JP5203308B2 - Transmission directivity control apparatus and transmission directivity control method - Google Patents

Description

  The present invention relates to a transmission directivity control apparatus and a transmission directivity control method for efficiently realizing SDMA (Spatial Division Multiplexing) -OFDM (Orthogonal Frequency Division Multiplexing).

  In recent years, in mobile phones and wireless LAN systems, studies for realizing ultrahigh-speed wireless communication of about 100 Mbps to 1 Gbps in a limited frequency band have been performed. In order to realize such a wireless communication system, not only the frequency, time, and code are divided for each terminal, but also the frequency utilization efficiency is improved by a technique using a spatial domain, and the transmission speed is improved. It is necessary to consider. As a technology for that purpose, MIMO (Multiple-Input Multiple-Output) -OFDM (Orthogonal Frequency Division Multiplexing) technology has attracted much attention in recent years. This MIMO technology is such that different independent signals are transmitted on the same channel from a plurality of transmitting antennas on the transmitting station side, and signals are received using the same plurality of antennas on the receiving station side, between each transmitting antenna / receiving antenna. The transfer function matrix is obtained, the independent signal transmitted from each antenna is estimated on the transmitting station side using this matrix, and the data is reproduced. In order to combine OFDM and MIMO, MIMO signal processing may be realized in units of subcarriers. The theoretical maximum transmission capacity C using the MIMO technique can be obtained by the equation (1) (see, for example, Non-Patent Document 1).

（１）式において、ρは信号対雑音電力比、Ｍは送信アンテナ素子数、Ｉ_Ｎは、受信素子数Ｎ×Ｎの単位行列である。また、Ｈは、送信アンテナと受信アンテナ間の伝搬チャネル応答を表す伝達関数行列であり、（２）式で記述することができる。

(1) In the formula, [rho is the signal-to-noise power ratio, M is the number of transmit antenna elements, I _N is the identity matrix of the received number of elements N × N. H is a transfer function matrix representing the propagation channel response between the transmitting antenna and the receiving antenna, and can be described by equation (2).

ここでｈ_ｉｊはｉ番目の送信アンテナからｊ番目の受信アンテナへの伝搬路のチャネル応答である。

Here, _hij is the channel response of the propagation path from the i-th transmitting antenna to the j-th receiving antenna.

  Incidentally, it is known that the communication capacity obtained by the MIMO technology increases in proportion to the number of antenna elements for both transmission and reception. Since the access point antenna has relatively few hardware restrictions, the number of elements can be increased. However, when a small terminal is considered, a large number of antenna elements cannot be arranged.

  As a technique for solving this problem, a multi-user MIMO (Multi User-MIMO) technique has been proposed. Multi-user MIMO is also called SDMA (Spatial Division Multiplexing). MU-MIMO and SDMA are disclosed in Non-Patent Document 2. In SDMA, a large number of antenna elements are provided on the access point side, a relatively small number of elements are provided on the terminal side, and a virtual MIMO channel is simultaneously formed between the access point and a plurality of terminals. Here, assuming that the total number of terminals simultaneously connected to the access point is N and the number of antennas of the access point is M, ideally, the channel capacity obtained by the equation (1) can be obtained.

  Therefore, multi-user MIMO is attracting attention as a technology that can increase the communication capacity of the total system even when a small terminal is considered. FIG. 13 shows a configuration when an SDMA transmitter is applied to OFDM. In FIG. 13, a data generation unit 1 excluding a transmission weight forming unit 5 and a transmission weight calculation unit 8, an error correction unit 2, an interleaver 3, a modulation unit 4, an IFFT (Inversed Fast Fourier Transform) unit 6, and a GI (Guard Interval) The addition unit 7 and the N antennas 9 are equivalent to a conventional OFDM modulator (see, for example, Non-Patent Document 3). In OFDM, since transmission / reception channel information is obtained for each subcarrier, equation (2) is obtained for each subcarrier, and the transmission weight is determined for each subcarrier. Various methods for determining the transmission weight have been proposed, and the method shown in Non-Patent Document 2 is a well-known method.

Daigane "MIMO System Basics and Elemental Technology" Design and Analysis Workshop on Antennas and Propagation, W29, 30 " Q.H.Spencer et.al, IEEE Trans.Sig.Processing, vol.52, no.2, Feb.2004 Revised 3rd Edition 802.11 High Speed Wireless LAN Textbook, Chapter 4, pages 88-97

  However, the above-described SDMA technique has the following problems. As shown in FIG. 14, generally, in a wireless communication system, a plurality of (two in FIG. 14) access points (APs) AP1 and AP2 are multi-cell environments each having a service area. Signals not only from terminals in the area served by the access point AP1 but also from neighboring cells (area served by the access point AP2) arrive as interference. Furthermore, this problem becomes serious when a large number of access points are installed in a certain area.

  The example illustrated in FIG. 14 illustrates interference from the access point AP2 to the terminal 1-1 in downlink transmission when the access point AP2 performs SDMA. In FIG. 14, when the access point AP2 performs SDMA on the terminal 2-1 and the terminal 2-2, the access point AP2 prevents the interference from reaching each of the terminals 2-1 and 2-2 in SDMA. Send directivity on the side. However, since attention is not paid to the terminal 1-1 communicating with the access point AP1, if the terminal 1-1 is located near the end of the service area of the access point AP1 as shown in FIG. 14, the terminal 2-1 and the terminal 2 -2 is transmitted to the terminal 1-1 as interference.

