iGPS?
Anyone know anything about "iGPS"? Apparently the Iridium low orbit
communications sats are now modified via software update to send
signals that when combined with GPS allow for a receiver that is MUCH
more precise and harder to jam and can work in urban areas better.
Apple just bought a company that is building iGPS receivers. Looks
like something that they might want to put inside a cell phone but
when you have an orders of magnitude important in position you'd
expect better timing too, or so I would think.
Seems like a very smart idea if all that was required was a software
upload to existing spacecraft. From what I read this is real, not a
proposal another are real receivers being tested.
--
Chris Albertson
Redondo Beach, California
On 2015-05-17 17:07, Chris Albertson wrote:
Anyone know anything about "iGPS"? Apparently the Iridium low orbit
communications sats are now modified via software update to send
signals that when combined with GPS allow for a receiver that is MUCH
more precise and harder to jam and can work in urban areas better.
Apple just bought a company that is building iGPS receivers. Looks
like something that they might want to put inside a cell phone but
when you have an orders of magnitude important in position you'd
expect better timing too, or so I would think.
Seems like a very smart idea if all that was required was a software
upload to existing spacecraft. From what I read this is real, not a
proposal another are real receivers being tested.
News:
http://www.iphoneincanada.ca/news/apple-has-reportedly-acquired-gps-firm-coherent-navigation
--
Take care. Thanks, Brian Inglis
Hi
“Orders of magnitude” more accurate …
Right now, you can get around ~1 M in most areas. One order of magnitude would be <10 cm.
More than one order of magnitude would be <10 mm. To me “orders” implies more than two, so that
would be <1 mm.
I guess everybody can toss out all their multi band GPS gear, there’s no need for it anymore. No need
to put up all those expensive block III GPS sat’s either :)
hmmmmm……I do believe the marketing boys have been playing with the numbers. You would have to start
from a >50 M error to get them to make much sense based on what they are doing.
===========
If you dig a bit more, Apple bought Coherent Navigation almost a half year ago. The main purpose appears
to be merging their mapping software into Apple’s ill-fated maps program. Given that Iridium is a “pay’
service (as in $$$$$) you probably will not see it in run of the mill cell phones very soon ….
Bob
On May 17, 2015, at 7:07 PM, Chris Albertson albertson.chris@gmail.com wrote:
Anyone know anything about "iGPS"? Apparently the Iridium low orbit
communications sats are now modified via software update to send
signals that when combined with GPS allow for a receiver that is MUCH
more precise and harder to jam and can work in urban areas better.
Apple just bought a company that is building iGPS receivers. Looks
like something that they might want to put inside a cell phone but
when you have an orders of magnitude important in position you'd
expect better timing too, or so I would think.
Seems like a very smart idea if all that was required was a software
upload to existing spacecraft. From what I read this is real, not a
proposal another are real receivers being tested.
--
Chris Albertson
Redondo Beach, California
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Hi Bob:
In the link in the message from Brian it explains that iGPS is for military users of the Iridium system.
The key feature is to allow a moving vehicle to lock on the GPS signal while being jammed. They do that and also get a
more accurate fix by using signals from the Iridium satellites.
I see a potential problem in that the Iridium signals are close in frequency to GPS and a broad band jammer might cause
a problem for both of them.
Mail_Attachment --
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
http://www.prc68.com/I/DietNutrition.html
Bob Camp wrote:
Hi
“Orders of magnitude” more accurate …
Right now, you can get around ~1 M in most areas. One order of magnitude would be <10 cm.
More than one order of magnitude would be <10 mm. To me “orders” implies more than two, so that
would be <1 mm.
I guess everybody can toss out all their multi band GPS gear, there’s no need for it anymore. No need
to put up all those expensive block III GPS sat’s either :)
hmmmmm……I do believe the marketing boys have been playing with the numbers. You would have to start
from a >50 M error to get them to make much sense based on what they are doing.
===========
If you dig a bit more, Apple bought Coherent Navigation almost a half year ago. The main purpose appears
to be merging their mapping software into Apple’s ill-fated maps program. Given that Iridium is a “pay’
service (as in $$$$$) you probably will not see it in run of the mill cell phones very soon ….
