JP4889756B2 - Radio access system and mobile station apparatus - Google Patents

Description

  The present invention relates to a radio access system using an OFDM (Orthogonal Frequency Division Multiplexing) system and a mobile station apparatus thereof.

As a next-generation mobile communication system such as the 3.9th generation and the 4th generation, a wireless access system (OFDMA system) using the OFDM system is considered promising.
Various methods are known for effective use of frequencies when a service such as an OFDMA system is developed.
FIG. 12 is a diagram illustrating an example of a method for improving the geographical reuse rate of a frequency by increasing the distance between base stations using the same frequency and reducing the interference of the same frequency. (B) is a diagram of FFR (Fractional Frequency Reuse).
FIG. 12A shows N-cell frequency repetition when N = 3. In this case, the frequency utilization rate is approximately 1/3.
The example of FFR shown in FIG. 12B divides a common frequency band into four, uses the same frequency band at the center of each cell, and repeatedly uses other frequency bands at the peripheral part. It is. In this case, the frequency utilization factor is approximately ½, and the frequency utilization factor can be improved as compared with the conventional N-cell frequency repetition.
On the other hand, FIG. 13 is a diagram illustrating an example of repetition. The repetition is a method of realizing 1-cell frequency repetition using a common frequency band in all cells by repeatedly transmitting the same data M times to improve SIR. In the case of the example shown in the figure, the frequency reuse ratio is 1 because the cell frequency repetition is 1. However, since M = 3, the frequency utilization ratio considering the time axis is approximately 1. / 3.

In addition, an interference cancellation technique for removing the same frequency interference with high accuracy using a replica of a desired signal and an interference signal has been proposed (Patent Documents 1 and 2 and Non-Patent Document 1).
Furthermore, a method for suppressing an interference wave using an adaptive array antenna is also known. This is a technique for receiving a desired wave satisfactorily by adaptively controlling a directivity pattern that increases the gain in the desired wave direction and decreases the gain in the interference wave direction. This method is highly expected as a technology for increasing the frequency utilization efficiency in the third generation and later mobile communication systems (DS-CDMA and the like).

In recent years, a MIMO (Multiple-Input Multiple-Output) system having a plurality of antennas for a transmitter and a receiver has attracted attention. There are several transmission methods in a MIMO system, that is, a multi-antenna transmission method. The signal-to-noise ratio is improved by the diversity effect obtained by transmitting a single stream by space-time coding or beamforming, It is roughly divided into MIMO diversity whose main purpose is to improve transmission reliability and MIMO spatial multiplexing whose main purpose is to improve the transmission rate by transmitting a plurality of streams by spatial multiplexing (Non-patent Document 3). . Furthermore, in recent years, a method positioned as a hybrid type of MIMO diversity and MIMO spatial multiplexing has been proposed and studied (Non-Patent Documents 4 and 5). Note that these multi-antenna transmission methods and the reception methods thereof are described in detail in Non-Patent Document 3 and the reference thereof, and thus detailed description thereof is omitted here, but in the MIMO system, transmission is performed simultaneously. As a technique for separating and detecting a plurality of signals with high accuracy, that is, as one of elemental techniques essential for realizing the signal separation technique, various methods have been proposed and studied (Non-patent Document 3). .
Representative examples of signal separation techniques in MIMO spatial multiplexing include spatial filtering methods (ZF (zero-forcing) method, MMSE (minimum mean square error) method, etc.), signal detection based on maximum likelihood estimation (maximum likelihood determination, MLD: (maximum likelihood detection) method and MMSE QRD-M algorithm using the MMSE QR decomposition of the MIMO channel matrix and the M algorithm. MMSE-QRM-MLD method) is known (Non-Patent Documents 2 and 3).
In addition, for a MIMO system that has been error-corrected code (channel code), the maximum a posteriori probability (MAP: Maximum A posteriori Probability) An iterative signal detection method (MAP detection method) based on estimation has been proposed (Non-Patent Document 7). As a simplified algorithm for MAP detection, an SD (Sphere Decoding) algorithm (Non-Patent Documents 7 and 10). And Soft-Output M-Algorithm (Non-Patent Document 8) are known. It is known that these techniques can realize superior MIMO transmission characteristics compared to the above-mentioned ZF method, MMSE method, and MLD method by linking the signal separation technology and error correction decoding technology in error correction MIMO spatial multiplexing. Yes.
Furthermore, a system in which MIMO is applied to the OFDM system (Non-Patent Documents 2 and 6) and a simplified algorithm for soft input / soft output error correction decoding are also known (Non-Patent Document 11).

There is a demand for more efficient use of radio frequencies in wireless access systems.
However, as described above, it is difficult to achieve a frequency utilization factor of 1 with the methods shown in FIGS.
If one cell (sector) frequency repetition can be realized without repetition by inter-cell interference cancellation, the frequency utilization factor in the OFDMA system is greatly improved.
Although a method of performing inter-cell interference cancellation using a conventional interference cancellation technique is also conceivable, the conventional interference cancellation technique, for example, the technique described in Non-Patent Document 1, does not assume the OFDM scheme. In addition, in the inter-cell interference suppression technology using spatial filtering such as an adaptive array antenna, the number of interference waves that can be canceled simultaneously is (the number of elements of the array antenna-1), that is, not only the degree of freedom of the array, In order to suppress the interference wave, it is necessary to prepare a large number of elements. This restriction becomes severe when a spatial filtering technique based on linear signal processing such as the MMSE method used in an adaptive array antenna or the like is applied to a mobile station that cannot take up a large antenna installation space. In particular, when adopting a MIMO configuration that uses multiple antennas for transmission and reception, multiple signals are often transmitted simultaneously, and interference suppression technology using spatial filtering based on linear signal processing causes interference from neighboring cells. It becomes difficult to respond to waves. Therefore, it is necessary to apply an interference cancellation method based on nonlinear signal processing such as maximum likelihood estimation and MAP estimation, which is not limited by the number of antennas used on the transmission side and the reception side.
In order to efficiently eliminate inter-cell interference in OFDM, a reception timing shift (timing offset) including a multipath in a propagation path between a desired signal and an interference signal transmitted from different base stations is an OFDM guard interval ( GI), that is, synchronization between symbols is desirable. That is, when the reception timing difference between the desired signal and the interference signal exceeds the OFDM guard interval (GI), the demodulation accuracy is greatly deteriorated, so that synchronization control between base stations is necessary.

In addition, in order to realize highly accurate interference cancellation, parameters of a desired signal to be detected on the receiving side, that is, a signal modulation method / multi-antenna transmission method (for example, the number of transmission antennas and a precoding method) ) Etc., as well as parameters related to interference signals to be considered, that is, the number of neighboring cell base stations that cause interference and the transmission methods such as the signal modulation method and multi-antenna transmission method in each neighboring cell base station. It is necessary to grasp. In a simple system with a fixed transmission method, there is no need to acquire information such as the modulation method and multi-antenna transmission method on the receiving side, but at least the reception level that cannot be ignored compared to the reception level of the desired signal Information regarding the number of interference signals (hereinafter referred to as the number of interference signals) varies depending on the base station arrangement and the propagation environment, and thus needs to be acquired dynamically.
As a method for acquiring the information on the number of interference signals, it is possible to estimate by analyzing the received signal, but it is desirable that the method for acquiring the information can be simplified.
On the other hand, in recent years, an increasing number of systems have applied adaptive transmission (link adaptation) that performs adaptive switching control of transmission methods such as modulation methods and error correction coding rates according to the state of the propagation path. In the system, a mechanism for enabling the receiving side to recognize the adaptively switched transmission method is essential. However, the method of performing inter-cell interference cancellation using the conventional interference cancellation technique described in Non-Patent Document 1 or the like does not assume such adaptive transmission. Therefore, there is a problem that cannot be directly applied to a system that performs adaptive transmission.

Therefore, the present inventor has realized a one-cell frequency repetition (N = 1) without using repetition by an inter-cell interference canceller technique for removing an interference signal from a neighboring cell, so that a radio access system using OFDM is used. Have proposed a radio access system, a base station apparatus, and a mobile station apparatus in which the frequency utilization rate is greatly improved (Japanese Patent Application No. 2007-268108, Non-Patent Document 9).
This proposed radio access system uses all the base stations that interfere with each other when a plurality of base stations use a common frequency band in downlink transmission in a radio access system in which a base station and a mobile station communicate with each other by OFDM. The transmission timing of the station is controlled so that the shift of the reception timing including the multipath of the signal from each base station in the mobile station falls within the OFDM guard interval. Each base station is a pilot including a pilot signal. The mobile station transmits an OFDM signal in which a control channel including control information necessary for communication with at least a mobile station and a traffic channel including user data information are multiplexed. The own cell base station based on the pilot signal included in the received signal in the pilot signal section Means for acquiring channel information between the own mobile station and between each neighboring cell base station that causes interference and the own mobile station, and the control channel is demodulated for the own cell base station and neighboring cell base stations that cause interference And means for acquiring the control information of the own cell base station and each neighboring cell base station that causes interference, the obtained channel information, the obtained own cell base station, and control information for each neighboring cell base station that causes interference Based on the above, the desired signal from the own cell base station is detected from the received signal by detecting the desired signal from the own cell base station and the interference signal from the neighboring cell base station using MLD (maximum likelihood detection method) or the like. The signal separation means for separating the signal and the interference signal from the neighboring cell base station is provided, and the interference signal removal from the neighboring cell is realized by taking out only the desired signal from the plurality of separated signals.

