Re: [Paparazzi-devel] Wireless communications

[Kitts]

On Saturday 04 Jun 2005 11:17 pm IST, Filipe Varela wrote:
> I'm developing a project for long range wireless communications for
> both telemetry+video downlink and simmultaneous control uplink.
>
> The idea is not to have an a/v transmitter + r/f receiver on the
> platform and r/f transmitter + a/v receiver on the ground but to
> merge these two "streams" together on a single long-range radio link.

That is interesting. I have always stayed away from RF designing as it 
can get very tricky. When you are done, i would be very interested to 
know and if its OK with you, i would like your support in building one 
for myself. :-)

> Now, has anyone experimented with radio-modems? My only doubt is
> whether it is feasable to multiplex a telemetry packet plus a video
> packet and transmit it to the ground and at the same time demux a
> control packet from the ground and still maintain real-time video.
>
> If course that multiplexing control, telemetry and video on a single
> channel requires transferring the pwm generation from an r/f
> "joystick" to the computer which is an idea i like a lot.

I have done something like this using standard radio modems. The problem 
with Video is the high bit rate. Most video transmitters use analog 
transmitters but multiplexing would require to shift to Digital 
transmission. This would require high signal processing not easy to do 
in most of our applications as most modems are in the range of 9600 bps 
not good enough for video.

> BTW, by long range i mean 1Km to 10Km. Any more than that is not of
> any interest and should be addressed with propper expensive
> transmitters.

Wow!

> To the paparazzi developer: what's your tried and tested max range
> for both telemetry/video transmission (air-to-ground) and control
> transmission (ground-to-air)?

I am not a paparazzi developer but have done similar activity. I have 
used commercial radio modems to achieve a range of about 5 Km. I do 
not, however, transmit video on the same link for the reason i 
mentioned above.

-- 
Cheers!
Kitts