JP4538039B2 - Communication system and communication method - Google Patents

Description

  The present invention provides a communication system and communication for efficiently performing space division multiplex transmission in a multi-user environment by using cooperative interference cancellation technology using a relay station even in an environment where interference waves from adjacent cells exist. Regarding the method.

  In recent years, in mobile phones and wireless LAN systems, techniques for realizing ultrahigh-speed wireless communication of about 100 Mbps to 1 Gbps with a limited frequency Teshiro have been studied. In order to realize such a wireless communication system, not only the frequency, time, and code are divided for each user terminal, but also the transmission rate is improved while the frequency utilization efficiency is improved by the technology using the spatial domain. Is being studied.

  As a technology for that purpose, MIMO (Multiple-Input Multiple-Output) technology has attracted much attention. 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 on the receiving station side using the same plurality of antennas. 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.

  The theoretical maximum transmission capacity C using the MIMO technology can be theoretically derived from the following equation (1). This fact is described in Non-Patent Document 1, for example.

In the above equation (1), ρ is a signal-to-noise power ratio, M is the number of transmitting antenna elements, and the vector I _N is a unit matrix of N × N receiving elements. A vector H is a transfer function matrix representing a propagation channel response between the transmission antenna and the reception antenna, and can be described by the following equation (2).

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 MIMO increases in proportion to the number of both antenna elements for transmission and reception. Here, since the base station antenna has relatively few hardware restrictions, it can be allowed to increase the number of elements. However, when considering a small terminal, a large number of antenna elements cannot be arranged.

As a technique for solving this problem, a multi-user MIMO technique shown in FIG. 11 has been proposed. This fact is disclosed in, for example, Document 1 (QH Spencer et. Al IEEE Trans. Sig. Processing, vol. 52, no. 2, Feb. 2004). As shown in the figure, in multi-user MIMO, a large number of antenna elements are provided on the base station 1 side, and a relatively small number of elements are provided on the terminals MS # 1, MS # 2, and MS # 3 side. A virtual MIMO channel is simultaneously formed with terminals MS # 1-MS # 3. Here, assuming that the total number of terminals simultaneously connected to the base station 1 is N and the number of antennas of the base station 1 is M, ideally, the channel capacity obtained by the equation (1) can be obtained. Therefore, multi-users are attracting attention as a technology that can increase the communication capacity of the total system even when considering a small terminal.
Mohinder Jankiraman, Space-time codes and MIMO systems, Artech House Inc., 2004, p.23-24.

  The above-described MIMO and multi-user MIMO techniques have problems as shown in FIG. As shown in FIG. 12, generally, in a wireless communication system such as an outdoor system represented by a cellular system or the like, a multi-cell environment in which a plurality of base stations have respective service areas, and the own cell (a certain base station serves) Signals not only from terminals in the area) but also from neighboring cells (areas served by other base stations) arrive as interference.

  Here, when the signal transmission / reception timing is synchronized between the cells, the amount of interference can be suppressed relatively, but in this case, control in the system becomes complicated. On the other hand, let us consider operating autonomously between the access points AP shown in FIG. In this case, for example, as shown in the figure, when an access point AP with which a certain terminal (mobile station) MS communicates is located at the end of a zone (inside the dotted circle) formed by this access point AP, The signal from the terminal MS from the neighboring cell causes the largest interference (thick arrow).

  In general, MIMO or multi-user MIMO technology is assumed to be used in an environment such as an indoor wireless LAN or a hot spot, not in such a multi-cell environment, and has been evaluated in a so-called single cell environment. However, in an actual outdoor environment, it is necessary to assume a multi-cell environment. In this case, there is a problem that interference from surrounding cells degrades the MIMO transmission characteristics.

  In the MIMO and multi-user MIMO techniques, generally, a process of separating a plurality of signals on the receiving side is performed. As a method for separating the plurality of signals, a ZF (Zero Forcing) method and an MMSE (Minimum Mean Square) method are well known. This fact is disclosed in Document 2 (Daibell, basic and elemental technology of MIMO system, design / analysis method workshop in antenna / propagation, W29, 30) and the like.

