Research On Fairness Problem Of Relay Selection And User Scheduling In Cooperative Communications

In recent years, cooperative communication technology has obtained widespread attention due to its ability to improve system capacity, enhance data transmission rate, combat the detrimental effects of multi-path fading and lower system outage probability. The selection of relay node is cruical in cooperative communication systems and it matters much whether cooperation can bring a promotion in performance gain. Recent researches in this field mainly focus on how to improve the transmission performance between the source node and the destination node by sharing resources among different nodes, but fail to take the fairness among them into account. However, this will affect system performances when taking the network as a whole. Aiming at the fairness problem of relay selection and user scheduling strategy in cooperative communication networks, the following contributions are made in this thesis.1) By introducing different quantitative and qualitative fairness measurements, we give some object methods to judge how fair a resource allocation mode or a system can be. And also presented are the disadvantages and advantages of these measurements. Subsequently, further analysis of two kinds of fair cooperation protocol is given. One is based on the network lifetime and the other is about user throughput fairness. These two protocols improve the fairness among all the users in the network from different perspectives and can efficiently promote system performances.2) Based on conventional OR scheme, in order to guarantee that all the nodes in the network have equal selected times and the same power consuming, we propose a novel Fair Relay Selection(FRS) method by setting up a counter for each node to record the times it has been hired by the source node. When selecting active relay node, both the selected times and end-to-end channel quality should be taken into consideration. Through Matlab simulation, we prove that this strategy can balance the selected times of all the nodes in the network, keep their lifespan approximately the same, prolong network lifetime and improve system throughput.3) FRS strategy is extended and applied into uplink transmission of cooperative cell as well as the Proportional Fair Cooperation(PFC) scheduling. It is shown that the combination of FRS strategy and PFC scheduling can not only guarantee the fairness among all the relay nodes and prolong the network lifetime, but also can get an excellent tradeoff between system throughputs and relay fairness. Besides, all the nodes in the network can achieve the same throughput and keep the nodes in poor channel condition from starvation.