Old GPS systems may display incorrect information from next month
Old devices that use GPS may give incorrect information starting next month. This is due to an internal weekly counter that is reset every 19.7 years. Devices use this weekly counter to determine the date and sometimes the location.
PNT company Orolia warns about this. GPS satellites transmit accurate clock time information, among other things. This signal contains the current week and the amount of seconds since the beginning of that week. The receiver can translate this signal back into a format based on days, months and years.
The problem is that that week information is sent in a 10-bit binary number. This means that a total of 1024 weeks can be sent via the signal. Week 0 started on August 21 in 1999, so on April 6, 2019 the 1024 weeks will be over and the satellites will start counting from ‘0’ again.
Systems use an internal date as a reference point for the weekly information. If that date is set on August 21, 1999 and it receives 0 as week information via GPS, then the system could think on April 6, 2019 that it is still August 21, 1999. That reference point may also be placed at a later date, allowing the bug to resurface at a later time.
According to Orolia, users of newer systems do not have to worry that their devices will no longer work. This is the second time this rollover has taken place, the first being in 1999. As a result, many manufacturers are aware of this problem and are prepared for it, Orolia said. They may have worked around the issue by specifying a different reference date through an update.
However, if a device has not had any firmware updates for more than ten years, there is a chance that the GPS system will give incorrect information. To find out, Orolia advises you to contact the manufacturer of the GPS system. In some cases, the reference date can also be adjusted in the firmware itself.
TomTom, among others, warns about the roll-over. “Resetting the calendar can lead to miscommunication between GPS satellites and the receivers. As a result, some chips in navigation systems can no longer handle certain functions,” the company writes on its site. Owners of TomTom navigation devices can enter the serial number on the website to check whether the system will still work in the future. Users of certain Renault and Smart systems are also advised to go to the TomTom page. TomTom does not specify what will happen if users do nothing.
It is possible that GPS receivers that have not been updated will display incorrect location information. To determine the position, the receivers make use of time differences between the receiver and at least three satellites, at least four if the height must also be determined. Since the receiver knows where the satellites will be at any given time, the receiver also knows its own location. But if the internal date is no longer correct, the receiver can assume where the satellites were 19.7 years ago. If that happens, the receiver will no longer be able to determine the location, or not properly.
According to Orolia, it is probably the last time that systems will suffer from the rollover. Gps is currently undergoing a program to upgrade the systems to a 13bit number. That equates to about 157 years per rollover.