PRN133 ranging now useable for SoL, at non precision approach level

On 2011-11-01 02:34 , macpacheco wrote:
On Oct 31, 11:56 am, Alan
wrote:
On 2011-10-30 20:08 , HIPAR wrote:

On Oct 30, 4:44 pm, wrote:

NASA JPL operates a Global Differential GPS system with worldwide
coverage. They claim 10cm performance.

http://www.gdgps.net/

'The NASA Global Differential GPS (GDGPS) System is a complete, highly
accurate, and extremely robust real-time GPS monitoring and
augmentation system'.

I believe the John Deere Starfire commercial service is based upon the
NASA system.

Why can't airplanes use it ?

First off it's proprietary - something WAAS/EGNOS avoid. Airlines are
loathe to add equipment and pay operating fees for it. (Not to mention
that JD would have to build (or have an avionics firm design, build and
certify) airborne Starfire receivers.

Secondly, Starfire receivers are L1+L2. More expensive than L1
receivers. L1+L2(codeless) phase comparisons provide for a lot of local
PR correction due to ionospheric delays. The data downloaded by
Starfire is thus limited to non-iono effects (ephemeris error, clock error).

So, an aviation certified L1/L2 antenna would be needed as well (I don't
know if any exist but surely a military antenna could be put through the
paces for DO-160D and whichever TSO applies to GPS antennas,
appropriately modified to cover L2 reception).

It doesn't provide (I assume) integrity signals - though likely it could
with little additional effort.

Aparently Starfire also uses the WAAS ephemeris/clock data even if it is
not as accurate as Starfire's own eph/clk data.

Finally, there may be various forms of liability issues both on the part
of JD and the national airspace services.

--
gmail originated posts filtered due to spam.

L2 isn't ARNS protected, so they are forbidden for aviation SBAS
receivers.

I was just answering HIPAR's general question. The same list applies to
L5 use as well. Of course L5 birds are rare so it will be a long time
before there are enough for actual aviation use.

The only means for IONO corrections on SBAS receivers will be with L1/
L5, both in ARNS protected band, hence the importance of GPS L5
becoming operational for dual frequency SBAS (we might get Galileo
operational prior to GPS L5, and use Galileo dual frequency + GPS
single frequency for EGNOS).

L5 isn't exactly usable yet with all of 2 sats in orbit. Will be a long
wait before any advance with any system. For simplicity sake (a good
thing in avionics) mixing GPS with EGNOS in a system won't be seen in
avionics for quite a while yet.

--
gmail originated posts filtered due to spam.

On 2011-11-01 09:25 , Alan Browne wrote:
On 2011-11-01 02:34 , macpacheco wrote:
On Oct 31, 11:56 am, Alan
wrote:
On 2011-10-30 20:08 , HIPAR wrote:

On Oct 30, 4:44 pm, wrote:

NASA JPL operates a Global Differential GPS system with worldwide
coverage. They claim 10cm performance.

http://www.gdgps.net/

'The NASA Global Differential GPS (GDGPS) System is a complete, highly
accurate, and extremely robust real-time GPS monitoring and
augmentation system'.

I believe the John Deere Starfire commercial service is based upon the
NASA system.

Why can't airplanes use it ?

First off it's proprietary - something WAAS/EGNOS avoid. Airlines are
loathe to add equipment and pay operating fees for it. (Not to mention
that JD would have to build (or have an avionics firm design, build and
certify) airborne Starfire receivers.

Secondly, Starfire receivers are L1+L2. More expensive than L1
receivers. L1+L2(codeless) phase comparisons provide for a lot of local
PR correction due to ionospheric delays. The data downloaded by
Starfire is thus limited to non-iono effects (ephemeris error, clock
error).

So, an aviation certified L1/L2 antenna would be needed as well (I don't
know if any exist but surely a military antenna could be put through the
paces for DO-160D and whichever TSO applies to GPS antennas,
appropriately modified to cover L2 reception).

It doesn't provide (I assume) integrity signals - though likely it could
with little additional effort.

Aparently Starfire also uses the WAAS ephemeris/clock data even if it is
not as accurate as Starfire's own eph/clk data.

Finally, there may be various forms of liability issues both on the part
of JD and the national airspace services.

--
gmail originated posts filtered due to spam.

