Zero-intermediate frequency (IF) zero-crossing demodulators (ZIFZCDs) have been developed for many applications to digital phase and/or frequency modulation, e.g., minimum shift keying (MSK), generalized MSK (GMSK), /spl pi//4-differentially encoded quadrature phase shift keying (/spl pi//4-DQPSK), and multi-level continuous phase frequency shift keying (CPFSK). The ZIFZCDs have exhibited better than and nearly the same performance as the existing demodulators for FM modulation index h/spl ges/1.5 and 0.5/spl les/h>1.5, respectively. The implementation complexity of the ZIFZCDs is much simpler than existing demodulators, e.g., limiter discriminator integrate and dump (LDI). Perfect symbol synchronization was assumed in the previous analyses of the ZIFZCDs. A new efficient symbol synchronization scheme is proposed for the practical application of the ZIFZCDs. The bit error rate performance of a four-level CPFSK with the ZIFZCDs using the proposed symbol synchronization shows a 2 dB and a 1 dB (average 1.5 dB) better than that of an existing scheme for the phase bit and magnitude bit, respectively. In addition, the ZIFZCDs with the proposed synchronization algorithm reduces the implementation complexity significantly compared to the existing synchronization schemes. Therefore, the battery life can be increased and the size of a portable receiver (a pager or cellular phone) can be smaller.
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机译：零中频（IF）零交叉解调器（ZIFZCD）已开发用于数字相位和/或频率调制的许多应用，例如最小频移键控（MSK），广义MSK（GMSK），/ spl pi // 4 -差分编码的正交相移键控（/ spl pi // 4-DQPSK）和多级连续相频移键控（CPFSK）。对于FM调制指数h / spl ges / 1.5和0.5 / spl les / h> 1.5，ZIFZCD分别具有优于和接近于现有解调器的性能。 ZIFZCD的实现复杂性比现有的解调器（例如，限幅器鉴别器集成和转储（LDI））要简单得多。在以前对ZIFZCD的分析中，假定了完美的符号同步。针对ZIFZCD的实际应用，提出了一种新的高效符号同步方案。使用提议的符号同步的具有ZIFZCD的四级CPFSK的误码率性能分别显示出比现有方案的相位比特和幅度比特分别高2 dB和1 dB（平均1.5 dB）。此外，与现有的同步方案相比，具有所提出的同步算法的ZIFZCD大大降低了实现复杂度。因此，可以延长电池寿命，并且可以减小便携式接收器（寻呼机或蜂窝电话）的尺寸。
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