An OFDM receiver employing turbo equalization for multipath environments with delay spread greater than the guard interval

Abstract

This paper proposes a new OFDM turbo equalizer for mobile radio communications in the multipath environments where the delay difference is greater than the guard interval. In the OFDM transmission, the excess delay causes both inter-symbol interference (ISI) to the adjacent OFDM symbols and inter-carrier interference (ICI) within the same symbol. The proposed equalizer consists of the decision feedback equalizer for ISI cancellation and the low-complexity turbo equalizer for ICI cancellation. The latter consists of an ICI canceller, the optimal detection filter and a MAP detector. The iterative joint processing of the equalization and the decoding can effectively reduce ICI. Moreover, an ISI combiner is introduced so as to exploit the signal energy leaked to the next symbol. Computer simulations for the 5 GHz wireless LAN outdoor applications show that the proposed OFDM equalizer can effectively cancel both ISI and ICI, and that its performance is much better than that of the conventional coherent detector.