GPS and WAAS
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Joined: Oct 2003
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From: Worcestershire UK
GPS and WAAS
Hi All
There was a thread running a couple of days ago where hand held GPS units were under discussion and I brought up the subject of WAAS.
A couple of posters shot me down and said that the WAAS system was operational in the USA only and did not work in the UK.
I was sure I had read somewhere that it did work here, but doing a Google search revealed evidence to the contrary, and I backed down and said I was wrong.
However, upon browsing the manual for my GPS (a Magellan Spor Trak) I found the following:
quote/
Your Magellan GPS receiver has been upgraded to include the latest WAAS
(Wide Area Augmentation System) technology. With WAAS your GPS receiver
can compute position locations with an accuracy never before possible in a commercial receiver.
What is WAAS?
WAAS is a means of improving the accuracy of GPS beyond
the standard civilian signal. WAAS was developed by the FAA to provide the accuracy needed for aircraft to perform approaches for landings.
WAAS improves the accuracy of GPS by calculating the errors in the GPS signal at several monitoring stations around the country and then transmitting the error corrections to special WAAS satellites. In turn, these satellites broadcast the error corrections to WAAS-capable GPS receivers around the world. I
WAAS is a free service and, with the small exception of two additional satellites displayed on the Satellite Status screen, it will be transparent to you. There is nothing you need do, it’s all ready to go.
How accurate will my GPS receiver be with WAAS?
The FAA reports that expected accuracy can be improved to around 7 meters vertically and horizontally.
Our own testing suggests that Magellan GPS receivers will typically experience accuracy improvements to around 3 meters. You can expect to see this level of accuracy for 95% of the time that you are receiving WAAS signals.
What are some of the problems with WAAS?
The signal coverage with WAAS is not global like GPS satellites. In some locations, receiving WAAS signals can be difficult and intermittent. There are two satellites transmitting WAAS for corrections in the Americas There are two satellites transmitting WAAS for corrections in the Americas and two more over Africa and India providing similar coverage for Europe.
These satellites are geostationary, i.e., they stay in the same spot over the Earth equator. The two satellites for the Americas are over the Pacific and Atlantic Oceans. Chances are then, they will probably be near the horizon from where you are using your GPS receiver. This increases the chance that buildings, foliage, terrain and other obstacles could block the WAAS signal.
Also WAAS is a relatively new system and is still in its developmental stage. So on occasion you may experience service outages. Even during these outages, your GPS receiver will still be working, computing position fixes and helping you get to where you want to go using the GPS signals. The only difference is you will not be getting the precision that WAAS was providing. You can expect to see these outages diminish as the system matures and stabilizes.
/unquote
Regards
There was a thread running a couple of days ago where hand held GPS units were under discussion and I brought up the subject of WAAS.
A couple of posters shot me down and said that the WAAS system was operational in the USA only and did not work in the UK.
I was sure I had read somewhere that it did work here, but doing a Google search revealed evidence to the contrary, and I backed down and said I was wrong.
However, upon browsing the manual for my GPS (a Magellan Spor Trak) I found the following:
quote/
Your Magellan GPS receiver has been upgraded to include the latest WAAS
(Wide Area Augmentation System) technology. With WAAS your GPS receiver
can compute position locations with an accuracy never before possible in a commercial receiver.
What is WAAS?
WAAS is a means of improving the accuracy of GPS beyond
the standard civilian signal. WAAS was developed by the FAA to provide the accuracy needed for aircraft to perform approaches for landings.
WAAS improves the accuracy of GPS by calculating the errors in the GPS signal at several monitoring stations around the country and then transmitting the error corrections to special WAAS satellites. In turn, these satellites broadcast the error corrections to WAAS-capable GPS receivers around the world. I
WAAS is a free service and, with the small exception of two additional satellites displayed on the Satellite Status screen, it will be transparent to you. There is nothing you need do, it’s all ready to go.
How accurate will my GPS receiver be with WAAS?
The FAA reports that expected accuracy can be improved to around 7 meters vertically and horizontally.
Our own testing suggests that Magellan GPS receivers will typically experience accuracy improvements to around 3 meters. You can expect to see this level of accuracy for 95% of the time that you are receiving WAAS signals.
What are some of the problems with WAAS?
The signal coverage with WAAS is not global like GPS satellites. In some locations, receiving WAAS signals can be difficult and intermittent. There are two satellites transmitting WAAS for corrections in the Americas There are two satellites transmitting WAAS for corrections in the Americas and two more over Africa and India providing similar coverage for Europe.
These satellites are geostationary, i.e., they stay in the same spot over the Earth equator. The two satellites for the Americas are over the Pacific and Atlantic Oceans. Chances are then, they will probably be near the horizon from where you are using your GPS receiver. This increases the chance that buildings, foliage, terrain and other obstacles could block the WAAS signal.
Also WAAS is a relatively new system and is still in its developmental stage. So on occasion you may experience service outages. Even during these outages, your GPS receiver will still be working, computing position fixes and helping you get to where you want to go using the GPS signals. The only difference is you will not be getting the precision that WAAS was providing. You can expect to see these outages diminish as the system matures and stabilizes.