JP-A-8-331025 No. 94/17600

Hitoshi Yoshino, Kazuhiko Fukawa, and Hiroshi Suzuki, "Interference Cancelling Equalizer (ICE) for Mobile Radio Communication," IEEE Transactions on Vehicular Technology, vol.46, no.4, pp.849-861, Nov. 1997. Sunmei Sun, Yongmei Dai, Zhongding Lei, Kenichi Higuchi, and Hiroyuki Kawai, "Pseudo-Inverse MMSE Based QRD-M Algorithm for MIMO OFDM," in Proceedings of IEEE VTC2006-Spring, vol.3, pp.1545-1549, Melbourne , Australia, May 2006. Takeo OHGANE, Toshihiko NISHIMURA and Yasutaka OGAWA, "Applications of Space Division Multiplexing and Those Performance in a MIMO Channel", IEICE Transactions on Communications, Vol.E88-B, No.5, pp.1843-1851, May 2005. EN Onggosanusi, AG Dabak, and TM Schmidl, "High Rate Space-time Block Coded Scheme: Performance and Improvement in Correlated Fading Channels," in Proccedings of IEEE WCNC2002, vol.1, pp.194-199, Orland, Florida, USA , March 2002. M.V.Do, W.H.Chin, and Y. Wu, "Performance Study on a Hybrid Space Time Block Coded System", in Proceedings of IEEE ISWPC2006, Phuket, Thailand, Jan. 2006. A. van Zelst, R. van Nee and G.A. Awater, "Space Division Multiplexing (SDM) for OFDM systems", in Proceedings of IEEE VTC2000-Spring vol.2, pp.1070-1074, Tokyo, Japan, May 2000. H. Vikalo, B. Hassibi, and T. Kailath, "Iterative decoding for MIMO channels via modified sphere decoding", IEEE Transactions on Wireless Communications, vol.3, no.6, pp.2299-2311, Nov. 2006. KKY Wong and PI McLane, "Low-complexity space-time turbo equalization with the soft-output M-algorithm for frequency-selective channels", in Proceedings of IEEE ICC2005, vol.4, pp.2251-2255, Seoul, Korea, May 2005. M. Mikami and T. Fujii, "A downlink transmission method for OFDM cellular systems with inter-cell interference cancellation using simplified MLD based MMSE QRD-M algorithm," in Proceedings of IEEE VTC2008-Spring, pp.2011-2015, Marina Bay , Singapore, May. 2008. B.M.Hochwald and S. ten Brink, "Achieving near-capacity on a multiple-antenna channel," IEEE Transaction on Communications, vol.51, no.3, pp.389-399, March 2003. A.J.Viterbi, "An intuitive justification and a simplified implementation of the MAP decoder for convolution codes," IEEE Journal Selected Areas in Communications, vol.16, pp.260-264, Feb. 1998.

According to the radio access system proposed by the present inventor, one cell frequency repetition can be realized by detecting not only a desired signal but also an interference signal and performing signal separation processing. Improvement of performance is desired.
In addition, the proposed radio access system does not perform cooperation with error correction decoding processing in the multiple signal separation processing for separating the desired signal and the interference signal.
Therefore, the present invention aims at cooperation with error correction decoding processing in multiple signal separation processing, and can achieve a significant improvement in frequency utilization rate and cell edge throughput performance in the downlink of an OFDM cellular system. And it aims at providing the mobile station apparatus.

In order to achieve the above object, a radio access system of the present invention is a radio access system in which a base station and a mobile station communicate with each other by OFDM, and uses a common frequency band in a plurality of base stations in downlink transmission. When the transmission timing of all the base stations that interfere with each other is controlled so that the shift in reception timing including the multipath of the signal from each base station in the mobile station falls within the OFDM guard interval, Each base station is an OFDM in which a pilot channel including a pilot signal, a control channel including at least control information necessary for communication with a mobile station, and a traffic channel including information of error correction encoded user data are multiplexed. It transmits a signal, and the information about the transmission scheme of the traffic channel of the local station in the control information Mase is configured to transmit, the mobile station, between on the basis of the received signal self-cell base station and the mobile station in the pilot signal section of the signal from each base station, and each peripheral to be interfering Means for acquiring channel information between the cell base station and the own mobile station, and demodulating the control channel for the own cell base station and the neighboring cell base station that causes interference, and each neighboring cell that causes the own cell base station and interference Means for obtaining the control information of the base station, and a transmission method for demodulating the control information received from the own cell base station and the neighboring cell base station causing interference to obtain information on the transmission method of the traffic channel of each base station includes an information acquisition unit, a maximum a posteriori (MAP) soft output MIMO signal detector and soft-input soft-output channel decoder that operates on the basis of the estimation algorithm, the obtained tea Using Le information and control information of each neighboring cell base station serving as the acquired own-cell base station and interference, by using the information acquired by the transmission method information obtaining means, desired from the own cell base station from the received signal Signal separation that separates the desired signal from its own cell base station and the interference signal from the neighboring cell base station by simultaneously detecting the signal and the interference signal from the neighboring cell base station by repeated signal detection based on maximum posterior probability estimation The soft input soft output channel decoding is an external log likelihood ratio, which is a difference between a posterior probability log likelihood ratio and a prior log likelihood ratio output from the soft output MIMO signal detector, as a prior input value. An external log likelihood ratio, which is the difference between the a posteriori logarithmic likelihood ratio output from the soft input soft output channel decoder and the prior input value, as the prior log likelihood ratio. Signal separation means configured to be input to the soft output MIMO signal detector, and by extracting only the desired signal from the signals separated by the signal separation means, the interference signal removal from the neighboring cells and the Demodulation of the desired signal from the cell base station is realized at the same time .
Or, a wireless access system base station and the mobile station performs communication using OFDM, when using a common frequency band in a plurality of base stations in the transmission of downlink interference become of all base stations to each other The transmission timing is controlled so that the shift of the reception timing including the multipath of the signal from each base station in the mobile station falls within the OFDM guard interval, and each base station has a pilot channel including a pilot signal and An OFDM signal in which at least a control channel including control information necessary for communication with a mobile station and a traffic channel including error correction encoded user data information are multiplexed, and a traffic channel transmission method information about by including in the control information also neighboring cell base station serving as interference in addition to the own station It is configured to transmit, the mobile station, between the self-cell base station and the mobile station based on the received signal in the pilot signal section of the signal from each base station, and each neighboring cell base serving as interference Means for acquiring channel information between the mobile station and the own mobile station, and demodulating the control channel with respect to the own cell base station and neighboring cell base stations that cause interference, and each neighboring cell base station that causes interference with the own cell base station And a soft output MIMO signal detector and a soft input / soft output channel decoder that operate based on a maximum a posteriori (MAP) estimation algorithm, the acquired channel information and the acquired self-information. using the control information of each neighboring cell base station as a cell base station and interference, said acquired by demodulating the control information received from the own cell base station, a self-cell base station and interference Based on the information about the transmission scheme of the traffic channel side cell base station, simultaneously detected from the received signal by repeating the signal detection based on maximum posterior probability estimation and interference signals from the desired signal and the peripheral cell base station from the own cell base station A signal separation means for separating a desired signal from the own cell base station and an interference signal from a neighboring cell base station, wherein a posterior probability log-likelihood ratio output from the soft output MIMO signal detector An external log likelihood ratio, which is a difference from the log likelihood ratio, is input to the soft input / soft output channel decoder as a pre-input value and output from the soft input / soft output channel decoder, Signal separation means configured to input an external log likelihood ratio, which is a difference from the prior input value, to the soft output MIMO signal detector as the prior log likelihood ratio. It has a shall be realized demodulation of the desired signal from the interference cancellation and the own-cell base station from the neighboring cell by taking out only the desired signal from the separated signal simultaneously by the signal separating means.

Furthermore, the mobile station apparatus of the present invention is a mobile station apparatus in a radio access system in which a base station and a mobile station communicate with each other by OFDM, and the radio access system is common to a plurality of base stations in downlink transmission. When using this frequency band, the transmission timings of all base stations that interfere with each other should be within the OFDM guard interval so that the reception timing deviation including the multipath of the signal from each base station in the mobile station falls within the OFDM guard interval. Each base station is controlled, and each base station has a pilot channel including a pilot signal, a control channel including at least control information necessary for communication with the mobile station, and traffic including user-correction-encoded user data information. It transmits the OFDM signal and the channel are multiplexed, and the transmission scheme of the traffic channel of the local station The information is what is adapted to transmit included in the control information, based on the received signal in the pilot signal section of the signal from each base station, between the self-cell base station and the mobile station And means for acquiring channel information between each neighboring cell base station and its own mobile station causing interference, and demodulating the control channel for the own cell base station and neighboring cell base station causing interference, And means for obtaining the control information of each neighboring cell base station that causes interference, a soft output MIMO signal detector and a soft input soft output channel decoder that operate based on a maximum a posteriori probability (MAP) estimation algorithm, acquired channel information and said acquired using the control information of each neighboring cell base station as a self-cell base station and interference, each peripheral cell base serving as the acquired own-cell base station and interference It included in the control information, based on information relating to the transmission scheme of the traffic channel of each base station, the maximum a posteriori estimation and interference signals from the desired signal and the peripheral cell base station from the received signal the own cell base station A signal separation means for separating a desired signal from the own cell base station and an interference signal from a neighboring cell base station by simultaneously detecting by repetitive signal detection based on the posterior signal output from the soft output MIMO signal detector; The external log likelihood ratio, which is the difference between the probability log likelihood ratio and the prior log likelihood ratio, is input to the soft input soft output channel decoder as a prior input value and output from the soft input soft output channel decoder An external log likelihood ratio, which is the difference between the posterior probability log likelihood ratio and the prior input value, is input to the soft output MIMO signal detector as the prior log likelihood ratio. Signal separation means, and by extracting only the desired signal from the signals separated by the signal separation means, the interference signal removal from the neighboring cells and the demodulation of the desired signal from the own cell base station can be realized simultaneously. is there.

According to such a radio access system and mobile station apparatus of the present invention, it is possible to remove the same frequency interference from neighboring cells with high accuracy, so that one cell (sector) frequency repetition can be performed without using repetition. And the frequency utilization factor in the OFDMA system can be greatly improved.
In other words, by controlling the deviation of the reception timing of signals from each base station to be within the OFDM guard interval, symbol synchronization can be achieved between the desired signal and the interference signal, and highly accurate interference removal can be achieved. It becomes possible.
Furthermore, not only a desired signal but also an interference signal is detected and signal separation processing is performed, thereby enabling highly accurate interference removal. In particular, based on the maximum posterior probability (MAP) estimation, the posterior probability information of each bit of the desired signal and the interference signal obtained from the soft input soft output channel decoder (soft input soft output error correction decoder) is subjected to soft output MIMO signal separation. By performing an iterative process that feeds back as prior probability information for the detector, the signal separation accuracy is extremely higher than MIMO signal separation (MLD: Maximum Likelihood Detection) based on conventional maximum likelihood estimation that does not use prior probability information of each bit Can be realized. Further, in an OFDM system, generally, a signal after error correction coding is interleaved in the frequency direction. For this reason, since the randomness of the received signal is increased in a frequency selective fading environment, when an error correction code suitable for correcting a random error such as a convolutional code is applied, the accuracy of error correction decoding increases. There is also an effect that it is easy to obtain the effect of repeated signal separation detection used in the invention.
In addition, by transmitting the number of transmission antennas and the number of transmission streams of each neighboring cell base station that causes interference through the control channel of the base station of the own cell in the control information, each neighboring cell base station at the receiving side It is possible to obtain information necessary for realizing highly accurate interference removal such as the number of transmission antennas of interference stations and the number of streams of interference signals without decoding the control channel on the receiving side.
Furthermore, by adapting to the state of the radio channel by notifying information on the transmission method such as the traffic channel modulation method, error correction coding (channel coding) method, and multi-antenna transmission method via the control channel. The present invention can also be applied to transmission.

