JP2007124358A - Wireless communication equipment, and communication control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simplify communication control with improvement of transmission property in a wireless communication system of an SDMA system. <P>SOLUTION: This wireless communication equipment is provided with a demodulation means which judges a transmitted signal based on a received signal point with the reception value of each sub-carrier as coordinates and a reference signal point being the combination of coordinates which the received signal point can take originally in a signal space composed of the subcarriers in a range where one modulation signal is spread regarding a signal to which code spreading in a frequency direction is carried out to carry out frequency multiplication by two or more subcarriers. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a spatial division multiple access (SDMA) wireless communication apparatus and a communication control method.

  In a mobile communication system, improvement of frequency utilization efficiency is one of important issues. In a cellular environment where a plurality of wireless terminals exist in a communicable area (cell) formed by a wireless base station, the wireless terminal uses the communication capacity of the wireless base station in the time domain and frequency to improve frequency utilization efficiency. Shared in the area or code area, and communicates by multiple access. These techniques are called time division multiple access (TDMA), frequency division multiple access (FDMA), and code division multiple access (CDMA), respectively.

  In recent years, a Spatial Division Multiple Access (SDMA) system has attracted attention as one of such multiple access systems. In the SDMA system, for example, by performing spatial filtering using an array antenna in a radio base station, signals for each user are spatially separated and transmitted / received (parallel transmission). As a result, a plurality of users in the same cell using the same frequency can be accommodated at the same time, and the frequency utilization efficiency can be improved. In the SDMA system, each user is identified by the angle (arrival angle) at which each user's signal reaches the base station. For example, as shown in FIG. 6, when the mobile station 1_510 and the mobile station 2_510 exist in the same cell 501, the base station 500 dynamically controls the antenna directivity using, for example, an adaptive array antenna. As a result, the radiation patterns 521 and 522 of each radio wave toward the mobile station 1_510 and the mobile station 2_510 are narrowed down. Thereby, the base station 500 can simultaneously communicate with the mobile station 1_510 and the mobile station 2_510 with the same channel and the same transmission timing.

  FIG. 7 shows a reception configuration example of an adaptive array antenna. The adaptive array antenna is described in Non-Patent Document 1, for example. In the adaptive array antenna, a plurality of antenna elements 1201 are arranged, and a weight controller 1212 controls weights for weighting the signals of the antenna elements 1201 by the multipliers 1202. Thereby, the directivity of the antenna is adaptively controlled by independently controlling the amplitude and phase of excitation of each antenna element 1201.

In addition, a multi-carrier transmission system has attracted attention as a communication system that is being considered for application to a new generation mobile communication system. Typical examples of the multicarrier transmission system include an orthogonal frequency division multiplexing (OFDM) system and a multi-carrier code division multiplexing (MC-CDM) system. It is done. In the MC-CDM system, modulation symbols are spread and multiplexed on a plurality of subcarriers, and thereby a frequency diversity effect can be obtained and inter-cell interference can be made uniform. However, it is known that signal-to-noise power and interference energy ratio after despreading deteriorate due to occurrence of intersymbol interference in a frequency selective transmission line. As a countermeasure, Non-Patent Document 2 discusses multi-dimensional demodulator that demodulates a signal without despreading.
Nobuyoshi Kikuma, "Adaptive signal processing with array antenna", Science and Technology Publishing, 1998. 3GPP TSG RAN WG1 # 42 bis, R1-051261, “Enhancement of Distributed Mode for Maximizing Frequency Diversity,” Oct. 2005. Edited by Masaaki Shinji, "Radio wave propagation in wireless communication", IEICE, 1997. A. Harada, S. Tanaka, M. Sawahashi, F. Adachi, “Experiments on Adaptive Antenna Array Transmit Diversity in W-CDMA Forward Link,” July 2002. T. Suzuki, N. Miyazaki, Y. Hatakawa, “A Proposal of Twin Turbo Detector and Its Evaluation for M-QAM OFDM,” Shingaku So, B-5-6, Sep. 2005.

