Distributed antenna systems and in-building connectivity

by Mindy Whisman, Director of Product Management and Development at AT&T Business

A distributed antenna system (DAS) is an in-building solution that enhances the carrier’s signal, distributes it to where it’s needed, then broadcasts it for smartphones and other devices to use. It’s a type of on-premises cellular network. It helps ensure your cell signal is strong everywhere. For large facilities like schools, hospitals, stadiums, and other large venues that rely on cell connections, DAS is a must-have for superior guest experiences, critical safety and security applications, and more.

Building materials like concrete and tempered glass can weaken even the most robust wireless connectivity signals—the same signals that power your data-hungry technologies like Internet of Things (AI), edge computing, and augmented reality. That’s why enterprises turn to a DAS to ensure that strong, reliable cell signals are available throughout their large facilities.

Why does a tempered glass building interfere with connectivity?

While tempered glass itself doesn’t block radiofrequency (rf) signals, the construction of buildings, especially those with energy-efficient features or materials like low-emissivity (Low-E) glass, can affect cell signals. Low-E glass is coated with a thin metallic layer that reflects infrared light while allowing visible light to pass through. This coating can block rf signals.

Also, building materials such as reinforced concrete or metal coatings in windows can weaken cellular signals to some extent. The impact on cell signals depends on the specific materials and construction methods used in the building.

In urban areas, the density of buildings, their materials, and the presence of obstacles or clutter, and other factors can contribute to signal attenuation, which means it can contribute to  the signal force or strength. The signals from cell towers may not be able to penetrate dense structures. Reflective surfaces can also be a challenge for cell signals. The arrangement of furniture, walls, and equipment within a building can also impede a signal’s path and interfere with the ability for a cellphone or other device to receive a strong signal.

Fortunately, there are multiple in-building solutions available for expanding coverage and boosting signal strength. A distributed antenna system is a good option for large structures like schools, hospitals, convention centers, and arenas.

What is a distributed antenna system (DAS) or in-building solution?

A distributed antenna system is an in-building solution that uses antennas and other components to enhance a cell signal’s performance, distributing it for phones and other devices to use. It's one solution for designing an on-premises cellular network.

Signal performance is measured by two qualities: capacity and coverage. Think of a big-name concert or a large sporting event and the thousands of fans who post video and photos to social media. Without added capacity to supplement the signal from a nearby cell tower, the cell network would quickly become overloaded and sluggish.

Sometimes coverage needs to be enhanced: a building that’s far from a cellular antenna, a city setting where dense structures weaken an antenna signal, or mountainous areas where antenna coverage is sparse. An in-building solution can fill gaps where a cell signal is weak or extend a signal’s boundaries to enhance coverage. Often, the ideal solution is a balance that enhances both coverage and capacity.

The size of a facility is an important factor in the type of solution you deploy. For buildings under 100,000 square feet, small cells often make sense. A single femtocell has a range of about 40 feet, and femtocells can be combined to cover larger areas. One advantage of femtocells is their ability to send signals through physical barriers, including dense materials like concrete and tempered and tinted glass. They’re also relatively easy to install and manage without help from outside professionals.

For facilities that are larger than 100,000 square feet, small cells can be used in combination with a distributed antenna system to enhance coverage and capacity. For some perspective, consider that only about 2% of U.S. buildings are larger than 100,000 square feet or more.1 That may not seem like much, but the ones that do exist are very large. They occupy about 35% of the total floorspace.

Some other fun facts:

  • About half of U.S. convention centers offer meeting space that is 100,000 sq. ft. and larger.2
  • One of the largest indoor sports arenas, United Center in Chicago, is almost 10 times that at nearly a million square feet.3
  • Of the 30 professional football stadiums in the U.S., the ten largest are more than a million square feet.4

How does a distributed antenna system (DAS) work?

A distributed antenna system provides wireless coverage to hotels, subways, airports, hospitals, businesses, roadway tunnels, and more. A DAS has two basic components: a signal source and a distribution system.

