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

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