However, the above-described conventional SDMA system has the following problems.
In a mobile communication environment, the existence of multipaths becomes a problem. A scattering ring model described in Non-Patent Document 3 is known as a propagation path model that simulates multipath in an urban area (see FIG. 8). As shown in FIG. 8, an infinite number of scatterer secondary wave sources are considered at a position of radius r _s with mobile station 510 as the center. Transmitted from the base station 500 radio, after being reflected and diffracted by buildings or the like existing on the circumference of radius r _s about the mobile station 510, a plurality with a delay time corresponding to each path It arrives at the antenna of the mobile station 510 as a signal. The electric field strength of the signal received by the mobile station 510 as a composite wave of the plurality of signals exhibits a random fluctuation of the standing wave property according to the Rayleigh distribution law. Such fading is called multipath Rayleigh fading.

  As shown in FIG. 8, when the transmission beam 520 of the base station 500 formed by an adaptive array antenna has a certain angular spread, the received electric field strength at the mobile station 510 is severe frequency selective characteristics due to multipath Rayleigh fading. It has. For this reason, there is a problem in that the transmission characteristics are greatly deteriorated when the received electric field intensity in the used frequency band is instantaneously severely attenuated.

  Further, even if the frequency diversity effect is obtained by using the MC-CDM method, characteristic deterioration due to intersymbol interference becomes a problem. Further, Non-Patent Document 4 proposes a method for controlling an adaptive array antenna so that the instantaneous received electric field strength at each mobile station 510 is maximized in order to cope with instantaneous fluctuations in the received electric field strength in the used frequency band. However, there are problems that the control method is complicated, such as narrowing the transmission beam width and shortening the control time interval, and increasing the circuit scale of the control device.

  The present invention has been made in view of such circumstances, and an object of the present invention is to improve a transmission characteristic and simplify communication control in an SDMA wireless communication system and communication control. It is to provide a method.

  In order to solve the above problems, a wireless communication apparatus according to the present invention is an SDMA wireless that realizes multiple access by spatially separating signals for each user by adaptively controlling antenna directivity characteristics. A wireless communication apparatus in a communication system, in which a signal that has been subjected to code spreading in the frequency direction and frequency-multiplexed with a plurality of subcarriers is transmitted in a signal space composed of subcarriers in a range in which one modulation symbol is spread. And demodulating means for determining a transmitted signal based on a received signal point whose coordinates are the received value of each subcarrier and a reference signal point that is a combination of coordinates that can be originally taken by the received signal point. Features.

  The wireless communication apparatus according to the present invention is characterized in that a control means for adaptively controlling the directivity characteristics of the antenna is provided based on a parameter related to the frequency diversity effect.

  The radio communication apparatus according to the present invention has means for decoding an error correction code from the determination result of the demodulation means and feeding back the probability of the received signal obtained in the decoding process as the appearance probability of the reference signal point It is characterized by that.

  The radio communication apparatus according to the present invention is characterized in that the turbo code as the error correction code is decoded by twin turbo demodulation.

  A communication control method according to the present invention is a communication control method in an SDMA wireless communication system that realizes multiple access by spatially separating signals for each user by adaptively controlling antenna directivity, Coordinates the received value of each subcarrier in a signal space composed of subcarriers in the range where one modulation symbol is spread, with a signal that has been subjected to code spreading in the frequency direction and frequency-multiplexed with multiple subcarriers And a demodulation process for determining a transmitted signal based on a received signal point and a reference signal point that is a combination of coordinates that can be originally taken by the received signal point.

  The communication control method according to the present invention is characterized by having a control process for adaptively controlling the directivity of the antenna based on parameters related to the frequency diversity effect.

  The communication control method according to the present invention includes a process of decoding an error correction code from the determination result of the demodulation process and feeding back the probability of the received signal obtained in the decoding process as the appearance probability of the reference signal point. It is characterized by that.

  According to the present invention, in the SDMA wireless communication system, transmission characteristics can be improved and communication control can be simplified.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
FIG. 1 is a block diagram showing the overall configuration of an SDMA wireless communication system according to the first embodiment of the present invention. The wireless communication system shown in FIG. 1 applies the MC-CDM method as an example of the multicarrier transmission method.

In FIG. 1, a transmitter 100 includes a modulator 104, a serial / parallel converter 105, a spreader 106, an inverse Fourier transformer 107, a parallel / serial converter 108, and cyclic prefix insertion related to processing of information bits to be transmitted. 109, serial / parallel converter 111, inverse Fourier transformer 112, parallel / serial converter 113, cyclic prefix inserter 114, time multiplexer 110, adaptive array for processing pilot symbols to be transmitted An antenna (AAA) 120 and an array controller 130 are provided.
The receiver 200 includes a time demultiplexer 201, a cyclic prefix remover 202, a serial / parallel converter 203, a Fourier transformer 204, an equalizer 205, and a parallel / serial converter for processing the received data signal. 206, a symbol generator for maximum likelihood estimation 207 and a demodulator 208, a cyclic prefix remover 209, a serial / parallel converter 210, a Fourier transformer 211, and a transmission path estimator 212 for processing the received pilot signal Is provided.

