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On Thu, 24 Aug 2000 03:45:11 GMT, Jack wrote:

>George Adams wrote:
>
>> Why should GPS units require the user to update a database at all?
>> Let the unit update itself....
>
>Of course, why not?

The immediate issue that comes to mind is bandwidth.

While I agree that having the constellation satellites update the
aviation database automatically in the background while you are using
them for navigation is logical, I fear that there is inadequate
data-channel bandwidth to provide megabytes to multiple receivers
simultaneously. But, the concept is certainly meritorious. Perhaps,
if only the _changes_ (rather than an entire database) were
transmitted, it might be feasible (providing the satellite knew which
region and revision of the database was currently in your receiver).

But, data transmission requires a 2-way link (for Flow Control), so
that the receiving unit can acknowledge the correct receipt ion of
data packets, and request retransmission of corrupt packets. And,
what about the issue of incomplete database transmissions that might
occur when you arrive at your destination and shut the GPS receiver
off prematurely during the update transmission? The concept of a
self-updating GPS is noble, and one day (after all the issues are
carefully thought out and resolved) it will doubtless be implemented.

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