L2 isn't ARNS protected, so they are forbidden for aviation SBAS
receivers.

I was just answering HIPAR's general question. The same list applies to
L5 use as well. Of course L5 birds are rare so it will be a long time
before there are enough for actual aviation use.

The only means for IONO corrections on SBAS receivers will be with L1/
L5, both in ARNS protected band, hence the importance of GPS L5
becoming operational for dual frequency SBAS (we might get Galileo
operational prior to GPS L5, and use Galileo dual frequency + GPS
single frequency for EGNOS).

L5 isn't exactly usable yet with all of 2 sats in orbit. Will be a long
wait before any advance with any system. For simplicity sake (a good
thing in avionics) mixing GPS with EGNOS in a system won't be seen in
..............
avionics for quite a while yet.

Sorry - meant to say mixing GPS with Galileo.


--
gmail originated posts filtered due to spam.

On Nov 1, 1:18*pm, Alan Browne
wrote:
On 2011-11-01 09:25 , Alan Browne wrote:







On 2011-11-01 02:34 , macpacheco wrote:
On Oct 31, 11:56 am, Alan
wrote:
On 2011-10-30 20:08 , HIPAR wrote:

On Oct 30, 4:44 pm, wrote:

NASA JPL operates a Global Differential GPS system with worldwide
coverage. They claim 10cm performance.

http://www.gdgps.net/

'The NASA Global Differential GPS (GDGPS) System is a complete, highly
accurate, and extremely robust real-time GPS monitoring and
augmentation system'.

I believe the John Deere Starfire commercial service is based upon the
NASA system.

Why can't airplanes use it ?

First off it's proprietary - something WAAS/EGNOS avoid. Airlines are
loathe to add equipment and pay operating fees for it. (Not to mention
that JD would have to build (or have an avionics firm design, build and
certify) airborne Starfire receivers.

Secondly, Starfire receivers are L1+L2. More expensive than L1
receivers. L1+L2(codeless) phase comparisons provide for a lot of local
PR correction due to ionospheric delays. The data downloaded by
Starfire is thus limited to non-iono effects (ephemeris error, clock
error).

So, an aviation certified L1/L2 antenna would be needed as well (I don't
know if any exist but surely a military antenna could be put through the
paces for DO-160D and whichever TSO applies to GPS antennas,
appropriately modified to cover L2 reception).

It doesn't provide (I assume) integrity signals - though likely it could
with little additional effort.

Aparently Starfire also uses the WAAS ephemeris/clock data even if it is
not as accurate as Starfire's own eph/clk data.

Finally, there may be various forms of liability issues both on the part
of JD and the national airspace services.

--
gmail originated posts filtered due to spam.

L2 isn't ARNS protected, so they are forbidden for aviation SBAS
receivers.

I was just answering HIPAR's general question. The same list applies to
L5 use as well. Of course L5 birds are rare so it will be a long time
before there are enough for actual aviation use.

The only means for IONO corrections on SBAS receivers will be with L1/
L5, both in ARNS protected band, hence the importance of GPS L5
becoming operational for dual frequency SBAS (we might get Galileo
operational prior to GPS L5, and use Galileo dual frequency + GPS
single frequency for EGNOS).

L5 isn't exactly usable yet with all of 2 sats in orbit. Will be a long
wait before any advance with any system. For simplicity sake (a good
thing in avionics) mixing GPS with EGNOS in a system won't be seen in

* * * * * * * * * * * * * * *..............

avionics for quite a while yet.

Sorry - meant to say mixing GPS with Galileo.

The FAA stated that GPS L5 WAAS will only be allowed once GPS L5 is
FOC, so 22 GPS launches to go before we get there. This was reiterated
in the current issue of FAA Sat Nav News (issued in the last few
days).

One of the reasons is they will replace the whole thing, all reference
receivers will then work only with L1+L5, all current ground semi
codeless will go at once, so once they migrate to L5 for the ground
infrastructure, even GPS IIR-M will no longer be used for WAAS.

It will be a temporary big step backwards, cause we'll go from using
all operational GPS satellites to using only L5 capable satellites,
reducing from 29-31 operational satellites to 24 initially.

That's stupid in my opinion, but that's their prerogative, they should
include support for L2C for the ground receivers, using L2C for IIR-M
and L5 for IIF + III, that would keep 29+ birds usable at all times.
And Galileo + Glonass should be rolled into WAAS as well.

