Forum: GNU Radio Receiving Spread Spectrum signals in Gnuradio

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5b956b6b52e6bd83ad6da9815f4442a4?d=identicon&s=25 Mir M. Ali (Guest)
on 2009-05-24 09:52
(Received via mailing list)
Hi,
I have a few questions regarding receiving Direct Sequence Spread
Spectrum
signals using USRP and gnuradio. I am transmitting a signal that is
spread
using gold codes at 2.4GHz. The USRPs that I have show a frequency
offset of
about 8kHz. In order to receive the signal so as to be able to de-spread
and
demodulate them I must implement a signal acquisition and tracking
scheme.
Can someone suggest me ideas to do this. I came across a few things that
gave me an idea of accomplishing this.

"Fundamentals of Global Positioning System Receivers - A software
approach"
was once suggested to me on this list. The acquisition scheme suggested
in
this book is FFT based and the tracking scheme consists of
Early-Late-Prompt
Correlation scheme for code tracking and Costas loop for carrier
tracking.

1. Is there any such acquisition scheme already present in Gnuradio? I
looked at usrp_spectrum_sense and I have an idea of what to do. I want a
system that should work in real time with simultaneous transmissions
from
different Tx.
2. If I know the offset then by tuning my usrp to a frequency such that
the
offset is negated will I be able to skip the acquisition part?
3. What other things should I be looking into or taking care of in order
to
implement a DSSS system.

I have just started working on my "Communication Systems" knowledge so
please bear with me.

Thanks,
Ali
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