He's Off-The Race is on

The thing is, they're all different. Every new phone is maybe 90% same
hardware, different case, modified software, added features. They're geared
up to make variants, as a business model.

Surely it's just encryption? A bit of processing to clean up the end of the
signal? And the people with the ability to modify the consumer design
probably know more about implementing that sort of thing than the military
do.

 

Using the patented Mavis Beacon "Hunt&Peck" Technique, Jim

I can't help feeling you're both missing the point here. If the consumer
units were 'good enough' for use by the forces, then there's really no
need for the hugely expensive enhanced stuff, is there?

 

No, the Military and Civil GPS services use different frequencies.
The Military channel uses a 10 Mbps bitrate to give a 3m basic accuracy [1]
rather than the civil 1 Mbps which gives 30m.
The crypto on the civil channel is trivial whereas the Military codes are
VERY secure and highly classified.
The Military codes are only required for precision weapons delivery, not
for general navigation.

Chalk and cheese.

[1] 3m is equivalent to a single bit time at 10 Mbps, any larger error
causes loss of sync. Sync accuracy is always much better than this,
actual positional accuracy is limited by other factors.

 

Only if the consumer units are rugged enough and squaddieproof enough
to stand any chance of survival in reality. Given the rate at which
military grade equipment gets wrecked this is never going to be practical.

 

I'm assuming from the poster that the info provided is all wrong, but
I suppose there's always a first time...

--
_______
..'_/_|_\_'. Ace (b.rogers at ifrance.com)
\`\ | /`/
`\\ | //' BOTAFOT#3, SbS#2, UKRMMA#13, DFV#8, SKA#2, IBB#10
`\|/`
`

 

fucking moaned...>

Isn't the answer obvious?

Make all the GPS/radio operator squaddies women.

Because they're not so violent as men they equipment will last forever.
So long as the GPS is build to operate upside down all the time...

 

Indeed, Selective Availability was a deliberate degradation to the civil
channel. This was intended to ensure that it could not be used for
non-precision weapons delivery. Modern terrain following and inertial
reference systems are more accurate than the degraded civil channel so
the degradation became irrelevant.

 

Check the facts, I worked on the early GPS systems. All interesting stuff.

 

Hmm. Mobile technology relies on radios talking to base stations, so
the protocols that were developed for such a network, which is a
pretty large part of it, would have to be modifed for battlefield
conditions where radios would have to be able to talk to each other
instead and over a few km, though one could use a multi-path sytem to
spread the comms load or work around dead areas. You'd still have the
noise-cancelling & voice compression technology and I guess some of
the actual radio technology would be reusable but it would probably
have to be higher-powered.

 

Indeed, but I did not consider it necessary to go into a long screed
to answer the original question. How much detail do you want ?.

 

Perhaps you misunderstand me. The bit rate determines the fundamental
accuracy. It is not possible to synchronise a code division multiplex
if the timing error exceeds the bit lenth. A good correlator should
maintain lock to better than 1/10 of the bit lenth. Hence the deliberate
introduction of jitter to the civil signal (AKA selective availability)
limits the acheivable accuracy.

I refer you to Bart Batson's original works on which the system was
based. Whilst there have been considerable improvements in signal
processing [1] since the mid 1970s the basic design is unchanged.

The best case accuracy for the civil channel is limited by the single
frequency. The use of 2 frequencies for the military signal allows
the variation in velocity of propagation [2] to be calculated and
corrected for.

[1] Improved computing power allows such things as improving accuracy
by averaging. None of this was practical when I worked on the design
of early receivers in the late 1970s so they were horribly simplistic
when compared to modern practice.
[2] Contrary to common belief radio signals do not travel at the speed
of light because the atmosphere is not a vacuum. The actual velocity
is weather dependant, the primary factor being moisture content.
The difference is small but rather important for precision weapons.

 

'Mark Olson' wrote...>

Ok, I'm thinking of a number from one to ten.

What is it?

 

But *someone* has to be *the* expert, surely?

 

There's this bloke called Godel on the phone, wants a word.

 

Tell him I'll call him back. What's his number?

 

Which makes no difference to my point.
Either you sync to within the 1 microsecond bit time of the civil signal
and get the possibility of 30m accuracy or you do not sync and get
bugger all.
You can do a lot better with modern signal processing or you can do
a lot worse if they bring back the deliberate jitter. The basic accuracy
is still determined by the bit rate.

 

It's a bit complicated...

 

I thought I had it but my address book is incomplete.

 

I thought I had it in my book of all my address books, but then I
wondered if it was in my book of address books that don't contain
address books.

 

OK, you win.