| Optical code division multiple access technology from coding to decoding all in the optical area can deal with real-time and abruptly operation, is one of important communication project in synchronisms, high speed, Broad Band and secrecy communication area in future. This paper mainly focuses on the research in variables distribution of Optical code division and the method of designing of optical orthogonal code, A new two -dimensional variable -weight optical orthogonal code is proposed in this paper, the main structure as follows:1. OCDMA system, structure principle and characteristics are introduced in this paper, and two key points of code division multiple access technology - structure of Optical code and design of code to realization of code are analyzed in this paper. In addition, research faced challenges and latest research achievements of OCDMA technology at home and abroad in recent years are introduced.2. The method of calculating cross-correlate average of one-dimensional invariable -weight optical orthogonal codes is presented in this paper, and the cross-correlate average of some kinds of primed code and optical code are analyzed with this method, Based on the algorithm of one-dimensional codes, cross-correlate average and distribution of quadratic symmetrical optical orthogonal code are researched, which affords a new method of analyzing cross-correlate for other optical codes.3. The process of constructing variable -weight optical orthogonal codes with Balanced Incomplete Block Design is analyzed, analysis results and the simulation of multi-access interference bit error rate (BER) are researched, the relationship between variable -weight optical orthogonal codes and rigorous subtraction is also researched, the method of constructing variable -weight optical orthogonal codes based on rigorous subtraction is introduced, Analysis results and simulation of multi access interference BER are showed. Variable -weight optical orthogonal codes based on BIBD makes strict demands on code weight and has high convergence rate in finite area when constructed code, but it can only constructed two orthogonal codes with different weight. Variable -weight optical orthogonal codes based on strict subtraction has flexible construction method, which can constructed variable -weight optical orthogonal codes when code multi-set and basic variable are given, but it is complicated in time domain. 4. By using one-coincide sequence for wavelength hopping and strict VW-OOC for time spreading named OCS/SVW-OOC, the cross-correlate average of code is analyzed in detail, Analysis and simulation of multi access interference bit error rate of different weight codes. A new two-dimensional frequency hopping/time-spreading variable -weight optical orthogonal codes is designed, which using the single superposition sequence as wavelength frequency hopping and variable -weight optical orthogonal codes based on rigorous subtraction as time-spreading. Compared with other variable -weight optical orthogonal codes, the number of wavelength and slide of time are not only limited primed number or primed number power, According to the custom's different needs, It can be any integer, this constructed method is flexible and makes the full use of the effective wavelength of the system, at the end of the paper, the auto correlation and cross correlation are analyzed in detail the equation of Cross correlation average is concluded, multiple access interference simulation of multi-access interference bit error rate is finished in this paper. |
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