What is a Distributed Antenna System?

What is a distributed antenna system (DAS)?

A DAS or Distributed Antenna System is a network of spatially separated antennas connected to a common source that delivers wifi connectivity within a structure or building.

Serving to enhance wireless coverage within designated areas such as buildings, stadiums, campuses, or other venues. The primary purpose of a Distributed Antenna System is to optimise cellular and wireless communications by efficiently distributing the signal from a centralised source to strategically positioned antennas throughout the target area. This approach effectively mitigates signal obstacles, ensuring superior coverage and increased capacity for mobile devices. A distributed antenna system may be deployed indoors (an iDAS) or outdoors (an oDAS).

What does a distributed antenna system do?

Distributed Antenna Systems (DAS) are pivotal in delivering wireless signal coverage to areas that typically lack service. This system employs multiple smaller antennas placed in various locations, as opposed to using a single, more powerful antenna. These smaller antennas are interconnected through cables to a central signal source.
A great way to understand the effectiveness of DAS, consider this analogy: When playing music for a large outdoor audience, a single powerful speaker is sufficient. However, in an indoor setting like an office building, this approach would create uneven sound distribution, with some areas being too loud and others too quiet, not to mention the issue of sound distortion due to echoes. A more efficient solution is to install smaller speakers throughout the building, ensuring a consistent volume level everywhere.
Similarly, cellular networks use strategically placed cell towers in outdoor areas to provide uniform coverage. These towers, akin to large speakers, are effective in open environments but less so inside buildings. External walls can block or weaken the signal, internal walls can cause signal reflection, and the presence of many people can lead to signal competition. DAS addresses these challenges by placing smaller antennas inside the building, ensuring a more even distribution of the signal.
It's important to note that DAS typically refers to cellular signal coverage and not Wi-Fi connectivity, which is often termed as Wi-Fi deployment or mesh network. However, Wi-Fi and DAS can sometimes be deployed together or even integrated into the same equipment, as seen in the New York Metropolitan Transportation Authority's use of both systems in subway stations.
When designing a DAS, the key considerations include the source of the signal and the type of signal distribution. There are different types of DAS based on the signal source:

iDAS, oDAS, eDAS, active DAS, passive DAS, hybrid DAS, off-air DAS, and numerous others.

Off-air

Off-air (via an antenna usualy placed on a roof) are the most common signal sources for a Distributed Antenna System.

Off-air can connect to various operators simultaneously but performance relies on signal strength, quality and congestion. An off-air signal isn't always provided when a signal from the donor antenna is very weak or the closest tower is fairly congested.

On-Site BTS

an On-site BTS or Base Transceiver Station can also be referred to as the node B (in 3G networks) or, the base station (BS).

(NodeB, eNodeB, gNodeB refer to the technology used inside cell phone towers to generate a cellular signal). A base transceiver station links-up to the antenna network through fiber optic cables to a telecommunications providers core network, seperated from enterprise IT infrastructure that may have been installed previously. Multiple BTS systems can be deployed to receive signals from seperate carriers with increased performance for each carrier, an extra layer of capacity can be applied to high-occupancy areas could contain hotels, stadiums, train stations, airports, or venues. BTS systems are more complex to install as providers need to run signals throuh their own dedicated cables, they require bigger space, more cooling, and consume more power resulting in higher overall operating costs.

Small Cells

Small cells are low-powered cellular radio access nodes that operate in licensed and unlicensed spectrum that have a range of 10 meters to a few kilometers.

Recent FCC orders have provided size and elevation guidelines to help more clearly define small cell equipment.[2][3] They are "small" compared to a mobile macrocell, partly because they have a shorter range and partly because they typically handle fewer concurrent calls or sessions. As wireless carriers seek to 'densify' existing wireless networks to provide for the data capacity demands of "5G", small cells are currently viewed as a solution to allow re-using the same frequencies,[4][5][6] and as an important method of increasing cellular network capacity, quality, and resilience with a growing focus using LTE Advanced.

What is a Distributed Antenna System?