Re: [time-nuts] Speaking of Costas loops (WAAS)
On Wed, Jul 10, 2013 at 07:40:50PM -0400, David I. Emery wrote:
But if the satellite radiates what a local GPS package would and
transmits ephmerides defining its position and motion it could be
included in a GPS solution and could be used for timing and frequency
purposes the same as any other GPS satellite subject to whatever degree
of relative accuracy the bent pipe clock obtains and the degree to which
the ephemerides in the format transmitted allow an accurate position to
be determined.
And from what I have read it seems very likely the WAAS birds
meet these criteria..
Thinking some more about the bent pipe repeater aspect of
WAAS, aside from allowing any kind of WAAS like signal someone might
invent in the future to be retrofitted to existing satellites without
a long replacement cycle and expensive launches being involved - there
are some interesting properties of the design.
One is that one COULD bury in the WAAS uplink cryptographic
(eg essentially random to users not in possession of the key) spreading
sequence transmissions that would be radiated globally and could be
received with "unique" GPS hardware... such a covert channel in civilian
GPS could have various purposes... and would look rather noise like
to the rest of the world.
--
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."
Hi
If there are no receivers using the service (WAAS as a full GPS sat), it's either because:
- Nobody knows about it
- It does not work
Either way why spend the money to keep it running much better than needed for WAAS simply for it to be there unused?
Bob
On Jul 10, 2013, at 8:14 PM, Magnus Danielson magnus@rubidium.dyndns.org wrote:
On 07/11/2013 01:45 AM, Bob Camp wrote:
Hi
If the WAAS birds are run in a fashion that gives a true GPS payload performance, why not assign them a SN 32 or below and use them?
If the WAAS birds are not in the "right numbers", why bother to set them up and spend the bucks to make them behave like a nav sat? What's the payoff?
In the old days (receiver channels are sparse resource):
If you devote a receiver channel to receive it, let it contribute to position while it provides the core corrections.
In todays world:
Channels and GPS birds are many, WAAS only contribute to precision and validation.
This assuming relatively normal commodity receivers.
The fancy receivers (double-frequency, full-blown carrier-phase pseudo-ranges) had little extra use of the WAAS, except possibly somewhat quicker lock-in if not being fed from a national reference grid.
Cheers,
Magnus
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Hi
I read the patent and understand how you can get timing off of a WAAS sat. The carrier does not need to have fancy steering on it to enable that function. The thing that it does not show is doing carrier phase off of a WAAS sat.
Bob
On Jul 10, 2013, at 9:54 PM, David I. Emery die@dieconsulting.com wrote:
On Wed, Jul 10, 2013 at 07:45:39PM -0400, Bob Camp wrote:
Hi
If the WAAS birds are run in a fashion that gives a true GPS payload performance, why not assign them a SN 32 or below and use them?
If the WAAS birds are not in the "right numbers", why bother to set them up and spend the bucks to make them behave like a nav sat? What's the payoff?
The patent cited here recently explains... for fixed timing
purposes and basic anti jam a simple directional antenna pointed at the
WAAS bird allows rejection of many interferers without elaborate and
expensive active steered phased array nulling technology.
And because - given a known fixed ground position - timing and
frequency can work with only one bird visible, this allows
timing/frequency using just the WAAS signal (or signals, they do provide
more than one WAAS frequency).
And potentially if the timing accuracy via the hosted payload is
respectable at least for the needs of many fixed time/frequency users
this might supply a solution MUCH less resistant to local (nearby)
interferers than the usual more or less hemi pattern GPS antenna would -
as fixed dishes with considerable gain toward the satellite could be
used and in most places they would point well above the horizon and
could be shielded by nearby structures to further reduce jamming
susceptibility from jammers (intentional or unintentional) below or at
the horizon for the site. For timing/frequency users (certainly an
important subset of the GPS user population) this provides some
protection by antenna pattern that is hard to obtain otherwise (and
users interested in higher precision or redundancy of timing could still
just use another GPS timing system based on normal hemi GPS antennas as
the primary - using the normal SVs - and rely on the dedicated dish
pointed at the WAAS bird only as backup in the event of jamming).
The choice of using different spreading codes from the normal
GPS set for WAAS or using a slightly different one is an overall system
architecture decision... which I guess was made in favor of not tying
up codes for regular SVs for the WAAS birds. But AFAIK a receiver with
suitable firmware could still extract pseudo ranges and use them.
