A Sky, cable and digital tv forum. Digital TV Banter

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » Digital TV Banter forum » Digital TV Newsgroups » uk.tech.digital-tv (Digital TV - General)
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

uk.tech.digital-tv (Digital TV - General) (uk.tech.digital-tv) Discussion of all matters technical in origin related to the reception of digital television transmissions, be they via satellite, terrestrial or cable. Advertising is forbidden, with no exceptions.

Galileo ever come on stream?



 
 
Thread Tools Display Modes
  #21  
Old February 21st 18, 12:59 PM posted to uk.tech.digital-tv
tim...[_2_]
external usenet poster
 
Posts: 619
Default Galileo ever come on stream?



"NY" wrote in message
...
"Unsteadyken" wrote in message
T...
In article ,
says...
Originally GPS had clear acquisition (good for CEP of 50 - 100m) and
what
was called p-code (good for CEP of 5 - 10m) only available to military

types. Fortunately for all of us on 1st May 2000 William Jefferson
Clinton made it public domain see: -
http://www.presidency.ucsb.edu/ws/?pid=58423

In 1990, using an aircraft GPS unit fitted in a taxi, the accuracy was
sufficient to show which side of the road or lane of a motorway the cab
was driving on, even tracking them accurately round roundabouts.
Plenty good enough for civilian use.


If clear acquisition had an error of 50-100 m before 2000, that suggests
that the 1990 aircraft GPS in the taxi could see p-code if it had
sufficient accuracy to distinguish one lane or side of the road from the
other - ie that it was military spec. Mind you, if you average enough
readings to eliminate noise, you can probably get a position which is
known to much better than 50-100 m.

I presume Bill Clinton's decree made p-code available to all.


no

He (!) simply turned off the insertion of the random error.

All GPS receivers gave correct results the day after it was done with no
update to their hardware/software

tim





Ads
  #22  
Old February 21st 18, 01:02 PM posted to uk.tech.digital-tv
tim...[_2_]
external usenet poster
 
Posts: 619
Default Galileo ever come on stream?



"NY" wrote in message
o.uk...
"R. Mark Clayton" wrote in message
...
2. Assisted GPS. Current almanac can be downloaded in seconds from the
web, instead of waiting up to 25 minutes for it to arrive directly from
the satellite(s). This means location can be quickly established on
start up.


A-GPS is a really godsend when trying to get a GPS fix when a receiver's
GPS has been switched off (to save battery power) and if the receiver has
been moved during the off-time. On my Android phone I use an app called
GPS Status (by MobiWIA) which can use wifi or mobile phone internet to get
the almanac.

How large is the almanac? Why is it transmitted so infrequently, given the
worldwide problem of switching a GPS receiver off and on, rather than
leaving it on all the time and thus draining the battery?


It's not transmitted "infrequently"

it's transmitted slowly

It's a very large amount of data, but as it isn't primary data has to fit in
the gaps between the location data. And at a resultant 1 bit per second (or
whatever) takes ages for you to accumulate the complete set

tim



  #23  
Old February 21st 18, 02:36 PM posted to uk.tech.digital-tv
NY
external usenet poster
 
Posts: 1,329
Default Galileo ever come on stream?

"tim..." wrote in message
news


"NY" wrote in message
...
"Unsteadyken" wrote in message
T...
In article ,
says...
Originally GPS had clear acquisition (good for CEP of 50 - 100m) and
what
was called p-code (good for CEP of 5 - 10m) only available to military
types. Fortunately for all of us on 1st May 2000 William Jefferson
Clinton made it public domain see: -
http://www.presidency.ucsb.edu/ws/?pid=58423

In 1990, using an aircraft GPS unit fitted in a taxi, the accuracy was
sufficient to show which side of the road or lane of a motorway the cab
was driving on, even tracking them accurately round roundabouts.
Plenty good enough for civilian use.


