Earth shattering news for GNSS, commercial availability of Chip ScaleAtomic Clock (CSAC)

On Jan 19, 3:43*pm, Alan Browne
wrote:
On 2011.01.18 22:36 , macpacheco wrote:

CSACs might also make their way into all DPGS stations, improving
their calculated corrections. All current WAAS stations have a
standard Rb atomic clock (costs US$ 35000 each, lasting less than 10
yrs), replacing each Rb atomic clock with a triple redundant CSAC
facility will save a bundle on WAAS maintenance (with three clocks a
single faulty unit can be detected, excluded and marked for
replacement without stopping the station). Regular atomic clocks also
are temperature sensitive, requiring air conditioning, this CSAC can
handle temperatures from -10C to +50C.

The CSAC is not a deploy-able product. *It has to be integrated into a
receiver. *That, with design, integration, testing and certification
will drive up the cost considerably. *The $1500 will go to about $10 -
$15K as an educated guess.

For a fielded WAAS station, the -10°C may be unacceptable. *(There is
the military version which is likely more expensive, that goes lower,
-40°C).

--
gmail originated posts filtered due to spam.

From what I've seen all WAAS stations today are co-located with Air
traffic control centers. Perhaps one or two in alaska are stand alone.
Even -40C is probably not cold enough for Alaska, there it will need
some climatization.

Anything new will take years before the FAA is willing to touch it.
They are a lot more conservative even than the military. The current
WAAS network is operational, what's the need to replace things out of
the blue. By the time they start considering it, price will have
dropped considerably, probably when they perform the migration from
semi codeless to L1 CA+L5, probably circa 2020 (they stated that their
plan is an all or nothing thing, once they migrate, all WAAS reference
stations won't receive nor P(Y) nor L2C, L1 CA+L5 only, so they can't
migrate before L5 reaches FOC anyways, its a step backwards in my
opinion, but I digress) ... But as far as integration, atomic clocks
are a misnomer anyways, they are actually frequency sources, a timing
signal, or am I wrong ? I mean... they don't really keep time
(nanoseconds since a given date), they make a 10 MHz timing output
plus one or two other formats, that in turn is used not only to track
time, but also used for all kinds of very important receive/transmit
actual RF hardware (the more accurate clock available for the GPS RF
receive can improve receive SNR margins for instance and can transmit
a more precise signal for instance when generating the C band uplink
for the GEOs). A 10 MHz clock is a 10MHz clock, sure it will require a
ton of testing, but making it work, is it that expensive ?

Marcelo Pacheco - Not an electronics expert.

There's a lot of literature describing how a precise clock can
mitigate the strong correlation between the clock and vertical
position states, hence improve VDOP, improve integrity monitoring,
etc. Pratap Misra has written quite a bit on the topic.

An early paper on clock coasting (there were earlier experiments):

Sturza, Mark A., "GPS Navigation Using Tbree Satellites and a Precise
Clock", NAVIGATION, Vol. 30, No. 2, Summer 1983, pp. 146-156,
http://www.3csysco.com/Pubs/GPS%20Na...se%20Clock.pdf

Can't find an on-line copy of this one:

“The Role of the Clock in a GPS Receiver” by P.N. Misra in GPS World,
Vol. 7, No. 4, April 1996, pp. 60–66.

A dissertation that involved flight testing with a Boeing 767 at the
FAA's Atlantic City test site:

Kline, Paul A., "Atomic Clock Augmentation For Receivers Using the
Global Positioning System," Ph.D. Dissertation, Virginia Polytechnic
University, 1997, http://scholar.lib.vt.edu/theses/ava...2516142975720/

A thesis sponsored by Misra:

Sean G. Bednarz, "Adaptive Modeling of GPS Receiver Clock for
Integrity Monitoring During Precision Approaches," M.S. Thesis,
Massachusetts Institute of Technology, 2004, http://dspace.mit.edu/handle/1721.1/17756

A GPS World Innovations column from 2007:

http://tf.boulder.nist.gov/general/pdf/2267.pdf

How sensitive are these CSACs to other environmental variables? What about
shock, or position? Are they robust enough to be used in wris****ches and
portable timepieces (disregarding cost)?

