Method of processing a digital signal derived from a direct-sequence spread spectrum signal

Abstract

In a GNSS receiver data sequences derived from a digital signal each with an internally generated correlation sequence derived from a basic sequence and mixed with frequency signals corresponding to various Doppler frequencies and in various phase positions with respect to the data sequence are correlated and the correlation values evaluated. In difficult conditions, e.g., RF levels of the signal of −145 dBm and less, correlation values produced with the same correlation sequence and phase position but with a plurality of data sequences are evaluated together in that, in an evaluator (), every-correlation value is, in a comparator (), compared with at least a first value threshold and a second value threshold, with the latter having a value between 1.3 and 1.7 times the value of the first and values −1, 0 or +1 assigned accordingly to a correlation term which is then added to an integer correlation counter which varies over a counter interval, e.g., [0, 15], in an adding unit (). The correlation counters corresponding to the various Doppler frequencies and phase positions are stored in a memory unit (). In an arbitration unit () a correlation indicator is derived from each correlation counter and the latest corresponding correlation value and the six largest correlation indicators selected and stored together with their Doppler frequencies and phase positions.