If clear acquisition had an error of 50-100 m before 2000, that suggests
that the 1990 aircraft GPS in the taxi could see p-code if it had
sufficient accuracy to distinguish one lane or side of the road from the
other - ie that it was military spec. Mind you, if you average enough
readings to eliminate noise, you can probably get a position which is
known to much better than 50-100 m.

I presume Bill Clinton's decree made p-code available to all.


no

He (!) simply turned off the insertion of the random error.

All GPS receivers gave correct results the day after it was done with no
update to their hardware/software



Ah, so the civilian signal was simply a full-precision signal with a random
value added to it? I'd thought that it was a value that was truncated by
masking off the more precise bits.

  #24  
Old February 21st 18, 02:59 PM posted to uk.tech.digital-tv
NY
external usenet poster
 
Posts: 1,329
Default Galileo ever come on stream?

"tim..." wrote in message
news


"NY" wrote in message
o.uk...
"R. Mark Clayton" wrote in message
...
2. Assisted GPS. Current almanac can be downloaded in seconds from the
web, instead of waiting up to 25 minutes for it to arrive directly from
the satellite(s). This means location can be quickly established on
start up.


A-GPS is a really godsend when trying to get a GPS fix when a receiver's
GPS has been switched off (to save battery power) and if the receiver has
been moved during the off-time. On my Android phone I use an app called
GPS Status (by MobiWIA) which can use wifi or mobile phone internet to
get the almanac.

How large is the almanac? Why is it transmitted so infrequently, given
the worldwide problem of switching a GPS receiver off and on, rather than
leaving it on all the time and thus draining the battery?


It's not transmitted "infrequently"

it's transmitted slowly

It's a very large amount of data, but as it isn't primary data has to fit
in the gaps between the location data. And at a resultant 1 bit per
second (or whatever) takes ages for you to accumulate the complete set


I suppose the system was designed on the assumption that GPS receivers would
be left switched on all the time and so didn't need fast start-up from a
clear-memory state.

https://en.wikipedia.org/wiki/GPS_signals (section Navigation Message) says
"Subframes 4 and 5 contain components of the almanac but each frame contains
only 1/25th of the complete almanac; a receiver must process 25 whole frames
worth of data to retrieve the entire 15,000 bit almanac message. At this
rate, 12.5 minutes are required to receive the entire almanac from a single
satellite."

So that's a bit rate of 15000 / (12.5*60) = 20 bits/second.

I presume different satellites transmit different sections of the almanac at
different times (rather than all transmitting the same part of the table
simultaneously) so if you can see many satellites you can receive the
almanac much more quickly than 12.5 minutes.

At least as long as you are in receiving range of mobile-phone internet,
getting A-GPS is not a problem. The problem is if you are at sea (eg on a
cruise) and are out of range of land-based mobile phone signals and are too
stingy to pay for the rip-off satellite internet on the ship.

  #25  
Old February 21st 18, 06:17 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
external usenet poster
 
Posts: 2,448
Default Galileo ever come on stream?

On 21/02/2018 09:33, tim... wrote:

Encryption on the more accurate service - cf eg Sky's charges for TV
packages.


So they can charge you for the "technology" in a chip that decrypts it

but how can they do that on anything other than a "one time fee" model.


Individually addressable receivers, same as Sky

Bill
  #26  
Old February 21st 18, 06:38 PM posted to uk.tech.digital-tv
R. Mark Clayton[_2_]
external usenet poster
 
Posts: 649
Default Galileo ever come on stream?

On Wednesday, 21 February 2018 12:26:48 UTC, NY wrote:
"Unsteadyken" wrote in message
T...
In article ,
says...
Originally GPS had clear acquisition (good for CEP of 50 - 100m) and what
was called p-code (good for CEP of 5 - 10m) only available to military

types. Fortunately for all of us on 1st May 2000 William Jefferson
Clinton made it public domain see: -
http://www.presidency.ucsb.edu/ws/?pid=58423

In 1990, using an aircraft GPS unit fitted in a taxi, the accuracy was
sufficient to show which side of the road or lane of a motorway the cab
was driving on, even tracking them accurately round roundabouts.
Plenty good enough for civilian use.


