| Cooperative diversity enables single-antenna mobiles to share their antennas and generate a virtual antenna array that could achieve transmit diversity to combat multipath fading in wireless channels, it can improve the uplink channel performance.The thesis focuses on the protocols and Distributed Space-time Code(DSTC), Distributed Space-time-freqeucy Code(DSTFC) used in cooperative communication.There are three kinds of basic protocols: fixed relaying which is based on relaying mode, includes amplify-and-forward and decode-and-forward, selection relaying that adapt based upon the channel state between cooperating nodes, and incremental relaying that adapt based upon limited feedback from the destination node. An improvement scheme based on cooperation using Alamouti code is given,which does not need extra feedback and has good performance when SNR is high.Based on space-time code design criterion and the characteristics of cooperative system, design criterion for DSTC are given as rank criteria,determinant criteria and power-control criteria.A kind of DSTC scheme and its simulations are introduced.A randomized space time code which does not need central control is introduced and its improvement scheme is given, it can get maximum coding gain.In wideband wireless systems, to combat multipath fading and increase spectral efficiency,MIMO and OFDM can be combined together, we can code in space and frequency or in space, time and frequency to get corresponding gains. The implementation and performance of DSFC baesd on decode-and-forward and amplify-andforward are introduced. In the thesis, a kind of orthogonal space-time-frequency code in asynchronous cooperative system is given, its main idea is to distribute the code on time dimension onto time and frequency dimension, and the distributing mode is adaptive dependent on the channel state between nodes. This scheme can combat timing errors between relays by using OFDM, get full space diversity and has simple linear decoding structure. |
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