DAS 101 - The Cold Hard Facts

DAS 101: An Introduction to Public Safety DAS and Cell DAS.

Do I need a DAS in my building?

DAS is an invisible technology that is absolutely vital to the day to day functions of large scale commercial buildings.

The purpose of this guide is to explain what DAS is (and is not) and provide some basic fundamentals to understanding invisible systems that help buildings operate.

RF is a physics term that means “radio frequency”. There are all types of radio frequency waves in our every day environment (Both inside and outside). Some of these RF frequencies are carrier bands from Verizon, AT&T, T-Mobile and Sprint that allow a direct connection to the core cellular network. Other RF bands are responsible for first responder radio systems, and ensuring their two-way radios can function to send and receive audio.

What do both of these systems have in common? They both don’t make it into buildings very well. In the case of both cellular signal and first responder signals, commercial buildings will block the incoming signal and cause poor functionality for phones and radios within the building.

So why is this a big deal?

For cellular, the answer is simple. In all building types, cellular is an essential function that is vital to the operations of the building. Multi-family, Commercial Office Space, Healthcare, Hospitality/Hotels, Higher Ed, Government, Industrial and Manufacturing all have use cases that necessitate strong cellular throughout the building.

For the first responder signals, the issues are more severe. IFC and NFPA ERRC Code mandates minimum service levels throughout the building. If these service levels are not met, the building will not get their CO (Certificate of Occupancy) unless a public safety DAS system is installed to meet the requirements.

Cellular DAS

When the cellular coverage inside a building is not functional or is impacted for the vast majority of the property, a cellular DAS will be installed.

What is Cell DAS?

At its core, all DAS systems operate from the same fundamental principles. They are a “Distributed Antenna System”

This means there is a network of cabling and antennas through the building that is utilized to disperse signal through the building.

There are multiple types of DAS systems, and some of the most common elements can be seen in the glossary below.

Donor Antennas- Antennas that capture the existing outdoor signal and bring it into the building.

Trunk Line- Main run of cabling that runs vertically in the building to bring coverage to data closets on each floor

Head End- The “Brains” of the system where the signal will be amplified and routed to disperse through the building.

Remote Units- Devices that provide extended coverage in large square footage buildings. Think of them as an extension to the head end.

Signal Source- The carrier hardware where signal is generated.

Interior Antenna- The indoor antennas that propagate the signal into the building. Function similar to a wireless access point where they bring coverage to an end user

Horizontal Cabling- The cabling that runs above ceiling throughout the building floors to

Within the subset of cellular DAS, there are different methods of deploying the system in the property, and different financing/purchasing options that will define the type of engagement.

The two main distinctions (But by no means a comprehensive or exhaustive list) are passive and active DAS. These are the methodologies by which signal is brought into the building. An intentionally simple summary along with context is included below.

At their core, all DAS systems are a network of cabling both vertical and horizontal, along with antennas that propagate coverage in the building and allow for better connectivity. The base levels of infrastructure for the systems are relatively straightforward and will look largely the same to the untrained eye in a project.

The key difference, is how the signal is generated and supplied inside the building. Those classifications can be seen in the next section. Keep in mind, the purpose of this post is to provide high levels of information, as the technology expands, hybrid solutions that blur lines between traditional terms have started to become more prevalent.

Passive DAS:

A passive DAS system utilizes the existing macro environment, and repeats the signal inside the building. Said another way, the system receives signal from surrounding cell towers (Using antenna(s) on the roof) and brings the coverage into the building to redistribute throughout the property. This method is fast to deploy, cost-effective, and perfect for scenarios where the building is blocking coverage.

These systems do not generate their own signal, however. So, the building is somewhat beholden to the existing cell coverage and capacity in the area. Meaning, if the coverage outside is either poor, or beyond network capacity, the cellular repeater/passive DAS system may have a limited efficacy.

