JP2007214995A - Wireless communication system and wireless communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless relay system capable of reducing a processing/arithmetic amount during operations of the multiuser MIMO communication. <P>SOLUTION: A base station apparatus multiplies a transmission weight vector set at random with a known signal and transmits the resulting signal, each of terminal station apparatuses acquires an estimate SNR from a transfer function vector acquired on the basis of the received signal, selects a transfer function vector denoting an excellent SNR, and reports other transfer function vector the inner product of which with the selected transfer function vector is smallest to the base station apparatus, and the base station apparatus determines the transmission weight matrix at data transmission on the basis of the reported information. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a radio communication system and a radio communication method using a multi-user MIMO (Multiple Input Multiple Output) communication technique in which one base station apparatus performs spatial multiplexing and communication simultaneously with a plurality of terminal station apparatuses.

  In recent years, the IEEE802.11g standard, the IEEE802.11a standard, and the like are remarkable as high-speed wireless access systems using the 2.4 GHz band or the 5 GHz band. In these systems, an orthogonal frequency division multiplexing (OFDM) modulation scheme, which is a technique for stabilizing characteristics in a multipath fading environment, is used, and a transmission rate of 54 Mbps at the maximum is realized. However, the transmission rate here is a transmission rate on the physical layer, and the transmission efficiency in the MAC (Medium Access Control) layer is actually about 50 to 70%. It is about 30 Mbps. On the other hand, in the world of wired LAN, including Ethernet 100Base-T interface, FTTH (Fiber to the home) using optical fiber is popular in every home, and the provision of high-speed line of 100Mbps is widespread. In the world of wireless LAN, further increase in transmission speed is demanded. As a technology for that purpose, the MIMO technology is promising. With this MIMO technology, the transmitting station apparatus side spatially multiplexes and transmits different independent signals from a plurality of transmitting antennas on the same channel, and the receiving station apparatus side receives signals using the same plurality of antennas. A transfer function matrix between the transmitting antenna and the receiving antenna is obtained, and an independent signal transmitted from each antenna on the transmitting station apparatus side is estimated on the receiving side using this matrix, and data is reproduced.

  As an ultimate form of this MIMO communication, there is multi-user MIMO communication in which one base station device performs spatial multiplexing and communication simultaneously with a plurality of terminal station devices. In the conventional MIMO communication technology, terminal station devices communicating with a base station device are segregated in a time division manner, and always have a one-to-one communication. This is usually called single user MIMO communication. In this single user MIMO communication, the terminal station apparatus has a relatively small number of antennas in a small casing, and the correlation between the antennas is very strong. In such a state, the space-time resources cannot be fully utilized effectively. In general, high-order spatial multiplexing is realized by increasing the distance between antennas and lowering the correlation between antennas, and the SNR of each subchannel (virtual channel used for transmission of each signal sequence in MIMO transmission). Can be kept high.

  In multi-user MIMO communication, the number of MIMO channels to be spatially multiplexed in each terminal is reduced, while spatial multiplexing is performed on the same frequency channel simultaneously with a plurality of different terminals. As shown in FIG. 1, it is assumed that the multi-user MIMO system includes a base station apparatus 101 and terminal station apparatuses # 1 to # 3 (102 to 104). At this time, although the number of terminal station apparatuses actually accommodated by one base station apparatus is large, several station apparatuses are selected (terminal station apparatuses # 1 to # 3: 102 to 104) to perform communication. Each terminal station apparatus generally has a smaller number of transmission / reception antennas than the base station apparatus. For example, consider a case where communication (downlink) from the base station apparatus to the terminal station apparatus is performed. The base station apparatus 101 uses a plurality of antennas to form a plurality of directional beams. For example, consider a case in which three MIMO channels are allocated to each of the terminal station apparatuses 102 to 104 and nine signal sequences are transmitted as a whole. At that time, the signal transmitted to the terminal station apparatus 102 is adjusted so that the directivity gain becomes extremely low in the direction of the terminal station apparatus 103 and the terminal station apparatus 104. As a result, the terminal station apparatus 103 and the terminal station Suppresses interference with the device 104. Similarly, the signal transmitted to the terminal station apparatus 103 is adjusted so that the directivity gain becomes extremely low in the direction of the terminal station apparatus 102 and the terminal station apparatus 104. Similar processing is performed on the terminal station device 104. The reason why the directivity control is performed in this way is that, for example, in the terminal station apparatus 102, there is no way of knowing the information of the signals received by the terminal station apparatus 103 and the terminal station apparatus 104. I can't. That is, it is very difficult to separate all nine signal sequences in the reception process of only the terminal station apparatus 102 having only three antennas. Therefore, interference separation is performed in advance on the transmission side so that each terminal station device does not receive signals addressed to other terminal station devices.