That's only for aviation, other receivers outside the FAA's authority
could even use semi codeless today with any SBAS.

As far as Galileo or Glonass support for WAAS, theres no word
whatsoever in adding WAAS support for that, but the ARAIM work (which
makes WAAS obsolete) would include multi constellation end user
support.

On Nov 1, 9:25*am, Alan Browne
wrote:

....

L5 isn't exactly usable yet with all of 2 sats in orbit. *Will be a long
wait before any advance with any system. *For simplicity sake (a good
thing in avionics) mixing GPS with EGNOS in a system won't be seen in
avionics for quite a while yet.

--

I couldn't agree more that we need simplicity .. too many
constellations transmitting signals that are compatible only by the
definition of not interfering with each other. My head would be
spinning if I were tasked to perform a trade study defining the next
generation of avionics. But the GNSS community thinks this kind of
diversity is great so those geniuses like Marcelo (just joking) can
sort it out.

Would it have been nice if Galileo L5 and NAVSTAR L5 shared a common
ICD? Would it have been nice if there were a common L1 modernized
signal. That would be 'bound' the problem.

Regarding WDGPS, I really don't understand who actually controls
access to the system. If NASA operates the core system, what kind of
agreement does the US government have with Deere allowing them
exclusive commercial marketing rights under the Starfire trademark?
NASA/JPL doesn't say much about that.

I looked over a few of the easier to read references concerning the
JPL system. This one addresses the expected performance for a GDGPS
corrected C/A code system:

http://www.gdgps.net/system-desc/pap...leFreqCorr.pdf

Receiving L1 only, I'd say it might provide WAAS grade performance.
Getting back to simplicity, the need to receive the corrections from
another satellite system would complicate the actual operations.
Along with the other issues discussed, WAAS remains a more practical
system for airplanes.

--- CHAS

On 2011-11-01 17:47 , HIPAR wrote:
On Nov 1, 9:25 am, Alan
wrote:

...

L5 isn't exactly usable yet with all of 2 sats in orbit. Will be a long
wait before any advance with any system. For simplicity sake (a good
thing in avionics) mixing GPS with EGNOS in a system won't be seen in
avionics for quite a while yet.

--

I couldn't agree more that we need simplicity .. too many
constellations transmitting signals that are compatible only by the
definition of not interfering with each other. My head would be
spinning if I were tasked to perform a trade study defining the next
generation of avionics. But the GNSS community thinks this kind of
diversity is great so those geniuses like Marcelo (just joking) can
sort it out.

Would it have been nice if Galileo L5 and NAVSTAR L5 shared a common
ICD? Would it have been nice if there were a common L1 modernized
signal. That would be 'bound' the problem.

That wouldn't fly far - there are only so many viable gold codes -
though possibly many more on L5 with its longer code length.

Regarding WDGPS, I really don't understand who actually controls
access to the system. If NASA operates the core system, what kind of
agreement does the US government have with Deere allowing them
exclusive commercial marketing rights under the Starfire trademark?
NASA/JPL doesn't say much about that.

No idea. But with the network of ground stations collecting the data
for GDGPS that data can be "sold" to J-D for further use. In that sense
JD depend on the network, but they package the data for Starfire (and to
finer resolution and accuracy than WAAS).

I looked over a few of the easier to read references concerning the
JPL system. This one addresses the expected performance for a GDGPS
corrected C/A code system:

http://www.gdgps.net/system-desc/pap...leFreqCorr.pdf

Receiving L1 only, I'd say it might provide WAAS grade performance.
Getting back to simplicity, the need to receive the corrections from
another satellite system would complicate the actual operations.
Along with the other issues discussed, WAAS remains a more practical
system for airplanes.

But EGNOS provides SBAS for both GPS and GLONASS...

--
gmail originated posts filtered due to spam.

On Nov 1, 3:21*pm, Alan Browne
wrote:

That wouldn't fly far - there are only so many viable gold codes -
though possibly many more on L5 with its longer code length.


There are actually around 500 balanced (roughly equal number of 0s and
1s) Gold codes in GPS, if you ignore the 2-tap mechanization shown in
the ICD. The 4-asterisk footnote was added to Tables 3-I and 3-II a
few years ago when the first list of expanded codes was published in
the ICD ( " **** The two-tap coder utilized here is only an example
implementation that generates a limited set of valid C/A codes.").

