| To employ multiple antennas in a single terminal is limited by its size and power consumption in MIMO systems, but cooperative communication is a promising technique to solve this issue. Using the distributed relay nodes to constitute a virtual MIMO system, we can obtain the cooperative diversity, also known as space diversity, and cooperative technology has attracted more and more attentions recently. The single-relay cooperative protocol includes AF and DF protocol. Once receiving the message from the source, the relay will amplify and forward the signal. This scheme is called AF protocol, which is simple and has low system complexity. However, while the signal is amplified, the noise may also be amplified and forwarded to the destination. The relay node will decode the message in DF protocol, if it can decode the signal correctly, it will forward the message to the destination. Owing to the decoding process, the system can achieve good performance but requires complicated relay nodes. Laneman proposed the concept of incremental relay combined with ARQ technique in2004. If the transmission of the direct link fails, the relay forwards the message and the destination will combine the signal from the relay and the source. If the direct transmission succeeds, the relay will withdraw from the cooperation. With the utilization of the ARQ and the cross-layer joint optimization, the incremental relay technique can improve the spectral efficiency and acquire ideal system outage performance. Space-time coding was introduced into the cooperative communication to construct distributed space-time codes, and has been applied widely in multi-relay cooperative scene.In this thesis, we firstly introduce several cooperative scenarios and analysis three cooperative protocols, then we discuss several key technologies related to cooperative diversity. According to the impact of the distance between nodes on the performance of the relay protocol, we proposed an adaptive cooperative protocol switch scheme based on the distance information. For the classical three-relay cooperative model, considering the path loss factor, we get the critical distance by theoretical analysis and system simulation based on the optimal outage probability. Using the cooperative protocol switch scheme, we can reduce the system complexity while remaining a better outage performance. For the two-relay distributed STBC cooperative scenario, we analysis the impact of SNR and distance between the nodes on the system performance, and design a cooperative protocol switch model on the basis of network topology structure.Next we put forward a two-user incremental cooperative system based on STBC and ARQ, and we make use of the adaptive cooperative protocol switch scheme based on the distance information proposed before. According to the decoding results at the destination we can get different cooperative scenes. When the destination node decode the message from both two users wrong, cooperative protocol switch will happen at the users. According to the distance information between any two nodes, we can choose STBC-IDF protocol or STBC-IAF protocol. When the destination node can decode the message from one of the two users correctly, in light of the distance information between any two nodes, we can choose IDF protocol or IAF protocol.Finally, we make a study of EO-STBC, and proposed a distributed multi-relay STBC scheme using the limited feedback information. The encoding program is flexible, and there is no limit on the number of relays joining in the cooperation. Every relay has its own encoding principle, so communication between relay nodes is unnecessary. At last, we provide the average BER analysis at high SNR according to different codes. Following the works above, we bring up a relay selection proposal based on incremental relay. We make full use of ARQ feedback slot and the closed-loop EO-STBC feedback slot, and get the different distributed EO-STBC matrixes by combining the message from the source and the message from the relay set. |
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