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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

        • Nicolas > Paul Hammond July 14, 2015 at 6:05am

          Two way communication also wouldn't be very good, because it would cause collisions (=video dropouts) when the ground-station sends something at the same moment with the air-station. In this regard wifi works similarly to the "plain old ethernet without switches" (with coax cables or hubs).

          But I think it should be possible to set up two wifibroadcasts with two wifi cards on different wifi channels, one that sends stuff from the air-station to the ground-station and one that sends stuff from the ground-station to the air-station.

          If one would want to use only one wificard/channel for bi-directional communication, one would have to implement some kind of time division multiplexing, but that's far from being trivial.

    • malkauns > Paul Hammond July 13, 2015 at 3:12pm

      Should be simple if you follow the latest post from Befinitiv: https://befinitiv.wordpress.com/2015/07/06/telemetry-osd-for-wifibr...

      Telemetry OSD for wifibroadcast
      This post shows how to add an overlay with telemetry information onto a video stream — Since the last flyaway of my quad having a telemetry link that…
  • malkauns July 9, 2015 at 10:47pm

    Had some fun in the park today.  Camera wobble gone.  The lense I'm using doesn't do justice to the cause though and creates an unwanted blur.  Overall, I was very pleased with how well things improved with CP antennas.  Antennas are everything!

    www.youtube.com/watch?v=vXa4HRqKj1M

    :)

  • malkauns July 6, 2015 at 12:26am

    My latest concoction.  2 TX radios!  Wish me luck!! :)

    FSuZihM.jpg

    aOC0YIT.jpg

    • Cameron Baker > malkauns July 6, 2015 at 4:26am

      To our non euro counterparts, has anyone successfully ordered the CSL 300mbit wifi units? I've found some but they're 20 euro a pop and freight is 40 euros, so I'd be looking at 80 euros total just for the RX side of things. 

  • Homeschool Jay July 3, 2015 at 10:58pm

    Did first test flight today. Worked pretty well when very close to the ground and within 15m's or so.

    The setup:

    Alien H4 Pixhawk with Frsky 2.4Ghz TX/RX

    Video TX WN722 w standard omni

    Video RX WN722 w standard omni

    Wifibroadcast setup Ch7

    Resolution: 1280x720

    FPS=48

    Bitrate=3,000,000

    Keyframerate=120

    Retransblocksize=8

    I was getting a lot of this happening when I went further than 15m's away:

    3702040843?profile=original

    I moved the antenna so it was pointing below the quad and that improved it slightly.

    What do the experts think? I'm thinking the antenna's need to be changed over to something different and do you think the TX/RX running at 2.4GHz will be adding to this. I've ordered a UHF Rx/Tx but haven't got it yet...

    Thoughts/comments welcome..

    Cheers

    • malkauns > Homeschool Jay July 4, 2015 at 10:47am

      w9m6FfT.jpgThis is the antenna i'm using for the TX and RX side (on the left):

      It's a 2.4GHz biquad antenna.  Getting good results with it.  I'll be making a couple Circular Polarized versions next.

      DIY instructions here:

      youtube.com/watch?v=4t6OliwhJ5g

      • Homeschool Jay > malkauns July 4, 2015 at 8:19pm

        Cheers Maulkans - I'll fire up the soldering iron and make some! 

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