Apple iPhone is GSM

>
> how it works is here:
>
> http://people.howstuffworks.com/9-1-13.htm

There is an improvement on how this works but I am not sure which providers
implements it.

If you ever used a GPS (non-radio) device, you have noticed it takes several
minutes for the device to find you when first turned on. This is
problematic for a 911 solution. So in order to help this, the cellular
sight also has a GPS receiver in it and always has the preliminary data
ready when a cellphone calls in. If you turn your radio on and call
911(from a cold start), the cell sight sends the radio the preliminaries,
i,e, time, lat/lon map offset, all viewable satellite locations and other
data I can't remember. Then the cell phone can bypass this "setup and
finding" step and go right to calculating it's position step. Then it sends
it in. This cut off minutes of set up time which could be critical for a
911 call.

BTW, the GPS receivers in cell phones use for 911 purposes are cut down
versions of full receivers. They are intended to be activated for only
seconds and then go to sleep. Battery power is the issue. There may be
other cellphone GPS receivers capable of staying on for longer times but
recognize that these are more full blown GPS receivers, serve a different
market (tracking) and are not required for the 911 mandate. It will cost
you battery life when activated.

r. Bob F.

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› See More: Apple iPhone is GSM

On Wed, 18 Jul 2007 14:43:13 -0400, "Bob F." <[email protected]>
wrote in <[email protected]>:

>If you ever used a GPS (non-radio) device, you have noticed it takes several
>minutes for the device to find you when first turned on. This is
>problematic for a 911 solution. So in order to help this, the cellular
>sight also has a GPS receiver in it and always has the preliminary data
>ready when a cellphone calls in. If you turn your radio on and call
>911(from a cold start), the cell sight sends the radio the preliminaries,
>i,e, time, lat/lon map offset, all viewable satellite locations and other
>data I can't remember. Then the cell phone can bypass this "setup and
>finding" step and go right to calculating it's position step. Then it sends
>it in. This cut off minutes of set up time which could be critical for a
>911 call.

Assisted GPS as used in most handsets is actually quite a bit different
in that the assistance server computes position solutions, leaving the
GPS receiver in the handset with the sole job of collecting range
measurements.

--
Best regards, FAQ FOR CINGULAR WIRELESS:
John Navas <http://en.wikibooks.org/wiki/Cingular_Wireless_FAQ>

"John Navas" <[email protected]> wrote in message
news:[email protected]...
> On Wed, 18 Jul 2007 14:43:13 -0400, "Bob F." <[email protected]>
> wrote in <[email protected]>:
>
>>If you ever used a GPS (non-radio) device, you have noticed it takes
>>several
>>minutes for the device to find you when first turned on. This is
>>problematic for a 911 solution. So in order to help this, the cellular
>>sight also has a GPS receiver in it and always has the preliminary data
>>ready when a cellphone calls in. If you turn your radio on and call
>>911(from a cold start), the cell sight sends the radio the preliminaries,
>>i,e, time, lat/lon map offset, all viewable satellite locations and other
>>data I can't remember. Then the cell phone can bypass this "setup and
>>finding" step and go right to calculating it's position step. Then it
>>sends
>>it in. This cut off minutes of set up time which could be critical for a
>>911 call.
>
> Assisted GPS as used in most handsets is actually quite a bit different
> in that the assistance server computes position solutions, leaving the
> GPS receiver in the handset with the sole job of collecting range
> measurements.
>
> --
> Best regards, FAQ FOR CINGULAR WIRELESS:
> John Navas <http://en.wikibooks.org/wiki/Cingular_Wireless_FAQ>

Why and how would a GPS receiver collect "range measurements". I think what
you are talking about is "location assist" where trilateration is used to
find the handheld. No GPS device required in the handheld in this case. I
believe this is the most popular implementation (cheapest).

r, Bob F.

On 2007-07-18, Bob F. <[email protected]> wrote:
> "John Navas" <[email protected]> wrote:
>> "Bob F." <[email protected]> wrote:
>>
>>>If you ever used a GPS (non-radio) device, you have noticed it takes
>>>several
>>>minutes for the device to find you when first turned on. This is
>>>problematic for a 911 solution. So in order to help this, the cellular
>>>sight also has a GPS receiver in it and always has the preliminary data
>>>ready when a cellphone calls in. If you turn your radio on and call
>>>911(from a cold start), the cell sight sends the radio the preliminaries,
>>>i,e, time, lat/lon map offset, all viewable satellite locations and other
>>>data I can't remember. Then the cell phone can bypass this "setup and
>>>finding" step and go right to calculating it's position step. Then it
>>>sends
>>>it in. This cut off minutes of set up time which could be critical for a
>>>911 call.
>>
>> Assisted GPS as used in most handsets is actually quite a bit different
>> in that the assistance server computes position solutions, leaving the
>> GPS receiver in the handset with the sole job of collecting range
>> measurements.
>
> Why and how would a GPS receiver collect "range measurements". I think what
> you are talking about is "location assist" where trilateration is used to
> find the handheld. No GPS device required in the handheld in this case. I
> believe this is the most popular implementation (cheapest).

What GPS receivers measure are the arrival times of signals from the
GPS satellites. The signals from the GPS satellites are DSSS, and the
arrival times are measured by observing the time offset at which the
receiver finds precise code alignment (arrival times of signals from
CDMA towers, which are also DSSS, can be measured in exactly the same
way).

A CDMA phone is closely time-synchronized to the tower it is homed to
(which in turn is closely time-synchronized to GPS time) since CDMA
requires this. When the base station wants a position fix from the
phone it tells the phone the satellite PRNG codes it should listen for
and the approximate arrival times it should expect those signals at
(since the phone is close to the tower the values observed from the
tower will be nearly the same). This eliminates the need for the phone
to do its own satellite acquisition. The phone makes precise measurements
of any of those GPS signals it can hear, along with measurements of tower
signals, and sends the arrival times of all of these back to the network.
A computer in the network uses all the GPS and tower data returned
to come up with a best estimate of the phone's position; the phone
doesn't need to be aware of any of the additional data it would need
to come up with a position fix on its own.

Note that the phone doesn't need to know anything about GPS satellite
locations, or tower locations, to do this, nor is it ever aware of
its own position. It just makes ToA measurements of the signals it is
told to look for, both GPS and tower, and sends them back; the network
does the heavy lifting. Also note that GPS and tower positioning data
aren't processed separately; if all the phone can hear is one tower and
two GPS satellites, all the arrival time data is used to compute a
positioning solution better than either tower or GPS data alone could
provide.

Dennis Ferguson