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Fiber-to-the-Antenna systems bundle up for the elements

Thu, 11/21/2013 - 10:12am
Chris Warner, ECN Executive Editor

Standard components and rugged connectors harden all-in-one FTTA systems and ensure quick and easy installation

You can’t drive very far without seeing a cellular tower.

As more Americans curtail or ditch their landlines in favor of mobile phones, and increasingly smartphones that require high-speed internet, network operators must keep pace with the incredible amount of data traveling through their infrastructures. They continually work to increase capacity, but building new towers – particularly in densely populated areas – and retrofitting old ones is very expensive. Of course, users aren’t interested in the capacity limits of these networks. They just want their high-speed connections to work.

Fiber-to-the-antenna (FTTA) is steadily replacing coaxial cable as operators look to increase capacity while keeping the costs of upgrading their infrastructure low. Fiber cables typically run alongside or in combination with power cables from a baseband unit to multiple remote radio units (RRUs) at the top of the antenna and are able to maintain desirable signal integrity. Additionally, FTTA supports the latest networking standards such as 3G, LTE/4G and LTE-Advanced and it can accommodate multiple-in and multiple-out (MIMO) channels to enhance the bandwidth.

Throughput and signal integrity, however, are only the most obvious considerations for network operators. When choosing a cabling solution for cellular towers, network operators must also consider the rugged environments in which they are being deployed, the challenges and safety issues for installation and maintenance personnel trying to access the hard-to-reach equipment, and they must be sure that the cable systems are connected properly for reliability.

Many of these challenges can be addressed with an all-in-one solution. Wireless equipment providers are combining both the fiber optic signal cables and power cables and their associated components into a single enclosure that can be mounted at the top or bottom of the antenna and installed in a single day. Los Angeles-based Talley Inc. offers a system, for instance, that connects incoming tower trunk fiber and DC power cables to individual ODVA (Open Device Vendor Association) 2 or optional ODC (outdoor connector)-compatible, fiber output RRU (radio head) feeder cables and DC power cables. The Fiber+Power-to-the-Antenna system’s enclosure can feed up to 24 radio heads.

Withstanding wind, weight and weather
Talley set out to design a system that would withstand the punishment caused by oscillation due to the wind, and the weight of the cables – particularly the power and hybrid cables -- and their housings had to be supported by a single housing grip while suspended. “The construction of the power and/or hybrid cable has to take these vertical forces into consideration,” says Patrick Flynn, VP of marketing development at Talley Inc. “At the design phase, adding structural elements to the cable allows for eliminating negative impacts the power cable can have on the fiber units in hybrid cables, and providing the strength to remain suspended vertically in the copper conductors of the power units of the cable.”

In the field, Flynn has seen first-hand how bad weather can lead to system failures. Therefore, the Fiber+Power-to-the-Antenna system was designed and hardened with inclement weather in mind so service can continue uninterrupted during inclement weather and, should a failure occur, service can be restored quickly. The company ensured the system is compatible with existing tower architecture and uses industry standard components, so technicians can make fast, easy repairs.

Industry standard components also make installation and testing easy because the product requires less training. “I always recommend that the customer select solutions that use industry-standard products,” says Brian DiMarco, President of Fibersource, which manufactured the FTTA Combination cabinet for the Fiber+Power-to-the-Antenna system. “This minimizes costs and reduces lead time. Industry standard products generally have better quality and reliability since more engineering, development and testing can be performed.”

Installers and technicians using a hybrid-fiber-and-power-to-the-antenna system also appreciate the safety characteristics of the latest cabinets. Rounded edges and light weight are important to personnel working at heights of 500 feet or more, and cabinets with dielectric construction present less shock hazards than metallic cabinets. The Fiber+Power-to-the-Antenna system’s distribution box uses a UV-resistant polycarbonate that is more than 40 percent lighter than fiberglass, steel or aluminum. The box was constructed to withstand impact of over 900 inch/pound, tested in accordance to UL-746.

Secure, plug-and-play fiber connectors withstand punishment
In fiber-to-the-antenna applications, “jumpers” are installed from the distribution box to the RRU. ODVA (Open Device Vendor Association)-compliant fiber optic connectors are desirable because they are intermatable and interchangeable with other suppliers’ ODVA connectors, and are therefore positioned to offer leadtime and reliability benefits. Fiber optic connectors in FTTA applications should meet the International Electrotechnical Committee (IEC)’s 61300-3-35 standard which mandates proper connectivity and describes “methods for quantitatively assessing the endface quality of a polished fiber optic connector” (www.iec.ch), and they must withstand a variety of harsh conditions at cell tower installations such as moisture, temperature, dust, vibration and UV exposure.

Connectors that are rated to NEMA level 3 are hardened to protect against heavy rain, snow and ice. For extremely rugged environments, consider IP67-rated connectors, which offer protection equivalent to NEMA level 6 requirements. Connectors with a plug and play ODVA design help installers using Talley’s Fiber+Power-to-the-Antenna system to easily connect multiple fiber pairs to the Fibersource ODVA fiber couplers on the distribution box. Input cables install directly to the box, so technicians do not have to access the cabinet’s interior. For this system, Talley chose a duplex LC connector from CONEC with a secure bayonet locking which helps save installation time and effort.

Jim Lieb, Vice President of Sales at CONEC explains, “The cost…is a slight premium over the grommet type that requires a field install of the fiber trunk in and the multiple fiber out to the radio heads. The fiber distribution box is completely done in the production facility, and the fiber assemblies are pre-installed in length.” Brian DiMarco adds, “The ¼-turn latching ensures consistent mating compared to threaded connectors which can be over or under torqued, leading to field problems.”

Standardized components and rugged enclosures help future-proof FTTA systems
Field safety and ease of installation/maintenance are clearly major considerations when selecting products for FTTA systems, and standardized components address these concerns while keeping costs low. One additional benefit standardized components offer is flexibility. Since Americans’ appetite for high-speed internet connectivity on their mobile devices will not be satisfied any time soon, always keep your options open with future bandwidth demand in mind.

“Don’t tie yourself to proprietary product,” cautions Flynn. “(Proprietary products) are designed to limit your options, drain your budget and leave you with a ball and chain secured to your network.”

Robust, weather-proof enclosures help future-proof the tower installation as multiple fibers are added and terminated within the cabinet as demand increases. ODVA fiber optic connectors, meanwhile, are progressing with MPO 12 and 2-4-fiber trunk cable-in for quickly connecting into the fiber distribution box. Expect to see connectors that can accommodate DC trunks that use two-pin power. These connector advances, along with rugged equipment and industry standard components help make all-in-one FTTA systems appealing to cellular network operators looking to scale up their tower infrastructures for future bandwidth demands quicker, safer and smarter.

1 Stephen C. King, White Paper: Fiber Management Solutions for the Cell Tower, 3M Communication Markets Division, 2013. Accessed September 28, 2013. (http://bit.ly/GBcpnX)

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