Next, a method for forming a directional beam will be described below. For example, a transfer function between the j-th antenna of the base station apparatus 101 and the first reception antenna of the terminal station apparatus 102 is denoted as h _1j . The row vector h ₁ is expressed as (h ₁₁ , h ₁₂ , h ₁₃ ,..., H ₁₈ , h ₁₉ ) using transfer functions related to all antennas j = 1 to 9 of the base station apparatus 101. Similarly, the transfer functions of the second receiving antenna and the third receiving antenna of the base station apparatus 101 and the terminal station apparatus 102 are h _2j and h _3j , and the corresponding row vectors h ₂ and h ₃ are (h ₂₁ , h ₂₂ , h ₂₃ ,..., H ₂₈ , h ₂₉ ), (h ₃₁ , h ₃₂ , h ₃₃ ,..., H ₃₈ , h ₃₉ ). Similarly, the receiving antennas of the terminal station device 103 and the terminal station device 104 also use the row vectors h ₄ to h ₉ as (h ₄₁ , h ₄₂ , h ₄₃ ,..., H ₄₈ , h ₄₉ ) to (h ₉₁ , h ₉₂ , h ₉₃ ,..., h ₉₈ , h ₉₉ ). In addition, nine signals transmitted by the base station apparatus 101 are denoted as t ₁ to t _9, and column vectors having these as components are represented by Tx ^[all] = (t ₁ , t ₂ , t ₃ ,..., T ₈ , t ₉ ) ^T Here, the letter T on the right shoulder indicates transposition of a vector or a matrix. Similarly, received signals at the nine antennas of the terminal station apparatuses 102 to 104 are denoted as r ₁ to r ₉ , and a column vector having these components as components Rx ^[all] = (r ₁ , r ₂ , r ₃ ,..., R ₈ , r ₉ ) ^T. Finally, a matrix having the row vectors h _{1 to} h ₉ as the first to ninth row components is denoted as an overall transfer function matrix H ^[all] . When expressed in this way, the following relational expression holds for the entire system.

  Here, transmission directivity control is performed on the transmission station apparatus side so that signal separation can be performed efficiently on the reception side. Here, a 9 × 9 transmission weight matrix W is introduced, and (Equation 1) is rewritten as follows.

Furthermore, the transmission weight matrix W is decomposed into column vectors _{w 1 ~w 9, W = (} w 1, w 2, w 3, ..., w 8, w 9) when that notation can be represented as follows .

Here, for example, the multiplication of six row vectors h _{4 to} h ₉ and three column vectors w _{1 to} w ₃ (the sum of those obtained by multiplying each component, which is different from the inner product in the case of a complex vector) is all zero. Consider selecting w ₁ to w ₃ as follows. Similarly, the product of the row vector _h 1 to h ₃ and _h 7 to h ₉ column vector _w 4 to w _6, all the product of a row vector _h 1 to h ₆ column vector _w 7 to w ₉ becomes zero I will choose as follows. Then, the matrix of 9 rows and 9 columns shown in (Equation 3) can be expressed as follows using 9 submatrices of 3 rows and 3 columns.

Here, the sub-matrices H ^[1] , H ^[2] and H ^[3] are 3-by-3 matrices, and the sub-matrix shown as “0” in this equation has all the components of 3 by 3 A matrix of columns. By selecting a transformation matrix W that satisfies such conditions, (Equation 4) can be decomposed into the following three relational expressions.

_{^{Here, Tx [1] = (t}} 1, t 2, t 3) T, Tx [2] = (t 4, t 5, t 6) T, Tx [3] = (t 7, t 8, t ^{_{9) T, Rx [1]}} = (r 1, r 2, r 3) T, Rx [2] = (r 4, r 5, r 6) T, Rx [3] = (r 7, r 8, r ₉ ) ^T In this way, it can be regarded as three single user MIMO communications. The above is the outline of the multi-user MIMO system.

  In multi-user MIMO communication, calculation of the transmission weight matrix shown in (Equation 3) is essential. In the case of a general terminal station apparatus, the propagation channel fluctuates with time due to the location movement of the terminal station apparatus and surrounding movement. In the case of single-user MIMO communication, transmission directivity control may be performed for eigenmode transmission, but optimization is performed considering only the MIMO channel between one transmission station apparatus and one reception station apparatus. I should have done it. For example, in single-user MIMO communication, a unitary matrix that diagonalizes a transfer function matrix related to a MIMO channel is used as a transmission weight matrix, but the size of the transfer function matrix (number of rows and columns of the matrix) is relatively small. Matrix operations also require a relatively small amount of calculation.

  However, in multi-user MIMO communication, the size of a matrix increases with an increase in the number of terminals that are simultaneously spatially multiplexed, and the amount of calculation for various arithmetic processes including matrix diagonalization increases exponentially. On the other hand, even when a certain terminal station device is stationary, if there is movement in another terminal station device, it is necessary to optimize the entire transmission weight matrix again. This is because, when directivity control is performed so that signal transmission to a certain terminal station apparatus does not interfere with other terminal station apparatuses, if there is movement in one terminal station apparatus, the transmission directivity of the other terminal station apparatus This is because it is necessary to readjust all genders.

Further, when a large number of terminal station devices are under the control of a single base station device, the number of terminals that can be spatially multiplexed simultaneously is a part of the total terminals and a small number. At the time of communication, it is necessary to select a combination of terminals suitable for spatial multiplexing from a large number of terminals at the same time, but how much interference a transmission signal to a certain terminal station apparatus has on other terminal station apparatuses. In order to influence the characteristics of the entire system, it is important to select a combination of terminal station apparatuses that perform spatial multiplexing simultaneously. However, since the optimal solution of the combination changes with time variation of the channel, the combination optimization process must be sequentially performed. For example, when there are terminal station apparatuses of N station apparatuses as a whole, and the apparatus of M station is selected from among them and spatial multiplexing is performed, there are _N C _M combinations. For each of these enormous combinations, a transmission weight matrix for transmission directivity control is obtained, and the superiority or inferiority of the characteristics can be evaluated for the first time. However, as described above, the calculation of the transmission weight matrix is not easy. Therefore, in such an environment in which the environment changes violently in this manner, the load of transmission directivity control required in multiuser MIMO becomes very large. As described above, reduction of the amount of processing / computation during operation of multi-user MIMO communication has become an essential issue. As a countermeasure for this, a method shown in Non-Patent Document 1 has been proposed.
Jaehak Chung, Chan-Soo Hwang, Kiho Kim and Young Kyun Kim “A Random Beamforming Technique in MIMO Systems Exploiting Multiuser Diversity” IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 21, NO. 5, JUNE 2003

