Methods and apparatus for efficient and accurate coarse timing synchronization in burst demodulators

Abstract

Burst detection with high accuracy is achieved with a single autocorrelation circuit. Autocorrelation is performed using a preamble-embedded correlation sequence chosen such that a steeply sloped peak characterizes the autocorrelation response. The autocorrelation circuit is preferably used multiple times per clock period to deliver correlation moduli at sub-clock multiples. A contrast function makes a weighted comparison of each correlation modulus output by the autocorrelation circuit relative to adjacent correlation moduli. The contrast output defines a burst start-time uncertainty-window in a manner that is independent of signal level variability attributable to different operating conditions. A search is performed within the uncertainty window to identify the correlation maximum. Depending on the system mode (e.g., traffic mode vs. ranging mode), a priori knowledge may be preferred to the contrast output for defining the timing uncertainty window of the search. The time associated with the correlation maximum is the approximate time of the start of the burst. Burst-start indications so identified are accurate within the sub-clock multiple associated with the autocorrelation results. Parabolic interpolation is subsequently preferably used to deliver an overall burst-start indication with additional accuracy.