A method of processing offset carrier modulated, OCM, ranging signals in a radionavigation system including a plurality of satellite-borne transmitters and at least one ground-based receiver includes receiving a first radionavigation signal from at least one of the plurality of satellite-borne transmitters and down-converting and digitizing the first radionavigation signal to derive therefrom a first OCM signal SA, receiving a second signal SB synchronously broadcast with the first OCM signal SA, the second signal SB having the same or substantially the same center frequency as the first OCM signal SA, coherently combining the first OCM signal SA with the second signal SB at the receiver to generate a combined signal SC, generating a combined correlation value YC corresponding to a correlation of the combined signal SC with a local replica of the first OCM signal SC, and deriving ranging information based on the combined correlation value YC.

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for modulating and demodulating transpositional modulated (TM) signals. One aspect features a method of modulating a carrier signal that include the actions of generating a TM signal by generating a sinusoidal signal, and modulating the sinusoidal signal based on a data signal to provide the TM signal. Inserting the TM signal into a carrier signal to provide a TM modulated carrier signal. Modulating the TM modulated carrier signal with a non-TM signal to provide a combined signal. Transmitting the combined signal.