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
Shouldn't be a big problem cause the transmitters use very low power and they are relatively far away from your receiver. Using a directional antenna and maybe even circularly polarized antennas should improve the signal to noise ration even further.
I still haven't managed to do an outside range test due to a busy work week and bad weather. Indoors I get significantly less range compared to my analog immersionrc transmitters. TX in same place, walking down two floors through with signal having to pass two concrete ceilings. I just cracked the plastic cover off the rubber duckies. Both antennas have 26mm long whips, so they are 2.4GHz antennas. Switching the antenna to a 5.8GHz with circular polarisation should help increase range. I also find that the video quality using wifibroadcast is worse compared to gstreamer on standard wifi using the same CSL dongles. That might just be down to these dongles being crap. How can I check the injection rate? Is this the console output "interface rate" of the wifibroadcast tx? It is showing values between 550.xxx and 750.xxx I've just seen befinitiv's screenshot here showing his lossrate displayed on the rx terminal around 0.001xxx The CSL dongles show lossrates of around 0.3 to 0.8 so significantly worse!! Might be time now to ditch those and try the WN722N?
I managed to replicate the broad cast wifi video two using the images provided by Tommy Larsen.
2x RPI (not RPI2s) + 1 x RPI camera
2x Alfa AWUS036NHA (2.4Ghz)
1x Black Pearl FPV Monitor(which accepts hdmi input from receiving RPi)
I measured the latency from "lense to screen" as 0.23 seconds (3:07.101 - 3:06.872 = 0.229 seconds) which is fine for my purposes. I'll do a ground range test tomorrow and probably write an ardupilot wiki page with a setup for beginners and then include links to befinitiv's blog).
Small update, I found Tommy Larsen's images also worked on an RPI2 (at least when used as a receiver).
The Latency with the RPI2 as the receiver (TX was still an RPi) was strangely slightly worse at 0.28 seconds. Perhaps there was an environmental issue.
I performed a ground test today and I could walk as far as 160m before losing contact. I think I could have gone further if I could have maintained a clear line of sight to the transmitter - there are a lot of trees in my area. I then remembered a land mark nearby and used the MP to measure the distance.
I did the test with my regular gear: 2 x RPI, 2xAlfa AWUS051NH (2.4Ghz), BlackPearl FPV monitor with HDMI input. I left the transmitter on my porch capturing and transmitting the estopwatch.net output and then I carried around the receiver gear walking as far as I could while trying to maintain a line-of-sight to the TX. I noticed that I'd lose the signal if a building or crop of trees blocked the line back to the TX.
It's probably too much detail but here's a picture of the setup.
Please let me know if you get 5GHz working on that card.
No such thing as too much detail Randy! :P
My images is made on Rpi 2.
I get a latency close to zero on my setup... Much better than my 4g setup using IP measured to 110ms. I will measure my exact numbers and see what i get, but i Guess around 40ms.
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