Network Coding In Wireless Communications Research

With the rapid development of science and technology, more and more people are eager to exchange information quickly and reliably at any time, and therefore the demand for communication is increasing. Wireless communication has become a hot topic for its flexibility and rapidity, and has made a radical change in people's life, having a profound impact in economic and social development. On the other hand, with the explosion in the number of wireless users, the variety of network services, and the increasing demand for transmission quality, how to ensure reliable and secure wireless link transmissions, and how to improve the utilization of the existing wireless network resources to optimize the transmission performance of wireless networks are becoming important issues.In traditional wireless communications, data transmission is accomplished by store-and-forward scheme, and the packets from the source node are sent to the destination node through intermediate nodes. In general, there is no data processing at the intermediate nodes except replication, so it is difficult to achieve the maximum throughput of wireless.In 2000, Ahlswede et al proposed the concept of network coding based on the information flow. Network coding put forward the idea of integration of routing and coding, and the intermediate nodes process the packets received from the source nodes before forwarding them, which greatly improves the throughput of the network. Network coding changes the approach of information processing in communication networks, and is a profound breakthrough. It has been applied in various aspects of research to improve network throughput, link reliability, network safety, energy efficiency and so on. It is universally considered that network coding has an important theoretical value and an immense potential in practical applications, and one of the key next-generation techniques.The unreliability of wireless links and the broadcast property of physical layer provide a good platform for the application of network coding in wireless networks. So far, the relay technology based on network coding, cooperative diversity, physical layer network coding and joint channel coding and network coding have attracted wide attention with an abundant number of achievements.This paper first briefly introduces the basic theory of network coding, and then focused on its application in wireless communications. Two new data transmission protocols combining Network Coding with decode-and-forward (DF) or amplify-and-forward (AF) of Cooperative Relay are proposed. Expressions of data rate for these two protocols are derived. Theoretical derivation and simulation show that compared with conventional store-and-forward and independent Network Coding, the data transmission rate of the network is greatly improved by these two protocols; A new adaptive DF and AF scheme with network coding for two-way relay networks is proposed. Traditional network coding has a limited application for assuming the input packets from two destination nodes can be simultaneously decoded correctly at the relay node. The method proposed in this paper still forwards the network-coded information at the relay node, even when it cannot simultaneously decode correctly the two packets. Two destinations receive the packet from the relay node, and decode it relatively with the adaptive method proposed. Numerical simulation shows that the proposed scheme can achieve around 2dB performance improvement over the traditional network coding based on two-way relay protocol in block fading channels.