Novel Approach of Designing Spreading Code using Genetic Algorithm

Modern communication systems extensively use Code Division Multiple Access (CDMA) technology that associates one unique code to each user. Therefore the generation of these spreading codes has drawn considerable attention amongst the researchers with a fundamental requirement of having as much distinct members as possible along with a constraint of minimizing the inter-code correlation. Since the operation of trade-off between the number of unique codes and peak cross-correlation value is nothing but a task of optimization; one such intelligent technique called Genetic Algorithm (GA) has been employed in this paper for the design of spreading codes. This has proved the uniqueness of our code generation algorithm over existing ones as it provides flexibility in selecting the number of orthogonal code pairs even when the codelength is constant. Interdependence between the characteristics of the designed code and the parameters of genetic optimization has been revealed by means of a number of design examples. Inherent properties of the GA-optimized spreading code have been analyzed from a number of perspectives. Finally, the worth of the proposed code in current wireless system has been substantiated by comparing its performance with other stateof-the-art spreading codes. Key-words: Code Division Multiple Access (CDMA), Genetic Algorithm (GA), Kasami sequence, Orthogonal Gold code, Semi-Orthogonal Modified Large Set Kasami (SOMLK) sequence, Small Set Orthogonal Kasami (SSOK) code, Walsh code