Diversity In Wireless Cooperative Relay Communication System Research

As a special space diversity technique, cooperative communication can combat the fading of wireless channels effectively by making use of one or more relays to help user’s transmission to its destination. Cooperative commu-nication is a good means to enlarge the system coverage area and throughput with lower complexity. Nowadays, cooperative communication has been one of the hottest techniques in wireless and is a key technique in the future mobile communication system.In wireless relay communication system, opportunistic relaying can yield a full cooperative diversity by the way of relay selection. However, with the number of users increasing sharply, its bandwidth efficiency is usually very low. By the combination of relay cooperative scheme and network coding tech-nique with high bandwidth efficiency, a better bandwidth efficiency and larger ergodic capacity can be gained while maintaining the full cooperative diversity. On the basis of study about the network coding technique and relay coopera-tive scheme, a cooperative scheme based on opportunistic network coding is proposed in this dissertation. Furthermore, this dissertation also proposed an asynchronous detection algorithm based on orthogonal projection for the net-work coding technique. The major contributions of this dissertation can be summarized below.Firstly, in a multi-user multi-relay system, a cooperative scheme based on opportunistic network coding is proposed. The existing cooperative scheme ap-plies the network coding to the process of relay cooperation by making use of the broadcast nature of wireless links. Different from it, the proposed scheme further takes the multi-user nature into consideration. That is, after all user-s broadcasting in one time slot, during the subsequent relay phase only the information which belongs to the "worse" user having weak channel is al- lowed to be involved into the network coding operation by relay. Through this way, signaling overhead used for channel information feedback can be reduced. Meanwhile, the proposed scheme can also achieve better diversity and ergodic capacity.Besides, during the study on network coding technique, an asynchronous detection algorithm is proposed. The proposed algorithm provides a solu-tion to the detection at relay node in two-way relay network under the time-asynchronization. The existing detection algorithms can yield a good trade-off between system performance and complexity. Based on a research on the essence of the existing algorithms, the proposed algorithm reformulates the oversampled information sequence in term of MIMO-like matrix, and then u-tilizes the orthogonal projection technique to achieve the detection at the relay node. Numerical simulations confirm that the proposed scheme achieves a n-ear performance with the existing optimal detection algorithm at a much lower complexity and yields a good tradeoff between system performance and com-plexity.