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
That is a shame. The AWUS036H is superior in all respects though, with the exception of "N" support. I'd love to hear if anyone has tried that unit. It really is the best wifi unit on the market, so it would be a shame not to support it.
Do I need to manually patch the kernel ? Or has this been done already?
"Optinally, you can also patch the kernel driver to set the output power of the card to a fixed level as describedhere. "
I am up to the part of "git clone https://github.com/raspberrypi/linux.git" but its on 1% and has taken 10 mins already!
Paul,
It's not necessary but it helps if you want to get the TX to output at it's maximum power. I've never actually successfully completed that step. I hope the first person that does will put the resulting binary somewhere so the rest of us can just grab it and use it.
Interesting, that site has the 5510 at $193:
http://embeddedsoftwarestore.com/store/em/EMController/Gateworks-Co...
Still pretty steep though..
Rpi encoder will have more options as it has direct access to the camera so can control exposure, resolution etc.
Maybe it's better to look for a UVC/rtsp camera after all, and hook it up to a raspberry.
BTW, I have mentioned this before. The sensors for the RPi camera are not produced anymore. So there should be support for a hopefully higher megapixel sensor coming soon.
UVC/USB will definitely add some unwanted latency.
Sorry if this was mentioned already, but has anyone thought of using a high quality/power wifi like the Alfa AWUS036H?
AFAIK the AWUS036H is still the king of all wifi models. Highest power, best sensitivity amongst all wifi units with proper promiscuous/injection support.
I've bought 3-4 of them over the years, and they're definitely FAR superior to most units out there. I've had a couple other higher end models come close, but they're definitely the best I've used.
The Realtek Alfa cards are mentioned here:
https://befinitiv.wordpress.com/2015/02/22/finding-the-right-wifi-d...
Yes, here is more info on that topic:
http://yo3iiu.ro/blog/
http://www.qsl.net/kb9mwr/projects/wireless/modify.html
2487Mhz would possibly be a nice frequency. Still inside the ISM band, but 25Mhz away from standard wifi channels 1-11.
Isn't that just for Atheros chipsets? Was hoping for something for Realtek chipsets in the Alfas on 2.3GHz.
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