Improved zero-crossing demodulator for minimum shift keying under static environments

An efficient baseband receiver, called zero-IF zero crossing demodulator (ZIFZCD), was recently developed for implementation of digital-FM receiver exploiting inexpensive low-power very large scale integrated (VLSI) or application specific oriented integrated circuits (ASIC). An advantage of the ZIFZCD is that its complexity is much lower, implementation is simpler, and power consumption is smaller than those of the conventional limiter-discriminator integrate and dump (LDI) or cross-differentiate multiply (CDM) FM receivers. However, a disadvantage is that the bit error rate (BER) performance of the ZIFZCD is worse than those of the LDI or CDM especially when small numbers of phase axes were employed. But, the merit of ZIFZCD is reduced complexity, which is inversely proportional to the number of phase axes. An objective of this paper is to improve BER performance of the recently developed ZIFZCD with insignificant additional complexities. The ZIFZCD makes a symbol decision by observing only one symbol period. However, narrowband digital FM signals have memory between symbols due to modulation characteristics and intersymbol interference (ISI) effects of filters. If these memory effects are exploited by taking multiple symbol observations for a symbol decision, then performance can be improved. In this paper, rather than increasing the number of phase axes for BER improvement of ZIFZCD, the sliding window, multiple symbol observation design will be employed for a symbol decision. Thus, the merits of ZIFZCD can be preserved by the sliding-window ZIFZCD design.