not described here, there are actually cells using other frequency channels. The remote base stations 102-1 to 102-5 installed in the cells 104-1 to 104-5 are connected to the control station 101 via the wired transmission path 105. The control station 101 collectively manages wireless communication between each of the remote base stations 102-1 to 102-5 and the terminal stations 103-1 to 103-5 subordinate thereto, and performs various signal processing.

  The remote base stations 102-1 to 102-5 and the terminal stations 103-1 to 103-5 are provided with a plurality of antennas in the figure, and configure the MIMO channel for each of the cells 104-1 to 104-5. Although shown, each may constitute a SISO channel with one antenna. Furthermore, a configuration may be adopted in which a plurality of remote base stations are provided in each cell, and a plurality of antennas are provided as a whole. Further, the terminal stations 103-1 to 103-5 may exist in a plurality of stations in the cell, and may be configured to realize multiuser MIMO communication in which communication is performed in parallel using the same frequency channel at the same time.

  It is assumed that the control station 101 can acquire the channel information of the MIMO channel between the remote base stations 102-1 to 102-5 and the terminal stations 103-1 to 103-5 by some method. Since this channel information acquisition method is a general technique discussed in various documents, the details are omitted here because the channel information is known.

Next, the overall channel matrix H _all in the wireless communication system is defined as follows.

Here, N represents the total number of cells using the same frequency channel constituting the wireless communication system. Further, each component H _{i, j} constituting the channel matrix H _all itself constitutes a matrix. For example, in the example of FIG. 6, N = 5 because the cell is composed of five cells, and the diagonal components H _1,1 , H _{2,2 ,.} -1 to 104-5 represents a MIMO channel between each of the remote base stations 102-1 to 102-5 and each of the terminal stations 103-1 to 103-5. H _i, j for i ≠ j, which is a non-diagonal component, represents a channel matrix corresponding to interference from the remote base station 102-j in the j-th cell to the terminal station 103-i in the i-th cell. Since this matrix H _{i, j} is different for each terminal station that is a communication partner, it should be marked with a subscript corresponding to that terminal station, but only the terminal that is to be communicated at a certain moment. Here, for convenience of explanation, subscripts corresponding to terminal stations are omitted.

Here, when the norm of the off-diagonal matrix is sufficiently smaller than the norm of the diagonal matrix, that is, when the following condition is satisfied, the interference canceller functions effectively.

In the following description, the matrix H _{d in} which only the diagonal terms of the channel matrix H _all are extracted and zeros are inserted, and the matrix H _{nd in} which only the non-diagonal terms are extracted and the diagonal terms are zero-inserted are as follows: Define as follows.

Further, when the transmission weight that the remote base station multiplies the transmission signal as necessary in the i-th cell is W _{i, i} , the entire transmission weight matrix in which this partial matrix is arranged in the diagonal terms is as follows: Define.

Similarly, if the transmission information from the remote base station in the i-th cell is S _i , the signal received at the i-th cell terminal station is R _i , and the noise signal at the i-th cell terminal station is n _i , As a whole, it can be expressed as follows.

The signal T in Expression (10) is a signal obtained by multiplying transmission information by a transmission weight, and is positioned as a precoded signal that is actually transmitted from the transmission side. Here, since the transmission weight matrix W _{i, i} is a transmission weight calculated by ignoring interference from cells other than its own cell, the inter-cell interference signal is mixed in Equation (6). ing. In the interference canceller described in Non-Patent Document 1, it is estimated how the sum of interference signals from other cells is received at the terminal station, and a replica of the signal with the opposite sign of the estimated signal is transmitted to the remote base station. Is generated and added to the original signal and transmitted. A specific transmission signal T ′ in consideration of the interference replica signal is given by the following equation.

Here, equation (11) can be understood as calculating the following converted transmission weight W ′ in place of the previous transmission weight W and multiplying the transmission information S by W ′ to obtain the transmission signal.

  FIG. 7 shows a transmission signal calculation processing procedure in consideration of interference cancellation in the prior art. Fig. 7 (a) is a channel information acquisition process periodically performed between the remote base station and each terminal station, Fig. 7 (b) is a previous transmission preparation process for performing an actual transmission process, and Fig. 7 (c) is each process. A transmission signal calculation process in symbol units when transmitting a bit string is shown.

In FIG. 7 (a), the propagation channel between the remote base station and each terminal station generally changes with time. Therefore, each channel information is periodically acquired at a predetermined cycle. Specifically, when processing is started (S101), channel information is acquired (S102), and it is recorded as a partial channel matrix H _{i, j} of Equation (3) and Equation (4) (S103). The process ends (S104). Since the partial channel matrix H _{i, j} is originally different for each terminal station, a subscript corresponding to the terminal station should be given, but is omitted here for convenience of explanation.