FIG. 13 is a conceptual diagram showing interference removal when the ZF method is used. If this method is applied and the propagation channel can be estimated even for the interference signal, the ZF method or the MMSE method can be used to remove the interference wave from the neighboring cells. In FIG. 13, h represents the channel response between the transmitting station and the receiving station. In FIG. 11, assuming that the desired signal and the interference signal are S and I, the signals x ₁ and x ₂ received by the antennas # 1 and # 2 of the terminal MS are given by the following equations (3) and (4).

  Here, n represents thermal noise. Formulas (3) and (4) are expressed as a matrix by the following formula (5).

  In the above formula (3), if the noise power is ignored, the interference signal can be estimated by the following formula (6).

  Here, tilde (~: superscript wavy line symbol) s and tilde (~) i are estimated values of the desired signal and the interference signal, respectively. The desired signal can be restored by ZF according to Equation (6). At this time, the interference signal is completely removed.

  However, in general, when implementing MIMO or multi-user MIMO, it is assumed that the number of signals equal to or close to the number of antennas of the terminal is space division multiplexed. In other words, if additional interference waves are added, the total number of signals is the same as or exceeds the number of antennas of the terminal. In such an environment, it is known that the characteristics of the ZF method and the MMSE method due to interference removal are greatly deteriorated. This is because the noise power is ignored in deriving the equation (6) from the equation (5). However, if the number of signals increases, the noise power cannot actually be ignored. This fact is disclosed in, for example, Reference 3 (Nishimori et al., Effect of MIMO-ZF Configuration Using Transmission Selection Diversity in Indoor Real Environment, IEICE Society Conference Proposal, B-243). Therefore, it is necessary to provide a technology capable of realizing multi-user MIMO transmission even in an environment such as multi-cell.

  The present invention has been made in view of such circumstances, and an object of the present invention is to realize efficient multi-user MIMO transmission in a multi-cell environment even when there is interference from neighboring cells. It is an object of the present invention to provide a communication system and a communication method.

  In order to solve the above-described problem, the present invention communicates with the base station in an environment in which other interference waves arrive when the base station and at least one terminal communicate at the same frequency. The base station includes two or more antenna elements, the terminal includes one or more antenna elements, and the relay station includes the interference station. First estimation means for estimating a section in which the interference wave arrives and a section in which the interference wave does not arrive based on a training section that is known by the base station and the terminal, and a received signal in the training section, And a second estimating means for estimating a first transfer function between the interference wave and itself using the training section and a received signal from the training section, and the relay station, Interference wave With incoming non interval, a communication system, characterized by transferring the interference wave to the terminal.

  According to the present invention, in the above invention, the base station includes transmission timing determining means for adjusting a transmission timing to the terminal at a time when the interference wave arrives, the transmission timing, and the interference wave Transmission control means for transmitting a signal to the terminal using directivity such that a received signal is substantially zero with respect to the relay station in a data section other than a training section.

  According to the present invention, in the above invention, the relay station estimates third interference means for estimating an interference wave in the data section based on a received signal in the data section and the first transfer function, Interference signal transmission means for temporarily stopping the transmission signal from the base station and transmitting the interference wave estimated by the third estimation means to the terminal using a section in which the interference wave does not arrive. It is characterized by.

  According to the present invention, in the above invention, the terminal uses a training interval for the interference wave to perform a second transfer function between the base station and the terminal, and a third transfer function between the interference wave and the terminal. And a fourth estimation unit for estimating a fourth transfer function between the relay station and the terminal, and the transmission timing from the base station to a data section other than the training section of the interference wave The received signal at the terminal of the transmitted signal, the received signal at the terminal of the interference wave transmitted from the relay station using the section where the interference wave does not arrive, and the third transfer function And an interference wave removing means for removing the interference wave.