/unquote
Regards
Last edited by oscarmike; 21st January 2004 at 21:18.
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From: TL487591
I'm not aware of any published, useable WAAS coverage in Europe. However, this doesn't of course prevent your GPS from being capable of receiving it. Most of the more recent GARMIN Panel-mounts are either WAAS-capable or WAAS-upgradeable.
However, the big buzz around WAAS is not to do with improved enroute navigation. Rather, the US has been trialling WAAS-GPS approaches - the key feature of these approaches being that they provide VNAV guidance and not just Lateral guidance.
The implication is that with WAAS available, pseudo-ILS GPS-based precision approaches will be available to normal Cat 1 minima in fairly short order.
Wait and see how long it takes the CAA to approve that
You can be sure though, that handhelds (to return to the original question) will not get that approval.
So the bottom line is that it is all a bit academic whether or not your handheld can or cannot receive WAAS. The primary advantage that WAAS is set to give, will not be authorised for handheld units.
2D
However, the big buzz around WAAS is not to do with improved enroute navigation. Rather, the US has been trialling WAAS-GPS approaches - the key feature of these approaches being that they provide VNAV guidance and not just Lateral guidance.
The implication is that with WAAS available, pseudo-ILS GPS-based precision approaches will be available to normal Cat 1 minima in fairly short order.
Wait and see how long it takes the CAA to approve that
You can be sure though, that handhelds (to return to the original question) will not get that approval.So the bottom line is that it is all a bit academic whether or not your handheld can or cannot receive WAAS. The primary advantage that WAAS is set to give, will not be authorised for handheld units.
2D
Last edited by 2Donkeys; 21st January 2004 at 20:04.
Joined: Sep 2003
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From: UK,Twighlight Zone
I just called Garmin support in the UK as both my GNS430 and my 196 are WAAS enabled and I was curious. They told me that the WAAS satelites are not available in Europe yet but following the apparantly highly successful implementation of WAAS in NA we are likely to get our own WAAS satelites soon.
The 2 WAAS satelites in Geostationary orbit for the US will transmit the signal to any WAAS capable device, however as with GPS they are line of sight and we can't see them very well in Europe.
WAAS works by timing corrections that are made at specific ground stations which is then transmitted onto the WAAS capable device from the satelites which then corrects the timing.
It is the building of these ground reference stations in Europe that is underway at the moment. The corrections from the US stations are useless as they are too far away and therefore would not elliminate any of the timing errors.
So your reciever will benefit from WAAS but not in Eurupe YET!
The service is pretty good and my 196 picked them up without any problems on my last Florida trip.
The 2 WAAS satelites in Geostationary orbit for the US will transmit the signal to any WAAS capable device, however as with GPS they are line of sight and we can't see them very well in Europe.
WAAS works by timing corrections that are made at specific ground stations which is then transmitted onto the WAAS capable device from the satelites which then corrects the timing.
It is the building of these ground reference stations in Europe that is underway at the moment. The corrections from the US stations are useless as they are too far away and therefore would not elliminate any of the timing errors.
So your reciever will benefit from WAAS but not in Eurupe YET!
The service is pretty good and my 196 picked them up without any problems on my last Florida trip.
Joined: Mar 2003
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From: surrey
In fact, WAAS makes your GPS LESS accurate in Europe, because it blindly applies corrections which are irrelevant. This is more likely to occur in the air due to the improved 'over the horizon' view of the satellites.
The European equivalent of WAAS is EGNOS, which consists of 1 extra satellite (#33). The system is due to go live this year and is fully compatible with your WAAS GPS.
Sat 33 is currently transmitting a test signal with a 'DO NOT USE' message. Magellan receivers decode the flag and ignore the signal. Garmin receivers (consumer versions) see the flag and ignore it (i.e. try and use the signal), on the grounds that the correction signal may be valid and you shouldn't be using their consumer units for anything important anyway!
EGNOS and WAAS will probably become redundant when Galileo is fully operational in a few years. The increased number of satelites and more advanced coding should acheive VNAV atleast as good as WAAS.
[edited to add that by redundant I mean 'a useful backup system' and not 'a waste of space and money - throw it all away' !]
The European equivalent of WAAS is EGNOS, which consists of 1 extra satellite (#33). The system is due to go live this year and is fully compatible with your WAAS GPS.
Sat 33 is currently transmitting a test signal with a 'DO NOT USE' message. Magellan receivers decode the flag and ignore the signal. Garmin receivers (consumer versions) see the flag and ignore it (i.e. try and use the signal), on the grounds that the correction signal may be valid and you shouldn't be using their consumer units for anything important anyway!
EGNOS and WAAS will probably become redundant when Galileo is fully operational in a few years. The increased number of satelites and more advanced coding should acheive VNAV atleast as good as WAAS.
[edited to add that by redundant I mean 'a useful backup system' and not 'a waste of space and money - throw it all away' !]
Last edited by Tall_guy_in_a_152; 22nd January 2004 at 06:21.
