The Global Positioning System (GPS) is a radionavigation system operated by the US government that enables users to determine their position and accurate time by receiving signals from a constellation of satellites. GPS is used ubiquitously in products and systems ranging from consumer electronics to complex vehicle navigation systems. Each device or system that uses GPS has a GPS receiver, produced by a variety of manufacturers, which receives the signals from the satellites.
As part of the GPS system's design, when the satellites transmit the date and time, the data contains the current week number from a starting reference week, which was January 6, 1980. However, the data field that contains the week number is a 10-bit binary number, which means its range is limited from 0 to 1023. When the week counter rolls over, it begins again from zero. This occurred on August 21, 1999 and will occur again on April 6, 2019.
This week rollover can interfere with the proper calculation of time by some GPS receivers.
Which Xsens MTi sensor modules may be affected by the GPS week rollover?
The Xsens MTi sensor modules that may be affected by the rollover are the modules with internal GPS receivers.
The currently-supported MTi sensor modules with GPS receivers are the 4th generation MTI-G-700 and MTi-G-710 and the 5th generation MTI-G-710.
In addition, the MTi-7 GNSS/INS module is able to utilize GPS information in its sensor fusion algorithms, although the MTi-7 hardware itself does not have a GPS receiver. However the MTi-7 does does have a development kit which has a GPS/GLONASS/Beidou receiver, so we will address it as well.
Does the GPS week roll over affect Xsens MTi sensor modules with GPS?
No, the good news is the GPS week rollover occurring April 6, 2019 will not adversely affect the Xsens MTi products.
All MTi-G-7x0 products as well as the MTI-7 Development Kit have a u-blox GPS or GPS/GLONASS/Beidou receiver. u-Blox handles the GPS week rollover by entering a reference rollover week number in their firmware when they are manufactured. With this implementation, u-blox receivers print out the correct date for 20 years after the firmware was compiled.
As a rough guideline, MTi devices produced in 2011 will not be affected until 2030.
For further explanation of u-blox's solution, please refer to documentation on their website (http://www.u-blox.com), for example the u-blox M8 Receiver Description at https://www.u-blox.com/sites/default/files/products/documents/u-blox8-M8_ReceiverDescrProtSpec_%28UBX-13003221%29_Public.pdf (last accessed 17 March 2019).