Compensation of frequency pulling in a time-division duplexing transceiver

Abstract

A carrier-recovery loop for compensating frequency pulling in TDD and TDMA radio transceivers. The digital carrier-recovery loop includes a signal input, a digitally-controlled oscillator (DCO), a phase detector, a loop filter, and a memory. The memory stores an initializing value for the DCO, so that its frequency can be rapidly initialized at the start of a received frame. This initializing value is preferably either a sample of a control signal for the DCO, or a sample of the integrated value of a phase-error signal generated by the phase detector. Also described is a method for compensating the frequency pulling in a TDD or TDMA radio transceiver. The transceiver preferably receives data frames that have a preamble followed by a payload portion that holds the transmitted data. The method includes steps of (a) performing a carrier recovery during the preamble of a received frame, (b) storing a digital word indicative of a recovered carrier frequency at the end of the preamble, (c) continuing the carrier recovery during the payload portion of the received frame, (d) using the stored digital word to set an initial frequency for carrier recovery at the start of a subsequent frame, and (e) repeating said steps (a)-(d) for each frame in the series of data frames.