Upcoming 5G deployments will force major disruptions to the status quo for mobile network operators. In preparing their networks to handle the massive demands for more bandwidth, new applications, lower latency, and ubiquitous coverage, mobile network operators have begun the process of cell densification in their existing 4G networks. The result is a significant increase in the number of small cells being installed. This, in turn, results in an increase in both the number of locations where power is required and the total amount of power consumed by the network.
The advanced capabilities of today’s 5G-ready small cells mean added power requirements. Increased data traffic requires more computational power. A single small cell site or node that covers three sectors and multiple frequency bands can require 200 W to 2,000 W of power, depending on the size of the sector(s). Further, typical distances between these sites are in the range of 200 m to 500 m. This presents mobile network operators with a significant challenge: how to get power to large numbers of small cells in a cost-effective, fast, and efficient manner.
The traditional model for powering macro cell sites does not apply to small cells. Mobile network operators are used to the deliberate and structured process involved in permitting, building, and provisioning their macro cell locations. Each tower location is carefully planned and specific to a site, in order to eliminate any surprises once construction begins.
Cell densification requires a wholesale shift in that mindset. The sheer number of small cells means operators must accelerate deployment with “cookie-cutter” processes. At the same time, they must be equipped and agile enough to adapt their siting, backhaul, and power solutions on the fly. There are also power-specific challenges operators must address. When it comes to tackling the various issues of powering small cells, there are a few existing options, and each has its opportunities and obstacles.
Power from the Grid
Obtaining an AC power feed from the utility grid has been the typical solution for powering wireless networks. The solution is very familiar to those working within 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 (Figure 1). 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.
Power from the grid can continue to be a good solution, in particular, when access to fiber for backhaul is already present at the location. OEMS make AC versions available of their radios. Hardened AC/DC rectifiers, some with integrated battery backup are also available. However, service providers and installation companies are actively experimenting with alternative solutions to work around the problem of cost, deployment speed, and clutter at the site—and to anticipate the need for centralized battery backup.
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 (Figure 2). Estimates are that 80 percent of HFC plant miles have network power availability. This includes fiber portions of the plant where the 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 WiFi hotspots or small cells. The challenges are that HFC networks are not ubiquitous, that existing HFC networks do not always have sufficient spare power-carrying capacity, and where operators do not own their own backhaul networks, they must lease from other providers.
Another possibility involves tapping the power-carrying capability of the legacy copper telephone networks, also known as a remote feed telecommunications (RFT) circuit. 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 m, the 100 W of injected power drops to about 60 W of effective power. Additionally, there is a general lack of documentation regarding available copper wires within the public-switched telephone network. Identifying the right power injection points is also a challenge.
Twisted pair RFT powering schemes have been used in DSL deployments as alternative solution to powered street cabinet in some instances (examples can be found in Italy and Argentina) but this did not happen at massive scale. Today, some cases of small cell deployments have been reported using this technology.
Power over Ethernet (PoE)
Since PoE was introduced—in the early 2000s—manufacturers, industry organizations, and standards bodies have made good progress in expanding its capabilities and applications. The latest PoE standard, IEEE P802.3bt (PoE++), was in 2018 and will support up to 71.3 W (DC) per device port6. 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, PoE is also distance limited, with PoE++ rated for a maximum distance of 100 meters. There are solutions that enable operators to use PoE over longer distances. But the speed and latency requirements for small cell backhaul dictates the use of fiber, which further weakens the business case for PoE.
Distributed Power Connectivity
A new approach being developed and being considered for industry standardization 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.
The solution being considered for standardization is an end-to-end connectivity solution combining power and fiber effectively in an end to end system (Figure 3), using a code compliant method. Several major service providers and OEMs are involved in a number of standardization activities around this principle.
- The concept of clustering devices and power them remotely is being introduced as ‘cluster powering’ in “ETSI EN 302 099 V2.1.x, Powering of equipment in the access network”, under Revision—introduction of Cluster Powering concept.
- Several activities are also on the way to standardize the 400 VDC input at the radio equipment which will eliminate the need for separate down-conversion at the site; driving power efficiency up and cost of deployment down at the same time:
- ITU-T L.1200: Direct current power feeding interface up to 400 V at the input to telecommunication and ICT Equipment
- ETSI EN 301-132-x: Power supply interface at the input to telecommunications and datacom (ICT) equipment
- New ETSI work item on universal AC & DC interface: EN 300 132-4 Operated by 400VDC and AC input interface
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 connects dozens of small cell locations—spaced 200-500 m 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, such as an existing macro site or power cabinet.
We believe up to 50 percent of site deployments could benefit from this approach. Operators can apply this solution to effectively drive cost efficiencies in the rollout of converged access networks, intelligently combining the ability to serve residential customers, business customers and wireless sites from the same fiber network and enabling distribution of power to edge devices at the same time.
Adding a pair of copper pairs in the fiber feeder network at the time of deployment comes at a marginal cost over the total investment. It is something every operator should consider, as opens a path to monetization opportunities around power and fiber distribution—driving up the intrinsic value of their network assets.
By reducing the number of uncontrolled variables—scheduling delays, electrician availability, and additional meters—the distributed power connectivity approach 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.