It is a figure for demonstrating the basic composition of the radio | wireless access system of this invention, and the basic concept of a receiving process of a mobile station. It is a figure for demonstrating 1st Embodiment of the radio | wireless access system of this invention, (a) is the structure of 1st Embodiment of the radio | wireless access system of this invention, (b) is transmitted from a base station It is a figure which shows an example of the format of the signal performed. It is a figure which shows the structure of 2nd Embodiment of the radio | wireless access system of this invention. It is a figure which shows the structure of 3rd Embodiment of the radio | wireless access system of this invention. It is a figure which shows the structural example of the base station apparatus in the radio | wireless access system of this invention, and a mobile station apparatus, (a) is a block diagram which shows the structural example of the transmitter in a base station, (b) is a block diagram of the receiver in a mobile station It is a block diagram which shows the example of a structure. It is a figure for demonstrating the concept of the structure of the repetition signal detection with an inter-cell interference cancellation function in this invention, and a channel decoder. It is a figure which shows the structural example of the iterative signal detection with an inter-cell interference cancellation function and channel decoder in the mobile station receiver of this invention. It is a figure which shows the structure of the system model for evaluation for the simulation regarding the radio | wireless access system of this invention. It is a figure which shows the simulation item regarding the radio | wireless access system of this invention. It is a figure which shows the block error rate characteristic which is a simulation result regarding the radio | wireless access system of this invention. It is a figure which shows the throughput characteristic which is a simulation result regarding the radio | wireless access system of this invention. It is a figure for demonstrating the conventional method which improves the space utilization factor of a frequency, (a) is N cell frequency repetition, (b) is a figure which shows the example of FFR. It is a figure for demonstrating repetition.

FIG. 1 is a diagram for explaining a basic configuration of a radio access system according to the present invention.
In FIG. 1, 1 is a base station where the mobile station 3 is located (own cell base station), 2 is a base station adjacent to the base station 1 (peripheral cell base station), and 3 is a mobile station.
The radio access system of the present invention is intended for the downlink of a cellular system using OFDM modulation. As shown in FIG. 1, the present system is used as a one-cell frequency repetition method that uses a common frequency band f0 in all cells. The base stations 1 and 2 are synchronously controlled so that the reception timing shift of signals transmitted from the base stations 1 and 2 in the mobile station 3 is within the OFDM guard interval (GI) as much as possible. ing. In addition, each base station 1 and 2 transmits user data that has been subjected to error correction coding on subcarriers of the same frequency, to the mobile stations belonging thereto.
As shown in the figure, the mobile station 3 receives the desired signal s transmitted from the own cell base station 1 and the interference signal u transmitted from the neighboring cell base station 2 at the same time. The desired signal s and the interference signal u are OFDM signals in the same frequency band. The mobile station 3 of the radio access system according to the present invention detects the repetitive signal based on the MAP estimation for the received signal (s + u) (in actuality, s and u are distorted by fading in the radio propagation path). Using the method (MAP detection method), the desired signal s and the interference signal u are estimated at the same time, and then only the desired signal s is extracted to achieve the removal of the interference signal u and the highly accurate decoding of the desired signal s. Yes.
That is, the mobile station 3 according to the present invention transmits, for each OFDM subcarrier, a desired signal transmitted from the own cell base station 1 and an interference signal transmitted from the neighboring cell base station 2 to a plurality of antennas in a MIMO system. The signal is estimated by using the signal separation technique based on the MAP detection method and estimating both the desired signal and the interference signal, and extracting the estimation result of the desired signal from the own cell base station 1. Demodulate the signal.
Thereby, 1-cell frequency repetition is realizable without using repetition.

Then, the radio signal of the present invention can be easily removed from the received signal in which the desired signal s from the own cell base station 1 and the interference signal u component from the neighboring cell base station 2 are mixed. In the access system, the transmission timing is controlled in each base station so that the deviation of the reception timing including the multipath delay of the signal transmitted from each base station falls within the OFDM guard interval (GI) ( Inter-base station synchronization control). In addition, information on the transmission method is notified from each base station to the mobile station so that the parameters of the interference signal can be grasped in advance.
In the above description, it is assumed that there is only one neighboring cell base station 2. However, even if there are a plurality of neighboring cell base stations 2, they can be handled in the same manner. Further, in order to exert the application effect of the signal detection method in the present invention, it is necessary to improve the estimation accuracy of the interference signal in the multiple signal separation. In order to improve the estimation accuracy of the interference signal, by assigning subcarriers of different frequencies to a plurality of users in the same cell, when applied to an OFDMA scheme in which a plurality of users are multiplexed, inter-cell interference occurs. It is desirable that sub-carriers of the same number and the same frequency are allocated to the user in cooperation with each base station.

A first embodiment of such a radio access system of the present invention will be described with reference to FIG.
2A is a diagram showing a schematic configuration of the first embodiment of the radio access system of the present invention, and FIG. 2B is a diagram showing an example of a format of a signal transmitted from a base station. .
As shown in FIG. 2A, the own cell base station 1 is provided with one or more antennas 4, and the neighboring cell base station 2 is provided with one or more antennas 5. . Signals transmitted from the antenna 4 of the own cell base station 1 and the antenna 5 of the neighboring cell base station 2 are received by one or a plurality of antennas 6 provided in the mobile station 3. Each base station is connected by a core network 7. The base stations 1 and 2 can share various information via the core network 7. In addition, synchronization control between base stations is performed between the base stations using, for example, GPS, and a shift in reception timing of signals from the base stations including multipath in the mobile station 3 is an OFDM guard. The transmission timing is controlled to be within the interval.

FIG. 2B is an example of a channel configuration of a signal transmitted from each base station, and each base station 1 and 2 is common to all users in the pilot channel 11 mainly in the same cell in the downlink. A common control channel (or broadcast channel) for transmitting the control information and an individual control channel (hereinafter referred to as the common control channel (or broadcast channel) and the individual control channel) for transmitting individual control information specific to each user. (Referred to as “control channel”) 12 and a signal including the traffic channel 13 are transmitted to the mobile station. In this example, the pilot channel 11 and the control channel 12 are simply expressed as a time-multiplexed concept with respect to the traffic channel 13, but it is not always necessary to follow this configuration. For example, the pilot channel 11 has a scattered pilot configuration in which the pilot channel 11 is scattered on the time axis and subcarriers and multiplexed on the traffic channel 13, or the traffic channel is only at a specific timing of a specific subcarrier. A method of assigning a configuration is conceivable.
In addition, the signals of the pilot channel 11 and the control channel 12 need to be able to be demodulated by the mobile station 3 in both the signal transmitted from the own cell base station 1 and the signal transmitted from the neighboring cell base station 2. Is done. Therefore, the pilot channel 11 and the control channel 12 use a TDMA technique in which transmission timings are shifted from each other, or a CDMA technique in which these channels are spread using different codes. It is necessary to reduce the amount of interference between stations and between transmission antennas, and to transmit signals so that signals from each base station and each transmission antenna can be identified on the mobile station side. In addition, for the control channel 12, by using a method such as transmission using an error correction code with a low coding rate, the signal included in the control channel of each base station can be transmitted even when there is large interference. It can also be made to identify correctly.

The pilot channel 11 is a channel for transmitting a known pilot signal (pilot symbol) to the transmission side and the reception side, and a unique pilot symbol is transmitted on each subcarrier for each base station and transmission antenna. By receiving the pilot signal, the mobile station 3 can detect the reception timing of the signal and estimate the fluctuation amount of the amplitude and phase in the radio propagation path (channel estimation).
The control channel 12 is mainly information necessary for system control, a common control channel (or broadcast channel) for broadcasting control information common to all users in the same cell, and mainly for each user. This is composed of an individual control channel for notifying the desired user terminal of the control information. In order to cancel inter-cell interference, it is necessary to grasp not only the parameters of the desired signal to be detected in advance but also the parameters of the interference signal to be removed. At least, even in a simple system with a fixed transmission method, the minimum control information necessary for communication between the own cell base station and the mobile station, such as the number of transmission antennas, and the number of interference signals to be removed are known in advance. There is a need to. The first embodiment of the present invention relates to a simple system that does not use adaptive transmission in which a transmission method such as a modulation method or a multi-antenna transmission method is fixed. In this first embodiment, Each base station controls information on the number of transmission signals of its own base station (in the simple spatial division multiplexing method that does not use beamforming on the transmission side, since it corresponds to the number of transmission antennas, hereinafter, it is simply referred to as the number of transmission antennas). The channel 12 is used for transmission to the mobile station. In another embodiment of the present invention, information on the transmission method for the own station, information on the number of transmission antennas of neighboring cell base stations that cause interference, and information on the transmission method are transmitted via the control channel 12. Will be described later.
The traffic channel 13 is a channel used for transmitting user data. Each base station has a function of transmitting user data after performing error correction coding and a function of transmitting data after performing OFDM modulation, and the user data subjected to error correction coding is subjected to I / Q mapping in units of subcarriers, It is converted into a time domain signal and transmitted to the mobile station 3 via the traffic channel 13. The error correction coding method may be any method as long as it can perform soft input / soft output error correction decoding. For example, a convolutional code, a turbo code, LDPC (low density parity check), ) Can be used.

The mobile station 3 recognizes not only the base station of the cell to which the mobile station belongs, that is, the own cell base station 1 but also the base station that causes interference, that is, the neighboring cell base station 2 at the cell search stage. When transmitting user data, the reception timing of the signals transmitted from the base stations 1 and 2 is detected by receiving and demodulating the pilot channel 11 signals transmitted from the own cell base station 1 and the neighboring cell base station 2 respectively. In addition, channel estimation can be performed for each subcarrier from each transmitting antenna 4 of the own cell base station 1 and each transmitting antenna 5 of the neighboring cell base station 2 to each receiving antenna 6 of the own station, and a channel matrix can be obtained. .
Then, by receiving and demodulating the signal of the control channel 12 transmitted from the own cell base station 1 and the neighboring cell base station 2 based on the result of channel estimation, the communication between the own cell base station 1 and the mobile station 3 is achieved. It recognizes the minimum necessary control information and parameters of signals transmitted from the neighboring cell base station 2. Thereby, the number of desired signals and the number of interference signals can be recognized and acquired. The minimum control information necessary for communication between the own cell base station 1 and the mobile station 3 includes, for example, OFDM subcarrier allocation information for the mobile station 3 of the own cell base station 1 and information on the number of transmission antennas. Conceivable.

