Analysis And Optimization On Link Interference And Information Transmission In Wireless Ad Hoc Networks

Wireless ad hoc network is a kind of new network architecture which has no center, no organizer, and multi-hop routing. Such characteristics make it distinguish from other wireless networks and have extensive applications in both military and civilian fields. However, every coin has a flip side. Due to variable network topology, finite node energy and limited frequency bandwidth, how to improve the whole transmission performance of wireless ad hoc networks is a complicated and open problem. Facing the problem, many studies are done internally and externally, and two fundamental questions are investigated in the dissertation: the first one is how to construct a network topology with minimum interference globally; the other one is how to increase the transmission performance in a structural unit locally.To external research, we first present a quantitative model of network interference starting from the analysis to network interference. We describe the pair-wise interference condition theoretically. By the condition, it has been proved that the interference condition is identical for two power allocation strategies: the equal-power allocation strategy and the minimum-power allocation strategy. Based on the analysis above, a new metric, the average partial interference co-efficient, is given. Theoretical research and simulation analysis indicate that the average partial interference coefficient has no relationship with node density in the network, and it can be approximated as a linear function of link distance. Then, we present two particular interference optimization topology control algorithms, BIMA (Blocked Interference Minimum Algorithm) and LIMA (Local Interference Minimum Algorithm). Simulation results show that both BIMA and LIMA can not only provide a good performance in controlling network interference and conserving node energy, but also can maintain good spanner property and keep low node degree. Besides, both BIMA and LIMA show a good robustness to node mobility.To internal requirement, the relay network based on three nodes model is given as the basic structural unit. And we adopt cooperative communication using fountain codes to improve the transmission performance in the basic structural unit. Firstly, under the precondition of end-to-end invariable transmission rate, a simplified model is analyzed. Over binary erasure channels, the capacities of the relay network under several cooperative modes are analyzed. The results show that it will bring better transmission performance than others in the relay network if the cooperative mode can keep the status of each channel in busy mode as far as possible. According to such property, we present a greedy decode-and-forward cooperative scheme based on the flow control at the relay node after inducing the concept of the asymptotically optimal fountain codes. In the scheme, two requirements are considered. One is to prevent the relay from accumulating too many blocks because of the limited buffer size; the other one is to keep all the three channels as busy as possible in order to improve the overall throughput. To the requirements, the optimal power allocation strategy is studied by queue theory. Simulation results indicate that the greedy decode-and-forward cooperative scheme under the optimal power allocation strategy can not only keep the relay buffer from overflowing, but also improve the performances of achievable rate and bitwise signal-noise-rate in the relay network based on three nodes model.