Research On Physical Layer Network Coding In Two-Way Relay System

Network coding breaked the traditional way of route node that is "storing-and-forwarding", and introduced the new mode which supposed forwarding the coding combination of different information flows. The new scheme can be thought as the expansion of the traditional route mode. It indicates that more complicated and advanced processing can be carried out on the route node. It also arranges the route process of information from the scope of the whole network rahter than the local links. With the enhancement of hardware processing, the research on network coding is developing to the direction of practice verification.With the development of wireless communication, the introduce of network coding to wireless communication can improve the performance of system in many ways. Especially the combination of network coding with wireless relay has become one of the most significant and highest potential directions. Under this background, this thesis aims at solving some key theoretical and technical problems of Physical layer network coding on wireless two-way relay. Make use of network coding to improve the performance of wireless networks.The main work and innovation of the dissertation includes as follows:First of all, some research achievements on network coding in wireless communication have been unfolded. The fundamental of network coding, linear network coding and its principle of construction are explained, which make the base for the following discussion on network coding in wireless two-way relay (TWR) system.Then, some current processing modes of network coding in two-way relay are introduced, and the network coding symbol error ratios (SER) of denoising-and-forwarding (DNF) for symmetric modulation is deduced. But for the asymmetric modulation types, DNF network coding is rarely discussed till now, which is the main point of thesis.For the realization way of DNF network coding for asymmetric modulation in TWR, the constellations distribution map of superimposed signals received by TWR has been analyzed. The untraditional detection areas for signal relationship of the two users are redefined. The detecting thresholds for different signals relationships are derived. And the remapping scheme for realization of DNF network coding of asymmetric modulation are analyzed.Based on these works, the SER performance of DNF network coding of asymmetric modulation in TWR system is deduced. Then, the two users’ power-matching influence to the performance of DNF network coding in TWR is analyzed. Moreover, this problem has been constructed as an optimum problem, and through analysis the optimum power-matching ratio has been investigated, which can make the performance of DNF network coding in TWR to be improved most efficiently with the total transmitting Power.As the continuity of previous work, the following research works are focused on the downlink way of asymmetric DNF network coding in TWR system. In fact, the remapping for the realization of DNF network coding is a hierarchical modulation to satisfy the different modulation types of two transmitters. The decoding way of DNF network coding of asymmetric modulation at the receivers (also transmitters in the uplink way) are discussed. The SER performance of two receivers with asymmetric modulation types are deduced respectively.At last, in order to take the previous theoretical analysis into to practice and consider some practical problems, we consider a CDMA TWR system using DNF network coding. In fact, in the real multiple access system with DNF network coding a pair of users, communicating with each other, only need one multi-access carrier(time slot, subcarrier, spreading code). In this system model we mainly focus on multiple access interference and point forward the pair of users with a common spreading code. This scheme can decrease the multi-access interference (MAI) efficiently. And based on the analysis of the interference mode in the system, we practice the corresponding interference modeling, and investigate a interference cancelling scheme. The scheme can be practiced at TWR and user points. With the population of iterative signal processing, we also introduce the turbo iterative interference cancelling scheme, and through the simulation, it is proved that the iterative interference cancelling scheme is efficient.