Frequency Domain Estimation and Compensation of Intercarrier Interference in OFDM Systems

Abstract

Orthogonal Frequency Division Multiplexing (OFDM) is a transmission technique which is robust in multipath channels. It is though sensitive to frequency errors that may be caused by several factors such as frequency offset at the local oscillator, phase noise and mobility of the receiver. These errors introduce Inter-Carrier Interference (ICI) that may be represented in the frequency domain by means of an ICI matrix. Since these types of errors greatly affect the performance of an OFDM system, estimation of this matrix is crucial. In this work we propose an iterative method that uses pilot tones in the frequency domain and converges very quickly. It works in two steps. In the first, correlation between received signal and estimated transmitted signal is used to estimate the channel matrix, and the second estimates the actual transmitted data by means of Minimum Mean Square Error (MMSE) equalization. Results, in the case of high frequency offset and of a time varying flat fading channel, show that the proposed method is very effective.