Performance Analysis And Improvement Of Near-ground And Short-space Wireless Optical Communication System

As a kind of new wide-band wireless communication technique and one of the developing directions of the next generation optical communication, wireless optical communication combines the superiorities of microwave and fiber communication. It is rich in frequency resources. It has large information capacity and good performance of resisting electromagnetic interference and keeping secrets. Its equipments have small size and very portable. The cost is relatively low. The link of it can be quickly arranged and it is flexible to make up network. It also has other advantages, such as quickly forming network, transparent network transmitting protocol, well performance of broadening, etc. The wireless optical communication can be used in'last mile'wide-band accepting, temporary communication for meeting emergency, extending the city area network, expanding the capacity of the local area network, interconnecting the inner-network of the enterprise or small districts, data resending of the wireless mobile base station, backuping the communication link of the fiber lines, short-space military communication in secret way, battlefield mobile commanding communication, some other places where are not fit to lay out or hard to working on the communication links or the region environment is limited.To realize the reliable all-day communication transmitting of the wireless atmospheric laser communication system in near-ground short-space and complicated atmospheric channel, this text studies and designs the system parameters,analyzes and improves the system's certain performance indexes. To transmit information directly in the atmospheric channel, making laser as the wave-carrier, the light wave is strongly influenced by a series of interfered effects. The text make some factors as the important affecting performance indexes, analyze and discusses these factors then uses them to build the channel model of the wireless atmospheric laser communication. These factors contains the atmospheric attenuation caused by absorption and scattering that made by atmospheric molecule and aerosol particles in stable and static state atmosphere, the intensity scintillation at the receiving port caused by atmospheric turbulence in unstable and dynamic state atmosphere, the free-space optical loss, the efficiency of the optical sending and receiving ports'antennas, the background noise and the noises of the received system. Gamma-Gamma scintillation distribution is used to model the atmospheric turbulence channel, which well matches and predicts the characteristics of the received intensity fluctuation. Subcarrier PSK intensity modulation/direct-detection technique is used to realize the digital bits transmitting. Based on the block diagram of the system, the important error performance parameters are deduced theoretically and simulated. The error performance and the preferable properties of the system are discussed. The ways to improve the performance like different sorts of coding are analyzed and simulated.