Method and apparatus for performing signal correlation for signals received from satellites in multiple satellite systems

A method for computing correlations of a digital signal with a pseudorandom reference code comprising:

• receiving at least one of either a first signal from a first satellite system or a second signal from a second satellite system, where said first signal has additional coding;
• single sideband filtering the first signal to create a filtered first signal;
• correlating the filtered first signal or the second signal with a pseudo-random reference code to produce first partial correlations;
• accumulating the first partial correlations to generate a full convolution;
• using the full convolution to establish timing and frequency synchronization dividing the pseudorandom reference code into a plurality of code segments;
• selecting a code segment;
• forming an inner product between the selected code segment and the first signal or the second signal to produce a second partial correlation, wherein the additional coding is removed from the first signal before the inner product is formed;
• repeating the selecting and forming steps to produce a plurality of second partial correlations;
• and
• summing the plurality of second partial correlations to form a plurality of second correlations.

Apparatus for processing signals from a plurality of satellite systems comprising:

• a tuner operable to select a first signal from a satellite in a first satellite system or a second signal from a satellite in a second satellite system;
• a single sideband filter operable to filter the first signal;
• a decimation circuit operable to subsample the filtered first signal or the second signal, wherein a subsample spacing is selectable;
• and
• a convolution processor operable to correlate the subsampled signal with a reference code to produce a full convolution.