Key Problems And Technologies On Wireless Network Coding

Network Coding is a momentous achievement of information technology in the 21st century. It breaks the convention that a router can only simply store and forward messages. Through combining multiple packets together and using the correlation among packets for decoding, network coding solves some classical theoretical problems such as the maximum multicast flow in directed networks in a very smart way, greatly increases the network capacity and the utilizing efficiency of resources, and has remarkable significance in enhancing the robustness of network management and data security. The broadcast nature of wireless channel endows network coding with extraordinary merit and potential in wireless networks. As a newly emerging technology, wireless network coding is faced with many challenges such as the mobility of wireless node, the variance of channel and limited resources of wireless equipments, and there are a lot of key questions to answer. This work aims at solving some key theoretical and technical problems of wireless network coding, completing the current theory framework, and using the idea of network coding to improve the performance of wireless networks, which lays the foundation for its practice.For the basic theory, the random graph model will be established for wireless networks, and put forward the strategies of maximum flow multicast routing, coding node selection as well as an optimized capacity allocation scheme on output links based on network coding, and further propose the whole framework of wireless network coding. Based on these works, we will study the distribution of the maximum flow for both end-to-end and multicast communication theoretically, and analyze the benefit and complexity of wireless network coding quantitatively. Network Coding in undirected networks will also be studied, with the original discovery on the collision phenomenon of information flows. Moreover, the relation between delay and efficiency will be investigated to the queuing and waiting delay that is peculiar to network coding, and optimized scheduling algorithms will be given.For engineering, we combine network coding with traditional cross-layer techniques to improve the network performance. The first job is an interference eliminating technique based on network coding. Through the content of packets that is known to the receiver, this technique can effectively eliminate the interference without synchronization and power control, thus increase the space reusing and the transmission efficiency is increased. The other job is distributed network error correction code in the form of product code, which can reduce the bit error rate of multicast.Finally, to make the concerning techniques practical, we will discuss the issues to deal with when network coding is implemented, such as error control, retransmission, delay, QoS guarantee and its compatibility with current systems, and present the corresponding solutions. The feasibility of these solutions is proved by the hardware experimental bed of wireless network coding designed in this work.