Phase-locked loop initialization via curve-fitting
AssigneeTexas Instruments Incorporated
InventorsChris Heegard, Peter A. Murphy
Life of this patent
Estimating the term…
Abstract
A method and apparatus for accurately estimating the carrier frequency offset and the carrier phase offset of a digitally modulated signal using a signal processing algorithm to initialize the state variables of a Phase-Locked Loop (PLL) is disclosed. A sequence of phase values is estimated from a received sequence of symbols and the angular effect due to the modulation format is removed from the sequence of phase values. A curve-fit algorithm based in one embodiment on the RLS algorithm is then applied to a sequence of unwrapped phase values to estimate the carrier frequency offset and the carrier phase offset.
Claims16
A method for estimating carrier frequency and phase offsets of a digitally modulated signal, comprising:
- (a) estimating one or more phases of a sequence of digitally modulated symbols;
- (b) removing from each of the estimated phases an angle rotation introduced by a modulation format, wherein the rotation is determined based on a reference symbol;
- (c) deriving a set of values from the estimated phases after removal of said angle rotation, wherein said values are a function of the carrier frequency and phase offsets to be estimated;
- and
- (d) processing said values to determine estimates of the carrier frequency and phase offsets.
A method for recovering a carrier phase offset and a carrier frequency offset comprising the steps of:
- (a) receiving a modulated signal containing a plurality of symbols;
- (b) determining an angular location of first symbol;
- (c) determining an angular location of a second symbol;
- (d) removing the modulation from the second symbol to produce an unmodulated angular sequence;
- and
- (e) estimating the carrier phase and frequency offsets by curve fitting the unmodulated angular sequence.
An apparatus for estimating a carrier phase offset and a carrier frequency offset, comprising:
- (a) a phase calculator for estimating phases of a sequence of digitally modulated symbols;
- (b) a remove modulation module for removing an angle rotation introduced by a modulation format to generate a sequence of phase values representative of the carrier frequency offset and the carrier phase offset;
- and
- (c) an estimation module for estimating the carrier frequency offset and the carrier phase offset, whereby the estimation module applies a curve-fitting algorithm to the sequence of phase values to generate a linear function dependent of the carrier frequency offset and the carrier phase offset.
Dependencies are inferred from the claim text.