In FIG. 7B, when processing is started upon obtaining a transmission opportunity (S111), a communication partner terminal station is selected (S112), and the partial channel matrix H _{i, j} associated with the terminal station stored in the memory is selected. Is read (S113). Further calculates versus partial channel matrix H _i corner _components, transmission weight W _i for _i, a _i (S114). The transmission weight here is, for example, a transmission weight for eigenmode transmission in MIMO transmission or a transmission weight for null formation for inter-terminal-station interference suppression in multi-user MIMO. It doesn't matter. In addition, a simple unit matrix may be used without particularly defining a transmission weight. In this case, the transmission weight calculation process (S114) has no meaning effectively. Next, a converted transmission weight W ′ represented by the equation (12) is calculated for the transmission weight W having the transmission weights Wi _{, i} as diagonal components (S115), and the process is terminated (S116).

  In FIG. 7 (c), when the processing is started as the calculation processing of the transmission signal that is actually precoded based on the bit string (S121), the transmission information S is input (S122), and the transmission information S according to the equation (11) is input. Is multiplied by the converted transmission weight W ′ to calculate the transmission signal T ′ (S123), and the processing is terminated to determine the transmission signal T ′ (S124). The transmission information S is processed as a signal vector obtained by synthesizing the components for each cell according to the equation (7).

Kazuteru Maruta et al., “Improvement efficiency of frequency utilization using inter-cluster interference canceller in multi-user MIMO distributed antenna system”, IEICE Technical Report RCS2009-231, pp.139-144, January 2010

  The interference canceller described in Non-Patent Document 1 has been described above. In order for this interference canceller to function effectively, the condition of equation (2) must be satisfied, and the repetition was originally performed with a small number of frequency channels. However, inter-cell interference could not be sufficiently suppressed.

Therefore, in an environment that does not sufficiently satisfy the condition of Equation (2), it is effective to further increase the estimation accuracy of the interference replica signal. First, the replica signal for canceling the interference signal shown in Equation (11) is considered only for a single cell, ignoring the interference signal from an adjacent cell that can be an interference source in the cell for which the replica signal is obtained. It was obtained on the assumption of the transmission signal of the case. If this is expanded, the replica signal for canceling the signal is calculated again, and the signal is subtracted on the assumption that the signal given by Equation (11) is transmitted from a cell that can be an adjacent interference source. This makes it possible to increase the accuracy of approximation. A specific transmission signal T ″ in consideration of the interference replica signal in this case is given by the following equation.

However, looking at the third term on the right side of this equation, it was included in equation (11).
(H _d・ W) ⁻¹・ H _nd・ W
Even if the term is used as it is, an operation of squaring this matrix and further multiplying the matrix W from its left side is required. In general, N ³ multiplications are required for multiplication between N × N matrices. As described in Non-Patent Document 1, the service area as a whole becomes wide, and as the number of antennas of remote base stations in the entire area increases, the number of multiplications increases in proportion to N ³ . That is, although it is possible to increase the accuracy of approximation, application in an environment in which the size of the entire matrix _Hall is increased is impractical because the circuit scale increases and the calculation load increases. It was.

  The present invention improves the signal-to-interference power ratio (SIR) by increasing the estimation accuracy of interference replica signals while suppressing the amount of computation, and further reduces the number of frequency channels for frequency repetition to reduce frequency resources. An object of the present invention is to provide a wireless communication method and a wireless communication system that can effectively utilize the above.

In the first invention, one or more base stations are arranged in each of a plurality of cells, each base station is connected to a network via a wired line, and each base station communicates with a terminal station in the cell via a wireless line. A first step of acquiring channel information between a base station and a terminal station in the same cell and between different cells, and measuring the estimation accuracy of the channel information acquired in the first step And when the channel information estimation accuracy measured in the second step satisfies a predetermined quality, the channel information is transferred from the base station in the j-th cell to the terminal station in the i-th cell. The third step of managing the channel matrix H _{i, j} corresponding to the interference and discarding the channel information when the estimation accuracy of the channel information does not satisfy the predetermined quality is the same as the base station in the i-th cell. In cell When the transmission weight used for the terminal station of W _{i, i} is expressed as Wi _i ,
M _{i, j} = W _{i, i} (H _{i, i} W _{i, i} ) ⁻¹ · H _{i, j}
The fourth step of obtaining the matrix M _{i, j} and the transmission information in the i-th cell is S _i, and the 0th-order transmission signal T _i in the i-th cell is multiplied by the transmission weight W _{i, i.} The fifth step of acquiring ^[0] and the jth i that corresponds to the channel matrix H _{i, j} stored and managed among the peripheral cells that perform communication using the same frequency channel as the i-th cell. ^a sixth step of acquiring the a-th transmission signal T _j ^[a] in the j cell, summing up the integration results of the transmission signal T _j ^[a] and the matrix M _{i, j} for a predetermined j, and By subtracting the result from the 0th-order transmission signal T _i ^[0], the seventh step of calculating the a + 1-order transmission signal T _i ^{[a + 1]} in the i-th cell is repeatedly performed to generate a transmission signal. To do.

