Research On D2D Relay Selection Techniques Based On LTE-A System

In LTE-A system, compared to the traditional cellular communication of station, D2 D communication which is a short-range communications technology has great advantages and potential in terms of saving wireless resources, reducing system interference, local data service sharing, etc. However, because of the channel fading in wireless channel, the D2 D straight link can't be established when two D2 D users are distant. We can introduce the relay technology in D2 D communication that collaborate D2 D user to communication using the relay nodes. There are much idle user equipment can be alternative relay nodes. The performance of relay system is influenced by the different relay nodes. This dissertation mainly studies the selection problems of relay nodes in D2 D relay system.Firstly, based on single cellular network, the system performances of having or not having relay nodes in D2 D communication are researched and analyzed. By analyzing the application situation, resource sharing and interference models of D2 D relay system; we conclude that the choice of multiplexing uplink resource of cellular user is better than the choice of multiplexing downlink resource. When multiplexing uplink resource, the channel capacity and outage probability of relay communication link in SD direct link and AF or DF relay forwarding model are derived and simulated. Simulation results show that the appropriate introduction of relay in D2 D communication link improves the system performance.Secondly, the relay selection algorithm of D2 D relay system is researched and analyzed.On the understructure of relay selection algorithm based on instantaneous channel state information, an improved relay selection algorithm which considers the user service quality transmission delay, packet loss rate and so on is proposed. The service quality of communication link is judged by queue status information in the relay node cache and the feasibility of the propose algorithm is theoretically derived and analyzed. Simulation results show that the proposed algorithm improves the system throughput, reduces the system transmission delay and packet loss rate, and optimizes the performance of D2 D relay system.Finally, the relay selection algorithm of D2 D multi-hop relay system is researched and analyzed. Alternate relay nodes are chosen preliminarily by the power limitation of each relay node which is derived by using the interference threshold of cellular user and the correct decoding threshold of DF relay forwarding model. D2 D multi-hop relay system is achieved by front multi hop and last two hop. In front multi-hop relay communication, the best relay node is chosen by optimal channel state. In last two hops, the channel state information of two hop link is sorted according to maximum and minimum principle. Then in the first few relay sets, the relay nodes which have the biggest sum of the channel coefficients of two hop linkare regarded as the best relay nodes. Simulation results show that the proposed algorithm reduces the failure probability of relay selection.