What do Packet Encoder and Packet Decoder do?

GNU Radio
1

Hi all,

Can anyone tell me what do Packet Encoder and Packet Decoder blocks
do?
and it would be great if you can give me some example :slight_smile:
Thanks in advance

Van-Ly

Van-Ly Nguyen,
Signals and Systems of Laboratory - SSL
Faculty of Electronics and Telecommunications - FET
University of Engineering and Technology - UET
Vietnam National University, Hanoi - VNU

Tel: (+84) 978 819 406

2

On Wed, Jul 30, 2014 at 4:44 AM, Nguyễn Văn Lý
[email protected]
wrote:

Hi all,

Can anyone tell me what do Packet Encoder and Packet Decoder blocks
do? and it would be great if you can give me some example :slight_smile:
Thanks in advance

Van-Ly

These are very simple example blocks to show you how to packetize data.
Packet bytes go in, they get wrapped into a packet of a given payload
length with a header, access code, and preamble. The header is just a 2x
repetition of the payload length (16 bits for each field). Leaving the
preamble and access code blank just chooses the defaults.

The decoder just looks for the access code with the number of available
bits wrong. When it’s found, it reads the header to get the payload
length,
extracts the payload, and outputs the payload.

Hope this helps.

Tom

3

Thank you Tom,

I found a note in documentation of the *Packet Encoder *block where it
declares that the Packet Encoder is for use with the gnuradio
modulator
blocks: GMSK, DPSK, QAM. I don’t know why only these modulator blocks
are
supported, but not some popular things like BPSK or QPSK. Another thing
is
that my task requires the use of OFDM.

Suppose now I have a simple flow graph as below:
File Source -------> Packet Encoder -------> Packet Decoder --------->
File
Sink
I wonder what types of file can be loaded and processed properly in the
File
Source block (text, image, or video …), and the same question for the
File
Sink block :slight_smile:

Thank you so much
Van-Ly

Van-Ly Nguyen,
Signals and Systems of Laboratory - SSL
Faculty of Electronics and Telecommunications - FET
University of Engineering and Technology - UET
Vietnam National University, Hanoi - VNU

Tel: (+84) 978 819 406

4

On 07/30/2014 04:14 PM, Nguyễn Văn Lý wrote:

Thank you Tom,

I found a note in documentation of the Packet Encoder block where it
declares that the Packet Encoder is for use with the gnuradio
modulator blocks: GMSK, DPSK, QAM. I don’t know why only these modulator
blocks are supported, but not some popular things like BPSK or QPSK.
Another thing is that my task requires the use of OFDM.

These should also work (they are basically subsets of QAM), but you
have to make sure the absolute phase is correct before going into the
packet decoder.

Suppose now I have a simple flow graph as below:
File Source -------> Packet Encoder -------> Packet Decoder --------->
File Sink
I wonder what types of file can be loaded and processed properly in the
File Source block (text, image, or video …), and the same question
for the File Sink block :slight_smile:

Any file. The packet blocks really don’t care about the contents.

M

5

Hi Martin,

Consider the following flow graph.
File Source ------->Throttle --------> Packet Encoder -------> Packet
Decoder --------->File Sink 2
\

---------------> File Sink 1
If the File Source loads a small-size image (around 50 kB), then the
Packet
Decoder works properly and File Sink 2 can open the image. However if
the
File Source load a bigger image or video (9 MB, for example), then the
File
Sink 2 achieve only more than 1 MB, and it can only display a part of
the
image/video. This surprised me.

Then I added a File Sink right after the Packet Encoder (it’s called
File
Sink 1) to see what happened after the Packet Encoder. If I let the
Sample
Rate = 32k, then the File Sink 1 receives more than 9 MB, but the File
Sink
2 still receive more than 1 MB. If I let the Sample Rate be faster, 1M
or
4M, then both the File Sink 1 and File Sink 2 only get more than 1MB.
I wonder if something related to CPU got out of ability with high Sample
Rate or Packet Encoder - Packet Decoder

Best Regards,
V-L

Van-Ly Nguyen,
Signals and Systems of Laboratory - SSL
Faculty of Electronics and Telecommunications - FET
University of Engineering and Technology - UET
Vietnam National University, Hanoi - VNU

Tel: (+84) 978 819 406

On Wed, Jul 30, 2014 at 9:19 PM, Martin B. [email protected]

6

Hm, interesting. You know, in this specific configuration, you don’t
need a throttle. What happens if you leave it out? It shouldn’t change
anything, but then, it should work in any case.

Also, you are letting the fg terminate itself, right?

M