Coding And Modulation Techniques For Wireless Optical Communications

In wireless optical communications, differential pulse-position modulation(DPPM) has advantages of high bandwidth efficiency and no need of symbolsynchronization. However, the variable-length symbols of DPPM lead tosynchronization errors, in forms of insertion/deletion in symbol level. In order tocorrect insertion/deletion errors in DPPM, researchers propose Marker schemes,Among them, the error-correcting ability of detection and correction scheme ofmultiple DPPM symbols inserted Marker codes is not excellent and Marker location isnot accurate. To solve this problem and further lower the frame error rate, two piecesof work are introduced as follows.On one hand, to improve the synchronization error-correcting performance ofthis scheme, this thesis studies the design of Marker codes, proposing two improvedtransmission schemes, following the idea of DAPPM and adopting hard decisionmethod. The proposed methods can achieve performance gains by properly adjustingthe amplitude and the form of inserted Marker codes. Simulation results show thatthese two improved transmission schemes provide a good trade-off betweentransmitted power, time delay and performance gains.On the other hand, to solve the problem of low accuracy of Marker location insoft decision method of the above scheme, an improved detection method usingMarker codes is proposed. The Marker location process in the improved methodemploys the presented interval combination method, instead of merge closest deletionmethod, to improve the accuracy of Marker location. Simulation results show that,compared with the previous soft decision method, the improved method can improvethe performance of DPPM systems.Above all, two improved transmission schemes and an advanced Markerdetection method for detection and correction scheme of multiple DPPM symbolsinserted Marker codes are proposed in this thesis. Therefore performance gains aswell as enhancement of Marker location accuracy can be achieved, thus to provide anefficient scheme to solve the synchronization problem in DPPM systems.