Linear precoding assisted blind channel estimation for OFDM systems

We propose a novel precoding approach for single transmit/receiver antenna orthogonal frequency-division multiplexing (OFDM) systems that enables blind channel estimation. A nonredundant nonunitary linear precoder is applied on each pair of blocks before they enter the OFDM system. The structure induced to the transmitted blocks allows for blind channel estimation at the receiver based on simple cross-correlation operations. At the same time, the multipath diversity of the system is increased. An optimal precoding scheme is pursued that, for quadrature phase-shift keying signals results in minimum channel error and asymptotically minimum bit error rate. Analytic performance evaluation of the proposed approach, and Cramer-Rao bound for the proposed channel estimate, are presented.

I. Introduction

Orthogonal frequency-division multiplexing (OFDM) has emerged as a modulation technique that can achieve high speed data transmission by effectively handling multipath effects. It has become a standard in a number of high data rate applications including ADSL, IEEE 802.11, and HiperLAN, and has been adopted by the European digital audio and video broadcasting standards, i.e., DAB and DVB. The basic idea of OFDM is to divide the available spectrum into several parallel overlapping subchannels (or subcarriers), on which data streams are transmitted at a lower rate. Thanks to the cyclic prefix, the channel matrix becomes circulant, and the data transmitted on each subcarrier experience flat fading. The equalization at the receiver can be implemented by a set of complex multipliers, one for each subcarrier, provided that knowledge about the channel is available.