Modulators – Frequency shift keying modulator or minimum shift keying...
Patent
1997-10-30
2000-02-15
Kinkead, Arnold
Modulators
Frequency shift keying modulator or minimum shift keying...
375274, 375275, 375305, H04L 2728, H04L 2710
Patent
active
06025758&
ABSTRACT:
The present invention includes a method for generating a GMSK modulating signal from a serial digital data bit stream whereby the GMSK modulating signal modulates a carrier frequency signal associated with a GMSK transmitter of a digital communications system. Specifically, the method includes converting each set of m consecutive data bits of the bit stream into a parallel symbol, whereby there are 2.sup.m possible symbols. Each symbol is generally defined as (B.sub.-(m-1). . . B.sub.0), where B.sub.0 is the current data bit and B.sub.-(m-1) is the mth previous data bit with respect to B.sub.0. Next, a corresponding phase advance is assigned to each of the 2.sup.m symbols, each phase advance being substantially equivalent to a percent phase advance contributed by the m consecutive data bits of each symbol. Also, four corresponding accumulated phases are assigned to each of the 2.sup.m symbols, each accumulated phase being derived from a multiple of 90 degrees. Still further, digitally represented waveform portions are stored in a memory unit, each waveform portion respectively representing a time varying waveform that advances in phase by an amount respectively equal to each of the four accumulated phases. Next, the phase advance assigned to the current symbol is added to the phase advance accumulated from the previous symbol to yield a current accumulated phase for the current symbol. The memory unit is searched for the waveform portion that corresponds to the current accumulated phase and the portion is then outputted from the memory unit. The adding, searching and outputting steps are performed for each data bit of the digital data bit stream to form a digital representation of the GMSK modulating signal.
REFERENCES:
patent: 4339724 (1982-07-01), Feher
patent: 4567602 (1986-01-01), Kato et al.
Modem Principles and Architectures by Dr. Kamilo Feher, pp. 164-175.
Kinkead Arnold
Uniden San Diego Research & Development Center, Inc.
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