Fast Fading Compensation Schemes for OFDM Transmission

A decision feedback compensation scheme that successively updates the channel estimate based on the decision values of the channel estimate (CE) symbols inserted in the frame header and the symbols in the data section is an effective fading compensation scheme for orthogonal frequency-division multiplexing (OFDM). However, when rapid phase fluctuations are produced as the received signal level drops in the frame, errors are propagated in successive symbols, and the accuracy of the fading compensation severely degrades. In this paper, we propose a fading compensation scheme for information symbols that places CE symbols in the last section in addition to those in the header section in one frame, which should lessen the error propagation effect. Specifically, we propose a direction-controlled unidirectional fading compensation scheme that adaptively controls the compensation direction based on the instantaneous signal-to-noise ratio (SNR) estimated from the CE symbols on both ends for each subcarrier and a bidirectional fading compensation scheme that detects drops in the received signal level in a frame and switches the direction of the fading compensation. The results of the performance evaluation showed that the performance was improved by the former scheme in a fast fading environment, and a significant improvement in the transmission performance was possible by applying the latter scheme.