  In general, the SDMA technique is assumed to be used in an environment such as an indoor wireless LAN or a hot spot, not in an environment where such multiple access points exist, and has been evaluated in a so-called single cell environment. In this environment, it is necessary to assume an environment in which a plurality of access points operate at the same frequency. In this case, there is a problem that interference from other cells deteriorates the SDMA transmission characteristics.

  In the prior art, in order to remove interference, on the receiving side, interference from other cells can be removed by controlling the amplitude and phase of each antenna of the array antenna. On the transmitting side, the use of the array antenna amplitude and phase values obtained on the receiving side can be avoided. In the MIMO and multi-user MIMO techniques, a process of separating a plurality of signals on the receiving side is performed, and the technique of separating a plurality of signals can be used for interference signal removal. As this method, a ZF (Zero Forcing) method, an MMSE (Minimum Mean Square) method, etc. are generally well known (see Non-Patent Document 1). When these methods are used, it is necessary to correctly estimate a predetermined known signal (training signal) in the interference signal on the reception side or to perform propagation channel estimation for the interference signal.

  However, the communication cell of the access point AP1 and the communication cell of the access point AP2 operate independently, and the access point and terminal on the access point AP2 side can estimate when the interference signal arrives. Since it is difficult, it is difficult to estimate a known signal or a propagation channel of an interference signal. Considering application to OFDM, in the conventional configuration shown in FIG. 13, it is necessary to calculate and form weights in units of subcarriers. For this purpose, the FFT timing of the desired signal and the interference signal is set to one on the receiving side. There is a problem that the transmission weight calculation unit 8 and the transmission weight formation unit 5 shown in FIG. 13 cannot cope with interference from other cells.

  The present invention has been made in view of such circumstances, and even in an environment where a plurality of communication cells operate independently, only information at the time of receiving an interference signal, without giving interference to other cells, An object of the present invention is to provide a transmission directivity control apparatus and a transmission directivity control method capable of efficiently realizing SDMA-OFDM.

The present invention is a transmission directivity control apparatus for controlling the transmission directivity of an access point apparatus that combines an orthogonal frequency division multiplex communication system and a space division multiple access system, each having a plurality of antennas and the same number of transmitters as the antennas. The transmission weight calculation result values are all set to 1, first means for causing the access point apparatus to acquire channel information from terminals in its own cell, and a signal-to-noise power ratio between the access point apparatus and the terminal. A second means for measuring, a third means for transmitting a prohibition signal not to be transmitted only by a terminal in the own cell for a certain period of time from the access point apparatus to the terminal, and another cell for the certain period of time And a fourth means for estimating the interference power and a value of a power ratio between the signal power and the power obtained by adding interference and noise from the interference power. And when the minimum value of the power ratio value in the terminal is equal to or less than a threshold value, a weight value for realizing interference cancellation is calculated, and the weight value is given to the received signal. And when the minimum value of the power ratio value is equal to or greater than the threshold value, the seventh means for setting all the weight values to 1, and the access point device using the weight value. Eighth means for acquiring channel information from a terminal in the own cell, and ninth means for calculating a transmission weight value for the space division multiple access scheme from the channel information and giving the weight value. Features.

The present invention is a transmission directivity control apparatus for controlling the transmission directivity of an access point apparatus that combines an orthogonal frequency division multiplex communication system and a space division multiple access system, each having a plurality of antennas and the same number of transmitters as the antennas. A first means for causing the access point apparatus to acquire channel information from a terminal in its own cell with a weight value of all 1, and a second means for measuring a signal-to-noise power ratio between the access point apparatus and the terminal. Means, and a third means for transmitting a control signal for preventing a signal from being transmitted for a certain period to an access point apparatus or terminal capable of receiving a signal from the access point apparatus or terminal in the own cell; A fourth means for estimating interference power other than that of the access point device or terminal for which transmission is prohibited, and the interference power A fifth means for obtaining a value of the power ratio between the signal power and the power including interference and noise; and when the minimum value of the power ratio value in the terminal is equal to or less than a threshold value, interference cancellation When the weight value that realizes the weight value is calculated and the weight value is given to the received signal, and the minimum value of the power ratio value is equal to or greater than the threshold value, all the weight values are set to 1. Seventh means for setting to the access point, eighth means for causing the access point apparatus to acquire channel information from the access point apparatus or terminal prohibited from transmission using the weight value, and an access point other than the own cell Ninth means for calculating a transmission weight value for interference cancellation from channel information from the apparatus or terminal, and multiplying the channel weight information of the access point apparatus or terminal of the own cell by the transmission weight value. 10 means calculates the transmission weight values for SDMA, and having a eleventh means for providing the weight values for the signal obtained by multiplying the transmission weight value.

