Distributed Antenna Systems

What Are Distributed Antenna Systems?

A distributed antenna system (DAS) is a network of antennas that are connected to one common source which enables them to send and receive cellular signals. The antenna system is spread throughout a building or designated area to improve the overall network performance. A DAS network is much more powerful and efficient than compared to a single large antenna covering the area.

Each antenna is intentionally spaced out to provide the network with the best coverage without any overlap. This method reduces the number of antennas needed to cover the whole area.

Distributed antenna systems can be used indoors and outdoors. DAS are most commonly used in subways, airports, hotels, office buildings, tunnels, and hospitals. They provide wireless coverage for PCS, cellular, Wi-Fi, and emergency services, including fire rescue and the police. You likely enter dozens of places daily that have a DAS network running through them without even realizing it.

How Does Structured Cabling Work?

A DAS network is comprised of two essential components: A signal source and a distribution source.

The signal source is responsible for the input to the DAS network. There are several signal sources that can be used to feed into the system. There’s the off-air source, the on-site base transceiver station (BTS), and a newer approach known as small cells.

Off-Air

A DAS that uses an off-air signal source (also referred to as a repeater), works by using a donor antenna. The donor antenna is typically positioned on the roof of the building where it can receive and transmit signals from a cell carrier.

Off-air signals are the most common of the signal sources used in a DAS network because they’re generally the lowest-cost option and offers fast signal deployment. Their primary purpose is to extend the coverage within the building from the very edges of the network. They do not, however, add to the network’s capacity.

For an off-air signal source to work properly, the donor signal must be strong and clear. If the donor signal is weak or congested, the off-air signal source won’t perform well.

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BTS

The BTS, which includes NodeB and eNodeB, refers to the technology being used within cellular towers to generate a signal. For a cell carrier’s BTS to connect to your core network, a dedicated fiber connection must be installed. A DAS using a BTS signal source in large buildings and arenas typically have multiple dedicated fibers to make a strong connection and cover each carrier. BTS signal sources are among the highest performing and can provide as much capacity as needed for a given space. BTS signal sources also require space, cooling, and power sources as well as careful planning for hands-off zones. Small Cells Enterprise small cells and their variations known as Femtocells, Picocells, Nanocells, and Metrocells, are the latest in cellular service technology. Small cells are used by carriers to provide cellular service indoors.

Small cells and their variations all work in a similar way to create a secure tunnel that leads back to the carrier’s network over a regular internet connection. From there they generate a much higher quality wireless signal. Small cell signal sources will cover up to 15,000 square feet of space with a building. However, their coverage area will expand significantly when being used a signal source for a DAS. An enterprise-level small cell signal source can support up to 200 users. Small cells require a reliable backhaul internet connection to work properly, and careful planning around the hands-off zones that exist between the small cells and the macro network. The second component of the DAS—the distribution source—is what distributes the signal throughout the building or area once it’s received by the signal source. There are four types of distribution sources: Active (using fiber optics or ethernet cables), passive, hybrid, and digital.

Types of Distributed Antenna Systems

Passive DAS

A passive DAS uses passive RF components (coaxial cables, splitters, and taps) to distribute the signal inside a building. Passive DAS are the most simple to install since they don’t require any converters are specialized equipment.

For a passive DAS distribution source to function properly, the antenna must be close to the signal and any amplifiers. The further away from the antenna, the more attention (loss) there will be in the power broadcast.

Active DAS

An active DAS is able to convert analog radio frequency transmissions to a digital signal before distribution. A master unit is required to perform the conversions and can digitize the signals from one or multiple carriers.

The new digital signal is transmitted via fiber optic or ethernet cables to remote radio units (RRUs) which convert the signal back to analog. The fiber optic or ethernet cables run directly to the antenna unit with no limits

Hybrid DAS

A hybrid DAS is a combination of the active and passive DAS. The hybrid DAS works by keeping the RRUs separate from the antennas, enabling the system to use both a fiber optic cable and a coaxial cable to distribute the signal throughout a building.

Typically with a hybrid DAS, the RRUs are configured on each floor of a building to convert the digital signal to an analog RF signal. The analog RF signal then connects to multiple antennas on each floor using the coaxial cable.

Digital DAS

The Common Public Radio Interface (CPRI) specification is the latest in digital technology. It allows for the baseband unit (BBU) which is a type of BTS to connect with the master unit through remote units—without any digital to analog conversions.

Digital DAS has only been experimentally deployed so far, but theoretically, it’ll be much easier and cost-effective to deploy in the future.

Nationwide Communications Services

With today’s ever-changing communication environment, you need to have options when it comes to your connectivity needs. Nationwide Communications Services is an industry leader in implementing digital technology solutions. We specialize in reliable structured cable installments and can take care of all your DAS installation needs.

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