Research On Iterative Technology In Wireless Optical Communication Based On Photon Count

Optical wireless, or free-space optical (FSO) communications, integrating the advantages of conventional radio frequency (RF) and fiber communications, guarantees the high speed data transmission with relatively low costs and system complexity, and is a key building block of wide area ultra-high data speed data network in the future. Recently FSO has become one of the research hotspots. The turbo-like iterative technology could be used inTurbo principle based iterative technology could not only be used for decoding of parallel concatenated convolutional codes, but for a series of problem such as multiuser detection, equalizations, iterative demodulation/decoding of bit interleaved coded modulation (BICM), decoding of serial concatenated codes as well. The core of turbo-like iterative processing is updating and feedback of the extrinsic information or log-likelihood rations (LLRs) between the two constituent soft-input soft-output (SISO) mudules. The extrinsic information transfer (EXIT) chart as a powerful tool to analyze the turbo iterative process and its convergence behavior has been widely used.Interleave-division multiple-access (IDMA), originated from CDMA, utilizes user-specified interleaver rather than orthogonal spreading codes to identify different users and soft interference cancellation (SoIC) detection algorithm is used at receiver site to make easier realization of system.The thesis focuses on the study of turbo technology in photon-counting based FSO system. We first have a research on the iterative demodulation/decoding of different channel codes and modulation schemes in single-user BICM FSO over deep-space Poisson channel. Then we research the iterative detection of IDMA multiuser system in Poisson FSO links and analyze the impacts of two multiuser detection (MUD) algorithms, the optimum Bayesian (OB) and SoIC, the errer-control codes and numer of users in system on convergence behavior. Finally, based on IDMA and multiple antennas techniques, we propose two schemes to mitigate the FSO atmospheric turbulence, one for lower turbulence and the other for higher, respectively.