FTTA

What is FTTA (Fiber To The Antenna)?

Fiber-to-the-antenna (FTTA) is a wireless site architecture where optical fiber is run all the way up the tower to replace much of what was traditionally completed with heavier coax cabling. Important components such as remote radio units (RRUs) are also positioned at the top of the tower instead of at the base location.

In a FTTA configuration case, a baseband unit (BBU) situated near the bottom of the tower is connected via a fiber optic antenna and runs to a remote radio head (RRH) positioned near the antennas at the top of the tower. The RRH converts the digital signals to analog, and the short span between RRH and antenna is still completed using traditional coax cabling.

The Need for FTTA

The rapidly growing purchase and use of smartphones and tablets require more and more cellular bandwidth, and the increasing demands on cellular infrastructures are often underappreciated.

The term "cellular" is derived from the innovative way that networks of antenna towers provide seamless coverage, using a system of frequency zones or "cells." Each cell is serviced by a central antenna and defined by the associated transmission range. Increasing available bandwidth requires more cells and, therefore, more antennas.

These antennas naturally require cable runs up their towers to connect them to high frequency and power, so using the more efficient optical fiber to the tower process to complete these connections has been an amendable paradigm shift in broadband antenna architecture.

FTTA: The Good and the Bad

The shift to FTTA obviously brings numerous benefits to consumers, operators, and technicians alike. However, as with most advancements in technology, there are some complications and challenges to work out.

Fiber-to-the-Antenna (FTTA) Advantages

Perhaps the most obvious advantage of fiber-to-the-antenna stems from the physical content of the cable itself. The smaller diameter and lighter weight allow many fiber optic cables to occupy the same amount of space as a single coax cable. Because cellular towers are naturally subject to the elements, the physical size and properties of optical cabling are much less susceptible to damage from gusts of wind.

Other advantages of fiber-to-the-antenna technology relate to the shift from analog to digital. Due to signal losses, coax cable limited the distance between the antenna and base station to as low as around 100 meters. Optical cabling can span up to 20 kilometers with minimal losses. This allows for central housing of base stations and other similar efficiencies in architecture.

FTTA also provides improved energy consumption and signal integrity. Tower amplifiers are no longer required to combat the inherent noise floor of extended coax runs. The cooling of power amplifiers through air conditioning in a traditional base unit is replaced by ambient air cooling of the RRH, which significantly reduces the electrical power consumption of the system.

Fiber-to-the-Antenna (FTTA) Disadvantages

Fiber-to-the antenna obviously offers many key advantages. However, there are a couple of potential drawbacks to FTTA that relate to the change of media and the challenges inherent to optical fiber. Fiber is more fragile and therefore requires careful handling. Dirt and dust are the enemies of fiber, and cable runs exposed to the external elements are especially vulnerable, therefore the deployment of FTTA requires the use of FTTA fiber cables, waterproof fiber optical distribution boxes, and IP67 fiber adapters in harsh environments. Custom optical fibers are typically not interchangeable, and damaged fiber typically has to be replaced instead of just repaired.

Termination in the field can be more difficult, leading to more costly factory-terminated cable runs. These pre-fabricated runs sometimes include hybrid (fiber and power) cables because the power must be provided to the RRH separately. Should a pre-fab cable run require adjustment during installation, this could lead to schedule delays.

In FTTA architecture all RF functions reside on the RRH, and RF information is sent in the digital domain over fiber using the Common Public Radio Interface, or CPRI. Any RF maintenance or troubleshooting such as interference analysis requires reaching the top of the tower to get access to the RRH. This represents a higher operational expense and security concern.