Which reminds me: why are there no wris****ches that use GPS just for a time
reference, without the geolocation functions? Or are there? Seems like there'd
be a market for such watches to replace "radio-controlled" watches depending
on WWVB and the like, if the price isn't too high. They wouldn't need a CSAC,
although that would be a nice bonus.

Mxsmanic wrote:
How sensitive are these CSACs to other environmental variables? What about
shock, or position? Are they robust enough to be used in wris****ches and
portable timepieces (disregarding cost)?

Which reminds me: why are there no wris****ches that use GPS just for a time
reference, without the geolocation functions? Or are there? Seems like there'd
be a market for such watches to replace "radio-controlled" watches depending
on WWVB and the like, if the price isn't too high. They wouldn't need a CSAC,
although that would be a nice bonus.

No GPS unit is low-power enough to be used as a pure wris****ch, where a
single button battery is supposed to last for years.

You might get away with a very good crystal plus a GPS that only wakes
up once (or a few times) per day or so, in which case you have made
yourself a very expensive chronometer. :-)

Instead of spending power on an oven for a TCXO you could use the Garmin
approach of a tiny temperature sensor (_very_ low power) plus an
automatically calibrated temp adjustement table for the XO.

Terje

--
- Terje.Mathisen at tmsw.no
"almost all programming can be viewed as an exercise in caching"

On Jan 20, 5:37*am, Terje Mathisen "terje.mathisen at tmsw.no"
wrote:
Mxsmanic wrote:
How sensitive are these CSACs to other environmental variables? What about
shock, or position? Are they robust enough to be used in wris****ches and
portable timepieces (disregarding cost)?

Which reminds me: why are there no wris****ches that use GPS just for a time
reference, without the geolocation functions? Or are there? Seems like there'd
be a market for such watches to replace "radio-controlled" watches depending
on WWVB and the like, if the price isn't too high. They wouldn't need a CSAC,
although that would be a nice bonus.

No GPS unit is low-power enough to be used as a pure wris****ch, where a
single button battery is supposed to last for years.

You might get away with a very good crystal plus a GPS that only wakes
up once (or a few times) per day or so, in which case you have made
yourself a very expensive chronometer. :-)

Instead of spending power on an oven for a TCXO you could use the Garmin
approach of a tiny temperature sensor (_very_ low power) plus an
automatically calibrated temp adjustement table for the XO.

Terje

--
- Terje.Mathisen at tmsw.no
"almost all programming can be viewed as an exercise in caching"

Military CSAC applications include field radios and soldier automation
platforms that require temperature, shock tolerance anyways.
Even if CSACs don't make it to your typical individual GI equipment,
one should expect them to make it to special forces and other elite
units and platoon level systems. In Afghanistan alone, GPS clock
coasting is extremely desirable for accurate targeting in mountain
riddled terrain. Notice that was the trigger behind the last 24+3 GPS
constellation improvement.
Even if this first generation clock isn't fully able to handle
significant shock, you can be sure someone is working on it. You can't
put it on special forces gear unless it can handle a great deal of
shock.

Marcelo

On Jan 20, 4:46*am, Mxsmanic wrote:
How sensitive are these CSACs to other environmental variables? What about
shock, or position? Are they robust enough to be used in wris****ches and
portable timepieces (disregarding cost)?

Which reminds me: why are there no wris****ches that use GPS just for a time
reference, without the geolocation functions? Or are there? Seems like there'd
be a market for such watches to replace "radio-controlled" watches depending
on WWVB and the like, if the price isn't too high. They wouldn't need a CSAC,
although that would be a nice bonus.

This first generation chip atomic clocks are still in the US$ 1000+
price scale. That should keep it's use down to where really needed.
Probably another 20 yrs until we have a micro chip scale atomic clock.
No clarification were given in the accuracy of the equipment at its
temperature limits. It's very likely that CSAC measures its own
temperature and compensate its output with measured temperature, so
its entirely possible that its accuracy stay within specs for its
entire operating temperature envelope.

A wrist watch that can keep time down to one second per year precision
is more than good enough, except for those who want to waste money on
pricey status objects.

