FOA Guide to Fiber Optics

Topic: Fiber Optics For Wireless - Small Cells

Table of Contents: The FOA Reference Guide

Small Cells

Wireless traffic is growing at a phenomenal rate. AT&T says their cellular data traffic grew more than 80,000% (that's 800 times) between 2007 (the introduction of the iPhone) and 2017. The landscape is covered with cellular towers but the capacity of these systems is inadequate for planned traffic levels, especially as cellular service providers move to 5G.
Here is why wireless is so much in the news - look at these graphs from CTIA, the US trade association for the wireless business, with data from the end of 2016:

Wireless Subscribers

and the one below shows the wireless traffic growth:

Wireless Data traffic

That looks like Internet growth 10-15 years ago. That kind of growth gets attention because it means that service providers have to invest in capacity - in wireless that means fiber backbone and cell sites. The next graph shows that growth - the number or cell sites in the US.

Wireless Cell Sites

This data represents "traditional cell sites" - those giant towers along roadways with big antennas at the top or buildings with multiple antennas along the roofline. You can see how the number of sites has grown in parallel to the number of subscribers over the last two decades to provide adequate coverage.

Today the focus is on "small cells." Small cells use much lower power and cover much smaller areas - as shown schematically in the graphic below. Generally small cells will subdivide large cell areas to provide more local service.

small cell coverage
Regular cells (L) and small cells (R)

Small cells have the advantage of being small and unobtrusive. Cities have always had problems with cell coverage because of the blocking of signals by large buildings and many of the local citizens being against large, ugly cell towers in their neighborhoods. Small cells look like the ideal solution. They can be installed on light poles, traffic signals or the side of buildings and are small and almost unnoticeable. 

Small cells go by other names including micro-cells. They are small, low-power, integrated radios and antennas intended for small geographic areas. They typically operate in the frequency range of 700MHz to 2.6GHz with power outputs from <1W to 5W, much less than regular cellular antennas. (5G has proposed to move to frequencies >50GHz, but there are technical problems at those frequencies.)

Small cells are intended to be be mounted on typical urban fixtures – walls, street lights, traffic lights, bus stops, whatever gets them slightly up off the ground. They only need a single fiber and power to operate. The electronics to control them is in a CO or head end, connected to them by fiber.


Alcatel-Lucent pioneered the concept of the small cell when they unveiled their LightCube Radio Small Cell in 2011.

Because small cells cover smaller areas than regular cellular antennas, they will have fewer users connecting to them to increase the bandwidth available per user. Most will require only a single SM fiber and DC power making installation easy where municipal cable plants are available. Fiber technology for installations is standard OSP and premises – nothing new required. They can even use PONs (passive optical networks - like FTTH)  to reduce the fiber needed and electronics near the antenna. You can place several of these small cells in one dome providing extended coverage over many frequencies.

Look at what is happening in Santa Monica, CA. The Santa Monica Seascape, the city's newsletter for its citizens, recently ran this article about small cells.

Small cells in Santa Monica

"In 2016, the City of Santa Monica adopted a new wireless telecommunication ordinance to protect the city from uncontrolled expansion, while streamlining the review process to meet statutory deadlines. Adherence to city design standards, compliance with Federal Communications Commission (FCC) safety standards for radio frequency emissions, and mail notification to adjacent neighbors are all part of the local review and approval process.

In response to the surge in customer data demands, the private cellular industry has already begun preparing for the deployment of micro-cell sites over the next few years. Micro-cell equipment is often as small as a toaster and, in Santa Monica, will be mounted to existing light standards and telephone poles across the city. These low-power, short-range devices (pictured above) can process a lot of data very quickly. As the systems go online, cell phone users will experience fewer dropped calls, faster data transfer speeds and a more reliable network.

An estimated 600 of these sites will be installed in Santa Monica over the next  five years."

We know Santa Monica and know the cellular coverage is marginal in many parts of the city. At one point some service providers were giving out personal "microcells" that connected to your Internet in areas with poor coverage. But the interesting thing is the number of small cells that are estimated to be installed - 600 - in a town that is only 8.4 square miles (about 22 square km) and has a population of just over 90,000 people. That's an antenna for every 150 people!

Within the first year, more than 130 small cell permits were taken.

Installing all those small cells in Santa Monica is probably going to be much easier than in many cities because of the extensive metro network the city has installed. Santa Monica CityNet has most of the city covered with large fiber count underground cables and a network operating at 100Gb/s - one of the world's fastest metro networks.

Walking the city streets, you are often seeing techs splicing in new drops or working on the fiber connections for the traffic controls.

Santa Monica CityNet  Santa Monica CityNet

Palo Alto, CA was an early adopter of small cells and they had a unique way of integrating them into the city without being obtrusive. Here is an installation of a small cell in Palo Alto.
They put the electronics in a mailbox like box and ran an antenna up a street light! You can see the yellow singlemode cable that connects the electronics in the photo.

Small cell Palo Alto  Small Cell

Other cities are also installing small cells. Below are photos from downtown San Francisco of three different types of small cells on street lights on Polk Street.

SF small cell  SF small cell  SF small cell

Boston also has a number of small cells installed.

Boston small cell  Boston small cell  Boston small cell

The city of Los Angeles has also been installing small cells, but in some locations it is combining the small cell with other innovative technology.

LA small cell  LA Smart Node

On the left is a new smart LED street light from Philips with an Ericsson small cell in the wide part of the pole near the top. On the right is a En-Hub, a radical new pole with options for street lights (inside the pole, not hanging off to the side), small cells, smart city sensors and even a charging station for electric cars.

Small Cells On Fiber Backbones
Small cells are designed to operate on fiber backbones directly from the small cell to a central office or head end, similar to the "fronthaul" or "C-RAN" (Centralized Radio Access Network) used with regular active antennas on cell towers. That means that every small cell site needs several fibers direct back to a central facility.
In metro areas, that will require lots of fiber. If it's not there, it will need to be installed. Some talk of using PONs (passive optical networks used with fiber to the home (FTTH) because it uses less fiber than point-to-point links) to connect small cells.

Wireless fronthaul
Cellular "Fronthaul" or "C-RAN" network has fiber going from a central office/head end directly to the antenna.

Metropolitan networks to support small cells can be shared with other services, including fiber to the home, security systems, traffic systems, including vehicle to vehicle (V2V) and vehicle to infrastructure (V2I) communications. All this adds to the demand for fiber optic communications to support the city of the future. Articles have appeared both indicating the urgency to install fiber (Deloitte) and questioning if the parties involved have the commitment and resources to actually build such networks (Bloomberg.)

Evolution Of Small Cells

Ericsson small cell

At a 2017 IWCE (wireless) conference, Ericsson had this device in their booth. It's a small cell that connects over Category 6 cable and is powered over the cable by POE (power over Ethernet.), just like a wireless access point. The implication seems to be that a DAS (distributed antenna systems) can be the same as small cells and even use conventional structured cabling like WiFi. Interesting. Sharing premises (LAN) cabling could make a big cost  difference for the installation of DAS in office buildings.

Learn more about how small cells and other technologies contribute to "smart cities."

More On Fiber For Wireless
FTTA- Fiber To The Antenna  
Testing FTTC Fiber  
DAS - Distributed Antenna Systems  
WiFi - Premises Wireless  

Comparing WiFi, Small Cells and DAS


(C)2018, The Fiber Optic Association, Inc.