Research On Relaying Technologies For The Improvement Of Cell-edge Performances In LTE And LTE-A

As the next generation broadband mobile communication system, LTE and LTE-Advanced take the cell-edge performance as the key system demand. In the main techniques of the cell-edge performance improvement in current, the cellular multi-hop technology and the cooperative diversity technology through relay nodes can improve throughputs of cell-edge users and the system coverage efficiently. Being different with the user relay, the fixed relay has become the key technology of the next generation broadband mobile communication system, such as the layer 3 relay and the layer 2 relay in LTE-Advanced.However, as an independent cell, the layer 3 relay brings a series of potential problems such as more complex inter-cell interference, handover scenes and resource allocation when it improves the system throughput and coverage. With the rapid development and wide use of the WLAN technology, a large number of mobile devices are equipped with the WLAN interface in addition to the cellular interface. With the increasing popularity of the LTE, dual-mode mobile devices equipped with interfaces of both LTE and WLAN will appears gradually, which makes novel relay networks based on LTE and WLAN possible.This thesis proposes an integrated LTE/WLAN heterogeneous relay network for the tri-sector site of LTE networks in order to improve throughputs of cell-edge users and the system coverage. Firstly, studies the architecture of the novel network, and present the coverage model of the network. Secondly, studies working principles of the network, including the two-hop access mechanism, the protocol stacks and the handover mechanism of two-hop users. Finally, through theoretical analysis and simulations we evaluate the performance of the network.Being different with the layer 3 relay which controls independently, the layer 2 relay assists data transmissions of cell-edge users through in manner of decoding and forwarding. And the cooperative diversity technology through the layer 2 relay brings diversity gains to cell-edge users, and improves their transmission performances. As the network size increases, the limited frequency resource increasingly becomes the bottleneck of the system throughput. The cooperative diversity technology brings in the network coding to improve the resource utilization rate and system throughput. Among them, the cooperative diversity technology based on the Complex Field Network Coding (CFNC) achieves the highest resource utilization rate. However, due to the existence of the direct link, if used directly in LTE-Advanced networks, the current cooperative diversity technology based on the CFNC will result in more serious inter-cell interference, and even deteriorate system throughput.This thesis proposes an two-hop cooperative diversity technology based on the CFNC for LTE-Advanced layer 2 relay networks to improve the uplink transmission performance of cell-edge users. Through the combination of the two-hop transmission and the CFNC, the cooperative diversity technology improves the transmission performance of cell-edge users with lower inter-cell interference and higher resource utilization rate. Firstly, studies the two-hop cooperative diversity technology based on the basic scene, and then extends it to the general model. Finally, through theoretical analysis and simulations to evaluate the performance of two-hop cooperative diversity technology.