Research On Variable-rate Space-time Coding

With the integration of Internet and multimedia applications in the next generation wireless communications, the demand of broadband and high-speed data communication services continues to increase. Due to the limitation of available wireless spectrum resources, high-speed data can only be achieved through efficient signal processing. The research of information theory indicates that multiple input multiple output (MIMO) system can significantly increase the capacity and efficiency of spectrum in wireless communication channel. In wireless communication systems, especially high-speed wireless communication systems, space-time coding has broad application prospects because of its anti-fading transmit diversity technology.Currently, the study of space-time coding is mainly based on the fixed rate, and the study of variable-rate space-time coding technology mostly focuses on variable-rate space-time block coding, the other type of variable-rate space-time coding is still without answer. The existing variable-rate space-time block coding scheme requires to regrouping the transmission antennas. Because of the complexity of grouping, coding in the transmitter as well as decoder in the receiver gets much more complex, and leads to more difficult to achieve in software and hardware systems. Moreover, almost all studies are on the assumption that the channel state information (CSI) is known in the transmitter, which requires the system sending training sequences from the transmitter. After receiving training sequence, the receiver estimates channel state of the system, and feed back CSI to transmitter. This process may introduce CSI error and increase the complexity of the system.Variable-rate space-time coding technology can be used in the different environment of the channel, as well as the different needs of users, by choosing a different antenna grouping scheme, considering transmitting power, transmission speed and transmission quality to provide users with the best communication environment. Therefore, this thesis conducts a study of variable-rate space-time coding in MIMO system.Main content of this thesisChapter one summarizes the actuality of variable-rate space-time coding, and analyzes the effect of using variable-rate space-time coding in wireless communication system. Finally introduces the researching purport and main content of this thesis.Chapter two summarizes the correlation MIMO system model and the basic channel model. In accordance with the channel capacity formula of block fading channel and correlation MIMO channel, simulate out the relationship among the channel capacity, the number of transmitting antennas and the receiving antennas. From the simulation curve can be seen that with the increase in the number of receiving antennas and transmitting antennas, channel capacity increased, and channel capacity declined when its correlation increased.Chapter three summarizes the system model and basic principle of STBC, STTC, LSTC and DSTBC.Chapter four constructs a system model of space-time coding over block fading channel, and discusses PEP bound in detail over Rayleigh and Rician fading channel model.Simulate out the bit error rate (BER) and symbol error rate (SER) performance in 4-Phase-Shift-Keying (4PSK) modulation with one and two transmitting and receiving antennas, BER and SER performance in 16-Phase-Shift-Keying (16PSK) and 16-Quadrature Amplitude Modulation (16QAM) with 3 and 4 transmitting antenna and two receiving antenna, BER and SER performance in 4PSK modulation with two transmitting and receiving antenna when the correlation coefficients are 0, 0.5, 0.8 and 1 as well as BER and SER performance in differential space-time block coding.Chapter five constructs a basic system model of variable-rate space-time block coding, study the variable-rate space-time block coding carefully over two transmitting and receiving antenna, three transmitting and receiving antenna as well as four transmitting and receiving antenna. Code rate table for two, three and four transmitting and receiving antenna variable-rate space-time block coding are given. Simulate out the BER and SER performance in 4PSK modulation when slots L=8.A variable-rate space-time block coding scheme based on antenna reuse is proposed, and the system model is constructed. A conclusion of maximum code rate in variable-rate space-time block coding system based on the antenna reuse was summarized: For any one space-time block coding system with transmitting antenna n, receiving antenna m (m≤n) and slots L, it is possible to achieve the maximum code rate m by antenna reuse at the same frequency. However, a number of information symbols are transmitted simultaneously at the same antenna, multiplexing signal can be considered as noise interference for primitive symbols and vice versa. With the same transmission power, the signal-to-noise ratio (SNR) in the receiver becomes lower. Simulate and analyze the variable-rate space-time block coding performance based on antenna reuse, and compare the performance of this scheme with the former scheme.Introduce the idea of differential space-time coding to variable-rate space-time block coding system, as the use of a differential, there is no need to estimate the CSI at the receiver for variable-rate space-time coding, and we can also get the greatest diversity gain, simplify the structure of the receiver. But the differential space-time decoding will introduce more interference and noise, and increase the total transmitting power. Simulate out the BER and SER performance of two transmitting and receiving antenna in 4PSK modulation when slots L=9.Chapter six summarizes the conclusions of this thesis.The main contribution of this thesis1. A variable-rate space-time block coding scheme based on antenna reuse is proposed, and the system model is constructed. Simulate out the BER and SER performance of this scheme. It is easy to code but requires much more transmit power.2. A conclusion of maximum code rate in variable-rate space-time block coding system based on the antenna reuse was summarized: For any one space-time block coding system with transmitting antenna n, receiving antenna m (m≤n) and slots L, it is possible to achieve the maximum code rate m by antenna reuse at the same frequency.3. Introduce the idea of differential space-time coding to variable-rate space-time block coding system, as the use of differential, there is no need to estimate the CSI at the receiver for variable-rate space-time coding, and we can also get the greatest diversity gain, simplify the structure of the receiver. But the performance of this scheme is 3dB worse than coherent demodulation...