Bob
On May 17, 2015, at 7:07 PM, Chris Albertson albertson.chris@gmail.com wrote:
Anyone know anything about "iGPS"? Apparently the Iridium low orbit
communications sats are now modified via software update to send
signals that when combined with GPS allow for a receiver that is MUCH
more precise and harder to jam and can work in urban areas better.
Apple just bought a company that is building iGPS receivers. Looks
like something that they might want to put inside a cell phone but
when you have an orders of magnitude important in position you'd
expect better timing too, or so I would think.
Seems like a very smart idea if all that was required was a software
upload to existing spacecraft. From what I read this is real, not a
proposal another are real receivers being tested.
--
Chris Albertson
Redondo Beach, California
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
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On 5/18/15 11:06 AM, Brooke Clarke wrote:
Hi Bob:
In the link in the message from Brian it explains that iGPS is for
military users of the Iridium system.
The key feature is to allow a moving vehicle to lock on the GPS signal
while being jammed. They do that and also get a more accurate fix by
using signals from the Iridium satellites.
I see a potential problem in that the Iridium signals are close in
frequency to GPS and a broad band jammer might cause a problem for both
of them.
Any system that is concerned about jamming is probably going to be
immune to broadband jamming: after all, GPS signals are already below
the noise floor. Broadband jamming is a pretty ineffective use of RF power.
Any wide area and broadband military jammer is taking a big risk
because the jammer is very easy to find.
If Apple is buying into this then it is not military and they are
looking to put it inside a phone or maybe a car.
On Mon, May 18, 2015 at 11:06 AM, Brooke Clarke brooke@pacific.net wrote:
Hi Bob:
In the link in the message from Brian it explains that iGPS is for military
users of the Iridium system.
The key feature is to allow a moving vehicle to lock on the GPS signal while
being jammed. They do that and also get a more accurate fix by using
signals from the Iridium satellites.
I see a potential problem in that the Iridium signals are close in frequency
to GPS and a broad band jammer might cause a problem for both of them.
Mail_Attachment --
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
http://www.prc68.com/I/DietNutrition.html
Bob Camp wrote:
Hi
“Orders of magnitude” more accurate …
Right now, you can get around ~1 M in most areas. One order of magnitude
would be <10 cm.
More than one order of magnitude would be <10 mm. To me “orders” implies
more than two, so that
would be <1 mm.
I guess everybody can toss out all their multi band GPS gear, there’s no
need for it anymore. No need
to put up all those expensive block III GPS sat’s either :)
hmmmmm……I do believe the marketing boys have been playing with the
numbers. You would have to start
from a >50 M error to get them to make much sense based on what they are
doing.
===========
If you dig a bit more, Apple bought Coherent Navigation almost a half year
ago. The main purpose appears
to be merging their mapping software into Apple’s ill-fated maps program.
Given that Iridium is a “pay’
service (as in $$$$$) you probably will not see it in run of the mill cell
phones very soon ….
Bob
On May 17, 2015, at 7:07 PM, Chris Albertson albertson.chris@gmail.com
wrote:
Anyone know anything about "iGPS"? Apparently the Iridium low orbit
communications sats are now modified via software update to send
signals that when combined with GPS allow for a receiver that is MUCH
more precise and harder to jam and can work in urban areas better.
Apple just bought a company that is building iGPS receivers. Looks
like something that they might want to put inside a cell phone but
when you have an orders of magnitude important in position you'd
expect better timing too, or so I would think.
Seems like a very smart idea if all that was required was a software
upload to existing spacecraft. From what I read this is real, not a
proposal another are real receivers being tested.
--
Chris Albertson
Redondo Beach, California
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
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To unsubscribe, go to
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--
Chris Albertson
Redondo Beach, California
Hi Brooke:
In the original post that I was replying to, the concept was advocated as a
“it goes into every iPhone on the planet”. That’s what I was commenting on.
Bob
On May 18, 2015, at 2:06 PM, Brooke Clarke brooke@pacific.net wrote:
Hi Bob:
In the link in the message from Brian it explains that iGPS is for military users of the Iridium system.
The key feature is to allow a moving vehicle to lock on the GPS signal while being jammed. They do that and also get a more accurate fix by using signals from the Iridium satellites.
I see a potential problem in that the Iridium signals are close in frequency to GPS and a broad band jammer might cause a problem for both of them.