The signal source is the input to the DAS network. It comes from a wireless cell service provider like AT&T Business which licenses portions of the cellular spectrum and feeds the 4G LTE or 5G cell signal to its business subscribers. There are three ways the subscriber can retrieve the signal: off-air from a nearby antenna, a base transceiver station (BTS) or hub that is on site, or a small cell which acts as a miniature or wireless network base station.

The subscriber then uses a passive, active, or hybrid system to distribute the signal.

Passive DAS

A passive system captures the carrier’s cell signal, amplifies it, then sends it to other locations using coaxial cables and splitters. There is a range of amplifier sizes available, depending on the size of the area your amplified signal needs to cover. A system can be comprised of multiple amplifiers and signals woven together to form a blanket of coverage.

Passive DAS is less expensive to deploy compared to active DAS. But a signal transported through coaxial cable degrades over long distances. So you may need multiple amplifiers to transport the signal without losing strength. A big advantage of passive DAS is that it’s carrier agnostic. It can receive signals from multiple carrier frequencies. Passive DAS is generally a good solution for buildings on the smaller side: schools, hospitals, hotels, retail stores, and shopping malls.

Active DAS

Active DAS converts the carrier’s licensed radio frequency (rf) to a digital signal then distributes it using Ethernet or fiber optic cables to a remote access unit. The remote access unit (RAU) converts the signal back to rf, amplifies it, then sends it through coaxial cables to antennas throughout the facility. The antennas broadcast it so it can be picked up by cell phones and other devices.

There’s little to no signal loss in an active DAS that uses fiber optic cables, so it’s good for very large spaces like convention centers and stadiums that require long cable runs. Active DAS is generally more expensive and complex than passive systems. FCC regulations require carrier approval for active cellular DAS. It has to be coordinated and integrated with the carrier’s network, so your cell carrier’s engineers must be involved in the deployment.

Unlike a passive DAS, active DAS is not carrier agnostic. It is tuned to receive one carrier’s frequency. So you will need multiple active systems if you want to ensure all of your customers and employees have a strong, reliable signal regardless of which carrier service they use.

Hybrid DAS

Very large facilities like convention centers and stadiums don’t need to provide all signals at equal strength throughout the entire facility. They tend to be more strategic in how they deploy and manage a DAS. They typically use a hybrid DAS that includes both active and passive systems.

For example, they may use a passive DAS to ensure patrons can use their smartphones for talk, text, and data, regardless of the patron’s cell service provider. The venue might also combine private 5G service with a fiber network to ensure low latency and high reliability for IoT sensors used in their critical fire detection systems. 

Use cases for a distributed antenna system (DAS)

Read through some DAS use cases and it quickly becomes clear that modern cell service is much more than a signal. It’s key to your business success. Your customers and employees are accustomed to having the world at their fingertips. With 5G, your cell signal powers evolving technologies like edge computing, IoT, and augmented and virtual reality—technologies that help you engage customers and be more productive and efficient. Your cell signal could be your next competitive edge.

Healthcare: Improve efficiency and outcomes through connectivity

Short-staffing is a challenge for many industries but may be most critical when it comes to healthcare. As demands on their time and attention increase for doctors, nurses, and technicians, an on-premises cellular network deployed with Multi-Access Edge Computing (MEC) can help. It’s a powerful solution for processing high-bandwidth applications like telemonitoring, locally. Using smart cameras, staff can check on patients remotely. A distributed antenna system delivers the reliability, bandwidth, low latency, and privacy these technologies need for optimal performance.

It enhances coverage and capacity in settings that can quickly become overwhelmed by patients, staff, and visitors and that are often subject to interference from equipment and machinery and building materials like brick, concrete, glass, and steel. A DAS supplements network capacity so hospital staff can operate efficiently and improve patient care.