  Transmitter 100 modulates information bits, serial / parallel-converts the modulation symbols in accordance with the spreading factor, and then spreads them on subcarriers on the frequency axis using orthogonal codes such as Walsh codes to generate data subcarriers. To do. At this time, information on the spreading factor and the subcarrier arrangement of each data symbol is provided to the array controller 130. Various spreading codes can be used for the spreading. The data subcarrier is converted into a time-domain signal by inverse Fourier transform, and after parallel / serial conversion, a cyclic prefix is inserted and time-multiplexed with the pilot signal.

  The time-multiplexed signal A1 is transmitted with the radiation pattern directed in the direction in which the receiver 200 exists by the adaptive array antenna 120. Here, adaptive array antenna 120 performs antenna directivity control in accordance with control signal A 2 received from array controller 130. Array controller 130 generates control signal A2 based on the spreading factor received from spreader 106, information on the subcarrier arrangement of each data symbol, and the like.

  FIG. 2 is a block diagram showing a configuration of adaptive array antenna 120 shown in FIG. FIG. 2 shows a transmission configuration example of an adaptive array antenna. In the adaptive array antenna 120 of FIG. 2, a plurality of antenna elements 1201 are arranged to constitute an array antenna. The time-multiplexed signal A1 is distributed by the distributor 1203 corresponding to each antenna element 1201. The distributed signal is weighted with each weight from weight control section 1204 by multiplier 1202 for each antenna element 1201. Weight control section 1204 controls the weight for each antenna element 1201 in accordance with control signal A2 received from array controller 130. Thereby, according to the control from array controller 130, the amplitude and phase of excitation of each antenna element 1201 are independently controlled, and the antenna directivity is adaptively controlled.

  As a method of controlling the antenna directivity by the array controller 130, the antenna directivity is finely controlled when the frequency diversity effect cannot be obtained. For this reason, the array controller 130 controls the antenna directivity based on a parameter related to the frequency diversity effect. Examples of parameters related to the frequency diversity effect include spreading factor, number of subcarriers, subcarrier frequency bandwidth, information on subcarrier arrangement of each data symbol, and the like. As a specific example of the antenna directivity control method based on the parameters related to the frequency diversity effect, for example, when the spreading factor is small, or when consecutive data symbols are arranged on nearby subcarriers with high correlation, the frequency Since the diversity effect is difficult to obtain, the antenna directivity is precisely controlled. Fine antenna directivity control means, for example, that the radiation pattern (transmission beam) of a radio wave transmitted from a base station to a specific mobile station is accurately matched to the direction of the mobile station, and that the transmission beam width is narrowed. And shortening the control time interval. In the present embodiment, such fine antenna directivity control is not always performed, but only when it is difficult to obtain the frequency diversity effect. Thereby, the control of the antenna directivity by the adaptive array antenna 120 is simplified.

  The signal transmitted from the transmitter 100 is subjected to frequency selectivity in the transmission lines 301 and 302, and reaches the receiver 200 after adding additive white Gaussian noise.

  In the receiver 200, the received signal is first separated into a pilot signal and a data signal, and the cyclic prefix is removed. The signal from which the cyclic prefix has been removed is subjected to serial / parallel conversion, and converted into pilot subcarriers and data subcarriers by Fourier transformation. Transmission path fluctuation is estimated from the pilot subcarrier, and the equalizer compensates the transmission path fluctuation for the data subcarrier from the estimation result. The equalized data subcarriers are converted into maximum likelihood estimation symbols by the maximum likelihood estimation symbol generator 207 after being subjected to parallel / serial conversion, and obtained by comparison with distances to all possible signal points. Is output as the channel value. The demodulator 208 uses the communication channel value, and in a signal space composed of subcarriers in a range where one modulation symbol is spread, a received signal point having the received value of each subcarrier as coordinates, and the received signal The transmitted signal is determined based on a reference signal point that is a combination of coordinates that the point can originally take. An information bit is output as the determination result.