Mail_Attachment --
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
http://www.prc68.com/I/DietNutrition.html
Bob Camp wrote:
Hi
“Orders of magnitude” more accurate …
Right now, you can get around ~1 M in most areas. One order of magnitude would be <10 cm.
More than one order of magnitude would be <10 mm. To me “orders” implies more than two, so that
would be <1 mm.
I guess everybody can toss out all their multi band GPS gear, there’s no need for it anymore. No need
to put up all those expensive block III GPS sat’s either :)
hmmmmm……I do believe the marketing boys have been playing with the numbers. You would have to start
from a >50 M error to get them to make much sense based on what they are doing.
===========
If you dig a bit more, Apple bought Coherent Navigation almost a half year ago. The main purpose appears
to be merging their mapping software into Apple’s ill-fated maps program. Given that Iridium is a “pay’
service (as in $$$$$) you probably will not see it in run of the mill cell phones very soon ….
Bob
On May 17, 2015, at 7:07 PM, Chris Albertson albertson.chris@gmail.com wrote:
Anyone know anything about "iGPS"? Apparently the Iridium low orbit
communications sats are now modified via software update to send
signals that when combined with GPS allow for a receiver that is MUCH
more precise and harder to jam and can work in urban areas better.
Apple just bought a company that is building iGPS receivers. Looks
like something that they might want to put inside a cell phone but
when you have an orders of magnitude important in position you'd
expect better timing too, or so I would think.
Seems like a very smart idea if all that was required was a software
upload to existing spacecraft. From what I read this is real, not a
proposal another are real receivers being tested.
--
Chris Albertson
Redondo Beach, California
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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The parts of the iGPS story that I actually understand, make it sound like
it will decrease acquisition time and especially decrease acquisition time
in presence of jamming. Like how cellphone tower fixes can give a
cellphone's GPS an initial guess at time/position and speed up GPS
acquisition (aka aGPS).
As cellphones move more towards wifi and away from traditional cellphone
technologies, the initial Iridium fix may become more important.
My grasp above, has nothing to do with "orders of magnitude" more precision
in a fix. But I could see at least an order of magnitude or more in faster
acquisition, as compared to a complete cold start.
Tim N3QE
On Sun, May 17, 2015 at 10:10 PM, Bob Camp kb8tq@n1k.org wrote:
Hi
“Orders of magnitude” more accurate …
Right now, you can get around ~1 M in most areas. One order of magnitude
would be <10 cm.
More than one order of magnitude would be <10 mm. To me “orders” implies
more than two, so that
would be <1 mm.
I guess everybody can toss out all their multi band GPS gear, there’s no
need for it anymore. No need
to put up all those expensive block III GPS sat’s either :)
hmmmmm……I do believe the marketing boys have been playing with the
numbers. You would have to start
from a >50 M error to get them to make much sense based on what they are
doing.
===========
If you dig a bit more, Apple bought Coherent Navigation almost a half year
ago. The main purpose appears
to be merging their mapping software into Apple’s ill-fated maps program.
Given that Iridium is a “pay’
service (as in $$$$$) you probably will not see it in run of the mill cell
phones very soon ….
Bob
On May 17, 2015, at 7:07 PM, Chris Albertson albertson.chris@gmail.com
wrote:
Anyone know anything about "iGPS"? Apparently the Iridium low orbit
communications sats are now modified via software update to send
signals that when combined with GPS allow for a receiver that is MUCH
more precise and harder to jam and can work in urban areas better.
Apple just bought a company that is building iGPS receivers. Looks
like something that they might want to put inside a cell phone but
when you have an orders of magnitude important in position you'd
expect better timing too, or so I would think.
Seems like a very smart idea if all that was required was a software
upload to existing spacecraft. From what I read this is real, not a
proposal another are real receivers being tested.
--
Chris Albertson
Redondo Beach, California
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Yes GPS can do better than 50M but we are talking about a single fix
from a cell phone in a moving car not a survey receiver. . The
displayed location is better because the phone applies a filter to the
location data. Some thing like a Kalman filter. I doubt the iPhone
can get within 10M from a moving car.
