Array Signal Processing Based Space-Time Coding

MIMO (Multiple-Input Multiple-Output) based STC (Space-Time Coding) technology can meet the need of high data-rate transmission in future wireless communications without any loss in bandwidth and transmitting power. In the STC schemes available, BLAST and STBC have been adopted by 3rd Generation Mobile Communication Standard;however, many problems arising from actual application are still open. Among the problems to be solved are how to increase the transmission rate of STBC, improve the combating-fading performance of BLAST and improve the performance of Space-Time Codes over correlated fading channels. This paper incorporates the idea of array signal processing methods into STC to study two architectures over independent fading channels. Also, the scheme to realize STC in correlated fading environments is studied in this dissertation. The primary contributions included in this dissertation are summarized below:1. To increase the transmission rate of STBC, a layered Space-Time Block Coding scheme (LSTBC) based on GIS (Group Interference Suppressing) algorithm is proposed. The proposed transmitter divides transmit antennas into groups and independently encodes each group by an STBC encoder and this results in the increase of the transmission rate. At the end of the receiver, each group is independently decoded by an ML decoder using GIS algorithm. Also presented is a simple method to estimate the propagation channel. The theoretical analysis and simulation results show that LSTBC greatly outperforms BLAST under the same conditions (including the propagation channel, bandwidth efficiency, antennas configuration and transmission power). It is also found that LSTBC is superior to STBC in the low SNR region. Furthermore, two OFDM based LSTBC schemes are put forward for frequency selective fading channels. The SVD (Singular Value Decomposition) and SCSM (Sub-Carrier Selection Matrices) algorithms are utilized in the two schemes respectively to suppress the interferences between different groups. It can be seen from the theoretical analysis that the scheme based on SCSM can be applied to downlink transmission while the SVD based scheme can not and hence only one receive antenna is enough to decode the input signals in the SCSM scheme.2. Attempts to improve the combating-fading performance of BLAST led to a novel DSSS (Direct Sequence Spread Spectrum) based BLAST architecture (termed as DSSS-BLAST). The proposed transmitter, based on the layered transmissionarchitecture of BLAST, spreads signals of each branch. Via de-spreading at the receiver, co-channel interferences are effectively eliminated and thus signals from different transmit antennas are distinguished and independently detected. In addition, the proposed receiver adopts RAKE reception to achieve the optimal performance. DSSS-BLAST combining spreading and RAKE reception attains spreading and receiving diversity gains simultaneously and simplifies the estimation of channels. The theoretical analysis and simulation results show that DSSS-BLAST greatly outperforms BLAST on the same terms and can be applied to downlink transmission. DSSS-BLAST scheme over frequency selective fading channels is presented. Moreover, we incorporates the idea of DSSS-BLAST and DSTC (Differential Space-Time Coding) into LSTBC to develop a novel layered differential Space-Time detection scheme which dispenses with the need of estimating the channel and can be used in downlink transmission. 3. The effect of the correlation of the channel fading on STBC is investigated. The relation of the distance between transmit antennas and that between receive antennas to the correlation coefficients is determined via the 'single ring' channel model. Based on the relation between receive deiversity and transmit diversity, the closed-form expression of BER (Bit-Error Rate) over STBC in correlated fading environments is obtained. The validity of the formula is verified by the Monte-Carlo simulation experiments. It is the obtained formula rather than the Monte-Carlo experiment that is utilized to compute the BERs of STBC for different correlations or antennas distances. It can be seen from the simulation results that the STBC scheme designed for independent fading channels is comparatively robust in correlated fading environments.4. Also proposed in this paper is a Space-Time Eigenbeam Coding (STEBC) scheme for downlink transmission channels in which fading at the transmitter is correlated but independent at the receiver. The transmitter performs eigenvalue-decomposition on the SCM (Spatial Covariance Matrix) and utilizes the obtained eigenvectors as weighting vectors to form orthogonal eigenbeams to carry the space-time codes. Combining the diversity and beamfonning techniques properly, STEBC attains the array and diversity gains simultaneously. Moreover, the complexity of the system is remarkably reduced by performing the dimension-reduction operation in STEBC. Therefore, STEBC is especially suitable for the wireless environments with many paths around the transmitter. The validity of STEBC under different conditions is verified by simulation experiments. The simulation results show that theperformance of the proposed system is improved with the increase of either the number of paths or that of transmit elements. In addition, the effect of channel estimation error on the performance is also analyzed. The analysis results show that the error does not have any influence on eigenbeamforming performed at the transmitter. Finally, a layered STEBC scheme based on DSSS for correlated fading channels is proposed. The new scheme has characteristics similar to that of the DSSS-BLAST designed for independent fading channels.