The growth in mobile data consumption has been putting pressure on the mobile network operators (MNOs) to build out small cell networks. All this traffic needs to be backhauled to the mobile core. While traditional choices for backhaul focus on fiber and microwave, hybrid fiber coaxial (HFC) networks have been making advancements. HFC is now being considered as a backhaul contender by the MNOs thanks to its capacity growth, cost efficiency and speed of deployment.
Traditional mobile base stations need to be frequency synchronized to guarantee handover performance, and this service is provided by the backhaul. In the DOCSIS 3.1 specification, the DOCSIS Time Protocol(DTP) was designed into the DOCSIS 3.1 specification to support precision timing from the CMTS to the cable modem (CM). This would allow a CM to provide backhaul services to a mobile base station for backhauling via the DOCSIS link. However, DTP is just one piece of the puzzle, as it needs to work with other elements of the operator network to provide timing to the base stations. This synchronization framework has yet to be defined. Furthermore, each operator network has differing levels of timing support in their existing hardware. This complicates system level designs.
In addition to frequency synchronization, Long-Term Evolution Time-Division Duplex (LTE-TDD) and LTE-Advanced features such as coordinated multipoint (CoMP) and enhanced inter-cell interference coordination (eICIC) all require stringent time and phase synchronization. Supporting these features places additional requirements on the synchronization framework.
In this paper, we review the technologies that can support frequency, time, and phase sync. We propose several architecture options, discuss their corresponding deployment scenarios, and the implications of each option on operations, cost of ownership, and time to market. Finally, we make recommendations on the device requirements and identify optimal designs based on operator deployments.