The Effect of Cyclic Intersymbol Interference of Frequency-Domain Decision-Feedback Equalizer

This paper investigates an inherent but adverse phenomenon called cyclic intersymbol interference (cyclic ISI) occurred in frequency-domain decision-feedback equalizer (FD-DFE). It is due to the cyclic-prefix insertion and modulo operation of the time-domain feedback filter. To analyze this problem, we first formulate the FD-DFE signal model in a compact and insightful vector-matrix form, which allows an efficient derivation of the MMSE receiver coefficients. Next, the cyclic ISI effect can be viewed in terms of the bit-error-rate profile (BERP) which plots the BER with respect to different starting symbol position within a symbol block. From the BERP, it is shown that those leading data symbols suffer more from the cyclic-ISI effect and lead to a high error floor, and the severity depends on the channel eigenvalue spread. Finally, a simple mitigation scheme using zero postfix (ZP) is presented to eliminate the cyclic ISI effect