Current quartz frequency standards already can keep time down to 30 ms
per year (source wikipedia) ! Though its likely that accuracy is
attained by larger chip sized quartz oscillator instead of the tiny
quartz circuits found in wrist watches. Even smaller last generation
micro quartz oscillators should be able to reach one second per year
accuracy, so why would you want a GPS receiver just to set the
clock ???? Just so you don't need to ever set your watch again ?

Mxsmanic wrote:

How sensitive are these CSACs to other environmental variables? What about
shock, or position? Are they robust enough to be used in wris****ches and
portable timepieces (disregarding cost)?

Which reminds me: why are there no wris****ches that use GPS just for a time
reference, without the geolocation functions? Or are there? Seems like there'd
be a market for such watches to replace "radio-controlled" watches depending
on WWVB and the like, if the price isn't too high. They wouldn't need a CSAC,
although that would be a nice bonus.

Radio controlled watches do the same thing more cheaply,
and work in most of the inahabited world,
at a much lower power consumption.

There would be at best a small niche market for such a thing,

Jan

On Jan 20, 12:08*am, "Ed M." wrote:
There's a lot of literature describing how a precise clock can
mitigate the strong correlation between the clock and vertical
position states, hence improve VDOP, improve integrity monitoring,
etc. *Pratap Misra has written quite a bit on the topic.

An early paper on clock coasting (there were earlier experiments):

Sturza, Mark A., "GPS Navigation Using Tbree Satellites and a Precise
Clock", NAVIGATION, Vol. 30, No. 2, Summer 1983, pp. 146-156,http://www.3csysco.com/Pubs/GPS%20Na...Three%20Satell...

Can't find an on-line copy of this one:

“The Role of the Clock in a GPS Receiver” by P.N. Misra in GPS World,
Vol. 7, No. 4, April 1996, pp. 60–66.

A dissertation that involved flight testing with a Boeing 767 at the
FAA's Atlantic City test site:

Kline, Paul A., "Atomic Clock Augmentation For Receivers Using the
Global Positioning System," Ph.D. Dissertation, Virginia Polytechnic
University, 1997,http://scholar.lib.vt.edu/theses/ava...2516142975720/

A thesis sponsored by Misra:

Sean G. Bednarz, "Adaptive Modeling of GPS Receiver Clock for
Integrity Monitoring During Precision Approaches," M.S. Thesis,
Massachusetts Institute of Technology, 2004,http://dspace.mit.edu/handle/1721.1/17756

A GPS World Innovations column from 2007:

http://tf.boulder.nist.gov/general/pdf/2267.pdf

Coasting studies I've read seem to assume usage of a worse CSAC than a
Cs atomic clock, something with at least one order of magnitude less
stability than your typical Cs atomic clock. Taking Symmetricon's
claims at face value here... Top of the line quartz oscillators = 30ms
per year stability, four orders of magnitude better would be roughly 3
micro seconds per year stability, 8 ns per day stability, or 1 ns
every 4 hours. Or 10 cm per hour drift. In an unjammed environment,
today even in the middle of a GPS maintenance event, PDOP spikes don't
last 2 hrs for the same area. And a 20cm error would be acceptable
even for a CAT I autoland (VPL around 10 meters). Expecting the need
to coast for more than 2 hours would be an nuclear war or extreme
military jam requirement, not a civilian need.

The most exciting aspect is this is only the first generation
implementation. There are no competitors yet. 2nd generation should be
here in lets guess 5 yrs. Imagine a CSAC on par with current Rb atomic
clock for short term stability ! This not only helps with GNSS
applications, but also helps every radio transmitter/receiver, 4g/
WiMax cell towers, ultra high speed laser transceivers, the list goes
on and on. CSACs will directly replace current 10 MHz GNSS based
frequency standards, used on any serious data communication/telecom
environment, even small rural ISPs are more and more using WiMax or
high end WiFi towers that require a more accurate frequency standard
than a quartz oscillator. 5g cell systems might use upcoming 100 MHz
atomic clock frequency standard to improve current RF performance by a
mile.

Marcelo Pacheco