Author: Tim Frost, Strategic Technology Manager, Calnex Solutions Ltd. tim.frost@calnexsol.com

Abstract:
There is much discussion on the increasingly tight synchronization requirements for co-ordinated radio techniques in 5G. However, these techniques are only implemented between a small cluster of radio units. The radio protocols originate in the Distributed Unit (DU), which operates the lower-layer radio protocols, and all radio units (RU) attached to the DU must be synchronized to each other to participate.

This is driving cluster architectures in the fronthaul network. The synchronization requirements on these clusters are very tight, but they only apply within the cluster – they don’t need to be synchronized to other clusters in the network. Therefore the requirement is for tight relative time error limits within the cluster, and much looser time error limits between clusters.

This paper will look at some of the cluster architectures being proposed by bodies such as the ORAN Alliance and ITU-T, and the relative time error requirements within the clusters.