JP4402127B2 - Transmission method and apparatus for spatial multiplexing transmission - Google Patents

Description

The present invention, high-speed wireless access system using the same frequency channels, and spatial multiplexing independent signal sequences from different transmit antennas, and transmitted to a plurality of communication partners, to realize the transmission of information to a plurality of communication phases hand The present invention relates to a transmission method and apparatus for spatial multiplexing transmission for determining the number of spatial multiplexing of transmission signals.

In recent years, as the high-speed wireless access system using the 2.4 GHz band or the 5 GHz band, the IEEE802.11g standard, the IEEE802.11a standard, and the like are remarkable. In these systems, orthogonal frequency division multiplexing is a technique for stabilizing the characteristics of a multipath fading environment (OFDM: Orthogonal Frequency Division Multiplexing) using a modulation scheme, thereby realizing a transmission path of 54Mbps at maximum .

  Here, the transmission rate is the transmission rate on the physical layer, and the transmission efficiency in the MAC (Medium Access Control) layer is actually about 50 to 70%, so the upper limit of the actual throughput is about 30 Mbps. Yes, this characteristic further deteriorates as the number of communication partners that require information increases. On the other hand, in the world of the wired LAN (Local Area Network), the 100 Mbps high-speed line of 100 Mbps has been used due to the widespread use of FTTH (Fiber to the home) using an optical fiber in each home, including the Ethernet (registered trademark) 100Base-T interface. In the world of wireless LAN, further increase in transmission speed is demanded.

  As a technique for that purpose, a multi-user MIMO (Multiple Input Multiple Output) transmission method is effective. The BD directivity control method is a technique for transmitting different independent signals from a plurality of transmission antennas on the same channel to a plurality of communication partners on the transmitting station side (Non-patent Document 1). Many techniques have been proposed as a transmission system for a multi-user MIMO system, but all of them suffer from deterioration in characteristics due to time fluctuations in the propagation environment. As an example of the prior art, the realization of characteristics with respect to time variation will be described using a block diagonalization method (Non-Patent Document 2) that can be decoded by a simple calculation on the receiving side.

  FIG. 7 is a configuration example of a conventional MIMO system. Here, the number of antenna elements of the transmitting device is Mt, the number of communication partners is Mu, the number of reception antenna elements of the i-th communication partner is Mr (i), and communication is simultaneously transmitted to the i-th communication partner in the same frequency band. It is assumed that transmission is performed with the number of sequences as L (i) and Mt ≧ Mr (i).

7, reference numeral 101 denotes a data generating circuit, 102 is data dividing circuit, the transmission signal conversion circuit 103, 104-1 to _{104-M T} wireless unit, 105-1 through _{105-M T} is the antenna element, the 106 A channel information acquisition circuit 107 is a transmission weight determination circuit.

Antenna 105-1 through _{105-M T} and the radio unit 104-1 to _{104-M T} is capable of transmitting and receiving radio signals, the antenna 105-1 through 105-M of the transmitter via these Channel information acquisition circuit 106 can estimate the channel response matrix between _T and each antenna of the communication partner. Although this method obtains the channel response matrix is not specified here, the feedback included in the estimate based on whether or received signal information obtained when performing the reception of the known signal in the antenna 105-1 through 105-M _T Information on the channel response matrix is acquired based on the information included in the information.

  When the communication partner for transmission is determined, the channel information acquisition circuit 106 outputs the channel information of the corresponding communication partner to the transmission weight determination circuit 107. The transmission weight determination circuit 107 calculates an orthogonal spatial channel response matrix that does not cause interference with each other's communication partner from the input channel response matrix.

  From the obtained orthogonal spatial channel response matrix, a transmission mode and a modulation mode including a modulation scheme and a coding rate are output to the data generation circuit 101, the data division circuit 102, and the transmission signal conversion circuit 103.

Next, transmission data is output from the data generation circuit 101 to the data division circuit 102, and one system of signals is divided into designated signal sequences and input to the transmission signal conversion circuit 103. Here, a preamble signal or the like for MIMO channel estimation is added and encoded, and then input to radio sections 104-1 to 104-M _T ), and radio signals are transmitted via antennas 105-1 to 105-M _T. As sent.