As for Iridium being an expensive for pay service. But that is
because most users SEND data. This new service is broadcast and costs
do not depend on the number of users. Apple has sold 130,000,000
phones already just in this half of 2015. A one time payment of about
$1 per phone might cover the costs.
hmmmmm……I do believe the marketing boys have been playing with the
numbers. You would have to start
from a >50 M error to get them to make much sense based on what they are
doing.
--
Chris Albertson
Redondo Beach, California
On 5/18/15 7:59 PM, Chris Albertson wrote:
Yes GPS can do better than 50M but we are talking about a single fix
from a cell phone in a moving car not a survey receiver. . The
displayed location is better because the phone applies a filter to the
location data. Some thing like a Kalman filter. I doubt the iPhone
can get within 10M from a moving car.
As for Iridium being an expensive for pay service. But that is
because most users SEND data. This new service is broadcast and costs
do not depend on the number of users. Apple has sold 130,000,000
phones already just in this half of 2015. A one time payment of about
$1 per phone might cover the costs.
Why iridium? Why not Sirius or XM or DBS. Unless you want something
world wide, as opposed to "populated areas served by broadcast radio and
TV"
Heck, you could probably buy transponder time on a C-band satellite and
radiate a GPS assist signal (that's what WAAS is, after all)
hmmmmm……I do believe the marketing boys have been playing with the
numbers. You would have to start
from a >50 M error to get them to make much sense based on what they are
doing.
On Mon, May 18, 2015 at 09:52:03PM -0700, Jim Lux wrote:
Why iridium? Why not Sirius or XM or DBS. Unless you want something
world wide, as opposed to "populated areas served by broadcast radio and
TV"
Well it seems to me I remember Iridium is time domain duplex
around 1610 MHz or thereabouts... which isn't too far from the L1
civilian GPS at 1575.42 and quite possibly inside the bandwidth of
some civilian L1 LNAs and antennas.
Sirius XM is not that close at 2320-2345 Mhz.
And inside its spot beam the Iridium signal is quite a bit more
powerful and coming at one from constantly changing angles... whilst
the Sirius XM birds are either geosync or in Molninya orbits and don't
move much over short intervals - as does an Iridium signal.
And of course (for the military especially) it IS worldwide and
not just restricted to NA (where such an anti-jam capability is less
useful at least at the moment). Something that works world wide
is of course what the military folks need.
And I suspect timing can be derived from the satellites TDD
and message timing pretty easily if that is accurately synced to some
reference...
Others more familiar with the details may comment here...
--
Dave Emery N1PRE/AE, die@dieconsulting.com DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in
celebration of what could have been, but wasn't and is not to be now either."
Have you seen the orbit of the Sirius satellites?
http://www.tiger-usa.com/satellite_animation.htm
Dave
-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces@febo.com] On Behalf
Of Jim Lux
Sent: Monday, May 18, 2015 21:52
To: time-nuts@febo.com
Subject: Re: [time-nuts] iGPS?
On 5/18/15 7:59 PM, Chris Albertson wrote:
Yes GPS can do better than 50M but we are talking about a single fix
from a cell phone in a moving car not a survey receiver. . The
displayed location is better because the phone applies a
filter to the
location data. Some thing like a Kalman filter. I doubt
the iPhone
can get within 10M from a moving car.
As for Iridium being an expensive for pay service. But that is
because most users SEND data. This new service is
broadcast and costs
do not depend on the number of users. Apple has sold 130,000,000
phones already just in this half of 2015. A one time
payment of about
$1 per phone might cover the costs.
Why iridium? Why not Sirius or XM or DBS. Unless you want something
world wide, as opposed to "populated areas served by
broadcast radio and
TV"
Heck, you could probably buy transponder time on a C-band
satellite and
radiate a GPS assist signal (that's what WAAS is, after all)
hmmmmm..I do believe the marketing boys have been playing with the
numbers. You would have to start
from a >50 M error to get them to make much sense based
on what they are
doing.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Hi
If we’re talking about a corrected survey receiver, you can get a lot better than 1 M. Single
frequency corrected (WAAS etc) fixes from multiple systems (GPS + GLONASS + …) are
indeed doing ~ 1 M (horizontal) in urban environments. The correction data is often applied via remote
acquisition (cell tower or what ever). For $10 you can get a multi system USB stick from China.
