Abstract: In this paper genetic algorithm (GA) is applied on a method known as adaptive symbol transition (AST) used for suppressing the sidelobes in orthogonal frequency division multiplexing (OFDM) based cognitive radio (CR) technology. CR is an effective technique for meeting the increasing demand of frequency spectrum. It allows transmission of licensed (primary) user as well as unlicensed (secondary) user within the same spectral vicinity, depending upon the spectrum requirement by the primary user. The non-contiguous OFDM is a better signalling technique for CR as it provides high data rate and is resilient to the multipath propagation effects. Regardless of the advantages of NC-OFDM it highly suffers from out of band radiation (OOB), which results in distorted communication in adjacent wireless channel. GA is a heuristic search technique that works similar to the process of natural selection by iteratively finding the optimal solution from a set of solutions. Thus in order to reduce the OOB radiation in the NC-OFDM GA can be useful in reducing the sidelobe power levels significantly by giving the optimal solution to the value of extension added to the OFDM symbol in the AST method. In AST method the OFDM symbols are extended so as to minimize adjacent channel interference (ACI) and the value of extension to be added is obtained using optimization. The algorithm used in the AST technique is complex to implement and the time taken is also more, hence using GA is essential. Comparison of performance of the proposed GA technique along with AST and other two methods is conducted and presented in this paper.

Keywords: Non-contiguous OFDM (NC-OFDM), Cognitive Radio (CR), Out of band Radiation (OOB), Genetic Algorithm, Adaptive symbol transition (AST).