I'm reading "Fundamentals of Global Positioning System Receivers" section 7.3 "Maximum data length for acquisition" and it's talking about phase transition:
Theoretically, if there is a navigation data transition, the transition will spread the spectrum and the output will no longer be a cw signal. The spectrum spread will degrade the acquisition result. Since navigation data is 20 ms or 20 C/ A code long, the maximum data record that can be used is 10 ms. The reasoning is as follows. In 20 ms of data at most there can be only one data transition. If one takes the first 10 ms of data and there is a data transition, the next 10 ms will not have one.
In actual acquisition, even if there is a phase transition caused by a navigation data in the input data, the spectrum spreading is not very wide. For example, if 10 ms of data are used for acquisition and there is a phase transition at 5 ms, the width of the peak spectrum is about 400 Hz (2/ (5 × 10−3)).
My understanding was that the C/A signal is a pseudo-random Gold code that is XORed with the data (each data bit being 20*1023 chips long) and the resulting binary signal is BPSK-modulated.
So I would think phase transitions in the C/A signal (caused by the BPSK modulation) would occur much more often, not just between data bits but between chips, every few chips.
What is wrong in my understanding of the modulation of the text?