GPS Week Rollover Issue

Brian D · Mar 20, 2019

Based on what I read, only the time function will be affected. It may cause your fix to be correct but your fix might not be when you said it was. I haven't heard of GPS units completely failing except for units made before the first roll over. However, it is wise to monitor your devices and see what happens. I have 2 Garmins which I have photoed for comparison. But I do not think anything will happen to them.

Personally I think that image of "Error" is a marketing ploy. Of course they want you to buy a new GPS. But like I said, I doubt the units we use will be affected.

Jackdaw · Mar 20, 2019

LOL maybe it dates me, but I was in the GPS business the FIRST time this rolled around. About the same time as Y2K fears were hitting, so-called pundits proclaimed the end of GPS as we knew it. Well, most of the prehistoric devices of the day survived then. The industry has has 20 years (OK, 1024 weeks) to prepare for this round. Remain calm. If ANYONE has an issue with a device, send me a pic of it failing and I'll buy you a beer.

Brian D · Mar 20, 2019

@Hunter216, understood. Not trying to steal your thunder, just putting some light on the subject. First roll over happened in 1999. So if some sailors have units that old (I have two that I know of) then the time might be off. But I do not think the GPS will "die" or stop working altogether. Like Jackdaw says, reminds me of the Y2K scare. We will see in a couple of weeks. It will be interesting.

So for all who are interested, take a photo of your GPS with a good fix. Then on April 7th post the old photo and a new photo with the broken GPS. This will be interesting indeed. Here are mine just waiting for 4/6. The ones I expect to have issues, if any, are the two Garmins.

All U Get · Mar 21, 2019

Jackdaw said:
LOL maybe it dates me, but I was in the GPS business the FIRST time this rolled around. About the same time as Y2K fears were hitting, so-called pundits proclaimed the end of GPS as we knew it. Well, most of the prehistoric devices of the day survived then. The industry has has 20 years (OK, 1024 weeks) to prepare for this round. Remain calm. If ANYONE has an issue with a device, send me a pic of it failing and I'll buy you a beer.

Y2K, not again.

Gene Neill · Mar 21, 2019

My older brother filled his garage with storage food and bought a bunch of silver bullion in preparation for Y2K. He was answering his phone with "Northwest Y2K Preparedness Center" or some such thing.

My younger brother was in jail at the time. I thought it was a pretty crappy moment for the world to end, since I was gonna have to go bust him out somehow when the entire planet's grid went down.

It didn't stop the raging bonfire party in my back yard, though. My job was to maintain a sense of normalcy, in the face of impending doom.

Sailboat.Sequoyah · Mar 21, 2019

Gene Neill, I can't say I'd find that normal, but tip o' the hat anyway.

Project_Mayhem · Mar 21, 2019

Do GPS calculate the time it takes for the signal from the satellites to reach the unit in order to more accurately determine position?

Johann · Mar 21, 2019

Project_Mayhem said:
Do GPS calculate the time it takes for the signal from the satellites to reach the unit in order to more accurately determine position?

Yes. Actually that is how the unit calculates position. Imagine a signal traveling out from the satellite. It travels in a sphere. If you know how long it took to get to your gps, you know you are somewhere on that sphere of a certain radius. Then you add a second satellite and you know you’re somewhere on the intersection of the two spheres, which is a circle. A third satellite intersection gives you two points, and a fourth tells you which of those two points is your position. Of course there is ALOT more involved... clock syncing, error detection, relativity... but that’s the basic principle.

Project_Mayhem · Mar 21, 2019

I assume weather can also affect signals and thus the system has to rely on other parameters to calculate position?

Jackdaw · Mar 21, 2019

Project_Mayhem said:
I assume weather can also affect signals and thus the system has to rely on other parameters to calculate position?

The biggest sources of inaccuracy (beyond sub-optimal solution geometry) are:
Orbital error
Timer/clock error
Atmospherics

WAAS can eliminate most of this. Weather does not really factor.

Johann · Mar 21, 2019

Project_Mayhem said:
I assume weather can also affect signals and thus the system has to rely on other parameters to calculate position?

I believe the frequencies selected for gps minimize the interference weather may cause. But the satellite signals (and sometimes terrestrial stations) are all you get. How your particular navigation unit handles the gps signal is another story...