  Here, the principle of random beam forming used in the above-described prior art is as follows. First, the base station apparatus uses some means to determine a transmission weight matrix for spatially multiplexing and transmitting a predetermined number of signal sequences using the antenna of the local station apparatus. For example, it may be a randomly selected orthogonal vector or a unitary matrix obtained by performing singular value decomposition on a randomly assumed transfer function matrix. Using this transmission weight matrix, a channel estimation signal having a known pattern is transmitted in the same manner as in (Equation 2). Each terminal station apparatus performs channel estimation based on the received signal, and acquires a transfer function matrix with the base station apparatus. When reception directivity formation is performed based on this transfer function matrix, an estimated SNR (Signal to Noise Ratio) when each spatially multiplexed signal sequence is received is obtained, and this is obtained as a base station apparatus. Return to. The base station apparatus selects a combination of terminals to be spatially multiplexed so that each terminal can receive a signal with a desired SNR based on the returned estimated SNR for each signal sequence. For this combination, the number of spatial multiplexing and the transmission mode (combination of modulation scheme and error correction coding rate) are optimized.

  Specifically, for example, a case where the base station apparatus spatially multiplexes and transmits four signal sequences will be described. When a random transmission weight matrix is used, the estimated SNR of signal sequence # 1 to signal sequence # 2 is high in terminal station apparatus 102, but the estimated SNR of signal sequence # 3 to signal sequence # 4 is very low. In terminal station device 103, it is assumed that the estimated SNR of signal sequence # 3 to signal sequence # 4 is high, but the estimated SNR of signal sequence # 1 to signal sequence # 2 is very low. In this case, a signal addressed to terminal station apparatus 102 is assigned to signal sequence # 1 to signal sequence # 2, and a signal addressed to terminal station apparatus 103 is assigned to signal sequence # 3 to signal sequence # 4, thereby simultaneously spatially multiplexing the signals. Even if the signal is transmitted, the signal addressed to the other station apparatus can be suppressed if the signal is received using the reception weight matrix for the reception directivity formation learned by the terminal station apparatus in advance. The actual determination of the base station apparatus is based on a signal-to-interference noise ratio SNIR (Signal to Noise Interference Ratio) in consideration of the estimated SNR of the interference signal, not just the estimated SNR, and is determined.

FIG. 7 is a diagram showing a transmission processing flow of the base station apparatus in the prior art.
When the base station apparatus performs signal transmission, a random transmission weight matrix is appropriately generated (S101), a transmission signal vector having a plurality of known preamble signals as elements is multiplied by a transmission weight matrix (S102), and these are performed while performing spatial multiplexing. Is transmitted (S103). Thereafter, a return signal containing estimated SNR information from the terminal station apparatus is received (S104), and a combination of terminals capable of spatial multiplexing is searched from these reported estimated SNR information (S105). As a result, a signal is transmitted to the terminal station apparatus determined to be capable of spatial multiplexing while performing spatial multiplexing using the previous transmission weight matrix (S106).

FIG. 8 is a diagram showing a reception processing flow (pre-processing) of the terminal station apparatus in the prior art.
The pre-processing flow is a process before receiving an actual signal, and corresponds to a process performed between step S103 and step S104 in FIG. From FIG. 8, first, when the terminal station apparatus receives a preamble signal multiplied by a random transmission weight matrix (S111), a transfer function matrix is obtained by channel estimation (S112). Thereafter, singular value decomposition of the transfer function matrix is performed (S113). An estimated SNR is calculated using the eigenvalue and eigenvector obtained by the singular value decomposition (S114). Thereafter, the estimated SNR information is notified to the base station apparatus (S115).

FIG. 9 is a diagram showing a reception process flow (data reception process) of the terminal station apparatus in the prior art.
In the base station apparatus, data is transmitted in step S106 of FIG. The terminal station apparatus performs reception processing of data transmitted from the base station apparatus as shown in FIG. 9, following the previous processing of FIG. First, when a signal is received (S121), the received signal vector is multiplied by a unitary matrix that diagonalizes the transfer function matrix obtained in step S113 of the pre-processing in FIG. 8 (S122), and suppression of signals addressed to other station apparatuses is performed. I do. Thereafter, channel estimation of the signal addressed to the local station apparatus is performed (S123), the subsequent data signal detection processing is performed using the transfer function matrix obtained here (S124), and the signal after signal detection is synthesized. Data is reproduced and output (S125). The above is the outline of the conventional random beam forming.

  However, this random beamforming method can be used when there is a combination of terminal station apparatuses suitable for one random transmission directivity control, and transmission data addressed to these terminals is stored in the transmission buffer. It is only meaningful if it is accumulated in However, in reality, it is unlikely that there is a terminal station apparatus suitable for only one random transmission weight matrix among limited terminal station apparatuses having transmission data. In other words, this random beamforming method is effective when there are a large number of terminal station apparatuses and data to be transmitted to each of them is steadily present, but in reality there are no such conditions. . Therefore, the development of a method for reducing the amount of processing / computation in new multi-user MIMO communication is an issue.