  The present invention relates to a transmission directivity control apparatus for controlling the transmission directivity of an access point apparatus that combines an orthogonal frequency division multiplex communication system and a space division multiple access system, each having a plurality of antennas and the same number of transmitters as the antennas. A directivity control method, wherein all values of transmission weight calculation results are set to 1, and the access point apparatus acquires channel information from a terminal in its own cell, and between the access point apparatus and the terminal. A second step of measuring a signal-to-noise power ratio; a third step of transmitting, from the access point apparatus to the terminal, a prohibition signal for preventing only terminals in the own cell from transmitting for a certain period of time; A fourth step of receiving signals from other cells and estimating the interference power for a period of time, and the signal power, interference and noise from the interference power. And calculating a weight value for realizing interference cancellation when the minimum value of the power ratio value in the terminal is less than or equal to a threshold value. And a sixth step for giving the weight value to the received signal, and a seventh value for setting all the weight values to 1 when the minimum value of the power ratio value is not less than the threshold value. And an eighth step in which the access point apparatus acquires channel information from a terminal in its own cell using the weight value, and calculates a transmission weight value for the space division multiple access scheme from the channel information. And a ninth step for giving the weight value.

  The present invention relates to a transmission directivity control apparatus for controlling the transmission directivity of an access point apparatus that combines an orthogonal frequency division multiplex communication system and a space division multiple access system, each having a plurality of antennas and the same number of transmitters as the antennas. A directivity control method, wherein the access point apparatus obtains channel information from terminals in its own cell with a weight value of all 1, and a signal-to-noise power ratio between the access point apparatus and the terminal And a third step of transmitting a control signal for preventing a signal from being transmitted for a certain period to an access point device or terminal capable of receiving a signal from the access point device or terminal in the own cell. And estimate the interference power of other than the access point device or terminal for which transmission is prohibited during the predetermined period. A fourth step of obtaining a power ratio value between the signal power and the power obtained by adding interference and noise from the interference power, and a minimum value of the power ratio value in the terminal. Is equal to or less than the threshold value, the sixth step of calculating a weight value for realizing interference cancellation, and giving the weight value to the received signal, and the minimum value of the power ratio value is the threshold value If this is the case, a seventh step of setting all of the weight values to 1 and the access point device acquires channel information from the access point device or terminal prohibited from transmission using the weight value. An eighth step of calculating an interference removal transmission weight value from channel information from an access point device or a terminal other than the own cell, and the transmission weight value A tenth step of multiplying channel information of the access point device or terminal of the network, an eleventh step of calculating a transmission weight value for SDMA and giving the weight value to the signal multiplied by the transmission weight value; It is characterized by having.

  In the present invention, when another cell is a conventional system and communication with an access point device for acquiring propagation channel information is not possible, the eighth step, the ninth step, the tenth step, the eleventh step, A twelfth step of calculating a weight value for realizing interference cancellation and giving the weight value to the received signal, and the access point device using the weight value in the own cell. A thirteenth step of acquiring channel information from a terminal and a fourteenth step of calculating a transmission weight value for the space division multiple access scheme from the channel information and giving the weight value are performed.

  In the present invention, before starting the ninth step from the first step, the tenth step of increasing the transmission power of the access point apparatus and the ninth step from the first step are executed. Then, when the obtained number of interference signals exceeds the number of antennas of the access point device, the transmission power of the access point device is reduced, and the number of obtained interference signals does not exceed the number of antennas of the access point device. And an eleventh step of increasing the transmission power of the access point device.

  In the present invention, before starting the eleventh step from the first step, the twelfth step of increasing the transmission power of the access point apparatus and the eleventh step from the first step are executed. Then, when the obtained number of interference signals exceeds the number of antennas of the access point device, the transmission power of the access point device is reduced, and the number of obtained interference signals does not exceed the number of antennas of the access point device. And a thirteenth step of increasing the transmission power of the access point device.

  In the present invention, the weight value for realizing the interference cancellation is an arbitrary value in which a signal of a terminal not communicating with the access point apparatus is received, and an inverse matrix of the correlation matrix of the received signal and all elements are other than zero. It is obtained by vector multiplication.

  According to the present invention, even if the system of another cell is a conventional system and the apparatus of the present invention is not provided in an adjacent cell, the present invention can interfere with the conventional system. Even if there is an influence of interference from other cells without receiving or giving, good communication can be realized. In addition, if the terminal measures the interference signal during a section in which the signal in the own cell is only the interference signal, it can be applied to a terminal having a plurality of antennas. Further, since the mechanism for receiving only the interference signal can be realized by the control signal of the conventional wireless LAN, an effect of high compatibility with the conventional system can be obtained.

It is a block diagram which shows the structure of the 1st Embodiment of this invention. It is a figure which shows the relationship between transmission weight calculation part 11, transmission weight formation part 10, and input / output. It is a flowchart which shows the transmission operation | movement of the transmission directivity control apparatus shown in FIG. It is a figure which shows the case where a communication cell overlaps. It is a flowchart which shows operation | movement of the transmission directivity control apparatus in 2nd Embodiment. It is a flowchart which shows operation | movement of the transmission directivity control apparatus in 3rd Embodiment. It is a figure which shows operation | movement of the transmission directivity control apparatus in 4th Embodiment. It is a figure which shows operation | movement of the transmission directivity control apparatus in 4th Embodiment. It is a figure which shows operation | movement of the transmission directivity control apparatus in 4th Embodiment. It is a figure which shows operation | movement of the transmission directivity control apparatus in 4th Embodiment. It is a figure which shows operation | movement of the transmission directivity control apparatus in 4th Embodiment. It is a figure which shows operation | movement of the transmission directivity control apparatus in 4th Embodiment. It is a block diagram which shows the structure at the time of applying SDMA to OFDM. It is a figure which shows the problem of a prior art.