  In order to solve the above-described problem, the present invention communicates with the base station in an environment in which other interference waves arrive when the base station and at least one terminal communicate at the same frequency. A communication method using a communication station that has not been used as a relay station, based on a training section that the interference wave has known by the base station and the terminal and a received signal in the training section. A first step of estimating a section in which the interference wave arrives and a section in which the interference wave does not arrive, and the relay station using the training section and a received signal from the training section, A second step of estimating a first transfer function between the base station and the terminal, and a second step of notifying the base station and the terminal of the first transfer function estimated in the second step by the relay station The step of adjusting the transmission timing to the terminal at the time when the interference wave arrives by the base station, and the base station and the base station using the training period of the interference wave by the terminal. A fifth step of estimating a second transfer function between terminals, a third transfer function between the interference wave and the terminal, and a fourth transfer function between the relay station and the terminal; and In the data period other than the training period of the interference wave at the transmission timing, a signal is transmitted to the terminal using directivity such that the reception signal becomes almost zero with respect to the relay station. A sixth step, a seventh step of estimating an interference wave in the data section based on a received signal in the data section and the first transfer function by the relay station; An eighth step of temporarily stopping the transmission signal from the base station by a station and transmitting the interference wave estimated in the seventh step to the terminal using a section in which the interference wave does not arrive; By the terminal, the signal received at the terminal of the signal transmitted from the base station in the sixth step, and the signal received at the terminal of the interference wave transmitted from the relay station in the eighth step, And a ninth step of removing interference waves based on the third transfer function estimated in the fifth step.

  In the present invention according to the above invention, in the eighth step, when the number of antennas of the relay station is N and the number of antennas of the terminal is M, the interference wave estimated in the seventh step is It is characterized by performing K division (K is the minimum value of M and N) and transmitting from K antennas.

  In the present invention according to the above invention, the fifth step divides the training section into a first section, a second section, and a third section. In the first section, the base station Stop transmission, stop transmission of the relay station, and based on the received signal of the terminal in the first section and the interference wave in the first section, a third between the interference wave and the terminal In the second interval, the base station transmits a signal, the relay station stops transmitting, the received signal of the terminal in the second interval, and the second interval A fourth transfer function between the relay station and the terminal is estimated on the basis of the interference wave at and the third transfer function, and the transmission of the base station is stopped in the third interval, and the relay Transmitting a signal to a station, and the terminal in the third section A reception signal, the interference wave in the third section, on the basis of said third transfer function to estimate the second transfer function between the said base station terminal, characterized in that

  According to the present invention, in the relay station, based on the training section known by the base station and the terminal that the interference wave has and the received signal in the training section, the section in which the interference wave arrives and the section in which the interference wave does not arrive The first transfer function between the interference wave and itself is estimated using the training section and the received signal from the training section, and the interference wave is calculated using the section where the interference wave does not arrive. Transfer to the terminal. Therefore, even if there is interference from neighboring cells in a multi-cell environment, there is an advantage that efficient multi-user MIMO transmission can be realized.

  Further, according to the present invention, the base station adjusts the transmission timing to the terminal to the time when the interference wave arrives, and the relay station transmits the transmission timing in a data section other than the interference wave training section. On the other hand, the signal is transmitted to the terminal using directivity such that the received signal becomes almost zero. Therefore, even if there is interference from neighboring cells in a multi-cell environment, there is an advantage that efficient multi-user MIMO transmission can be realized.

  Further, according to the present invention, the relay station estimates the interference wave in the data section based on the received signal in the data section and the first transfer function, temporarily stops the transmission signal from the base station, and performs interference. The estimated interference wave is transmitted to the terminal using a section in which no wave arrives. Therefore, even if there is interference from neighboring cells in a multi-cell environment, there is an advantage that efficient multi-user MIMO transmission can be realized.

  Also, according to the present invention, the terminal uses the interference wave training section to use the second transfer function between the base station and the terminal, the third transfer function between the interference wave and the terminal, and between the relay station and the terminal. The fourth transfer function of the received signal, the transmission timing, and the received signal at the terminal of the signal transmitted from the base station in the data section other than the training section of the interference wave, and the section where the interference wave does not arrive Is used to remove the interference wave based on the received signal at the terminal of the interference wave transmitted from the relay station and the third transfer function. Therefore, even if there is interference from neighboring cells in a multi-cell environment, there is an advantage that efficient multi-user MIMO transmission can be realized.