  According to the first embodiment described above, since the signal is demodulated without despreading by the maximum likelihood estimation symbol generator 207 and the demodulator 208, in the MC-CDM system, the code interval due to the influence of the frequency selective transmission path is increased. Interference can be avoided. As a result, the frequency diversity effect can be obtained remarkably and the transmission path characteristics are improved. In addition, since it is possible to reduce the influence of instantaneous fluctuations in the received electric field strength in the used frequency band due to multipath Rayleigh fading, it is possible to reduce the degradation of transmission path characteristics when the antenna directivity control direction is shifted in the SDMA scheme. Can do. In addition, it is possible to efficiently reduce the influence of instantaneous fluctuations in the received electric field strength.

  Further, according to the present embodiment, since the transmission path characteristics are improved as described above, it is possible to simplify the control of the antenna directivity by the adaptive array antenna 120. That is, the antenna directivity may be finely controlled when the frequency diversity effect cannot be obtained without always finely controlling the antenna directivity. Thereby, for example, the antenna control in the base station can be simplified.

[Second Embodiment]
FIG. 3 is a block diagram showing the overall configuration of an SDMA wireless communication system according to the second embodiment of the present invention. In FIG. 3, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted.

  In the wireless communication system shown in FIG. 3, a turbo code is applied. The transmitter 100a of FIG. 3 is provided with a turbo encoding 101, a puncture 102, and a bit interleaver 103. The turbo encoder 101 turbo encodes information bits to generate encoded data including information bits and two parity bits. The puncture 102 generates a code sequence having an arbitrary coding rate by puncturing the parity bits in the encoded data. The bit interleaver 103 bit interleaves the code sequence. The signal after the bit interleaving is input to the modulator 104. The operation after the modulator 104 is the same as that of the first embodiment shown in FIG.

  The receiver 200 of FIG. 3 is provided with a twin turbo demodulator 208a. The operations up to the maximum likelihood estimation symbol generator 207 are the same as those in the first embodiment shown in FIG. The twin turbo demodulator 208a uses the maximum likelihood estimation symbol (communication channel value) input from the maximum likelihood estimation symbol generator 207 to perform demodulation and turbo code decoding.

  FIG. 4 is a block diagram showing the configuration of the turbo encoder 101. FIG. 5 is a block diagram showing the configuration of the twin turbo demodulator 208a.

4, a turbo encoder 101, the information bit vector _{X a,} by constituent encoder 1_1011 generates parity bit vector _{X b.} The information bit vector _{X a} is from interleaved data by the turbo interleaver 1012 to generate a parity bit vector _{X c} by constituent encoders 2_1011.

FIG. 5 shows a demodulation configuration related to a turbo code called “twin turbo demodulation” disclosed in Non-Patent Document 2 and Non-Patent Document 5. According to the twin turbo demodulation, the turbo code correction capability can be improved.
In a general turbo decoder, two element decoders are connected by a bit interleaver, and the posterior value of the bit updated in each element decoder is fed back as a prior value of the other element decoder. Thus, efficient MAP (Maximum A posteriori Probability) decoding is achieved.

On the other hand, in the twin turbo demodulator 208a shown in FIG. 5, the feedback loop for probability propagation (in FIG. 5, the external value (X _a ) after the output of the element decoder 2_2081 is converted into an element via the turbo deinterleaver 2083. In addition to a path that is input as an _a priori value (X _a ) to the decoder 1 — 2081), a stochastic coupling feedback loop (the posterior values (X _a , X _c ) after the output of the element decoder 2 — 2081 in FIG. 5 is a turbo deinterleaver 2083. And the post-value (X _a , X _b ) after the output of the element decoder 1_2081 are input to the demodulator 2_2080) to form a multi-level modulation symbol. The error probability of the turbo code is improved by calculating the joint probability of the likelihood of each bit.

  According to the second embodiment described above, the error correction capability of the turbo code is improved by performing twin turbo demodulation, so that the transmission path characteristics in the MC-CDM system are further improved.

  According to each embodiment described above, in the SDMA wireless communication system, it is possible to improve transmission characteristics when the MC-CDM method is applied and simplify communication control.

