Design And Simulation Of Improved Physical-Layer Network Coding Scheme In Wireless Relay Networks

Physical-layer network coding (PNC), as a promising cooperative communication technique, is being extensively interested due to its ability to improve the performance of wireless networks. In the typical setting of PNC, two source/destination nodes and one relay are involved in the PNC process. Making use of the superposition nature of electromagnetic fields, the source nodes can transmit their packets simultaneously to the relay. The relay processes the superposed signal and sends an encoded version of the superposed signal to the destinations. Then, from the encoded packet, each destination decodes the packet it intends to receive, based on its knowledge of the packet transmitted by itself. The process of PNC can be done within two time slots, and double the throughput compared to the traditional store-and-forward method, In practical wireless relay networks, there is usually more than one PNC opportunity for a relay. Encoding three or more packets with PNC may further enhance the performance. To achieve this goal, an improved physical-layer network coding scheme is proposed by combining several typical PNC processes in two-way relay topology.This thesis firstly depicts the considered network topology and the specific process of the improved PNC scheme, and then analyzes the key points of this new scheme. The solutions of those key points are discussed in the following.To ensure that each node can decode the packet it intends to receive form the jointly encoded result of more than two packets, a new encoding method is needed for the relay. This thesis firstly studies three encoding constraints. Then, a two-level encoding scheme is designed. Based on different goals of the lower-level encoding, three different encoding methods are proposed. Simulation results reveal that each method has its own advantage.On the other hand, since for each node involved in the same PNC process, there should be overhearing links between itself and all other nodes except its destination, thus, another important issue that arises in this thesis is how to determine which pairs of nodes should be grouped together. According to channel conditions, two different grouping algorithms are proposed to achieve two different goals. Numerical results indicate that these two algorithms have close results, but have different computational complexities and are suitable for different situations.Finally, several improved PNC schemes can be achieved consisting of different relay encoding schemes and grouping methods with different goals. Simulation results show that all the improved PNC schemes can further improve the average throughput compared with the typical PNC scheme in two-way relay topology.