Method and apparatus for use in carrier recovery in a communications system
View Patent ↗A receiver includes a digital phase locked loop (PLL) for performing carrier recovery. The digital PLL further includes a phase error estimator driven by hard decisions and an integrator, which accumulates a phase error signal provided by the phase error estimator. To reduce the acquisition time, the digital PLL is run in an open-loop mode during which an estimate of the carrier frequency offset is determined as a function of the phase error signal. After the estimate of the carrier frequency offset is determined, the integrator is pre-loaded with the determined estimate and the digital PLL is run in a closed-loop mode.
1. A method for use in a receiver, the method comprising:
using the receiver to perform the steps of
processing a received signal with a phase-locked loop (PLL);
generating a carrier frequency offset estimate as a function of a phase error signal of the PLL; and
detecting a false lock condition as a function of comparing the carrier frequency offset estimate to a closed loop value of the PLL.
2. The method of claim 1 , wherein the processing step includes the step of setting the PLL in an open loop mode of operation.
3. The method of claim 1 , wherein the generating step includes the steps of:
determining a rollover count value for the phase error signal;
determining a symbol count value of the received signal; and
generating the carrier frequency offset estimate from the determined rollover count value and determined symbol count value.
4. The method of claim 1 , further comprising the step of updating the PLL with the carrier frequency offset estimate.
5. A receiver comprising:
a carrier tracking loop (CTL) for processing a received signal; and
a processor for estimating a carrier frequency offset as a function of a phase error signal of the CTL;
wherein the processor detects a false lock condition as a function of comparing the estimate of the carrier frequency offset to a closed loop value of the CTL.
6. The receiver of claim 5 , wherein the CTL includes a rollover counter and a symbol counter accessible by the processor for use in estimating the carrier frequency offset.
7. The receiver of claim 5 , wherein the receiver is a set-top box.