Assisted Partial Timing Support (APTS)

APTS operation is a simple concept. In this scenario, both the core PRTC and edge PRTC have a GNSS input referenced to UTC time. The core PRTC Server delivers PTP time stamps to the downstream edge PRTC clock using a PTP profile. The edge PRTC compares the PTP time stamp to the local GNSS time. The edge PRTC accumulates information about the PTP flow from the PTP time stamps and from message exchanges with the Core PRTC. Consequently, it understands the actual overall delay and time error on that specific PTP path. The edge PRTC adjusts the PTP flow information and calibrates the incoming PTP flow by compensating for the measured time error so that it is now equivalent to the local GNSS time.

This calibration process improves the performance of the edge PRTC in the event of a GPS loss of signal at this site. With APTS, the time error on a single PTP input path is removed. Once the APTS algorithm is operating, the incoming PTP flow can be used as a proxy for the GNSS. If the GNSS on the local PRTC is lost, then the system will use the calibrated incoming APTS flow as the reference clock. As mobile networks evolve from frequency-based networks to dense, highly distributed radio heads that require phase alignment to provide advanced 4G/5G services, it will be increasingly necessary to deploy PRTC clocks around the edge of the network. These PRTC can be protected by implementing assisted partial timing support, G.8273.4, an engineering tool that can be used to back up the PRTC at the edge from a core PRTC clock.