Study On The Space-time Coding Technology Of MIMO-OFDM System

With the fast development of internet and multimedia services, MIMO and OFDM tend tobe two powerful techniques for the next generation telecommunication. MIMO can offerdiversity gain and frequency reuse gain, increasing wireless channel capacity and frequencyefficiency without extra frequency band and antenna transmitting power. OFDM caneffectively reduce ISI and overcome the frequency selective fading. MIMO-OFDM systemcombines the advantages of two techniques and plays an important role in future broadbandwireless system. Because of STBC’s good performance in increasing wireless channelcapacity and improving link quality, it has become a hot spot in MIMO research. This paperworks on researches of STBC in MIMO-OFDM system, such as STBC, LASTC and PCSTC.It can be divided into6sections which is summarized as followings.Firstly, this paper makes an introduction of multi-antenna and multi-carrier technologyand its development in home and abroad. In the second part, some related knowledge ofMIMO and OFDM is mentioned. The system and channel model is also given. Next, thedesign criterion of space-time code is presented. Meanwhile, STBC and its application inMIMO-OFDM system is discussed and simulated. Then this paper moves on to the study ofLASTC and its application in MIMO-OFDM system. Decoding algorithm of LASTC isanalyzed and simulated. It is found that optimal detection has the best performance buthighest complexity while the performance and complexity of the nonlinear algorithm aremediate. Considering the error diffusion and high complexity in LASTC, an improved MLQRalgorithm is given. Such algorithm makes a maximum likelihood detection to receipt signal sothat the performance of the first signal layer can be improved. According to theory deductionand simulation results, this improved algorithm is superior to other traditional QR methods.Further, STBC and LASTC is combined and used in MIMO-OFDM system. A self-adaptionSTBC-VBLAST is given. It can select different coding schemes depending on the currentstate of channel. Its application can reduce error diffusion, promote BER performance and, toa certain extent, improve systematic integral capability.