| With the rapidly increasing demand of high-rate wireless services, it is an urgent problem how to provide all users with ubiquitous communication with high-capacity by the wireless cellular network. Although long-term evolution (LTE) system has improved the communication capacity greatly compared with 3G systems, it is still far away from the requirement of IMT-Advanced system. In order to further improve the performance of LTE system,3GPP released the requirement of LTE-Advanced (LTE-A) system in May 2008, and then began to engage in specifications. Generally speaking, LTE-A system results from the evolution of LTE system in the direction of high data-rate, low latency, and full coverage. With the purpose of meeting the LTE-A system requirement,3GPP proposed several key techniques including relaying communication, carrier aggregation, and coordinated multi-point. As a result, relaying communication obtained a lot of research attention because it can not only enhance the capacity of cell-edge users but also improve the performance of the whole cellular network.In the relay-enhanced network, users can access the network not only through base station but also through relay station. It means that the introduction of relay into cellular networks will inevitably alter the network architecture to some extent. In order to serve two-hop users, the relay station should be with the ability of processing and forwarding the signal from the transmitter to the receiver through the air interface. Thus, LTE-A system should allocate a part of in-band wireless resource for the backhaul link between base station and relay station. Besides the change in terms of network architecture, the temporal, frequency, spatial characteristics of wireless channel in LTE-A system are quite different from that in LTE system due to the existence of the relay station. For example, the sum-of-sinusoid method is not suitable for modeling the temporal characteristic of the wireless channel between base station and relay station, because there is no relative movement between the receiver and the transmitter. Accordingly, we should carefully exploit the suitable techniques according to the wireless channel characteristics so as to improve the channel capacity. SDMA, one sort of multi-antenna technique, is an excellent candidate to improve the backhaul link capacity by exploiting the spatial dimension.The introduction of relay into cellular networks makes it necessary to reallocate the wireless resource to improve the spectral efficiency. Generally, the wireless resource is divided into two parts in time domain:Relay Zone and Access Zone, and there are two resource division modes of Access Zone:orthogonal resource division mode and multiplexing resource division mode. Orthogonal resource division mode says that each resource unit in Access Zone can only be used by one user while multiplexing resource division mode says that each resource unit in Access Zone can be used by multiple users. Similarly, there are two control modes in the LTE-A system:centralized control mode and distributed control mode. In centralized control system with the orthogonal resource division, it is a crucial problem how to allocate the resource in Access Zone, and we developed two strategies, resource allocation based on user number and resource allocation based on user average throughput, to address this problem. In centralized control system with multiplexing resource division, it is a key issue how to allocate the resource in Relay Zone to lst-hop and 2nd-hop transmission of two-hop users, and we proposed two principles for this issue:link quality principle and buffer length principle. We also extended the three classical scheduling algorithms (Round Robin, Max C/I, and Proportional Fair) into the centralized control system and distributed control system, respectively. Moreover, we proposed a proportional fair scheduling algorithm which can dramatically reduce the feedback overhead when compared to the classical proportional fair scheduling algorithm.This thesis is organized as follows. In the first chapter, we reviewed the development history of wireless cellular communication. In addition, we introduced the requirement of LTE-A system and the key techniques to meet the requirement. In the second chapter, the wireless channel models of LTE-A relay system are introduced and the corresponding multi-antenna techniques are proposed to improve the communication capacity. In the third chapter, we researched on the key techniques in LTE-A relay system, including multiple-access technique, link-adaptive technique, and resource-allocation technique. The resource allocation and scheduling algorithms in centralized control system are proposed in the fourth chapter. In fifth chapter, the resource allocation and scheduling algorithms are proposed, and the performance of LTE-A relay system with various relay density, diverse relay transmit power, and different backhaul channel quality are evaluated by system-level simulation. |
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