By performing the second to seventh steps, the transmission information is not multiplied by calculating a higher-order transmission weight matrix considering interference cancellation for the entire service area. On the other hand _, by using the matrix M _{i, j} which is a common small-scale matrix and calculating the a-order transmission signal T _i ^[a] by a recurrence formula while measuring the signal quality, the higher order while reducing the amount of calculation. The solution of the transmitted signal can be obtained.

  In the wireless communication system of the second invention, one or more base stations are arranged in each of a plurality of cells, each base station is connected to a network via a wired line, and each base station is connected to a terminal station in the cell and a wireless line It is the structure which communicates by the radio | wireless communication method of 1st invention via this.

  According to the present invention, in processing related to an interference canceller that suppresses mutual interference / interference from neighboring cells using the same frequency channel, channel information between a base station and a terminal station, and a transmission signal of each base station By generating a replica of the interference signal that the transmission signal of each base station gives on the terminal station while exchanging the transmission weight, and asymptotically repeating the process of superimposing the signal that cancels the interference signal on the main signal The transmission weight can be calculated. In this method, since the matrix operation can be converted into an asymptotic repetitive operation, the amount of operation can be reduced.

  Furthermore, according to the present invention, when the calculated channel information does not satisfy a predetermined criterion when performing the above-described repetitive calculation, interference removal processing is performed by excluding the interference component corresponding to the channel information. Here, the predetermined reference is a reference such as a reception level of a training signal used for calculation of channel information being lower than a threshold. That is, the quality of the signal received by the terminal station can be improved by performing interference cancellation using only replicas (interference components) generated based on highly reliable channel information.

  In addition, it is not necessary to consolidate all signal processing itself into one control station, and processing can be executed in a distributed control station or base station. As a result, computation of individual distributed control stations or base stations is possible. The amount can be suppressed to a practical amount of calculation that does not depend on the number of cells in the entire service area, and can be expanded to an extremely wide service area in the limit.

It is a figure which shows the structural example of the control station and remote base station in the basic technique of this invention. It is a flowchart which shows the transmission signal calculation process which implement | achieves the interference cancellation in the basic technique of this invention. It is a figure which shows the structural example of the radio | wireless communications system using the intercell interference canceller in the basic technique of this invention. It is a figure which shows the structural example of the control station and remote base station in the Example of this invention. It is a flowchart which shows the transmission signal calculation process which implement | achieves the interference cancellation in consideration of the signal quality in the Example of this invention. It is a figure which shows the structural example of the radio | wireless communications system using the intercell interference canceller in a prior art. It is a flowchart which shows the transmission signal calculation process in consideration of the interference cancellation in a prior art.

First, a basic technique (Japanese Patent Application No. 2010-233264) to which the present invention is applied will be described.
First, the transmission signal vector T defined by Equation (10) is decomposed into signals for each cell according to the following definition.
T = (T ₁ ^[0] T ₂ ^[0] ... T _N ^[0] ) ^T ... (14)
Similarly, the transmission signal vector T ′ on the left side of Equation (11) is defined as follows.
T '= (T ₁ ^[1] T ₂ ^[1] ... _TN ^[1] ) ^T ... (15)

Next, if the transmission weights are extracted from the right side of the right side of Expression (11) and Expression (10) is used, it can be developed and modified as follows.

This means that a signal obtained by subtracting the interference replica when it is assumed that a signal of T _i ^[0] is transmitted as a transmission signal is given as a signal of T _i ^[1] in Equation (16). Yes. That is, as a zero-order approximation signal, a signal obtained by subtracting an interference replica when T in Equation (10) is assumed is T ′ in Equation (11), and interference when T ′ is assumed as a first-order approximation signal. The signal obtained by subtracting the replica can be understood as T ″ in the equation (13). By generalizing in this way, the a + 1-order approximation signal for the a-order approximation signal is given by the following equation.

Furthermore, if this formula is extracted line by line, it can be summarized as follows.

Here, the matrix M _{i, j} in equation (20) is constant regardless of the value of a. Equation (19) is a recurrence formula expressed as a matrix × vector, and the summation Σ may be executed for a range in which the interference level that cannot be ignored as interference is likely to be a certain value or more.

For example, if the matrix M _{i, j} is a 2 × 2 matrix and the total number of cells is N, the original matrix H _all is a 2N × 2N matrix, and its inverse matrix operation is 8N ^3. It becomes an order. On the other hand, if the effective range of the sum Σ is 10 cells in the vicinity, the number of multiplications in the sum of products of M _{i, j} and T _j ^[a] is 40. When this is performed for N cells, the total number of multiplications is on the order of 40N. Even if a = 3 is obtained, the amount of calculation is three times that, so the order of 120N is sufficient. In the calculation of the matrix given by equation (20), the order is approximately 100N under the above conditions. If N = 100, the difference between 8N ³ and 220N is about 360 times or more.

Furthermore, since the calculation of equation (19) can be performed independently for each cell if the calculation results of T _j ^[a] at each a can be shared with each other, each process can be performed by a distributed process. It is also possible to suppress the calculation amount of distributed processing. The differences from the prior art related to this distributed processing will be described in detail below.

In Equations (11) and (13) in the prior art, the transmit signal vector was described using a matrix for the entire service area, but distributed processing can be performed even in the case of the conventional method. Met. In consideration of this point, the calculation when the signal processing is performed by limiting the expression (11) to a cell in the range where the influence of interference should be considered is expressed as follows.

Here, n (i) means a set of n cells adjacent to the i-th cell that is the operation target of the transmission signal vector, and in order to clarify the range of addition of the sum Σ, It was decided to indicate above. A similar calculation can be performed for the transmission signal vector shown in Expression (13), and the calculation expression is shown below.

  As in the case of Equation (21), the range of addition of Σ in the second term on the right side is a set of n (i) cells adjacent to the i-th cell that is the operation target of the transmission signal vector. Σ in the third term is duplicated, and the range of addition of the sum ΣΣ is expanded to the outside of the region added by Σ in the second term on the right side. Specifically, if the second term on the right-hand side is to be added within a circle having a radius X centered on the i-th cell (where X is a predetermined distance determined by the propagation attenuation condition), each cell in this circle A range in which a circle with a radius X is drawn is an addition target, and as a result, the addition target of the sum ΣΣ of the third term on the right side is expanded to a circle with a radius 2X centered on the i-th cell. Furthermore, in consideration of higher-order interference replica signals, various information (channel matrix, transmission weight matrix, transmission signal, etc.) in these areas are required for calculation of the transmission signal vector for the i-th cell. . Therefore, the calculation of Expression (22) cannot be performed unless the mutual exchange of such a large amount of information and a circuit for calculating all of them are separately provided.

  However, the sum Σ of the second term on the right-hand side of Equation (19) in the operation example of the above basic technique is in consideration of Equation (21) (and Equation (22)) even though higher order interference replica signals are considered. Is limited to the range of addition of the sum Σ of the second term on the right-hand side. Therefore, if information can be exchanged between adjacent cells (between cells in a circle with a radius X in the example described above), independent calculation is performed on a cell-by-cell basis within a range enclosed by these pieces of information. Is possible. As a result, in addition to a reduction in the overall calculation amount, the calculation amount per apparatus for performing distributed processing can be further greatly reduced, and the circuit scale can be reduced to a sufficiently realizable area.

  Therefore, with the above basic technique, it is possible to reduce the amount of computation in the entire system, reduce the circuit scale per apparatus when performing distributed processing, and obtain a solution to the approximation for higher order a. Hereinafter, an operation example of the basic technique will be described with reference to the drawings.

FIG. 1 shows a configuration example of a control station and a remote base station in the basic technique of the present invention.
In FIG. 1, 1a to 1c are control stations, 2a to 2c are channel information acquisition / management means, 3a to 3c are transmission data input means, 4a to 4c are modulation units, 5a to 5c are transmission signal generation means, and 6a to 6c. Are interference cancellation means, 7a-7c are neighboring cell information acquisition means, 8a-8c are interference signal replica generation means, 9a-9c are information transmission means, 10a-10i are remote base stations, and 11a-11c are terminal stations.

  The feature of the present technology is that the control stations 1a to 1c include interference cancellation means 6a to 6c, neighboring cell information acquisition means 7a to 7c, interference signal replica generation means 8a to 8c, information transmission means 9a to 9c, and information transmission means Information on neighboring cells (transmission signals and channel information that causes interference) notified from 9a to 9c to neighboring cell information obtaining means 7a to 7c via a wired transmission path and the like, and channel information obtaining and managing means 2a to 2c Using the managed channel information, the interference signal replica generation means 8a to 8c generate interference signal replicas, and the interference removal means 6a to 6c repeat the process of combining with the transmission signal.

Information transmission from the control station or base station to the terminal station will be described.
First, when receiving training signals in the uplink from the terminal stations 11a to 11c, the channel information acquisition / management means 2a to 2c acquire channel information between the remote base station and the terminal station, and generate reception weights and the like. save.

  On the other hand, in the downlink, when signals addressed to the terminal stations 11a to 11c are input to the transmission data input means 3a to 3c from an external network or the like, the signals are modulated as radio signals by the modulators 4a to 4c. Here, error correction coding, primary modulation such as digital modulation for modulating a plurality of bit strings into one symbol, and secondary modulation processing for assigning these symbols to a carrier wave such as OFDM are included.

  Next, the transmission signal generation means 5a-5c multiplies the modulated signal by the reception weights generated by the channel information acquisition / management means 2a-2c as the 0th order transmission weight, and the 0th order transmission signal is multiplied. Generate.

  When performing the interference removal processing, the a-order received signal including a = 0 held by the control station through the interference removal means 6a to 6c is transmitted to other control stations by the information transmission means 9a to 9c. At the same time, the transmitted information is acquired by the neighboring cell information acquisition means 7a to 7c.

  Next, the interference signal replica generation means 8a-8c generates an interference signal replica using the acquired transmission signal of the neighboring cell and the channel information stored in the channel information acquisition / management means 2a-2c, The removing means 6a to 6c generate the a + 1-order transmission signal according to the equation (19) using the interference signal replica and the 0th-order transmission signal stored in the transmission signal generation means 5a to 5c. A high-order estimated signal is generated by repeatedly performing the above-described series of processing. When the iterative processing is completed, the interference canceling means 12a to 12c output transmission signals to the remote base stations 10a to 10c, and the signals are transmitted to the terminal stations 11a to 11c.

  FIG. 2 shows a transmission signal calculation processing procedure for realizing interference cancellation in the basic technique of the present invention. Fig. 2 (a) is a channel information acquisition process periodically performed between the remote base station and each terminal station, Fig. 2 (b) is a transmission preparation process in the previous stage for performing a transmission signal calculation process, and Fig. 2 (c) is a data Represents a transmission signal calculation process in symbol units when each bit string is transmitted.

In FIG. 2 (a), the propagation channel between the remote base stations 10a to 10i and the terminal stations 11a to 11c generally changes with time. Therefore, each channel information is periodically acquired at a predetermined cycle. Specifically, when processing is started (S1), channel information is acquired (S2), and it is recorded as a partial channel matrix H _{i, j} in equations (3) and (4) (S3), and processing is terminated. (S4). Since the partial channel matrix H _{i, j} is originally different for each terminal station, a subscript corresponding to the terminal station should be given, but is omitted here for convenience of explanation.

In FIG. 2 (b), when processing is started upon obtaining a transmission opportunity (S11), a terminal station to be a communication partner in the cell of interest is selected (S12), and the portion related to the terminal station stored in the memory The channel matrix H _{i, j} is read (S13). Further, a transmission weight matrix W _{i, i} is calculated for the matrix corresponding to the diagonal term of i = j (S14). The transmission weight here is, for example, a transmission weight for eigenmode transmission in MIMO transmission or a transmission weight for null formation for inter-terminal-station interference suppression in multi-user MIMO. It doesn't matter. In addition, a simple unit matrix may be used without particularly defining a transmission weight. In this case, the transmission weight calculation process (S14) has no effect. Next, the matrix M _{i, j} is calculated according to the equation (20) (S15), and the process ends (S16).

In FIG. 2 (c), as a calculation process of a transmission signal that is actually precoded based on a bit string, when the process is started (S21), transmission information S _i is input (S22), as shown in equation (10). Multiply the transmission weight matrix to calculate T _i ^[0] as the 0th-order transmission signal (S23). Next, the counter value a is reset to zero (S24), the transmission signal T _i ^[a] of the neighboring cell is acquired (S25), and the a + 1-order transmission signal T _i ^{[a + 1]} is calculated according to the equation (19). (S26). Further, 1 is added to the counter value a (S27), and it is determined whether or not a predetermined threshold value b is exceeded (S28). If Yes in step S28, the process is terminated and the b-th transmission signal T _i ^[b] is determined (S29). On the other hand, if No in step S28, the process returns to step S25, and the processes from step S25 to step S28 are repeated.

Here, the neighboring cell in step S25 is a cell to be summed by Σ in equation (19), and specifically, is a cell having a predetermined reception level or higher where mutual addition / interference cannot be ignored. Since this condition is usually determined by station design, it is generally fixed. However, the degree of successive interference is investigated, and cells that cannot be ignored at that time are dynamically managed. It doesn't matter. Further, since only information on the transmission signal T _i ^[a] obtained as an approximate solution of order a needs to be exchanged between neighboring cells, the amount of information notified to each other is limited.

  In addition, when the processes from step S25 to step S28 are repeatedly executed, the same circuit is repeatedly used. Therefore, the calculation amount slightly increases in terms of the number of calculations, but the circuit scale is increased from step S25 to step S28. The circuit scale can be kept constant without depending on the number of repetitions of the above process.

FIG. 3 shows a configuration example of a radio communication system using an inter-cell interference canceller in the basic technique of the present invention.
In FIG. 3, 201-1 to 201-2 are control stations, 202-1 to 202-5 are remote base stations, 203-1 to 203-5 are terminal stations, and 204-1 to 204-5 are the same frequency channels. The cells used, 205-1 to 205-3, represent wired transmission lines.

  The difference between this configuration and the conventional configuration shown in FIG. 6 is that the remote base stations 202-1 to 202-5 in all the cells 204-1 to 204-5 are not connected to a single control station. , Connected to any one of a plurality of distributed control stations 201-1 to 201-2 via wired transmission paths 205-1 to 205-2, and further distributed to a plurality of distributed control stations 201-1 to 201-2. They are also connected through a wired transmission line 205-3.

For example, in the cell 204-1 of interest, the cells 204-2 and 204-5 are the cells that cannot be ignored / interfered with each other. In this case, in the control station 201-1 to which the remote base station 202-1 in the cell 204-1 is connected, between the cell 204-1 and between the cell 204-1 and the cell 204-2 / cell 204-5. Channel information is acquired, and the matrix M _{i, j} shown in Equation (20) is calculated. Further, when the signal is actually transmitted, T _i ^[a] in the equation (19) is replaced with the control station 201-1 to which the remote base station 202-2 of the cell 204-2 is connected (actually, the same control station). Therefore, the information is not required to be transmitted) and is acquired from the control station 201-2 to which the remote base station 202-5 of the cell 204-5 is connected (step S25 in FIG. 2 (c)). This information exchange is repeated while repeating the processing of steps S25 to S28 in FIG. 2C, and finally the transmission signal T _i ^[a] of the cell 204-1 is determined.

  For example, it is assumed that cells 204-3 and 204-5 are cells 204-4 and 204-5 that cannot be ignored or interfered with each other in the focused cell 204-4. In this case, since these cells are all connected to the common control station 201-2, no information exchange is required on the wired transmission path 205-3 between the control station 201-1 and the control station 201-2. However, in reality, the calculation processing of the transmission signals in all cells is performed in parallel, so the information required in any cell is exchanged via the wired transmission path 205-3, and they are exchanged. Share.

  If the number of control stations is not two, but three or more, the wired transmission paths may be interconnected in a tree shape, mesh shape, or ring shape in addition to being connected in a star shape. Here, since an important point may be a plurality of hops, it is possible to transfer necessary information to a necessary control station.

In addition, when one cell is configured from a plurality of base stations, multi-user MIMO transmission by base station cooperation may be performed. In this case, if the mutual interference / interference between the cells can be ignored, the cells do not need to exchange information on the transmission signal T _i ^[a] with each other, and the signal processing can be performed completely within each cell. Information exchange between cells is necessary unless the mutual interference / interference between cells is negligible.

  Furthermore, the control station and the remote base station do not need to be separated. For example, the control station and the remote base station may be realized by a base station having a function corresponding to the aggregated control station and remote base station shown in the operation example. Absent.

  In the above operation example, the case where there are a plurality of control stations has been described. However, if the processing of the above formulas (19) and (20) is performed, the number of control stations does not necessarily have to be plural. It is possible to distribute signal processing to a plurality of control stations in a distributed manner if only necessary information exchange is performed with respect to the conventional method in which signal processing is intensively performed by one control station. Since the calculation amount for each control station can be reduced, the circuit scale can be reduced as a result. Also, even when there are a plurality of remote base stations in one cell, it is not always necessary to apply multi-user MIMO, and single-user normal MIMO transmission may be used.

  In addition, loops are repeated for the processing from step S25 to step S28 in FIG. 2 (c). However, in terms of hardware, individual circuits may be mounted for each loop, or the same circuit may be used repeatedly. Either one does not matter.

Further, in the above description, the partial channel matrix H _{i, j} has been described as a matrix. However, if a simple scalar quantity is also understood as a 1 × 1 matrix, the partial channel matrix H _{i, j} does not necessarily have to be a matrix. Expansion is also possible when H _{i, j} is a scalar quantity. In this case, the transmission weight W _{i, i} can also be regarded as a 1 × 1 matrix, and essentially has the effect of simply multiplying by a constant. Therefore, in this case, the transmission weight W _{i, i} is calculated. Can be regarded as a process of setting a constant 1 to W _{i, i} . Further, even if the partial channel matrix H _{i, j} is a vector, if it is understood as a matrix of 1 × m (m is an integer of 2 or more), the same extension is possible.