  The channel response matrix Hi (Mr (i) × Mt matrix) representing the channel information for the i-th communication partner obtained in the channel information acquisition circuit 106 is expressed by the right singular matrix Vi (Mt) by singular value decomposition as shown in the following equation. × Mt matrix), left singular matrix Ui (Mr (i) × Mr (i) matrix) and square root √λ of eigenvalues as a diagonal element, and a matrix D having a non-diagonal matrix of 0 (Mr × Mt matrix) Can be divided into

Here, H _{i, j, k} represents a transfer coefficient from the k-th antenna of the transmission device to the j-th antenna at the i-th communication partner. In communication for a single user, the signal power that can be expressed by the corresponding eigenvalue λi can be obtained as (λ ₁ ≧ λ ₂ ≧... ≧ λ _Mr ) by using the column vector of Vi as the transmission weight. In the formula, bold 0 is a matrix composed of 0, and it is assumed that Mt ≧ Mr. Therefore, the matrix is Mr × (Mt−Mr). The superscript H represents a conjugate search matrix.

  Further, the channel information acquisition circuit 106 outputs the channel response matrix of the communication partner of Mu that performs communication to the transmission weight determination circuit.

The transmission weight determination circuit 107 calculates a non-interference space vector group for each communication partner among Mu communication partners. Focusing on the i-th communication partner, first, a set matrix H _i ⁺ of the channel response matrix of the communication partner that transmits in the same timing and the same frequency band other than the i-th communication partner is obtained as follows.

Here, Ri is a reception weight assumed for the i-th communication partner, and if a diagonal matrix with 1 as a diagonal element is used, the condition without reception weight is assumed. When singular value decomposition is performed on this Hi ⁺ , it can be expressed as follows.

Vi ⁺ is a vector corresponding to the eigenvalues Di ^+, vi ^- has no eigenvalues, or a non-interfering space vector group corresponding to the eigenvalue 0. Here, when transmission is performed in the transmission space of Vi ⁻ , interference does not occur with the reception weights of communication partners other than i. This non-interfering space vector group, the orthogonal spatial channel response matrix HiVi ^- computes, with respect to i-th orthogonal spatial channel response matrix of the communication partner performs the singular value decomposition.

In the BD method, by using Vi ⁻ Vi ⁰ as a transmission weight, the quality corresponding to the null space eigenvalue, λ _j ⁰ , which is the square value of the diagonal component of Di ⁰ , without causing interference to other communication partners. can get. The transmission weight defined for the jth communication partner is Wj = Vj ⁻ Vj ⁰
The received signal at the i-th communication partner when transmission is performed can be expressed as follows.

here,
RiHiVj = 0 (i ≠ j)
Therefore, only the signal for the i-th communication partner can be received. Since RiUi ⁰ is a base vector and a unitary matrix, transmission quality proportional to the square of the diagonal component of Di ⁰ is obtained without affecting the signal quality.

Here, a case is considered in which there is a time lag between channel estimation and actual transmission, and the propagation environment changes. The estimated channel response matrix is defined as Hi (t) with respect to the channel response matrix Hi at the time of transmission. t represents a time lag required for transmission, and when t = 0,
Hi = Hi (0)
It is. For the jth communication partner, the transmission weight obtained from Hj (t) is
Wj ^(t) = Vj - and represents a ^{(t) Vj 0 (t)} . The received signal at the i-th communication partner at the time of transmission can be expressed as follows.

here,
RiHiVj ≠ 0 (i ≠ j)
Therefore, the second term in the third row of the equation (6) is received as an interference signal, and the transmission quality is greatly reduced. Here, as an example, the influence of time variation in the BD method has been shown. However, in the other multiuser MIMO transmission techniques described in Non-Patent Documents 1 and 2, characteristic deterioration due to time variation occurs.
QH Spencer, CB Peel, A. L, Swindlehurst, and M, Haardt, "An introduction to the multi-user MIMO downlink." IEEE Comm. Magazine, Oct. 2004, pp. 60-67. QH Spencer, AL Swindlehurst, and M. Haardt, '' Zero-Forcing Methods for Downlink Spatial Multiplexing in Multiuser MIMO Channels, "IEEE Trans. Sig. Processing, vol. 52, issue 2, Feb. 2004, pp. 461-71 .

