Suppression of impulsive noise in OFDM system using imperfect channel state information

Abstract

Multi-carrier modulation is a scheme that transmits the data by dividing the serial high data-rate streams into a number of parallel low data rate streams. Orthogonal frequency division multiplexing (OFDM) is a form of multi-carrier modulation, which divides the available spectrum into a number of parallel subcarriers and each subcarrier is modulated by a low data-rate stream at different carrier frequency. OFDM is the division of the frequency selective transmission channel into several subchannels, which can be characterized as flat fading channels. Impulsive noise severely affects the performance of OFDM system, if the amplitude of impulsive noise is very high. It is generated by power lines, heavy current switches, and other sources. A simple method to improve the performance of OFDM system in an impulsive noise environment is the blanking nonlinearity. It is implemented in the time-domain. Whereas another method for the impulsive noise suppression is implemented in the frequency-domain after OFDM demodulation and channel equalization. This method is called impulsive noise compensation method. This thesis propounds the OFDM system working under the Nakagami-m multipath fading channels, which utilizes the impulsive noise excision technique. Its performance is also evaluated under the imperfect channel state information (CSI) constraint. Although the impact of noise reduces due to the noise bucket effect appearing in the OFDM systems with longer symbol duration, yet the impulsive noise energy spreads over OFDM subcarriers, which appears as a hazard in the demodulation and detection, when the energy of impulsive noise exceeds a certain threshold level. Under realistic conditions, the channel estimators can’t provide perfect/ideal channel state information. In this work, we use the impulsive noise compensation method as a technique for the suppression of impulsive noise in the frequency-domain. Under the aforementioned scenario, the simulation results are demonstrated for the performance evaluation of underlying OFDM communication system, under the Nakagami-m multipath fading channel, which also focuses on the adverse effects of imperfect CSI at the receiver, in terms of bit error rate. It is also apparent from that approximately 3 dB improvement is observed m =2 relative to m = 1 and 3 dB performance degradation is observed m = 0.5 relative to m=1 at BER 0.04 under perfect CSI at the receiver.