Mobile signal is designed outdoors, but most calls and data sessions happen indoors. Concrete cores, low-emissivity glass, basements and steel frames all weaken the signal coming from nearby towers, and the bigger the building, the worse the problem gets. A distributed antenna system (DAS) is the most widely used way to fix it.
This guide explains what a distributed antenna system is, how it works, the main types, and how to tell whether your building needs one.
What is a distributed antenna system?
A distributed antenna system is a network of small antennas spread throughout a building or campus, all fed from a common signal source. Instead of relying on one strong signal from outside, a DAS brings the mobile network inside and shares it out evenly, floor by floor and room by room.
Because the antennas are close to users and transmit at low power, a DAS gives consistent coverage in places a single outdoor tower cannot reach, such as lift lobbies, car parks, stairwells and internal offices.
How does a DAS work?
Every DAS has three building blocks:
- Signal source. The mobile signal enters the system either from an outdoor donor antenna on the roof (an “off-air” source, amplified by a repeater or bi-directional amplifier) or directly from operator equipment installed on site, such as a base station or small cell. On-site sources add capacity as well as coverage.
- Head-end and distribution. The head-end combines and conditions the signals. They are then carried through the building over coaxial cable, fiber optic cable, or a mix of both, using splitters and couplers to divide the signal between floors and zones.
- Antennas. Ceiling-mounted omni antennas cover open areas, directional panel antennas cover corridors and long spaces, and leaky coaxial cable is often used in tunnels and lift shafts.
The result is a two-way system: it delivers the operator’s signal to phones indoors and carries the phones’ signal back to the network.
The main types of DAS
Passive DAS
A passive DAS uses only coaxial cable, splitters, couplers and antennas, with no powered equipment beyond the signal source. It is simple and cost-effective for small and medium buildings, but signal is lost over long cable runs, which limits how far it can reach.
Active DAS
An active DAS converts the radio signal to an optical signal at the head-end and sends it over fiber to powered remote units on each floor or zone. Fiber carries the signal over long distances with very little loss, so active systems suit large buildings, campuses and multi-operator projects.
Hybrid DAS
A hybrid DAS combines both: fiber to remote units on each floor, then passive coaxial distribution to the antennas on that floor. It is a common middle ground for mid-size and large buildings.
We compare the first two in detail in our guide to active vs passive DAS.
Single-operator and neutral host DAS
A DAS can carry one mobile operator or several. A neutral host DAS is shared by multiple operators on one set of infrastructure, which avoids each operator installing its own system.
Public safety DAS
Separate from commercial mobile coverage, a public safety DAS (also called ERRCS or ERCES) keeps firefighter and police radios working inside a building. In the United States, many jurisdictions require it under the International Fire Code (Section 510) and NFPA 1225. These systems carry public safety radio bands, such as P25, rather than consumer mobile networks. See our public safety radio solutions for more.
DAS vs repeaters vs small cells
| Option | Best for | Main limitation |
|---|---|---|
| Single repeater / signal booster | Small areas with a usable outdoor signal | Covers a limited area and adds no capacity |
| Distributed antenna system | Medium to very large buildings, multiple operators and bands | Higher design and installation effort |
| Small cells | Adding capacity in busy areas, often for one operator | Usually tied to one operator’s network |
Many real projects combine these. For example, a hotel might use a DAS for the whole building and add capacity in the conference areas.
Signs your building needs a DAS
- Calls drop in lifts, car parks, basements or the building core.
- Tenants or guests complain about slow mobile data indoors, even with full bars outside.
- The building uses energy-efficient glass or heavy concrete construction.
- The building is large: hospitals, hotels, airports, malls, stadiums, factories and office towers almost always need help indoors.
- A local authority or fire code requires in-building public safety radio coverage.
- You are planning a new build and want coverage designed in from the start, which is far cheaper than retrofitting.
How a DAS project runs
- Site survey. Engineers measure existing signal levels and record the building’s layout and construction.
- RF design. The system is modelled in specialist software such as iBwave to predict coverage, place antennas and size the equipment before anything is installed. Our article on in-building wireless design covers this stage in more depth.
- Approvals. Mobile operators must approve any system that connects to their network. Public safety systems also need sign-off from the local authority.
- Installation. Cabling, antennas, head-end and remote units are installed, ideally alongside other building works.
- Commissioning and testing. The system is tuned, and coverage is measured against the design targets.
- Monitoring and maintenance. Ongoing checks keep performance steady as the building and the networks change.
Frequently asked questions
What does DAS stand for?
DAS stands for distributed antenna system: a network of antennas spread through a building and fed from one signal source to improve indoor mobile coverage.
Is a DAS the same as a signal booster?
No. A signal booster (repeater) amplifies an outdoor signal for a limited area. A DAS distributes signal across a whole building through many antennas, and it can be fed by operator equipment that adds capacity as well as coverage.
Does a DAS support 5G?
It can. Support depends on the frequency bands the equipment and antennas are rated for. Older systems may need upgrades to carry newer 5G bands.
Who pays for a DAS?
It depends on the project. Building owners, mobile operators or third-party neutral host providers may fund the system, alone or together.
Talk to Aegotel about your building
Aegotel designs and delivers in-building coverage solutions, from survey and iBwave design to DAS supply and installation. If people in your building struggle to get a signal, contact our team to discuss a site survey.
