Research Of Turbo Reserver Of WIFI System

With the growth of the requirements of the capacity and quality, the wireless communication technology grows fast. MIMO (Multiple Input and Multiple Output) is one of the key techniques in wireless communication system. It employs multi-terminal at both the transmitter and receiver. It can obtain different spatial characteristics by the space vector in the wireless communication channel. It divides the channel into a plurality of independent non-interfering parts and obtains sufficient space diversity gain.The traditional MIMO system transfers information from the detection and demodulation to the decoder directly. However, the method loses the information and also degrades the system’s performance.The model of the Turbo-MIMO-OFDM (Orthogonal Frequency Division Multiplex) system established in this thesis enables the exchanging of soft information between the detector and decoder. In the frequency selective fading channel, it ensures the reliability of the communication and increases the system’s capacity and the communication’s quality.The main contents and contributions are following:Firstly, since interleaver has a relatively large influence on the performance of turbo codes. The thesis simulates the performance in several different interleavers:including block interleaver, S-random interleaver and QPP interleaver. The method of designing the interleaver is according to the rules and the distance spectrum of turbo code. Finally we use QPP interleaver in the fading channel. The thesis also gets turbo performance of different parameters through simulation, such as rate, code length and the number of iteration.Secondly, based on WLAN (wireless local area network) standard and simulation platform, the thesis designs the channel interleaver. It also analyses the algorithm of the detection module. It analyses and simulates the ML (maximum-likelihood) detection and MMSE (minimum mean square estimation) detection, The result shows that the performance of the ML detection is better than the MMSE detection, but the complexity of the ML algorithm is exponential increasing with the number of space streams and the modulation order. Therefore we design the iterative MMSE detection by considering the tradeoff of the complexity and performance. The simulation is performed in fading channels by using different factors.Thirdly, the thesis designs the iterative receiver system based on the MMSE detection. It exchanges the soft information between the detection and decoder. It indicates the gains of performance of the iterative detection/decoding outperforms traditional MIMO by analysis and simulation.