Lucent Technologies Inc.

Nima Brardjanian

Mohsen Sarraf

Sheng-Jen Tsai

Yong J Lee

Alex Matusevich

Walid E Nabhane

A simplified method for frequency offset estimation in a TDMA cellular PCS environment using &pgr;/4-shifted DQPSK comprises the steps of multiplying a complex conjugate of a received complex-valued symbol and a succeeding symbol to produce a comparison vector having an angle equal to the phase angle between the received complex-valued symbol and the succeeding symbol, rotating the comparison vector so that the angle thereof is between 0&deg; and 90&deg;, and estimating the frequency offset by determining a constant deviation of the phase angle from an ideal phase angle value of 45&deg; by calculating an average phase angle for a plurality of successive comparison vectors or correlating the rotated comparision vector against a bank of unit vectors to determine a maximum correlation.

Method and apparatus for frequency offset compensation

A simplified method for sampling timing adjustment and frequency offset estimation in a TDMA cellular PCS environment using &pgr;/4 - shifted DQPSK comprises the steps of oversampling a received signal resulting from transmission of sequences of complex-valued symbols at a rate N times the symbol rate thereof so as to produce N sets of samples, comparing for each set of samples the differential phase angle between successively received complex-valued symbols, and determining which set of the N sets of samples has differential phase angles closest to ideal values to thereby obtain an optimal sampling timing. The differential phase angles are measured by multiplying a complex conjugate of a received complex-valued symbol and a succeeding symbol to produce a comparison vector having an angle equal to the differential phase angle between the received complex-valued symbol and the succeeding symbol. The differential phase angles are optionally rotated so that the angle thereof is between 0&deg; and 90&deg;. Frequency offset is estimated by determining a constant deviation of the differential phase angles from an ideal differential phase angle value for a plurality of successive comparison vectors by correlating the rotated comparison vectors against a bank of unit vectors to determine a maximum correlation.

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Eatontown, NJ, United States of America

Nima Brardjanian