If clear acquisition had an error of 50-100 m before 2000, that suggests
that the 1990 aircraft GPS in the taxi could see p-code if it had sufficient
accuracy to distinguish one lane or side of the road from the other - ie
that it was military spec. Mind you, if you average enough readings to
eliminate noise, you can probably get a position which is known to much
better than 50-100 m.


There was another problem the full constellation was not available until December 1993, so you accuracy would fall off at certain times, when not enough satellites were in view.

Maybe the taxi was using differential GPS, but I suspect the story is apocryphal. OTOH UK tanks of the time had inertial navigation, which was described to me as "good enough to drive all the way down the M1". Obliviously a tank doesn't need to worry about lane discipline or even going off road occasionaly!

OTOH, my 2009 Nokia N79 could / can tell what lane etc. one was in at roundabouts.


I presume Bill Clinton's decree made p-code available to all.

Currently, inside a stone-walled cottage, I can see 9 satellites and have a
reported error (in GPS Status app) of 25 m. Out in the open, with more
satellites in view, I've had errors of about 5 m.


  #27  
Old February 21st 18, 06:40 PM posted to uk.tech.digital-tv
R. Mark Clayton[_2_]
external usenet poster
 
Posts: 649
Default Galileo ever come on stream?

On Wednesday, 21 February 2018 15:16:50 UTC, tim... wrote:
"NY" wrote in message
...
"Unsteadyken" wrote in message
T...
In article ,
says...
Originally GPS had clear acquisition (good for CEP of 50 - 100m) and
what
was called p-code (good for CEP of 5 - 10m) only available to military
types. Fortunately for all of us on 1st May 2000 William Jefferson
Clinton made it public domain see: -
http://www.presidency.ucsb.edu/ws/?pid=58423

In 1990, using an aircraft GPS unit fitted in a taxi, the accuracy was
sufficient to show which side of the road or lane of a motorway the cab
was driving on, even tracking them accurately round roundabouts.
Plenty good enough for civilian use.


If clear acquisition had an error of 50-100 m before 2000, that suggests
that the 1990 aircraft GPS in the taxi could see p-code if it had
sufficient accuracy to distinguish one lane or side of the road from the
other - ie that it was military spec. Mind you, if you average enough
readings to eliminate noise, you can probably get a position which is
known to much better than 50-100 m.

I presume Bill Clinton's decree made p-code available to all.


no

He (!) simply turned off the insertion of the random error.


I did know that, but had forgotten.


All GPS receivers gave correct results the day after it was done with no
update to their hardware/software


I didn't know that, I thought my 2000 car was one of the first to be able to use it. What it does do is use the ABS sensors to do some sort of dead reckoning on movement and orientation / turning.


tim


  #28  
Old February 21st 18, 06:47 PM posted to uk.tech.digital-tv
R. Mark Clayton[_2_]
external usenet poster
 
Posts: 649
Default Galileo ever come on stream?

On Wednesday, 21 February 2018 11:19:49 UTC, NY wrote:
"R. Mark Clayton" wrote in message
...
2. Assisted GPS. Current almanac can be downloaded in seconds from the
web, instead of waiting up to 25 minutes for it to arrive directly from
the satellite(s). This means location can be quickly established on start
up.


A-GPS is a really godsend when trying to get a GPS fix when a receiver's GPS
has been switched off (to save battery power) and if the receiver has been
moved during the off-time. On my Android phone I use an app called GPS
Status (by MobiWIA) which can use wifi or mobile phone internet to get the
almanac.


Indeed - e.g. after a flight (for a phone) or a trip in a ferry (for a car).


How large is the almanac? Why is it transmitted so infrequently, given the
worldwide problem of switching a GPS receiver off and on, rather than
leaving it on all the time and thus draining the battery?


It is not very big, but the data rate from the GPS satellites is pitifully slow at 50bps, so it takes around 25 minutes to download.