<First Embodiment>
Hereinafter, a transmission directivity control apparatus according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the embodiment. In this figure, the same parts as those of the conventional apparatus shown in FIG. The apparatus shown in this figure is different from the apparatus shown in FIG. 13 in that, in addition to the transmission weight forming unit 5, a new transmission weight calculating unit 11 and a new transmission weight calculating unit 11 are added. Is a point provided. A so-called time-series signal after IFFT (Inversed Fast Fourier Transform) and GI (Guard Interval) is added by the IFFT unit 6 and the GI adding unit 7 becomes an input of the transmission weight forming unit 10 that forms a transmission weight. The transmission weight calculation unit 11 performs the calculation for giving.

  Further, as shown in FIG. 1, the transmission weight forming unit 5 needs to obtain weights by the number of transmission data streams (= <the number of antennas or less) × the number of subcarriers of OFDM, whereas the transmission weight forming unit 10 has antennas. A number of weights are required, and the number of weights required to be obtained is smaller than that of the transmission weight forming unit 5. The transmission weight calculation unit 8 calculates a transmission weight in units of OFDM subcarriers using a propagation channel response between the access point whose input is estimated on the reception side and a terminal in the own cell. On the other hand, since it is difficult to estimate the position of the known signal section of the interference signal of another cell, it is difficult to estimate the channel of the interference signal. Also, when there is an interference signal, the channel estimation between the access point of the own cell and the terminal does not work well, so the transmission weight calculation unit 8 does not operate correctly. Therefore, in the present invention, the transmission weight calculation unit 11 receives only the interference signal in advance and forms transmission directivity for reducing the interference signal. In addition, the transmission weight calculation unit 11 has a configuration in which only the received signal of the interference wave is input and the interference wave is removed only by the correlation matrix of the received signal, and the estimation of the known signal of the interference signal, the estimation of the timing, It is characterized by not requiring channel estimation for interference signals. Furthermore, by reflecting the weight calculated by the transmission weight calculation unit 11 in the transmission weight forming unit 10, it is possible to perform channel estimation for the terminal of the own cell in a form in which interference from other cells is removed and avoided. Become.

ここで、Ｘは受信信号ベクトル（Ｎｘ１：Ｎはアンテナ数）を表し、上添え字Ｈ、Ｔはそれぞれ複素共役転置と転置を表している。 FIG. 2 shows the input / output relationship between the transmission weight calculation unit 11 and the transmission weight formation unit 10. As shown in FIG. 2, the received signals x ₁ , x ₂ ,..., X _N ∈C (C is a complex number) input to the receivers _{1 to N} are temporarily stored in the memory 12, and these are calculated for transmission weight. Input to section 11. The transmission weight calculation unit 11 obtains the correlation matrix R _XX of the received signal by the equation (3).

Here, X represents a received signal vector (Nx1: N is the number of antennas), and the superscripts H and T represent complex conjugate transpose and transpose, respectively.

ここで、ＷはＮｘ１のベクトルを表し、Ｐは拘束ベクトルである。Ｐはすべての要素が０でなければどのようなベクトルを与えてもよい。 Next, provide the transmission weight by using the inverse matrix of R _XX, calculated using equation (4).

Here, W represents an N × 1 vector, and P is a constraint vector. P may be any vector if all elements are not zero.

  Since this method only requires information on only the received signal of the interference signal, the interference wave is removed only by the correlation matrix of the transmission signal. Does not require estimation of Finally, the obtained weight and the transmission signal are multiplied by a multiplier. Therefore, if this calculation can be obtained in advance, interference from other cells can be avoided and channel estimation for determining the transmission weight for SDMA in the own cell can be realized.

  Since the purpose of the weight control of the transmission weight calculation unit 11 is to reduce interference from other cells, if there is no change in the interference wave, the weight is not updated even if the terminal in the own cell changes. . In other words, the control interval of the transmission weight calculation unit 11 is performed at a period equal to or greater than the control interval of the transmission weight calculation unit 8. For the change of the interference signal, the result obtained by the expression (3) is compared at a predetermined time interval, and when the similarity becomes low, the weight calculation of the transmission weight calculation unit 11 may be performed again.

  In order to actually realize the transmission directivity control apparatus shown in FIGS. 1 and 2, it is necessary to receive only the interference signal and use this as an input to the transmission weight calculation unit 11. Here, the transmission operation of the transmission directivity control apparatus shown in FIG. 1 will be described with reference to FIG. FIG. 3 is a flowchart showing a transmission operation of the transmission directivity control apparatus shown in FIG. First, in order to receive only interference signals from other cells, a prohibition signal is transmitted from the access point to the terminal so that only the terminal in the own cell does not transmit for a certain period of time (step S1). For example, in FIG. 4, when avoiding an interference signal to the terminal 1-1, the terminal 2-1, the terminal 2-2, and the access point AP2 stop transmitting. As described above, the processing operation for sending a signal for stopping transmission to the access point and the terminal is a technique that is actually introduced in a wireless LAN system or the like. However, in the present invention, the terminal existing in the own cell is used. It is the feature that only sends a control signal to stop transmission. By this operation, the access point AP2 and the terminal 2-1 and the terminal 2-2 shown in FIG. 4 can receive an interference signal from the access point AP1 and the terminal 1-1. In step S1, the terminal is instructed to stop transmission for a certain interval.

