Design Of The Code And Analysis Of The BER In OCDMA System

Optical code division multiple access (OCDMA) is a communication mode which introduces the code division multiple access (CDMA) technology into optical fiber communication. OCDMA has many advantages, like well confidentiality, random access, overcome the electronic bottleneck. The design of the optical code, the structure of the optical encoder/decoder, the multiple access interference (MAI) suppression are all the key issues in OCDMA. Currently, because of not find the good performance optical code, optical CDMA system still failed to commercialize. This paper focuses on the design of optical code and analyzing their BER. The main contents can be outlined as follows:1 Introduced the performance of different optical and design same different optical codes, which include one and two dimensional codes, SAC code, multi-weight code and multi-length code. The method of constructing the all interval set without repeating elements uses in the design of one dimensional code, multi-weight code and multi-length code. And obtaining the entire code family by constructing the code matrix. Latin matrix. Integer square matrix and power of 2 sequence are using in the design of two dimensional code. The SAC code is derived by the mathematical formulas. Furtherly, using MATLAB programming to get entire code family easily. Just enter the code weight and capacity,we can get the code family.2)In view of the different codes in respective system, in theory, analyzed the influence of the dark current noise, laser extinction ratio, background light and MAI in different systems, which include the ordinary system with OOCs, multi-BER requirement system with multi-weight code, multi-rate system with multi-length code,2D coding system and spectral amplitude coding system. According to the different system, derived the BER formula depend on the different constructional characteristic of codes, and analysis of the performance.3)For different codes, design and build a suitable simulation system. Using fiber Bragg grating (FBG) or wavelength division multiplexer (WDM) to be codecs in the frequency domain. Using optical fiber delay line to be codecs in the time domain. The one dimensional codes are used the codecs in time domain or frequency domain. The two dimensional code will be a combination of both. The part of decision threshold detection in spectral amplitude coding system uses a balanced detection method. Observation and analysis of the BER performance, which used different codecs or design schemes. Through the above analysis, to determine the performance of codes.