About the influence of GPS week number rollover on JRC GPS

Introduction to GPS week number rollover and its impact

Recently, the Civil GPS Service Interface Committee (CGSIC) of the United States issued a warning on the website of the US Department of Homeland Security that the GPS weekly count will usher in the second rollover event at 0:00 UTC on April 6, 2019.

The reason why the GPS week number rollover occurs is due to the communication method of the GPS navigation system. The current week number is encoded into a 10-bit field in the use data field, and a cycle is from 0 to 1023 weeks. The current GPS cycle started on August 1, 1999, and the Japanese cycle week number returns to zero on April 6, 2019. It will start to count from 0 weeks to 1023 weeks again. This is the week number rollover.
 

Turnover of the GPS week number may cause some GNSS devices to work abnormally and output time errors and other problems. For ships, the date of abnormal GPS operation will automatically jump back to the date of 1999-12-19, which may affect the normal operation of a series of integrated GPS system information or systems that require GPS feedback.
 

The different effects of GPS week number reversal on GPS equipment of different manufacturers, the effect of GPS week number reversal on JRC GPS equipment and countermeasures:
 

The JRC manufacturer’s technical bulletin (NA18AL0406A-E) issued in May 2018 listed the manufacturer’s GPS-influenced device models including: JLR-7700MK2 (serial number KD76578~KE50478), JLR-4330, JLR-4330W, Six models of JLR-4331W, JLR-10, JRL-10T are affected. At present, JRC ships mainly use three types: JLR-7700MK2, JLR-7800, and JLR-7900. The comparison shows that the JLR-7700MKII used by some ships may have an impact. JRC also provides solutions for each type of equipment that may have problems with some JLR-7700MK2. You only need to re-enter the current coordinates and time in the initialization mode without replacing the equipment. For details, please refer to the technical part in the JRC notification.

In the GPS modernization plan, in order to improve the week number rollover, the message type (CNAV and MNAV) uses a 13-bit field to indicate the GPS week number, and new GPS receivers using this 13-bit field will not appear in the 1024-week period. problem. At the same time, some manufacturers such as JRC have taken the initiative to upgrade the software of equipment parts to solve this problem, and there will be no problems with this part of the equipment.