DPSK Modulator and Demodulator

Hi,

I am having trouble the the DBPSK mod and demod blocks. My flow graph
is:
file source -> DBPSKmod -> DBPSKdemod -> file sink

The file source is a 2 byte text file set to not repeat
The default parameters were used for the DBPSKmod and demod blocks
(including 2 Samples/Symbol)
When I run the graph the output text file becomes 13 bytes long and they
are almost all zeros. I am not sure how it gets to be that length.

I tried connecting the ouput of the DBPSKmod directly to the file sink
and the file size was 256 bytes. This matched my expectations based on:
2bytes input file * 8bits/byte * 1Symbol/bit  2 complex
samples/Symbol
8bytes /complex sample = 256 byte output file.

If anyone knows why the output file of the whole graph would be 13
bytes or if I am missing something please let me know.

Thanks,
Dave

You can’t connect the file source directly to the Modulator. If you are
Using
DBPSK, the modulator will be looking for 1 bit at a time, or in this
case a
byte with only 1 significant bit.

Use

File Source > packed to unpacked [1 bit per chunk] MSB first > DBPSK
Modulator

Marcin

David B.-4 wrote:

are almost all zeros. I am not sure how it gets to be that length.
Dave


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My mistake, i didn’t realise you were using the available DBPSK block.
The
Packed to Unpacked block is already part of this Modulator, so disregard
my
comment.

Marcin

marcin_w wrote:

Marcin

The default parameters were used for the DBPSKmod and demod blocks
or if I am missing something please let me know.


View this message in context:
http://old.nabble.com/DPSK-Modulator-and-Demodulator-tp28319509p28323370.html
Sent from the GnuRadio mailing list archive at Nabble.com.

Hi,

I am having trouble the the DBPSK mod and demod blocks. My flow graph is:
file source -> DBPSKmod -> DBPSKdemod -> file sink

If anyone knows why the output file of the whole graph would be 13 bytes
or if I am missing something please let me know.

Thanks,
Dave
On Wed, Apr 21, 2010 at 9:46 PM, marcin_w [email protected]
wrote:

My mistake, i didn’t realise you were using the available DBPSK block. The
Packed to Unpacked block is already part of this Modulator, so disregard my
comment.

Does the bpsk block you’re using have some form of timing correction
in it? More than likely the data is being run through some sort of
filter (either explicitly or effectively) and the zeros at the
beginning are a warm up from the padding.

If you’d like the output to be ‘nice’ from a mathematical point of
view you will have to deconstruct the mod/demod blocks a little bit
and remove the timing correction stages and make sure that your
simulated channel does not introduce any timing corrections.

Jason

Â


From: Jason U. [email protected]
To: [email protected]; [email protected]
Sent: Thu, April 22, 2010 7:51:41 AM
Subject: Re: [Discuss-gnuradio] DPSK Modulator and Demodulator

Thanks Jason. I have not delved into the code of the dbpsk demodulator
GRC block yet so I am unsure. I was hoping someone with experience using
this GRC block could answer quicker.

I believe the block has a root raised cosine filter in it so it would
make sense that it would have zeros to start but I am not sure why I get
13 bytes of output data back from 2 bytes of input data.

Thanks,
Dave

Â

Hi,

I am having trouble the the DBPSK mod and demod blocks. My flow graph is:
file source -> DBPSKmod -> DBPSKdemod -> file sink

If anyone knows why the output file of the whole graph would be 13 bytes
or if I am missing something please let me know.

Thanks,
Dave
On Wed, Apr 21, 2010 at 9:46 PM, marcin_w [email protected]
wrote:

My mistake, i didn’t realise you were using the available DBPSK block. The
Packed to Unpacked block is already part of this Modulator, so disregard my
comment.

Does the bpsk block you’re using have some form of timing correction
in it? More than likely the data is being run through some sort of
filter (either explicitly or effectively) and the zeros at the
beginning are a warm up from the padding.

If you’d like the output to be ‘nice’ from a mathematical point of
view you will have to deconstruct the mod/demod blocks a little bit
and remove the timing correction stages and make sure that your
simulated channel does not introduce any timing corrections.

Jason

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