OEM4 Receivers will be Reporting Inaccurate Week Numbers Starting September 24, 202217 December 2021
OEM4 receivers were first introduced to the market over two decades ago, providing high precision, dual constellation, dual frequency multi channel GNSS receivers to the world. OEM4s were subsequently end-of-life’d in 2006 and reached end of service in 2011. Due to the high quality of the OEM4 receivers, some receivers are still in service over 20 years later. However, as of September 24, 2022, OEM4 receivers will start reporting a GPS week number in the past. While the receivers will continue to operate, this may cause interoperability issues with receivers that are reporting a different week number.
GPS Time is reported in weeks since January 6, 1980. The GPS ICD defined navigation data format limits the number of weeks before a rollover to 1023. This means that roughly every 19 years the GPS week goes back to zero and starts incrementing again. This “era” rollover happened in 1999, and again on April 6, 2019.
In order to help the receiver determine the actual calendar date, NovAtel has historically pre-configured a date as a reference to figure out the current GPS “era”. From time to time, NovAtel has updated the pre-configured date in a new firmware version to allow the receiver to determine the correct era for the next 10-18 years. This allowed the NovAtel receivers to successfully transition over the era rollover that happened on April 6, 2019.
What happens when the receiver base week is not valid?
When the receiver’s base week is no longer valid, the receiver will continue to operate and output a correct position. However, the GPS week reported by the receiver will be incorrect. This may impact receiver operation if it is interacting with an external system that is sending data with a different GPS week number as there will be a time mismatch.
When will this be an issue?
OEM4: The latest firmware on the OEM4 family of receivers is 2.322, with a current base week that is valid until September 24, 2022, 11 years beyond the end of service date. Customers still using OEM4s are encouraged to upgrade to the latest NovAtel platform (OEM7) prior to September 2022.
For more information on the latest products to replace the OEM4, visit: