Nowadays, in-building distributed antenna systems (DAS) are widely used in enterprise infrastructure. It is mainly used for improving cellular connectivity and range inside commercial buildings. The technology evolved to the point that there are different types of it like active DAS, passive DAS, off-air DAS, hybrid DAS, iDAS, eDAS, oDAS, and so on. One of the more popular one among these is the passive DAS, also known as the cell phone service booster, used in offices, homes, vehicles, commercial establishments, etc. Read on to know more about distributed antenna systems (DAS).
The Working Of A Distributed Antenna System (DAS)
A distributed antenna system (DAS) consists of a network of antennas that receives and sends cellular signals of a carrier. This ensures better call quality, data speeds, and connectivity for the end-user. All DAS consists of two basic components, and they are:
A DAS distributes cellular signals received from a source, and it must be fed to it. There are four types of signal sources: an onsite Base Transceiver Station (BTS), off-air (antenna on the roof), and small cells.
The cellular signal fed from the signal source is distributed throughout a building with the distribution system, and there are mainly four types of it: active, passive, hybrid, and digital.
Finally, the performance of a distributed antenna system (DAS) is measured by two metrics, and they are capacity and coverage.
Capacity And Coverage
To understand the difference between the performance metrics of a DAS, i.e. capacity and coverage, let us analyze two scenarios.
At times, some places experience higher cellular data usage due to reasons like a huge crowd for watching events in a sports stadium, at a music concert, etc. In such a situation, the local cellular tower and network will be overwhelmed, making cellular services unstable. This can be resolved by using a DAS with high capacity at the venue of the crowd.
In some places the cellular signal reception is poor either due to the cellular tower being far away or the signal is attenuated by construction materials. The latter phenomenon is observed in buildings constructed under LEED guidelines because they use low-E windows. In such places or buildings, a DAS with high coverage is ideal. They are also used inside high rises because radio frequency noises at high altitudes reduce the quality of cellular signals, and hence they become unusable.
It is important to understand what is causing the drop in cellular signals and choose the right type of DAS technology accordingly.
Signal Sources In Distributed Antenna Systems (DAS)
One of the common sources of signal used in a distributed antenna system is the off-air signal. It is received using a donor antenna, especially in a passive DAS or cell phone service booster. The performance of the DAS technology deployed depends on the strength of the cellular signal. So, if it is weak or the cellular network is congested, an off-air signal is not usable. Besides, a DAS using an off-air signal source is a cost-effective solution that increases the coverage at the edge of the carrier’s network.
BTS, eNodeB, NodeB
Base Transceiver Station (BTS), NodeB, and eNodeB generate signals inside cellular towers. The BTS of the carrier is connected to the distribution network of antennas using a dedicated optic fiber connection, and this is usually installed by the carrier. This type of DAS technology is used inside large stadiums, airports, etc., and takes a long time for deployment.
Small Cells Like Femtocells, Picocells, And MetroCell
Small cells are like mini cellular towers, and carriers use them inside buildings to provide high-quality cellular services. They connect securely to the carrier’s network over a normal internet connection and have a typical coverage area ranging from 5,000 to 15,000 sq ft. But, using it as a signal source for a DAS significantly increases its coverage area. A typical enterprise-grade small cell can provide services for up to 200 people. However, they are relatively expensive and require a stable internet connection for uninterrupted cellular services.
Signal Distribution Technologies
Active DAS converts an analog radio frequency signal from the signal source into a digital signal for transmission using a master unit. This digital signal is carried over the fiber optic cable to the Remote Radio Units (RRUs). The RRU reconverts the digital signal into an analog signal before broadcasting the cellular signal.
Passive DAS, commonly known as the cellular signal booster is a radio frequency device for distributing cellular signals inside a building. Some of its main components are coaxial cables, amplifiers, taps, and splitters. When deploying this system, the length of the coaxial cables and the distance or separation between the antennas must be considered. These factors influence the performance of the passive DAS technology used inside a building.
A hybrid DAS uses the features of both active and passive DAS, i.e. both fiber optic and coaxial cables are used for signal transmission. Also, it requires fewer RRUs because they are separate from the antennas in the distribution network.
Digital DAS is the latest DAS technology where there is no signal conversion. Because of this, it is cheaper and simpler to deploy.
The choice between different DAS technologies depends on your requirement and the budget allocation for the purpose.