Relative Timing Agreement in Small PTP Networks

Wednesday | 2:25 - 2:45 pm

Many applications require timing accurate to a standard timescale, such as UTC, to scale to large networks. However, when applications are localized it is often enough to have relative timing agreement. In such cases it is possible to achieve a greater timing precision, since many of the errors with respect to UTC at the timing nodes are common mode. One application which is anticipated to use relative timing is the synchronization of radio heads in 5G networks to support functions such as MIMO and location services. Here the elimination of common mode error with respect to UTC allows for tighter timing requirements, at least within a localized cluster of radio heads.

A method for achieving high relative precision among timing nodes is for each of the nodes to synchronize to the same PTP boundary clock. Factors affecting the agreement of timing at the end nodes include port to port timing consistency on the boundary clock, and differences among the PTP slaves. The latter includes differences among the servo loop algorithms and local oscillators in the end nodes. Differences due to local oscillators are likely to be most significant during temperature gradients, such as might be experienced in outdoor applications. We present measurements of the port to port agreement on BCs. Also measurements of PTP slaves connected to a common BC, including the effects of different servo loop algorithms, oscillator types, with and without temperature gradients.