  Next, during the time specified in step S1, a signal from another cell is received and the interference power is estimated (step S2). In the case of the example shown in FIG. 4, since the interference power from the access point AP1 is small and the terminal 1-1 is located at the end of the service area, the interference power from the terminal 1-1 is large.

  Next, a threshold value α for determining whether or not the interference power is a problem is provided, and it is determined whether or not the interference power is larger than α (step S3). In the example illustrated in FIG. 4, it is determined that the interference from the terminal 1-1 that increases the interference power is a problem.

  When the interference power is larger than the threshold value α as a result of this determination, the transmission weight calculation unit 11 is operated, and the transmission weight calculation unit 11 calculates a weight for realizing interference removal for the signal received in step S2. The obtained weight value is given by the transmission weight forming unit 10 (step S4). The transmission weight is calculated using the method shown in FIG.

  On the other hand, when the interference power is smaller than the threshold value α and it is determined that the interference does not become a problem, the transmission weight forming unit 10 sets all the weights to be obtained to 1 (step S5). In other words, this case is equivalent to passing through the transmission weight forming unit 10.

  Next, the access point acquires channel information from the terminal in the own cell using the weight value obtained by the transmission weight calculation unit 11 set in steps S4 and S5 (step S6). In this state, it is possible to exchange signals for channel estimation within the own cell while avoiding problematic interference with other cells.

  Next, the transmission weight calculation unit 8 is used to calculate the transmission weight for SDMA from the channel information obtained in step S6, and the weight value obtained by the transmission weight forming unit 5 is given (step S7). This processing operation may use a conventional SDMA transmission directivity control method, but when performing SDMA, it is necessary to set the number of spatial multiplexing to be equal to or less than (the number of antennas−the number of interference signals).

<Second Embodiment>
Next, a transmission directivity control apparatus according to the second embodiment of the present invention will be described with reference to FIG. FIG. 5 is a flowchart showing the operation of the transmission directivity control apparatus in the second embodiment. The processing operation shown in FIG. 5 is the same as the processing operation shown in FIG. 3 in the basic operation, but the processing operation shown in FIG. Different. In the processing operation shown in FIG. 3, when the interference power threshold value is obtained, the power of the desired signal differs between the service area edge of the own cell and the vicinity of the access point, and the influence of the interference power threshold value is to differ greatly. Therefore, if the power of the desired signal is estimated, a problematic interference signal can be estimated regardless of the position of the terminal.

  First, all the weight values output by the transmission weight calculation unit 11 are set to 1, and the access point acquires channel information from terminals in its own cell (step S11). In this case, the signal from the terminal is not a channel estimated signal, but may be a received signal as in the case of estimating an interference signal.

  Next, an SNR (Signal to Noise power Ratio) that is a signal-to-noise power ratio between the access point and the terminal is measured (step S12). Subsequently, in order to receive only interference signals from other cells, a prohibition signal is transmitted from the access point to the terminal so that only the terminal in the own cell does not transmit for a certain period of time (step S13). .

  Next, during the time specified in step S13, signals from other cells are received and interference power is estimated (step S14). Next, SINR (Signal to Interference plus Noise power Ratio) which is desired signal power / (interference signal power + noise power) is obtained, and the obtained SINR value is determined in consideration of the desired signal power in advance. It is determined whether it is smaller than the value β (step S15). As a result of this determination, if the SINR is smaller than the threshold value β, the transmission weight calculation unit 11 is operated to calculate a weight for realizing interference removal by the transmission weight calculation unit 11 for the signal received in step S14. The obtained weight value is given by the transmission weight forming unit 10 (step S16).

  On the other hand, if the SINR is larger than the threshold value β, the transmission weight forming unit 10 sets all the weights to be obtained to 1 (step S17). In other words, this case is equivalent to passing through the transmission weight forming unit 10.

  Next, the access point acquires channel information from the terminal in its own cell using the set weight value of the transmission weight calculation unit 11 (step S18). In this state, it is possible to exchange signals for channel estimation within the own cell while avoiding problematic interference with other cells. Subsequently, the transmission weight calculation unit 8 is used to calculate the transmission weight for SDMA from the channel information obtained in step S18, and the weight value obtained by the transmission weight forming unit 5 is given (step S19).

<Third Embodiment>
In the processing operation described above, it is assumed that the communication cell of the own cell is stopped and the interference is taken out. However, in reality, the communication cells may further overlap as shown in FIG. Specifically, in the case of FIG. 4, for the access point AP2, it is only necessary to consider the terminal 1-1 as an interference source, but interference from the access point AP1 is also a problem. In such an environment, the interference power becomes considerably large, and on the contrary, channel estimation becomes possible. If the channel of the interference signal can be estimated, it is possible to avoid the interference signal with higher accuracy by calculating the weight for removing the interference signal using the transmission weight calculation unit 8 shown in FIG. The method according to the third embodiment is to operate favorably in such an environment by using a conventional wireless LAN protocol. First, as a premise, in the standard for performing access control in a wireless LAN, each station sends a signal called CTS (Clear to Send), and all access points and terminals that can receive the CTS signal receive NAV (Network Allocation Vector). There is a function to prohibit transmission for a certain period.

