FTTA - Fiber To The Antenna
PDLC ODVA FIBER OPTIC PATCH CORD FOR FTTA:
Today's users of mobile devices depend on wireless connections for their voice, data and even video communications. Even homes and businesses may depend on wireless, especially those who are not in urban or suburban areas served by FTTH (fiber to the home) or FTTC (fiber to the curb.) Some of us in the business now use the term FTTW for fiber to wireless, since wireless depends on fiber for the communications backbone and increasingly the connection to the wireless antennas, no matter what kinds of wireless we use.
Wireless is not entirely wireless. The easiest way to understand wireless is to think of it as a link that replaces the cable that connects your cellular or wireless phone to the phone system or the patchcord that connects your computer or other portable Internet device to the network. To understand wireless, it is necessary to look at several different and unique types of wireless systems, including cellular wireless phones, wireless in premises cabling, municipal or private wireless links and even some of the short distance links used for computer peripheral connections.
This FOA page focuses on fiber to the antenna, primarily looking at cell towers, but also antennas mounted on rooftops, small cells and distributed antenna systems (DAS.) Because of its variety, DAS will be covered in a separate page in more detail.
Why fiber to the antenna?
The reason fiber is being used to connect towers and then go up the tower to connect the antennas is consumers insatiable desire for bandwidth. To accommodate more bandwidth in the cellular systems, new cellular protocols being are used (4G, LTE, and whatever comes next) but also more antennas are needed to support more frequencies. Thus cell towers that once had 3 antennas for coverage may have two dozen antennas.
The increased demand for cellular bandwidth to support fast growing data usage from smartphones and tablets requires upgrading towers – more bandwidth means more antennas. More antennas means more cables up the towers. If those cables are coax, it means more weight and wind resistance, perhaps more than the tower was designed for. And RF (radio frequency) signals require lots of power to transmit up the tower since the coax cable attenuates the signals at high frequencies.
Today’s cell towers are being modified to replace older copper coax cables with fiber optic cables to reduce weight and cost. Like other applications of fiber, the small size and light weight allows one fiber cable (which often includes power conductors also) to replace many coax cables. This diagram shows what a current cell tower looks like. The diagram is way too complicated for a quick view so we’ll focus on various areas of the tower to show how fiber is used, then we’ll go into issues of installation and testing.
Cellular phone systems have grown to dominate the telecommunications marketplace. Countries that have had extensive landline phone systems for a century now already have more cell phones than land lines. Countries that had not developed landline-based phone networks skipped them entirely and went directly to cellular wireless where the adoption rates have been extremely high.
While cellular wireless started out as a voice network, text messaging became very popular, eclipsing voice for most users. Smart phones brought the Internet to the phone, and soon data became the largest traffic generator for cellular networks. In the first 3-1/2 years of the iPhone, AT&T claimed their data traffic grew 8000% - 80 times! Now video is coming to these same devices, creating an even faster growth rate for cellular network traffic.
To accommodate this traffic level, wireless needs new systems with more radio frequency spectrum. Current systems (CDMA for some systems, in the US, GSM for the rest of the US and the world) are evolving into new generations of systems (4G, LTE) that have more data bandwidth. Almost from the beginning, cellular towers were connected to the telco networks over fiber optics, just like any other connection. Wireless towers have small huts at the base that connect to fiber backbones that connect towers to the various phone companies. As traffic grows, towers need more antennas. Instead of 3-4 antennas on a tower, now one sees dozens, so towers and buildings now look like this:
or on buildings.
All these antennas on a tower or the side of a building have created another problem. In the past, each antenna has been connected by a large (~2", 50mm) coax cable that carries both signal and power to the antenna. But with all these antennas, the size, weight and even wind resistance of these cables has become a big problem, as has the cost. These towers which have been upgraded to add many antennas show the problem with these large coax cables.
This is another application where copper cable is being replaced by optical fiber. One small fiber cable can replace all those coax cables and a separate power cable is used for the drivers on the antennas. These applications use mostly prefab cable assemblies since making terminations on top of the tower is difficult to say the least. Some applications use prefab at the top of the tower and conventional termination at the base. Many of these systems use multimode fiber because the distances are so short and the transceivers are much less expensive for MM fiber.
Below are photos from Corning showing a remote antenna head end and antenna and the fiber terminal serving the antennas. Note the use of a prefab cable system at the top of the tower, making installation much easier. Some installations use a composite cable that includes both fiber and power conductors so only one cable need be installed up the tower.
Many cell towers are independently owned and space for antennas is rented to the service providers. Installation of fiber to the towers and fiber up to the antennas is generally done by independent contractors who specialize in this kind of work.