Performance Analysis of Optical CDMA Using Fuzzy Logic Generator

Abstract

Multiple accesses which uses the spread spectrum technology for transmission has become very popular in cellular radio networks. Optical CDMA is a technique in which user uses a specific unique code rather a specific wavelength or a time slot. Optical CDMA uses the spread spectrum technique of CDMA combined with the optical link for transmission of data. Optical CDMA provides the large communication bandwidth along with the capability of secure data transmission. The key advantage of Optical CDMA is the multiple access technique which allows many users to share the same optical link simultaneously. This is done by giving each user a specific code which can be decoded only by the required user. OCDMA has many unique features that make it favorable data transmissions. Its characteristics make it suitable to increase the capacity and number of users in bursty networks. OCDMA can accommodate a large no. of channels on a single carrier frequency. It can utilize the bandwidth effectively through coding system. OCDMA systems provide high degree of scalability and security. It provides high noise tolerance. Optical CDMA had the potential to generate some of the previously unused bandwidth of the optical fiber and to carry over to the optical domain the benefits of CDMA in radio frequency systems. The early attempts of implementing of optical CDMA were not so successful. At that time technology available was not so advanced. In the last 20 years the optical CDMA field has matured substantially. The Optical CDMA systems suffer from the problem of Multiple Access Interference (MAI).As the number of users increase the BER error rate degrades because the effect of MAI increases.So, there is a limitation in number of users, as the number of users increase SNR decrease and probability of error increase. There is a limitation of speed also in optical CDMA systems-since very short pulses are to be required within each bit time, therefore it limits the bit rate for a finite pulse width transmitter. There is also a problem of high optical splitting at encoder/decoder. Now as the complexity of the system increases it becomes difficult and eventually impossible to make precise statements about its behavior. At such a point of problem we use fuzzy logic. Fuzzy Logic provides a simple way to arrive at a definite conclusion based on imprecise, vague and ambiguous data. Fuzzy Logic systems have a high XIV potential to understand the complex systems. Complex systems can be new systems that have not been tested..Fuzzy logic theory can also be utilized for assessing some conventional, less complex systems. Hence Fuzzy Logic is is very useful in two cases:(1) in situation involving highly complex system whose behavior is not understood and (2)in situations where an approximate but fast solution is required. A fuzzy logic system can be thought as combination of both of them as it attempts to understand the system for which no model exists and it does so with information that can be uncertain in a sense of being vague or fuzzy. Systems whose behavior is understood and controllable exhibit certain robustness to spurious changes. In this way robust systems are the ones whose output does not change significantly under the influence of changes in input. In this thesis, a highly spectral-efficient transmission technique based on optical codedivision multiplexing (OCDM) is investigated. Optical transmission systems have to meet the rapid increase in the demand of data bandwidth and spectral efficiency Over the years several modulation formats and optical receiver designs have been proposed. OCDM is one of spectrally efficient technique. OCDM multiplexing technique is different from optical time-division multiplexing and wavelength-division multiplexing (WDM). OCDM provides asynchronous transmission, secure communication, soft capacity on demand, and high degree of scalability. In this paper, we have applied OCDM technique alongwith fuzzy logic generator which gives us improvement .Fuzzy Logic generator accepts Vπ and Ron/Roff and generates I/I0 in a non – linear fashion.Such fuzzy logic augmented OCDM has shown better performance which is quite evident from various diagrams of BER Tester Decision Eye Diagrams, BER Tester Eye Lids Diagram, IstmpEye Eye Diagrams and autocorrelation Diagrams.