Speaking at the Goldman Sachs Communacopia + Technology Conference, AT&T’s CEO John Stankey said, “There’s a fallacy to say there’s fixed networks and wireless networks. There are only fiber networks with different access technologies on the end of them. That’s where this is all going.”

He’s right, but not everyone understands that wireless networks are not wireless. Wireless networks are built on fiber optics. Here is an explanation of how telephone systems have evolved to use fiber optics for most connections, right out to the antennas on cell towers that your mobile phone connects to. 

Cellular wireless

Cellular phone systems have grown to dominate the telecommunications marketplace. The United States, which has had extensive landline phone systems for a century now, has more cellphones than land lines, and the number of land lines continues to decline by 5%-7% per year. 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.

Cellular phone networks are just another extension of the worldwide phone network. Switches and fiber optic networks (plus a few leftover copper wires and microwave relay links) create a network all around the world. Some subscribers connect to the network by the local loop on a landline. Others connect using wireless devices that connect to cellular antennas.

Telephone networks connect users either on wireless links from cell sites or on local loop connections with copper or fiber landlines.

While cellular wireless started out as a voice network, text messaging became very popular, eclipsing voice for most users. Smartphones, led by the introduction of the iPhone in 2007, brought the internet to the phone, and soon data became the largest traffic generator for cellular networks. Now streaming video is available on these same devices, creating an even faster growth rate for cellular network traffic.

To accommodate this increase in traffic, wireless needs new systems with new protocols like 5G and more radio frequency spectrum. In the beginning, cellular towers were connected to the telco networks over microwave radio links or copper wires, but fiber optic connections, called “backhaul,” quickly began taking over the connections to cell towers to meet bandwidth demands.

How wireless towers are set up

Wireless towers have small huts at the base that connect to fiber backbones, which in turn connect the towers to the various phone companies. As traffic grew, towers needed more antennas for more bandwidth to more users. Instead of 3-4 antennas on a tower, now one sees dozens, so towers now look like this:

Cell towers with dozens of antennas and large bundles of coax cables up to the antennas

All these antennas on a tower have created another problem. In the past, each antenna has been connected by a large (approximately 2 inches, or 50mm) coaxial 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. Fiber optics solved the weight problem, so most antennas are now connected on fiber, called FTTA, or "fiber to the antenna."

Diagram of connections on a cell site. FTTA replaces bundles of large, heavy coaxial cables to the antenna.

Adding fronthaul to wireless towers

The large amount of bandwidth on wireless networks means that technology is being developed to make it faster, more available and cheaper. One of the interesting developments is traceable directly to the capabilities of fiber for long links and high bandwidth. It's called “fronthaul” by one of the developers, or more generally “C-RAN” for centralized radio access network.

Fronthaul moves the electronics to a central location and connects the tower over fiber.

Fronthaul or C-RAN replaces backhaul by moving the electronics (base band unit) at the cell tower back to a telco central office or head end. At the tower, you basically leave just a small electronic unit to drive the antennas. Moving the electronics from the tower to a head-end saves costs, power and field maintenance.

Replacing big wireless towers with small cells

In urban areas, cell towers are being replaced by “small cells.” They are small, integrated radios and antennas intended for small geographic areas, just a few city blocks. They are typically mounted on the usual urban fixtures, such as walls, streetlights, traffic lights, bus stops—whatever gets them slightly up off the ground. They only need a single fiber and power to operate.

Small cells are often placed in urban or suburban residential neighborhoods on utility poles.

The diagram for a small cell looks just like a fronthaul network. All the electronics are located in a central office or head end. As small cells proliferate in cities, it is necessary to create large metropolitan networks to connect the small cells that must be placed just a few blocks apart.

Stay tuned for the second part of this article, which will cover metro and rural Wi-Fi.

Photos and illustrations by Jim Hayes.