Linearly precoded or coded OFDM against wireless channel fades?

Abstract

Orthogonal frequency division multiplexing (OFDM) converts a dispersive channel into parallel subchannels and thus facilitates equalization. But when the channel has nulls close to or on the FFT grid, OFDM faces serious symbol recovery problems. As an alternative to various error-control coding techniques that have been proposed to ameliorate the problem, we linearly precode (LP) symbols before they are multiplexed. We identify the maximum achievable diversity order for iid or correlated Rayleigh fading channels and also provide design rules for achieving maximum diversity gains with LP-OFDM. Simulated performance comparisons of LP-OFDM with existing block and convolutionally coded OFDM alternatives favor LP-OFDM in a HiperLan2 experiment.