Telemetry and data transmision Q

[beepbeep]

Dude, if ground station has 7TB server, it kinda means they expect rather high data rate. While hi-speed microwave data links can be arranged in stationary fashion, doing so for moving target while keeping high bandwidth and reasonable BER (bit error rate) gets *really* expensive. As your transmission protocol would need to cater for dropouts, multipath/doppler errors etc. you end up with needing double the bandwidth as half of data being sent would be error correction, parity etc.

So unless you are transferring less than 500kB/sec or have a budget of a small county, I recommend packning a 4-bay NAS + power converter on a plane. 10TB can be nowadays kept in a small 4-bay NAS, running four 4TB discs in RAID-5 and happily swallowing 100MB/sec while using 100W of power.

Thus, unless they are doing something really funky on ground and need real-time telemetry there is no point transmitting data. You could theoretically fly 1PB worth of storage even on a Cessna.

COTS, 8TB:
ReadyNAS Business Desktop Storage - RN31442E | ReadyNAS | Storage | Business | NETGEAR

[beepbeep]

P.S. This is basically "office" stuff and needs to stay pressurized and reasonably vibration free. If you plan to keep it unpressurized and/or exposed to vibration you need a Flash array storage. It means 10X the cost (but will still be doable, compared to hi speed 200 mile data link which is rather unpractical in my book)

[Seahawk]

Originally Posted by beepbeep

...compared to hi speed 200 mile data link which is rather unpractical in my book)

Yup. I was going to share that with Cash but I like your style.

[GH85Carrera]

Originally Posted by beepbeep

P.S. This is basically "office" stuff and needs to stay pressurized and reasonably vibration free. If you plan to keep it unpressurized and/or exposed to vibration you need a Flash array storage. It means 10X the cost (but will still be doable, compared to hi speed 200 mile data link which is rather unpractical in my book)

Yep, all of our data storage hard drives used in the airplane are solid state. A spinning drive quits at a surprisingly low altitude.

[cashflyer]

beepBeep and others - I am appreciating all of this input.

Glen... This client is one that I am working with on some other projects, so I really don't want to just dismiss their request. What I prefer to do is to work with them and guide them toward a better solution, and I feel you guys are certainly giving me some good feedback with which to move forward with this client.

There is another aspect of this project that it sounds like you guys would have input on, and this is a (hopefully) more realistic endeavor.

Could you deploy a truck or van sized vehicle (like a U4000) as a relay station? The idea is to create a chain from the aviation downlink, across areas with zero infrastructure, back to a city or to a permanent ground station. Or is there any reason a mobile station would need to be as large as a semi trailer with a containerized office. My concerns are power requirements (generators) equipment footprint, and need for air conditioning for both personnel and equipment. Would a 50 mile range be realistic for a mobile unit? 100 miles?



I'm sorry that I cannot post every bit of the information that I do have on this Geological Survey project but I have signed a confidentiality agreement with the client, and some of the stuff I have should not be posted due to those sensitivities.


As a related side story, once upon a time when I was in the Army, we flew "mapping" and "training" missions. Strangely (or not so much) every one of our missions were parallel to a another countries border, and all of our sensors and cameras were aimed at the border. (We must have needed a LOT of maps of that area.)

At that time, all of our data was recorded on mag tape, and all of our video and photos were on film. We could drop film canisters to waiting ground units, but other than for training purposes, we never did that. We would just hold them until we landed and the ground crew would retrieve them from the plane. In practice, the only time we would have made a canister drop was if we were going to be flying back and forth into an area where we may have been shot down. The drop was to assure that critical data was not lost with the plane.

I hope this helps clarify a few things.

[beepbeep]

Data security is really not a issue, even if you carry storage on board, as most NAS/SAN storage racks offer strong on-the-fly data encryption. So even if plane crashes, nobody would be able to restore the data without correct key.

But if you really insist on data link through radio, your best bet is probably ad-hoc LTE (=4G) network. It's made with moving radio datagram transmission in mind and has all the stuff to cope with it. (But due to time+frequency division multiplex scheme, I believe there is a hard limit of 100 km regardless of signal power due to timing issues.)

Basically, you would need a portable LTE cellphone station(s) for each cell within 100km of the plane. Such stations usually need fibre backhaul in-between but I suppose something could be cobbled together with microwave links.

[id10t]

Originally Posted by beepbeep

Dude, if ground station has 7TB server, it kinda means they expect rather high data rate. While hi-speed microwave data links can be arranged in stationary fashion, doing so for moving target while keeping high bandwidth and reasonable BER (bit error rate) gets *really* expensive. As your transmission protocol would need to cater for dropouts, multipath/doppler errors etc. you end up with needing double the bandwidth as half of data being sent would be error correction, parity etc.

So unless you are transferring less than 500kB/sec or have a budget of a small county, I recommend packning a 4-bay NAS + power converter on a plane. 10TB can be nowadays kept in a small 4-bay NAS, running four 4TB discs in RAID-5 and happily swallowing 100MB/sec while using 100W of power.

Thus, unless they are doing something really funky on ground and need real-time telemetry there is no point transmitting data. You could theoretically fly 1PB worth of storage even on a Cessna

Never underestimate the bandwidth of a Cessna full of RAID enclosures ....

[beepbeep]

Originally Posted by id10t

Never underestimate the bandwidth of a Cessna full of RAID enclosures ....

Haha...I was just to post the same thing. NEver underestimate the bandwidth of 40-ton semi filled with LTO-6 tapes

[GH85Carrera]

With our 9x9 film camera we can fly 600 pictures at high altitude or many thousands at low altitude before we have to land for fuel. Each frame of film is 1.1 gig when scanned. The digital camera has a 2 TB solid state RAID. That will outlast the fuel as well unless it is low altitude.

The logistics is totally different. During a big mapping project we can just keep adding another roll of film no problem. With digital after a day of shooting it takes a while to copy all the data off and you have to do that twice for redundancy. Then erase the data cartridge before the next flight or get a different very expensive data cartridge.

Try to copy one TB of data with error checking from one drive system to another. It just takes a while. You have to do it twice to have a redundant copy in case of a bad hard drive or copy error.