Businesses are rapidly migrating to 4G mobile services, and the challenge is to ensure strong and consistent 4G service throughout the enterprise facility. Unlike 2G and 3G mobile services, 4G promises multiple megabits of downstream bandwidth to each user, so the network must have the capacity and coverage to ensure this. There are several issues to be overcome.
4G mobile signals often don’t penetrate buildings as well as 2G and 3G signals, so there must be a signal source inside the building to deliver adequate coverage. The network must also have the capacity to deliver multi-megabits of service to each user.
In addition, a high-rise office building may be receiving signals from several cell sites in the outside macro cellular network, and users’ phones hunt from one site to another, degrading service and reducing device battery life. Again, a strong signal emanating from inside the building overcomes this problem because user devices lock on to the internal signal.
High-density areas in a building, such as conference rooms and cafeterias, must deliver extra capacity to serve peak crowds of users.
Distributed Antenna Systems (DAS) are products that bring mobile signals indoors. A DAS works by connecting to an on-site cellular base station, and then channeling that base station’s signal throughout the building with a group of ceiling- or wall-mounted antennas. DAS have been used inside buildings for many years, but as the 4G era dawns, they will be a requirement for effective service in many instances.
A DAS consists of a head-end unit or host unit that is installed adjacent to the on-site base station. There are two key approaches to DAS technology. One is to use thick, heavy coaxial cabling to connect the head-end to a series of antennas. This so-called passive approach requires fewer electronics, but it doesn’t always provide the coverage and capacity needed.
A coaxial cable attenuates the mobile signal the farther it gets from the base station, so each connected antenna receives a different strength signal. When an antenna is very far from the base station, users almost have to stand directly underneath it to get a strong signal.
This feature of passive systems makes it difficult to plan an installation because each antenna has a different output power, so the area it covers is different from that of other antennas. In addition, the heavy coaxial cable is difficult to bend, so it is more difficult to install in tight utility raceways above ceilings. Often, special hangers must be installed to carry these cables.
Another approach is an active DAS. From the head-end, the cellular signal is carried over fibre to expansion hubs installed in wiring closets on various floors or sections of a building. From the expansion hubs, CATV cabling is used to carry the mobile signal to remote antenna units, which amplify the signal and route it to actual antennas. Because the signal is digitised and amplified at each antenna point, every antenna puts out a uniformly strong signal.
This type of DAS is easier to plan and deploy because antenna points can be spaced equal distances apart to provide consistent coverage throughout a building. In addition, the thin fibre and CATV cable is much easier to install than heavy coax. In many instances, the building already has dark fibre running throughout, and one of these fibres can be used to connect the head-end with the expansion hubs.
As we can see, an active DAS is easier to deploy and provides more consistent coverage and capacity within a building. It is the preferred type of DAS especially for large buildings or corporate campuses because heavy coax attenuates the cellular signal too much to provide adequate service in these locations. In contrast, active DAS has been used in installations that run for miles.
4G mobile services are coming to every enterprise, and the enterprise must be prepared to ensure strong and consistent service for every user. DAS makes this possible by bringing the mobile signal indoors and distributing it evenly throughout the building.