WiFi For telemetery

[vector_vortex]

Just thinking very preliminary about my project for final year (next year). One project is a wireless telemetry link for a UAV. My initial thoughts were WiFi due it's spread spectrum, cheap and relatively robust nature, oh and you don't need a licence to operate it!
Has anyone had experience with long-ish range telemetry links, if so what are the problems faced with these sorts of systems. The UAV has GPS onboard so I though you could use a directional antenna to track the base for better range or use a form of mesh network with relay points. What sort of range should I expect for 1Mbps transmission rate? Any other problems I can expect to come across?

Thanks

Joel

Melbourne
Victoria
Australia

[treehog]

WiFi in the outback stikvilles or empty Australia should work OK except it rains as most WiFi is 2.4ghz and that signal is useless if it rains

Also close to city like Melbourne or similar the abilty to be lose the signal will be much higher as lots of competring WiFi systems

If there is too much WiFi in a place non of the WiFi works such as in office with 100 computer 100 mobiles and umpteen blue tooth items most nothing works as signal collision ratio get saturated and shut it all down

Wi fi is not very robust for real time mission critical must have have connection and is more suited to computers surfing on the net where if you got to twidle your thumbs waiting for page to download its a non event compared to emminent termination of UAV in a tail spin which needs imeadiate updates :eek:

Radio units that similar to WiFi such as spectrum have two 2.4ghz signals going to model craft and two recievers to rectify these issues but again probably is useless if it rains or if it is in New York times square

For Wifi it probably better to think in terms of total UAV and transmit non time critical new mission updates with WiFi or use RC unit and WiFi back up for longer ranges

WiFi ranges tend to operate on the signal get through over long distance some few kilometres but packet loss rates can be high often 95 to 98% so response seems to be there but in fact your operating on the ragged edge and outback wont show this so much but as soon as you try the same thing near a small wifi enabled town you will probaly get shot down

Sooner you than me

Ralf

[Bg~]

Our project uses a 802.11b link for communication to the onboard computer. I would not use a 802.11 link for flight critical controls. We have a separate 900Mhz, 1watt radio modem for manual flight control backup. The 802.11 link works fine for us within visual range. I think it would suffice for a telemetry downlink, however, latency can be a problem. One thing to consider is the power output of 802.11 wireless cards. The one we use is a 200mW card (Senao NL-2511CD PLUS EXT2), and there is a 300mW card out there (Zcom Zcomax XI-325HP+). The senao card seems highly regarded on the internet, and it has performed well for us in flight.

One more thing...if you get a card with more than one external antenna hookups, and plan to only use a single antenna, you need to find out which antenna port is the one intended for single use. It does make a difference. We learned this the hard way with our Senao card (it doesn't come with much documentation).

[vector_vortex]

Interesting, thanks for your comments. It is after all a telemetry system and therefore line of sight, lots of lost packets etc. can be managed with software. Bg~ I am interested in the Senao cards and have been trying to acquire some of them. Which is the correct antenna port for single antenna installation.
Thanks
Joel