A definitive guide to Distributed Antenna Systems

A Distributed Antenna System (DAS) is a network of antennas that sends and receives cellular signals on a carrier’s licensed frequencies, thereby improving voice and data connectivity for end-users. It has become a critical part of both carrier cellular networks and enterprise infrastructure.

A DAS has two basic components: a signal source and a distribution system. A Distributed Antenna System doesn’t generate the cellular signal itself. A DAS needs to be fed signal from somewhere. Once received, the cellular signal must be distributed throughout the building. There are four main types of distribution systems: active (using fiber optic or ethernet cable), passive, hybrid and digital.

The signal sources for a DAS system are one of the single most important factors in determining both the coverage area and capacity. A DAS is always limited by the performance of the signal supplying the network. The signal source also determines what kind of signal the DAS distributes. The three main signal sources are off-air, BTS/NodeB/eNodeB and small cell.

A DAS that uses an off-air signal (sometimes called a repeater) utilizes a donor antenna on the roof to receive and transmit signals from a cell carrier. If the signal at the donor antenna is very weak or the nearest tower is quite congested, using an off-air signal isn't typically feasible. But if the donor signal is strong and clear, then an off-air signal is often the easiest and most cost-effective signal source.

A DAS that uses an off-air signal source does not add any extra capacity to the carrier’s network and is primarily used to extend coverage at the edges of the network. These deployments are often the lowest cost option and are most suitable when the primary reason for deploying a DAS is to extend coverage inside a building. Choosing an integrator with a strong RF experience is critical.

Base Transceiver Station (BTS), NodeB, eNodeB, gNodeB refer to the technology used inside cell phone towers to generate a cellular signal. The connection between a cell carrier’s BTS and the core network typically requires a dedicated fiber connection. A distributed antenna system in a large stadium or airport may even connect to multiple BTSes to handle the load.

Small cells are the latest technology used by carriers to provide cellular service inside buildings. There are several variations of small cells, including femtocells, picocells, nanocells and metrocells. These are all basically the same technology—they create a secure tunnel back to the carrier’s network over a normal Internet connection and generate a high-quality wireless signal.

Depending on the setup of the DAS, it’s possible to mix and match the different signal sources listed previously in a single venue. Whichever signal source a system uses, a DAS needs to amplify, distribute and rebroadcast it through the building. There are four main types of signal distribution technology: active, passive, hybrid and digital.

A passive DAS uses passive RF components such as coaxial cable, splitters, taps and couplers to distribute signal. The farther the antenna is from the signal source and any amplifiers, the more attenuation (loss) there will be in the power broadcast. Designing a passive DAS correctly requires calculating precise link budgets to make sure the outputted power at each antenna is equal.

An active DAS converts the radio frequency transmissions from the signal source so they can be distributed via an optical or ethernet cable. A ‘master unit’ combines the signals from multiple carriers and performs this conversion. Once converted, an active DAS transmits the digital signal over fiber optic or ethernet cables to remote radio units that convert the signal back to an RF signal.

A hybrid DAS combines the characteristics of passive and active systems. The RRUs are separate from the antennas, allowing the system to use both fiber optic cable and coaxial cable to distribute signal. A typical hybrid DAS configuration includes an RRU on each floor that converts from the digital signal to analog RF. The analog RF signal is connected to multiple antennas on that floor with coaxial cable.

A digital DAS converts each carrier’s signal to zeros and ones before combining them and transmitting over fiber optic or ethernet cable. One of the biggest benefits of deploying a digital DAS is that it is much less susceptible to interference, and thus more performant. A second benefit is that digital DAS allows the capacity of the signal sources to be directed to different areas of a venue.

Glow’s role

Here at Glow, we work hard to stay at the forefront of the wireless industry and deliver exceptional wireless coverage solutions. We specialize in providing turn-key systems that are effective and affordable. With more than 20 years of experience, we have the expertise to implement a system that works in virtually any setting.