I guess there is an issue in any frequency translation scheme
with the relationship of carrier and code phase... a homodyne
distortion... due to the random phase of the LO(s)... but this too can
be predistorted on the ground to come out right and that kept in line
via closed loop tracking of the downlink from a ground site.
I do understand that this insight into a potential further use
of WAAS beyond its use as a data channel and propagation beacon seems
to have happened later and not initially.
--
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."
time-nuts mailing list -- time-nuts@febo.com
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and follow the instructions there.
Hi
The pseudo random spreading / looks like noise / buried signal thing is the most common way people piggyback low level signals on a bent pipe.
Bob
On Jul 11, 2013, at 12:00 AM, David I. Emery die@dieconsulting.com wrote:
On Wed, Jul 10, 2013 at 07:40:50PM -0400, David I. Emery wrote:
But if the satellite radiates what a local GPS package would and
transmits ephmerides defining its position and motion it could be
included in a GPS solution and could be used for timing and frequency
purposes the same as any other GPS satellite subject to whatever degree
of relative accuracy the bent pipe clock obtains and the degree to which
the ephemerides in the format transmitted allow an accurate position to
be determined.
And from what I have read it seems very likely the WAAS birds
meet these criteria..
Thinking some more about the bent pipe repeater aspect of
WAAS, aside from allowing any kind of WAAS like signal someone might
invent in the future to be retrofitted to existing satellites without
a long replacement cycle and expensive launches being involved - there
are some interesting properties of the design.
One is that one COULD bury in the WAAS uplink cryptographic
(eg essentially random to users not in possession of the key) spreading
sequence transmissions that would be radiated globally and could be
received with "unique" GPS hardware... such a covert channel in civilian
GPS could have various purposes... and would look rather noise like
to the rest of the world.
--
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."
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,
On 07/11/2013 12:32 PM, Bob Camp wrote:
Hi
If there are no receivers using the service (WAAS as a full GPS sat), it's either because:
- Nobody knows about it
- It does not work
Either way why spend the money to keep it running much better than needed for WAAS simply for it to be there unused?
There are receivers that produce pseudo-ranges for it [1], and hence can
use it in nav solutions. I just found a list of such receivers. The
typical receivers does not discloses exactly how they use the
WAAS/EGNOS/SBAS signal beyond the obvious correction data.
There is also published works on using the WAAS and EGNOS carrier phase
reception [2]. There is more if you dig around.
[1] Egnos User Guide.
http://ec.europa.eu/enterprise/policies/satnav/egnos/files/brochures-leaflets/egnos-user-guide_en.pdf
[2] US 6469663. http://www.google.com/patents/US6469663
Cheers,
Magnus
On 7/11/13 3:36 AM, Bob Camp wrote:
Hi
The pseudo random spreading / looks like noise / buried signal thing is the most common way people piggyback low level signals on a bent pipe.
Assuming that the bent pipe isn't running saturated, which I'm not sure
is a valid assumption. Running TWTAs with enough backoff to be
linear(ish) consumes a lot more power.
I think that most of the transponders on commercial comsats are running
linear (or linearized) at least for C and Ku band type applications.
However, I wouldn't be so sure for more specialized applications.
Consider the S-band Sirius/XM system, they basically designed the
satellites for that service, and it could be run saturated, carrying a
single high rate data stream that the single channel ground receiver in
the car looks at.
In fact, a bit of wikipedia research shows that each of the two Sirius
satellite broadcasts only one carrier with 4 MHz bandwidth (different
frequencies for different satellites). The receiver does both, to get
diversity. XM uses 6 frequencies, in a similar scheme.
i did find a block diagram of the Sirius payload using google in a book
by Elbert (p 267), and while they use a huge pile of TWTAs all combined
to radiate about a kilowatt, it does look like they're running two
carriers through them (2322.1 and 2330.4 MHz) so they must be running at
least somewhat linear.
Sirius is S band, but there are also L-band DARS services in other parts
of the world. I recall seeing some of the TWTAs for these things in a
display case at the tube mfr (Thales, these days) in Ulm, and they are
huge beasts. (I'm used to seeing the little helix X, Ku or Ka-band tubes
we use for deep space comm or earth observing radar. A dual 300 Watt
L-band cavity coupled TWTA is physically quite large.)
This doesn't really answer the question about what the payload for
WAAS/EGNOS looks like, though.
Hi
From the US patent:
"... and possibility of extending the operating range by allowing increased
separation of reference and base receivers by incorporating ionospheric
models provided by WAAS"
To me that says - position data from WAAS, carrier from GPS.
I have not seen a receiver that produces pseudo range for WAAS (as opposed
to EGNOS).
