James Cloos wrote: >Obviously GPS needs to provide quicker almanac sync.
There used to be a notable problem with GPS that all the satellites transmitted the almanac in unison. This is highly redundant, and means that the receiver has to wait the full 12(?) minutes to compile a complete almanac. There was a proposal that the satellites could instead transmit the almanac at offset phases, so that a multi-channel receiver could compile a complete almanac, by combining the pieces received from different satellites, in one or two minutes. Anyone know whether this has been implemented? >But I have to ask: why should navigation systems care about time of >day? Shouldn't seconds since an epoch be enough? A good point. GPS time lacks leap seconds precisely in order to make it easy to convert to a linear scale for the purposes of computation. I suspect that much of the need for UTC in navigation systems comes from adherence to an established dumb design/standard rather than from fundamental requirement. GLONASS notably makes gratuitous use of UTC, and suffers operational glitches at every leap second. (GPS is not immune from dumb design either: consider the signal format for GPS time, and, for that matter, the concept of representing GPS time as a date and time-of-day in the first place.) -zefram _______________________________________________ LEAPSECS mailing list [email protected] http://six.pairlist.net/mailman/listinfo/leapsecs