  Although the above means enables a plurality of communication partners to obtain a high transmission capacity by spatial multiplexing in the same time and the same frequency band, characteristic deterioration due to time variation is unavoidable.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a spatial multiplexing transmission method and apparatus capable of reducing characteristic deterioration due to time variation.

In order to solve the above-described problem, the present invention is provided with a plurality of antenna elements, and estimates channel information between a reception antenna formed by a communication partner or a reception beam formed in the antenna element and a transmission antenna that performs transmission, The transmission weight is determined using the channel information, and the transmission signal is weighted for transmission, and then MIMO communication is performed by spatially multiplexing one or a plurality of signal sequences at the same frequency channel and the same time for a plurality of communication partners. A spatial multiplexing transmission method, a channel information estimation step for estimating channel information with a communication partner performing simultaneous communication, and a change amount for estimating a change amount of channel information with respect to time variation for each communication partner data for performing the estimating step, the amount of change in channel information with respect to the variation when the estimated transmission from the time when the channel estimation A delay time until the timing, the deterioration amount calculating step of calculating a deterioration amount of the transmission capacity for the time variation of the total communication partner, for the communication partner, respectively, based on a comparison of a specified value of the deterioration amount and the deterioration amount For spatial multiplexing transmission , comprising: a number-of-streams determination step for increasing / decreasing the number of transmission streams; and a transmission data generation step for generating transmission data for each communication partner when the deterioration amount satisfies a specified value It is a transmission method.

Further, the present invention is characterized in that the spatial multiplexing transmission method reduces the number of transmission streams to the communication partner when the deterioration amount does not satisfy the specified value in the number of streams determination step.
In addition, the present invention is characterized in that the spatial multiplexing transmission method reduces the number of transmission streams to the communication partner having the greatest deterioration amount due to time variation in the transmission stream number determining step.
Further, the present invention provides a spatial multiplexing transmission method using a degree of freedom on the transmission side, which is a value obtained by subtracting the number of transmission elements from the number of antenna elements on the transmission side after subtracting the transmission stream. An additional communication partner existence determination step for determining whether there is a communication partner that can be added to the communication partner, and if there is a communication partner that can be newly added, assign a transmission stream to the communication partner, and again, Calculating the amount of deterioration of the transmission capacity with respect to time variation, and generating the transmission data for the communication counterparts when the amount of deterioration satisfies the specified value.
Further, the present invention provides the spatial multiplexing transmission method in which the deterioration amount satisfies the specified value in the stream number determination step, and the antenna element number is compared with the total transmission stream number to compare the antenna number. When the number of elements is large and the number of transmission streams of the same communication partner is not increased or decreased, the number of transmission streams is subtracted from the communication partner or the number of antenna elements with the least amount of transmission capacity degradation with respect to the time variation. Increase the number of streams to the communication partner with a large degree of freedom as a value, and again calculate the amount of deterioration of the transmission capacity with respect to the time variation of all communication partners. If the amount of deterioration satisfies the specified value, Generating transmission data for the communication partner.

Further, the present invention is a transmission apparatus including a plurality of antenna elements, and MIMO (Multiple Input Multiple Output) configured by the transmission apparatus and a plurality of communication partner station antenna elements or beams formed on the antenna elements. In a wireless communication system capable of performing MIMO communication by spatially multiplexing one or a plurality of signal sequences at the same frequency channel and the same time to a plurality of communication partner stations via a channel, Mj A transmission device for spatial multiplexing transmission that transmits to a communication partner , which is connected to each antenna element, receives a channel information from a received signal or feedback information included in the received signal, and each communication partner channel for variations when the fluctuation estimation circuit when estimating the amount of change in channel information with respect to the variation were estimated Comparison of the amount of change in distribution, the delay time from the time that the channel estimation until the timing for transmitting, to calculate a deterioration amount of the transmission capacity for the time variation of the total communication partner, the prescribed value of the amount of degradation and the deterioration amount A spatial multiplexing number determination circuit that increases or decreases the number of transmission streams for the communication partner, and a data generation circuit that generates transmission data for each communication partner when the deterioration amount satisfies a specified value. Is a transmitter for spatial multiplexing transmission.

