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Re: [Discuss-gnuradio] Doubt in digital modulation chain

From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] Doubt in digital modulation chain
Date: Mon, 14 Jul 2014 09:06:15 -0400

On Mon, Jul 7, 2014 at 4:08 PM, Manu T S <address@hidden> wrote:
Dear All,

I am constructing the flow graph(screen capture, grc) attached.

I am expecting the data at the output of packed-to-unpacked block to be the same as the data at the output of differential decoder, except for some stray bits in the beginning. When I search for patterns in the transmit chain, in the receive chain, I don't get any match. This it the code(also attached) that I use to compare data in the transmit chain and the receive chain.
import scipy

template_len = 20

temp = scipy.fromfile(open("/tmp/diff-encode-out.bin"),
        dtype=scipy.uint8, count=1000)
template = temp[100:template_len+100]
print len(template)
match = False
rec = scipy.fromfile(open("/tmp/rec-map-out.bin"), dtype=scipy.uint8, count=100000)
for i in range(9950):
    if (template == rec[i:template_len+i]).all():
        print i

The program works for BPSK, but fails to find pattern in QPSK, DQPSK etc.
 Would anyone know what is going wrong in my flow-graph?

Thank you in advance.
Manu T S

Hi Manu,

This generally looks correct, but you'll want to see about that map block (or the constellation pre-diff coding) to translate the symbols->bits correctly. And if you think you've done it right, try again :)


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