  Further, according to the present invention, the relay station causes the interference wave that is known to be received between the base station and the terminal, and the interval in which the interference wave arrives and the period that does not arrive based on the received signal in the training interval. The relay station estimates the first transfer function between the interference wave and itself using the training section and the received signal from the training section, and the relay station uses the first transfer function to estimate the first transfer function. To the base station and the terminal, the base station adjusts the transmission timing to the terminal at the time when the interference wave arrives, and the terminal uses the interference wave training section to set the second interval between the base station and the terminal. Estimate the transfer function, the third transfer function between the interference wave and the terminal, and the fourth transfer function between the relay station and the terminal, and the transmission timing by the base station and other than the training interval of the interference wave Data area In this case, a signal is transmitted to the terminal using directivity such that the received signal becomes substantially zero with respect to the relay station, and the relay station transmits data based on the received signal in the data section and the first transfer function. Interference waves in the section are estimated, the transmission signal from the base station is temporarily stopped by the relay station, and the estimated interference wave is transmitted to the terminal using the section in which no interference wave arrives. The interference wave is removed based on the received signal of the transmitted signal at the terminal, the received signal of the interference wave transmitted from the relay station at the terminal, and the estimated third transfer function. Therefore, even if there is interference from neighboring cells in a multi-cell environment, there is an advantage that efficient multi-user MIMO transmission can be realized.

  Further, according to the present invention, assuming that the number of antennas of the relay station is N and the number of antennas of the terminal is M, the estimated interference wave is divided into K (K is the minimum value between M and N). , Transmit from K antennas. Therefore, it is not necessary to use all the time in the section where the interference wave does not arrive, and there is an advantage that communication efficiency can be improved.

  Further, according to the present invention, the training section is divided into the first section, the second section, and the third section, and the base station transmission is stopped and the relay station transmission is stopped in the first section. The third transfer function between the interference wave and the terminal is estimated based on the received signal of the terminal in the first section and the interference wave in the first section, and the signal is sent to the base station in the second section. , And the transmission of the relay station is stopped. Based on the received signal of the terminal in the second section, the interference wave in the second section, and the third transfer function, the fourth between the relay station and the terminal is transmitted. In the third interval, the transmission of the base station is stopped, the signal is transmitted to the relay station, the received signal of the terminal in the third interval, the interference wave in the third interval, Based on the transfer function of 3, the second transfer function between the base station and the terminal is estimated. Therefore, even if there is interference from neighboring cells in a multi-cell environment, there is an advantage that efficient multi-user MIMO transmission can be realized.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a conceptual diagram showing a communication operation by the communication system according to the present embodiment.
In this embodiment, as shown in FIG. 1, in order to send a signal received by a relay station IS (Interference station) to terminals MS # 1 and # 2 and to estimate a propagation channel of an interference signal, an access point AP and the terminal MS # 1, the communication timing between # 2, is characterized in that the interval t ₁ shown in FIG. Further, when the interference wave is transmitted from the relay station IS to the terminals MS # 1 and # 2, it is characterized by a section where the interference wave does not arrive (section t _{2 in} FIG. 2 described later).

  FIG. 2 is a conceptual diagram showing a format of an interference signal. FIG. 2 shows the arrival timing of signals when using TDMA (Time Division Multiple Access). In TDMA, signals are periodically transmitted as shown in FIG. In addition, a signal for establishing synchronization between the access point AP and the terminal MS called a preamble or a unique word is provided at the head of the communication signal. Such a signal is generally called a training signal. Even if this signal is an interference wave of a neighboring cell, this form does not change.

  Further, the signal sequence of this training signal, that is, the bit pattern is different between the uplink (MS → AP) and the downlink (AP → MS). Therefore, in the relay station IS shown in FIG. 1, when interference is received from neighboring cells when signals are transmitted from the access point AP to the terminals MS # 1 and # 2, they can be distinguished. Therefore, the relay station IS can estimate the interference wave from the neighboring cell.

