Re:Super-Accurate GPS Chips Coming to Smartphones in 2018
by nullc on Friday September 22, 2017 @07:25AM
(#15311118)
P code itself has a period of a week but the W code that scrambles it doesn't have a known period AFAIK.
Semi-codeless receivers can use it anyways. The reason is that the W code has a much lower data-rate (500KHz I think).
Take the incoming signal, correlate with the aligned P code. The resulting signal will be a MHZ wide signal, bandpass to it, and square the result. The squaring wipes off the residual W code. Because you bandpass filtered before the squaring you don't get so much squaring loss. Lock the resulting carrier, and use RTK signals and long observations to resolve integer ambiguities.
For a dual frequency rx you can exploit that P(Y) is the same on both frequencies and correlate them against each other to find the ionospheric delays.
Semi-codeless receivers can use it anyways. The reason is that the W code has a much lower data-rate (500KHz I think).
Take the incoming signal, correlate with the aligned P code. The resulting signal will be a MHZ wide signal, bandpass to it, and square the result. The squaring wipes off the residual W code. Because you bandpass filtered before the squaring you don't get so much squaring loss. Lock the resulting carrier, and use RTK signals and long observations to resolve integer ambiguities.
For a dual frequency rx you can exploit that P(Y) is the same on both frequencies and correlate them against each other to find the ionospheric delays.