Prateek Mohan Dayal prateek[at]iitg.ac.in
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Software based Radio Signal
Processing
This page discusses some of the
preliminary results that I have obtained in my BTP, “Software based Radio
Signal Processing”. Objective of the BTP is to demodulate NTSC TV signal
totally in software using the GNU Radio software platform. Click
here to download a write up on introduction to Software Radio and the basic
problem of TV Signal demodulation.
In the first stage of the BTP, I was able
to setup GNU Radio successfully on my system using the CVS version of the
source code of GNU Radio. Here is a write-up on the
same.
This semester, until now I have been able
to decode a monochrome frame, detecting even/odd field and extracting timing
information. As the jitter is generally small, I have used a novel correlation
method to determine the location of horizontal and vertical sync pulses and to
detect if the frame is even or odd.
The input signal is sampled at 8 M
Samples/sec and this explains the duration and spacing of the pulses above. The
above sequence is used for detecting the first horizontal pulse and after that
only a single pulse is used to make small error correction due to jitter
etc. The output of the correlator is something like
Similarly,
And the corresponding output is
After this we detect is the field is even or odd and then decode both the fields and
build the frame. A sample output frame is shown below
The above is hazy because of the lack of
a comb filter. I am currently implementing the comb filter. Currently I have
tested these algorithms in Matlab.
DATA FILE
CONTAINING NTSC SAMPLES
POINTER
TO NTSC DECODING DISCUSSION ON GNU RADIO LISTS
DOWNLOAD UNDERGRADUATE DISSERTATION ON NTSC PROCESSING
Please send me an email if you have any
problems trying out the above …..
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