Research On Differential Space-Time Block Coding Technology In Wireless Communication Systems

Space-time coding (STC) combines channel coding with antenna diversity, which can increase the capacity of wireless communication systems and achieve diversity gain and coding gain. The technique can improve the bandwidth efficiency of traditional single-antenna systems, and provide new solutions to the problem of limited channel bandwidth in wireless communication. Differential space-time coding (DSTC) is suitable for the future communication under rapid fading channels. Compared with other STC technology, the decoding does not need the perfect channel state information (CSI) . The transmitted matrices must satisfy some restriction for the procession of differential encoding and decoding. Since the orthogonal space-time block codes (STBC) satisfy unitary matrices, many studies about differential STBC have been proposed in the past years.Firstly, the encoding principle of DSTBC is investigated, and the design rules of coefficients vector set of DSTBC are obtained. Secondly, the performances of the traditional DSTBC are analyzed by the simulation results. An improved method of traditional DSTBC is proposed for two transmit antennas, which solves the constellation expansion and provides a coding gain, as the simulation results are shown. Since the traditional DSTBC based on complex signal constellation does not satisfy the design criteria rules in which the coefficient vector must have a unitary length, it is only suitable for real signal constellation with four transmit antennas. An improved algorithm is presented by dividing signals into real and imaginary parts, and the simulation results verify the validity of this algorithm.Finally, the combination of DSTBC and orthogonal frequency division multiplexing (OFDM) technique is investigated to solve the diversity problem in a frequency-selective fading channel. OFDM can greatly eliminate Inter-Symbol Interference (ISI) which is caused by fading multi-path effect. By the performance analysis of STC-OFDM in frequency-selective fading channels, the structure of DSTBC-OFDM systems is proposed. Simulation results show that DSTBC-OFDM can achieve frequency diversity and space diversity, and performs very well.The research results show that DSTBC performs about 3dB worse than coherent detection which knows the correct CSI. In the meantime of paying costs in capacity, DSTBC gets rid of the reliance upon the CSI and have a specific application background.