Research On Physical Layer Network Coding In Wireless Communication Networks

In an effort to further improve the spectral efficiency,3GPP LTE-Advanced increases network density through heterogeneous networks (HetNet) with small cell access points (SCAP), e.g. mirco cells, pico cells, femto cells, and relay nodes (RN). Those low power nodes (LPN) are either connected to macro base stations (BS) through wired linkage, i.e. optical fiber and X2cable, or wireless backhaul. By exchanging channel state information (CSI), adjacent cells can apply coordinated multi-point (CoMP) to avoid interferences or jointly serve cell-edge users.Meanwhile, another arising technique network coding (NC), or physical layer network coding (PLNC), has developed into a hot topic due to its attractive feature: achieving outer cut-set bounds in two way relaying channel (TWRC). It is interesting that network coding transforms interferences into effective signals, and double the spectral efficiency compared to conventional four-stage communication protocol. Since the researches on PLNC in heterogeneous networks are limited, this paper will explore the potential gain provided by joint consideration of PLNC and CoMP.This paper considers applying PLNC to HetNets, where the base stations, user terminals (UT) are all equipped with multiple antennas. At first, we theoretically analyze the problems in a mathematical form. Then the paper proposes effective designs of transmitters and receivers, according to different optimization objectives and constraints. Finally, simulation results are given to validate the proposed scheme. Specifically, the two novelties are described as follows.Firstly, a coordinated PLNC joint transmitter and receiver design is proposed, tackling the interference problem between two-way relaying channel in small cell and uplink channel in macro cell. The basis is that the data streams from two-way communication nodes are aligned to the same direction to perform multi-stream decode-and-forward physical-layer network coding, while other streams are adjusted to orthogonal direction for spatial multiplexing. Secondly, a network coding interference coordination (NCIC) scheme is proposed for a heterogeneous network of a macro site covering wireless relay node. Considering the property of network coding that transforms interferences into effective signals, it provides a larger degree of freedom for macro-relay coordination. This paper provides an enhanced scheme in decode-and-forward multiple-input multiple-output channels. At first, we derive its achievable rate with nested lattice codes, and then maximize the sum-rate of the cooperating region through iterative algorithm and Lagrange multiplier method.Finally, numerical results based on Monte-Carlo simulator are given in support of our algorithms. The conclusion is that network coding helps to achieve much better performance in HetNet scenarios. On the other hand, coordination and Tx-Rx design are quite crucial.