1. A method comprising: obtaining one or more pseudorange measurements based, at least in part, on one or more received satellite positioning system (SPS) signals acquired at a receiver of a mobile device; selecting one of a plurality of filter models for application to said pseudorange measurements to obtain a navigation solution for said mobile device based, at least in part, on a likelihood that said mobile device is in a motion state computed based, at least in part, on a difference between a measured pseudorange rate and a reference pseudorange rate associated with at least one of said received SPS signals; processing a plurality of said SPS signals to determine pseudorange rate measurements associated with said plurality of SPS signals, and wherein said likelihood is computed based, at least in part on differences between said pseudorange rate measurements and associated reference pseudorange rates; selecting a primary SPS signal from among said plurality of SPS signals; and determining a primary difference comprising a difference between measured and reference pseudorange rates associated with said primary SPS signal, wherein said likelihood is computed based, at least in part, on differences between said primary difference and said differences between said pseudorange rate measurements and associated reference pseudorange rates for SPS signals other than said primary SPS signal.