  According to the present invention, the time variation amount of the transfer coefficient is obtained, the signal deterioration amount is estimated from the time variation amount, and the number of multiplexed signals (number of streams) to be transmitted simultaneously is calculated. Can be selected with a small amount of calculation, and the influence of transmission quality deterioration due to time fluctuations can be reduced.

  Hereinafter, various embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration example of a transmission unit in the first embodiment of the present invention.

In Figure 1, reference numeral 11 denotes a data generating circuit, 12 a data dividing circuit, the transmission signal conversion circuit 13, 14-1 to _{14-M T} radio unit, 151 to _{15-M T} antenna, 16 channels An information acquisition circuit, 17 is a time variation estimation circuit, 18 is a spatial multiplexing number determination circuit, and 19 is a transmission weight determination circuit.

Antenna 151 to _{15-M T} and the radio unit 14-1 to _{14-M T} is capable of transmitting and receiving radio signals, the antenna 151 to 15-M of the transmitter via these The channel response acquisition circuit 16 can estimate the channel response matrix between _T and each antenna of the communication partner.

Although this method obtains the channel response matrix is not specified here, the feedback included in the estimate based on whether or received signal information obtained when performing the reception of the known signal at the antenna 151 to 15-M _T Information on the channel response matrix is acquired based on the information included in the information. Further, the channel information acquisition circuit 16 can also estimate items for which information can be obtained with respect to the time variation of the propagation environment transmitted from the terminal, the installation method, and the terminal of the communication partner.

  When the other party to be transmitted is determined, the information estimated by the channel information acquisition circuit 16 is output to the time variation estimation circuit 17 to evaluate the resistance against the time variation of the propagation environment of each communication partner. The time variation estimation circuit 17 outputs the channel information of the corresponding communication partner and the resistance against the time variation to the spatial multiplexing number determination circuit 18.

  The spatial multiplexing number determination circuit 18 determines the number of transmission streams to be spatially multiplexed and transmitted to each communication partner from the tolerance against time variation and the number of reception antennas of the communication partner, and outputs the number to the transmission weight determination circuit 19.

  The transmission weight determining circuit 19 determines a modulation mode including a transmission encoding method, a modulation scheme, and a coding rate from the number of input transmission streams and a channel response matrix, and the data generation circuit 11, the data division circuit 12, and the transmission signal Output to the conversion circuit 13.

Next, transmission data is output from the data generation circuit 11 to the data division circuit 12, and one system of signals is divided into designated signal sequences and input to the transmission signal conversion circuit 13. Here, granted preamble signal or the like for MIMO channel estimation, after being encoded, is input to the radio unit 14-1 to _{14-M T,} as a radio signal via the antenna 151 to _{15-M T} Sent.

  3 shows a method for determining the number of transmission streams according to the present invention. In the present invention, the channel information acquisition circuit 16 evaluates the tolerance of the communication partner against time variations. There are two evaluation methods, one based on the information given by the communication partner and the other that the channel information acquisition circuit calculates using the estimated channel response matrix. Either or both of these are used to estimate the channel information. In consideration of the delay time from transmission to transmission, the influence of time variation is determined.

  The information given by the communication partner is, first, the stability of the received signal obtained by periodically receiving the signal from the base station. A method for evaluating time variation will be described using a channel response matrix Hi acquired at the communication partner and estimated at the i-th communication partner.

For example, it is assumed that a known signal transmitted from the transmission antenna of the base station is received every 10 msec, and a channel response matrix for communication from the base station to the communication partner obtained by obtaining at the k-th timing is represented by _{Hi, If} the channel response matrix is defined as _{k i and} the j th row vector of H _{i, k} is defined as h _{i, j, k} , the channel time variation can be defined as follows.

