By Chris Bastian
SVP, Engineering and CTO for SCTE•ISBE
Following up on my CableFax 5G article in February, I’d like to expand on the opportunities that cable operators have to offer backhaul and fronthaul connectivity (known collectively as x-haul) to wireless operators. Let’s first start with an overview of the cellular architecture that the cable operator is being asked to transport.
The fundamental cellular signal flow is from the cell site radio (or radio head) to the radio controller, then from the radio controller to the mobile switching center (MTSO). “Fronthaul,” the newer term, is the segment from the radio head to the controller. The more traditional “Backhaul” term is the segment from the controller to the MTSO. There are multiple emerging 5G architectures to support this flow, as summarized in this figure, in which we use 3rd Generation Partnership Project (3GPP) designations for the radio unit (RU), the distributed unit (DU) and the central unit (CU), which controls the DU:
How the Media Access Control (MAC) and Physical (PHY) network functions are overlaid on these architectures will result in different outcomes: Significant analysis has been performed to determine how bandwidth, capacity and latency are impacted by locating these functions at different points of the network. These requirements are placed on the underlying transport network provided by the cable operator.
Common Public Radio Interface
The Common Public Radio Interface (CPRI) is a specification for the interface between the radio head (RU) and the radio controller (CU). It was defined and has been adopted by several major vendors in the cellular industry, who cooperated so that the architecture was simplified, and their equipment could interoperate. While not a standard, enhanced CPRI (eCPRI) follows the overall 3GPP specifications and will support the 5G fronthaul requirements.
The cable industry needs to support these different architectures and service requirements, in order to provide reliable x-haul transport. CableLabs is developing specifications and conducting testing for this wireless/wireline convergence. They have been focusing on coordinating cable DOCSIS® and wireless LTE/5G network control, in order to reduce end-to-end latency, as well as providing a timing reference for cell sites over DOCSIS. Recent testing and demonstrations at the Mobile World Congress have shown that through proper coordination, upstream latency can drop to the 1-2ms range.
With the global push towards deploying 5G, including the deployment of small cells much closer to the cellular customers, there will be a large demand for wireline connectivity to support these new cell locations. New, emerging services supported by IoT, VR/AR, as well as higher resolution video services will increase this demand.
Does the cable industry provide much x-haul support today?
The cable industry is already providing significant backhaul connectivity to cellular operators, including more than 50% of the total backhaul traffic in many service areas. As the architectures shift to including fronthaul, the cable industry is working to be in lock step with cellular industry counterparts.
With the industry-recognized CPRI specification, and the ongoing work CableLabs is doing for low-latency and synchronization, cable is well-positioned to continue providing backhaul connectivity, as well as to support the emerging fronthaul connectivity requirements. This may signal the beginning of true fixed mobile convergence which has been envisioned for years.
SCTE-ISBE Cable-Tec Expo® 2019, scheduled for Monday, Sept. 30 through Thursday, Oct. 3 in New Orleans, will once again have a Wireless Access Network track at which many papers will be presented on topics including 5G, fixed mobile convergence and Wi-Fi.