Improved Equalization For Coded, Zero-Padded OFDM (ZP-OFDM) Systems

Zero-padded OFDM (ZP-OFDM) systems have recently been adopted in certain wireless systems, such as the multiband-OFDM based WiMedia standard, instead of the more commonly used cyclic-prefix OFDM (CP-OFDM). ZP-OFDM offers potentially superior performance in multipath channels only if more complex equalization, such as minimum-mean- squared-error (MMSE) or least-squares (LS) is performed at the receiver instead of the more commonly used overlap-add (OLA) equalizer. These complex schemes usually involve inversion of a non-diagonal, channel-dependent matrix that cannot be precomputed. In this paper we first develop two simplified algorithms for equalization of uncoded OFDM signals that improve performance in channels with spectral nulls compared to the OLA equalizer. We then develop a novel, iterative metric-calculation method for coded OFDM that with proper initialization requires only two iterations to approach the performance of a LS equalizer, without the need for matrix inversions. Simulation results will be presented to demonstrate the performance of the proposed algorithms.