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FPV range test in a park

March 7, 2015

Just a quick update on my FPV project: Today I went to a park and tested the video transmission over wifi. I contrast to the last test this environment was free of other wifi networks. So this fits more the usual FPV environment.

Test setup

I’ve mounted the standard 3dBi dipole at a height of 50cm for tx and used my double biquad on the rx side. Air data rate was 26mbit/s which allowed me to transfer 5mbit/s of video data at a retransmission rate of 3.

Result

The results were quite promising. The longest line of sight (with a some trees in between. Actually the perfect line of sight was not usable since my FPV system guard insisted on a bench πŸ˜‰ ) I’ve found in that park was 500m. At that distance there wasn’t a single packet drop. Thus the video stream was perfect. That is quite good for HD video transmission at 100mW (which means it’s perfectly legal to use). This is a satellite image of the setup:
length_test

The RSSI at 500m was at -70dBm. I’ve found that with the 3dBi dipole on the RX side at 300m I was still able to receive a more or less usable video. This was received with a RSSI of -82dBm. So I’m quite confident to reach 1km with the double biquad and the antenna more elevated (-> in the air on the quad).

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5 Comments
  1. Excellent work, I think your approach with the graceful degradation will be required in the field and none of the other projects in this space seem to be using it. I’m sure you’re already aware of it but there’s similar work going on http://www.swat-drones.de/index.php/hd-fpv/einleitung and http://openfpv.org/ although the latter has yet to release source code.

    • Thanks! πŸ™‚ Indeed, flying with normal wifi has some (serious) risks (disassociation, image stall due to missing acks, unpredictable high latency due to rate control algorithms , …). The downside of my approach is that you can’t use anymore the normal network stack. This makes app development like on the projects you linked to quite a pain. Actually I was able to port all my stuff to android using a custom kernel (for the wifi card driver) and chroot linux (for the wifibroadcast stuff). It was quite a pain and is still not 100% usable due to high latency… For now I’ll stay with linux.

      • Nearly all the projects are using gstreamer tx side to create the video stream but on the rx side theres more working going on to create rift integrations etc. I’m not that familiar with what they’re doing exactly (I need to read more) but I thought they’re using a tcp server to receive from the tx, I expected they could use a piped input rather than the tcp server to get the benefit of graceful degradation. I’m really interested in getting a hd stream into a set of rift goggles! πŸ™‚

  2. Henk permalink

    awesome project befinitiv, well done!
    Since the wifi module is in monitor mode, how can you measure the RSSI on the RX part?
    i have try some commands, but no signal strengt shown up.
    And is it possible to add /mix the RSSI to the monitor?

    thanks,

    Henk

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