# What do Packet Encoder and Packet Decoder do? **URL:** \ **Category:** GNU Radio\ **Created:** [July 30, 2014, 10:45am UTC](https://www.ruby-forum.com/t/what-do-packet-encoder-and-packet-decoder-do/231249 "2014-07-30T10:45:08Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\ **Post date:** [July 30, 2014, 10:45am UTC](https://www.ruby-forum.com/t/what-do-packet-encoder-and-packet-decoder-do/231249/1 "2014-07-30T10:45:08Z")
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 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 ---
**Author:** ![NguySSSn\_VSSn\_LS\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/9fc29f/32.png) [@NguySSSn\_VSSn\_LS\_S](https://www.ruby-forum.com/u/NguySSSn_VSSn_LS_S)\ **Post date:** [July 30, 2014, 3:27pm UTC](https://www.ruby-forum.com/t/what-do-packet-encoder-and-packet-decoder-do/231249/2 "2014-07-30T15:27:01Z")
On Wed, Jul 30, 2014 at 4:44 AM, Nguyễn Văn Lý [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) 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 ---
**Author:** ![NguySSSn\_VSSn\_LS\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/9fc29f/32.png) [@NguySSSn\_VSSn\_LS\_S](https://www.ruby-forum.com/u/NguySSSn_VSSn_LS_S)\ **Post date:** [July 30, 2014, 4:15pm UTC](https://www.ruby-forum.com/t/what-do-packet-encoder-and-packet-decoder-do/231249/3 "2014-07-30T16:15:12Z")
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 🙂 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 ---
**Author:** ![NguySSSn\_VSSn\_LS\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/9fc29f/32.png) [@NguySSSn\_VSSn\_LS\_S](https://www.ruby-forum.com/u/NguySSSn_VSSn_LS_S)\ **Post date:** [July 30, 2014, 4:20pm UTC](https://www.ruby-forum.com/t/what-do-packet-encoder-and-packet-decoder-do/231249/4 "2014-07-30T16:20:34Z")
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 ---
**Author:** ![NguySSSn\_VSSn\_LS\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/9fc29f/32.png) [@NguySSSn\_VSSn\_LS\_S](https://www.ruby-forum.com/u/NguySSSn_VSSn_LS_S)\ **Post date:** [July 31, 2014, 4:31am UTC](https://www.ruby-forum.com/t/what-do-packet-encoder-and-packet-decoder-do/231249/5 "2014-07-31T04:31:55Z")
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. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) ---
**Author:** ![NguySSSn\_VSSn\_LS\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/9fc29f/32.png) [@NguySSSn\_VSSn\_LS\_S](https://www.ruby-forum.com/u/NguySSSn_VSSn_LS_S)\ **Post date:** [July 31, 2014, 3:28pm UTC](https://www.ruby-forum.com/t/what-do-packet-encoder-and-packet-decoder-do/231249/6 "2014-07-31T15:28:28Z")
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