Adaptive Resource Allocation For OFDMA-MIMO Wireless Multi-Hop Relay Downlink Systems

Next generation mobile communication systems are envisaged to be able to provide high rate multi-service information transmission. Deploying orthogonal frequency division multiple access (OFDMA), multiple input multilple output (MIMO) and relay technologies into the future wireless broadband access systems or cellular networks can help improve the system spectral efficiency and expand network coverage.Due to the frequency-selective fading of wireless channel, the adaptive resource allocation algorithms are used in OFDMA systems for avoiding that the subcarriers assigned to a specific user experience deep fading. It assigns subcarriers to multi-user flexiblely according to the channel state information (CSI), thus the resource utilization is optimized. The introduction of MIMO and relay technologies has brought new problems for adaptive resource allocation, such as the joint optimization of the spatial, time and frequency domain resources, the extra resource allocation for relay link, the capacity balance between relay link and access link for relay users. It is therefore the objective of this thesis to investigate the adaptive resource allocation algorithms for application in OFDMA-MIMO multi-hop relay downlink systems.In this thesis, the theory of related technologies for OFDMA-MIMO multi-hop relay system is introduced firstly, including the principle of the multiple access methods, the analysis of the MIMO channel capacity and the new features of resource allocation arising for relay enhanced networks. Then the typical existing adaptive resource allocation algorithms are investigated in details. A system-level simulation model is built up for OFDMA-MIMO multi-hop relay systems. Based on the analysis of simulation results, the advantages and disadvantages of the typical algorithms are studied. The minimum frequency resource allocation unit in existing algorithms is mainly a subcarrier. Therefore a large amount of computation work would be done due to the large loop iteration number of subcarrier allocation. In order to reduce the computation complexity, a novel mode of building a resource unit (RU) composed of a set of subcarries is introduced. Based on the novel mode, adaptive resource allocation schemes are proposed for the OFDMA-MIMO multi-hop relay downlink system. The former is a base station (BS) centralized algorithm, and the latter is a relay station (RS) assisted method. The target of the proposed schemes is to maximize the average system capacity under the limited total power constraint. Meanwhile, the proportional fairness of the user data rate should be achieved. According to the analysis of the simulation results, the novel RU building mode reduces the computation complexity at the expenses of the system capacity by enlarging the granularity of the minimum resource allocation unit. And the results also show that the proposed resource allocation schemes can achieve an efficient tradeoff among proportional fairness, system capacity and computation complexity.