Fiber To The Antenna Advantage

In the evolution to advanced 3G and 4G services, wireless service providers are taking fiber to the top of the tower. Next-generation, fiber-fed architectures are quickly becoming the new norm for tower builds and retrofits.

These new Fiber To The Antenna (FTTA) architectures leverage tower-mounted radios to deliver a number of benefits over traditional coaxial-based systems. However, when it comes to installing fiber networks with an operation geared toward hard-line coax, operators face a new set of challenges, particularly in terms of connectivity.

They must weigh the pros and cons of factory-terminated versus field-terminated fiber cable. They have to consider the skill sets of their field technicians. And they should address the increased need for weatherproofing required by many new antenna designs in order to provide advanced services.

New solutions from connectivity suppliers are helping operators meet these challenges.

Why Fiber To The Antenna or FTTA?

Many operators around the globe have chosen to invest in fiber networks for new builds and retrofits of cell towers. They see it as the best architecture to meet current and future demand, reduce energy consumption and minimize footprint. Among the advantages of FTTA:

• Better signal integrity: Conventional systems use coaxial corrugated cables to transmit high-frequency radio signals from the base station on the ground to a passive antenna on the tower. As much as 50 percent of the signal can be lost along the way, according to many industry estimates. These losses increase the signal-to-noise ratio, degrading the quality of the received signal. Signal loss in not a concern when fiber is used. Fiber To The Antenna systems use tower-mounted remote radio units (RRUs) to generate the signal at the top of the tower, near the antenna, with a coaxial jumper cable connecting the two. With a short distance to travel over coax, signal loss is minimal.
• Increased energy efficiency: Reducing carbon footprint (and energy costs) has become a ubiquitous goal in the communications industry. Remote radio systems can significantly reduce a tower’s energy consumption, according to the 2010 “ATIS (Alliance for Telecommunications Industry Solutions) Report on Wireless Network Energy Efficiency.” In a traditional base station design, transmitted radio signal power travels up the coaxial feeder cable to the antenna. As the frequency of the radio signal rises, the corresponding signal losses in the coaxial feeder increase. In the worst cases, twice as much signal must be injected into the feeder coax as is needed to propagate out from the antenna. The radio frequency (RF) power amplifier in the base station is one of the least efficient components of the system, and much of the extra energy required to drive RF power up hard-line coax is simply wasted as heat. This, in turn drives up the energy costs even more because active cooling systems such as A/C are needed to keep the equipment within its operating temperature ranges. Cooling typically accounts for 25 percent of a tower’s energy use, according to the ATIS report. With a remote radio system, the RF power amplifier is located in the RRU. The tower-mounted RRU is cooled by ambient air flow, eliminating or decreasing the need for active cooling in the base station and saving energy.
• Increased capacity and coverage: Remote radio units often support advanced antenna techniques such as multiple In multiple Out (MIMO) and remote electrical tilt (RET), which enable denser, more flexible coverage with fewer service gaps and higher capacity.
• Smaller footprint: FTTA systems consume less space because the fiber cable is many times thinner and carries more signal than coaxial feeder cable. A fiber-fed system lessens – or at least doesn’t add to – coaxial congestion and tower loading issues, saving tower real estate, reducing physical complexity and minimizing visual impact. Also, the removal of the inefficient RF power amplifier and its associated cooling systems decreases the need for a shelter or a large equipment storage unit to house the base band unit.

The Fear of Fiber

While FTTA architectures boast many advantages, operators face a number of new practical challenges when it comes to installing fiber on towers. Operators realize that fiber is generally better suited than coax to achieve advanced 3G and 4G data rates and to prepare their networks to meet future demand.

However, a number of stumbling blocks stand in the way of implementation. The so-called “fear of fiber” has been coined to describe concerns that operators face as they consider next-gen architectures. The term alludes to the fact that fiber is relatively fragile and requires some care during installation.

But the real reluctance to switch from coax to fiber is steeped in fundamental unfamiliarity with the media. Indeed, installing fiber requires a new skill set. That means retraining technicians or hiring new ones, a time-consuming and costly proposition.

Companies can sidestep the training issue by purchasing factory terminated fiber. However, factory-termination adds to the cost of the cable and requires various lengths to be stocked. Additionally, because it comes in pre-defined lengths, factory-terminated cable may create either a slack storage situation or turn-up delays when the cable is too short, adding cost.

Those issues have fueled the emergence of field terminated fiber connectors in the Fiber To The Antenna space. Field termination fits well with the prevailing practices used for hard-line coax. Specifically, hard-line coax is always cut and terminated on-site to ensure a proper fit.

New field-mount fiber connectivity solutions allow the same paradigm to be used for fiber deployments – simply roll out a spool of fiber, field terminate at the site, and you have a custom installation every time with no messy slack storage or missed deadlines due to inadequate cable lengths.

To make fiber more craft friendly, connectivity suppliers have developed solutions to help mitigate the cost and complexity of installing fiber in the field.