A Study On The Key Techniques In The OCDMA Communication System

Optical fiber communication keeps in rapid development, from trunk lines to subscriber networks , stepping into more and more areas of the modern communication . While code-division multiple-access technology has been employed commercially world wide , its application in fiber-optic network become attractive . In this dissertation , the researches on the application of CDMA in fiber-optic communication systems have been reviewed , and several key techniques in the application are proposed with theoretical analysis.In traditional researches and applications of the HFC CDMA communication system , the GOLD sequence was used as the users' address code . In this paper , we analyze the characteristics of the m sequence in detail . Then , the address code can be designed by different phase sequence of an m sequence . Our studied method can attain better communication quality than before case . Of course , synchronization among all users is requested , i.e., our method is a S-CDMA communication . The self-correlation function of the m sequence is divided into the self-correlation between all same address users and the mutual-correlation between all different address users . A computer simulation experiment , which 100 users are communicating under our method , is given in this paper . The information of every user is known before the processing of S-CDMA communication start . After S-CDMA processing , the demodulated information and the original information of the same users are equally . We found that they are same in every user and prove the right of our method .In our communication method , synchronization between all users is requested . The key is that the Head-end emits the guide m sequence , which is non-correlative with any users' address code . The phase of all users address code and the Head-end address code are combined with the guide m sequence . Everyuser address code phase can attain after the guide m sequence phase is searched and tracked . After the circuit that can offer the point "0" of time coordinate is designed by myself, the most difficulty of our S-CDMA communication system is solved . In search processing of synchronization , one time search processing is improved by two time search processing . Therefore , the time spend on synchronization is saved , not only in the theory analysis but also in the computer simulation experiment are shown in this paper .The nonlinear effect has also been researched deeply in this paper . The nonlinear Schrodinger Equation (NLS) that consider all kinds of the nonlinear effects is derived . When every nonlinear effect is processed as perturbation , they can be simply put in the equation altogether . Then the different influence of each effect is discussed under different condition . By following the way of studying the nonlinear effect as a whole , the influence of the SPM and XPM to the phase matching condition of FWM is studied . From the achieved analytical expression it can be seen that the phase modulation can change the efficiency of the FWM . It is very important to the wavelength conversion through FWM . The result shows that a shorter fiber is necessary to get an enough efficiency when employing high optical energy.