Estimation and Compensation of Inter Carrier Interference in WiMAX Physical Layer Under Various Channel Models

WiMAX is Wireless Interoperability for Microwave Access has emerged as a promising solution fortransmission of higher data rates for fixed and mobile applications. IEEE 802.16d and e are the standardsproposed by WiMAX group for fixed and mobile. As the wireless channel have so many limitation Such asMultipath, Doppler spread, Delay spread and Line Of Sight (LOS)/Non Line Of Sight (NLOS) components.To attain higher data rates the Multi Carrier System with Multiple Input and Multiple Output (MIMO) isincorporated in the WiMAX. The Orthogonal Frequency Division Multiplexing (OFDM) is a multi carriertechnique used with the WiMAX systems. In OFDM the available spectrum is split into numerous narrowband channels of dissimilar frequencies to achieve high data rate in a multi path fading environment. Andall these sub carriers are considered to be orthogonal to each other. As the number of sub carriers isincreased there is no guarantee of sustained orthogonality, i.e. at some point the carriers are notindependent to each other, and hence where the orthogonality can be loosed which leads to interferenceand also owing to the synchronization between transmitter and receiver local oscillator, it causesinterference known as Inter Carrier Interference (ICI). The systems uses MIMO-OFDM will suffer with theeffects of ICI and Carrier Frequency Offset (CFO) “”. However these affect the power leakage in themidst of sub carriers, consequently degrading the system performance. In this paper a new approach isproposed in order to reduce the ICI caused in WiMAX and improve the system performance. In this schemeat the transmitter side the modulated data and a few predefined pilot symbols are mapped onto the nonneighboring sub carriers with weighting coefficients of +1 and -1. With the aid of pilot symbols thefrequency offset is exactly estimated by using Maximum Likelihood Estimation (MLE) and hence can beminimized. At demodulation stage the received signals are linearly combined along with their weightedcoefficients and pilot symbols, called as Pilot Aided Self Cancellation Method (PASCS). And also to realizethe various wireless environments the simulations are carried out on Stanford University Interim (SUI)channels. The simulation results shows that by incorporating this method into WiMAX systems it performsbetter when the Line Of Sight (LOS) component is present in the transmission and also it improves the BitError Rate (BER) and Carrier to Interference Ratio (CIR). The CIR can be improved 20 dB. In this paperthe effectiveness of PASCS scheme is compared with the Self Cancell