All the technical detail about cell phones is interesting but immaterial
to the Nexus since there is no cell function. But I have re-thought
what I said about the speed of the Nexus GPS in acquiring satellites.
It's just possible that it all cases it already knew its starting
position from earlier wi-fi use at home or from a hotel. I should think
at some time that I've cold booted it in a strange location without
wi-fi nearby but maybe not. I'll make a specific point of testing that
scenario. The Garmin definitely starts faster if it's proceeding from
the same position it was in when last powered down but even then usually
requires minutes (not seconds) to get it's bearings. If it's in a
strange starting location it can be a very long time punctuated with
messages "awaiting more satellites for better accuracy". But the Garmin
is at least 5 years old. The Nexus is new.
Chuck Norcutt
On 1/2/2013 10:36 AM, Ken Norton wrote:
>> No, it's not possible that CoPilot is getting anything from the
>> internet. When I'm using the device I'm in the car and have no wi-fi or
>> cell connection.
>
> Anytime that it is connected to the Internet it is either downloading
> for checking the date on the Almanac. The Almanac is the database of
> all the orbital and timing information for the constellation of GPS
> satellites.
>
> Cellphones have the additional benefit of knowing their general
> position thanks to the position of the serving cell-tower.
> Unfortunately, this isn't always correct if the antenna on the
> cell-tower is a remote off of another tower because it thinks the
> hosting tower, is the position, not the tower with the physical
> antenna. Regardless, what it does do is get the device in the
> neighborhood which vastly shortens the time to first fix. Then,
> because the Almanac is already downloaded, this saves the three
> minutes or so for the data to be received. The satellites broadcast
> their own empheris about every 30 seconds, so from acquiring the first
> satellite to getting basic positional information is no less than 30
> seconds in most cases--depending on when in the cycle the the
> acquiring begins.
>
> Once a standard stand-alone GPS receiver has loaded the almanac, and
> it isn't cold booted, the time to get position is usually quite short.
> People who rarely use their GPS units or force cold boots on them will
> complain because it always takes a long time for position acquisition.
>
> Cellphones have the advantage of not only having the Almanac
> downloaded into the device, but will either use the serving tower
> position or its own last-known position. Some phones use the WiFi
> location too.
>
> The cell-tower triangulization feature is one of those "sometimes"
> works features. Nice in theory, but highly impractical in most
> circumstances. It really only works when the phone is in overlapping
> coverage areas and there are no signal reflecting buildings nearby.
> The signal hand-off from one tower to the next and load-balancing
> features are nice, but rarely work as desired, so most carriers have
> those features dumbed down a lot.
>
> This last week, I ran into a problem with my carrier. We were in an
> area that was supposed to have tremendous coverage. But it looked like
> the wilt feature was enabled which greatly affected the service. Oh
> well... Mice and Men.
>
> AG
>
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