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RE: [Discuss-gnuradio] GNU Radio and USRP baseband demodulation/decoding

From: Tachwali, Yahia
Subject: RE: [Discuss-gnuradio] GNU Radio and USRP baseband demodulation/decoding
Date: Thu, 5 Feb 2009 21:49:03 -0600

Hello Einar,

Knowing your modulation type can simplify your symbol and carrier 
synchronization design. However, if your are not restricted with certain 
modulation type and you just want to use an arbitrary modulation to get you 
going then I suggest to use differential coding such as D-BPSK which does not 
require coherent detection (no carrier synchronization is required) and that 
can simplify your design.

I hope that help a little. If you are really after symbol synchronization, I 
have read several publications by Dr.F.Harris and Dr.C.Dick but they tend to do 
their implementations in FPGA.

Kind regards,
Yahia Tachwali
From: address@hidden address@hidden On Behalf Of Einar Thorsrud address@hidden
Sent: Thursday, February 05, 2009 5:42 AM
To: address@hidden
Subject: [Discuss-gnuradio] GNU Radio and USRP baseband demodulation/decoding

Hi all,

I am trying to use the USRP with the LFRX daughterboard to receive a
baseband signal coming from an external RF-frontend (the signal is
originally 2-PSK passband). I am a GNU Radio novice, and have some
difficulties understanding how to synchronize to and decode the
NRZI-coded baseband signal. I suppose ones the synchronization is done
the actual decoding will be easy.

I find it difficult to understand the process of synchronizing, what I
would like to see is some kind of guide or feedback on how to pick
exactly the correct number of samples for each symbol, enabling the
decoding of the signal symbol for symbol.

What would be the correct approach to solve this problem?

(I am in fact also having similar problems understanding this using the
OSSIE SDR system, so it may be a more general lack of understanding on
my behalf)

Einar Thorsrud

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