Performance Analysis of Super-Orthogonal Space-Time Trellis Coded MIMO-OFDM Systems over the One-Ring Channel

With the rapid development of wireless communications, the available bandwidth for wireless\napplications becomes more and more insufficient. Therefore, how to improve data\nrate without expending bandwidth becomes a main goal in modern communication system\ndesign. Recently, two wireless communication schemes, which can be used to effectively\ncombat with multi-path fading, are widely investigated around the world. One is\nthe multiple-input multiple-output (MIMO) technology and another is the orthogonal frequency\ndivision multiplexing (OFDM). As a result, a combined system, MIMO-OFDM,\ncan be used for wireless communications to jointly explore the advantages of the above two\nstrategies.\nIn the study of MIMO-OFDM systems, the space-time block codes (STBC) and the spacetime\ntrellis codes (STTC) are two efficient coding approaches. The former can be used to\noffer a full diversity gain, and the later can provide the systems with a large coding gain.\nSince 2003, super-orthogonal space-time trellis codes (SOSTTC), a new coding method\nprocessing the merits of both STBC and STTC, have been developed. However, whether\nor not it can perform just as well in a MIMO-OFDM system over a frequency-selective\nchannel is still unknown. In addition, a communication channel plays a very important\nrole on a communication system. A channel model is used to describe a realistic communication\nchannel and its various model parameters are considered to influence the system\nperformance such as symbol error rate (SER) as well as bit error rate (BER). Therefore,\nthe effects on SER and BER, caused by changing channel parameters, are worth to be\ninvestigated.\nIn the thesis, a new SOSTTC scheme for 16QAM constellation which can be used for\nhigh speed wireless communications is applied to a MIMO-OFDM system. To examine\nthe performance of the proposed MIMO-OFDM system based on SOSTTC, the one-ring\nMIMO channel model is studied by evaluating the effects of antenna spacing, channel profiles\nand maximum Doppler frequency shift.\nIn MATLAB simulations, the SER and the BER performance results show that enlargement\nof the antenna spacing can bring a higher diversity gain, and the enlargement of\nthe antenna spacing at base station can achieve better system performance than at the\nmobile station. In the channel profiles, the model E can gain more 1.5dB on the SER than\nthe other models at a SER of 10−2. In addition, the larger maximum Doppler frequency\nshift can cause more data errors by assuming non-perfect channel state information (CSI).\nFinally, by using SOSTTC, the system performance on SER can be improved by 0.5 to\n1dB at a SER of 5×10−4, comparing it with the STBC in the same MIMO-OFDM system.\nAccording to the above results, it will be more efficient to increase antenna spacing at the base station and it is necessary to adjust the coding scheme and signal power to avoid\nperformance decrease in a different communication environment and at a different speed\nof the mobile unite. Moreover, the SOSTTC can be integrated with MIMO-OFDM system\nto increase system performance.\nKeywords: MIMO-OFDM, SOSTTC, 16QAM, One-ringMIMO channel model, SER, BER.