RLS-based frequency-domain DFE for uplink SC-FDMA

The decision feedback equalizer is well known to outperform a linear equalizer in highly frequency-selective fading channels. In this paper, we develop a low-complexity Adaptive Frequency Domain Decision Feedback Equalizer (AFD-DFE) for Single-Carrier Frequency Division Multiple Access (SC-FDMA) systems. Both the feedforward and feedback filters operate in the frequency-domain and are adapted using the block Recursive Least Squares (RLS) algorithm. Since this DFE design operation is performed entirely in the frequency-domain, the complexity of the block RLS algorithm can be reduced substantially when compared to its time-domain counterpart by exploiting matrix structure in the frequency-domain. We also show that the RLS-based AFD-DFE not only enjoys a significant reduction in computational complexity when compared to the frequency-domain non-adaptive channel-estimate-based MMSE-DFE but its performance is also better than that of the practical MMSE DFE (with decision errors) and close to the ideal MMSE DFE (with correct decisions).