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From: EuroGA.org
Sadly all this is likely to remain practically irrelevant in the current century, until everybody at the CAA capable of using a rubber stamp, most of the flight training establishment worldwide (outside the USA) and the editors and (most of) the contributors of current GA related publications have all started drawing their old age pensions 
Joined: Feb 2001
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From: UK
Tall guy wrote [snip] "EGNOS and WAAS will probably become redundant when Galileo is fully operational in a few years. The increased number of satelites and more advanced coding should acheive VNAV atleast as good as WAAS." [snip]
Will existing GPS handhelds will work with Galileo, or will people have to buy new units to use it?
Chris N.
Will existing GPS handhelds will work with Galileo, or will people have to buy new units to use it?
Chris N.
Joined: Jun 2001
Posts: 191
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From: London, England
Chris
Dream on! The whole reason that the Europeans won't approve approaches using GPS is so that they can charge us for the Galileo-based service when is is eventually available. If they approved GPS then no-one would buy the new, more expensive units when they become available.
The Galileo units will undoubtedly be much more expensive because (a) the manufacturers will need to pay a big licencing fee to Galileo and (b) there will not be anything like the volume of business that there is for GPS.
I wonder how long it will take the CAA (or EASA, or whoever is in charge at the time) to approve approaches using Galileo? You can be sure that it won't be long, as they will be wanting to get at least some of the the investment in Galileo back.
Dream on! The whole reason that the Europeans won't approve approaches using GPS is so that they can charge us for the Galileo-based service when is is eventually available. If they approved GPS then no-one would buy the new, more expensive units when they become available.
The Galileo units will undoubtedly be much more expensive because (a) the manufacturers will need to pay a big licencing fee to Galileo and (b) there will not be anything like the volume of business that there is for GPS.
I wonder how long it will take the CAA (or EASA, or whoever is in charge at the time) to approve approaches using Galileo? You can be sure that it won't be long, as they will be wanting to get at least some of the the investment in Galileo back.
Joined: May 2001
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From: 75N 16E
GPS 101
The thing about WAAS or any differential GPS system is that you need to be close to the reference station. The reference station on the ground is at a known, surveyed location. When the ref station receives the GPS signal it calculates its location, and due to errors in the GPS signal (atmosperic disturbances etc) it is unlikely that the computed position will be accurate enough to equal the actual position. The reference station then applies a correction to correct the computed position to the surveyed position, then re-radiates these corrections. Anyone relatively close (ie. so atmospheric disturbances are roughly the same as what the ref station receives) will get a more accurate position. As pointed out, someone in the UK using corrections from the USA will just introduce a bunch of errors into their computed position.
Normal GPS is pretty accurate, most of the time more than 50m which is fine for non-precision stuff.....Better than any NDB anyway.
Cheers
EA
Normal GPS is pretty accurate, most of the time more than 50m which is fine for non-precision stuff.....Better than any NDB anyway.
Cheers
EA
Joined: Mar 2003
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From: surrey
ChrisN
Galileo will not be compatible with existing GPS receivers, but will not interfere with them either.
I suspect that we will see dual mode receivers appearing at some point in a year or so.
As PhilD points out, Galileo is supposed to pay for itself (atleast partly) but the pricing model has not been worked out yet. Possibilities are: (1) upfront license, (2) pay per use, (3) monthly charge, (4) some other devious method and (5) a combination of the above.
My opinion (and that is all it is) is that Galileo services will start out quite cheap so that we get hooked and then the price will go up (i.e the cable TV pricing model
).
Who knows, it may even be free for non-commercial use. For most of us who are still impressed that GPS works as well as it does, Galileo will have to offer something pretty special before parting with any money.
TallGuy.
Galileo will not be compatible with existing GPS receivers, but will not interfere with them either.
I suspect that we will see dual mode receivers appearing at some point in a year or so.
As PhilD points out, Galileo is supposed to pay for itself (atleast partly) but the pricing model has not been worked out yet. Possibilities are: (1) upfront license, (2) pay per use, (3) monthly charge, (4) some other devious method and (5) a combination of the above.
My opinion (and that is all it is) is that Galileo services will start out quite cheap so that we get hooked and then the price will go up (i.e the cable TV pricing model
).Who knows, it may even be free for non-commercial use. For most of us who are still impressed that GPS works as well as it does, Galileo will have to offer something pretty special before parting with any money.
TallGuy.
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From: EuroGA.org
What I've read is that the system will be free (i.e. not encrypted; the only way to stop some company making receivers for it would be encryption of some sort) but they will charge for the higher accuracy signal.
Presumably, for legal GPS approaches, they would demand that the higher accuracy signal is used.
The whole thing is bizzare. In any situation in which the Americans will shut theirs down, the European will be shut down also. It is just another project for career politicians to immortalise themselves on.
Presumably, for legal GPS approaches, they would demand that the higher accuracy signal is used.
The whole thing is bizzare. In any situation in which the Americans will shut theirs down, the European will be shut down also. It is just another project for career politicians to immortalise themselves on.
