G*/I* technical differences (via LOR yahoo thread)
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Tahoetech, Crisis, et al
by: lorlurker (35+/M/Palo Alto, CA)
13560 of 13561
Well, you guys asked for it by encouraging me, so here is some more rambling on the differences between G*
and I*. First, look at the difference in orbits and what that implies. G* flies at a higher orbit, therefore "sees"
more of the Earth at any given time than I*. Implication: needs fewer satellites, therefore less cost. Second,
G* flies at a 52 degrees inclination, while I* flies at about 90 degrees. Implication: I* spends a lot more time
over water and unpopulated regions, generating a lot less revenue.
Next, I* has at many times only one satellite in view of the user; G* usually has 3, but the range is 2-7 in the
heavily populated regions. Implication: I* has a fade-out problem when the user is behind a tree, G*
gateways combine the different signals from different sats and can recover from fading very nicely.
Next, TDMA vs. CDMA. Hey, I think TDMA is great, but it has real limitations, like needing to know the
time delay. When you are talking from a fixed ground station to a GEO bird, the time delay is known. When
you are I*, and your birds are at slightly different altitudes, and your users are moving and are in sight at
various points in view, well, you have to compensate by allocating slop to each signal. Implication: reduced
capacity. I think I* can only handle 2400 bps, while G* is 9600. I* cannot even send data packets, as I
understand it, but only voice. Another implication: I* demods and remods, making the flight electronics much
more complicated. More complicated = less reliable.
Handsets? I* handset is probably great if you are not getting to the gym regularly and need another form of
working out. G*, while not the size of a cell phone, is reasonable, and reasonably priced. (Maybe I* should
market their phones as a health aid <g>).
Finally, G* handsets have been and are being tested- so far, so good. Since the first launch the boys at
Qcomm have been playing with the sets, and the results are quite a bit better than the press on I*.
I know, a bit of a ramble. In my defense, you did encourage me...
Posted: 04/16/99, 2:11PM EDT as a reply to: Msg 13557 by tahoetech
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