EGNOS Status Update

[digimate]

Hi all,



Read this (posted in newsgroup sci.geo.satellite-nav (28-11-2002)!!:



Hi all,



Users of this group will know that the European Space Agency trialled

a new format EGNOS signal on Monday and Tuesday of this week.

Basically, the signal was transmitted with a "OK for testing" flag

rather than the normal "Do not use" during the EGNOS testing period.



I received the corrections in London UK using a Garmin Vista.



This test is the first time that Garmin receivers have recognised

valid corrections for UK by the AOR-E EGNOS satellite (PRN 33).



A few notes:



1. On Monday the EGNOS signal included ranging so that as well as

providing corrections (marked with 'D' on the display) to the GPS

satellites, the EGNOS satellite itself was included in the position

solution and turned black with a D. On Tuesday, the EGNOS signal

omitted ranging, therefore the EGNOS bar remained grey, although

corrections for the GPS sats were recieved.



2. The stated Estimated Position Error (EPE - which I think is set for

the Vista at a 50% probability level) was rather unstable. The minimum

reported EPE was about 2.5m (8ft in fact), however this varied

unpredictably from 2.5m to over 30m over about 30mins. The reception

conditions were reasonably good, the EPE without WAAS was 5 - 6metres.

Very exciting to get single figure accuracy though. It was noticeable

that it is possible to get an EPE of 6 metres with only 4 satellites

in view, which is a great bonus in the city.



3. I noted that no corrections were received for GPS PRNs 07 & 09,

after a long period of reception. Not sure why.



4. I believe no corrections were received from the IOR satellite (PRN

44) which is also broadcasting now, although a signal was detected

with the satellite low on the horizon.



5. I have read that these correction will be continuously available

from mid-December which is a great Christmas present to Garmin owners!



Regards,

***.



I think/hope it will be usable this month !!



Regards,



Nico

http://www.somerwil.nl/gps

[kerryburn]

Hi guys,



can anyone tell me how to make my Emtac pick up WAAS or EGNOS?



and can Tom Tom 2 benefit from the data.



Kerry Burn

[Oldie]

Satellite #33 was visible again today and for the first time I have managed to get a WAAS correction on my eTrex Legend. The D symbol was showing on all of the satellite strength bars including #33.



At one time (13:30 in the UK) the Garmin was showing an accuracy of 8ft.



Richard

[gulfstream]

Last Sunday (9/03/2003) I tried to get the EGNOS correction with the

newly USA-bought Garmin Vista in Milan, since the #44 was slightly

above horizon, EEES. I went to the ramp over A4 to have the most clear

sight, and managed to catch the #44 signal. It was rather fragile,

required careful unit orientation, although the optimal signal

strength was indicated quite good.



The #44 never became black but remained gray all the time. No "D"

appeared. Is it a temporary phenomenon, or the effect of the US

configuration of that Vista?



Nick

[Oldie]

I have a Garmin eTrex Legend with WAAS enabled and when out walking in the Farnham, Surrey area on 23/2/2003 I noticed that satellites 33 and 44 were visible. The signal from 33 showed quite strongly, but I did not see the D on the signal strength bars on the satellite display. It has been interesting to read what you have been saying in this forum. I will keep looking, here and on the Garmin, now!



Richard

[Les Newman]

Hi,



The latest information on the ESA site states that following the trial in Nov last year, the testbed will start transmitting a useable signal from 1st April 2003.



This means that Garmin & Magellen receivers should behave in the same fashion, and get differential corrections from the AOR-E Sat 33. I believe the IOR Sat 44 will remain unusable, but we'll see.



Still testing with full implementation in 2004.



I thought the description of WAAS and EGNOS on this site is one of the best I have seen.



Regards,


_________________
Les Newman

[MikeB]

I suppose that the same must be true for the Garmin GPSMAP76 as that was reporting differential fixes as can be seen from the screen images.



The European Space Agency did in their letter state:

Quote:

---

This signal is a test signal so it is not a guaranteed service signal. In reality, however, the performance of this test bed is quite good achieving accuracies of the order of 1-2m in core of Europe.



...



Today, however, EGNOS test bed (EGNOS mock up, the ESTB) and WAAS systems are currently under testing and as such are forced to transmit the message type 0.

---

I assume that OziExplorer ignores the fact that the message is a test message, and so does the Garmin GPSMAP 76.



I dont see differential fixes all day every day, nor did I with the Garmin, but I will often get a one when the GPS receiver is on my office windowsill.
_________________
Mike Barrett

[martynharrison]

I suppose it is reasonable for Oziexplorer to assume they have either a WAAS or not, and therefore if the differential flag is set, it must be because WAAS is operating on that fix.

[3GGG]

Quote: Originally posted by martynharrison on 02 December 2002

---

Does anyone have a link to which messages in NMEA are used for EGNOS? I'd have designed it to just give normal "you are here" messages with greater accuracy as the PC / whatnot isn't going to use the signals themselves. On the other hand, if you had a WAAS receiver in a ship with other GPS you might well want to export all the differential corrections to them as well?