  Accordingly, an object of the present invention is to provide a wireless communication system and a wireless communication method capable of reducing the amount of processing / computation during operation of multi-user MIMO communication.

  In order to achieve the above object, the present invention is configured by one first radio station apparatus and a plurality of second radio station apparatuses, and the first radio station apparatus includes a first antenna group including a plurality of antennas. The second radio station apparatus includes a second antenna group including a plurality of antennas, and the first antenna group of the first radio station apparatus and all or a plurality of the second radio station apparatuses A wireless communication system for performing MIMO communication by spatially multiplexing a plurality of signal systems at the same frequency channel and the same time through a MIMO (Multiple Input Multiple Output) channel configured by a part of the second antenna group, The first radio station apparatus stores means for storing a plurality of types of transmission weight vectors having a plurality of transmission weights provided when transmitting from each antenna of the first antenna group as components. Means for generating a signal obtained by multiplying a signal weight vector by a channel estimation signal having a known pattern in both the first radio station apparatus and the second radio station apparatus, and a plurality of transmission weight vectors corresponding to a plurality of types of transmission weight vectors Based on the received information, means for transmitting the signal via each antenna of the first antenna group, means for receiving information on the estimated SNR returned by the second radio station apparatus that received the signal, and And a means for calculating a transmission weight matrix to be used at that time, and a combination that can be simultaneously spatially multiplexed with a plurality of the second radio station devices, and the calculated simultaneous spatially multiplexed communication A means for recording a combination of the second radio station apparatuses that can be used and a correspondence of transmission weight matrices to be used in the database, and the data Means for searching for a combination of the second radio station apparatuses capable of spatial multiplexing between the second radio station apparatuses in which data to be transmitted exists from the converted information, and a second radio station apparatus capable of spatial multiplexing When the combination is retrieved, means for multiplying a transmission signal vector having a signal to be transmitted using a transmission weight matrix corresponding to the combination as an element, and the multiplication result as the first antenna group Means for transmitting from each of the antennas, wherein the second radio station apparatus receives a signal obtained by multiplying a channel estimation signal of a pattern known from the first radio station apparatus by a plurality of transmission weight vectors. And means for channel estimation for the received signal, and a vector having a transfer function as an element for each antenna of the second antenna group, that is, a transfer function vector, Means for calculating the sum of powers of the absolute value of each component of the vector or approximate values thereof for all antennas, means for selecting one or a plurality of transfer function vectors from the one having the larger sum, and selected For each transfer function vector, a means for calculating an inner product or an approximate value thereof with another transfer function vector other than the vector, and one or a plurality of transfer function vectors having an inner product value of a predetermined threshold value or less. A wireless communication system comprising: means for selecting an inner product value from the smaller one; and means for notifying the base station apparatus of the result.

  In addition, the present invention is configured by one first radio station apparatus and a plurality of second radio station apparatuses, and the first radio station apparatus includes a first antenna group including a plurality of antennas, and the second radio station apparatus The station apparatus includes a second antenna group including a plurality of antennas, and the first antenna group of the first radio station apparatus and all or part of the second antennas of the plurality of second radio station apparatuses. A wireless communication method in a wireless communication system for performing MIMO communication by spatially multiplexing a plurality of signal systems at the same frequency channel and the same time via a MIMO (Multiple Input Multiple Output) channel configured by a group, The station apparatus uses the first radio station apparatus and a plurality of types of transmission weight vectors having a plurality of transmission weights provided when transmitting from each antenna of the first antenna group as components. A process of generating a signal obtained by multiplying a channel estimation signal having a known pattern by both of the second radio station apparatuses, and a plurality of the signals corresponding to a plurality of types of transmission weight vectors for each antenna of the first antenna group A process of transmitting via the second wireless station apparatus, a process of receiving information on the estimated SNR returned by the second wireless station apparatus that has received the signal, and a plurality of second wireless station apparatuses based on the received information A combination that can be spatially multiplexed and communicated at the same time, a process for calculating a transmission weight matrix to be used at that time, and the calculated combination of the second radio station devices that can be simultaneously spatially multiplexed and communicated And the process of recording the correspondence of the transmission weight matrix to be used at that time in a database, and the data to be transmitted from the information stored in the database When a process of searching for a combination of the second radio station apparatuses capable of spatial multiplexing between existing second radio station apparatuses and a combination of the second radio station apparatuses capable of spatial multiplexing are searched, Performing a process of multiplying a transmission signal vector having a signal transmitted using a corresponding transmission weight matrix as an element, and a process of transmitting the multiplication result from each antenna of the first antenna group, The second radio station apparatus receives a signal obtained by multiplying a channel estimation signal of a pattern known from the first radio station apparatus by a plurality of transmission weight vectors, a process of channel estimation for the received signal, With respect to a vector having a transfer function for each antenna of the second antenna group as an element, that is, a transfer function vector, A process for calculating the sum of the approximate values for all antennas, a process for selecting one or a plurality of transfer function vectors from the one with the larger sum, and for each of the selected transfer function vectors, A process of calculating an inner product with another transfer function vector or an approximate value thereof, a process of selecting one or a plurality of transfer function vectors whose inner product value is a predetermined threshold value or less from the smaller inner product value, The wireless communication method is characterized by performing a process of notifying the base station apparatus of the result.

