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3+km HD FPV system using commodity hardware

Posted by befinitiv on May 6, 2015 at 12:43pm

Hi

Over the last couple of months I have been working on a project that might be of interest to you: https://befinitiv.wordpress.com/wifibroadcast-analog-like-transmission-of-live-video-data/

Basically it is a digital transmission of video data that mimics the (advantageous) properties of an analog link. Although I use cheap WIFI dongles this is not one of the many "I took a raspberry and transmitted my video over WIFI"-projects.

The difference is that I use the cards in injection mode. This allows to send and receive arbitrary WIFI packets. What advantages does this give?

- No association: A receiver always receives data as long as he is in range

- Unidirectional data flow: Normal WIFI uses acknowledgement frames and thus requires a two-way communication channel. Using my project gives the possibility to have an asymmetrical link (->different antenna types for RX and TX)

- Error tolerant: Normal WIFI throws away erroneous frames although they could have contained usable data. My project uses every data it gets.

For FPV usage this means:

- No stalling image feeds as with the other WIFI FPV projects

- No risk of disassociation (which equals to blindness)

- Graceful degradation of camera image instead of stalling (or worse: disassociation) when you are getting out of range

The project is still beta but already usable. On the TX and RX side you can use any linux machine you like. I use on both sides Raspberrys which works just fine. I also ported the whole stack to Android. If I have bystanders I just give them my tablet for joining the FPV fun :)

Using this system I was able to archive a range of 3km without any antenna tracking stuff. At that distance there was still enough power for some more km. But my line of sight was limited to 3km...

In the end, what does it cost? Not much. You just need:

2x Raspberry A+

2x 8€ wifi dongles

1x Raspberry camera

1x Some kind of cheap display

Happy to hear your thoughts/rebuild reports :)

See you,

befinitiv.

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Tags: fpv, linux, raspberry, wifi, wifibroadcast
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Replies

        • Homeschool Jay > Homeschool Jay July 5, 2015 at 3:56am

          Half way there - just need a connector to hook it up. Also some of that RG402 semi flex cabling would be nice...3702791419?profile=original

          • malkauns > Homeschool Jay July 5, 2015 at 10:14am
            Noice!! You can put some epoxy glue around the top middle part of the antenna where the elements join to protect it from bending and breaking when you crash. I love making these. So much cheaper than buying them. :)
    • malkauns > Homeschool Jay July 4, 2015 at 2:10am

      Definitely need to get rid of that 2.4GHz that you are using for control.  The interference decreases the range significantly.

    • Martin > Homeschool Jay July 3, 2015 at 11:32pm

      You should definitely increase the intra frame frequency (-g). Try 10 or below. I found 3 to be a good value - any artifacts are quickly removed. Also, try setting the intra refresh type (-if) parameter to cyclic or both.

      raspivid ... -g 3 -if both

      • malkauns > Martin July 5, 2015 at 2:37pm

        In my experience a lower intra-frame frequency is better when flying at the edge of reception as although the image is garbled I can still get a sense of what I'm seeing.  A higher intra-frame frequency seems to cut out the whole picture more and it's more difficult to surmise what you're actually seeing although the picture may appear "cleaner".

      • Homeschool Jay > Martin July 3, 2015 at 11:51pm

        Thanks Martin, I've changed the settings. I'll let you know how it goes. I quickly benchtested the video and when I first started it up it was lagging by a few seconds but it soon settles to around ~200ms after 30secs or so...

        • Homeschool Jay > Homeschool Jay July 5, 2015 at 4:00am
          • I changed to -g 10 and ended up with a lot less artifacts happening
          • With -g 10 a big delay built up. Up to about 5 secs after 5mins.
          • I tested without the quad's TX running and got a lot better range and quality so UHF will be a great addition
          • I also made a bi quad antenna but waiting on a connector (see below)
          • I will look too making a patch/directional antenna for the receiver
  • malkauns July 1, 2015 at 4:56pm

    Been getting decent results using 2 CSL's and 1 TPLink for rx and 1 Alfa for tx.  Still running on 2.4GHz for now.  I was getting a lot of break ups before in the video but I made a couple of 2.4GHz omni bi-quad antennas and things improved a lot!  Thought I'd post a video:

    https://www.youtube.com/watch?v=AqZyPGgBl8I

    • Developer
      Randy > malkauns July 2, 2015 at 1:24am

      Great!  nice to see the video!  I've got a bunch of new antennas as well that I hope to try in the near-ish future.

  • Homeschool Jay June 28, 2015 at 3:08pm

    Hi all, I've got the link working between 2 Pi's but it's not overly practical as I have a laptop with the latest Ubuntu and I don't have a screen to use in the field with the Pi.

    I've having trouble getting the streamgoing with gstreamer:

    jem@jem-N51Vf:~$ sudo ./rx -b 8 wlan2 | gst-launch-1.0 -v fdsrc ! h264parse ! avdec_h264 !  xvimagesink sync=false
    sudo: ./rx: command not found
    Setting pipeline to PAUSED ...
    Pipeline is PREROLLING ...
    ERROR: from element /GstPipeline:pipeline0/GstH264Parse:h264parse0: No valid frames found before end of stream
    Additional debug info:
    gstbaseparse.c(1155): gst_base_parse_sink_event_default (): /GstPipeline:pipeline0/GstH264Parse:h264parse0
    ERROR: pipeline doesn't want to preroll.
    Setting pipeline to NULL ...
    Freeing pipeline ...

    Any ideas? Cheers

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