Here, T represents a timing delay. When h _{i, j, k} is equal to h _{i, j, k + T} , the time variation coefficient ρ _{i, j} (T) is 1, and takes a small value between 1 and 0 with large variation.

The coefficient of variation at this time can be averaged at each receiving antenna of the communication partner terminal as follows, and ρ _i obtained by the averaging can also be used.

  It is also possible to select one or a plurality of reception antennas, perform an averaging process, and use the obtained value.

As a selection criterion, one having a high reception level can be selected, or weighted by the size of the reception level and averaged. _{Also, h i, j, k} is also not always necessary to use all the j-th row vector of _{H i, k,} can be used one or more of _{h i, j,} an element of _k. Further, a column vector of the right singular matrix obtained by the singular value decomposition of the equation (1) can be used instead of _{hi, j, k} .

  The second is that the terminal itself does not move much, such as a notebook personal computer where the shape and installation method of the communication partner terminal can be mentioned, and the terminal moves and changes with time as the user uses it, such as a PDA or mobile terminal. The shape of these terminals greatly influences time fluctuations. In addition, the terminal itself can be evaluated for stability from vibration, etc., and it can receive information on whether it is fixed on a desk or whether the user is installed on a fluctuating part such as on the hand or knee. it can. Depending on these situations, a value corresponding to the time variation coefficient can be output. The correspondence between the status of the terminal and the time variation coefficient accumulates case study information and uses an approximate value.

  Also, the time variation coefficient can be calculated and obtained in the same manner as Equation (7) using the channel response matrix included in the feedback information or the channel response matrix variation in the uplink.

  The amount of signal degradation is estimated according to the time variation coefficient obtained as described above and the delay time t from the estimated time of the channel response matrix to the transmission timing.

  For example, if the value of transmission capacity is used as a parameter representing transmission quality, the amount of deterioration of transmission capacity is the ratio Rf (i) of the surplus degree of freedom F (i) of the communication partner and the number of interference waves I (i). ) The surplus degree of freedom F (i) of the communication partner is a value obtained by subtracting the number L (j) of transmission streams to be transmitted to the communication partner from the number of communication partner receiving elements, and can be expressed as follows.

  Since the interference wave is the sum of the number of streams transmitted to other than the communication partner, it can be expressed as follows. In addition, when there is an interference wave coming from a base station other than the communicating base station, or there is a possibility of arrival, the number of the interference waves may be added to I (i). it can.

  Rf (i) can be obtained as Rf (i) = F (i) / I (i). By setting this Rf (i) to a large value, it is possible to suppress the deterioration amount of the transmission capacity with respect to the time variation. Therefore, by limiting the number of transmission streams for a communication partner that is considered to have a large amount of deterioration with respect to time variation, it is possible to reduce signal quality deterioration in a certain communication partner.

  The effect of this patent will be verified from the results of computer simulation. Considering a MIMO-OFDM system, a 128-point FFT (Fast Fourier Transform) is used, and the result of channel response matrix in 104 subcarriers is used. The delay spread is 100 nsec, and 32-tap time series data acquired every 50 nsec is used. The expected value of the received power of each tap is given to decrease exponentially, and it is assumed that 8 tap waves are received at each tap. Therefore, it was assumed that 32 × 8 = 256 arriving waves. The arrival angle and the radiation angle of each elementary wave were randomly given, the transmission array and the reception array were linearly arranged, and the element spacing was 1.0λ and 0.5λ, respectively. The average received signal-to-noise ratio (SNR) at one receiving antenna of the communication partner was set to 30 dB.

  Assuming that the receiving terminal moves at a constant speed in an arbitrary direction, the horizontal axis represents the multiplication value of the Doppler frequency FD and the delay time T, and the deterioration of the transmission capacity, the correlation value, and the fluctuation of the time variation coefficient were evaluated.

