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Abstract

In order to correctly demodulate a received sequential burst of symbols in a time division multiplexed/time division multiple access (TDM/TDMA) portable radio digital telephony communications system, proper timing of the sampling time in each received symbol of the burst is necessary. In addition, in order to compensate for component drift, an estimate of the frequency offset between transmitting and receiving units is also required. A method and circuitry for estimating symbol timing and frequency offset is disclosed in which the IF radio signal is sampled and digitized at a sampling rate which is sixteen times the symbol rate. The digitized samples are processed to obtain phase values. A one symbol delay is introduced and differential phase values derived, a differential phase value being derived for each of the sixteen sampling times per symbol. The differential values are collapsed into one quadrant in the phase plane and then expanded back to the full plane. For each of the sixteen sampling times, a separate vector sum is formed of the expanded and collapsed differential phase values over substantially the entire burst. Symbol timing is selected to be the particular one-of-the-sixteen sampling times at which the vector sum has the largest magnitude. Frequency offset is directly determined from the angle in the phase plane of that vector having the largest magnitude.

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First Claim