Chaotic Light Of Ocdma Systems Address The Encoding And Decoding Scheme,

OCDMA is a technolegy which is a combination of CDMA with optical fiber communication.There are many advantages to use it,such as:high capacity and random access;high security and excellent anti-interference. It implies a great challenge for the development of future communication networks,especially all optical networks.Chaos is produced by deterministic nonlinear systems,its phenomena is pseudorandom.Chaotic systems exhibit sensitivity to initial conditions,chaotic signals are reproducible and have broadband frequency spectrum.For all these special performance,chaos has a excellent outlook in the application of telecommunication,especially in the generation of PN(pseudo-noise) sequence.In the field of CDMA,the chaotic sequence has aroused a lot of study.How to generate chaotic sequence and apply them into optical COMA system is an interesting and new research topic.In this thesis,a great deal of research work is described as follow: the construction of chaotic sequence,the generator of chaotic sequence,the de/encoder scheme emloyed chaotic sequence,the performance and simulation of system.The main achievements are listed as follows.1.Binary chaotic sequences are applied into two coherent OCDMA systems.(a).A chaotic OCDMA system whose en/decoder is mach-zehnder modulater(MZM) is prorosed.Zhe MZM is drived by chaotic sequence generator.(b).A chaotic OCDMA system whose en/decoder are composed of optical fiber and phase shifter is proposed.The BER formula of the system is derived and the BER curves versus the user number of simultaneous transmiting are reported,the numerical simulation results show that the systems based on chaotic sequences outperform that using Gold sequence and these security for transmission is increased.2.A type of true balanced chaotic sequence is constructed.In the structure the number of "+1" and "-1" are equivalent.And the system with complementary balance structure based on true balanced chaotic sequence becomes simple,and its DC component is zero.The system performance in terms of BER is also improved.The numerical simulation results show that the system based on chaotic spreading sequences performs better than that based on Gold sequence.3.A chaotic bipolar sequence generator using Mach-zehender interferometers is designed.The arm lengths of MZI are taken as some special values.This generator can generate analog bipolar chaotic sequences which satisfy the logistic map.To enhance the security,this generator can be used as an encoder in an optical CDMA system.4.A chaotic OCDMA system is proposed,and its en/decoder is the generator designed above.The structure of this OCDMA system is described. Its BER formula is derived and the BER curves versus the user number of simultaneous transmiting are reported.The BER curves show that these chaotic sequences due to good property of correlation are suited for asynchronous OCDMA system.