| 摘要 |
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 2m possible symbols. Each symbol is generally defined as (B-(m-1). . . B0), where B0 is the current data bit and B-(m-1) is the mth previous data bit with respect to B0. Next, a corresponding phase advance is assigned to each of the 2m 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 2m 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.
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