[Discuss-gnuradio] GPS/DSSS question

[Krzysztof Kamieniecki]

I've been working on my GPS software, and I have a question as to the validity 
of one of my algorithms.

Simplified Background:

  Each GPS satellite broadcasts a DSSS(Direct Sequence Spread Spectrum) signal. The chipping rate 
is 1023M/s and the PRN code is 1023 chips long.

  To lock onto a satellite signal you have to:
    1. Find (and track) the correct carrier frequency (because of Doppler / Relativity effects, 
Receiver effects, etc...)
    2. Find (and track) the correct chip offset
    3. Find (and track) the correct chipping rate (same problems at carrier frequency, but this may 
not be a noticeable effect)


My Algorithm:
1. Look for signal peak by trying 1023 different chipping offsets at 
frequencies separated by 200Hz
2. When a peak signal is found, measure the signal coming out of DSSS 
integrators.
3. Adjust carrier NCO based on measured signal (frequency and phase offset)
4. Activate carrier PLL

So the question is, Is step 3 valid thing to do, or do I need a more 
complicated FLL/PLL?

--
Krzysztof Kamieniecki
mailto:address@hidden