On Joint Resource Allocation For OFDM Relay Diversity Systems Based On Limited Bit Feedback

Along with the rapid development of wireless communication technology,accuracy, high-speed and large capacity have become the main features of mod-ern communications. In the sequel, the expanding communication range andthe more complex communications environments result in serious channel fadingand interference. MIMO technology is proved to be an efcient way to combatchannel fading by spatial diversity. It can greatly improve the channel capacityand spectrum utilization without increasing the bandwidth. However, in somepractical scenarios, such as the wireless sensor networks and ad-hoc networks,due to the limitation of mobile terminals or network nodes with regard to thepower consumption, cost and size, multi-antenna can hardly be used. Then therelay diversity technology is proposed. The basic principle of relay diversity isthat the communication system formed a virtual MIMO model, with the aid ofrelay nodes, to obtain spatial diversity gain. Diferent to the traditional MIMO,the relay diversity technology did not have the restriction on mobile terminals,and meanwhile, it greatly increased the coverage and reliability of communicationsystems. Especially, it is more promising in wireless sensor networks, wireless Ad-Hoc networks, wireless Mesh networks and cellular systems. On the other hand,as an orthogonal multi-frequency modulation technology, OFDM has becomethe core technology in physical-layer of next generation communication systemsdue to its inherent ability to combat multi-path fading and high frequency spec-trum utilization. The combination of cooperative relaying with OFDM ofers aneven more promising perspective in improving the system performance. How-ever, the combination makes the joint resource allocation much more complex,since subcarrier allocation should also be considered besides the power allocation.Moreover, due to the independent fading on subcarriers in each hop, subcarrier pairing is also critical to system performance. In this paper, we focus on powerallocation and subcarrier pairing for OFDM relay diversity systems, and pro-pose a limited feedback based joint resource allocation algorithm. The followingcontents are the main work in this thesis:1. First of all, provided perfect channel state information is known at thesource and the relay node, we propose a low-complexity joint resource allo-cation algorithm, which including subcarrier pairing and power allocationon each subcarrier. Under total power constraint and individual power con-straints, both DF relay and AF relay are analyzed. The joint optimizationproblem turns out to be a mixed integer programming problem, we solvedit efciently with polynomial complexity by using the dual method. Thesimulation results verifed the analysis in the paper, it also revealed thatthe proposed algorithm is practicable and efective.2. In practical OFDM based relay diversity systems, due to circuitous delay,channel information estimation error and limited feedback channel capacity,perfect channel state information can not be obtained at the source andrelay nodes. We focus on resource allocation for OFDM relay channelsusing limited feedback. We propose a limited feedback based joint powerallocation and subcarrier pairing algorithm. Capacity maximization criteriais employed to design the codebook. Simulation results show that only afew feedback bits can bring remarkable performance improvement.3. We fnd that the relay in traditional three-node diversity model actuallyreduces to direct transmission, the relay does not forward in the second timeslot. In OFDM based systems, some subcarrier keep idle in the second timeslot. In order to overcome the drawback, we propose an improved relaydiversity scheme, in which we further allow the source node to transmitnew messages on these idle subcarriers in the second time slot. Based onthis, we propose a joint subcarrier and power allocation algorithm for theimproved relay systems. Simulation results verify that a remarkable rategain can be achieved with the extra direct-link transmission.4. To verify the fexibility of the proposed improved algorithm, we further con-sider the joint resource allocation for relay-aided down-link OFDM system with many users. In the model, we have to further consider the problemof subcarrier pair assignment. Simulation results prove the efectiveness ofthe proposed algorithm, that is, the improved algorithm is superior to theconventional algorithm with the help of the extra direct-link transmissionin the second time slot.