Bob
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Magnus Danielson
Sent: Thursday, July 11, 2013 9:25 AM
To: time-nuts@febo.com
Subject: Re: [time-nuts] Speaking of Costas loops (WAAS)
Hi Bob,
On 07/11/2013 12:32 PM, Bob Camp wrote:
Hi
If there are no receivers using the service (WAAS as a full GPS sat), it's
either because:
- Nobody knows about it
- It does not work
Either way why spend the money to keep it running much better than needed
for WAAS simply for it to be there unused?
There are receivers that produce pseudo-ranges for it [1], and hence can
use it in nav solutions. I just found a list of such receivers. The
typical receivers does not discloses exactly how they use the
WAAS/EGNOS/SBAS signal beyond the obvious correction data.
There is also published works on using the WAAS and EGNOS carrier phase
reception [2]. There is more if you dig around.
[1] Egnos User Guide.
http://ec.europa.eu/enterprise/policies/satnav/egnos/files/brochures-leaflet
s/egnos-user-guide_en.pdf
[2] US 6469663. http://www.google.com/patents/US6469663
Cheers,
Magnus
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
Having seen the number of signals being piggybacked on some transponders (>
100,000) it's safe to say that those transponders were not running
saturated.
Bob
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Jim Lux
Sent: Thursday, July 11, 2013 10:56 AM
To: time-nuts@febo.com
Subject: Re: [time-nuts] Speaking of Costas loops (WAAS)
On 7/11/13 3:36 AM, Bob Camp wrote:
Hi
The pseudo random spreading / looks like noise / buried signal thing is
the most common way people piggyback low level signals on a bent pipe.
Assuming that the bent pipe isn't running saturated, which I'm not sure
is a valid assumption. Running TWTAs with enough backoff to be
linear(ish) consumes a lot more power.
I think that most of the transponders on commercial comsats are running
linear (or linearized) at least for C and Ku band type applications.
However, I wouldn't be so sure for more specialized applications.
Consider the S-band Sirius/XM system, they basically designed the
satellites for that service, and it could be run saturated, carrying a
single high rate data stream that the single channel ground receiver in
the car looks at.
In fact, a bit of wikipedia research shows that each of the two Sirius
satellite broadcasts only one carrier with 4 MHz bandwidth (different
frequencies for different satellites). The receiver does both, to get
diversity. XM uses 6 frequencies, in a similar scheme.
i did find a block diagram of the Sirius payload using google in a book
by Elbert (p 267), and while they use a huge pile of TWTAs all combined
to radiate about a kilowatt, it does look like they're running two
carriers through them (2322.1 and 2330.4 MHz) so they must be running at
least somewhat linear.
Sirius is S band, but there are also L-band DARS services in other parts
of the world. I recall seeing some of the TWTAs for these things in a
display case at the tube mfr (Thales, these days) in Ulm, and they are
huge beasts. (I'm used to seeing the little helix X, Ku or Ka-band tubes
we use for deep space comm or earth observing radar. A dual 300 Watt
L-band cavity coupled TWTA is physically quite large.)
This doesn't really answer the question about what the payload for
WAAS/EGNOS looks like, though.
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
From the US patent:
"... and possibility of extending the operating range by allowing increased
separation of reference and base receivers by incorporating ionospheric
models provided by WAAS"
To me that says - position data from WAAS, carrier from GPS.
I had understood that WAAS provided data such as what were dead or
problematic satellites, and ionospheric data which allows the positions
derived from standard GPS satellites to be more accurately determined
through extra corrections, but WAAS satellite transmissions did not of
themselves contribute to to a position determination. Was I wrong in this,
or perhaps outdated?
Cheers,
David
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
On 10 Jul, 2013, at 14:08 , David I. Emery die@dieconsulting.com wrote:
It seems completely inconceivable to me that either the antenna
system (particularly feeds) or transponder RF hardware on any commercial
Ku or C or Ka or X band satellite could possibly be frequency agile
enough to tune to 1575.42 MHz unless it was purpose designed to radiate
on that frequency from the start.
So any hosted WAAS payload is completely application specific.
If you look at the pictures here
http://www.orbital.com/NewsInfo/Publications/Galaxy_Fact.pdf
the satellite on the right has things sticking out the bottom, in the
back corner, that are missing on the others and that look a lot like
the antennas on GPS satellites. The WAAS satellite is also 350 pounds
heavier than the other two even though the C-band payload is identical
on all three, so it seems like there could be a fair amount of extra
stuff added for WAAS support.
Dennis Ferguson