A comparison of synchronous and fractional-spaced DFEs in a multipath fading environment

The ability of a 6-tap decision feedback equalizer (3 forward, 3 backward) to combat multipath fading in a digital microwave environment is compared with that of an 8-tap (5 forward, 3 backward) fractionally spaced DFE. The tap spacings of the forward part are at T/2. The lengths are chosen to span the same time interval. The ability of the equalizers to combat multipath fading is estimated using computer modeling of a baseband 64-QAM (quadrature amplitude modulation) system, with a channel model based on a modification of W.D. Rummler´s (1981) two-ray model. Square-law timing recovery is used. Performance comparisons are based on minimum-mean-square error and eigenvalue spread (for tracking ability) criteria. The tracking ability if further tested by generating learning curves for different channel conditions