Active DAS:

An active DAS uses Carrier Signal Source inside the building the generate the signal rather than relying on existing cellular towers. Generally, this is carrier hardware that requires backhaul. This is a carrier specific piece of equipment which ultimately supplies the required number of user sessions in the building. This method provides the building with its own independent cellular coverage that is completely controlled by the property. This means that the building will always have proper coverage and capacity regardless of the outdoor environment. These systems have a higher associated cost and a longer lead time to build and coordinate with carriers. They will generally be seen in larger scale commercial/hospitality/healthcare projects where the user density requires a system built exclusively for the building.

Financing Models

I will spend less time on this section since this is HIGHLY variable depending on the DAS integrator that you choose to work with. There will be plenty of crossover and similar approaches between teams, but no list of financing models can be completely exhaustive. Some of the major options will be defined below.

Building Owner Funded- Purchased outright

In these engagements, the system will be paid for outright by the owner/management company/asset manager. These systems will immediately be owned outright by the building and may only need an additional contract for signal source. These engagements will typically still have a minor monitoring agreement and in some cases, a maintenance agreement.

Capital Lease

This is a highly variable style of system ownership, so we will keep this section general. These systems will generally have some amount of initial capitalization (or in some cases not be capitalized at all) and then paid for monthly.

Some of the systems will simply be a lease to own model, whereas others will intentionally have a structure built in where the lease can be extended in exchange for system upgrades to 5G/6G. These systems can function more as a “managed service” and work best in long term holds where additional contracts for the building will not negatively impact the building value.

Capital lease systems can have any manor of buyout and term period.

Carrier Funded

This section is included as it is technically a viable option, but it is being seen less and less as carriers pull back from funding these systems and push that burden onto the building owners. Generally, carriers may still fund systems in ultra large scale properties, or mass venues such as airports/stadiums/convention centers. In a typical building, it can be hard for carriers to justify funding a system, and even more difficult to put together the contracts.

Generally, a team will market the building/venue to the carriers with an intended cost for each carrier to participate in the cellular DAS. Carriers will give a verbal confirmation that they intend to participate and then move to more formal contracts.

In many cases, these engagements can last 2+ years and dematerialize at any point due to carrier feasibility. If this option is being pursued, it is best to have an alternate engagement model working concurrently where the building owner is funding the DAS system.


This technology is covered in other blog posts, so this section will just cover high level basics.

A fundamental concept in understanding ERRC is understanding the nomenclature associated with the systems. Depending on the jurisdiction or area, you may hear it referred to as

Public Safety DAS First Responder DAS

Emergency Responder Radio Coverage (ERRC) BDA Life Safety DAS

They all point to the same thing- a system that is engineered to provide proper coverage for first responder radios in the building.

All first responders rely on radio communication in order to communicate. Buildings can block coverage in much the same way that they can block cellular signal. If the signal is not strong enough for a radio to effectively operate, the fire marshall will determine that the building is not passing testing and mandate a first responder DAS be installed.

These systems are more binary than cellular. The systems are graded on a pass/fail basis.

The systems will all be built similar to a passive cellular DAS, meaning that signal is captured from the roof and brought into the building to redistribute. The system must be properly built including code compliance aspects such as 2 hour shafts, Battery backup, and proper radio frequencies. Once again, there is plenty to say about the build out of these systems, but for purposes of a general 101 overview, we will keep this brief.

The buildings must pass testing in two ways for them to be accepted by the fire marshall. Both the floor plate of every level must pass testing throughout, as well as the areas of egress (Critical points). These are most commonly stairwells.


For both cellular DAS and Public Safety DAS/ ERRCS, the building should be assessed prior to construction to determine the needs for each system. These systems are simple to integrate ahead of the build schedule, and more difficult to coordinate during the construction of the project.

A good DAS integrator will help you determine what is needed, the different options available, and give full transparency into the testing process at the site. Please reach out if you have any questions!

Alex Goge, National Director of Sales