[Discuss-gnuradio] Software GPS:: BPSK demodulation

[Saeed Beyty]

Hi
 
   Some while ago we started working on software
implementation of GPS user segment (handset).in the
usual GPS, a GP2015 chip is used to do the RF-Down
conversion and 2bit digitization, the sampled signal
is then passed to a GP2021 chip for the Correlation
and tracking procedure to be done. Here we first tried
to process the sampled 2bit signal from GP2015 using
the GPP (General Purpose Processors like PIV), but as
it’s a time-wasting parallel process, it’s still
better to be done in a FPGA.
    We decided to use a FPGA chip to process the IF
digital stream from GP2015.in fact we want to replace
the GP2021 chip with a FPGA (to get closer to the SDR
idea), and then pass its output to the PC to do the
remaining processes. 
    The only problem in the theorical section is:
"Where and in which phase the BPSK Demodulation is
taking place??” as you may know, the original message
from the Satellite is Spread Spectrum coded and BPSK
modulated before transmission.
    I asked the OpenGPS mailing list, but they
redirected me to this page as here are many peoples
with communication expertise.
    It is very kind of you to answer me, if you could!
   
Dec 8th, 2003
 -- Saeed


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