Optimum MMSE equalization for staggered modulation

"Staggered modulation" techniques have become prevalent in digital radio transmission. These techniques offset or stagger the modulation of the in-phase component with respect to the quadrature component of the signal. Examples include minimum shift keying (MSK), Gaussian MSK, offset QPSK, and offset QAM. Conventional equalization designed for QPSK/QAM is suboptimal for staggered modulation because it places unnecessary restrictions on the equalizer output. We derive a new decision feedback equalizer for staggered modulation that takes advantage of the signal's offset modulation nature. Given the channel pulse response, we compute the optimum DFE that minimizes the mean squared error only in the dimension of the modulated symbol, alternating the equalization and decision boundary from symbol to symbol. We show that this new equalizer achieves significant performance gain over conventional DFE structures.<>