Symbol rate conversion method for CDPD demodulator

Abstract

A method of converting GMSK modulated signals arriving at an integer multiple of the IS-54 standard sampling (or symbol) rate (24.3 KHz) to GMSK modulated signals at an integer multiple of the CDPD standard sampling rate (19.2 KHz). In the preferred embodiment, the GMSK signals arrive as serial in-phase (I) samples and quadrature-phase (Q) samples at the IS-54 sampling rate. The method of the present invention combines into one calculation the following operations 1) time-alignment of the serial I and Q samples into IQ pairs, 2) conversion of the time-aligned IQ pairs to the CDPD sampling rate of 4.times.19.2 KHz, and 3) sign correction of each time-aligned IQ pair. Because of the periodic nature of certain variables in the above calculation, efficiency is further achieved with the present invention by storing tables containing the possible values of these variables, then using pointers to access the stored values as needed, thereby saving considerable processing power and time. The above-describe calculations and tables allow CDPD demodulation to be carried out on low power, inexpensive digital signal processors.

Dependencies are inferred from the claim text.