  According to the present invention, a transmission weight matrix for performing transmission directivity control when performing multiuser MIMO communication can be simplified without performing enormous linear operations such as singular value decomposition and orthogonalization of higher-order matrices. It becomes possible to ask for. In addition, in the conventional random beam forming technique that has been proposed as a technique for simplifying this calculation, the base station apparatus unilaterally determines a transmission weight matrix that is a combination of transmission weight vectors, and a terminal that conforms to this transmission weight matrix. Since the search was performed for the station device and the multi-user MIMO communication was performed, there was a terminal station device that coincided with the condition by chance, and the data addressed to the terminal station device existed in the transmission buffer. Only effective if. However, according to the present invention, it is possible to freely use transmission weight vectors that are randomly generated according to the information returned from the terminal station apparatus, so that the frequency of situations in which the present technology can be effectively applied. Will increase dramatically. As a result, multi-user MIMO communication can be used stably and effectively, and frequency resources can be efficiently operated.

Hereinafter, a wireless communication system according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating a configuration of a wireless communication system using multi-user MIMO.
In this figure, 101 is a base station apparatus, and 102 to 104 are terminal station apparatuses # 1 to # 3. In a wireless communication system, although one base station apparatus actually accommodates a large number of terminal station apparatuses, several station apparatuses are selected (terminal station apparatuses # 1 to # 3: 102 to 104 in the figure). I do. Each terminal station apparatus generally has a smaller number of transmission / reception antennas than the base station apparatus.

  First, the base station apparatus 101 stores a number of different transmission weight vectors in the data table. The base station apparatus 101 also stores in the data table a converted preamble signal obtained by multiplying a predetermined preamble signal for channel estimation by these transmission weight vectors. For example, in the case of a system using the OFDM modulation method, a signal pattern per symbol is recorded. A large number of these converted preamble signals are continuously transmitted in batches. For example, when 100 transmission weight vectors are prepared, signal transmission is performed collectively over 100 OFDM symbols.

Each of the terminal station apparatuses 102 to 104 receives all of these converted preamble signals. The pattern of the preamble signal before conversion is known also in the terminal station apparatuses 102 to 104, and correlation is obtained for each reception antenna using the known pattern to acquire transfer function information. The terminal station apparatuses 102 to 104 store, as information for each transmission weight vector, a transfer function vector having the transfer function information thus obtained as a component corresponding to each antenna. The transmission of the converted preamble signal for the same transmission weight vector is repeatedly repeated as appropriate during communication. A transfer function vector is obtained each time, and this transfer function vector may be updated every time a signal is received, or may be a value averaged over a plurality of times of reception. Also, instead of uniform averaging, a forgetting factor μ (0 <μ <1) is introduced, and the updated transfer function vector is compared to the past vector V _old and the newly acquired vector V _new by μV _new + (1 -Μ) It may be given as V _old . It should be noted that the transmission weight vector used by the base station apparatus 101 is set so that correspondence can be established between the base station apparatus 101 and the terminal station apparatuses 102 to 104 according to the transmission order, other control information, and the like. In the above description, the converted preamble signals multiplied by different transmission weight vectors are transmitted at different timings. However, if they are patterns that are orthogonal to each other, the transfer function vectors are individually transmitted even if they are transmitted simultaneously. Can be obtained.

  Each of the terminal station apparatuses 102 to 104 uses the absolute value of each component or the sum of all components of the power of the absolute value (for example, the square) (hereinafter referred to as transfer function) for the plurality of transfer function vectors thus obtained. (Referred to as vector absolute value), and a predetermined number of transfer function vectors are obtained from the larger value. Here, this transfer function vector absolute value is a physical quantity proportional to the estimated SNR for each transfer function vector. Each of the terminal station devices 102 to 104 takes a vector product (inner product) of the transfer function vector obtained in this way with another transfer function vector, and searches for a transfer function vector having a smaller value. Here, in addition to searching for a transfer function vector from a smaller number by a predetermined number, it is also possible to search for a transfer function vector that is below a predetermined threshold. Note that the threshold value need not be single, and a plurality of threshold values may be provided.

  Each terminal station apparatus 102 to 104 notifies the base station apparatus 101 of the result of the above processing. The contents to be notified are simply the identification number of a transfer function vector having a large transfer function vector absolute value (for example, the order in which the signals are received) and the identification number of a transfer function vector having a small inner product value relative to the transfer function vector. It may be a pair. Furthermore, in addition to the transfer function vector identification number having a large transfer function vector absolute value, the transfer function vector absolute value is notified, or in addition to the transfer function vector identification number having a small inner product value for each transfer function vector. The inner product value may be notified. In addition, it may be a value obtained by dividing the absolute value of the transfer function vector by the inner product value (or its logarithmic value). In addition to notifying the value itself, each of the above values can be classified in a certain step size, and the class value to which the value belongs can be used for reporting. In this way, information processing is performed on the terminal station devices 102 to 104 side, and the processing results of the base station device 101 can be reduced by collecting the results in the base station device.

  The base station apparatus 101 obtains an efficient spatial multiplexing combination based on this result. For example, assume that 100 types of transmission weight vectors are set. In the terminal station apparatus 101, it is assumed that the absolute values of the first and second transfer function vectors among 100 types are large. It is assumed that a vector having a small inner product value with respect to the first transfer function vector is 20 to 30, for example. Similarly, a vector having a small inner product value with respect to the second transfer function vector is, for example, 25 to 35, and a vector having a small inner product value with respect to the third transfer function vector is, for example, 40 to 50, a fourth transfer function vector. It is assumed that the vector having a small inner product value is 60 to 70, for example. In this case, for example, even if a signal is transmitted to a terminal station apparatus with a base station apparatus 101 using any one of the transmission weight vectors from 25 to 30, the first and second transmission weights are superimposed on it. It is possible to spatially multiplex two signal sequences for the terminal station apparatus 102 using a vector.

