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Distributed Antenna Systems: A Crash Course

With so much of America dependent upon cellular connections, individuals and businesses alike understand the frustration of weak cell signal, dropped calls, or the inability to get online. Just as the technology of smartphones has evolved, so have the solutions for keeping the masses connected. Enter passive and active distributed antennas systems (DAS), which have become the most popular go-to solutions for addressing cellular connectivity issues.

DAS can address problems and ease frustrations, from the largest spaces to the smallest. In fact, despite the existing perception that DAS is only for large arenas and other similarly-sized spaces, 90 percent of DAS solutions in use today actually appear in smaller spaces, such as office buildings, residential buildings, and even small B&Bs.

Choosing the Best Distributed Antenna System (DAS)

DAS comes in active, passive, hybrid, and digital forms. While users with lower capacity needs can consider alternative wireless connectivity solutions for their businesses or homes, the decision for commercial users often comes down to one of two solutions: passive or active DAS. It’s the task of the integrator to determine whether passive or active DAS is the best solution for each client’s unique needs.

While integrators certainly understand the difference, sometimes it’s difficult to explain to the customer why one solution is better than an other. Let’s break down the differences between active and passive DAS so we can better prepare for these conversations.

What is Active DAS?

An active DAS is most robust and infrastructure-intensive cellular connectivity solution. It provides carrier-grade, high-capacity infrastructure solutions for large areas. An active DAS creates cellular signal to provide coverage. The system distributes the signal between a centralized signal source and remote nodes placed throughout a building. An active DAS system accommodates large areas where thousands of users access the network in a confined space. Think airports and arenas.

It’s commonly the first solution integrators and users turn to — but should it be? Despite the strengths of active DAS, the installation process can be complex and generally requires the installation of fiber optic cabling, which means tearing into walls and other structures. An active DAS also requires a significant investment of time and capital, including the construction of a dedicated backhaul. Customers with limited budgets and that do not have large spaces to deal with may opt for a passive DAS solution.

What is Passive DAS?

Passive DAS (also known as a cell phone signal booster system) eliminates cellular connectivity problems by enhancing existing cell signal up to 32 times through the use of antennas and amplifiers. It does not require the creation of an internal network like active DAS.

The hardware and installation requirements of a passive DAS system are far less expensive and can be installed faster than what’s required for active DAS:

  • Donor antennas installed on the roof or near a window bring in the outdoor signal.
  • Broadcast or indoor antennas on the interior wall (panel antennas) or ceiling (dome antennas) then transmit the amplified signal to phones and other cellular devices indoors.
  • Both types of antennas connect to the amplifier unit via coaxial cable.

Passive DAS conforms to FCC regulations and generally does not require outside regulatory approval. Since most systems are pre-approved, and because of the low infrastructure requirements for installation, a passive DAS can be installed in a matter of days or weeks.

With less overhead, fewer regulations, and lighter equipment than other options, a passive DAS is a financially viable option for a wide range of users. Costs for hardware and installation of passive DAS can range from 30 cents to 70 cents per square foot.

In addition, many passive DAS are carrier-agnostic and support multiple carriers simultaneously. So, whether your clients use major carriers like AT&T, T-Mobile, Verizon, or smaller regional carriers, a passive DAS ensures everyone gets the same amplified signal.

Applying DAS To Different Venues

With the exception of extremely large venues, such as airports and arenas where thousands of people are consuming cellular bandwidth, passive DAS is a feasible and effective connectivity solution, which is why it’s popular in industries including retail, real estate, hospitals and hospitality, education, and event venues like theaters and conference centers.

Additionally, passive DAS can literally save lives. When emergency medical teams and public safety officers can access a strong cellular network, they’re better able to communicate with one another and utilize critical location services and maps. Passive DAS can help improve cellular network access in police stations, firehouses, courthouses, and even emergency vehicles. With a passive DAS in place, the improved connection results in safer, more efficient operations and enhanced public safety.

First Step of Achieving Better Cell Service: Site Survey

As an integrator, you’re well-versed in the differences between active and passive DAS. However, your clients likely won’t be. Consider this your 101 guide to explaining options to your clients, ultimately helping them make the best choice. Once the choice between active and passive DAS has been made, it’s a good idea to stress to your clients the importance of the site survey. Here’s a review of site survey best practices, step by step:

  1. Before beginning, inform your client about the importance of roof access for your site survey. Without roof access, the site survey won’t be as effective. If necessary, offer to speak with the building owner on behalf of your client, if they are not the owner.
  2. Look at the building’s floor plan to familiarize yourself with the site. This will help you map out signal areas while performing the survey on site.
  3. Once you’re on site, start your survey on the roof. Walk around to different sides of the building and, using your signal meter or equivalent device, note the signal reading on each side. Record the readings for all channels and frequencies each time.
  4. After you find the location with the best signal, slowly swivel 360 degrees to find the source of the signal. Once you find it, note the direction it comes from. This tells you the direction of the nearest cell tower. (If installing a passive DAS, this is where you’ll install and orient the donor antenna.)
  5. Proceed down through the building, carefully noting signal strength in every room and corridor and making note of how signal strength fluctuates based on where you are in the building.
  6. Upon completion of the physical site survey, all the signal strength notations will allow you to go back to the floor plan and map out a strategy for placing indoor server antennas in order to maximize the boosted signal coverage inside. (Many integrators find the easiest and most effective way to accomplish this is by using iBwave or a similar network planning software.)

So there you have it: your easy guide to explaining DAS to your clients. If you’re interested in more information and a more thorough explanation of DAS, download our Ultimate Guide to Distributed Antenna Systems.

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