Research On Network Coding Based Wireless Network Communication Mechanism

Performance of wireless network is affected by various network characteristics, such as serious radio signal interference, limited network bandwidth, high dynamic mobility of wireless terminal and unstable wireless channel media. Network coding proposed in 2000, as a new coding mechanism for compressing bit stream, has been introduced to a wide range of applications. The main focus of traditional optimizing mechanism is to avoid col-lisions between data flows. While the core idea of network coding is to allow the informa-tion flow received from multiple incoming links to be mixed into a single coded flow. Then the amount of packets transmitted through the network is greatly reduced and the network capacity is improved. Network coding can not only provide a new way for im-proving network capacity, but also bring some other benefits, such as energy efficiency, robustness enhancement and security guarantee. Due to the widely penitential applications, network coding has been received increasing attention both from the academic and indus-try. Network coding can be inosculated with other technologies, and is becoming one of the most important research areas in next generation wireless network.This thesis focuses on addressing the problems in applying network coding to four main network layers. First, this thesis investigates how to restrict the coding times for en-ergy efficiency in network layer. Then we consider the combination of fair scheduling and network coding in MAC layer, which can ensure the capacity gain of multi-user system. After that, for enhancing the bi-direction data exchange in multi-relay network, a distrib-uted cooperative communication mechanism based on physical network coding is pro-posed. Finally, in application layer, we introduce a hierarchy network coding to construct reliable and flexible multi-hop and multi-path handover links for wireless network.The contributions of this thesis include:(1) Propose a network coding based data dissemination mechanism CRNC. To re-strict the inherent redundancy of traditional network coding, we propose a constrained network coding model inspired by classic epidemic model. The maximum duplication times of original coding data packets is the key parameter for adjusting the tradeoff be-tween transmission delay and amount of coded packets. The hot spot of network is also analyzed so as to make an optimal flow rate controlling strategy especially when energy is limited. CRNC can achieve a better tradeoff between resource usage and performance. (2) Propose a network coding awareness based fairly scheduling mechanism FSNC. Traditional network coding focuses on the overall capacity, while neglecting the difference of decoding ability and channel condition among multi-users. Without proper scheduling, network coding may cause negative effect on the capacity gain. FSNC introduces a bank credit model to balance the statistical short-term fairness. Meanwhile FSNC makes sched-uling policy based on the ARQ feedback messages from users, which contain knowledge space information. The simulation results verify that FSNC can provide service time fair-ness while improving the goodput for each user in multi-user system.(3) Propose a network coding based distributed cooperative communication mecha-nism NCCC. To utilize the interference between radio signals, physical network coding is introduced to construct coding matrix based on channel parameters. A distributed relay selection algorithm is designed to choose an appropriate set of relay nodes for maximizing the sum of instant mutual information. The simulation results show that NCCC can en-hance the performance on average capacity and outage probability for bidirectional data transmission between multi-source and multi-destination in wireless network.(4) Propose a network coding based multi-target handover mechanism NCHO. To improve the poor reliability and real-time performance of traditional multi-hop handover, a hierarchy network coding (HNC) is introduced. HNC can control the transmission direc-tion and amount of coded data packet in a wireless mesh network similar with potential energy field. In NCHO, multi-hop multi-path handover links can be established between mobile station and multiple network access points, which greatly enhance the robustness and flexibility of handover.The entire works of this thesis are exploring the problems in the application of net-work coding in wireless network. The research results can accelerate the development of network coding, which has forward-looking in theory and practicability in reality.