Reduction of Inter Carrier Interference by Pilot Aided Self Cancellation Compared to Self Cancellation Method

Abstract

Orthogonal frequency division multiplexing is a digital modulation technique in which the available spectrum is split into numerous narrow band channels of dissimilar frequencies to achieve high data rate in a multi path fading environment. In OFDM number of sub carriers is considered which are orthogonal to each other. As the number of sub carriers is increased there is no indemnity of sustaining orthogonality. At some point the carriers are not independent to each other, where the orthogonality can be loosed and which might escort to interference and also owing to the lack of synchronization among transmitter and receiver local oscillator, leads to interference known as inter carrier interference (ICI). The ICI cause power leakage amid sub carriers consequently degrading the system performance. In order to enhance the system performance and to diminish the inter carrier interference a novel scheme is proposed in this paper. In this scheme at the transmitter side the modulated data and a few predefined pilot symbols are mapped onto the non neighboring sub carriers with weighting coefficients of +1 and -1. With the aid of pilot symbols the frequency offset is exactly estimated by using maximum likelihood estimation and can be minimized. At demodulation stage the received signals are linearly combined along with their weighted coefficients and pilot symbols, called as pilot aided self cancellation method. By this the CIR can be improved ~10 dB. In this paper the effectiveness of pilot aided self cancellation scheme is compared with the self cancellation method. It provides accurate estimation of frequency offset and when residual CFO is less significant the ICI can be diminished successfully.