  For example, in the terminal station device 103, the transfer function vector absolute values of the transfer function vectors of 26 and 27 are large, and the inner product value of the transfer function vectors of 26 and 27 is the transfer function vectors of 1 and 2. If both are small values, four signal sequences are spatially multiplexed using a transmission weight matrix made up of transmission weight vectors of No. 1, No. 2, No. 26, No. 27, and transmitted to terminal station apparatus 102 and terminal station apparatus 103. Simultaneously, multi-user MIMO communication can be performed. As a supplement, for example, in the terminal station device 104, it is assumed that the absolute values of the transfer function vectors No. 45 and No. 65 are large values. However, if the inner product of No. 45 or No. 65 of the transfer function vector and Nos. 1 and 2 is large, terminal base station apparatus 104 is not suitable for spatial multiplexing at the same time. However, the inner product of the transfer function vectors for spatial multiplexing need not necessarily be reduced between the same terminal station apparatuses. In actual communication, correction may be necessary for the previous transmission weight vector due to channel time variations. However, since there is little variation up to the path unique to MIMO communication, it is considered that the variation is small up to a good combination pattern of the terminal station apparatus. Furthermore, in the base station apparatus 101, when information on the transfer function matrix between the transmission antenna of the base station apparatus 101 and the reception antenna of the terminal station apparatus can be acquired, the optimal solution or the quasi-optimal solution of the transmission weight matrix is “ Quentin H. Spencer, A. Lee Swindlehurst and Martin Haardt, “Zero-Forcing Methods for Downlink Spatial Multiplexing in Multiuser MIMO Channels”, IEEE TRANSACTIONS ON SIGNAL PROCESSING, VOL. 52, NO. 2, FEBRUARY 2004 ” Can be obtained by using.

  These methods use an iterative process (italic approach) to reduce the least square error starting from the initial value. However, if the transmission weight vector obtained earlier is used as the initial value, the convergence speed is increased. It becomes faster and the amount of calculation can be reduced.

Hereinafter, various processing flows according to an embodiment of the present invention will be described in order.
FIG. 2 is a diagram showing a transmission signal storage flow of the base station apparatus according to the embodiment of the present invention.
In the processing flow of FIG. 2, even if it is not actually performed in the base station apparatus 101, the same information can be separately created and stored in the memory in the base station apparatus 101. The relationship is shown in a contrast. First, the base station apparatus 101 generates a random transmission weight vector as appropriate (step S1). Here, the transmission weight vector may be given at random to each component, or may be generated so that the directivity generated as a result is random. In the latter case, a physical virtual directivity is assumed for the antenna arrangement of the base station apparatus 101, and the weight for forming this directivity is determined by the array antenna technique. The transmission weight vector is multiplied by a known preamble signal for channel estimation to generate a signal to be transmitted from each antenna (step S2). The generated signal is stored in the memory (step S3). The above is the pre-processing, but it may be sufficient if a signal separately created at the time of manufacturing the base station apparatus 101 is recorded in the memory.

FIG. 3 is a diagram showing a preprocessing flow of the base station apparatus according to the embodiment of the present invention.
Next, when the base station apparatus 101 periodically or particularly when there is no data to be transmitted / received and there is a free radio band, or when a new terminal station apparatus is newly accommodated, the transmission weight vector recorded in the memory is The multiplied signal is continuously transmitted (step S11). For example, if there are 100 types of transmission weight vector patterns, transmission is performed with over 100 symbols. Of course, these may be divided into a plurality of times and transmitted. Based on the signal transmitted in this way, the terminal station apparatus performs channel estimation by itself and calculates the estimated SNR, and receives the signal that returns this information to the base station apparatus 101 (step S12). Based on this reported information, the combination of the desired transmission weight vector between each terminal station apparatus and the transmission weight vector that does not cause interference even if paired at that time, all of which are compatible among a plurality of terminal station apparatuses. Is searched (step S13). For the selected combination, a transmission weight matrix composed of the transmission weight vectors (each row vector is a transmission weight vector) is generated (step S14). These combinations are stored in a database so as to belong to a plurality of combinations as well as one combination per terminal station apparatus (step S15). In actual data transmission, the information stored in the database is referred to, and the combination of terminal stations to be spatially multiplexed and the transmission weight matrix are determined.

FIG. 4 is a diagram showing a transmission processing flow of the base station apparatus according to the embodiment of the present invention.
When actually transmitting data, the base station apparatus 101 searches for a combination that can be spatially multiplexed among terminal station apparatuses in which data to be transmitted exists (step S21). The base station apparatus 101 determines whether or not a combination exists (step S22). If there is a combination, the base station apparatus 101 uses the combination and a transmission weight matrix corresponding to the combination, and uses the transmission weight as a transmission signal vector. The matrix is multiplied to transmit a signal (step S23), thereby realizing multi-user MIMO communication. When there is no combination in the determination in step S22, the base station apparatus 101 performs single user MIMO communication with a single terminal station apparatus, but uses a transmission weight vector having a high estimated SNR for the terminal station apparatus. The transmission signal is multiplied to transmit the signal (step S24). The above is the processing on the base station apparatus side. On the terminal station apparatus side, pre-processing performed between step S11 and step S12 of the base station apparatus 101 shown in FIG. 3 and step S23 (or step S24) of the base station apparatus 101 shown in FIG. A corresponding data reception process is performed after the process.

