The Research Of QOSTBC And Its Application In Relay System

MIMO(Multiple Input Multiple Output)wireless systems are capable of improving the reliability and data rate of the wireless link from the premise of not sacrificing the extra bandwidth. If channel knowledge is not available, at the transmitter, technologies such as space time coding and spatial multiplexing may be employed to improve the system performance by exploiting diversity and multiplexing gains. Otherwise, if full or partial channel information is available, technologies such as adaptive power allocation and antenna selection technique may be applied to improve the capacity or enhance the bit error rate. Quasi-Orthogonal Space-Time Block Code is very important. It can still obtain full rate transmission at the condition of more than two antennas. However, in some conditions, if the multiple antennas can’t be employed in the terminals, the relay technique may be used to realize the MIMO communication. Now, wireless relay communication is the trend in the next generation system. It satisfies the demand for the large network coverage and high transmission rate in the future and solves the problem of the low scalability and poor robustness in the communication system. In this thesis, it mainly discusses an optimal power allocation method of a relay communication system based on a quasi-orthogonal space time coding with feedback. As a prerequisite, the total transmit power is constant, the system allocate the power according to the channel state information of the source and the relay, then, the performance of symbol error rate will be the optimal. And thereby the reliability of the transmission system is improved. The content of this paper is organized as follows.First of all, the technology of the space time coding is described. Then, the guidelines of the space time coding design, the principles of the coding and decoding of Alamouti orthogonal space time code and the construction methods of three quasi-orthogonal space time codes are introduced detailedly. By the simulation of MATLAB, we compare the performance of the different space time coding methods. Meanwhile, combing the space time coding and cooperative diversity technology, we introduce the concept of space time cooperative technology, apply the space time cooperative technology to the relay system, compare the performance of different cooperative diversity protocols in the relay system and analyze the performance of space time cooperative relay system under the different protocols with Alamouti space time coding.Then, we introduce two different power allocation methods. One is based on the criterion of maximum channel capacity, the other is based on the criterion of minimum error symbol, the water filling algorithm of the criterion of maximum channel capacity are introduced in detail. By the simulation of MATLAB, we compare the channel capacity between the water filling algorithm and the average power allocation algorithm.Last but not the least, under a typical single relay wireless communication system, we apply the quasi-orthogonal space time coding with feedback to relay system and study the power allocation method based on the criterion of minimum symbol error rate. Through MATLAB simulation, we compare the SER performance of the optimal power allocation method and traditional average power allocation method. The result shows that the optimal power allocation method can obtain the minimum SER by allocating the power according to the channel state information of the source and relay.