With zero Doppler difference between two PRNs, any pair of the 500 or
so balanced Gold codes would have the same peak cross-correlations.
The cross-correlation peak comes up a few dB at some Doppler
differences. Gold's 1967 papers showed that the zero-Doppler peak for
a 10-bit code is limited to 20*log(65/1023) of 20*log(63/1023), where
63 and 65 represent the excess of bit by bit agreements over
disagreements (or vice versa) between the two codes at a given time
offset. His papers also showed the probability of occurrence.

The log works out to about -24 dB. But user antenna gain, as well as
differences in satellite power, can bring the peak up more.

The bigger issue is that the broadcast ephemeris doesn't include the
PRN number. It's just assumed by the receiver that it's tracking the
one it wanted. But that's not a deficiency of the Gold codes, nor
really a deficiency of the original signal design, which is quite
elegant -- an awful lot of information packed into very few bits.

All just a quibble -- you're right that the newer signals with longer
codes will work better.

On Nov 1, 7:54*pm, "Ed M." wrote:
On Nov 1, 3:21*pm, Alan Browne
wrote:



That wouldn't fly far - there are only so many viable gold codes -
though possibly many more on L5 with its longer code length.

There are actually around 500 balanced (roughly equal number of 0s and
1s) Gold codes in GPS, if you ignore the 2-tap mechanization shown in
the ICD. *The 4-asterisk footnote was added to Tables 3-I and 3-II a
few years ago when the first list of expanded codes was published in
the ICD ( " **** The two-tap coder utilized here is only an example
implementation that generates a limited set of valid C/A codes.").

With zero Doppler difference between two PRNs, any pair of the 500 or
so balanced Gold codes would have the same peak cross-correlations.
The cross-correlation peak comes up a few dB at some Doppler
differences. *Gold's 1967 papers showed that the zero-Doppler peak for
a 10-bit code is limited to 20*log(65/1023) of 20*log(63/1023), where
63 and 65 represent the excess of bit by bit agreements over
disagreements (or vice versa) between the two codes at a given time
offset. *His papers also showed the probability of occurrence.

The log works out to about -24 dB. *But user antenna gain, as well as
differences in satellite power, can bring the peak up more.

The bigger issue is that the broadcast ephemeris doesn't include the
PRN number. *It's just assumed by the receiver that it's tracking the
one it wanted. *But that's not a deficiency of the Gold codes, nor
really a deficiency of the original signal design, which is quite
elegant -- an awful lot of information packed into very few bits.

All just a quibble -- you're right that the newer signals with longer
codes will work better.


I suppose if cross correlation becomes a problem, it can be mitigated
by placing the conflicting satellites in antipodal positions.


Current L5 PRN assignments:

http://www.losangeles.af.mil/shared/...070530-041.pdf

And L1 C/A:

http://www.losangeles.af.mil/shared/...101124-042.pdf

Of course, 'modernized signal' would be the operative concept for a
universal open L1 signal conforming with a common ICD. Shame it will
never happen.

It's a 'minor miracle' that SBAS has been standardized.

http://www.elisanet.fi/master.naviga...S_Coverage.jpg

--- CHAS

On Nov 1, 10:58*pm, HIPAR wrote:
On Nov 1, 7:54*pm, "Ed M." wrote:









On Nov 1, 3:21*pm, Alan Browne
wrote:

That wouldn't fly far - there are only so many viable gold codes -
though possibly many more on L5 with its longer code length.

There are actually around 500 balanced (roughly equal number of 0s and
1s) Gold codes in GPS, if you ignore the 2-tap mechanization shown in
the ICD. *The 4-asterisk footnote was added to Tables 3-I and 3-II a
few years ago when the first list of expanded codes was published in
the ICD ( " **** The two-tap coder utilized here is only an example
implementation that generates a limited set of valid C/A codes.").

With zero Doppler difference between two PRNs, any pair of the 500 or
so balanced Gold codes would have the same peak cross-correlations.
The cross-correlation peak comes up a few dB at some Doppler
differences. *Gold's 1967 papers showed that the zero-Doppler peak for
a 10-bit code is limited to 20*log(65/1023) of 20*log(63/1023), where
63 and 65 represent the excess of bit by bit agreements over
disagreements (or vice versa) between the two codes at a given time
offset. *His papers also showed the probability of occurrence.