As for the sat vehicle being low on the horizon, that's really about how high europe is above the equator. WAAS are in geostationary orbit so have to be above the equator, just like satellite TV birds. A good question for trivia, though, will the SV be higher in summer..?

---

Martyn (I recognise your name from Satellite TV matters I believe) when I was looking at the NMEA sentences from my Holux GM-201, the only difference I saw was that the position fix indicator in the GPGGA protocol changed from 1 to 2.



I did not see any values being given for the corrections being applied. I suspect that SiRF binary format would be required to get that information, but that is purely my guess.



Here is the GPGGA NMEA format:



// Global Positioning Fixed Data

'$GPGGA,160816.999,5603.9569,N,00329.0685,W,0,00,50.0,118.3,M,,,,0000*23

// 1 Message ID            GGA protocol header

// 2 UTC time              hhmmss.sss

// 3 Latitude              ddmm.mmmm

// 4 N/S Indicator        N or S

// 5 Longitude             dddmm.mmmm

// 6 E/W Indicator        E or W

// 7 Position fix indicator 0=No Fix or invalid, 1= GPS SPS Mode - fix valid,

'                         2= Differential GPS SPS Mode - fix valid

'                         3= GPS PPS Mode - fix valid

// 8 Satellites used        00 to 12

// 9 HDOP                   horizontal dilution of precision

// 10 MSL altitude           (metres)

// 11 Units                  M

// 12 Geoid separation       (metres)

// 13 Units                  M

// 14 Age of Diff. Corr.     (seconds) Null fields when DGPS is not used

// 15 Diff. Ref Station ID   0000

// Checksum              note no comma between last field and the *

// <CR><LF>






_________________
David

[Dave]

Please post any comments about the EGNOS Status update in this message.



The EGNOS Status Update Article can be found here.

[martynharrison]

I think there is an important element missing from the article. WAAS is a technology that is implemented in Europe via EGNOS, but the implementation is under test.



Garmin WAAS enabled receivers use WAAS to correct their positions, for sure. However, the EGNOS signals are type zero test messages and should be discarded by Garmin receivers. This is because Garmin ones are WAAS enabled and will use EGNOS corrections *when these are operational*, i.e. not until 2004 (unless they've changed policy and not made a big noise about it).



Magellan receivers are now shipping with WAAS functionality just like Garmin ones, with an important difference - they accept type zero test messages as valid ones. AFAIK this applies from the Meridian up and the wording they tend to use is "egnos compatible", which actually means "egnos even when under test".



In 2004, both types of receivers will work fine with WAAS enabled, wherever they are in the world. The accuracy will only be provided for a given area, e.g. north america. However, you won't get enhanced accuracy with Garmin ones at the moment because they are designed to reject every EGNOS message currently being generated.



One difference is that Magellan are non-compliant with SOLAS (safety at sea) regulations. While they will normally be more accurate than Garmins, they will also be less accurate when the test signals are invalid.



For e.g. geocaching, where safety isn't a factor, accuracy is at a premium and the periods of gross error which may appear won't matter a lot.



I don't know which manufacturers have gone with waiting for operational EGNOS and which have gone for their own "interim standard". There's not a lot of discussion about it because it isn't relevant in America and not many people seem to know what the options are.



Here's a negative view:

http://www.gpsinformation.net/egnosdonotuse.htm



Personally, I don't rely on GPS accuracy for safety, so the enhanced accuracy in general tempts me much more than the "might sometimes be misleading" objections to it.

[martynharrison]

Does anyone have a link to which messages in NMEA are used for EGNOS? I'd have designed it to just give normal "you are here" messages with greater accuracy as the PC / whatnot isn't going to use the signals themselves. On the other hand, if you had a WAAS receiver in a ship with other GPS you might well want to export all the differential corrections to them as well?



As for the sat vehicle being low on the horizon, that's really about how high europe is above the equator. WAAS are in geostationary orbit so have to be above the equator, just like satellite TV birds. A good question for trivia, though, will the SV be higher in summer..?

[3GGG]

Many thanks for all the answers. I remember now that when I was playing with my own NMEA software with the Holux I did get diff indication OK, so the NMEA sentences could be used to determine EGNOS locks.



One problem is that the geosat used for WAAS is only about 25 degrees elevation as far as I recall, it can quite often be hidden by buildings in that direction, so it cannot be relied upon in the car.
_________________
David

[Dave]

So it would seem that most of the software vendor's do need to update their software to show a WAAS/EGNOS graphic so we can tell whether it's acquired with a differential fix or not.



Better start lobbying, we only have just over a year to go before it's fully operational in April 2004!

[MikeB]

David,



When I have a Differential fix (EGNOS) with the Emtac it does not show up in Tom Tom GPS Status display, but when I switch to OziExplorer the display shows the fact that I am getting a differential fix rather than a GPS fix by replacing the 'G' with a 'D'. This is using the GPS in exactly the same place without re-initialising it.
_________________
Mike Barrett

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