Research On Performance Of Physical Layer Network Coding Under Improved 16QAM Modulation In Two-way Relaying System

In the face of rapidly developing and widely used wireless communication technologies,how to accelerate the information transmission rate to a greater extent and ensure more reliable data transmission has become a problem that needs to be solved urgently.The proposed Physical-Layer Network Coding(PNC)technology provides important ideas for solving the above problems,because it can significantly improve the network throughput,so it has quickly become a research hotspot for many scholars.This dissertation mainly focuses on the PNC scheme based on 16 QAM modulation in the two-way relay channel model.In order to solve the problem of decoding at the relay,an improved scheme is given,especially the idea of nested lattice(Nested Lattice)is proposed to redesign the entire coding scheme of the relay communication process to improve the error performance.Firstly,this article takes the most basic relay communication model,the two-way relay channel(TWRC)model as an example.The traditional transmission mechanism,simple network coding mechanism,and physical layer network coding are analyzed,focusing on the analysis of the PNC working methods.Following the mapping relationship and its basic theory.Furthermore,the Maximum a posteriori(MAP)signal estimation method is introduced,and the receiving decision scheme at the relay node is analyzed for subsequent analysis of the PNC performance.It also analyzes the basic theory of Lattice code and Nested Lattice code in detail,and defines the modular Lattice Additive Noise(MLAN)channel,and analyzes the capacity of the MLAN channel.Secondly,the PNC communication process under BPSK modulation is described,and the mapping demodulation scheme at the relay is analyzed.The BER performance is theoretically derived and simulated and compared with traditional transmission and NC mechanisms.Also for the reason for the overlap of code words generated at the relay between two signals based on 16 QAM modulation,how to improve the 16 QAM so that it can be successfully applied to the PNC technology.Proposed the most direct solution,designed the mapping demodulation scheme at the relay node,calculated the decision threshold according to the MAP receiving mechanism,derived BER formula and conducted the simulation analysis of the error rate.Compared with the original 16 QAM modulation PNC scheme,this scheme improves the error performance.Finally,the encoding and decoding process in the MLAN channel based on Nested Lattice code is analyzed,and the transmission process of the PNC scheme based on Nested Lattice code in the two-way relay channel is considered.And analyzes the perfor-mance improvement brought by the Compute-and-Forward relay strategy for the communication speed,the specific communication process of Nested Lattice code and PNC technology is designed,and the 16 QAM modulation constellation is redesigned.Then the simulation analysis of this scheme verifies that it can further improve the error performance.