Research On Relay Selection In Cooperative Multicast

As the rapid development of communication technology, the wireless resources become increasingly tense. Multicast is a spectrum-efficient transmission which could provide group transmission, it has caused a great concern, and been widely used in the LTE system. However, the performance of conventional multicast is severely limited by the worst user in the group. Cooperative multicast could improve the overall system performance by providing path loss gains and diversity gains. This thesis focuses on the mechanisms design of two-stage cooperative multicast and relay selection strategy to expand research. The main contributions are listed as follows:1. Mechanisms design of two-stage cooperative multicastThe model of two-stage cooperative multicast is established, and to study the relay selection in high-density and low-density two scenarios. The corresponding relay selection scheme is proposed, and we design it to form the signaling process. In the high-density scenario, the first stage of cooperative multicast transmission is that the BS transmits the data to the UEs in the cell with the optimum power, since the number of relay and the relay position has been recorded when we search the optimal BS power, so that the optimum power of the BS corresponding to the repeater deployment diagram has been stored in advance in the BS, then the BS selects the successful UE as the relay, which has nearest distance from the ideal relay position. In the low-density scenario, the relay can’t adopt the relay selection strategy, which is similar to the fixed relay selection strategy of high-density scenario is used, because the near of ideal relay position may not exist UEs, and compared with the successful UE of cell center, the near successful UE which is at the edge of cell has more unsuccessful UEs, so in the second stage of cooperative, choosing the successful UE of the cell edge to transmit data may be more effective and energy efficient.2. Research on relay selection scheme of two-stage cooperative multicastSince the cooperative multicast system performance is closely related to the relay selection, this article will combine the two-stage cooperative multicast with stochastic geometry theory to study relay selection scheme. We established a mathematical analysis model of random relay selection to deduce relay density and cell coverage expression, and proposed three relay selection strategies. Comparing these three relay selection schemes, and select the best solution. By simulating numerical expression based on the cell coverage theoretical values and the actual geometric theory of stochastic simulation results, it can be verified the of the proposed numerical expression of the relay selection model is accurate and reasonable.