Performance Research And Simulation Of Space-Time Block Code Based On OFDM

Space-time coding technique is a very promising technology to implement broadband wireless data communication. It combines coding, modulation, transmit and receive diversity, and validly increases the anti-noise performance in fading channels. Space Time Block Coding, by virtue of its simple structure, easy to implement and better performance, has become a hot topic of research. But most of the existing researches are conducted in the flat fading channel. Based on OFDM technology which has the effective characteristic against multipath fading, this thesis detailed analyses STBC technique in frequency selective fading channels and present the STBC-OFDM system structure and encoding and decoding methods.This thesis is mainly focused on the space-time coding technique. Firstly, It introduces the principle of space-time code and gives the design criteria of it in quasi-static flat-fading channels. And, It analyzes the encoding and decoding theories, features of various space-time block code schemes. After studying the encoding and decoding methods of the traditional quasi-orthogonal space-time block codes, and to overcome its shortcoming that can not achieve full diversity gain, this thesis put forward an improved space-time code scheme by combining the quasi-orthogonal space-time coding techniques with constellation rotation and matrix rotation.Simultaneously, the OFDM basic principle and cyclic prefix are analyzed in detail. Combining adding and getting rid of cyclic prefix on data blocks, with the IFFT and FFT operation, OFDM technique can transform frequency-selective fading channel into a flat fading channel. This thesis analyzes the theoretical basis of the space-time coding technique combining with OFDM techniques, and presents the STBC-OFDM communication system. After studying and analyzing the coding and decoding principle of STBC-OFDM system, this thesis puts forward a design method of the system with precoding module.Finally, this thesis carries on the simulation and performance analysis for different coding scheme by different kinds of modulation by use of different decoding algorithm for STBC system in flat fading channel and STBC-OFDM system in frequency selective fading channel respectively. The simulation results show that the performance of the improved coding scheme in flat fading channel is superior than the traditional coding scheme, because it can ensure full data rate transmission and can get full diversity gain at the same time. In frequency selective fading channel, the error rate of the STBC-OFDM systems with precoding module have different degrees of reduce in different modulation methods, compared with QOSTBC-OFDM systems. Because the system with precoding module can use maximum likelihood decoding algorithm at a relatively low decoding complexity.