That’s a setup that will fit into a cell phone.
You can check and see if you are off by 50M fairly easily. Things like bridges and cross roads are
fairly easy to spot. The “put me on the road” algorithm has very little to do with their location. If you are
off by 1/4 block, you’ll notice.
Unless Apple buys them ( => iRidium), I don’t see them going for anything other than subscription
plans for their service. They simply have to much ongoing overhead. That’s been the problem
since Motorola was involved and it’s their problem today.
Bob
On May 18, 2015, at 10:59 PM, Chris Albertson albertson.chris@gmail.com wrote:
Yes GPS can do => better than 50M but we are talking about a single fix
from a cell phone in a moving car not a survey receiver. . The
displayed location is better because the phone applies a filter to the
location data. Some thing like a Kalman filter. I doubt the iPhone
can get within 10M from a moving car.
As for Iridium being an expensive for pay service. But that is
because most users SEND data. This new service is broadcast and costs
do not depend on the number of users. Apple has sold 130,000,000
phones already just in this half of 2015. A one time payment of about
$1 per phone might cover the costs.
hmmmmm……I do believe the marketing boys have been playing with the
numbers. You would have to start
from a >50 M error to get them to make much sense based on what they are
doing.
--
Chris Albertson
Redondo Beach, California
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Hi
The idea is that more sats in more directions = better fixes. The assumption
is that you are in an urban canyon. Most of the sky is blocked and you
“need” sats in just the right part of the sky. There’s always going to be
some configuration of buildings that could give you a problem.
Bob
On May 19, 2015, at 12:52 AM, Jim Lux jimlux@earthlink.net wrote:
On 5/18/15 7:59 PM, Chris Albertson wrote:
Yes GPS can do better than 50M but we are talking about a single fix
from a cell phone in a moving car not a survey receiver. . The
displayed location is better because the phone applies a filter to the
location data. Some thing like a Kalman filter. I doubt the iPhone
can get within 10M from a moving car.
As for Iridium being an expensive for pay service. But that is
because most users SEND data. This new service is broadcast and costs
do not depend on the number of users. Apple has sold 130,000,000
phones already just in this half of 2015. A one time payment of about
$1 per phone might cover the costs.
Why iridium? Why not Sirius or XM or DBS. Unless you want something world wide, as opposed to "populated areas served by broadcast radio and TV"
Heck, you could probably buy transponder time on a C-band satellite and radiate a GPS assist signal (that's what WAAS is, after all)
hmmmmm……I do believe the marketing boys have been playing with the
numbers. You would have to start
from a >50 M error to get them to make much sense based on what they are
doing.
time-nuts mailing list -- time-nuts@febo.com
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and follow the instructions there.
Not necessarily, you are assuming a single large jammer you could easily disperse a large number of small narrowband jammers over an area you wanted to deny GPS coverage to via airdrops or artillery and that would effectively deny coverage and make it almost impossible to suppress all the jammers.
Content by Scott
Typos by Siri
On May 18, 2015, at 3:56 PM, Chris Albertson albertson.chris@gmail.com wrote:
Any wide area and broadband military jammer is taking a big risk
because the jammer is very easy to find.
If Apple is buying into this then it is not military and they are
looking to put it inside a phone or maybe a car.
On Mon, May 18, 2015 at 11:06 AM, Brooke Clarke brooke@pacific.net wrote:
Hi Bob:
In the link in the message from Brian it explains that iGPS is for military
users of the Iridium system.
The key feature is to allow a moving vehicle to lock on the GPS signal while
being jammed. They do that and also get a more accurate fix by using
signals from the Iridium satellites.
I see a potential problem in that the Iridium signals are close in frequency
to GPS and a broad band jammer might cause a problem for both of them.
Mail_Attachment --
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
http://www.prc68.com/I/DietNutrition.html
Bob Camp wrote:
Hi
“Orders of magnitude” more accurate …
Right now, you can get around ~1 M in most areas. One order of magnitude
would be <10 cm.
More than one order of magnitude would be <10 mm. To me “orders” implies
more than two, so that
would be <1 mm.
I guess everybody can toss out all their multi band GPS gear, there’s no
need for it anymore. No need
to put up all those expensive block III GPS sat’s either :)
hmmmmm……I do believe the marketing boys have been playing with the
numbers. You would have to start
from a >50 M error to get them to make much sense based on what they are
doing.
