Space-Time Cooperative Diversity And Differential Detection Technique Research

Space-time coding was proposed by combining space diversity and coding technology to improve the system performance. Traditional space-time coding and multiple-input multiple-output (MIMO) techniques exploit space diversity through multiple transmit and/or receive antennas. However, due to the size of a mobile and carrier frequency constraints, achieving space diversity through multiple antennas may not be possible. Cooperative diversity has recently emerged as an alternative way to achieve diversity with a single antenna at the mobile. This paper concentrates on the cooperative diversity research. A new relay protocol is presented to get diversity gain. OFDM is introduced to resist ISI (Inter-symbol Interference).Firstly, paper introduces the principle of space-time diversity and discusses Alamouti transmit diversity scheme. Differential detection model is used in this scheme. Paper expounds the principle of differential encoding-decoding. Simulation is done using Matlab system, diversity gain is achieved compared with traditional single-antenna system.Secondly, cooperative diversity principle is studied. A new relay protocol based on fixed-forward-detection protocol is introduced. A cooperative diversity system is designed with Alamouti coding technique and TDMA. In order to resolve the problem of channel channel estimation, we introduce differential modulation schemes. System simulation is done in flat fading channel and frequence selected fading channel, result shows that diversity gain is obtained in flat fading channel, but it is not efficient in frequnce selected fading channel.Lastly, OFDM is used to eliminate ISI, in order to solve the gain problem in the multi-path enviroment, and the result is satisfying.Diversity and coding gain is achieved by cooperative diversity and diffential detection technique mentioned in the paper. This technique is extended to multi-channel system, owe to OFDM resisting ISI.