FIG. 3 is a block diagram showing a schematic configuration of the terminal MS according to the present embodiment. Note that the basic configuration is omitted. In FIG. 3, terminals MS # 1 and # 2 include a transfer function estimation unit 10-1 (fourth estimation unit) and an interference wave removal unit (interference wave removal unit) 10-2. Transfer function estimating unit 10-1, based on the interference wave of the preamble section _{(t 1),} between the access points AP- terminal MS, interference - between the terminals MS, and estimates the transfer function between the relay station IS- terminal MS . Interference wave removal unit 10-2, the received signal in the data section of the interfering wave (other than the preamble section in the t _1), in a section in which the interference wave does not arrive (t _2), when the divided transmitted from the relay station IS The interference wave is removed according to the received signal and the transfer function between the interference and the MS estimated by the transfer function estimating unit 10-1.

FIG. 4 is a block diagram showing a schematic configuration of the relay station IS according to the present embodiment. Note that the basic configuration is omitted. In FIG. 4, the relay station IS includes an interference wave arrival time estimation unit 20-1 (first estimation unit), a transfer function estimation unit (second estimation unit) 20-2, and a data section interference signal estimation unit ( (3rd estimation means) 20-3 and the interference signal transmission part (interference signal transmission means) 20-4 are provided. Interference arrival time estimation section 20-1, using the interference wave of the preamble section (t _1), the interference signal to estimate and time not arrive to the time arrives. The transfer function estimation unit 20-2 estimates the transfer function between interference and IS from the received signal and the preamble of the interference wave.

The data section interference signal estimation unit 20-3 uses the received signal by itself in the data section and the interference-IS transfer function obtained by the transfer function estimation unit 20-2 to generate the interference signal in the data section. presume. The interference signal transmission unit 20-4 divides the interference signal into K using the section (t ₂ ) where no interference wave arrives, and transmits it to the terminal MS using K antennas (K = min (M, N): M: number of IS antennas, N: number of MS antennas).

FIG. 5 is a block diagram showing a schematic configuration of the access point AP according to the present embodiment. Note that the basic configuration is omitted. In FIG. 5, the access point AP includes a transmission timing determination unit (transmission timing determination unit) 30-1 and a transmission control unit (transmission control unit) 30-2. Transmission timing determination unit 30-1 is notified of the transfer function from the relay station IS, adjust the transmission timing of itself in time interval t _1. Transmission control unit 30-2 in the data section of the interference wave (other than the preamble section in the t _1), transmits a signal to the terminal MS in directivity as the reception signal becomes 0 to the relay station IS.

FIG. 6 is a flowchart for explaining a control procedure according to the present embodiment.
First, the relay station IS utilizes the interference wave of the preamble interval (t _1), the interference signal to estimate a time that does not arrive to the time arrives, the interference -IS from the received signal and the preamble of the interference wave A transfer function is estimated (step S1: first and second steps). Specifically, first, the arrival of interference waves from neighboring cells is observed. As a reference for observation, a training signal of interference waves from neighboring cells is used. If the transfer function can be estimated from the training signal of this interference wave, it means that the interference signal is large.

That is, this interference signal affects multi-user MIMO transmission. Also, as shown in FIG. 2, if the training signal of the interference wave can be decoded, the interval t ₁ that arrives after that can also be estimated. Further, the interval t ₂ of the interference signal does not arrive can be estimated. Further, by using the received signal x (j) in the training signal i _p and its interference waves, it is possible to estimate the transfer function h _EI of interference between relay station IS _(j) by the following equation (7). Here, j represents the j-th antenna of the relay station IS.

Next, the relay station IS notifies the transfer function estimated in step S1 to the access point AP and the terminals MS # 1 and # 2 (step S2: third step). In response to this, the access point AP matches the transmission timing to the terminal MS with the section t ₁ where the interference wave arrives (step S2: fourth step). In practice, this starts with the next frame. By this processing, in the case of FIG. 1, the head of the transmission timing of the access point AP becomes the training section of the interference wave of FIG.

Next, the terminal MS # 1, # 2, the interference wave of the preamble section (FIG. 1: in _{t 1)} utilizing, inter access point AP- terminal MS, interference - between the terminal MS, between the relay station IS- terminal MS Is estimated (step S3: fifth step).

Here, FIG. 7 is a conceptual diagram showing a signal transmission section for transfer function estimation according to the present embodiment. As shown in FIG. 7, since the interference signal arrives in all the sections, first, in section 1, the transfer function h _EM between the interference and terminal MS is expressed as signal x _p1 received at terminal MS in section 1 The interference wave training signal _ip1 of this section is used for estimation. When the terminal MS includes a plurality of antennas, the same processing is performed on each antenna of the terminal MS according to the following equation (8).