  Hereinafter, a processing operation using an access control function to which a standard is applied when performing access control in a wireless LAN will be described with reference to FIG. FIG. 6 is a flowchart showing the operation of the transmission directivity control apparatus according to the third embodiment. First, all the weight values output by the transmission weight calculation unit 11 are set to 1, and the access point acquires channel information from terminals in its own cell (step S11). In this case, the signal from the terminal is not a channel estimated signal, but may be a received signal as in the case of estimating an interference signal. Next, an SNR (Signal to Noise power Ratio) between the access point AP and the terminal is measured (step S12).

  Next, by using CTS signal transmission from the access point, all access points and terminals that can receive the CTS signal are prevented from transmitting within the own cell (step S21). Such processing has an advantage that the access control of IEEE802.11a, n of the wireless LAN can be used as it is.

  Next, within the time specified in step S21, interference power from other than the access point and the terminal prohibited from transmission by the CTS signal is estimated (step S22). Subsequently, SINR (Signal to Interference plus Noise power Ratio) which is desired signal power / (interference signal power + noise power) is obtained, and the obtained SINR value is determined in consideration of the desired signal power in advance. It is determined whether it is smaller than the value β (step S15). As a result of this determination, if the SINR is smaller than the threshold value β, the transmission weight calculation unit 11 is operated to calculate a weight for realizing interference removal by the transmission weight calculation unit 11 for the signal received in step S14. The obtained weight value is given by the transmission weight forming unit 10 (step S16). On the other hand, if the SINR is larger than the threshold value β, the transmission weight forming unit 10 sets all the weights to be obtained to 1 (step S17).

  Next, using the value of the transmission weight calculation unit 11 set in Steps S16 and S17, the access point acquires channel information from the access point and the terminal whose transmission is prohibited in Step S21 (Step S23). That is, only channel information of a relatively high-accuracy signal is acquired. Subsequently, the transmission weight calculation unit 8 is used to calculate the interference removal transmission weight from the channel information obtained from step S23 from stations other than the own cell (step S24). Unlike the previous example, in a state where propagation channel information can be acquired, interference can be avoided more accurately by performing interference site removal in units of subcarriers.

Next, the transmission weight calculation unit 8 is used to multiply the transmission weight obtained in step S24 by the channel information of the access point and terminal of the own cell to obtain corrected channel information h ′ (step S25). When the terminal has one element and the access point has N elements, channel information for a certain terminal is set as h, interference information obtained in step S24 is set as W, and these are calculated by the number of subcarriers according to the equation (5). In equation (5), “·” represents an inner product of vectors.

  Next, an SDMA transmission weight is calculated for the multiplied signal, and the obtained weight value is given by the transmission weight forming unit 5 (step S26). In step S23 of the processing operation shown in FIG. 6, there are cases where the access points and terminals of other cells are conventional systems and cannot exchange with the access point AP2 for acquiring channel information. In this case, FIG. After step S23 shown in FIG. 5, steps S16, S18, and S19 in FIG. 5 are performed. That is, in this case, interference from signals from other cells can be avoided by performing the method described with reference to FIG.

<Fourth Embodiment>
In all the explanations so far, the power transmitted by the access point has been specified in advance. However, if the transmission power can be controlled when the terminal exists at the end of the service area, the transmission rate of the terminal can be improved. . However, interference with other cells increases. The fourth embodiment is for solving such a problem. 7-12 is a figure which shows operation | movement of the transmission directivity control apparatus in 4th Embodiment.

  7 to 10 show the operation of the transmission directivity control apparatus according to the third embodiment. 7 to 10, the access point is referred to as AP1 or AP2. FIG. 11 is a flowchart showing an operation when the transmission power control operation is combined with the processing operation of FIG. FIG. 12 is a flowchart showing an operation when the transmission power control is combined with the processing operation of FIG. The difference between FIG. 11 and FIG. 12 is whether the processing operation shown in FIG. 3 is used or the processing operation shown in FIG. 6 is used, and is essentially unchanged. Therefore, here, the operation will be described with reference to FIGS.

  First, in FIG. 7 <Step 1>, the access point AP1 is in a state of starting communication with the terminal 1-1. The access point AP2 has already realized SDMA with two terminals 2-1, 2-2. On the other hand, although the terminal 1-1 can communicate with the access point AP1, the transmission rate is extremely low because it exists at the end of the service area. Therefore, as shown in FIG. 11, in order to improve the transmission rate of the terminal 1-1 at the end of the service area, the transmission power of the access point AP1 is increased (step S31).

  Next, in this state, interference with the adjacent service area becomes a problem as shown in <Step 2> in FIG. That is, although the reception sensitivity of the terminal 1-1 is improved from the access point AP1, interference occurs with the access point AP2, and the transmission rate cannot be improved. Further, interference also occurs between the terminal 2-1 and the access point AP1.