FIG. 2 is a plot of the time variation coefficient ρ against the multiplication value (F _D × T) of the Doppler frequency and the delay time. In FIG. 2, the horizontal axis represents the product of the Doppler frequency and the delay time (F _D × T), and the vertical axis represents the time variation coefficient ρ. Here, it is an average value of data of 104 subcarriers that are generated at random and tried 10 times. Here, the number of transmitting elements is 8 and the number of receiving elements is 1, but this result does not depend on the number of transmitting elements or the number of receiving elements. It can be seen that the time variation coefficient increases as the multiplication value (F _D × T) of the Doppler frequency and the delay time increases. Therefore, the this case the variation coefficient, when knowing the delay time T when measuring the coefficient of variation, it is possible to estimate the Doppler frequency F _D. The relationship between the time variation coefficient ρ, the Doppler frequency, and the delay value (F _D × T) shown here is the result obtained from the channel response matrix generated by the independent correlation. In the actual propagation environment, data can be acquired by experiment to obtain a similar graph. In this case, the Doppler frequency does not need to be an exact solution and is treated as a time variation coefficient. Also, Doppler frequency F _D can be empirically estimated type of the remote terminal, and the like installation.

Next, when the number of transmitting elements is 16 and the number of receiving antennas of the terminal is 4 elements, the function of the deterioration degree of the transmission capacity and the multiplication value (F _D × T) of the Doppler frequency and the delay time is The graph shown is shown in FIG. In FIG. 3, the horizontal axis indicates a multiplication value (F _D × T) of the Doppler frequency and the delay time, and the vertical axis indicates the transmission capacity deterioration ratio. Here, it is an average value of data of 104 subcarriers generated 10 times by randomly generating channels, and the transmission capacity is given by the following equation.

SINR _{i, j} represents the SINR of the i-th spatial stream at the delay time t. Therefore, the transmission capacity deterioration ratio Rc (t) is as follows.

Here, L is the number of transmission streams by spatial multiplexing for the communication partner, I is the number of transmission streams formed in a communication partner other than the communication partner, F is the degree of freedom remaining at the communication partner, and Rf is the degree of freedom F. I ratio. It can be seen that when Rf is set to a large value, the transmission capacity is not easily deteriorated against time fluctuations. If the multiplication value (F _D × T) of the Doppler frequency and the delay time is estimated, a graph of the deterioration amount given in FIG. 3 is determined in advance, and the number of transmission streams is selected by selecting an allowable Rf. Can be determined.

From these results, the terminal in the form and method of installing the communication partner, the correlation values of different times acquired channel response matrix to estimate the Doppler frequency F _D, from the delay time T from the channel estimation when transmitting, Doppler A multiplication value (F _D × T) of the frequency and the delay time can be obtained, and a function of a deterioration ratio of Rf and the transmission capacity with respect to a multiplication value (F _D × T) of the Doppler frequency and the delay time or If a table is defined, the number of streams that maintain communication quality equal to or less than the degradation amount can be selected.

Here, the result of FIG. 3 is a result when the average reception SNR at the communication partner is 30 dB. In actual communication, when the communication partner is determined based on the reduction amount of the transmission capacity instead of the ratio of the transmission capacity, the result shown in FIG. 3 is corrected with the average received SNR and the transmission capacity of the communication partner, and the necessary value is obtained. You can also get For example, when attention is paid to the line of Rf 1.5 in FIG. 3, the transmission capacity deterioration degree is 0.95 when F _D × T is 0.6. If this communication partner can be achieved with F _D × T = 0 and a transmission capacity of 10 bits / sec / Hz, the degree of degradation of the transmission capacity is 0.5 bits / sec / Hz. Since the number of transmission streams is 1, conversion to an approximate SINR degradation amount from Equation (9) corresponds to a degradation amount of about 1.5 dB. On the other hand, when the reception SNR of the communication partner is low and the transmission capacity of 5 bits / sec / Hz can be achieved with F _D × T, the degradation amount of the transmission capacity is 0.25 bits / sec / Hz. , Corresponding to a degradation amount of about 0.75 dB. Therefore, the specified value can be set according to the receiving side SNR, the transmission capacity, and the number of transmission streams to the communication partner.

  Next, processing up to the transmission weight determination described above is shown in the flowchart. FIG. 4 shows a transmission flow in the embodiment of the present invention.

