The Simulation For Space-time Coding Of The MIMO-OFDM System

The lack of frequency resource is becoming serious with the development of the society and mobile communication. The novel transmit diversity technique, which can combines channel coding, modulation and signal processing at receive terminal, is required so as to make full use of the limited spectrum resource. Space-time coding (STC) combines the technique of channel coding and antenna diversity. It improves the diversity gain and coding gain remarkably and eliminates the interference and contradiction the multi-path fading effectively. So STC increases the capacity of wireless communication greatly. This technique provides a new solution to the problem of limited bandwidth in wireless communication.OFDM technology is a kind of transmitting way to solve effectively the inter symbol interference caused by multi-paths. Multiple Input Multiple Output (MIMO) technique, one of the most significant breakthroughs in wireless communications field, offers an effective way to combat and even exploit fading. However, in order to put this novel idea into practice, more effective signal processing techniques should be developed. Two advantages can be achieved by combing OFDM and MIMO technologies. One is to obtain very high system capacity, and the other is to obtain the very strong reliability through combination.At present space-time codes mainly have three categories: layered space-time codes, space-time lattice code and space-time block codes. The space-time Block Code as a new and emerging technology has significant performance advantages, and its encoding and decoding algorithms are relatively simple. Therefore it can be applied in many areas, such as the MIMO-OFDM system.In this paper, the basic principle of OFDM, the advantages and disadvantages of OFDM system, space-time channel model, the system model and coding method of space-time code are introduced in detail. The system block-diagram of space-time code and MIMO-OFDM are designed. The performances of space-time code in OFDM system are processed using theoretic analysis method. At last, the BER performances in different coding method and different channel environment are simulated, analyzed and compared. It can be seen from the simulation results: in MIMO-OFDM system, for the same number of receiving antennas, the use of space-time coding and non-use of space-time coding, performance has greatly improved: the use of a two-day launching accession to the line of space-time coding OFDM system error performance is superior to single-antenna accession to the launch of the space-time coding OFDM system performance, using four antennas accession to the launch of the space-time coding OFDM system is better than the two antennas to join the space-time coding OFDM system. If you do not use convolution encoding and intertwined, even to raise the sub-carrier OFDM system, has failed to achieve a certain performance requirements.