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Types of Distributed Antenna Systems

Defining DAS Solutions Types

Connecting to radio and cell towers inside a building can often be a challenge because the materials used in construction block RF signals.

When you want your customers and employees to be able to maintain a reliable cell signal inside your building, you often need to install a distributed antenna system (Cellular DAS). When you want your buildings to be safer, you need a Public Safety Radio (PSR DAS) system that boosts in-building emergency responder radio coverage (ERRC).

But there are four different types of DAS that you might install to suit each of those needs: passive DAS, active DAS, hybrid DAS, and digital DAS.

We will describe each system below so you can learn more about the right one for your building.

Passive DAS

Passive DAS is low-maintenance and easy to install, but it is not the strongest and most effective.

This system uses passive radio frequency components such as coaxial cables, splitters, taps, and couplers. Because it is hardwired with passive radio frequency components, you need longer cables for it to function, producing weaker connections.

Pros of Passive DAS

  • Passive DAS systems are cheaper to maintain in comparison to other DAS systems
  • The absence of extra and expensive equipment makes passive DAS simpler to maintain

Cons of Passive DAS

  • Passive DAS runs on coaxial cables, and running longer cables can cause breakdowns in your system
  • These breakdowns can lead to greater cost and expense in maintaining these systems

When are passive DAS systems most used? In small to medium size buildings for PSR DAS applications. Radios operate at lower frequencies, which allow a less powerful system to still effectively boost signal strength facility-wide.

Active DAS

Active DAS is much more complex than passive DAS. Typically used in larger spaces, buildings, and venues, active DAS deploys a series of antennas to capture and redistribute cell signals across an entire building.

From a large antenna on the roof, active DAS distributes coverage throughout buildings over fiber optic and ethernet cables. These systems might be necessary when you need coverage over a large area, or when the materials in your building or venue block radio frequency (RF) signals.

The fiber optic cables that comprise active DAS alter RF signals into light, before transmitting it back to a recognizable signal when it reaches its destination.

Advanced fiber optic technologies in active DAS are employed by approximately 65% of engineers of DAS design. These advanced fiber optic technologies greatly enhance the digital transportation of RF signals. In the majority of cases, active DAS greatly improves the coverage and capacity of in-building cellular by transmitting signals over Remote Radio Units (RRUs).

Pros of Active DAS

  • Compared to passive DAS, active DAS generally do not use coaxial cables —fiber and ethernet lines enable signals to travel much farther and pass through sturdier materials with lower loss than coaxial cables.
  • Active DAS is more expandable and better for larger buildings and venues

Cons of Active DAS

  • Active DAS can be much more expensive than passive or hybrid systems

When are active DAS systems most used? In large buildings or across wide spread campuses for either PSR or Cellular DAS applications. Active DAS systems can also be configured to boost signals for major network carriers (like Verizon, AT&T, and T-Mobile) and public safety specific carriers (like FirstNet).

Hybrid DAS

Hybrid DAS is a mix of passive and active DAS—as you may have already guessed from the name. It uses both RRUs and coaxial cables to distribute signal throughout your building. 

With hybrid DAS, the distributed antenna system’s RRUs are separated from the main antenna, allowing designers to include both fiber optic and coaxial cables. Hybrid DAS includes an RRU on each floor that is connected to additional antennas with a coaxial cable.

Pros of Hybrid DAS

  • Hybrid DAS is less pricey than fully active DAS as they require fewer RRUs to run
  • The system isn’t limited by the length of coaxial cables

Cons of Hybrid DAS

  • While less expensive than active DAS, hybrid DAS still costs more than passive DAS
  • Mixing fiber optic and coaxial cable can make installation more complicated 

When are Hybrid DAS systems most used? In medium to large buildings for either PSR or Cellular DAS applications. But mainly after a site survey is conducted, which helps determine whether a fully passive or fully active system is required. If your survey determines you need something in between, a Hybrid is what may be recommended.

Digital DAS

Another type of hybrid system is digital DAS, which converts carrier signals to ones and zeros, known as an analog to digital conversion. Digital systems are more accurate and precise, so you may encounter less interference. Digital DAS works like active DAS; the signal is captured by an antenna on top of the building before it is converted.

They deploy a Base Band Unit (BBU) that connects directly to a master unit without needing to make analog-to-digital conversions. 

Pros of Digital DAS

  • Digital DAS is more precise/accurate
  • Has the lowest loss of signal strength of all system options

Cons of Hybrid DAS

  • More expensive than an active DAS (due it to being an emergent technology)
  • Has the lowest amount of installations nationwide (limited active use cases)

When are Digital DAS systems most used? In massive structures and buildings for either PSR or Cellular DAS applications. Though as mentioned earlier, there are few use cases as the technology is relatively new and relatively cost prohibitive. We anticipate that as more use cases become available that this system may outstrip the Active DAS in its deployment nationwide.

What DAS is Right for My Building?

Now that you understand the four types of DAS, you can decide which one will work best in your building or venue.

If you find that your building, business, or venue can’t get by on Wifi alone, you need to consider your budget, along with the coverage and capacity you need, in choosing a distributed antenna system. 

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