  In FIG. 4, when a communication partner is determined (step S100), the channel information acquisition circuit 16 estimates a channel response matrix of the communication partner, tolerance against time fluctuation (Doppler frequency), and a delay time from estimation to transmission. (Step S101) In the spatial multiplexing number determination circuit 18, the number of transmission streams for each communication partner is determined, and it is verified whether the communication quality of each communication partner satisfies a predetermined value at the time of transmission (Step S102). For example, the number of transmission streams to the communication partner is reduced (step S103) and the test is performed again (step S102). If the communication quality deterioration with respect to the time variation for all communication partners satisfies a predetermined value, transmission data for the communication partner is generated (step S104).

  FIG. 5 shows another transmission flow in the embodiment of the present invention. In FIG. 5, when a communication partner is determined (step S200), the channel information acquisition circuit 16 estimates a channel response matrix of the communication partner, tolerance against time variation (time variation coefficient), and delay time from estimation to transmission. In step S201, the spatial multiplexing number determination circuit 18 determines the number of transmission streams for each communication partner, tests whether the communication quality of each communication partner satisfies a predetermined value at the time of transmission (step S202), and satisfies the predetermined value. If not, the number of transmission streams to the communication partner is reduced (step S203), and whether or not transmission to another communication partner can be performed using the degree of freedom on the transmission side due to the reduction of the number of transmission streams (step S205). ) If there is a communication partner to be added, a transmission stream is assigned to the communication partner (step S206), and communication of each communication partner is performed. Quality assaying whether not a default or less at the time of transmission (step S202). If the communication quality deterioration with respect to the time variation for all communication partners satisfies a predetermined value, transmission data for the communication partner is generated (step S204).

  FIG. 6 shows another transmission flow in the embodiment of the present invention. In FIG. 6, when the communication partner is determined (step S300), the channel information acquisition circuit 16 estimates the channel response matrix of the communication partner, tolerance against time variation (time variation coefficient), and delay time from estimation to transmission. In step S301, the spatial multiplexing number determination circuit 18 determines the number of transmission streams for each communication partner to be 1 or a sufficiently small number (step S302), and tests whether the communication quality of each communication partner satisfies a predetermined value at the time of transmission. If there is a communication partner that does not satisfy the default value (step S303), the number of transmission streams to the communication partner is reduced (step S304), and the test is performed again (step S303).

  If the predetermined value is satisfied, the number of transmission elements is compared with the total transmission stream, and it is determined whether the number of transmission elements is large and the transmission streams of the same communication partner are not increased or decreased in steps S304 and S305 ( (Step S306) If the above-mentioned conditions are satisfied, the number of transmission streams to the communication partner with the least deterioration with respect to the time variation or the communication partner with a large degree of freedom is increased (Step S305), and the communication quality deterioration amount with respect to the time variation is increased again. Evaluate it.

  If the number of repeated evaluations between step S303 and step S306 exceeds a certain number or if the condition of step S306 is satisfied, transmission data is generated for the determined communication partner (step S307).

  As described above in detail, according to the present invention, when performing MIMO communication using one or more signal sequences addressed to a plurality of communication partner stations using spatial multiplexing at the same time on the same frequency channel. The risk of transmission quality degradation due to time fluctuations can be reduced.

  Note that the present invention is not limited to the above-described embodiment, and various modifications and applications are possible without departing from the gist of the present invention.

It is a flock figure which shows the structural example of the transmission part in embodiment of this invention. It is a graph which shows the time variation coefficient with respect to Doppler frequency x delay time. It is a graph which shows the transmission capacity degradation ratio with respect to Doppler frequency x delay time. It is a flowchart which shows the 1st transmission flow in embodiment of this invention. It is a flowchart which shows the 2nd transmission flow in embodiment of this invention. It is a flowchart which shows the 3rd transmission flow in embodiment of this invention. It is a block diagram which shows the structural example of the transmission part in a prior art.

