Re: [Discuss-gnuradio] What do Packet Encoder and Packet Decoder do?

[Nguyễn Văn Lý]

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 Braun <address@hidden> wrote:

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 :-)

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

M
>
> 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
>
>
>
> On Wed, Jul 30, 2014 at 8:24 PM, Tom Rondeau <address@hidden

> <mailto:address@hidden>> wrote:
>
>     On Wed, Jul 30, 2014 at 4:44 AM, Nguyễn Văn Lý

>     <address@hidden <mailto:address@hidden>> 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
>         :-)
>         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
>
>
>
>
>

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