Phasetracking

Phasetracking, in signal processing, is the estimation of the instantaneous phase of a time-varying signal, typically to compensate Doppler shifts, oscillator drift, or noise, and to enable coherent demodulation or phase-sensitive analysis. A phasetrackers goal is to produce a phase estimate that follows the true signal phase as it evolves, often modulo 2π, and to maintain convergence in the presence of disturbances.

Common methods include phase-locked loops (PLLs) that lock an internal oscillator to the input signal, and their digital equivalents (DPLLs); Costas loops for carrier recovery in suppressed-carrier modulation; and quadrature detectors. Alternative approaches use Kalman or Bayesian filters for joint phase estimation, or Hilbert-transform methods to obtain instantaneous phase. Phase unwrapping and phase-noise models help manage ambiguities and inform design choices.

Implementation considerations include sampling rate, loop bandwidth, noise characteristics, and desired tracking speed. A wider bandwidth yields faster tracking but higher noise susceptibility; a narrow bandwidth improves noise rejection but slows response. Digital phasetracking may incorporate adaptive filters to cope with time-varying statistics.

Applications span carrier recovery and symbol timing in telecommunications, GPS receivers, coherent optical and microwave links, radar and sonar, and biomedical signal analysis where phase information is of interest. Limitations include phase ambiguity wrapping, non-stationary noise, and the need for accurate models of the signal's phase dynamics.