Next, in section 2, the transfer function h _IM (j) between the relay station IS and the terminal MS is estimated using the received signal x _P3 (j) and the training signal S _P ′ (j) from the relay station IS. (J is the j-th antenna of the relay station IS, j = 1 to L). However, since the interference signal is also included in this section 2, by using the result estimated in the section 1 and the training signal i _P3 (j) of the interference in this section 2, between the relay station IS and the terminal MS Estimate the transfer function. Further, since relay station IS has a plurality of antennas, time interval 2 is divided into the number of antennas (L) in time, and the transfer function between relay station IS and terminal MS is estimated for each division. . When the terminal MS includes a plurality of antennas, the same processing is performed on each antenna of the terminal MS according to the following equation (9).

Next, in section 3, the transfer function h _AM (k) between the access point AP and the terminal MS is estimated using the received signal x _P2 (k) and the training signal S _P (k) from the access point AP. (K is the k-th antenna of the access point AP, and k = 1 to M). However, since 3 includes an interference signal in this section, the result of estimation in section 1 and the training signal i _P2 (k) of interference in this section 3 are used between the access point AP and the terminal MS. Estimate the transfer function of. Further, since the access point AP has a plurality of antennas, the time interval 2 is divided into the number of antennas (M) in time, and the transfer function between the access point AP and the terminal MS is estimated for each division. . When the terminal MS includes a plurality of antennas, the same processing is performed on each antenna of the terminal MS according to the following equation (10).

Next, the access point AP, the data section of the interference wave: (Figure 2 preamble except interval in t _1), the terminal MS # 1 in such a directivity reception signal becomes 0 to the relay station IS, # 2 is transmitted (step S4: sixth step). By controlling in this way, the relay station IS can receive only the interference signal. Further, since the access point AP and the relay station IS are in the relationship between the base station and the relay station, the transfer function between the two can be estimated in advance, and since this fluctuation is small, the relay prepared by the access point AP in advance. From the transfer function of the station IS, it is possible to generate directivity such that the received signal is 0 from the access point AP to the relay station IS. Therefore, in the data section, the received signals obtained by the terminal MS and the relay station IS can be given by the following equations (11) and (12). Here, the desired signal and the interference signal in the data section are s _D and i _D , respectively.

Next, the relay station IS estimates the interference signal in the data section using the received signal in the data section and the transfer function between the interference and the relay station IS obtained in step S1, that is, Equation (13). Step S5: Seventh step). Here, i _D represents an interference signal in the estimated data section.

Next, the relay station IS divides the interference signal into terminals MS # 1 and # 2 using the section (t ₂ ) where no interference wave arrives, and transmits it to K terminals using K antennas (K = min (M , N): M; number of IS antennas, N: number of MS antennas), and the terminals MS # 1 and # 2 receive the interference signal divided and transmitted from the relay station IS (step S6: eighth) Step).

  Here, in the present embodiment, when the interference signal has a plurality of antenna elements in both the relay station IS and the terminals MS # 1 and # 2, the transmission signal of the interference signal is shortened by the MIMO technology. .

FIGS. 8A to 8C are conceptual diagrams showing the relationship of arrival timings of desired signal transmission (AP → MS), interference → MS, and IS → MS for each number of antenna elements of the MS. As shown in FIGS. 8A to 8C, if the relay station IS has the same number of antennas as the terminal MS, and the terminal MS has a plurality of antennas, FIGS. ), The interference signal can be divided and transmitted for each antenna. This is because it is not necessary to use all the time in the interval t _2, there is an advantage that it is possible to improve the communication efficiency.

  Next, the terminal MS uses the received signal of the terminal MS obtained in step S4, the received signal of the terminal MS obtained in step S6, and the interference-MS transfer function obtained in step 3 to The interference wave is removed according to equation (14) (step S7: ninth step).

  According to the above-described embodiment, a desired signal can be estimated using an interference wave training section and the relay station IS even in an environment where an interference wave from a neighboring cell exists. In particular, since the relay station IS can transfer an interference signal to the terminal MS at the same time, it is effective when a multi-user receives interference at the same time.

