Re: iPhone location

On Sun, 7 Jun 2009 13:33:56 +0100, tony sayer <tony@xxxxxxxxxxxx>
wrote:

But it's only going to be used for an initial idea of where the device
is and in low GPS signal conditions, so is better than nothing.

Well as you say better than nothing..

Tho if you were out in the country it could be out by several
kilometres.!..

The Google maps app on my phone shows a radius inside which you may be. My
phone has no GPS, so the radius can be large :-)

Large as in a few miles, which is all aGPS needs in order to speed up
getting a lock.

How does that speed it up if you are somewhere within the radius of
coverage of a base station terminal, then what do you -do- to improve
the navigation precision?.

My goodness, you haven't read anything I've said or read any of the
links I've posted, have you?

And what dose the aGPS lock onto?....

I don't know why you're contributing if you don't understand the
question the OP originally posted.

Read this (already posted by me in this thread):

http://en.wikipedia.org/wiki/AGPS

""
In certain conditions, Conventional Standalone GPS has difficulty
providing reliable positions in poor signal conditions. For example,
when surrounded by tall buildings (resulting in multipath), or when
the satellite signals are weakened when a GPS device is used indoors
or under trees. Some newer receivers are better at handling these
situations.

In addition, when first turned on in these conditions, some
non-assisted GPS units may not be able to download the almanac and
ephemeris information from the GPS satellites, rendering them unable
to function until a clear signal can be received continuously for up
to 40 seconds.

An A-GPS receiver can address these problems in several ways, using
network elements such as either an assistance server or other data
from a network. That assistance generally falls into two categories:
a) information used to more quickly acquire satellites, or b)
calculations done remotely:

The assistance server can locate the phone roughly by which cell site
it is connected to on the cellular network.

The assistance server has a good satellite signal, and lots of
computation power, so it can compare fragmentary signals relayed to it
by cell phones, with the satellite signal it receives directly, and
then inform the cell phone or emergency services of the cell phone's
position.

It can supply orbital data and/or almanac for the GPS satellites to
the cell phone, enabling the cell phone to lock to the satellites
faster in some cases.

The network can provide atomic time (Accurate Time Assistance)

Simply capturing a brief snapshot of the GPS signal, with approximate
time, for the server to later process into a position.

By having accurate, surveyed coordinates for the cell site towers, it
has better knowledge of ionospheric conditions and other errors
affecting the GPS signal than the cell phone alone, enabling more
precise calculation of position. (See also Wide Area Augmentation
System)
""
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.

Relevant Pages

  • Expert Advice: Surveyors Ask About Civil P(Y) Sunset
    ... The October webinar focused on the Department of Defense decision to discontinue supporting Pon GPS L1 and L2 for civilian users after December 31, ... In other words, your legacy dual-frequency GPS receivers may end up operating past December 31, 2020, without any problems. ... The only changes happening before 2010 are that a couple more Block IIR-M satellites will be launched. ... L5 signals, for example, should have lower multipath contamination and also less noise at low elevation angles. ...
    (sci.geo.satellite-nav)
  • Re: GPS Vs COMPASS
    ... keeping my Silva 4 in the map bag I've seen many times when my 16 channel GPS cannot sync with enough satellites to get a good enough fix, and sometimes locating me off cliffs. ... Very dense local cloud cover containing a large amount of water content can easily divert or impede a signal therefore giving a smaller QoS and phase changes in signals. ... It is also a possibility that your GPS receiver is not very healthy :-( what model is it? ...
    (uk.rec.walking)
  • Re: Re: Solar Bursts May Threaten GPS
    ... Many times they are launched as spares. ... Current GPS broadcast to signals, one for civilian usage and the other ... the known positions of satellites and calculate your position. ...
    (rec.outdoors.rv-travel)
  • Re: GPS Ideas
    ... I was thinking that one could attach to each satellites two frequencies ... The data that the satellite transmits would include the distance from ... signals to each other too and some power would be wasted. ... GPS receiver. ...
    (sci.electronics.design)
  • Re: Re:Irish electricity
    ... The cell phone maximises it's bandwidth by using the same frequency for many ... transponders to make the system work, next time you pass a mast you might ... If it was true that strong signals could filter up as lower frequency ... *The masts were never designed to transmit up and as I've said it would take ...
    (soc.culture.irish)