Preamble design for estimation and compensation of channel distortion parameters in OFDM systems

Abstract

I . I N T R O D U C T I O NOrthogonal frequency-division multiplexing (OFDM) has become a widely accepted technique for high data rate wireless access systems. Indeed, owing to its inherent robustness to multipath propagation, OFDM has become the modulation choice for many communication systems [1][2][3].A very promising technical approach for future wireless communication systems is to combine OFDM and direct-conversion receivers (DCRs). The DCR is a promising approach as it provides a low-cost and low-power receiver implementation over the traditional superheterodyne receivers [4,5]. However, DCRs front-ends are sensitive to component imperfections due to manufacturing non-uniformity, resulting to radio frequency (RF) impairments such as in-phase and quadrature (I/Q) imbalances and the carrier frequency offset (CFO) [4][5][6][7][8][9].Since RF impairments are unavoidable in low-cost and low-power DCRs front-ends, then, to obtain better performance for such communication systems, efficient estimation and compensation for the RF impairments is crucial [5,10]. CFO and I/Q mismatch seriously degrade the system performance, and their estimation and compensation are generally difficult as they are entangled in the received signal. I/Q imbalance results in a mirroring effect while CFO