Just did some latency tests using RUDP through wifi, 640×480@30fps, 2Mbps.
Both the laptop and the quadcopter are in the same room but they go through a router 3 walls away. Signal strengths are (as reported by iwconfig):
Link Quality=70/70 Signal level=-37 dBm
Link Quality=58/70 Signal level=-52 dBm
Ping reports these RTTs:
64 bytes from 192.168.1.110: icmp_seq=1 ttl=64 time=137 ms
64 bytes from 192.168.1.110: icmp_seq=2 ttl=64 time=160 ms
64 bytes from 192.168.1.110: icmp_seq=3 ttl=64 time=85.4 ms
64 bytes from 192.168.1.110: icmp_seq=4 ttl=64 time=108 ms
64 bytes from 192.168.1.110: icmp_seq=5 ttl=64 time=125 ms
64 bytes from 192.168.1.110: icmp_seq=6 ttl=64 time=149 ms
64 bytes from 192.168.1.110: icmp_seq=7 ttl=64 time=73.6 ms
64 bytes from 192.168.1.110: icmp_seq=9 ttl=64 time=119 ms
The quadcopter uses the more sensitive alfa card while the laptop has its own crappy RTL8723be card that has many issues under linux…
I happen to live in a building with a very noisy wifi situation so SNR is not good at all.
Average latency is around 100-160ms with random spikes of 3-400 ms every 10-20 or so seconds.
[Edit – just realized that both the brain and the GS are debug versions…]
To measure I pointed the raspicam at my phone’s stopwatch app and then took photos of the phone and the screen at the same time. Here are some of them: