PSK Modulation->Demodulation

Hello,

I know a similar question has been asked before on this mailing list but
I
didn’t quite get a solution out of it. I am generating a random byte
source, either ones or zeroes, modulating them with DBPSK and
immediately
demodulating them. The problem I am running into is that I get roughly 8
times the number of bytes out of the demodulation block than I am
inputting
into the modulation block. I believe its a packed vs. unpacked byte
problem
but every attempt at packing the output bytes yields an output that
doesn’t
match the input.

Attached are the GRC file, and the output file streams.

Does anyone have any suggestions? I appreciate all of your time,

Logan Washbourne
Electrical Engineering Graduate Student
(Electromagnetics)

On Tue, Jun 16, 2015 at 11:01 AM, Washbourne, Logan <
[email protected]> wrote:

Attached are the GRC file, and the output file streams.

Does anyone have any suggestions? I appreciate all of your time,

Logan Washbourne
Electrical Engineering Graduate Student
(Electromagnetics)

The problem is that you don’t know which bit to put where in the byte.
So
just packing the output bits into 8 bits per byte doesn’t necessarily
give
you the right information. Say you transmit a byte with bits [a b c d e
f g
h]. After the delays introduced by the transmit and receiver filter and
the
channel, when you pack the results, you could get something like [x x x
a b
c d e] [f g h 0 0 0 0 0], for some unknown number of x’s.

You need some logic that knows how to discover the start of your
information and get rid of those x’s. The framer blocks do this with
some
assumed formatting and expectations. Johnathan and I have been working
on a
better version of this, but we haven’t had a chance to finish it off.

Tom

So would a good solution to this be the packet encoder and packet
decoder
blocks? Since they utilize a preamble and access code? I tried to use
the
simple framer block in conjunction with the unpacked to packed byte
block
but was unsuccessful in getting a matching output, I will continue to
play
around with that configuration but for now do you think the packet
encoder
route would be a good solution?

Again, I really appreciate everyone’s willingness to help.

Logan Washbourne
Electrical Engineering Graduate Student
(Electromagnetics)

On Tue, Jun 16, 2015 at 12:05 PM, Washbourne, Logan <
[email protected]> wrote:

Electrical Engineering Graduate Student
(Electromagnetics)

Yep, those two blocks should handle this issue for you. It’s a
simplistic
approach to the problem, but it should work for just what you are
talking
about here.

Tom

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