Hybrid Laser/microwave Communication System Simulation And Switching Technology Research

The Atmospheric Laser Communication is one of the communication technologies, which takes the laser as the carrier and the air space as the transmission medium. Atmospheric Laser Communication has the features of high security, immunity to electromagnetic interference, low-cost, license-free spectrum and low power consumption. In the changeful climate regions and seasons, its transmission quality is seriously impacted by atmospheric conditions, which makes the availability of the communication significantly reduced. Wireless transmission channel is mainly affected by the atmospheric turbulence and aerosols such as clouds, fog, rain and snow. These above atmospheric effects will cause absorption and scattering phenomena of laser signal, and have a great impact on the communication performance of the laser communication system, which make the system not function properly, especially in severe case, make the communication interrupted. While the Microwave Communication has a strong ability to penetrate the cloud and fog, but in rain, Microwave Communication suffer from severe attenuation. A hybrid laser/microwave communication system is designed to take advantage of the two systems to achieve high-speed and high-availability wireless communication.Firstly, this thesis analyzed the characteristics of atmospheric channel in the wireless transmission environment, and briefly introduced the influence of three kinds of atmospheric effects on wireless communication performances in the term of the atmospheric absorption, atmospheric scattering, and atmospheric turbulence. Furthermore, the effects of various atmospheric conditions on the attenuation of laser and microwave links are deeply analyzed, especially in cloud, rain and fog. According to the attenuation models of cloud, rain and fog on laser and microwave link, the laser and microwave link models with characteristics of clouds, rain and fog attenuation are created, Based on these models, the hybrid laser/microwave communication systems is simulated.In order to solve the handover problem between the laser link and the microwave link under severe atmospheric conditions, one adaptive handover solution based on the dual-threshold switching theory is proposed. This solution can adaptively switchover between the laser link and the microwave link according to the change of SNR, which is caused by the change of atmospheric conditions. Simulation results show that the adaptive handover solution can maximize the availability of the network under the constraint of the quality of communication. In addition, considering different applications require various qualities of service (QoS) requirements (such as bit errors), one application-aware adaptive handover scheme is further investigated to minimize the number of switches in the mixed-link system. And the performance of the algorithm is verified by the simulations.