A Reduced Complexity Equalizer for OQPSK

This letter presents a reduced complexity equalizer for offset quadrature phase-shift keying (OQPSK), Gaussian minimum shift keying (GMSK), or any other staggered modulation format. Due to the relative time offset of the in-phase and quadrature components, the received signal must be sampled at a rate of at least twice the symbol rate of its corresponding nonstaggered signal, where using a symbol-spaced equalizer (SSE) is an option. The conventional approach doubles the number of equalizer coefficients required relative to QPSK. In this work it is shown that also for OQPSK it is possible to implement an equalizer spaced in symbol rate, with about half the complexity required for the linear equalizer (LE). For the decision feedback equalizer (DFE), savings are achieved only in the feed forward filter.