JamesG161 · Mar 21, 2019

I asked RayMarine about this issue 1/27/2019. They said they are investigating.
This is there comment as of this morning on a Specific Unit...

"It is presently expected that Raymarine will be releasing the results of its investigation on this subject at the end of this week and the corresponding FAQ will be updated early next week. In short the RS125 GPS Sensors, as well as most of the Raymarine products featuring GPS receivers produced within the timeframe that the RS125 was being manufactured, are not expected to be affected by a GPS rollover until 2025. Again, more details will be released next week."
So the previous update to their FAQ says this...

"The 2019 GPS Week Rollover would have a potential effect upon GPS receivers (including GPS sensors and GPS receivers embedded within MFDs, chartplotting products, AIS receivers, and VHF radios). Any features which are dependent upon date/time information (tide / current data, waypoint/route creation date, Time, Date, slow / no acquisition of GPS FIX, etc.) would potentially be affected by this feature. This feature is rooted in the make/model of GPS receiver which has either been constructed into the product or that the product has been interfaced and the GPS chipset used in it's manufacture. Accordingly, should one determine that the date/time information reported by the system is incorrect following the 2019 GPS Week Rollover event (April 6, 2019), then it may be necessary to either replace the system's GPS sensor, add an external GPS sensor to the system, or replace the GPS sensing device (should no software/firmware update be available to address the 2019 GPS Week Rollover event).

Raymarine is presently investigating this issue and will release updated information at a later date. At that time, this FAQ will be updated with the latest information on this subject. As of the date of this response, we are confident that each of the following products are unaffected:
- Axiom / Axiom Pro / Axiom XL MFDs
- a/c/e/eS-Series MFDs
- Raystar 130/150 GPS Sensors
- AR200 Augmented Reality Sensor
- AIS650/700 AIS Transceivers

Raymarine presently investigating potential impacts to other legacy Raystar GPS Sensors, legacy MFDs having internal GPS Sensors, chartplotting products having internal GPS sensors, legacy MFDs having internal GPS sensors (ex. A-Series Classic MFDs, C-Series Widescreen MFDs), and AIS transceivers. As additional information becomes available, this FAQ will be updated accordingly. Should a system's GPS receiver be affected, then most affected systems may be addressed by interfacing a Raystar 150 GPS Sensor to the system."

So they are still not done! But at least I am clear until 2025.

I would have linked that stuff, but I think it may not link inside the RayTech Forum.
Jim...

PS: Here is my question to Raymarine link, I hope you can follow their links..
http://forum.raymarine.com/showthread.php?tid=7275

JamesG161 · Mar 21, 2019

If you click on RayMarine FAQ link, you get this from Homeland Security.
https://ics-cert.us-cert.gov/sites/default/files/documents/Memorandum_on_GPS_2019.pdf

Enjoy
Jim...

Brian D · Mar 21, 2019

On top of all of what was said, there is this thing that is called Doppler Shift. Doppler plays a very important role here.

We know of Doppler Shift from standing near a railroad track when a train passes. Initially the train whistle is high pitched until it passes. Then the whistle appears to change frequency. That is due to the whistle's frequency wavelength getting longer, thus lowering in tone. (see Red Shift/Blue Shift dealing with light for another example) GPS, along with the other attributes listed, works on the same principle. With the gps ephemeris data being updated by the handheld unit, the doppler is known based on the speed the satellite is moving toward you or away from you. All of this plays well together.

In the case of the roll over, only time is affected. The clocks are reset and if the handheld units do not keep up then the time is incorrect. But the location should still be somewhat accurate because of other variables. Now, if they move the orbit (Medium Earth Orbit in this case) higher or lower, or the frequency is changed, then all is lost.

Science is so cool. LOL

Jackdaw · Mar 21, 2019

Amost every GPS device in current existence was programmed with this eventuality in mind. The trick is this is all software, and there was no real way to test it. You can run it through GPS simulators and that does a pretty good job. The first time this happened there were a lot of engineers sweating, because they actually hadn’t accounted for it and were kind of interested to see what would happen with Clocks. There were some devices affected but not as many as people as expected. I’m figuring it’s going to go much smoother this time.