INTERCARRIER INTERFERENCE SUPPRESSION SCHEMES IN FAST FOURIER TRANSFORM (FFT) BASED ORTHORGONAL FREQUENCY DIVISION MULTIPLEXING (OFDM) COMMUNICATION SYSTEMS

Abstract

The demand for high data rate transmission is rapidly increasing in the area of wireless communications. Orthogonal Frequency Division Multiplexing (OFDM) is known to be a promising technique for high-rate transmission that can overcome the inter symbol interference (ISI) which results from the time dispersive nature of wireless channels. One of the main problem in OFDM is its sensitivity to frequency offsets between the transmitted and received signals, thereby causing intercarrier interference (ICI). The study modelled OFDM transmitter, the channels (AWGN, Rician and Rayleigh) and OFDM receiver, to examine effects of two ICI reduction techniques. The first method was the self-cancellation (SC) scheme, in which redundant data was transmitted onto adjacent sub-carriers such that the ICI between adjacent sub-carriers cancelled out at the receiver. The second technique was maximum likelihood (ML) estimation in which the frequency offset is first statistically estimated using a maximum likelihood algorithm and then cancelled at the receiver. The results show that maximum likelihood (ML) method performs better in AWGN and Rician channels in terms of Bits Error Rate (BER), it had a gain of 1.4dB while self cancellation (SC) had a gain of 1dB at BER of 0.0004 when the frequency offset was 0.05. The choice of which method to employ depends on the specific application. Self-cancellation does not require very complex hardware or software for implementation but it creates redundancy in the subcarriers. The ML method provides a better BER performance and accurately estimates the frequency offset