Capacity And Performance Optimization Of Wireless Cooperative Communication System In Tunnels

With lots of branches, corners and ramps, tunnels are long, narrow and space-limited. Therefore electromagnetic waves may experience serious multipath fading when propagating in tunnels, which is the key problem to restrict the performance of wireless communication system in tunnels. Without increasing the number of antennas in each node, cooperative communication can improve the performance of wireless communication by utilizing multipath fading in tunnels. Capacity and performance optimization of the wireless cooperative communication system in tunnels are researched in the dissertation, and virtual MIMO is formed by the relay cooperation to enhance the ability of anti multipath fading.Firstly, wireless communication channel model in tunnels is established. The multimode channel model is modified by adding the rough loss factor of the tunnels, and the modified multimode channel model integrated with scattering loss is established. With the modified multimode channel model, simulation results of the propagation characteristics of electromagnetic waves in rectangular tunnels are consistent with the measurements. Besides, the near region model and far region model are built to simplify the modified multimode channel model, and the simulation results verify their rationality.Secondly, the cooperative communication system model in tunnels with single relay is built based on the modified multimode channel model, and the power allocation method, cooperative mode selection method and relay position selection method of cooperative communication system with single relay in tunnels are put forward to optimize the channel capacity. The power allocation methods of AF and DF modes are deduced, and as shown in the simulation results, the channel capacity of AF and DF modes have been improved 15-38% and 20-65% in the condition of the dual power constraint. In addition, the cooperative mode selection methods for both V-SISO and V-SIMO cooperative communication models are proposed, respectively. And the formulas of optimal relay positions of different modes are given.Afterwards, cooperative communication system model with multiple relays in tunnels is established, and the optimization methods of system performance are proposed. On the optimal criterion of the channel capacity, AFPAGA and DFMKPA algorithms are put forward based on the cooperation of multiple relays with dual power constraint, and the power allocation methods are designed with different cooperative modes. The simulation results indicate that the optimal effect of the channel capacity is better when the total system power is lower. Moreover, joint relay selection and power allocation method is presented, which reduces the outage probability of the cooperative communication system in tunnels.Finally, beamforming is adopted among multiple relays, and cooperative beamforming communication system model in tunnels is built. Joint power allocation and beamforming method is proposed for the channel capacity optimization, which can increase the channel capacity. Furthermore, joint relay selection and beamforming method is proposed based on the predetermined power gain thresholds of the channels, which can reduce the complexity of beamforming among relays, while obtain the similar channel capacity and bit error rate with those of the cooperative beamforming in which all the relays participate.The researches in this dissertation contribute to improve the reliability and efficiency of the wireless communication in tunnels, and provide the theoretical and technical supports for flexibly constructing the real-time, long distance, reliable and efficient safety monitoring and emergency rescue system in tunnels.