Research On Physical-layer Network Coding Based On Cooperative Diversity

To combat the deleterious effects of fading in wireless channel, cooperative diversity is generated by sharing antenna with its partner, thus allowing independently faded versions of the signal at the receiver. Recently relay communications have received considerable attention due to its ability to extend coverage and to mitigate channel impairments. Network coding (NC) was originally invented with application in the network layer in mind, which involves mixing of information at the relay node from multiple packets. Due to the broadcast nature of wireless channel, an interesting number of works have subsequently tackled the problem in a wireless environment.However, the broadcast nature will result in interference which causes throughput degradation on wireless networks and its negative effect for multi-hop ad-hoc networks is particularly significant. Physical-layer Network Coding (PNC) is then proposed to solve the problem. The core idea of PNC is that the electromagnetic waves received simultaneously from different sources are an additive superposition of signals. A form of network coding operation is performed automatically during the reception process when multiple sources transmit simultaneously. In other words, signal decoding and network coding can be merged into one, and collided signals could be turned into useful network-coded information with proper signal processing. Since its publication, PNC has developed into a subfield of network coding that has attracted the attention and follow-ups of many researchers.In this paper, we combine cooperative communication and network coding,and then we discuss the improvement of network coding on cooperative communications. After that, a physical layer network coding scheme based on single and multiple relay selection are studied. In the proposed dual relay selection scheme, two users first broadcast their respective information to all the relays, then two relays are selected based on some relay section scheme where Alamouti space-time coding and physical layer network coding are combined. Focusing on the bi-directional wireless relaying channels, outage probability is derived and then power allocation is analyzed. Simulation results show that this scheme can efficiently combat channel fading and the more relays involved, the better system performance can be obtained. In addition, up-to-date related issues of PNC schemes and future trends will be discussed. We can see that PNC in wireless networks is a promising research area and there is much room left for future contributions.