GPS week cycle rollover
GPS satellites work by continually broadcasting the time and date. To save repeatedly broadcasting redundant information, GPS satellites send a week number instead of broadcasting the full date. Every 1024 weeks, this week counter resets to zero. This happened for the first time on 21 Aug 1999 and is due to happen again on 6 Apr 2019.
Impact on GPS chips
Modern GPS chip designers have put software into their receivers that take this rollover into account, and will compare the week number with external sources to work out the true date. Our latest TETRA radios use these modern chips.
Older GPS chips are not able to tell the difference between week cycles and so may run into problems after 6 April. Although this affects all electronics that use GPS chips, the lifecycle of two-way radio products is long and they are frequently used with GPS, so two-way radio customers may be disproportionately impacted.
Our older TETRA radios have a programmable field to tell the GPS chip which week cycle we are in.
Impact on Motorola Solutions TETRA radios
The following Motorola Solutions TETRA devices need to be updated to set the GPS week cycle number to “2” before 6 April 2019. They will not send, or may send incorrect, position reports after 6 April 2019 unless action is taken:
MTP850 S/830 S
These radios will need to have their codeplug updated using CPS, iTM, or CPS Light.
How to update
A codeplug field to configure radios to use an appropriate GPS week cycle has been available since R5.9. Updates to software releases prior to R5.9 are not supported.
Users of “Short LIP” GPS reports will need to change the “Current GPS cycle” from 1 to 2 using CPS or ITM.
Users of “Long LIP” or “LRRP” GPS reports will need to do the same, but fields reported by the radio relating to the date or day will be reported incorrectly from the point when the change is applied until 6 Apr 19. Many backend systems ignore this data, and it can be corrected algorithmically if required, but the software receiving GPS updates (likely a dispatcher) will need to be checked, and potentially changed, to take this into account.
If you do not have iTM or CPS we have made a free tool available to perform the week cycle number change called CPS Light. Please complete the form below to download CPS Light.
Using CPS Light
Simply install and run CPS Light on a Windows computer, connect a Motorola TETRA radio using a USB cable, and if applicable the update will be applied and a log created. Full system requirements and details on how to use CPS Light are included in the download.
For further information or support, please use your normal Motorola Solutions support contacts.
Download the software