Next, the effect by this embodiment is demonstrated using computer simulation. The communication efficiency E _f was evaluated using the following equation (15). This is called normalized transmission efficiency.

Here, T _ew and T _eo are frequency utilization efficiencies [bit / s / Hz] that can be achieved when there is interference and when there is no interference in the case of one user. For simplification, the coefficient of propagation loss is set to 3.5. In the communication characteristics according to this embodiment, since estimation of the propagation channel is important, an error that is half proportional to the SNR (γ) is given to the actual channel as an actually assumed error. That is, assuming that the true transfer function is h, the channel h including an error is given by the following equation (16). Here, Δh represents a channel error. Here, h and Δh are complex numbers and follow a Gaussian distribution with an average of 0 and a variance of 0.

For the delay profile, an exponential distribution model was used. The delay dispersion is 100 ns, and the angular spread between the access point AP and the terminal MS is 10 degrees and 360 degrees. An environment where one interference wave exists was assumed. The number of antennas of the access point AP, the relay station IS, and the terminal MS is 12, 6, and 4, respectively, so that the interference wave + the desired wave becomes 4 waves. The SNR simulates the service area edge of the terminal MS, and changes with SNR = 10 to 20 dB. The terminal MS was placed at a plurality of positions, and 10000 trials were performed, and an average value of each achievable frequency utilization efficiency was obtained. The modulation method used for transmission was determined from SINR satisfying BER = 10 ⁻³ . Since the relationship between BER and SINR can be obtained by an error function, BER was obtained from SINR using this function. As a comparison, interference removal using the ZF method known as a MIMO decoding method was compared.

FIG. 9 is a conceptual diagram showing the positional relationship between the access point AP and the relay station IS. As shown in the figure, assuming that the communication area between the access point AP and the terminal MS is d _max , four relay stations IS are arranged at a half distance (d _max / 2).

  FIG. 10 is a diagram showing the effect of this embodiment. The horizontal axis represents the number of users, and the vertical axis represents normalized transmission efficiency. When the number of users is 1, transfer of interference waves is not efficient, so the ZF method according to the prior art can obtain higher efficiency. However, if the number of users increases, the interference waves can be transferred to the users at the same time. It can be seen that the communication method according to the embodiment shows higher efficiency. Therefore, this embodiment can perform efficient transmission with respect to the conventional method when interference exists in multi-user MIMO.

It is a conceptual diagram which shows the communication operation | movement by the communication system by this embodiment. It is a conceptual diagram which shows the format of an interference signal. It is a block diagram which shows the schematic structure of terminal MS by this embodiment. It is a block diagram which shows the schematic structure of the relay station IS by this embodiment. It is a block diagram which shows the schematic structure of access point AP by this embodiment. It is a flowchart for demonstrating the control procedure by this embodiment. It is a conceptual diagram which shows the signal transmission area for the transfer function estimation by this embodiment. It is a conceptual diagram which shows the relationship of the arrival timing of the time of transmission of a desired signal (AP-> MS), interference-> MS, IS-> MS for every number of antenna elements of MS. It is a conceptual diagram which shows the positional relationship of access point AP and relay station IS. It is a figure which shows the effect by this embodiment. It is a conceptual diagram for demonstrating the multiuser MIMO technique by a prior art. It is a conceptual diagram for demonstrating the problem by the MIMO and multiuser MIMO technique by a prior art. It is a conceptual diagram which shows the interference removal at the time of using the ZF method by a prior art.

