Research On Smart Antenna In MIMO System And Fast Decoder For Space-time Codes

With the development of communication technology and the growing demand for a variety ofapplications, communications networks are undergoing great change. It is can be expected thatmobile communications market will maintain rapid growth trend in the next few years. Whether it is2G, 3G or the upcoming 4G networks, the demand in wireless communication system is very highin quality, speed and reliability. In the situation of frequency resources come in increasingly tense,how to effectively improve the utilization of frequency resources become the focus of research inwireless communications. MIMO technology can exponentially increase spectrum efficiency,system capacity and reduce system error without increasing the system’s bandwidth. Therefore, it isthe trend that traditional SISO system involves into MIMO system. To achieve MIMO systemcapacity, it mainly relies on space-time coding. First, the space-time code design criteria is proposedunder the condition of sufficient the high signal to noise ratio (SNR) and multipath environment,therefore, the orthogonal space-time block codes (OSTBC) which is designed according to theabove criteria has excellent performance at high SNR. However, the performance of OSTBC is notoutstanding in low SNR. Second, the space-time codes with full rate, full diversity, for example,Golden Code shows a low error rate when decoded with Maximum-Likelihood (ML) detectors.But the complexity of decoding Golden Code with ML detectors is very high and is not conductiveto actual use.To solve the above problems, this paper covers the following aspects: first, the MIMO channelmodels were introduced, and thus gives the channel model of slow quasi-static flat fading channelmodel which are studied in this paper, then introduced the space-time code design criteria, severalcommon space-time codes and smart antennas in the fixed beam-forming technology. Second, forthe space-time code defects, we proposed a new system which is based on optimization ofperformance and combined OSTBC with fixed beam-forming. We give a specific mathematicalexpression of channel division, the derivation of the proposed system’s error probability upperbound. The simulation results show that the proposed system can effectively improve theperformance of Space-time Codes in low SNR. After the introduction of the basic obliqueprojection theory, we proposed a new fast decode method which combined oblique projection andthe advantage of ML decoder. Simulation results show the proposed method has lower decodingcomplexity with less BER loss.