Using firefly algorithm for total ICI cancellation of OFDM communication system

Orthogonal frequency division multiplexing is an efficient transmission strategy to combat frequency selective fading and is part of many of the emerging wireless standards. Orthogonality of subcarriers is an important attribute in the performance of OFDM system. Carrier frequency offset effects orthogonality of subcarriers and the resulting interference causes severe performance degradation in OFDM. Thus, frequency synchronization is a challenging problem especially in mobile scenario. Estimation based cancellation and self cancellation schemes are the common techniques employed in combating the effect of CFO. Both these strategies achieves performance improvement at the cost of reduced data rate and the performance achieved after compensation is far from ideal scenario. In this paper OFDM system is analyzed in the presence of CFO and using the results of analysis, a blind interference cancellation technique is proposed which transforms the ICI cancellation problem into a conventional optimization problem. Firefly algorithm which is a class of high performance metaheuristic algorithm, is used to find a solution for the optimization problem. The proposed scheme is simulated using matlab and tested under various channel conditions. The simulation result shows that proposed scheme ensures interference free performance without compromising on data rate. Also, the conventional firefly algorithm is modified based on the characteristics of the optimization problem for reduced computational load and early convergence.

I. Introduction

Orthogonal frequency division multiplexing (OFDM) received considerable acceptance as a transmission strategy because of its high spectral efficiency and resistance to impairments introduced by frequency selectivity of the channel. Local oscillator mismatches and doppler spread causes loss of orthogonality of subcarriers resulting in interference and performance degradation [1].