Channel Estimation using Differential Model of Fading Fluctuation for EM Algorithm Applied to OFDM MAP Detection

This paper proposes a new channel estimation method for the expectation-maximization (EM) algorithm applied to an OFDM receiver. Conventional schemes using the EM algorithm assume the random walk model as a process equation of a channel impulse response, and thus have insufficient tracking ability to fading fluctuation over fast fading channels. To improve the tracking ability, the proposed channel estimation method employs the differential model having the first and higher order differentials of the channel impulse response with respect to time. Computer simulations under the fast fading condition demonstrate that the proposed method is much superior in packet error rate to the conventional schemes employing the random walk model.

I. Introduction

Orthogonal frequency division multiplexing (OFDM) transmission has already been adopted as the standards of the wireless LAN and the digital terrestrial television broadcasting (DTTB), because it can realize high bit-rate and reliable transmission over multipath radio channels. The optimum receiver for the OFDM system is based on the maximum posteriori probability (MAP) criterion. Since the MAP-based receiver requires a prohibitively large amount of computational complexity, the application of the expectation-maximization (EM) algorithm, which can reduce such complexity to a feasible amount by recursive approximation, has been investigated [1], [2].