When it comes to tackling the various issues of power connectivity for 5G small cells, there are a few existing options and each has its opportunities and obstacles.
Power from the grid
For the vast majority of mobile network operators, obtaining an ac power feed from the utility grid is the go-to solution for powering wireless networks, and has been for a long time. As a result, the solution is very familiar to those working with it in the field.
However, the process requires intense planning and project management. This method becomes less attractive as mobile network operators shift from deploying fewer and larger-capacity macro-based cell sites to thousands of smaller capacity small cells.
Challenges include the cost and time involved in getting a power drop (metered or un-metered) to each individual node.
Additionally, network engineers must solve the issue of equipping each site with battery backup in space constrained urban locations and satisfying tougher aesthetic regulations.
Hybrid fiber coaxial (HFC)
HFC networks are now the mainstay of the cable television industry. By utilizing the power-carrying capability of the integrated coaxial cable, they also provide an alternative solution to the small cell power challenge. As operators work to meet increasing subscriber demand they continue to invest and improve their outside plant.
This involves upgrading their 60/90 VAC power plant, adding more power injection points, pushing fiber deeper into the network and deploying remote distributed-access architectures. Estimates are that 80 percent of HFC plant miles have network power availability.
This includes fiber portions of the plant where coaxial cable can run in parallel, as a back-feed from an optical node, to make power available. In most cases the power availability is more than adequate for Wi-Fi hotspots or small cells.
The challenges with HFC networks are that it is still not ubiquitous and, where operators do not own their own backhaul networks, they must lease from other providers.
Twisted pair
A second possibility involves tapping the power-carrying capability of the legacy copper telephone networks, also known as a remote feed telecommunications (RFT) circuit. There are essentially two approaches to this solution.
RFT-C is current limited to 60 mA and typically supports less than 20 watts of power at 320 volts. RFT-V, which typically operates at ±190 volts, is voltage-limited to 100 watts of injected power per pair. The main advantage of the RFT solution is the ability to re-use the existing copper plant.
However, the small diameter copper pairs provide limited power under the current standard and exhibit high power losses over extended distances. At a length of 3,000 meters, the 100 watts of injected power drops to about 60 watts of effective power.
Additionally, there is a general lack of documentation regarding available copper wires within the public-switched telephone network (PSTN). So identifying the right power injection points is also a challenge.
Power over Ethernet (PoE)
Since Power over Ethernet was introduced—in the early 2000s—manufacturers, industry organizations and standards bodies have made good progress in expanding its capabilities and applications. The latest Power over Ethernet standard, IEEE P802.3bt (PoE++), finalized in 2018 will support up to 71.3 watts (dc) per device port.
As such, its use in a small cell environment would be limited to very low-powered Wi-Fi access points. In addition to power restrictions, Power over Ethernet is also distance limited, with PoE++ rated for a maximum distance of 100 meters.
There are solutions that enable operators to use Power over Ethernet over longer distances which increases the span up to three kilometers. While it removes the distance limitations, the power limitation remains. Moreover, the speed and latency requirements for small cell backhaul dictates the use of fiber, which further weakens the business case for Power over Ethernet.
Distributed power connectivity
A new approach being developed uses hybrid fiber cabling to deliver power and connectivity from a central location to a cluster of neighboring small cells. A suitable centralized location can be anywhere that has access to power and the optical network, such as an outdoor distribution cabinet, telecom closet or macro base station location.
This approach takes advantage of evolving hybrid fiber cabling as well as advancements in dc power delivery. Such improvements have increased the efficiency of dc-dc conversion to more than 95 percent and enabled the use of higher voltage levels to transport more power over long distances more efficiently.
Meanwhile, the use of hybrid fiber cabling enables operators to combine power conductors and the fiber cables in the access network. For example, it becomes possible to power and connect dozens of small cell locations—spaced 200 meters apart—from a single location with local grid power and room for power backup.
By eliminating the excessive time and costs required for a utility drop, mobile network operators are able to deploy power to their small cells faster and less expensively in places where power is not quickly and easily available.
It also allows for battery backups or generators at the centralized location to support busy or mission-critical small cells. Therefore, the solution is ideal when both power and data connectivity can be deployed as part of a greenfield rollout, and where multiple new locations can be clustered around a single point of connection to the grid.
By reducing the number of uncontrolled variables—scheduling delays, electrician availability, additional meters— the distributed power connectivity solution gives operators full control over how, when and where to add small cell coverage.
This enables mobile network operators to swiftly respond to new market opportunities and increase speed to revenue capabilities that are critical in an increasingly competitive market place.