FIG. 5 is a diagram showing a reception processing flow (pre-processing) of the terminal station apparatus according to the embodiment of the present invention.
When the signal is transmitted by the process of step S11 of the base station apparatus 101, the terminal station apparatuses 102 to 104 receive a number of preamble signals multiplied by the random transmission weight vector (step S31). A transfer function vector is obtained by channel estimation for each signal individually (step S32). Then, an estimated SNR is calculated from the transfer function vector. Here, the estimated SNR is given by, for example, the sum of the powers of the absolute values of the components of the transfer function vector or approximate values thereof. Estimated SNR values for all the received transmission weight vectors are obtained (step S33), and a transfer function vector having a large estimated SNR value is searched for among them (step S34). Here, a predetermined number of larger estimated SNR values are selected, or a transfer function vector greater than or equal to a threshold value is selected.

  An inner product with another transfer function vector is obtained for the transfer function vector selected in this way (step S35), and a combination of transfer function vectors with a smaller inner product value is searched (step S36). Again, a predetermined number of inner product values are selected from the smaller ones, or a transfer function vector below the threshold is selected. Information on such a combination result is notified to the base station (step S37). The details of the content notified in step S37 may include all values of the estimated SNR value and the inner product value, or may be a value that belongs to which class these values are classified. Also, when specific information on the estimated SNR value and inner product value is omitted, and the mere combination information, for example, the inner product value of the transfer function vector selected in step S34 and the transfer function vector selected in step S36 becomes smaller. Only combination information with the determined transfer function vector (actually, combination information of identification numbers of the transfer function vectors) may be used. Further, as a middle part thereof, only a part of the entire information of the specific estimated SNR value or inner product value may be accommodated in a form added to the combination information.

  In the reported combination, the inner product value is large for a transfer function vector showing a good estimated SNR, while the inner product with the transfer function vector combined with this transfer function vector (small inner product value) is small. It is also possible to calculate such a reception weight vector and use it in the data reception process.

FIG. 6 is a diagram showing a reception process flow (data reception process) of the terminal station apparatus according to the embodiment of the present invention.
This is based on the result of the pre-processing shown in FIG. 5 and the reception on the terminal station devices 102 to 104 side when the base station device 101 transmits a signal including user data by the processing shown in FIG. 3 and FIG. It is processing.

  First, when each of the terminal station apparatuses 102 to 104 receives a signal (step S41), it performs MIMO channel estimation of each signal sequence (step S42). The channel estimation here is performed for at least the signal series addressed to the own terminal station apparatus. On the other hand, for other terminal station devices, channel estimation is performed if possible, and a reception weight matrix for suppressing interference of signals addressed to other terminal station devices is calculated (step S43). When the base station apparatus 101 has notified the transmission weight vector information in the transmission weight matrix used for spatial multiplexing, the reception weight matrix may be selected based on this information. Such a reception weight matrix is multiplied by the reception signal vector (step S44), and signal detection processing is performed based on the resultant signal (step S45). Thereafter, the detected signals are synthesized, and the data is reproduced and output (step S46).

  In order to describe the above-described embodiment, the description has been made assuming various parameters under specific conditions, but it is naturally possible to implement with other general parameters. That is, all of the embodiments described above are illustrative of the present invention and are not intended to be limiting, and the present invention can be implemented in various other modifications and changes. Therefore, the scope of the present invention is defined only by the claims and their equivalents.

  Although one embodiment of the present invention has been described above, according to the present invention, a transmission weight matrix for performing transmission directivity control when performing multi-user MIMO communication is converted into a singular value decomposition or transmission weight of a higher-order matrix. It can be easily obtained without performing enormous linear operations such as vector orthogonalization. That is, it is possible to reduce the amount of processing / computation in multiuser MIMO communication. In addition, in the conventional random beam forming technique that has been proposed as a technique for simplifying this calculation, the base station apparatus unilaterally determines a transmission weight matrix that is a combination of transmission weight vectors, and a terminal that conforms to this transmission weight matrix. Since the search was performed for the station device and the multi-user MIMO communication was performed, there was a terminal station device that coincided with the condition by chance, and the data addressed to the terminal station device existed in the transmission buffer. Only effective if. However, according to the present invention, it is possible to freely use transmission weight vectors that are randomly generated according to the information returned from the terminal station apparatus, so that the frequency of situations in which the present technology can be effectively applied. Will increase dramatically. As a result, multi-user MIMO communication can be used stably and effectively, and frequency resources can be efficiently operated.

  Each device described above may have a computer system inside. The process described above is stored in a computer-readable recording medium in the form of a program, and the above process can also be performed by the computer reading and executing this program. Here, the computer-readable recording medium means a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, a semiconductor memory, or the like. Alternatively, the computer program may be distributed to the computer via a communication line, and the computer that has received the distribution may execute the program.

  The program may be for realizing a part of the functions described above. Furthermore, what can implement | achieve the function mentioned above in combination with the program already recorded on the computer system, and what is called a difference file (difference program) may be sufficient.

It is a figure which shows the structure of the radio | wireless communications system which can be based on multiuser MIMO. It is a transmission signal storage flow of the base station apparatus. It is a figure which shows the pre-processing flow of a base station apparatus. It is a figure which shows the transmission processing flow of a base station apparatus. It is a figure which shows the reception processing flow (pre-processing) of a terminal station apparatus. It is a figure which shows the reception process flow (data reception process) of a terminal station apparatus. It is a figure which shows the transmission processing flow of the base station apparatus in a prior art. It is a figure which shows the reception processing flow (pre-processing) of the terminal station apparatus in a prior art. It is a figure which shows the reception process flow (data reception process) of the terminal station apparatus in a prior art.

