Video Latency

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):

Quad:
Link Quality=70/70  Signal level=-37 dBm

Laptop:
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:

20141128_212006

 

 

 

 

20141128_212010

 

 

 

 

 

20141128_212011

 

 

 

20141128_212007

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