The mobile station 3 includes a soft output MIMO signal detector and a soft input soft output channel decoder, and is based on the channel matrix obtained as described above, and the acquired information on the number of desired signals and the number of interference signals. The desired signal and the interference signal are estimated using the iterative signal detection method based on the MAP (maximum posterior probability) estimation, the desired signal and the interference signal are separated, and from the plurality of separated signals, the own cell base station 1 By extracting only the desired signal component, the inter-cell interference signal removal and the demodulation of the desired signal from the own cell base station 1 are realized at the same time.
Here, the repetitive signal detection method (MAP detection) based on the original MAP estimation is not limited, and the Sphere Decoding method (Non-Patent Documents 7 and 10) and the Soft-Output M-Algorithm (Non-patent Document) that simplify the MAP detection. Document 8) may be used. As soft input / soft output channel decoding (soft input / soft output error correction decoding) algorithms, algorithms such as BCJR algorithm, Max Log-MAP algorithm, SOVA (Soft-Output Viterbi Algorithm) are known. These algorithms, or modified versions of these algorithms can be used.

  Next, second and third embodiments of the present invention for a system to which link adaptation (adaptive modulation and adaptive coding rate control) including rank adaptation (adaptive substream number control) is applied will be described. . When targeting a system to which link adaptation (adaptive modulation and adaptive coding rate control) including rank adaptation (adaptive substream number control) is applied, the mobile station transmits a desired signal transmission scheme (modulation scheme, Not only information related to error correction coding schemes, MIMO spatial multiplexing / space-time coding schemes, etc., but also transmission schemes used for traffic channels in neighboring cell base stations (interference stations) as interference sources (modulation schemes, errors) It is necessary to grasp in advance information on correction coding schemes, MIMO spatial multiplexing / space-time coding schemes, etc.) in order to perform highly accurate inter-cell interference cancellation.

FIG. 3 is a diagram showing the configuration of the second embodiment of the wireless access system of the present invention. In this embodiment, each base station 1, 2, in addition to the information on the number of transmission antennas of its own station, via its control channel 12, its own transmission scheme (modulation scheme, error correction coding scheme, Information related to space multiplexing / space-time coding system, etc.) is transmitted. Thereby, the mobile station 3 decodes the information of the control channel 12 from the own cell base station 1 and the received signal of the control channel 12 from the neighboring cell base station 2, thereby It is possible to acquire information relating to a transmission scheme such as a modulation scheme, an error correction coding scheme, a spatial multiplexing / space-time coding scheme, etc.
This makes it possible to identify not only the desired signal but also the interference signal transmission method when applying link adaptation in which transmission is performed by selecting the optimal transmission method according to the state of the propagation path. Inter-cell interference signal cancellation can be performed.

FIG. 4 is a diagram showing the configuration of the third embodiment of the wireless access system of the present invention.
In this embodiment, in addition to the information on the number of transmission antennas of the own station and the information on the transmission method of the own station, the own cell base station 1 has information on the number of transmission antennas of the neighboring cell base station 2 that causes interference Information regarding the transmission method is notified to the mobile station 3 via the control channel 12. Each base station exchanges information such as information on the number of transmission antennas that use the same frequency via the core network 7 and information on the transmission method, so that the own cell base station 1 passes through the core network 7. Information on the number of transmission antennas used on each subcarrier of the neighboring cell base station 2 and information on the transmission method can be obtained. The own cell base station 1 notifies the mobile station 3 belonging to the own station of the information on the number of transmission antennas of the neighboring cell base stations and the information on the transmission method obtained in this way.
As a result, the mobile station 3 demodulates the information contained in the control channel 12 from the own cell base station 1, thereby information on the number of transmission antennas of the interference station (neighboring cell base station) 2 and information on the transmission scheme. Can be obtained. In the embodiment shown in FIG. 3, channel estimation between the neighboring cell base station 2 and the mobile station 3 and information on the control channel 12 from the neighboring cell base station 2 are demodulated and then decoded. On the other hand, since it is possible to obtain information on the number of transmission antennas of the neighboring cell base station 2 and the transmission method without performing these processes, reception signal processing is simplified, and acquisition of information on the number of interference signals is easy. It becomes.
When adaptive transmission (link adaptation) is not applied, only the information on the number of transmitting antennas of the neighboring cell base stations is notified to the mobile station 3 using the control channel 12 of the own cell base station 1. That's fine.

2, 3, and 4, it is described that each base station is installed in a different location and uses an omnicell configuration, but a plurality of different base stations are installed in the same location (site). However, the present invention can also be applied to a sector cell configuration in which the areas covered by each base station are shifted from each other depending on the directivity and location of the base station antenna. When applying the sector cell configuration, since a plurality of base stations are in the same place, synchronization between base stations (inter-sector synchronization) can be realized without going through the core network 7.
In addition, when the third embodiment is applied to the sector cell configuration, information transfer between base stations regarding transmission signal systems of neighboring cells (other sectors) can be realized without going through the core network 7, so The delay problem in information transfer can be greatly reduced. Therefore, the third embodiment has a feature that inter-cell interference (inter-sector interference) at the same site in the sector cell configuration can be realized very easily. On the other hand, a system called RRH (Remote Radio Head) is also used in the RF section of recent base station apparatuses. In the RRH system, the baseband section and the RF section of the base station are connected by an optical fiber or the like. It does not necessarily have to be installed at the same site. In the RRH method, only the RF part of each applicable base station is distributedly installed (overhanging installation) at the site where the base station antenna is installed, and the base station baseband processing unit of multiple sites is located at one place where the exchange station is located. It is possible to apply a method of installing in a batch (multi-site baseband processing unit centralized installation method). By applying the RRH method, base station baseband processing units installed at the same location can be regarded as substantially different sectors, so that interference between these sites (inter-cell interference) is treated in the same way as sector interference. be able to. Therefore, even when the third embodiment is applied to the multi-site baseband processing unit centralized installation method, since the baseband processing units of a plurality of base stations are in the same place, synchronization between base stations and between base stations Since information transfer can be realized without going through the core network 7, inter-cell interference cancellation can be realized very easily.

Next, specific configuration examples of the transmitters of the own cell base station 1 and the neighboring cell base station 2 and the receiver of the mobile station 3 will be described. The radio access system of the present invention uses, as a space division multiplexing (SDM) technique, a method of transmitting a plurality of codewords in parallel (MCW: Multiple CodeWord) and a method of transmitting a single codeword (SCW: Although it can be applied to any case of single-codeword), here, an example in the case of application to the MCW system will be described.
FIG. 5A is a block diagram showing a configuration example of a transmitter in the base stations 1 and 2. In FIG. 5A, the portion directly related to the present invention is mainly shown, and portions (filters and the like) that are naturally necessary in actual communication are omitted.
In the transmitter shown in FIG. 5 (a), user data to be transmitted is input to the serial-parallel converter 21 at a timing controlled by a transmission timing control unit (not shown) via a buffer (not shown). The data is converted into N _t0 series parallel data corresponding to the number N _{t0 of} transmission antennas provided. The data of each series output from the serial / parallel conversion unit 21 is supplied to the transmission units 22-1 to 22-N _t0 provided correspondingly. The transmission units 22-1 to 22-N _t0 have the same configuration.

In each of the transmission units 22-1 to 22-N _t0 , each series of data from the serial / parallel converter 21 is input to the channel encoder 31 and subjected to error correction coding. As described above, various codes such as a convolutional code, a turbo code, and an LDPC code can be used as the error correction code. Data that has been error correction encoded by the channel encoder 31 is channel interleaved by the interleaver 32 in order to reduce the influence of burst errors, and then modulated by the modulator 33. For example, when QPSK is adopted, the data is IQ-mapped and converted into complex symbols. The modulated signal is converted into a parallel signal by a serial / parallel converter 34, and the pilot channel and the control channel are multiplexed by a multiplexer 35 and input to an inverse fast Fourier transform unit 36. When link adaptation is applied, an optimal combination of modulation level and coding level is selected based on CQI (Channel Quality Indicator) fed back from each mobile station, and the selected combination information AMI (Adaptive Modulation and coding scheme level information: information on adaptive modulation and adaptive coding) is inserted into the control channel and transmitted.
The inverse fast Fourier transform unit 36 performs inverse Fourier transform on the input signal, and the time-domain signal output in parallel from the inverse fast Fourier transform unit 36 is converted into a serial signal by the parallel-serial converter 37. After that, a guard interval (GI) is added by the guard interval adding unit 38. The signal with the guard interval added is converted to an analog signal by the D / A converter 39, up-converted to the carrier frequency fc from the local oscillator 23 by the mixer 40, and precoded as necessary. Amplified by the power amplifier 41 and transmitted from the corresponding transmitting antennas 24-1 to 24-N _t0 .

FIG. 5B is a block diagram illustrating a configuration example of a receiver provided in the mobile station 3. In FIG. 5 (b), as in FIG. 5 (a), the portion directly related to the present invention is shown in the center, and portions (filters and the like) that are naturally necessary in actual communication are omitted.
Received signal of the receiving antenna 51-1 to 51-N _r of N _r this is input in response to the signal receiving unit 52-1 to 52-N _r provided respectively. Each signal receiving unit 52-1 to 52-N _r are the same structure.
In each signal receiving unit 52-1 to 52-N _r, the signal received by the corresponding receiving antennas 51-1 to 51-N _r is amplified by the not-shown low-noise amplifier, a local oscillator in mixer 61 53 is multiplied by the signal of the carrier frequency fc from 53, down-converted to baseband, and input to the A / D converter 62. The received signal converted into digital data by the A / D converter 62 is input to the guard interval removal unit 63 and also input to the timing detection, channel estimation and control signal demodulation unit 54.

Timing detection, channel estimation and a control signal demodulator 54 is provided in common to the signal receiving unit 52-1 to 52-N _r, the digital data is received by the receiving antennas 51-1 to 51-N _r The signal converted into is input. Timing detection, the channel estimation and the control signal demodulator 54 demodulates the signal of the signal and the control channel of the pilot channel included respectively in the received signal of each subcarrier of the receiving antennas 51-1 to 51-N _r To do.
As described above, the pilot signal is a unique symbol for each transmission antenna of each base station, and the reception timing of the signal from each transmission antenna of each base station is detected by demodulating this pilot channel signal. The transfer function (amplitude and phase fluctuations) for each subcarrier from the transmitting antenna to the receiving antenna is estimated. Then, by demodulating the received signal of the control channel and decoding information on the number of transmission antennas of the base station included in the control channel (and information on the transmission method), the own cell base station 1 and neighboring cells Information on the number of transmission antennas of the base station 2 (and information on the transmission method) is acquired. As a result, the channel matrix H (k) can be obtained, and parameters relating to the desired signal and the interference signal, such as information on the number of desired signals and the number of interference signals and information on the transmission scheme of each base station, can be obtained. .

In the case of the second embodiment shown in FIG. 3, the timing detection, channel estimation and control signal demodulation unit 54 decodes control channel information included in the received signal from each base station. By doing so, it is possible to obtain information on the transmission scheme of each base station.
In the case of the third embodiment shown in FIG. 4, the control channel from the own cell base station 1 also includes information on the number of transmission antennas and the transmission method of the interference station. The timing detection, channel estimation and control signal demodulation unit 54 only needs to decode the control channel information included in the received signal from the own cell base station 1.
In this way, the timing detection, channel estimation and control signal demodulator 54 uses the channel matrix, the number of transmission antennas of the own cell base station and the neighboring cell base stations, and information on transmission schemes (information on adaptive modulation and adaptive coding (AMI : Adaptive Modulation and coding scheme level Information)).
These pieces of information are supplied to the iterative signal detection with inter-cell interference cancellation function and the channel decoder 55, and used for signal separation processing to be described later.

In each signal receiving unit 52-1 to 52-N _r, the output signal from the guard interval removal unit 63 wherein the A / D converter 62 from which the guard interval is removed, the conversion to a parallel signal by the serial-parallel converter 64 Then, it is supplied to the fast Fourier transform unit 65, converted into a signal for each subcarrier, and output. Here, the number of subcarriers is N _sub .
Signals of each subcarrier respectively outputted from the signal receiving unit 52-1 to 52-N _r are input to the inter-cell interference cancellation function iterative signal detection and channel decoder 55. In this iterative signal detection and channel decoder 55 with the inter-cell interference cancellation function, the channel information (channel matrix) estimated by the timing detection, channel estimation and control signal demodulation unit 54 and the demodulated control information are used, and MAP is used. By repetitive signal detection based on estimation, the desired signal from the own cell base station and the interference signal from the neighboring cell base station are separated from the received signal of each subcarrier, and only the desired signal is extracted from these separated signals. Thus, the desired signal is reproduced with high accuracy simultaneously with the removal of the interference signal. The configuration of this iterative signal detection with inter-cell interference cancellation function and channel decoder 55 will be described later with reference to FIG.

Before describing the configuration of the iterative signal detection and channel decoder 55 with the inter-cell interference cancellation function with reference to FIG. 7, the repetitive signal detection and channel decoder with the inter-cell interference cancellation function for a single subcarrier will be described. A conceptual diagram of the configuration will be described with reference to FIG. Here, for the sake of simplicity, it is assumed that both the desired wave signal and the interference wave signal are one series.
In FIG. 6, reference numeral 91 denotes a soft output MIMO signal detector that operates based on the MAP algorithm, which separates a desired signal and an interference signal from received signals received by a plurality of receiving antennas, and a posteriori probability log likelihood of the desired signal. The ratio (a posteriori LLR) L _D1 ^(s) and the posterior probability log-likelihood ratio L _D1 ^(u) of the interference signal are output.
The adder 92, the deinterleaver 93, the soft input / soft output channel decoder 94, the hard decision unit 95, the adder 96, and the interleaver 97 constitute a signal estimation unit for a desired signal. A posteriori logarithmic likelihood ratio L _D1 ^{(s) of the} desired signal output from the soft output MIMO signal detector 91 and a priori log likelihood ratio (a priori LLR) (a priori value) L _A1 ⁽ the difference between ^s) is output as the external log likelihood ratios ^{_{(extrinsic LLR) L E1 (s}} ). The outer log likelihood ratio L _E1 ^(s) is deinterleaved by the deinterleaver 93 and supplied to the soft input / soft output channel decoder 94 as a pre-input value L _A2 ^(s) . SISO channel decoder 94 outputs a posteriori probability log-likelihood ratio L _D2 ^(s) performs error correction decoding processing based on pre-input value L _A2 ^(s). Difference posterior probability log-likelihood ratio L _D2 ^(s) and the pre-input value L _A2 ^(s) is output as the external information (external ^value) L _E2 ^(s), are re-interleaved in the interleaver 97 in advance logarithm The likelihood ratio (prior value) L _A1 ^(s) is input to the soft output MIMO signal detector 91. Further, the posterior probability log-likelihood ratio L _{D2, i} ^(s) after a plurality of iterative processes in the soft input / soft output channel decoder 94 is determined by the hard determiner 95 as reliability information of the user data portion of the desired signal. And output as a reproduction output of the desired signal.

The adder 98, the deinterleaver 99, the soft input / soft output channel decoder 100, the adder 101, and the interleaver 102 constitute a signal estimation unit for the interference signal. The signal estimation unit for the interference signal is configured in the same manner as the signal estimation unit for the desired signal, except that a hard discriminator is not provided. The difference between the posterior probability log likelihood ratio L _D1 ^(u) and the prior value L _A1 ^(u) of the interference signal output from the soft output MIMO signal detector 91 is output as the external log likelihood ratio L _E1 ^(u). The pre-input value L _A2 ^(u) is input to the soft input / soft output channel decoder 100 through the deinterleaver 99. Error correction decoding process in soft-input soft-output channel decoder 100 is to posterior probability log-likelihood ratio L _D2 ^(u) is output performed, the difference between the pre-input value L _A2 ^(u) is the external log likelihood It is output as the ratio (external value) L _E2 ^(u) . This external log likelihood ratio L _E2 ^(u) is reinterleaved by the interleaver 102 and input to the soft output MIMO signal detector 91 as a prior log likelihood ratio (prior value) L _A1 ^(u) . Note that the information on the posterior probability log-likelihood ratio L _{D2, i} ^(u) output after being repeatedly processed a plurality of times in the soft input / soft output channel decoder 100 is the data portion of other users included in the interference signal. Since it is reliability information, it is not necessary to make a hard decision.

In the first decoding process in MAP decoding, the prior log likelihood ratios (prior values) L _A1 ^(s) and L _A1 ^(u) are 0, and the soft output MIMO signal detector 91 is the same as in the MLD. That is, the posterior probability log-likelihood ratio L _D1 ^(s) of each bit of the desired signal in the initial decoding process and the posterior probability log-likelihood ratio L _D1 ^(u) of each bit of the interference signal are the timing detection, channel Calculation is performed based on the square Euclidean distance between the received signal and the replica of the desired signal or interference signal generated based on the output of the estimation and control signal demodulator 54.
As shown in FIG. 5 (a), the signal transmitted from each transmitter is error-corrected and encoded by the channel encoder 31 and then interleaved and transmitted by the interleaver 32. The outer log likelihood ratio L _E1 ^{(s) of the} desired signal and the outer log likelihood ratio L _E1 ^(u) of the interference signal are deinterleaved by the deinterleaver 93 and the deinterleaver 99, and then soft input soft output channel decoding Need to be input to the unit 94 and the soft input / soft output channel decoder 100. The external information L _E2 ^(s) from the soft input / soft output channel decoder 94 and the external information L _E2 ^(u) from the soft input / soft output channel decoder 100 are reinterleaved by the interleaver 97 and the interleaver 102. The prior log likelihood ratio (prior value) L _A1 ^(s) and the prior log likelihood ratio (prior value) L _A1 ^(u) are input to the soft output MIMO signal detector 91. The soft output MIMO signal detector 91 separates the desired signal from the received signal again using the prior value L _A1 ^(s) and separates the interference signal from the received signal again using the prior value L _A1 ^(u). Processing is performed to output the posterior probability log-likelihood ratio L _D1 ^{(s) of} the desired signal and the posterior probability log-likelihood ratio L _D1 ^(u) of the interference signal. Thereafter, the above process is repeated.
Thus, since the external value of the soft input / soft output channel decoder is fed back as a prior value for the soft output MIMO signal detector, it is possible to realize signal separation with higher accuracy than the conventional MLD-based technique.

FIG. 7 is a diagram showing a configuration example of the iterative signal detection and channel decoder 55 with the inter-cell interference cancellation function corresponding to OFDM. The configuration shown in FIG. 6 is a case where there is a single subcarrier and one sequence of each of the desired signal and the interference signal. However, the transmitter and the receiver shown in FIGS. In this case, the number of subcarriers is N _sub , and the number of transmission antennas of each base station is N _t0 . Also, in FIG. 7, when obtaining the external log likelihood ratio for the soft output MIMO signal detector for each subcarrier, the difference between the posterior probability log likelihood ratio and the prior log likelihood ratio is calculated as shown in FIG. Although there is a method for obtaining this, a portion corresponding to this processing is not shown. In the following description, for simplicity, it is assumed that the number of transmission antennas of all base stations is equal. Here, when the number of neighboring cell base stations is (N _B −1), the total number of transmission antennas of the own cell base station and each neighboring cell base station is N _t = N _t0 · N _B. As shown in FIG. 5A, since the MCW method is used in which channel coding is performed by a transmission unit provided for a transmission antenna, the number of data sequences is N _t .

In FIG. 7, 71-1 to 71-N _sub are soft output MIMO signal detectors provided for each subcarrier. As described above, each of the fast Fourier transform unit 65 provided in the receiving antenna 51-1 to 51-N _r provided in correspondence signal receiving unit 52-1 to 52-N _r, are received at each receive antenna The received signals are separated into output signals for each subcarrier and output. The received signal of each subcarrier from the signal receiving unit 52-1 to 52-N _r are input to the corresponding soft output MIMO signal detector 71-1 to 71-N _sub. That is, the soft output MIMO signal detector 71-1, the received signal (received signal vector x (1)) of the sub-carrier number 1 is output from the signal receiving unit 52-1 to 52-N _r are input, the soft output MIMO signal detector 71-2, the received signal of subcarrier numbers 2 respectively output from the signal receiving unit 52-1 to 52-N _r (received signal vector x (2)) is input, hereinafter the same In addition, the reception signal (reception signal vector x (N _sub )) of the subcarrier number N _sub output from each of the signal reception units 52-1 to 52-N _r is input to the soft output MIMO signal detector 71-N _sub. Is done.

