Precorrelation digital spread spectrum receiver

摘要

A precorrelation digital spread spectrum receiver includes a signal converter for amplifying and directly converting RF band spread spectrum signals received by an antenna to a digitized baseband signal comprising a sequence of N-bit quantized baseband values. The baseband signal is a linear composite signal containing signals from all satellite channels as well as noise and jamming. An N-bit digital correlator correlates successive N-bit baseband signal values with successive local code values to produce plural correlation signals. A vector processor processes the correlation signals to derive early, late and on-time code correlation signals. The processed correlation signals are accumulated to provide process gain and are used to form error signals for carrier and code tracking, and measurement purposes. A sequential-tracking multi-channel embodiment time shares a common set of circuit elements and digital processing instructions to successively track different channels. In a preferred embodiment, the vector processor uses micro-code instructions to remove the carrier Dopler shift by multiplying the correlation value with a stored complex constant corresponding to the Doppler contribution. The receiver provides coarsely quantized code delays to the correlator, and uses digital interpolation routines to estimate correlation values for code delays of interest, thus providing fine resolution in the code delay without using either a numerical control oscillator or crystal oven.