Diversity combining and equalization of frequency-selective fading signals with unequal mean strengths

This paper investigates the performance of unbalanced diversity structures combined with equalization techniques operating in a mobile radio environment with frequency-selective fading which is characterized by two Rayleigh-fading beams. The received signals are statistically independent, but the mean signal-to-noise ratios on various diversity branches are unequal. Quadrature amplitude modulation (QAM) and two optimum diversity structures, combining-diversity and selection-diversity, are considered in our analysis, Both linear and decision-feedback equalization with infinite taps and finite taps are used in the optimum diversity structures. Even though a degree of degradation that is proportional to the differences in mean power may result, unbalanced-diversity systems still can operate effectively in a frequency-selective fading channel. However, the diversity gain is almost lost when the unequal mean power is greater than 15 dB for 2-path diversity systems.