Sapce-time Coding And Arry Detection Techniques For MIMO Free-Space Optical Communication

Free space optical communication (FSO) has widely promising applications (especially military fields), since it is combined the advantages of fiber communication with other traditional wireless communication technologies, which include large capacity, such as good security performance, convenient deployment, flexibility and low cost.Because effects of atmospheric scattering, interception, turbulence and other factors, during the course of transmission, laser signals fading and light intensity flashing lead to the increase of error rate. Especially under strong atmosphere turbulence, the optical signal will be affected badly. This will bring about serious error rate or communication interruption in a short time. In such a case. it is difficult to solve the "last-mile" problem, because the stability and reliability of optical communication will become worse.To mitigate turbulence-induced fading and, therefore, to improve the error rate performance, spatial diversity can be used for FSO links which involves the deployment of multiple laser transmitters and multiple receivers. In this paper, Multiple-Input Multiple-Output (MIMO) transmitter and receiver designs for FSO communications are investigated and the achievable performance improvements are discussed.After searching on literatures about space optical communication technology characteristics and development, discusses unique advantages of FSO compared other means of communication; introduced the domestic and international research overview in this area, focuses on the MIMO optical communication systems, channel coding and detection technology development.The theory of atmospheric channel are summarized in the weakly or strong turbulent atmosphere respectively.Turbulence causes intensity scintillation and beam wander from propagation through turbulent eddies of varying sizes and refractive index, led to temporal coherence and spatial coherence. We also present channel estimation of FSO system for the lognormal distribution and the K distribution. Performance of estimation is evaluated by simulation and experiment.Performance of receiver diversity is introduced, and derived to maximum likelihood detection. signal to noise ratio (SNR) and bit error rate. In order to obtain full transmitter diversity. launch information symbol energy expand to not less than the number of transmitting antennas of the time intervals. When launch-training group X,is semi-unitary matrix, it is unbiased estimate for channel H by launch-training group X, and received-training data block.The MIMO technique is one of the effective means to mitigate the effect of atmospheric turbulence and reduce the packet error rate in Free-Space optical communications. We present the MISO link model and analyze the effect of atmospheric turbulence. also research channel correlation. Then it is presented that the probability density function of the received intensity with MISO link can be represented by equivalent those of single-beam with appropriate scaling G (the gain factor of log-amplitude variances). When number of beam increase, the probability density function of the received power with MISO link evolves as log normal distribution from gamma-gamma distribution at large zenith angles. The packet error rate is derived for MIMO Free-Space optical communication systems with DPIM modulation. With equal received power and equal background radiation Opt APD gain is much at one for different MIMO systems, so it must be considered when MIMO communication system is optimized.Owing to the particularity of FSO. the STBC of mobile communications must be improved to be made use of MIMO FSO systems. This paper presents the complemental space-time coding, cyclic orthogonal space-time coding, and differential space-time coding techniques. Error performance of PPM modulation cycle orthogonal space-time coding is the best in the above three kinds of space-time coding. The robustness of differential space-time coding is stronger than cyclic orthogonal space-time coding.Finally, multi-aperture array antenna signal detection is researched. The model of the APD signal and the array-receive electronic-counting probability density is presented. Then the optimal detection of maximum a posterior probability (MAP), suboptimal line detection and distributed detection are presented. Suboptimal line detection of MAP is better for flat Fading Channels. For Fast Fading Channels or low SNR. the distributed detection is better robustness.