Uniden San Diego Research & Development Center, Inc.

Keh-Shehn Lu

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.

Method and apparatus for performing digital data signal modulation

A method for determining the best time to sample data bits of a data bit stream of a received information signal in a digital communication system includes the steps of determining the current derivative of a respective sample of the information signal, weighting the sample by a predetermined amount, determining an accumulated derivative value for the same sample number of a previous symbol of the information signal, weighting the previous accumulated derivative value by another predetermined amount, summing the two weighted values together and assigning this accumulated derivative value to the respective sample. The method further includes the step of comparing the accumulated derivative values of a predetermined number of consecutive samples to determine which sample has the greatest accumulated derivative value. The sample having the greatest accumulated derivative value substantially corresponds to the beginning of a symbol. A bit determination sampling signal is generated and is timed to have a pulse or transition which occurs one-half symbol from the occurrence of the sample having the greatest accumulated derivative value.

Method for determining the best time to sample an information signal

A method for setting a bit determination threshold for determining the logic state of a bit in a data bit stream of an NRZ (non-return-to-zero) signal in a GMSK (gaussian minimum shift keying) communication system includes the step of sensing the occurrence of a 'flat top' bit in the data bit stream, which signifies the occurrence of a first string of successive same state bits in the data bit stream, where the bits are in a first logic state, such as logic 1. The average bit amplitude of the information signal corresponding to the 'flat top' bit of the first string is determined. The occurrence of a second 'flat top' bit in the data bit stream which signifies the occurrence of a second string of successive same state bits which are of an opposite logic state, such as logic 0, is then sensed, and the average bit amplitude of the second 'flat top' bit of the second string is determined. The average bit amplitude of the first 'flat top' bit of the first string is averaged with the average bit amplitude of the second 'flat top' bit of the second string to determine a threshold level which is used in setting a bit determination threshold. A circuit for carrying out this method may be in the form of a programmable DSP (digital signal processor).

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San Diego, CA, United States of America

Keh-Shehn Lu