Efficient Resource Allocation And Optimization In Ofdma Multi-Hop Relay Cellular Networks

Multi-hop relay has been deemed as one of the key technologies in the 4G systems. It can improve the cell-edge users'QoS, lower the network cost, enhance the system capacity and coverage, and it also plays an important role in emergency communications. Because of the benefits in network performance improvement, research on multi-hop relay cellular networks (MRCNs) has become one of the hot spots recently. Even though multi-hop transmission has advantages, it experiences a penalty:extra resources should be allocated for relay links. Therefore it has important significance that how to design efficient resource allocation and optimization schemes for MRCN to offset the additional frequency overhead.Two techniques, frequency reuse and local forwarding, have been mainly applied to MRCN for designing efficient resource allocation and optimization schemes in this thesis. The author's main research work and contributions are as follows:Firstly, a system-level simulation model is built for wireless multi-hop relay cellular networks. And the modeling scheme is mainly used for analyzing the system downlink throughput and the cell coverage.Secondly, efficient frequency reuse between RS (Relay Station) and BS (Base Station) is one of the solutions for MRCN to reduce the allocation of the extra relay resource. Considering both of the time and spatial reuse characteristics of RS, two adaptive frequency reuse schemes are presented for MRCN by using different reuse patterns in different time zones of a same frame. In our schemes, reuse pattern of 1×3×1 is applied in the Relay Zone (RZ), and 1×3×3 is applied in the Access Zone (AZ). The former allows only two RSs which are located farthest apart in one cell to share the same frequency portion; while in the latter two adjacent RSs may share the same resources. Analysis and simulation results show that both schemes improve the system throughput greatly. The comparison of coverage and throughput between the two schemes indicates that the latter scheme has better performance and an aggressive full reuse scheme could be utilized to all RSs.Thirdly, in current MRCNs, normally the communication path is not optimized, especially for two MSs (Mobile Stations) attached to the same RS need to communicate with each other. In this case, it is a wasteful use of the system resources that the same data are transmitted between BS and RS back and forth. In this thesis, a novel data transmission scheme:local forwarding data transmission mode, is proposed. In the local forwarding mode, data transmitted between two MSs attached to the same RS is forwarded without necessarily being sent to the BS. Thereby the spectral efficiency is improved. And then two local forwarding based slot resource allocation schemes (SRASs) are proposed. The first is a modified traditional SRAS (SRAS-MT), which implements local forwarding and allocates slots for MSs after relay selection. And the second is a SRAS specially designed for local forwarding (SRAS-LF), which takes the advantages of the local forwarding into account during relay selection and slot resource allocation. Numerical and simulation results show that the local forwarding data transmission schemes can improve the system capacity greatly. Moreover, the performance of SRAS-LF is shown to be superior to that of SRAS-MT.