  In an SDMA wireless communication system that realizes multiple access by spatially separating signals for each user by adaptively controlling the antenna directivity, a plurality of codes are spread in the frequency direction. In a signal space composed of subcarriers in a range in which one modulation symbol is spread, a signal frequency-multiplexed with subcarriers, a received signal point whose coordinates are the received value of each subcarrier, and the received signal point is Demodulating means for determining a transmitted signal may be provided based on reference signal points that are combinations of coordinates that can be originally taken. Further, control means for adaptively controlling the directivity characteristics of the transmission antenna based on parameters related to the frequency diversity effect (spreading rate of spread multiplexed signal, number of subcarriers, frequency bandwidth of subcarrier, information on subcarrier arrangement, etc.) It is more preferable to provide. Further, there may be provided means for decoding the error correction code from the determination result of the demodulating means and feeding back the probability of the received signal obtained in the decoding process as the appearance probability of the reference signal point. As the error correction code, for example, the above-described turbo code, low-density parity-check code (LDPC code), or the like can be used.

The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes design changes and the like within a scope not departing from the gist of the present invention.
For example, the present invention can be similarly applied to other multi-carrier transmission schemes (for example, OFDM scheme) other than the MC-CDM scheme described above.

1 is a block diagram showing an overall configuration of an SDMA wireless communication system according to a first embodiment of the present invention. It is a block diagram which shows the structure of the adaptive array antenna 120 shown in FIG. It is a block diagram which shows the whole structure of the radio | wireless communications system of the SDMA system based on 2nd Embodiment of this invention. FIG. 4 is a block diagram illustrating a configuration of a turbo encoder 101 illustrated in FIG. 3. FIG. 4 is a block diagram showing a configuration of a twin turbo demodulator 208a shown in FIG. It is a conceptual diagram for demonstrating the SDMA system using transmission beam forming. It is a block diagram which shows the receiving structural example of an adaptive array antenna. It is a conceptual diagram for demonstrating the scattering ring model which simulates an urban area propagation path.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100,100a ... Transmitter, 101 ... Turbo encoder, 102 ... Puncture, 103 ... Bit interleaver, 104 ... Modulator, 106 ... Spreader, 107, 112 ... Inverse Fourier transformer, 120 ... Adaptive array antenna ( AAA), 130 ... array controller, 200, 200a ... receiver, 204, 211 ... Fourier transformer, 205 ... equalizer, 207 ... symbol generator for maximum likelihood estimation, 208 ... demodulator, 208a ... twin turbo demodulation 212, transmission path estimator, 1011, element encoder, 1012, 2082 ... turbo interleaver, 1201 ... antenna element, 1202 ... multiplier, 1203 ... distributor, 1204 ... weight controller, 2080 ... demodulator, 2081 ... Element decoder, 2083 ... Turbo deinterleaver

Claims (7)

A wireless communication apparatus in an SDMA wireless communication system that realizes multiple access by spatially separating signals for each user by adaptively controlling antenna directivity,
Coordinates the received value of each subcarrier in a signal space composed of subcarriers in the range where one modulation symbol is spread, with a signal that has been subjected to code spreading in the frequency direction and frequency-multiplexed with multiple subcarriers And a demodulation means for determining a transmitted signal based on a received signal point and a reference signal point that is a combination of coordinates that can be originally taken by the received signal point.   2. The wireless communication apparatus according to claim 1, further comprising control means for adaptively controlling the antenna directivity based on a parameter related to the frequency diversity effect.   3. A means for decoding an error correction code from a determination result of the demodulating means, and feeding back a probability of a received signal obtained in the decoding process as an appearance probability of the reference signal point. A wireless communication device according to 1.   The radio communication apparatus according to claim 3, wherein decoding of the turbo code as the error correction code is performed by twin turbo demodulation. A communication control method in an SDMA wireless communication system that realizes multiple access by spatially separating signals for each user by adaptively controlling antenna directivity,
Coordinates the received value of each subcarrier in a signal space composed of subcarriers in the range where one modulation symbol is spread, with a signal that has been subjected to code spreading in the frequency direction and frequency-multiplexed with multiple subcarriers And a demodulation process for determining a transmitted signal based on a received signal point and a reference signal point that is a combination of coordinates that can be originally taken by the received signal point.   6. The communication control method according to claim 5, further comprising a control process for adaptively controlling the directivity of the antenna based on a parameter related to the frequency diversity effect. 7. The method according to claim 5, further comprising: a step of decoding an error correction code from the determination result of the demodulation process and feeding back a probability of the received signal obtained in the decoding process as an appearance probability of the reference signal point. The communication control method described in 1.

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