Distributed Antenna System in a Nutshell

Telecom Tech Outlook | Wednesday, January 12, 2022

A network of antennas linked to a common source and distributed throughout a building or area to improve network performance is known as distributed antenna system (DAS). The antenna spacing is designed to provide complete coverage without overlapping with other antennas, reducing the number of antennas required to cover the whole building.

Fremont, CA: This network of antennas is also more power-efficient than a single, larger antenna covering a larger area. A Distributed Antenna System can be designed for indoor or outdoor use and can provide wireless coverage in hotels, subways, airports, hospitals, businesses, and roadway tunnels, among other places. In addition, a DAS typically provides wireless services such as PCS, cellular, Wi-Fi, police, fire, and emergency services.

A DAS comprises two main components: a signal source and a distribution system. The signal source is the DAS network's input. It could be a BTS (Base Transceiver Station) on-site, a small cell, or an off-air system (via an antenna on the roof). The distribution system is the second component of a DAS network. The signal must be distributed throughout the building once the signal source receives it. The four types are:

• Active distribution systems (using fiber optic or ethernet cable).
• Passive distribution systems.
• Hybrid distribution systems.
• Digital distribution systems.

Active distribution systems: Active DAS systems convert the analog RF signal from the signal source to a digital signal for distribution. A master unit carries out this analog-to-digital conversion. This digital signal is then transmitted through fiber optic or Ethernet cables to the antenna systems, which convert it back to analog and transmit it throughout the building.

Passive DAS: A passive DAS distributes signal inside a building using passive RF components such as coaxial cable, splitters, tapers, and couplers. The wireless signals are routed through "leaky" feeder cables that serve as antennas throughout the building; signal leakage distributes the signals.

Hybrid DAS: A hybrid DAS system distributes signals throughout a building using fiber optic and coaxial cables. The analog RF signal from the signal source is converted into a digital signal for distribution in this system. This digital signal is transmitted to a Remote Radio Head (RRU) installed on each building floor via fiber optic or Ethernet cables. The digital signal to an analog RF signal by the RRU. This analog RF signal is then routed through coaxial cables and other passive components to multiple antennas on that floor.

Digital DAS: This system operates in accordance with the Common Public Radio Interface (CPRI) specification, which allows a baseband unit (BBU, which is a type of BTS) to communicate directly with the DAS master unit and through to the remote units without the need for any analog RF interface conversion.

Benefits of Using DAS:

• more precise coverage
• Fewer gaps in coverage
• The same coverage can be obtained with lower overall power.
• To provide the same coverage, individual antennas do not need to be as tall as a single antenna.

Disadvantages of using DAS include:

• Costlier as a result of the additional infrastructure required
• The increased number of antennas may have a more significant visual impact in some applications, even though they are much lower in height.