Study Of Resource Optimization In OFDM Relay System

OFDM relay communication system has become a research hotspot in the field of mobile communications because of its high channel capacity and wide signal coverage. The paper studies the resource optimization problem in the OFDM relay system based on maximum of system capacity. The primary contents of the thesis are as following:The principle of the OFDM relay communication system is introduced. The joint optimization problems of power allocation and subcarrier pairing under total power constraint and individual total power constraint are described respectively, and relevant mathematical models are also established.The joint optimization problem of power allocation and subcarrier paring based on maximum of OFDM multi-user relay system channel capacity under the total power constraint is investigated. The joint optimization problem of power allocation and subcarrier pairing in the traditional OFDM multi-user relay system is described. When some subcarriers are used for the direct transmission in the traditional OFDM multi-user relay communication system, some unpaired subcarriers in the second slot will not be used, which wastes spectrum resource. For the problem, the improved system which the source node can also make direct transmission at every unpaired subcarrier in the second slot is proposed. The joint optimization problem of power allocation and subcarrier pairing based on maximum of improved system capacity under total power constraint is deeply investigated and the simulation result shows that the improved system has larger channel capacity than traditional system.The joint optimization problem of power allocation and relay selection based on maximum of the OFDM multi-relay communication system channel capacity under individual power constraint is studied. In the traditional system, source node can only select one relay node, but in the improved OFDM multi-relay communication system, the source node can select one or more relays to form auxiliary channel. In order to improve spectral efficiency, the source node is allowed to make direct transmission in the second slot in direct transmission mode. The joint optimization problem of power allocation and relay selection based on maximum of improved system capacity under individual power constraint is analyzed. When dual method is used to optimize RA problem, the duality gap is close to zero only when the number of subcarriers is enough big. For the problem, a coordinate-ascent based iterative algorithm is put forward. The simulation results show that the effect of iterative algorithm is superior to that of dual algorithm in terms of improving the channel capacity when taking practical application into account and the improved system has larger channel capacity than traditional system.