By Ruoyu (Roy) Sun Ph.D., CableLabs; Aaron Quinto, Mark Poletti, CableLabs, Inc; Charles Cook, Vikas Sarawat, Praveen Srivastava, Lei Zhou, Charter Communications, Inc.; Elias Chavarria Reyes, Ph.D., Hitron Technologies, Inc.
Mobile networks require high accuracy time and frequency synchronization. 3GPP mandates 1.5 µs of timing accuracy from the base stations (BSs) to a common time reference [1]. Meeting this 1.5 µs target avoids inter-base station interference in time-division duplex (TDD) networks. In addition, inter-network synchronization is required by the FCC for Citizens Broadband Radio Service (CBRS) and is recommended for other bands. In outdoor environments, Global Positioning System (GPS) signals are reliable and can be used to derive an accurate timing signal. However, when BSs are deployed indoors where GPS signals are unreliable, BSs need an accurate timing signal delivered over the backhaul link. DOCSIS Time Protocol (DTP) is designed to provide such a high-accuracy synchronization signal on the Hybrid Fiber Coaxial (HFC) network, serving as the Xhaul (Xhaul refers to backhaul, mid-haul, or fronthaul) for mobile networks.