Stadiums: Power smart transactions and mass interactivity

For today’s stadiums the cellular connectivity experience can transcend the event itself. It touches nearly every aspect, from buying tickets, to wayfinding and getting fans safely to their cars, rides, or public transportation. It enables venues to combine close-ups and instant replays with fun and games that engage the audience. A distributed antenna system (DAS) can support state-of-the art concession experiences like in-seat ordering and grab-and-go transactions that eliminate the need to wait in line or check out. It enables IoT, artificial intelligence (AI), and machine learning that are used in security applications for facial recognition, predictive intelligence, and more. A DAS enables venues to use MEC, reducing the load on the network while delivering low latency and highly reliable cell connectivity.

Manufacturing: Enable digital transformation

With an in-building solution you can create a private local network that keeps your data close and secure. An on-premises cellular network forms a wireless infrastructure that has the capacity to support smart factory technologies like MEC to move data processing and storage from the data center to the network edge, closer to where it’s needed. With MEC and IoT you can get near-real-time insights from the sensors on machines and robotics, so you can monitor their health and status, track inventory levels, and more.

What all of these large venues have in common is this: there’s no one-size-fits-all approach. That’s why it’s important to complete a professional site analysis to arrive at a sound solution that meets your need for a strong, reliable wireless signal throughout your facility, both indoors and out, for every use case across the business.

Building a foundation for your in-building solution

Starting with a sound foundation for your distributed antenna system is key. What that foundation looks like depends largely on the size of the system and what you need from it. Will a portion of the system depend on MEC for lightning-fast editing and video playback? Will you deliver augmented or virtual reality for training or in-store customer experiences? Will sensors detect customer purchases for grab-and-go transactions or monitor sensitive equipment on a factory floor?

A reliable 4G LTE and 5G network built with fiber and available nearly everywhere is the starting point. And while each DAS is unique, systems of this size typically are supported by a state-of-the-art infrastructure that can include the reliability and hyper gig speeds of a dedicated internet connection combined with a business fiber network and secure cloud connectivity.

What you need to integrate a distributed antenna system (DAS)

Working closely with your carrier isn’t just an FCC requirement, it’s a best practice. Deciding which type of DAS system is right for your facility can be complex. It makes sense to start with a sound analysis and understanding of your facility and its environment and consider all your stakeholders’ needs. That’s where a thorough assessment from professionals who understand connectivity comes in.

You’ll also need to think about how you will manage your DAS. Large organizations with complex systems often opt for a hybrid approach. Their facilities and IT teams manage parts of the system. Their DAS provider manages others as a service. This can be cost effective because it reduces capital outlays and minimizes the burden on IT staff.

Don’t let building materials, terrain, location, data traffic density, or other factors affect your ability to conduct business and provide an outstanding customer experience. AT&T Business takes the time, and has the expertise, to understand your business so we can recommend a DAS solution that matches your needs—whether it’s better coverage, increased capacity, more control over your cellular network, or all of these. AT&T Business professionals will get you to the right solution by providing strong, reliable connectivity across your facilities to your customers, partners, and workforce.

Why AT&T Business?

See how ultra-fast, reliable fiber and 5G connectivity protected by built-in security give you a new level of confidence in the possibilities of your network. Let our experts work with you to solve your challenges and accelerate outcomes. Your business deserves the AT&T Business difference—a new standard for networking.

Learn more about the AT&T Managed In-Building Solution through our product brief. You can also visit our AT&T On-Premises Cellular Network page or contact your AT&T Business representative to connect with an expert who knows business.

1U.S. Energy Information Administration, Commercial Buildings Energy Consumption Survey (CBECS) 2018, December 2022

2US Convention Centers,” Cvent Supplier Network, accessed November 21, 2023, https://www.cvent.com/rfp/us-convention-centers-50e04fe6bd5e4dffbd1bebd80ea83db7.aspx

3United Center, “About Us,” LinkedIn, accessed November 21, 2023, https://www.linkedin.com/company/unitedcenter

4Top 10 biggest NFL stadiums by capacity and square footage,” Betway Insider, September 27, 2023, accessed November 21, 2023, https://usblog.betway.com/nfl/biggest-nfl-stadiums-by-capacity-and-square-footage