DAS is a network of antennas that transmits and receives cellular signals on a carrier's licensed frequencies, thereby improving end-user voice and data connectivity.
FREMONT, CA: In-Building Distributed Antenna Systems (DAS) have become a critical part of carrier cellular networks & enterprise infrastructure. Yet as technology has updated over the past 20 years, it has become progressively complex. The list of acronyms alone can be astonishing: iDAS, active DAS, oDAS, eDAS, passive DAS, hybrid DAS, off-air DAS, and several others. This guide will describe standard distributed antenna systems and practical implementation strategies.
Working process of A DAS
DAS is a network of antennas that transmits and receives cellular signals on a carrier's licensed frequencies, thereby improving end-user voice and data connectivity.
In its most streamlined form, a DAS has two essential components:
1 - A signal source
A Distributed Antenna System, as the name indicates, "distributes" signal. But it usually doesn't generate the cellular signal itself. Instead, a DAS needs to be fed a signal from somewhere. Whether it's 4G LTE or 5G, there are four normal signal sources: off-air (through an antenna on the roof), an on-site BTS (Base Transceiver Station), and ultimately, the newest approach: small cells.
2 - Distribution system
Once obtained, the cellular signal must be scattered throughout the building. There are four main distribution systems: active (using fiber optic or ethernet cable), passive, hybrid, and digital.
A distributed antenna system's performance relies on the type of technology it uses. To grasp what we mean by "performance," we first need to realize the two main performance metrics: coverage and capacity.
Coverage vs. Capacity
To compare the distinct technologies, we first need to review the two main reasons DAS solutions are deployed: to provide coverage and capacity.
Some locations experience considerably more cellular data utilization than others. Think of a sports stadium welcoming the Super Bowl or a large music venue hosting Justin Timberlake. If the platform relied on a nearby cell tower to cover all those users, the building and the local network would quickly become overpowered and unstable. In such applications, a DAS with high capacity is the primary need.
Suppose there's simply not enough usable signal reaching users, either because the cell tower is too distant or due to building materials like low-E windows in LEED Buildings blocking cell signals; the immediate need is coverage. For instance, a newly-built LEED-certified hospital with concrete walls might have no indoor range and require a DAS. In addition, highrises often use DAS deployments because the radio frequency noise levels at higher altitudes make the signal unusable.
Identifying one of these requirements as the principal requirement of your project is an essential first step. Choosing the right DAS technology implies making trade-offs between capacity, coverage, and price.
Signal Sources
The signal sources are one of the most critical factors in determining a DAS system's coverage area and capacity. No matter how great the distribution system performs, a DAS is always restricted by the performance of the signal supplying the network. The signal source also determines what sort of signal the DAS distributes. For instance, a 5G signal source is a requirement for a 5G DAS. The primary signal sources are off-air, BTS/NodeB/eNodeB, and small cells.
Off-Air
A DAS that utilizes an off-air signal (sometimes called a repeater) utilizes a donor antenna on the roof to receive and send signals from a cell carrier. Off-air signals are the most regular signal sources for a DAS. If the signal at the emission antenna is feeble or the nearest tower is quite congested, using an off-air signal isn't typically feasible. But if the donor signal is solid and transparent, and an off-air signal is often the easiest and most cost-effective signal source.
A DAS that utilizes an off-air signal source does not add extra power to the carrier's network and is mainly used to extend coverage at the network's edges. These deployments are often the minimum cost option and are most suitable when the main reason for deploying a DAS is to enlarge coverage inside a building.
Nearly all DAS systems can use off-air signals, but Wilson Electronics, SureCall, and Cel-Fi are most often associated with this deployment type. Off-air DAS deployments have observed a resurgence with the roll-out of 5G, especially on mmWave bands.