The log works out to about -24 dB. *But user antenna gain, as well as
differences in satellite power, can bring the peak up more.

The bigger issue is that the broadcast ephemeris doesn't include the
PRN number. *It's just assumed by the receiver that it's tracking the
one it wanted. *But that's not a deficiency of the Gold codes, nor
really a deficiency of the original signal design, which is quite
elegant -- an awful lot of information packed into very few bits.

All just a quibble -- you're right that the newer signals with longer
codes will work better.

I suppose if cross correlation becomes a problem, it can be mitigated
by placing the conflicting satellites in antipodal positions.

Current L5 PRN assignments:

http://www.losangeles.af.mil/shared/...070530-041.pdf

And L1 C/A:

http://www.losangeles.af.mil/shared/...101124-042.pdf

Of course, *'modernized signal' would be the operative concept for a
universal open L1 signal conforming with a common ICD. *Shame it will
never happen.

It's a 'minor miracle' that SBAS has been standardized.

http://www.elisanet.fi/master.naviga...S_Coverage.jpg

--- *CHAS

One interesting question, military and L5 signals both use a 10 mega
chip/sec signal, clearly better for jamming tolerance and ability to
acquire a signal under challenging conditions, but does 50 10 mega
chip/sec signals being received at the same band perform better than
50 1 mega chip/sec signals ?

As far as the common ICD, I believe this will take 20-30 years, and
will happen when L1 C/A gets retired and replaced by a brand new
signal, perhaps a 10 mega chip/sec signal, broadcast by all GPS
satellites (one can hope...).

Also there has been talk about a signal in the 5GHz band, maybe one
day we could have a sane, normalized signal there too. A 5GHz signal
would improve IONO corrections hugely, due to the multi GHz jump in
frequency.

SBAS has a common ICD due to FAA having no proprietary interest in the
signal, quite on the opposite, by making SBAS signal structure a
worldwide standard benefits the early manufacturers (Americans) to
come to market, and due to the obvious requirement that an American
aircraft needs to be able to fly elsewhere in the world and use the
other SBAS systems, much like ILS/VOR/NDB/DME allow that today and
vice-versa. The requirements for revision control, documentation and
testing of software onboard aircraft navigation systems is 100%
assinine and extremely expensive. Talk about burying yourself in
paperwork.

But are the ICD differences between GPS/Galileo and QZSS that big ? It
seems to me that the differences are 100% software stuff, nothing to
do with acquiring and tracking the signal, just in the higher level
functions, like a few ifs in the higher level software of a receiver.
I have not read those ICDs, I'm really asking.

Marcelo Pacheco

On 2011-11-01 19:54 , Ed M. wrote:
On Nov 1, 3:21 pm, Alan
wrote:

That wouldn't fly far - there are only so many viable gold codes -
though possibly many more on L5 with its longer code length.


There are actually around 500 balanced (roughly equal number of 0s and

To avoid x-correlation there are only 35 or so. Don't recall the
correct number.

--
gmail originated posts filtered due to spam.

Alan Browne wrote:
On 2011-11-01 19:54 , Ed M. wrote:
On Nov 1, 3:21 pm, Alan
wrote:

That wouldn't fly far - there are only so many viable gold codes -
though possibly many more on L5 with its longer code length.


There are actually around 500 balanced (roughly equal number of 0s and

To avoid x-correlation there are only 35 or so. Don't recall the correct
number.

I have read a white paper which stated that the number of available Gold
codes was (afair) in the 60-70 range.

For randomly generated 1023-bit codes we should expect collisions around
32 (sqrt(1024)), but since the codes can be selected by hand, they can
get away with approximately twice as many without having problems with
cross-correlation, with or without doppler corrections.

Several people have noted that you could theoretically get twice as many
sats if you set them up in pairs on opposite side of the globe, but
since there's no explicit sat nr in the transmitted msg, this won't work
with any currently deployed gps receivers.

(In theory, as long as the pairs were not exactly opposite, you should
be able to determine which hemisphere was the correct one by looking at
the residual errors for each of them?)

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