Explanation of symbols

IS relay station AP access point MS terminal 10-1 transfer function estimation unit 10-2 interference wave removal unit 20-1 interference wave arrival time estimation unit 20-2 transfer function estimation unit 20-3 data section interference signal estimation unit 20-4 Interference signal transmission unit 30-1 transmission timing determination unit 30-2 transmission control unit

Claims (7)

A communication system that uses a communication station that is not communicating with the base station as a relay station in an environment in which other interference waves arrive when a base station and at least one terminal communicate at the same frequency. ,
The base station comprises two or more antenna elements,
The terminal comprises one or more antenna elements;
The relay station has a section in which the interference wave arrives and a section in which the interference wave does not arrive based on a training section known by the base station and the terminal and a received signal in the training section. First estimating means for estimating, and second estimating means for estimating a first transfer function between the interference wave and itself using the training section and a received signal from the training section. And
The said relay station transfers the said interference wave to the said terminal using the area where the said interference wave does not arrive, The communication system characterized by the above-mentioned. The base station
Transmission timing determining means for adjusting the transmission timing to the terminal at the time when the interference wave arrives;
Transmission that transmits a signal to the terminal using directivity such that a reception signal is substantially zero with respect to the relay station in a data period other than the training period of the interference wave at the transmission timing. Control means;
The communication system according to claim 1, further comprising: The relay station is
Third estimation means for estimating an interference wave in the data section based on the received signal in the data section and the first transfer function;
An interference signal transmission means for temporarily stopping the transmission signal from the base station and transmitting the interference wave estimated by the third estimation means to the terminal using a section in which the interference wave does not arrive;
The communication system according to claim 2, further comprising: The terminal
Using the training period of the interference wave, a second transfer function between the base station and the terminal, a third transfer function between the interference wave and the terminal, and a fourth transfer function between the relay station and the terminal. A fourth estimating means for estimating a transfer function;
Using the received signal at the terminal of the signal transmitted from the base station in the data interval other than the training interval of the interference wave and the interval where the interference wave does not arrive at the transmission timing, Interference wave removing means for removing the interference wave based on the received signal of the interference wave transmitted from the relay station at the terminal and the third transfer function;
The communication system according to claim 3, further comprising: When a base station and at least one terminal communicate at the same frequency, a communication method using a communication station that is not communicating with the base station as a relay station in an environment in which other interference waves arrive. ,
The relay station estimates a section in which the interference wave arrives and a section in which the interference wave does not arrive based on a training section of the interference wave known by the base station and the terminal and a received signal in the training section. A first step to:
A second step of estimating, by the relay station, a first transfer function between the interference wave and itself using the training section and a received signal from the training section;
A third step of notifying the base station and the terminal of the first transfer function estimated in the second step by the relay station;
A fourth step of adjusting the transmission timing to the terminal by the time when the interference wave arrives by the base station;
The terminal uses the training interval of the interference wave to perform a second transfer function between the base station and the terminal, a third transfer function between the interference wave and the terminal, and between the relay station and the terminal. A fifth step of estimating a fourth transfer function of
The base station uses the directivity so that the received signal becomes almost zero with respect to the relay station in the data timing other than the training period of the interference wave at the transmission timing. A sixth step of transmitting a signal;
A seventh step of estimating an interference wave in the data section based on the received signal in the data section and the first transfer function by the relay station;
An eighth step of temporarily stopping a transmission signal from the base station by the relay station and transmitting the interference wave estimated in the seventh step to the terminal using a section in which the interference wave does not arrive; ,
The received signal at the terminal of the signal transmitted from the base station in the sixth step by the terminal, and the received signal at the terminal of the interference wave transmitted from the relay station in the eighth step. A ninth step of removing interference waves based on the third transfer function estimated in the fifth step;
A communication method comprising:   In the eighth step, when the number of antennas of the relay station is N and the number of antennas of the terminal is M, the interference wave estimated in the seventh step is divided into K (K is M and N 6. The communication method according to claim 5, wherein transmission is performed from K antennas. The fifth step includes
Dividing the training section into a first section, a second section, and a third section;
In the first section, the transmission of the base station is stopped, the transmission of the relay station is stopped, and based on the received signal of the terminal in the first section and the interference wave in the first section Estimating a third transfer function between the interference wave and the terminal;
In the second interval, the base station transmits a signal, the relay station stops transmission, the received signal of the terminal in the second interval, the interference wave in the second interval, and the first And a fourth transfer function between the relay station and the terminal based on the transfer function of 3;
In the third section, the base station stops transmission, the relay station transmits a signal, the received signal of the terminal in the third section, the interference wave in the third section, and the first section A second transfer function between the base station and the terminal is estimated based on a transfer function of 3;
The communication method according to claim 5.

Images