Each of the soft output MIMO signal detectors 71-1 to 71-N _sub includes an input received signal vector x (k) (k = 1,..., N _sub ) and a soft input soft output channel decoder 83-1. ˜83−N _t posterior probability log likelihood ratio L _E2 (d _j ) (where j = 1,..., N _t , and d _j represents the transmission data sequence of the j th stream) Based on the prior value L _A1 (c _i (k)) (i = 1,..., N _t M _c ) based on the transmission signal vector s (k) (k = 1,. N _sub ), the a posteriori probability log-likelihood ratio L _D1 (c _i (k)) of the encoded bit string c (k) = {c ₁ (k),..., C _NtMc (k)} (i = 1, ..., N _t M _c , k = 1, ..., N _sub ) are calculated bit by bit, and the external log likelihood is the difference from the prior value L _A1 (c _i (k)) The degree ratio L _E1 (c _i (k)) is output. Here, N _t is the total number of transmission antennas of all the base stations, and M _c is log ₂ (modulation multilevel number), that is, the number of bits per constellation symbol.

72-1 to 72-N _t is the data estimation unit provided for each data series, the data sequence output from the soft output MIMO signal detector 71-1 to 71-N _sub provided in each of the sub-carrier Corresponding logarithmic likelihood ratios L _E1 (c _i (k)) (i = 1, ..., N _t M _c , k = 1, ..., N _sub ) that serializer 81-1~81-N _t and, deinterleaver deinterleaves the converted signals in series said parallel-serial converter 81~1~81~N _t 82-1~82-N _t When, the deinterleaver 82-1~82-N output from _t pre input value _{L A2 (d j) (j} = 1, ..., N t) SISO channel decoder input as 83-1 to 83-N _t and external information L _E2 (d _j ) (a posteriori probability log likelihood ratio L _D2 (d _j ) output from the soft input / soft output channel decoders 83-1 to 83-N _t -Advance Interleaver 84-1~84-N _t to re-interleaving the input value L _A2 (d _j)), serial-to-parallel to the output from the interleaver 84-1~84-N _t corresponding to each sub-carrier conversion to advance the log likelihood ratio corresponding said soft output MIMO signal detector 71-1 to 71-N _sub (pre _{value) L A1 (c i (k} )) parallel converter supplied as 85-1 It has a ~85-N _t.

As in the case described with reference to FIG. 6, the MIMO signal detectors 71-1 to 71-N _sub receive soft output reliability information provided by the soft input soft output channel decoders 83-1 to 83-N _t ( Pre-log likelihood ratio L _A1 (c _i (k))), soft input soft output channel decoders 83-1 to 83-N _t are provided by MIMO signal detectors 71-1 to 71-N _sub . The soft output reliability information (prior value L _A2 (d _j )) is processed. Between the desired signal only soft output MIMO signal detector 71-1 to 71-N _sub reliability information for soft output of each bit to interfering signals not a soft input soft output channel decoder 83-1~83-N _t And repeat the process until the desired properties are obtained. Then, after the repetition process is completed, the posterior probability log-likelihood ratio L output from the soft-input / soft-output channel decoder of the data sequence corresponding to the desired signal transmitted from the own cell base station by the desired signal selection unit 73. By selecting _D2 (d _j ), inputting it to the parallel-serial converter 74, converting it to a serial signal, and making a hard decision with the hard decision unit 75, a decoded output of the desired signal can be obtained. Note that the output of the soft input / soft output channel decoder of the data series corresponding to the interference signal is not used.
In this way, by extending the MAP detection method to target not only the desired signal but also the interference signal, it is possible to simultaneously realize the interference signal removal and the high-precision demodulation of the desired signal.

ただし、行列Ｈ_D(k)及びＧ_nB(k)は、第ｋサブキャリアにおける自セル基地局から移動局間及び第ｎ_B周辺セル基地局から移動局間のＮ_r×Ｎ_t0次元のチャネル応答行列をそれぞれ表す。ベクトルｓ_D(k)及びｕ_nB(k)は、第ｋサブキャリアにおける自セル基地局からの送信信号ベクトル及び第ｎ_B周辺セル基地局からの送信信号ベクトルをそれぞれ表し、その次元はＮ_t0×１である。Δθ_nBは、周波数オフセットΔｆ_nBに伴う位相オフセットを表す。ベクトルｎ(k)は受信機雑音のベクトルであり、その各要素は複素ガウス分布に従うものとする。 The signal detection algorithm with inter-cell interference cancellation according to the present invention will be further described. Here, for the sake of simplicity, it is assumed that the number of transmission antennas of each base station is the same and each has N _t0 .
Assuming that the timing offset including the multipath delay does not exceed the OFDM guard interval (GI), the received signal vector x (k) of the k-th subcarrier at the mobile station uses an equivalent low band system expression, It is represented by an N _r × 1 dimensional vector shown in 1).

However, the matrices H _D (k) and G _nB (k) are N _r × N _t0 -dimensional channels between the own cell base station and the mobile station and between the n _B neighboring cell base stations and the mobile station in the k-th subcarrier. Each response matrix is represented. The vectors s _D (k) and u _nB (k) represent the transmission signal vector from the own cell base station and the transmission signal vector from the n _B neighboring cell base station in the k-th subcarrier, respectively, and the dimension is N _t0. X1. Δθ _nB represents a phase offset associated with the frequency offset Δf _nB . The vector n (k) is a receiver noise vector, and each element thereof follows a complex Gaussian distribution.

ただし、Ｎ_r×Ｎ_t次元の行列Ｈ(k)は仮想ＭＩＭＯチャネル行列であり、その各要素はＨ_D(k)及び各Ｇ_nB(k)ｅ^jθnBによって構成され、Ｎ_B×１次元のベクトルｓ(k)は仮想送信信号ベクトルであり、それぞれ以下の式（３）及び（４）のように表される。

ただし、Ｎ_t＝Ｎ_B・Ｎ_t0は全ての基地局についてのトータルの送信アンテナ数、上付き文字Ｔは行列またはベクトルの転置を表す。 When the timing offset and the frequency offset can be ignored, the base station antenna seen from the mobile station side can be regarded as one virtual large-scale array antenna. Therefore, the channel between the base station antenna and the mobile station antenna can be regarded as a virtual MIMO channel. The received signal vector x (k) of the k-th subcarrier at the mobile station is expressed by Equation (2).

However, the N _r × N _t dimensional matrix H (k) is a virtual MIMO channel matrix, each element of which is composed of H _D (k) and each G _nB (k) e ^jθnB , and is N _B × 1 dimensional. The vector s (k) is a virtual transmission signal vector, and is represented by the following equations (3) and (4), respectively.

However, N _t = N _B · N _t0 represents the total number of transmitting antennas for all base stations, and the superscript T represents transposition of a matrix or vector.

_Assuming that the frequency offset Δf _nB is sufficiently small to be negligible, the phase offset Δθ _nB can be approximated by 0, so the virtual MIMO channel matrix H (k) is expressed by Equation (5).

ただし、ｓ_D^(k)及びｕ_nB^(k)（n_B＝1,...,N_B-1）は、自セル基地局から送信された希望信号の最も確からしい候補、及びｎ_B番目の周辺セル基地局から送信された干渉信号の最も確からしい候補をそれぞれ表す。また、ｓ_m ^(rep)はＮ_t×１次元の信号ベクトル候補であり、その要素は、ｓ_D(k)及びｕ_nB(k)の候補から構成される。Bayesの定理を用いると式（７）が得られる。

In the radio access system of the present invention, a method in which the MAP signal detection method is extended is used in order to improve the signal detection accuracy of a desired signal under an inter-cell interference (ICI) environment. Specifically, the dimension of the signal path search space is expanded by adding an interference signal space in addition to the desired signal space. The basic principle of signal detection will be described below.
When both the MIMO channel matrix between the own cell base station and each neighboring cell base station and the AMI transmitted from each base station are obtained, the MAP-based MIMO signal detector has a posteriori probability P ( s (k) | x (k)) can be maximized, and its hard decision output s ^ _MAP (k) is expressed by equation (6).

Where s _D ^ (k) and u _nB ^ (k) (n _B = 1,..., N _B −1) are the most probable candidates of the desired signal transmitted from the own cell base station, and n each representing the most probable candidate of the transmitted interference signal from the _B-th neighboring cell base stations. Further, s _m ^(rep) is an N _t × 1 dimensional signal vector candidate, and its elements are composed of s _D (k) and u _nB (k) candidates. Using Bayes' theorem, equation (7) is obtained.

ただし、σ²は受信アンテナあたりの実部または虚部の平均雑音電力である。さらに、各シンボルs₁(k),s₂(k),...,s_Nt(k)がそれぞれ独立であるとすることにより、式（７）の事前確率（a priori probability Ｐ(ｓ(k))は式（９）で表される。

Note that the likelihood function P (x (k) | s (k)) included in the equation (7) is rewritten into the equation (8).

Where σ ² is the average noise power of the real part or imaginary part per receiving antenna. Furthermore, by assuming that the symbols s ₁ (k), s ₂ (k),..., S _Nt (k) are independent, the prior probability (a priori probability P (s ( k)) is expressed by equation (9).

ただし、s_m,nt ^(rep)はベクトルｓ_m,nt ^(rep)のｎ_t番目の要素を表す。図７に示したように、式（６）のｓ^_MAP(k)から,ｕ^_nB(k)（n_B=1,...,N_B-1）を捨てることにより、自セル基地局から送信された希望信号ベクトルｓ_D(k)をセル間干渉キャンセルと同時に正しく推定することができる。 Therefore, MIMO signal detection based on the MAP algorithm is equivalent to the following optimization problem.

_However, s _{m, nt} ^(rep) represents a n _t th element of vector s _{m, nt} ^(rep). As shown in FIG. 7, by discarding u _nB (k) (n _B = 1,..., N _B -1) from s ^ _MAP (k) in equation (6), the own cell base The desired signal vector s _D (k) transmitted from the station can be correctly estimated simultaneously with the inter-cell interference cancellation.

  Here, it should be noted that the soft input channel decoder needs to output not only the hard decision value but also its reliability information as the output of the MIMO signal detector. The MIMO signal detector processes soft output reliability information provided by the channel decoder, and the channel decoder processes soft output reliability information provided by the MIMO signal detector. In the signal detection method of the present invention, the reliability information of the soft output of each bit for not only the desired signal but also the interference signal is exchanged between the soft output MIMO signal detector and the soft input soft output channel decoder, and the desired characteristics are obtained. Repeat until it is received. Next, the calculation method of the soft output reliability information will be described in detail.