  Therefore, as shown in FIG. 9 <Step 3> and FIG. 11, the directivity control shown in FIG. 5 is operated (steps S11 to S19), and the increase in transmission power is stopped (step S33). By doing so, the access point AP1 can perform communication without lowering the transmission power and the terminal 1-1 without lowering the transmission rate. Further, there is no problem in communication with the access point AP2.

  Further, when there is a newly installed access point AP3 (FIG. 10 <Step 4>), and interference increases, if the number of problematic interference exceeds the number of antennas, the interference can be sufficiently avoided. Disappear. Therefore, as shown in FIG. 11, it is determined whether or not the number of interferences of other cells exceeds the number of antennas (step S34), and if it exceeds, the transmission power of the access point AP1 is lowered (step S35). Further, with the processing operation shown in FIG. 5 in between, the transmission power of the access point AP1 is increased when the number of interferences of other cells does not exceed the number of antennas, and the access point when the number of interferences of other cells exceeds the number of antennas. By reducing the transmission power of AP1, it is possible to supply the highest possible transmission rate to the terminal while considering the amount of interference. The processing operation shown in FIG. 12 is the same as the processing operation described above.

  When a plurality of cells composed of an access point and a plurality of terminals communicating with the access point come close to each other, interference between the cells occurs, and it is necessary to avoid it. The conventional SDMA technique does not consider the case where the same frequency channel is shared by a plurality of radio cells, and there is a problem that transmission characteristics deteriorate in an environment where such cells are close to each other. On the other hand, OFDM (Orthogonal Frequency Division Multiplexing) is a kind of digital modulation method in which signals are put on a large number of subcarriers. In general, it is necessary to form a weight for each subcarrier during transmission. Even when OFDM is applied to the SDMA modulation scheme, it has been known as a prior art to provide the access point apparatus with the configuration shown in FIG. In the present invention, in SDMA-OFDM that applies OFDM to the modulation scheme of SDMA, a second transmission weight forming unit 10 is provided in the access point apparatus in order to avoid radio wave interference with other neighboring cells. The transmission weight forming unit 10 forms a weight value determined so as to avoid interference between cells based on only information of interference signals from other cells. This weight value is determined not for each subcarrier as in the past but for a common subcarrier. This makes it possible to avoid interference between cells in an environment where a plurality of SDMA cells exist.

  A program for realizing the functions of the transmission weight forming unit 10 and the transmission weight calculating unit 11 shown in FIG. 1 is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into a computer system. The transmission directivity control process may be performed by executing the control. Here, the “computer system” includes an OS and hardware such as peripheral devices. The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Further, the “computer-readable recording medium” refers to a volatile memory (RAM) in a computer system that becomes a server or a client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line. In addition, those holding programs for a certain period of time are also included.

  The program may be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the “transmission medium” for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. 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, what is called a difference file (difference program) may be sufficient.

  SDMA (Spatial Division Multiplexing) -OFDM (Orthogonal Frequency Division Multiplexing) can be applied to applications indispensable to efficiently realize.

  DESCRIPTION OF SYMBOLS 1 ... Data formation part, 2 ... Error correction part, 3 ... Interleaver, 4 ... Modulation part, 5 ... Transmission weight formation part, 6 ... IFFT part, 7 ... GI adding unit, 8 ... transmission weight calculation unit, 9 ... antenna, 10 ... transmission weight forming unit, 11 ... transmission weight calculation unit, AP1, AP2, AP3 ... access point

Claims (8)

