Efficient Real-Time Generation of Bit-Wise Parallel Representations of Oversampled Carrier Replicas

Abstract

An algorithm has been developed that efficiently generates in-phase and quadrature carrier replicas over a range of Doppler shift frequencies and initial phase offsets. This algorithm provides a new method that aids in bit-wise parallel baseband mixing of signals in software radios, specifically targeted at GNSS radios. Bit-wise parallel correlation, of which one step is baseband mixing, provides a processing time speed-up when correlating signals that are digitized to a low number of bits, as opposed to the standard multiply-and-accumulate correlation. The new algorithm makes use of the small phase differences between a set of signals that have a large ratio of the IF to the Doppler shift frequency. It uses specially-designed look-up tables to generate carrier replicas on-the-fly. This new algorithm can efficiently generate bit-packed carrier replicas using a small look-up table (10-100 s of kBytes).