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To: JGoren who wrote (30096)5/15/1999 12:45:00 PM
From: engineer  Read Replies (4) of 152472
 
Purely from a technology point of view there are some reservations about how good I* will be versus G* over the long term. (3-5 years out...)

1. I* has alot of network functions in the satellites themselves. If there is a system upgrade or a system shortcoming, this would be very hard to upgrade and fix if it were not already anticipated before launch. G* has all it's network smarts on the ground, so if there were an oversight in systems design, the groundstation software and hardware could be upgraded as technology gets better.

I'll give an example of technology that changed while the sat was in flight. The original explorer probe was launched about 1980 with a simple processor and a single Viterbi encoder to send the data back. While the sat was on it's way to Jupiter and Pluto, Dr. Viterbi and others came up wiht a much more powerful scheme to gain back alot of dBs. They encoded in the processor over many months a new Reed-Solomon coder around the Viterbi Encoder in hardware, and came up with about 5 dB more signal. this allowed them to send data almost 3 times faster, so they could now send alot more pictures while flying by Jupiter. They since coded it again and gained some more. Technology had advanced while the bird was flying. So the analogy is that if the G* guys find a way to enhance the system (ala IS-95C...), then they can update it whereas the I* guys may not have that ability to do that.

2. The basic cost of the Sat is about 5 to 1. Long term maintenence costs will be higher just from the cost of replacing LEOs on an ongoing basis.

3. the reliability curves go as the compound failure curves of the components. this means that if one component has a 99.99% reliability rate and you use 1000 of them, then the failure is multiplied together and is more like 90% (99.99 to the 1000 power). Now mutiply that by the 100's of parts used in the computer they are flying versus the simpler RF only bird in the G* and the reliability times are like 1000 to 1. Since I do not know the specifics, I cannot compute it exactly, but the failures are mutiplicative.

4. The I* phone is about twice the size of the G* phone. Given that Mot has taken almost 5 years to produce a working CDMA IS-95 phone, how long will they take for the next gen I* phone if they do not have the resources to develop it? The G* phone is about 1 year old already.

Just a few thoughts....
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