Explanation of symbols

11: data generating circuit 12: data dividing circuit 13: the transmission signal converting circuit 14-1 to _{14-M T:} Radio unit 151 to _{15-M T:} Antenna 16: channel information acquiring circuit 17: time-variation estimation circuit 18 : Spatial multiplexing number determination circuit 19: Transmission weight determination circuit

Claims (6)

A plurality of antenna elements are provided, channel information between a receiving antenna formed by a communication partner or a receiving beam formed at the antenna element and a transmitting antenna that performs transmission is estimated, a transmission weight is determined using the channel information, and a transmission signal is determined. A transmission method for spatial multiplexing transmission that performs MIMO communication by spatially multiplexing one or a plurality of signal sequences at the same frequency channel and the same time for a plurality of communication partners after performing transmission weighting,
A channel information estimation step for estimating channel information with a communication partner performing communication at the same time;
For each communication partner, a change amount estimation step for estimating a change amount of channel information with respect to time variation,
A deterioration amount calculating step for calculating a deterioration amount of the transmission capacity with respect to the time variation of all communication partners from a change amount of the channel information with respect to the estimated time variation and a delay time from a channel estimation time to a transmission timing ;
A stream number determining step for increasing or decreasing the number of transmission streams for each of the communication partners based on a comparison between the deterioration amount and a specified value of the deterioration amount;
When the deterioration amount satisfies a specified value, a transmission data generation step for generating transmission data for each communication partner;
A transmission method for spatial multiplexing transmission, comprising: 2. The spatial multiplexing transmission method according to claim 1, wherein, in the step of determining the number of streams, if the amount of deterioration does not satisfy the specified value, the number of transmission streams for the communication partner is reduced. In the step of determining the number of transmission streams, the number of transmission streams to the communication partner with the greatest deterioration due to time variation is reduced.
  The transmission method for spatial multiplexing transmission according to claim 2. Addition to determine whether there is a communication partner that can be newly added using the degree of freedom on the transmission side, which is a value obtained by subtracting the total number of transmission streams from the number of antenna elements on the transmission side after subtracting the transmission stream A communication partner presence determination step;
When there is a communication partner that can be newly added, a transmission stream is allocated to the communication partner, and the degradation amount of the transmission capacity with respect to the time variation of all the communication partners is calculated again. If satisfying, the step of generating transmission data for the communication partner,
  The transmission method for spatial multiplexing transmission according to claim 3, further comprising: In the step of determining the number of streams, when the deterioration amount satisfies the specified value, the number of antenna elements is large by comparing the number of antenna elements with the total number of transmission streams, and transmission streams of the same communication partner If the number is not increased or decreased, the number of streams to the communication partner with the least amount of degradation of the transmission capacity with respect to the time variation, or to the communication partner with a high degree of freedom, which is a value obtained by subtracting the number of transmission streams from the number of antenna elements. And again calculating the degradation amount of the transmission capacity with respect to the time variation of all communication partners, and when the degradation amount satisfies the specified value, generating transmission data for those communication partners;
  The transmission method for spatial multiplexing transmission according to claim 1, comprising: A transmission device including a plurality of antenna elements;
One or a plurality of signals to a plurality of communication partner stations via a MIMO (Multiple Input Multiple Output) channel composed of a transmitting device and a plurality of communication partner station antenna elements or beams formed on these antenna elements. In a wireless communication system capable of performing MIMO communication by spatially multiplexing a sequence at the same frequency channel and the same time,
A spatial multiplexing transmission apparatus for transmitting to Mj communication partners at the same time ,
A channel information acquisition circuit that is connected to each antenna element and acquires channel information from the received signal or feedback information included in the received signal;
A time variation estimation circuit that estimates the amount of change in channel information relative to the time variation of each communication partner;
From the amount of change in channel information with respect to the estimated time variation and the delay time from the channel estimation time to the transmission timing, the amount of transmission capacity degradation with respect to the time variation of all communication partners is calculated. A spatial multiplexing number determination circuit that increases or decreases the number of transmission streams for the communication partner based on a comparison with a specified value of the amount;
A data generation circuit for generating transmission data for each communication partner when the deterioration amount satisfies a specified value;
A spatial multiplexing transmission apparatus characterized by comprising:

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