Explanation of symbols

101 ... Base station apparatus 102 to 104 ... Terminal station apparatus

Claims (2)

The first radio station apparatus includes a first antenna group including a plurality of antennas, and the first radio station apparatus includes a plurality of second radio station apparatuses. A second antenna group configured with a plurality of antennas, and configured by the first antenna group of the first radio station apparatus and the second antenna group of all or part of the plurality of second radio station apparatuses. A wireless communication system for performing MIMO communication by spatially multiplexing a plurality of signal systems at the same frequency channel and the same time via a MIMO (Multiple Input Multiple Output) channel,
The first radio station apparatus
Means for storing a plurality of types of transmission weight vectors whose components are a plurality of transmission weights assigned when transmitting from each antenna of the first antenna group;
Means for generating a signal obtained by multiplying the transmission weight vector by a channel estimation signal having a pattern known in both the first radio station apparatus and the second radio station apparatus;
Means for transmitting a plurality of signals corresponding to a plurality of types of transmission weight vectors via each antenna of the first antenna group;
Means for receiving information on the estimated SNR returned by the second radio station apparatus that has received the signal;
A combination capable of simultaneously multiplexing and communicating with a plurality of the second radio station apparatuses based on the received information, and a means for calculating a transmission weight matrix to be used at that time;
Means for recording the calculated combination of the second radio station apparatuses capable of performing spatial multiplexing at the same time and the correspondence of the transmission weight matrix to be used at that time in a database;
Means for searching for a combination of the second radio station apparatuses capable of spatial multiplexing between the second radio station apparatuses in which data to be transmitted exists from the information stored in the database;
When a combination of second radio station apparatuses capable of spatial multiplexing is searched, means for multiplying a transmission signal vector having a signal transmitted using a transmission weight matrix corresponding to the combination as an element, and the transmission weight matrix;
Means for transmitting the multiplication result from each antenna of the first antenna group,
The second radio station apparatus
Means for receiving a signal obtained by multiplying a signal for channel estimation of a pattern known from the first radio station apparatus by a plurality of transmission weight vectors;
Means for channel estimation for the received signal;
Means for summing up a power value of an absolute value of each component of the vector or its approximate value for all antennas with respect to a vector having a transfer function as an element for each antenna of the second antenna group, that is, a transfer function vector When,
Means for selecting one or a plurality of transfer function vectors from the one having the larger sum value;
Means for calculating, for each selected transfer function vector, an inner product of other transfer function vectors other than the vector or an approximation thereof;
Means for selecting one or a plurality of inner product values from the smaller inner product value from among transfer function vectors having a predetermined threshold value or less;
Means for notifying the base station apparatus of the result, a wireless communication system. The first radio station apparatus includes a first antenna group including a plurality of antennas, and the first radio station apparatus includes a plurality of second radio station apparatuses. A second antenna group configured with a plurality of antennas, and configured by the first antenna group of the first radio station apparatus and the second antenna group of all or part of the plurality of second radio station apparatuses. A wireless communication method in a wireless communication system for performing MIMO communication by spatially multiplexing a plurality of signal systems at the same frequency channel and the same time via a MIMO (Multiple Input Multiple Output) channel,
The first radio station apparatus
A pattern in which a plurality of types of transmission weight vectors whose components are a plurality of transmission weights assigned when transmitting from each antenna of the first antenna group are known by both the first radio station apparatus and the second radio station apparatus Generating a signal obtained by multiplying the channel estimation signal of
A process of transmitting a plurality of the signals corresponding to a plurality of types of transmission weight vectors via each antenna of the first antenna group;
A process of receiving information on the estimated SNR returned by the second radio station apparatus that has received the signal;
A process of calculating a combination capable of simultaneously multiplexing and communicating with the plurality of second radio station apparatuses based on the received information and a transmission weight matrix to be used at that time;
A process of creating a database and recording the correspondence of the calculated second radio station apparatus capable of performing spatial multiplexing at the same time and the correspondence of the transmission weight matrix to be used at that time;
A process of searching for a combination of the second radio station apparatuses capable of spatial multiplexing between the second radio station apparatuses in which data to be transmitted exists from the information stored in the database;
When a combination of second radio station apparatuses capable of spatial multiplexing is searched, a process of multiplying a transmission signal vector having a signal to be transmitted using a transmission weight matrix corresponding to the combination as an element, and the transmission weight matrix;
Performing the process of transmitting the multiplication result from each antenna of the first antenna group,
The second radio station apparatus
A process of receiving a signal obtained by multiplying a channel estimation signal of a pattern known from the first radio station apparatus by a plurality of transmission weight vectors;
Processing for channel estimation for the received signal;
Processing for summing up a power value of an absolute value of each component of the vector or an approximate value thereof for all antennas with respect to a vector having a transfer function as an element for each antenna of the second antenna group, that is, a transfer function vector When,
A process of selecting one or a plurality of transfer function vectors from the one having the larger sum value;
For each selected transfer function vector, a process of calculating an inner product with another transfer function vector other than the vector or an approximate value thereof;
A process of selecting one or a plurality of inner product values from the smaller inner product value from among transfer function vectors having a predetermined threshold value or less;
The wireless communication method characterized by performing the process which notifies the result to a base station apparatus.

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