well, as a simple example, consider if you had a 100MHz local oscillator and then two reference oscillators at 100.01 and 100.02MHz respectively. Your receiver will see both signals, you can mix the local oscillator with these signals (and a bit of filtering) to get the intermediate frequencies. The phase shift from the RF signals is now in the IF. Then you can perform a Fourier transform on the signal, extract the phase shift of the two components and hopefully (unless I neglected something) figure out how far (in terms of wavelengths) you are from the transmitter. If you know their positions, you should be able to compute your position.