Estimation and compensation of inter carrier interference in wimax physical layer under various channel models

Abstract

WiMAX is Wireless Interoperability for Microwave Access has emerged as a promising solution for transmission of higher data rates for fixed and mobile applications. IEEE 802.16d and e are the standards proposed. To attain higher data rates the Multi Carrier System with Multiple Input and Multiple Output MIMO is incorporated in the WiMAX. And all these sub carriers are considered to be orthogonal to each other. As the number of sub carriers is increased there is no guarantee of sustained orthogonality, i.e. at some point the carriers are not independent to each other, and hence where the orthogonality can be loosed which leads to interference and also owing to the synchronization between transmitter and receiver local oscillator, it causes interference known as Inter Carrier Interference (ICI).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 MLE and hence can be minimized. At demodulation stage the received signals are linearly combined along with their weighted oefficients and pilot symbols, called as Pilot Aided Self Cancellation Method PASCS. The simulations are carried out on Stanford University Interim (SUI)channels. The simulation results shows that by incorporating this method into WiMAX systems it performs better when the Line Of Sight (LOS) component is present in the transmission and also it improves the Bit Error Rate (BER) and Carrier to Interference Ratio (CIR). The CIR can be improved 20 dB. In this paper the effectiveness of PASCS scheme is compared with the Self Cancellation Method (SCM). It provides accurate estimation of frequency offset and when residual CFO is less significant the ICI can be diminished successfully.