The need to boost capacity in the backhaul network is the top priority right now for practically every mobile operator in developed countries. With so many subscribers using smartphones and other devices to access mobile broadband applications, the demand for bandwidth is straining backhaul capacity to its limits. The only cost-effective way to increase that capacity over the long term is to deploy fiber from the base station back into the mobile network.
Some mobile operators also are taking fiber all the way from the base station to the antenna which is sometimes called "fronthaul." In combination with a distributed antenna system (DAS), fronthaul fiber provides additional capacity and coverage where and when it's needed – and subscribers now need more of both, indoors as well as outside.
First Comes Fiber in the Backhaul
As operators deploy fiber in the backhaul, they will need connectivity solutions such as fiber panels to terminate and cross-connect it; some also may require Ethernet patch panels for organizing the physical connections between the base station equipment and the backhaul network. Finally, they will need equipment to terminate the fiber they're bringing into the hut or base station hotel. By splicing that fiber to a panel, they can use a plug-and-play approach for provisioning, testing and trouble shooting.
At the Mobile Switching Center (MSC), operators also will have to terminate and manage fiber, so they will need panels and frames there as well. Compared to the very-high-capacity (Multiple OC-192/10-GbE or 40 Gbps wavelengths) fiber backbone, the access network will have a lot less capacity but a lot more fiber. With hundreds of base stations linked to a given MSC, operators will need high-density frames within the MSC to terminate and manage all those fibers.
Because subscribers use their cell phones as mobile data terminals, the demand for more bandwidth stretches across the network. So, when operators boost their backhaul capacity, they'll also have to add capacity to the backbone network and data center. Thus, any operator with a data center, often co-located with an MSC, will need additional solutions, including:
• multi-fiber cables pre-terminated with multifiber push-on (MPO) connectors;
• high-density fiber frames, such as ADC's TrueNet ODF, which can manage 1,728 to 2,304 terminations; and
• high bandwidth cabling, such as OM3 laser-optimized multimode fiber.
Optical fiber cabling is backwards-compatible only, so operators must choose fiber today that will satisfy future bandwidth requirements.
Extend Fiber into the Fronthaul
Although subscribers use their mobile devices outdoors and within moving vehicles, most now use them indoors even more frequently. As a result, the industry must focus on high-capacity indoor technology, rather than high-coverage outdoor technology, and on different network designs.
The traditional design starts with a macrocell tower and then addresses coverage or capacity problems that arise when large groups of people get together at, say a stadium event. Savvy operators know that approach eventually will not be sufficient to deliver high-quality service. Instead, they are designing indoor networks, while still relying on microcells and traditional macrocell towers to provide outdoor coverage.
Specifically, they are replacing the fronthaul's coaxial cable with fiber and deploying a DAS. Although coax can deliver the same amount of bandwidth as fiber, it is characterized by a great deal of loss. Fiber helps operators not only overcome some of the distance limitations of coax but also avoid wasting energy in "heating up the coax." Now they can put the energy where it's needed – in the last stage of amplification of the antenna.
Within the distributed-antenna architecture, an operator can establish either a series of base station hotels, each of which houses the baseband equipment for each base station, or a small central office-type location to house the baseband equipment for several base stations. In either case, the operator then deploys the antennas wherever they're needed to provide the required capacity and coverage and uses the DAS to interconnect the components.
By creating smaller antenna points and placing them close to subscribers, the operator can replace the large amplifiers needed to drive a big cell tower with several small, lower-power, lower-cost amplifiers. With no need to build a big tower, the operator also can avoid – or at least defer – the costs and zoning headaches associated with towers, as well as the expense of equipment rooms.
Whether they do it themselves or hire outside resources, operators realize the only way they can boost capacity in the backhaul is to deploy fiber. Smart operators understand that for the same reason, they will have to do the same in the fronthaul.
Mike Day is vice president and chief technical officer at ADC.