===========
If you dig a bit more, Apple bought Coherent Navigation almost a half year
ago. The main purpose appears
to be merging their mapping software into Apple’s ill-fated maps program.
Given that Iridium is a “pay’
service (as in $$$$$) you probably will not see it in run of the mill cell
phones very soon ….
Bob
On May 17, 2015, at 7:07 PM, Chris Albertson albertson.chris@gmail.com
wrote:
Anyone know anything about "iGPS"? Apparently the Iridium low orbit
communications sats are now modified via software update to send
signals that when combined with GPS allow for a receiver that is MUCH
more precise and harder to jam and can work in urban areas better.
Apple just bought a company that is building iGPS receivers. Looks
like something that they might want to put inside a cell phone but
when you have an orders of magnitude important in position you'd
expect better timing too, or so I would think.
Seems like a very smart idea if all that was required was a software
upload to existing spacecraft. From what I read this is real, not a
proposal another are real receivers being tested.
--
Chris Albertson
Redondo Beach, California
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
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time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
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--
Chris Albertson
Redondo Beach, California
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Hi
The Iridium frequencies are even further “up band” than the Glonass signals. None of the
“GPS” antennas that I have tried work very well on Glonass. I doubt they would do well
at all trying to get Iridium.
Bob
On May 19, 2015, at 1:57 AM, David I. Emery die@dieconsulting.com wrote:
On Mon, May 18, 2015 at 09:52:03PM -0700, Jim Lux wrote:
Why iridium? Why not Sirius or XM or DBS. Unless you want something
world wide, as opposed to "populated areas served by broadcast radio and
TV"
Well it seems to me I remember Iridium is time domain duplex
around 1610 MHz or thereabouts... which isn't too far from the L1
civilian GPS at 1575.42 and quite possibly inside the bandwidth of
some civilian L1 LNAs and antennas.
Sirius XM is not that close at 2320-2345 Mhz.
And inside its spot beam the Iridium signal is quite a bit more
powerful and coming at one from constantly changing angles... whilst
the Sirius XM birds are either geosync or in Molninya orbits and don't
move much over short intervals - as does an Iridium signal.
And of course (for the military especially) it IS worldwide and
not just restricted to NA (where such an anti-jam capability is less
useful at least at the moment). Something that works world wide
is of course what the military folks need.
And I suspect timing can be derived from the satellites TDD
and message timing pretty easily if that is accurately synced to some
reference...
Others more familiar with the details may comment here...
--
Dave Emery N1PRE/AE, die@dieconsulting.com DIE Consulting, Weston, Mass 02493
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On Sun, 17 May 2015 16:07:05 -0700
Chris Albertson albertson.chris@gmail.com wrote:
Anyone know anything about "iGPS"? Apparently the Iridium low orbit
communications sats are now modified via software update to send
signals that when combined with GPS allow for a receiver that is MUCH
more precise and harder to jam and can work in urban areas better.
Apple just bought a company that is building iGPS receivers.
I think the main business idea is to supply people with indoor
navigation, which is impossible in most cases with GPS.
This is mostly due to the higher receive power of the Iridium satellites
(deeper penetration) and their fast movement (shadowing happens
only for a short time). On the other hand, the fast movement is
a problem for acquiring a fix (satellites are only visible for a
couple of minutes), but I guess they solved that issue for their
phone system already.
IIRC (been some time since i looked at it) the system is based
on triangulation based on doppler shift instead of the time-delay
GPS uses. Which allows the system to work with less than 4 satellites
visible.
More informations can be found here:
[1] "Boing Talks on Indoor Navigation at ION 2011"
http://www.youtube.com/watch?v=cHsGp7ykbv0
[2] "Iridium/GPS Carrier Phase Positioning and Fault Detection Over
Wide Areas", by Joerger, Neale, Pervan, 2009
[3] "iGPS: Integrated Nav & Com Augmentation of GPS",
presentation by David Whelan, 2010
http://scpnt.stanford.edu/pnt/PNT10/presentation_slides/10-PNT_Symposium_Whelan.pdf
--
< av500> phd is easy
< av500> getting dsl is hard