I am thinking on what is the practical limit of precision for VHF positioning system (like currently obsolete and gone "Transit" system).
It is well known how GPS receivers calculates pseudorange to each satellite to calculate the position of the receiver - GPS transmits PRN signal at 1 MBit, so by just counting the "chips" you can get pseudorange precision down to 1us which is 300m, and by tracking the phase you can get much more precise (ultimately to the point where you are limited by oscillator phase noise and ionospheric delays).
But in VHF we typically don't have bandwidth to transmit 1Mbit PRN signal even if it's below noise level, and one will have to use much lower speed, like 19200. Obviously length of 1 bit at 19200 is extremely long.
The question is what is the practical limit on precision of phase tracking of the signal given that it's VHF and bitrate is mere 19200?
Is it possible to track the phase with ultimate precision by recoding the data with SDR and after decoding the data we go back in history, and try every possible signal start time by maximum SNR using this now known data? It seems that in this case phase resolution will be limited by SDR sample rate and phase precision will be limited by length of the data packet and physical limitations (phase noise, ionosphere, e.t.c).