MMSE diversity combining for wideband digital cellular radio

Minimum mean-square error (MMSE) diversity combining for wideband digital cellular radio, designed to combat intersymbol interference (ISI) caused by frequency-selective fading, is presented. The systems analyzed use: (1) binary phase shift keying (BPSK), quaternary phase shift keying (QPSK), or 16-level quadrature amplitude modulation (16-QAM) with cosine rolloff spectral shaping; and (2) space diversity with selection, maximal ratio, or MMSE combining. A set of performance curves is presented for selected combining schemes showing the influence of the following system parameters: the diversity order (1 to 4), the cosine rolloff factor, the power delay spectrum (with its associated delay spread), the signal-to-interference ratio, and the number of modulation levels (2, 4, and 16). It is shown that MMSE combining offers a significant improvement in performance over both selection diversity and maximal ratio combining for channels with high delay spreads. This is particularly true for channels in which the delay spectrum consists of two strong spikes