  However, in the basic technique described here, the replica used in the repetitive processing from step S25 to step S28 in FIG. 2 (c) is important. When performing interference cancellation using a replica having a large error from the interference signal received at the terminal station, the accuracy of interference cancellation is low, and transmission errors are likely to occur.

  Hereinafter, a specific embodiment of the iterative process related to interference cancellation signal generation in consideration of signal quality in the present invention will be described.

FIG. 4 shows a configuration example of the control station and the remote base station in the embodiment of the present invention. The configuration of the wireless communication system to which this embodiment is applied is the same as that shown in FIG.
4, 1a to 1c are control stations, 2a to 2c are channel information acquisition / management means, 3a to 3c are transmission data input means, 4a to 4c are modulation sections, 5a to 5c are transmission signal generation means, and 6a to 6c. Is an interference canceling means, 7a to 7c are neighboring cell information acquisition means, 8a to 8c are interference signal replica generation means, 9a to 9c are information transmission means, 10a to 10i are remote base stations, 11a to 11c are terminal stations, and 12a to 12c indicates a channel estimation accuracy measuring means.

  The feature of this embodiment is that, in addition to the above basic technique, the channel estimation accuracy measuring means 12a to 12c of the control stations 1a to 1c determines the channel estimation accuracy, and the interference signal corresponding to the channel information with high estimation accuracy is obtained. Select and cancel preferentially. As a result, it is possible to minimize interference cancellation errors caused by using channel information with low estimation accuracy and prevent quality degradation. In addition, since the signals used for interference cancellation are selected in this way, it is possible to further reduce the information amount of signals exchanged between the control stations or base stations.

  Information transmission from the control station or base station to the terminal station will be described. First, when training signals are received in the uplink from the terminal stations 11a to 11c, channel information acquisition / management means 2a to 2c acquires channel information between the remote base station and the terminal station. Next, the channel information estimation accuracy measuring means 12a to 12c measure the estimation accuracy of the acquired channel information, store and manage those that satisfy a certain standard, and discard those that do not satisfy the standard. For the saved channel information, a reception weight or the like is generated and saved. Here, a certain standard is that the received power when acquiring channel information exceeds a threshold value or the like.

  On the other hand, in the downlink, when signals addressed to the terminal stations 11a to 11c are input to the transmission data input means 3a to 3c from an external network or the like, the signals are modulated as radio signals by the modulators 4a to 4c. Here, error correction coding, primary modulation such as digital modulation for modulating a plurality of bit strings into one symbol, and secondary modulation processing for assigning these symbols to a carrier wave such as OFDM are included.

  Next, the transmission signal generation means 5a-5c multiplies the modulated signal by the reception weights generated by the channel information acquisition / management means 2a-2c as the 0th order transmission weight, and the 0th order transmission signal is multiplied. Generate.

  When performing the interference removal processing, the a-order received signal including a = 0 held by the control station through the interference removal means 6a to 6c is transmitted to other control stations by the information transmission means 9a to 9c. At the same time, the transmitted information is acquired by the neighboring cell information acquisition means 7a to 7c. At this time, only the cell information corresponding to the channel information selected in the channel information estimation accuracy measuring means 12a to 12c is acquired from the neighboring cells.

  Next, the interference signal replica generation means 8a-8c generates interference signal replicas using the acquired transmission signals of neighboring cells and the channel information stored and managed by the channel estimation accuracy measurement means 12a-12c, The interference canceling means 6a-6c generates the a + 1-order transmission signal by the equation (19) using the interference signal replica and the 0th-order transmission signal stored in the transmission signal generation means 5a-5c. A high-order estimated signal is generated by repeatedly performing the above-described series of processing. When the iterative processing is completed, the interference canceling means 6a to 6c output transmission signals to the remote base stations 10a to 10c, and the signals are transmitted toward the terminal stations 11a to 11c.

  FIG. 5 shows a transmission signal calculation processing flow for realizing interference cancellation in consideration of signal quality in the embodiment of the present invention. FIG. 5 (a) is a channel information acquisition process periodically performed between the remote base station and each terminal station, FIG. 5 (b) is a transmission preparation process before the transmission signal calculation process, and FIG. 5 (c) is each bit string. Represents a transmission signal calculation process in symbol units when transmitting.

