What Is a Distributed Antenna System?

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What Is a Distributed Antenna System?

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Distributed antenna systems or DAS are networks of antennas installed in strategic locations inside a venue – often a massive building, like a sports arena or high-rise corporate building – designed to improve voice and data connectivity for users inside the establishment. 

Large structures often have poor indoor reception from telecommunications and wireless Internet providers. Signals from cell towers sometimes cannot pass through concrete, steel, and other composite materials often used in construction. As a result, large buildings have many “dead spots” or areas where there’s no cell signal. This explains the choppy signal or sudden disconnect when you’re on your phone while walking in a windowless corridor in your office building or a deep area of a multi-level car park.

Components of Distributed Antenna Systems

A distributed antenna system consists of the following parts:

1. Signal source

For distributed antenna systems to function effectively, there has to be a primary signal source that will feed the DAS network the signal it needs to distribute. 

There are three types of signal sources: off-air antennas, base transceiver stations (BTS), and small cells.

Off-air antennas are the most affordable signal sources and arguably the most commonly used in commercial buildings in the middle of an urban district. It is an external antenna installed on the roof of the building, and it sends and receives signals to and from macro cells like cell carriers and towers.  

BTS signal sources (also called NodeB, eNodeB, gNodeB) are directly connected to mobile operators via fiber optic cables. These devices perform better than off-air antennas, but venues and buildings often have to install one BTS for each carrier. If the occupants of a building use different networks, the administration must coordinate with the network provider because the latter will provide access to their fiber optic cable network. 

Small cells function the same way as macro cells. They amplify wireless signals to extend network coverage to all areas of a venue or building, similar to how a modem extends the WiFi signal to the more hidden areas of your house, like the basement and attic. 

2. Signal distribution system

Obtaining a strong signal source is the first step in establishing distributed antenna systems; the next is implementing antenna systems that transmit the signals and improve connectivity all over the building. 

The signal distribution system does three things: amplify, distribute, and broadcast signals throughout a building. More than extending coverage, it expands a building’s public network capacity so all occupants, guests, customers, and visitors can get mobile reception. Of course, signals weaken in high-density areas because there are too many simultaneous users. But with robust distributed antenna systems, venues can maintain strong cellular service throughout low-density and high-density areas, indoors or outdoors. 

The technology used for the signal distribution system defines the type of DAS a building uses. In the next section, we’ll delve deeper into the different types of antenna systems.

Four Types of Distributed Antenna Systems

1. Passive DAS

Passive distributed antenna systems have a repeater that sends signals through coaxial cables, splitters, couplers, and taps to distribute passive radio frequencies throughout a venue or building. Passive DAS is ideal when you only need to extend coverage over a small area and if your facility has thick masonry, concrete, and metal construction components. 

The simplest of all four distributed antenna systems, passive DAS is the most affordable. It doesn’t require many components to run, so it is also low-maintenance (except for the long coaxial cables, which tend to suffer from attenuation or signal weakening and will therefore need timely replacement). 

2. Active DAS

Active distributed antenna systems are more complex than passive DAS because the signals they broadcast undergo conversion. An active DAS consists of a master unit and remote radio units (RRUs). The former receives analog radio frequency (RF) transmissions from the signal source. It converts them to digital signals before transmitting them to RRUs all over the building via ethernet or fiber optic cabling. The RRUs convert the digital signal back to RF so mobile phones and other Internet-connected devices can recognize it.

Since it uses fiber optics, active DAS is ideal for massive venues with many structural barriers impeding signal distribution, i.e., thick concrete walls or steel dividers. The system converts source signals into light, transmitted through fiber optics, and then converted back to recognizable RF signals once they’ve reached their intended destination.

3. Hybrid DAS 

As the name suggests, hybrid distributed antenna systems combine active and passive DAS technologies. They use coaxial cabling, fiber optics, and RRUs.

Hybrid DAS captures signals from the source using fiber optic cables instead of coaxial cables (an upgrade from passive DAS) and sends them to RRUs installed on each building floor. The RRUs convert the light signal into RF and broadcast them using antennas connected to the RRUs via coaxial cables.

The price point for hybrid DAS sits between passive and active DAS. It’s also more flexible: it can accommodate scenarios in which only passive or active DAS is the answer. By combining both, IT technicians can have greater control over transmission strength and location.

4. Digital DAS

Digital distributed antenna systems are still in their infancy and aren’t widely adopted yet. However, it has a simple working principle: it does away with RF-to-digital signal conversions and distributes digital signals throughout. 

Digital DAS uses a base band unit (BBU) connected to a master unit, which distributes digital signals via fiber optic or ethernet cables. Since it doesn’t use RF, it is less susceptible to interference. IT technicians can direct a fixed capacity to specific areas inside a venue, such as a conference hall, cafeteria, or atrium. 

Digital DAS is promising but expensive and will only work if the signal source and DAS master unit support Common Public Radio Interface (CPRI) specification.

How Can Signals Defense Help?

Designing and installing distributed antenna systems delivers great benefits such as productive employees, happy tenants and customers, as well as an improved public perception of your building’s IT amenities. The rewards are significant for a business: augmented WiFi connectivity and cellular services increase the productivity of office workers, improve tenant retention rates, and satisfy customers so they will want to keep coming back. You must always choose the DAS system that will work best in your building and its users, guests, or occupants.

To Learn more about how Signals Defense can help your DAS system perform at its best contact us to learn more.

Want to read a case study on DAS success? Follow the link here.

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