| The paper deals with the techniques of MIMO, OFDM and space-time coding in the 4th generation of mobile communication. It studies the necessity of the system which combines space-time coding with MIMO-OFDM by the analyses of the three space-time codes.Firstly, the paper analyses the space-time channel model and space-time signal systematically, as space-time codes belong to the technology dealing with space and time.Secondly, the paper studies MIMO and OFDM technology, and analyzes the principle of OFDM, its advantages,disadvantages and capacity of MIMO system in details. It presents the communication system of combining MIMO with OFDM and its performance is analyzed.Thirdly, we continue our investigation with discussions of the three main space-time coding schemes, namely Layered Space-time Coding (LSTC), Space-time Trellis Coding (STTC) and Space-time Block Coding (STBC). We analyze the codec principles and their advantages and disadvantages. The STBC uses Maximum Likelihood (ML) decoding and its complexity of decoding is very low.Finally, STBC is applied to MIMO-OFDM systems, and the simulation model is built. The performance in multiple simulation condition is researched. The simulation results indicate that if transmitting and receiving antenna numbers are the same, the system performance is almost the same. If the receiving antenna numbers are different, the more receiving antenna numbers are, the better the performance is. If the subtraction of transmitting and receiving antenna numbers are different, the performance is decided by the difference. If the modulation order is different, the higher the order is, the worse the performance is, but the transmitting rate is bigger. If the Doppler frequency shift is different, the more the maximum Doppler frequency shift is, the worse the performance is. |
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