A transmission directivity control device for controlling the transmission directivity of an access point device combining an orthogonal frequency division multiplex communication system and a space division multiple access system, each having a plurality of antennas and the same number of transmitters as the antennas,
First means for setting all values of transmission weight calculation results to 1, and causing the access point apparatus to acquire channel information from a terminal in its own cell;
A second means for measuring a signal to noise power ratio between the access point device and the terminal;
Third means for transmitting from the access point device to the terminal a prohibition signal not to transmit only the terminal in the own cell for a certain period of time;
A fourth means for receiving a signal from another cell and estimating an interference power during the predetermined time;
A fifth means for obtaining a value of a power ratio between the signal power and the power obtained by adding interference and noise from the interference power;
Sixth means for calculating a weight value for realizing interference cancellation when the minimum value of the power ratio value in the terminal is equal to or less than a threshold value, and giving the weight value to the received signal; ,
A seventh means for setting all of the weight values to 1 when the minimum value of the power ratio is equal to or greater than the threshold;
Eighth means for causing the access point device to acquire channel information from a terminal in its own cell using the weight value;
Ninth means for calculating a transmission weight value for the space division multiple access scheme from the channel information and giving the weight value;
Transmission directivity control apparatus characterized by having a. A transmission directivity control device for controlling the transmission directivity of an access point device combining an orthogonal frequency division multiplex communication system and a space division multiple access system, each having a plurality of antennas and the same number of transmitters as the antennas,
First means for causing the access point apparatus to acquire channel information from terminals in its own cell with weight values all set to 1,
A second means for measuring a signal-to-noise power ratio between the access point device and the terminal;
A third means for transmitting a control signal for preventing a signal from being transmitted for a certain period to an access point apparatus or terminal capable of receiving a signal from the access point apparatus or terminal in the own cell;
A fourth means for estimating interference power of other than the access point device or terminal prohibited from transmitting during the certain period;
A fifth means for obtaining a value of a power ratio between the signal power and the power obtained by adding interference and noise from the interference power;
Sixth means for calculating a weight value for realizing interference cancellation when the minimum value of the power ratio value in the terminal is equal to or less than a threshold value, and giving the weight value to the received signal; ,
A seventh means for setting all the weight values to 1 when a minimum value of the power ratio value is equal to or greater than a threshold;
Eighth means for causing the access point device to acquire channel information from the access point device or terminal that has been prohibited from transmission using the weight value;
Ninth means for calculating a transmission weight value for interference cancellation from channel information from an access point device or terminal other than the own cell;
A tenth means for multiplying the channel information of the access point device or terminal of the own cell by the transmission weight value;
Eleventh means for calculating a transmission weight value for SDMA and giving the weight value to a signal obtained by multiplying the transmission weight value;
A transmission directivity control apparatus comprising: Transmission directivity control method in transmission directivity control apparatus for controlling transmission directivity of access point apparatus combining orthogonal frequency division multiplex communication system and space division multiple access system having a plurality of antennas and the same number of transmitters as the antennas Because
All values of transmission weight calculation results are set to 1, and the access point apparatus acquires channel information from a terminal in its own cell;
A second step of measuring a signal to noise power ratio between the access point device and the terminal;
A third step of transmitting, from the access point device to the terminal, a prohibition signal not to transmit only the terminal in the own cell for a certain period of time;
A fourth step of receiving a signal from another cell and estimating an interference power during the predetermined time;
A fifth step of obtaining a value of a power ratio between the signal power and the power obtained by adding interference and noise from the interference power;
A sixth step of calculating a weight value for realizing interference cancellation and giving the weight value to the received signal when a minimum value of the power ratio value in the terminal is equal to or less than a threshold value; ,
A seventh step of setting all the weight values to 1 when a minimum value of the power ratio value is equal to or greater than the threshold;
An eighth step in which the access point device acquires channel information from a terminal in the own cell using the weight value;
A transmission directivity control method, comprising: calculating a transmission weight value for the space division multiple access scheme from the channel information and giving the weight value. Transmission directivity control method in transmission directivity control apparatus for controlling transmission directivity of access point apparatus combining orthogonal frequency division multiplex communication system and space division multiple access system having a plurality of antennas and the same number of transmitters as the antennas Because
A first step in which the access point device acquires channel information from terminals in its own cell with a weight value of all 1;
A second step of measuring a signal to noise power ratio between the access point device and the terminal;
A third step of transmitting a control signal for preventing a signal from being transmitted for a certain period to an access point device or terminal capable of receiving a signal from the access point device or terminal in the own cell;
A fourth step of estimating an interference power other than an access point device or a terminal prohibited from transmitting during the certain period;
A fifth step of obtaining a value of a power ratio between the signal power and the power obtained by adding interference and noise from the interference power;
A sixth step of calculating a weight value for realizing interference cancellation and giving the weight value to the received signal when a minimum value of the power ratio value in the terminal is equal to or less than a threshold value; ,
A seventh step of setting all the weight values to 1 when a minimum value of the power ratio value is equal to or greater than a threshold;
An eighth step in which the access point device acquires channel information from the access point device or terminal that has been prohibited from transmission using the weight value;
A ninth step of calculating a transmission weight value for interference cancellation from channel information from an access point device or terminal other than the own cell;
A tenth step of multiplying the channel information of the access point device or terminal of the own cell by the transmission weight value;
A transmission directivity control method comprising: an eleventh step of calculating a transmission weight value for SDMA and giving the weight value to a signal obtained by multiplying the transmission weight value. If another cell is a conventional system and communication with the access point device for acquiring propagation channel information is not possible, the steps are replaced with the eighth step, the ninth step, the tenth step, and the eleventh step. And
A twelfth step of calculating a weight value for realizing interference cancellation and giving the weight value to the received signal;
A thirteenth step in which the access point apparatus acquires channel information from a terminal in its own cell using the weight value;
5. The transmission directivity control method according to claim 4, wherein a transmission weight value for the space division multiple access scheme is calculated from the channel information, and the fourteenth step of giving the weight value is performed. Before starting the ninth step from the first step, a tenth step of increasing the transmission power of the access point device;
After performing the first step to the ninth step, if the number of interference signals obtained exceeds the number of antennas of the access point device, the transmission power of the access point device is reduced and the obtained interference The transmission directivity control method according to claim 3, further comprising an eleventh step of increasing transmission power of the access point device when the number of signals does not exceed the number of antennas of the access point device. . Before starting the eleventh step from the first step, a twelfth step of increasing the transmission power of the access point device;
After performing the eleventh step from the first step, if the number of interference signals obtained exceeds the number of antennas of the access point device, the transmission power of the access point device is reduced and the obtained interference The transmission directivity control method according to claim 4, further comprising a thirteenth step of increasing transmission power of the access point device when the number of signals does not exceed the number of antennas of the access point device. .   The weight value for realizing the interference cancellation is obtained by multiplying an inverse matrix of the correlation matrix of the received signal and an arbitrary vector in which all elements are other than 0, by receiving a signal of a terminal not communicating with the access point device. The transmission directivity control method according to claim 3, wherein the transmission directivity control method is obtained.

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