In FIG. 5 (a), when processing is started (S41), channel information is acquired and temporarily recorded as partial channel matrix H _{i, j} of equations (3) and (4) (S42). Since the partial channel matrix H _{i, j} is originally different for each terminal station, a subscript corresponding to the terminal station should be given, but is omitted here for convenience of explanation.

Next, the estimation accuracy of the acquired channel information is measured (S43). Here, as an estimation method, any method may be used, such as measuring accuracy using the reception intensity of a preamble signal used for channel estimation or SNR (Signal to Noise power Ratio) as an index. Next, it is determined whether the measured channel information satisfies a condition (S44). As a determination method here, a threshold value in reception intensity is defined as a condition, and channel information having a reception intensity exceeding the threshold value is regarded as channel information satisfying a desired estimation accuracy condition. The channel information determined as Yes in step S44 is stored in a memory or the like as a partial channel matrix H _{i, j} (S45). On the other hand, the channel information determined as No in step S44 is discarded without being saved (S46). Through this series of procedures, the process is terminated (S47).

  In addition, as the condition determination in step S44, for example, an upper limit of the number of channels handled as effective channel information is determined in advance, and the number of channel information is used as a condition, and the estimation accuracy is high (that is, the received signal strength) Any method may be used such as selecting a predetermined number from the channel information. In this case, the condition determination in step S44 is not performed when the channel information is acquired, the received signal strength ranking is performed on the channel information temporarily recorded in step S42, and then the channel to be discarded corresponding to step S46 is discarded. Information will be selected.

The flow of the transmission preparation process in FIG. 5B is the same as the description in the basic technique shown in FIG. The flow of the transmission signal calculation process in FIG. 5 (c) is omitted because it is the same as the description in the basic technique shown in FIG. 2 (c), but in step S25, the transmission signal T _i ^[a] of the neighboring cell is omitted ^. Is different from FIG. 2C in that only the transmission signal of the other cell j corresponding to the channel information that satisfies the condition in step S44 of FIG.

1a to 1c control station
2a to 2c Channel information acquisition / management means
3a-3c Transmission data input means
4a to 4c modulator
5a to 5c Transmission signal generation means
6a-6c Interference canceling means
7a-7c Peripheral cell information acquisition means
8a-8c Interference signal replica generation means
9a-9c Information transmission means
10a to 10i remote base station
11a to 11c terminal stations
12a-12c Channel estimation accuracy measurement means
101, 201-1 to 201-2 Control station
102-1 to 102-5, 202-1 to 202-5 Remote base station
103-1 to 103-5, 203-1 to 203-5 Terminal stations
104-1 to 104-5, 204-1 to 204-5 Cells using the same frequency channel
105, 205-1 to 205-3 Wired transmission line

Claims (2)

A wireless communication method in which one or more base stations are arranged in a plurality of cells, each base station is connected to a network via a wired line, and each base station communicates with a terminal station in the cell via a wireless line. There,
A first step of obtaining channel information between the base station and the terminal station in the same cell and between different cells;
A second step of measuring the estimation accuracy of the channel information acquired in the first step;
When the channel information estimation accuracy measured in the second step satisfies a predetermined quality, the channel information is converted into a channel matrix corresponding to interference from the base station in the j-th cell to the terminal station in the i-th cell. A third step of managing as H _{i, j} and discarding the channel information when the estimation accuracy of the channel information does not satisfy a predetermined quality;
When the transmission weight used by the base station in the i-th cell for the terminal station in the same cell is denoted as W _{i, i} , the channel matrix H _{i, j is}
M _{i, j} = W _{i, i} (H _{i, i} W _{i, i} ) ⁻¹ · H _{i, j}
A fourth step of obtaining a matrix M _{i, j}
A fifth step of obtaining a 0th-order transmission signal T _i ^[0] in the i-th cell by multiplication with the transmission weights W _{i, i} when the transmission information in the i-th cell is S _i ;
Among neighboring cells that perform communication using the same frequency channel as that of the i-th cell, the a-order transmission signal T _j ^[ _{j j} in the j-th cell corresponding to the channel matrix H _{i, j} that is stored and managed is j ≠ i ^{. a)} to obtain ^a] ,
The sum of the transmission results of the transmission signal T _j ^[a] and the matrix M _{i, j} is obtained for a predetermined j, and the result is subtracted from the 0th-order transmission signal T _i ^[0] . A wireless communication method, wherein a transmission signal is generated by repeatedly performing a seventh step of calculating an a + 1-order transmission signal T _i ^{[a + 1]} in an i cell. The wireless communication device according to claim 1, wherein one or more base stations are arranged in each of a plurality of cells, each base station is connected to a network via a wired line, and each base station is connected to a terminal station in the cell via a wireless line. A wireless communication system characterized in that communication is performed by a communication method.

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