Research On The Cooperative Communication Algorithms In Future Wireless Networks

The rapid development of wireless communications in the world incurs the increasing service demanding from the human being. The next generation wireless communication systems are required to adopt more advanced algorithms and technologies, in order to provide higher transmission rate, more application functions and better quality of service for people. Cooperative communication is a capacity enhancement method, which can effectively increase the spectrum efficiency and robustness of wireless systems. For the past few years, this new technique draws widely attention of research worker. In this paper, several hotspots of cooperative communication field are investigated, their mathematics models are built, and corresponding solutions are proposed. This paper focuses on the moment of cooperation, partner selection algorithm, cooperative ARQ protocol and cooperative spectrum sensing. The contribution of the paper is listed as follows:1. Propose a QoS supported cooperative diversity algorithm in wireless LANs.a) According to different services, cooperative diversity is invoked only if the minimum data rate required to have a successful transmission cannot be achieved. This is a demand cooperation scheme. Direct transmission will be used if only it can meet QoS requirements of some type of application. When direct transmission fails, partners will assist the source nodes in retransmiting data, i.e. cooperative retransmission.b) Partners are determined based on user-specific QoS requirements. In a WLAN, each station will listen to all ongoing transmissions and maintain a table of rate statistics that can be used to select suitable partners when source nodes are in need of help.It is proved that the QoS-aware cooperative diversity algorithm can mitigate the negative effects of unconditional cooperation, and improve the system performance in terms of throughput and energy efficiency.2. Present an improved cooperative ARQ scheme for wireless Ad hoc networks.a) Cooperative and non-cooperative frames are distinguished so as to avoid ambiguous ACK or NAK. In addition, this method can prevent cooperation process diffuse from one cooperation group to another, and simplify cooperation compexsity.b) Introducing traffic categories within node so that each node first help other nodes to retransmit a frame and then send its own data, which prevent that a new cooperation process begins but the previous does not finish yet in the same cooperation group. As a result, the cooperation processes will not become disordered.c) Through implementing a priority-based back-off algorithm, the most appropriate node is selected to help the source node retransmit data frame according to instantaneous channel conditions. Theoretical analysis and simulation results indicate that the collision problem caused by cooperation can be alleviated.The improved cooperative ARQ scheme can increase the probability of successful retransmission, and then improve throughput greatly.3. Propose a robust cooperative spectrum sensing strategy based on multi-user diversity.a) In heterogeneous wireless environment consisting of TD-SCDMA and WiMAX, the WiMAX users are separated into a few clusters and the most favorable user is selected in each cluster to detect spectrum. This approach can enhance the sensing performance by reducing the false alarm probability.b) A softened hard decision scheme with two-bit overhead is adopted for the reliable transmission of decision results. This means achieve a good tradeoff between detection performance and complexity.Cooperative spectrum sensing strategy based on multi-user diversity guarantee the accuracy of spectrum detection, and achieves the end that improving spectrum efficiency and throughput.