ただし、P(c_i(k)＝±1|ｘ(k))は信号ベクトルｘ(k)を受信したときのc_i(k)＝±1となる条件付き確率を表す。また、式（１１）では、論理値０をc_i(k)＝＋１、論理値１をc_i(k)＝−１として表している。ｃ_m ^(rep)＝{c_m,1 ^(rep),...,c_m,NtMc ^(rep)}は、送信信号ベクトルのレプリカｓ_m ^(rep)に対応するビット列を表す。また、Ｌ_A1(c_i(k))及びＬ_E1(c_i(k)|ｘ(k))は、軟出力ＭＩＭＯ信号検出器における事前対数尤度比（a priori LLR）及び外部対数尤度比（extrinsic LLR）をそれぞれ表す。式（１１）における事前対数尤度比Ｌ_A1(c_i(k))の定義より、事前確率Ｐ(c_i(k))は、式（１２）で表される。

Let M _c = log ₂ M _ary be the number of bits per constellation symbol of each OFDM subcarrier. Let c (k) = {c ₁ (k),..., c _{Nt, Mc} (k)} be an encoded bit string included in the virtual transmission signal vector s (k). In general, by assuming that the encoded bit sequences c ₁ (k),..., C _{Nt, Mc} (k) are independent, the i-th (i = 1) of s (k) at the MIMO signal detector output. , ..., N _t M _c ) bit soft output reliability information is expressed as a posteriori log-likelihood ratio (a posteriori LLR) and expressed by equation (11) (see Non-Patent Document 10). .

However, P (c _i (k) = ± 1 | x (k)) represents a conditional probability that c _i (k) = ± 1 when the signal vector x (k) is received. In the expression (11), the logical value 0 is represented as c _i (k) = + 1, and the logical value 1 is represented as c _i (k) = − 1. c _m ^(rep) = {c _{m, 1} ^(rep) , ..., c _{m, NtMc} ^(rep) } represents a bit string corresponding to the replica s _m ^(rep) of the transmission signal vector. L _A1 (c _i (k)) and L _E1 (c _i (k) | x (k)) are the prior log likelihood ratio (a priori LLR) and the external log likelihood in the soft output MIMO signal detector. Each represents the extrinsic LLR. From the definition of the prior log likelihood ratio L _A1 (c _i (k)) in Equation (11), the prior probability P (c _i (k)) is expressed by Equation (12).

ただし、ｃ_m,[i] ^(rep)は（N_tM_c-1）×１のベクトルであり、送信信号ベクトルのレプリカｓ_m ^(rep)をビット単位のベクトルに変換したブロックc_m ^(rep)のうち、第ｉビットを除いたものである。また、Ｌ_A1,[i]は（N_tM_c-1）×１のベクトルであり、信号分離の単位となるN_t個の送信信号に含まれる全ての事前対数尤度比（a priori LLR）Ｌ_A1(c_p(k))から構成されるベクトルＬ_A1に対し、第i番目の要素を除いたものである。 Since the transmission signal vector s (k) of the k-th subcarrier is obtained by multileveling the block c (k) of the encoded bit string, performing Gray encoding, and mapping it on the I / Q plane. The external log likelihood ratio (extrinsic LLR) L _E1 (c _i (k) | x (k)) in equation (11) is rewritten as equation (13) using equation (12).

^{_{However, c m, [i] (}} rep) is (N _t M _c -1) is a vector of × 1, block c _m ^(rep converted replica s _m of the transmission signal vector ^(rep) vector bitwise ⁾ Except the i-th bit. Further, L _{A1, [i]} is a vector of (N _t M _c −1) × 1, and all prior log likelihood ratios (a priori LLR) included in N _t transmission signals serving as signal separation units. ) A vector L _A1 composed of L _A1 (c _p (k)) is obtained by removing the i-th element.

ただし、ｓ_m ^(rep)＝map{ｃ_m ^(rep)}である。ただし、map{ } は{ }内のビット列を多値化し、Gray符号化を行った後、I/Q平面上にマッピングするマッピング関数を表す。さらに、式（１１）、式（１２）、及び式（１４）より、事後確率対数尤度比（a posteriori LLR） L_D1(c_i(k)|ｘ(k))は式（１５）で近似できる。

式（１１）より、外部対数尤度比（extrinsic LLR）L_E1(c_i(k)|ｘ(k))は、式（１４）に基づいて直接計算することも可能である。一方、式（１１）から式（１６）が成り立つ。

すなわち、式（１６）より、図６に示したように、事後確率対数尤度比（a posteriori LLR） L_D1(c_i(k)|ｘ(k))から事前対数尤度比Ｌ_A1(c_i(k))を差し引くことで、外部対数尤度比（extrinsic LLR）L_E1(c_i(k)|ｘ(k))を計算できる。従って、実際には式（１５）に基づき事後確率対数尤度比（a posteriori LLR） L_D1(c_i(k)|ｘ(k))を求めた後、式（１６）に基づき軟入力軟出力誤り訂正符号器からフィードバックされる事前対数尤度比Ｌ_A1(c_i(k))との差をとることで軟入力軟出力誤り訂正符号器へ渡す外部対数尤度比（extrinsic LLR）L_E1(c_i(k)|ｘ(k))を求めることもある。 By using the Max-log approximation, the external log likelihood ratio (extrinsic LLR) L _E1 (c _i (k) | x (k)) can be approximated by Expression (14).

However, s _m ^(rep) = map {c _m ^(rep) }. However, map {} represents a mapping function that multi-values the bit string in {} and performs mapping on the I / Q plane after performing Gray encoding. Furthermore, from Equation (11), Equation (12), and Equation (14), the posteriori log likelihood ratio (a posteriori LLR) L _D1 (c _i (k) | x (k)) is given by Equation (15). Can be approximated.

From equation (11), the external log likelihood ratio (extrinsic LLR) L _E1 (c _i (k) | x (k)) can also be directly calculated based on equation (14). On the other hand, Expression (16) is established from Expression (11).

That is, from the equation (16), as shown in FIG. 6, the prior log likelihood ratio L _A1 (a posteriori LLR) L _D1 (c _i (k) | x (k)) By subtracting c _i (k)), the external log likelihood ratio (extrinsic LLR) L _E1 (c _i (k) | x (k)) can be calculated. Therefore, in practice, after obtaining the posterior probability log-likelihood ratio (a posteriori LLR) L _D1 (c _i (k) | x (k)) based on the equation (15), the soft input soft External log likelihood ratio (extrinsic LLR) L passed to the soft input soft output error correction encoder by taking the difference from the prior log likelihood ratio L _A1 (c _i (k)) fed back from the output error correction encoder _E1 (c _i (k) | x (k)) may be obtained.

The soft output MIMO signal detector 71-k (k = 1,..., N _sub ) in FIG. 7 includes channel observation values (received signals) x (k) and a priori log likelihood ratio (a priori LLR) L _A1. (c _i (k)) (i = 1,..., N _t M _c ), N _t M _c encoded bits for each received signal vector x (k) according to equation (13). An extrinsic LLR L _E1 (c _i (k) | x (k)) is calculated. External log likelihood ratio _{(extrinsic LLR) L E1 (c} i (k) | x (k)) is de-interleaved prior input value for SISO channel decoder 83-1~83-N _t (a priori input) L _A2 (d _j ) (j = 1,..., N _t ), and the soft input / soft output channel decoders 83-1 to 83-N _t receive the external information L _E2 (d _j ). Then, L _E2 (d _j ) is re-interleaved and fed back to the soft output MIMO signal detector 71-k as a prior log likelihood ratio (a priori LLR) L _A1 (c _i (k)). Repeat or complete the cycle. In each iteration, the bit error rate is reduced by exchanging these pieces of information.
Note that it is generally difficult to implement the iterative MIMO signal detection algorithm based on MAP unless the calculation amount reduction method is applied when the number of modulation multi-levels or the number of transmission antennas is large as in the case of MLD not using calculation amount reduction. , Calc Decoding method using Sphere Decoding (Non-Patent Documents 7 and 10 etc.), Soft-Output M-Algorithm (Non-Patent Document 8 etc.), etc. Has been. In the repetitive signal detection of the present invention, these calculation amount reduction methods may be applied.

The result of evaluating the characteristics of the iterative signal detection method with inter-cell interference cancellation according to the present invention in the error correction coded MIMO-OFDM cellular system by computer simulation will be described.
FIG. 8 shows a system model for evaluation, and FIG. 9 shows simulation specifications.
Here, a two-cell model (ie, N _B = 2) was assumed as shown in FIG. The number of transmitting antennas of each base station was N _t0 = 2 and the number of receiving antennas of the mobile station was N _r = 2. Therefore, under this condition, the number of receiving antennas N _r (= 2) is smaller than the total number of transmitting antennas N _t = N _B · N _t0 (= 4) of all base stations. Therefore, since the degree of freedom of the array of receiving antennas is insufficient, signals cannot be detected correctly by linear signal processing such as MMSE (Minimum Mean Square Error). The guard interval length Tg is ¼ of the effective OFDM symbol length. The frame length is 1 ms, which corresponds to 12 OFDM symbol length. A convolutional code with a constraint length K = 3 was used as the channel code. For simplicity, the same modulation scheme QPSK and the same coding rate R = 1/2 are used for transmission signals from the own cell base station and adjacent base stations. The reception timing shift (timing offset) between the signal from the own cell base station and the signal from the neighboring cell base station is fixed, and the length is 1/8 effective OFDM symbol. The FFT time window detection and channel estimation are ideally performed. In addition, both the control symbols transmitted from the own cell base station and the control symbols transmitted from the neighboring cell base stations can be completely restored on the mobile station side. In the mobile station receiver, the desired signal and the interference signal are separated based on the above-described repetitive MIMO signal detection method, and the separated desired signal and the interference signal are subjected to the Max Log-MAP algorithm (Non-Patent Document 11). Based on the soft input soft output channel decoding. After completing the iterative process, the user data sequence is estimated by hard-decision of the value of the a posteriori log-likelihood ratio (a posteriori LLR) for each bit of user data at the output of the channel decoder.

In FIG. 10, the horizontal axis is the average received energy to noise power density ratio (received Es / N0) per symbol, and the average desired signal power to interference signal power ratio CIR = 0 dB (desired signal and interference signal between mobile station MS). Average reception power is the same), average block error rate (BLER: BLock Error Rate) characteristics when the number of repetitions N _iter = 1 and N _iter = 4 in repetitive MAP signal detection, and a conventional method that does not use repetitive signal detection It is a figure which shows the average BLER characteristic at the time of applying the signal separation method (nonpatent literature 9) based on MLD (equivalent to the repetition frequency N _iter = 0), respectively. However, here, the block length is the number of information bits included in one frame (12 OFDM symbols). In the figure, for reference, the characteristics when there is no inter-cell interference (ICI) (No ICI, CIR = ∞), that is, the characteristics when an ideal inter-cell interference canceller can be realized. It is indicated by a broken line. From this figure, it can be seen that when the iterative MAP signal detection method of the present invention is applied, the BLER characteristics can be improved as the number of iterations _Niter is increased. For example, the required reception Es / N0 that achieves the average BLER ≦ 10 ⁻² should be improved by about 3 dB and 4 dB, respectively, compared to the conventional MLD-based method when the number of repetitions N _iter = 1 and N _iter = 4. Can do. In particular, when the number of repetitions N _iter = 4, it can be seen that the BLER characteristic asymptotically approaches when the average reception Es / N0 is about 7 dB or more and there is no inter-cell interference, and an almost ideal inter-cell interference cancellation can be realized. . Thus, the number of reception antennas N _r is despite to less than the total number of transmit antennas N _t from all the base stations, the signal detection method of the present invention is obtained excellent transmission characteristics.

