GPS Synchronization

Document Number FSB9079
Revision 000v002
Download the PDF version Application Global
Effective Date January 2, 2020
Expiry Date N/A
  Warranty Service   High – Perform immediately
X Informational X Medium – Perform at next scheduled maintenance
  Customer Specific   Low – Perform when system exhibits symptoms

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SUBJECT: Loss of GPS Synchronization

MODEL / SYSTEM AFFECTED:    uGPS receiver running firmware version AXN_5.1.1 
                                                        cnPulse receiver running firmware version AXN_5.1.1
                                                        ePMP1000/2000/3000 Access Points with integrated GPS running firmware AXN_5.1.1

REASON FOR BULLETINThis bulletin addresses a GPS synchronization issue that started around 13:00 CST on 12/31/2019.
This Field Service Bulletin address the recovery procedures and root cause of the issue.

Customers are reporting a loss of GPS Sync when:

  1. Using a uGPS receiver connected to a CMM5 Injector via the UGPS port.
  2. Using a uGPS receiver directly attached to an Access Point’s AUX port.
  3. When using the internal GPS on a PMP450 or ePMP Access Points.

The loss of sync is causing radios with “AutoSync + Free Run” Enabled and “Free Run Before GPS Sync” Disabled to stop transmitting following a reboot. Radios configured for “AutoSync” only will cease to transmit immediately after sync is lost.

Radios that have “AutoSync + Free Run” Enabled might experience interference from neighboring APs due to the loss of sync.

CURRENT STATUS OF INVESTIGATION: The issue was cause by the GLONASS System Days Since Leap Year rollover that happens on every Leap Year at 00:00 Moscow Time. The GPS Chipset did not handle this rollover properly in firmware AXN_5.1.1 and it affects both UGPS and cnPulse devices with a GPS chip running this firmware. By now, it may have self-recovered, but if anything is lingering, a power cycle of the GPS device is required. This can be done via the AP if it is powered by the AP otherwise it will have to be done manually.


  • The current fix for a uGPS receiver connected to a CMM5 injector via the UGPS port is to either power cycle the CMM5 injector or unplug the uGPS receiver from the UGPS port and plug it back in again.
  • For Access Points that have directly attached or internal GPS receivers, power cycling the Access Point will reset the internal GPS receiver.
  • For units that have uGPS receivers is powered via an external POE or PSU then the uGPS will need to be power cycled by removing power to the POE/PSU.

If you encounter an issue please open a support ticket with the Cambium Support team at the following URL:

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