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.
Replies
I can see why you guys would want to use 5.8 GHz, but it's direct line of sight only. You fly behind a tree and the signal's gone. It's ok if you only fly on open fields above any obstacles, but what's the fun in that.
UAVs are used for lots of things other than 'fun'. The most common use of drones/uavs is probably pictures or filming for all sorts of applications, and fpv is a crucial part of that to frame the shot. The majority of these use cases will be direct line of sight - it's likely to be irresponsible or illegal to do otherwise.
2.4ghz is pretty busy these days and it's not generally a good idea to swamp the primary control method (standard RC) even if there are ways to mitigate this. I tried this method with the WN722Ns mounted as far away as possible from the rx (at the very end of large landing gear) and still got major interference as soon as I turned on my tx. 5ghz offers an easy way around this, and although it attenuates quicker, it has inherently higher bandwidth and at least in the UK can be used at up to 10-40 times the radiated power.
I was interested in using 5.8Ghz to avoid interference with the RC but I haven't seen that yet although my testing has been limited to putting the RC on the transmitter. I didn't see any jitter but perhaps the problems will only appear if the vehicle is near the edge of it's RC range.
I'm close to doing a flight test with the NAVIO+ board which can work as both the autopilot and the wifi video transmitter but I've noticed that the RPi camera seems to be interfering badly with the GPS. Hopefully some aluminum tape will resolve the problem.
As far as I know the WiFiBroadcast is still withing the 2.4ghz regulations. So If you maximize the distance between the video TX and R/C RX, and make sure you start the RC radio after the video stream so that it can see the 2.4ghz band used for video and select a different one, in theory it should be fine.
The RC RX will see an increased noise floor, it's sensitivity will decrease and so will range. The frequencies do not have to even overlap. Radios don't just output one frequency, there will be leakage to the surrounding frequencies also.
fair point. Maybe I need to try the WN722N for video and look at openLRSng again. I tried it a year ago but found it a bit too flaky. Currently using the taranis with X8R I have a really solid control link and also telemetry displayed on the taranis using the teensy/LUA script combo. How does 2.4GHz video work when other flyers around use their 2.4GHz transmitters?
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