In FIG. 11, the horizontal axis represents the average received energy to noise power density ratio (received Es / N0) per symbol, the average desired signal power to interference signal power ratio CIR = 0 dB in the mobile station MS, and the repetition in the repeated MAP signal detection When the number of times N _iter = 1 and N _iter = 4, and when the signal separation method based on the conventional MLD not using repetitive signal detection (Non-Patent Document 9) (corresponding to the number of repetitive times N _iter = 0) is applied It is a figure which shows each average throughput characteristic. In the figure, for reference, the characteristics when there is no inter-cell interference (ICI) (No ICI, CIR = ∞), that is, the characteristics when an ideal inter-cell interference canceller can be realized. It is indicated by a broken line. For example, consider the required average Es / N0 to achieve an average throughput of 1.8 bits / s / Hz. From FIG. 11, when CIR = 0 dB, the signal detection method of the present invention can reduce the required average Es / N0 by about 5 dB when N _iter = 4 as compared with the conventional MLD-based method. Furthermore, in the signal detection method of the present invention, when N _iter = 4, the average throughput when the average Es / N0 = 10 dB at CIR = 0 dB can be improved about twice as compared with the conventional signal detection method. As a result, the signal detection method based on the MAP algorithm of the present invention plays a role in the throughput characteristics of the mobile station at the cell edge in the error-correction coded MIMO-OFDM cellular system, compared with the conventional signal detection method based on MLD. Can be confirmed.

1: own cell base station, 2: neighboring cell base station, 3: mobile station, 4: own cell base station transmitting antenna, 5: neighboring cell base station transmitting antenna, 6: mobile station receiving antenna, 7: core network, 11 : Pilot channel, 12: broadcast channel and control channel, 13: traffic channel, 21: serial-parallel converter, 22-1 to 22-N _t0 : transmitter, 23: local oscillator, 24-1 to 24-N _t0 : Transmit antenna, 31: channel encoder, 32: interleaver, 33: modulator, 34: serial-parallel converter, 35: multiplexer, 36: inverse fast Fourier transform unit, 37: parallel-serial converter, 38: The guard interval adding unit, 39: D / A converter, 40: mixer, 41: power amplifier, 51-1 to 51-N _r: receiving antenna, 52-1 to 52-N _r: signal receiving section, 53: Local oscillator, 4: timing detection, channel estimation and control signal demodulation unit, 55: repetitive signal detection and channel decoder with inter-cell interference cancellation function, 61: mixer, 62: A / D converter, 63: guard interval removal unit, 64 : serial-to-parallel converter, 65: fast Fourier transform unit, 71-1 to 71-N _sub: soft output MIMO signal detector, 72-1 to 72-N _t: data estimating unit, 73: desired signal selecting section, 74 : parallel-serial converter, 75: hard decision unit, 81-1~81-N _t: parallel to serial converter, 82-1~82-N _t: deinterleaver, 83-1~83-N _t: soft input soft output channel decoder, 84-1~84-N _t: interleaver, 85-1~85-N _t: serial to parallel converter, 91: soft output MIMO signal detector, 92,96,98,101: adding , 93, 99: Deinter Lever, 94, 100: Soft input / soft output channel decoder, 95: Hard discriminator, 97, 102: Interleaver

Claims (3)

A wireless access system in which a base station and a mobile station communicate with each other by OFDM,
When a common frequency band is used by a plurality of base stations in downlink transmission, the transmission timing of all the base stations that interfere with each other is the reception timing including the multipath of the signal from each base station in the mobile station. The deviation is controlled to be within the OFDM guard interval,
Each base station
Transmitting an OFDM signal in which a pilot channel including a pilot signal, a control channel including at least control information necessary for communication with a mobile station, and a traffic channel including error correction encoded user data information are multiplexed; And, it is configured to transmit the information related to the transmission method of the traffic channel of the local station included in the control information,
The mobile station
Based on the received signal in the pilot signal section of the signal from each base station, channel information between the own cell base station and the own mobile station and between each neighboring cell base station and the own mobile station that cause interference are acquired. Means,
Means for demodulating the control channel with respect to the own cell base station and neighboring cell base stations that cause interference, and obtaining the control information of the own cell base station and each neighboring cell base station that causes interference;
Transmission method information acquisition means for demodulating control information received from the own cell base station and neighboring cell base stations that cause interference to acquire information on the transmission method of the traffic channel of each base station ;
A soft output MIMO signal detector and a soft input / soft output channel decoder that operate based on a maximum a posteriori probability (MAP) estimation algorithm, the acquired channel information, the acquired own cell base station, and each neighboring cell serving as interference Using the control information of the base station and using the information acquired by the transmission method information acquisition means , the desired signal from the own cell base station and the interference signal from the neighboring cell base station are estimated from the received signal to the maximum posterior probability A signal separation means for separating a desired signal from the own cell base station and an interference signal from a neighboring cell base station by simultaneously detecting by repetitive signal detection based on the posterior signal output from the soft output MIMO signal detector; The external log likelihood ratio, which is the difference between the probability log likelihood ratio and the prior log likelihood ratio, is input to the soft input / soft output channel decoder as a prior input value. The soft log MIMO signal detection is performed by using the external log likelihood ratio, which is the difference between the posterior probability log likelihood ratio output from the soft input soft output channel decoder and the prior input value, as the prior log likelihood ratio. and a signal separating means is inputted to the vessel are configured so that,
No line access system that is characterized in that to achieve a demodulation of the desired signal from the interference cancellation and the own-cell base station from the neighboring cell by taking out only the desired signal from the separated signal simultaneously by the signal separating means. A wireless access system in which a base station and a mobile station communicate with each other by OFDM,
When a common frequency band is used by a plurality of base stations in downlink transmission, the transmission timing of all the base stations that interfere with each other is the reception timing including the multipath of the signal from each base station in the mobile station. The deviation is controlled to be within the OFDM guard interval,
Each base station
Transmitting an OFDM signal in which a pilot channel including a pilot signal, a control channel including at least control information necessary for communication with a mobile station, and a traffic channel including error correction encoded user data information are multiplexed; and it is configured to transmit the neighboring cell base station serving as the interference information related to the transmission scheme of the traffic channel in addition to the own station is also included in the control information,
The mobile station
Based on the received signal in the pilot signal section of the signal from each base station, channel information between the own cell base station and the own mobile station and between each neighboring cell base station and the own mobile station that cause interference are acquired. Means,
Means for demodulating the control channel with respect to the own cell base station and neighboring cell base stations that cause interference, and obtaining the control information of the own cell base station and each neighboring cell base station that causes interference ;
A soft output MIMO signal detector and a soft input / soft output channel decoder that operate based on a maximum a posteriori probability (MAP) estimation algorithm, the acquired channel information, the acquired own cell base station, and each neighboring cell serving as interference Based on the control information of the base station, the control information received from the own cell base station is demodulated and acquired based on the information on the transmission method of the traffic channel of the own cell base station and the neighboring cell base station that causes interference. By simultaneously detecting the desired signal from the own cell base station and the interference signal from the neighboring cell base station from the signal by repeated signal detection based on the maximum posterior probability estimation, the desired signal from the own cell base station and the neighboring cell base station are detected. Separating means for separating an interference signal from a posterior probability log-likelihood ratio output from the soft-output MIMO signal detector A posterior probability log-likelihood ratio output from the soft-input / soft-output channel decoder is input to the soft-input / soft-output channel decoder as a pre-input value that is a difference from the prior log-likelihood ratio. And an external log likelihood ratio that is a difference between the prior input value and the prior log likelihood ratio as signal input to the soft output MIMO signal detector,
No line access system that is characterized in that to achieve a demodulation of the desired signal from the interference cancellation and the own-cell base station from the neighboring cell by taking out only the desired signal from the separated signal simultaneously by the signal separating means. A mobile station apparatus in a radio access system in which a base station and a mobile station communicate by OFDM,
When the radio access system uses a common frequency band in a plurality of base stations in downlink transmission, the transmission timing of all the base stations that interfere with each other is the multipath of the signal from each base station in the mobile station. The base station is controlled so that the shift in the reception timing including the frequency falls within the OFDM guard interval, and each base station includes at least control information necessary for communication with the pilot channel including the pilot signal and the mobile station. An OFDM signal in which a control channel and a traffic channel including error correction encoded user data information is multiplexed is transmitted , and information on a transmission method of the local traffic channel is included in the control information. Is intended to send ,
Based on the received signal in the pilot signal section of the signal from each base station, channel information between the own cell base station and the own mobile station, and between each neighboring cell base station and the own mobile station that cause interference. Means to obtain,
Means for demodulating the control channel with respect to the own cell base station and the neighboring cell base station causing interference, and acquiring the control information of the neighboring cell base station serving as the own cell base station and interference;
A soft output MIMO signal detector and a soft input / soft output channel decoder that operate based on a maximum a posteriori probability (MAP) estimation algorithm, the acquired channel information, the acquired own cell base station, and each neighboring cell serving as interference From the received signal based on the information regarding the transmission method of the traffic channel of each base station, which is included in the control information of the own cell base station and each neighboring cell base station that causes interference , using the control information of the base station By simultaneously detecting the desired signal from the own cell base station and the interference signal from the neighboring cell base station by repeated signal detection based on the maximum posterior probability estimation, the desired signal from the own cell base station and the neighboring cell base station Signal separating means for separating an interference signal, the posterior probability log-likelihood ratio and the prior log likelihood output from the soft output MIMO signal detector An external log-likelihood ratio, which is a difference from the ratio, is input as a pre-input value to the soft-input soft-output channel decoder and output from the soft-input soft-output channel decoder and the a priori log-likelihood ratio Signal separation means configured to input an external log likelihood ratio that is a difference from an input value to the soft output MIMO signal detector as the prior log likelihood ratio;
A mobile station apparatus that simultaneously realizes removal of interference signals from neighboring cells and demodulation of desired signals from the own cell base station by extracting only desired signals from the signals separated by the signal separation means.

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