Digital Phase Sampling for Microcomputer Implementation of Carrier Acquisition and Coherent Tracking

By sampling zero crossings at the Nyquist rate (i.e., the predetection bandwidth) the phase of a narrow-band signal may be extracted directly with respect to an arbitrary, stable reference. Analysis, simulation, and experimental results are presented validating this all-digital technique for acquisition and coherent tracking of a Doppler-shifted carrier at a low carrier/noise ratio and a large percentage bandwidth. The key advantage of this scheme for microcomputer-based implementation is that phase comparison is accomplished by arithmetic subtraction, without the coordinaterotation transformation which is necessary for conventional I , Q sampling. Also, the phase-sampling process is independent of the phase error, which exists only as a numerical representation in the digital tracking algorithm. The technique is applicable to Costas suppressed-carrier tracking and to BPSK bit synchronization and demodulation, by programming the appropriate digital algorithms.