Hi Shaun,
we are working in the satellite area of highly portable (Inmarsat like)
satcom and are offering services similar to your requirements using L-band
GEO satellites in Europe.
If you are looking for satellites for your application you will always (mid
term 5-10 yrs future) need a line-of-sight to the satellite, independent of
the orbit.
GEO systems are available serving your bandwidth requirements. However, if
you think of Ku/Ka-band systems, the antenna pointing is critical (in
particular with this speed). If you are looking for GEO L-, S-band systems
you could most get an autotracking antenna, which is fast enough for your
trains. However it is rather bulky (would assume around 1 m in diameter),
very much depending on the satellite you use. Additionally you would always
need a line-of-sight (difficult with tunnels). Second problem for L- and
S-band systems will be the prices for capacity on satellites (just as a
reference: Inmarsat takes around US$ 7 / min for a 64 kbit/s link)
LEO systems offering 1 Mbit/s are not on the market tody, but will evolve,
however I do not expect them before 2003 or later ?) and they will also
require a direct line-of-sight to the satellite (with the advantage, that
there is usually more than one in sight...), at least for high bandwidths.
The antennas should be smaller, the transmission delay is shorter and
spectrum costs will be lower than with L-band GEO systems. But you need some
hand-over mechanism and there is a significant doppler shift due to the
movement of the satellites...
Another alternative are as mentioned by others already mobile radio systems.
In particular 3rd Generation UMTS/IMT-2000/3GPP (cf www.3gpp.org )could be
interesting in this context.
Another idea which strikes me: it should be possible to use a DAB (Digital
Audio Broadcast, specified up to around 2 Mbit/s and high speed vehicles
[cars, trains]) like system for the forward (to the train) link and a
cellular phone link in return (e.g. GSM-GPRS or UMTS/IMT-2000).
All in all, it very much depends on your further requirements (costs, time
frame, space on the trains, possibilities to set up antennas along the
tracks, regulations etc.)
If you have further questions you are welcome to contact me directly.
Kind regards
Andreas
--- ------------------------------------ Dr.-Ing. Andreas Timm-Giel MediaMobil Communication GmbH Fahrenheitstr. 1 D - 28359 BREMEN GermanyPhone: +49 (0) 421 20 10 088 Fax: +49 (0) 421 22 39 418
email: [email protected] ------------------------------------
> -----Urspr�ngliche Nachricht----- > Von: [email protected] [mailto:[email protected]]Im > Auftrag von [email protected] > Gesendet am: Samstag, 30. September 2000 07:51 > An: [email protected] > Betreff: Moving Targets > > Hi, > > I'm doing a research project about providing Internet access to moving > targets on the eastern seabord of Australia. In this case, the moving > targets are trains. > > We really need to provide around 1MB or so downstream, maybe 56k or so > uplink. I've been doing a lot of searching but facts seem to be hard > to come by. > > By my reckoning something like a link to an LEO constellation is > needed to make this work because: > - GEO satellites can't easily provide this type of bandwidth > > - GEO satellites require reasonably large dishes and need to > fairly precisely targetted at the sat > - Line of sight is needed for GEO links to work > > Basically, I'm hoping that with LEO links a dish won't even be > required, some sort of antenna? Do any of the currently existing LEO > constellations provide this sort of service? Future ones? > > Am I completely barking up the wrong tree here? Is there a better way > of providing reasonably high speed internet access to moving vehicles > without cabling etc. > > Thanks in advance, > Shaun >
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