Normal WiFi is not what you want to send video from your quadcopter back to the first-person-view (FPV) goggles strapped on your head, because it’s designed for 100% correct, two-way transmission of data between just two radios. Transmission of analog video signals, on the other hand, is lossy, one-way, and one-to-many, which is why the longer-range FPV flights all tend to use old-school analog video transmission.
When you’re near the edge of your radios’ range, you care much more about getting any image in a timely fashion than about getting the entire video sequence correctly after a delay. While WiFi is retransmitting packets and your video is buffering, your quadcopter is crashing, and you don’t need every video frame to be perfect in order to get an idea of how to save it. And finally, it’s just a lot easier to optimize both ends of a one-way transmission system than it is to build antennas that must receive and transmit symmetrically.
And that’s why [Befinitiv] wrote wifibroadcast: to give his WiFi FPV video system some of the virtues of analog broadcast.
In particular, two Raspberry Pis combined with WiFi radios that can be put into monitor mode enable him to custom tailor the packets that get sent, allowing his rig to sidestep WiFi’s acknowledgment scheme, add in a custom retransmission routine that helps limit lost packets, and even allow multiple receivers to listen in to the same signal so that a diversity reception scheme could be implemented.
If you’re flying WiFi video on planes or ‘copters, you should give wifibroadcast a look, and check out [Befinitiv]’s 3km WiFi video trial for inspiration.
Filed under: drone hacks, Network Hacks, Raspberry Pi, wireless hacks
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