Most receivers make the reasonable assumption on start up that they are still where they were last switched off and the last almanac (last a week) still current.


GPS position errors are weird. I can understand that a small number of
satellites in view, maybe with multipath reflections, can cause random
errors in readings. But what causes systematic errors such that maybe
several minutes of readings are all displaced by a constant amount, leading
to a track that follows the map perfectly (ie with very little *random*
error), but is offset from it by a fixed distance.


You need four [widely spaced] for a full fix. On the open seas only three (since your altitude is known!).
  #29  
Old February 21st 18, 11:08 PM posted to uk.tech.digital-tv
Unsteadyken
external usenet poster
 
Posts: 11
Default Galileo ever come on stream?

In article ,
says...
Maybe the taxi was using differential GPS, but I suspect the story is apocryphal.

I drove the cab myself a couple of times and sat in the office watching
as it plotted itself around the map.

I imagine the device was using the most advanced tech available at the
time, you wouldn't want a Jumbo landing 100 meters off the runway.

It was certainly expensive enough. 3,500 per card. If my memory serves
me well, which since a stroke a few years ago it doesn't:-( For the life
of me I cannot remember the name of the company which provided the demo
GPS kit.

The kit was a bare full length PC isa card with several antenna
connectors for an external dome antenna or 2. It had no real onboard
processing. As I say it was designed to be fitted into a rack on an
aircraft.

To get meaningful output from it when fitted in a London type black cab
meant that the card had to be fitted into a laptop with a suitable ISA
slot and RS232 port.
This meant a ginormous fragile greyscale laptop costing about
2,000. Hardly hand held. While this contraption plus its external dome
antenna could just be fitted into the luggage compartment in a black cab
it was totally impracticable in a private hire car, this plus the cost
of installing it in a 50+ mixed vehicle fleet, the risk of damage, the
problems of providing a reliable power supply and the near certainty
that some bugger would nick it within a week meant the idea was binned.
The output from the RS232 port was fed to a device which converted
it into a suitable format for transmission alongside the output from the
meter as data via a modified PMR radio.

The reason for all this was that a GPS unit does not and supposedly
cannot lie about where it is in order to nab a juicy fare.

Unlike the pesky drivers using a prototype version of this Datahead,
http://www.halda.co.uk/old/MDS12.html and its descendants:
http://www.datamaster.co.uk/about-us/our-history
and software by
http://www.cabmaster.com/

In 1992 the taxi radio circuit of which I was in some sort of control
succeeded in carrying out a taxi booking in which the only voice
communication was between the punter and the telephonist.
It had taken nearly 3 years of hard work by many hardware and software
companies to get the one of the first Automated booking and data
despatch systems up and running. The trials were overseen by the then
Radiocommunications Agency who were not sure about data in those days
but hey saw the light and aproved its use.

The time saved in despatching by data as against the interminable
bawling, bickering, lying and arguing which the voice method usually
involved was enormous.

The whole thing proved so efficient and the data from the meters showed
beyond doubt the private hire cars made more money than the Hackney
cabs, which led to all out war for a time but things settled down.

http://www.skycabs.org.uk/index.asp

Great fun at the time, now all you need is the uber app.











  #30  
Old February 22nd 18, 07:25 AM posted to uk.tech.digital-tv
tim...[_2_]
external usenet poster
 
Posts: 619
Default Galileo ever come on stream?



"Bill Wright" wrote in message
news
On 21/02/2018 09:33, tim... wrote:

Encryption on the more accurate service - cf eg Sky's charges for TV
packages.


So they can charge you for the "technology" in a chip that decrypts it

but how can they do that on anything other than a "one time fee" model.


Individually addressable receivers, same as Sky


Sky have a way of contacting the owners of their boxes

There is no realistic way to contact the owner of a GPS receiver, which
might be installed inside a boat or a car or a tank

tim



 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT. The time now is 09:51 AM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.SEO by vBSEO 2.4.0
Copyright 2004-2018 Digital TV Banter.
The comments are property of their posters.