Distributed antenna systems improve cellphone reception within office buildings.
IN TODAY'S FAST-PACED, digitally connected world, dependence on mobile devices has dramatically increased. Cellphones are no longer simple devices used only for voice communications. Smartphones and tablets are utilized for multiple tasks such as online shopping, navigation, social media, phone calls, video, etc. In the past, cellphone users were simply hoping to stay connected as they roamed from building to building. Now, users not only want to maintain voice communications when away from their home or office, but also expect to continue their voice and high-speed data communications seamlessly while inside these buildings.
Most large venues in the U.S. — shopping malls, stadiums and arenas — have addressed cellphone voice and Long Term Evolution (LTE) data coverage by either working with carriers to increase their macro networks (cell towers) outside the building or providing a distributed antenna system (DAS) inside the building. Although most office, industrial and residential buildings have not yet increased their macro networks or provided a DAS, tenants and other users of these spaces have the same expectations of continuous voice and high-speed data service.
Understanding the Problem
Some of the issues surrounding poor cell signals within a building can be attributed to the lack of cell towers within the proximate area or spotty coverage throughout the building. In a typical scenario, the lower floors of a high-rise office or multifamily residential building may have a usable signal, but the upper floors do not, even though cellphones indicate five bars. Locations on higher floors generally show strong signal strength, but cellphones cannot make a connection due to the high level of radio-frequency (RF) noise at those elevations. Although low-rise industrial buildings don’t have this problem, they also suffer from poor cell coverage because most are constructed with metal or concrete block walls, which block the RF signal.
The main reason for lack of cell signal within most buildings today, however, is low-E glass. This type of glass, which is designed to significantly improve the thermal efficiency of the building envelope as required by energy codes, blocks the RF signal. Since the glass effectively blocks the cellphone signal from entering the building from outside, the solution is to provide a system that will receive and broadcast the signal within the building. This is what a DAS system does.
How It Works
The distributed antenna system creates a virtual cell tower within the building. The goal of a DAS is to produce a strong cell signal throughout the entire building, so that when a cellphone initiates a call or a data connection, it immediately finds the signal from within and does not search for a signal from outside. The call or data connection is then routed from the DAS to the provider’s network via fiber-optic cables. The carriers benefit from a DAS because the traffic from within the building does not travel over the macro network, but rather from the DAS through the fiber-optic cable connected to their network equipment.
The DAS is comprised of head-end equipment typically located within a building’s service entrance room (SER). From there, fiber is run to each floor and terminates within a remote unit placed in an intermediate distribution frame (IDF) closet on the floor. The remote unit then connects to several antennas placed strategically throughout the floor, based on an RF signal test and predictive software. A 20,000-square-foot floor, for example, will typically require four or five antennas.
A distributed antenna system (DAS) uses antennas, repeaters, fiber-optic and coax cabling to create a virtual cell tower within a building, producing a strong cell signal throughout the structure. 568Systems Inc.
The main challenges facing a DAS installation include cost and space issues. Installation costs are generally about $1.25 per square foot. Developers and building owners should ask carriers to contribute to funding the installation.
Space can also be an issue. Do the building’s telecom rooms have enough space to accommodate the DAS equipment? A head-end equipment room requires approximately 240 to 2,000 square feet, depending on the total size of the area to be served, as well as how many carriers will be supported. The DAS vendor may want to isolate its equipment from other equipment within the room with fencing, which will require additional space. The DAS equipment also requires electrical power and cooling.
In order to accommodate a DAS in a new building or a redevelopment project, the design team should work with a reputable DAS integrator early in the design process to help identify and address all budget and space implications.
What Does the Future Hold?
Small-cell technology (low-powered radio access nodes) will help pave the way for DAS to be implemented within most buildings. Small-cell technology provides cell coverage similar to a cell tower, but with a much smaller footprint and reduced costs. However, small-cell systems can be accessed by a limited number of users, typically in the range of 300 to 400 people.
Other carriers are exploring the use of Wi-Fi to integrate cellphone use within buildings. This technology allows cellphones to connect to a Wi-Fi network for voice calls as well as data connections. It has some limitations, which include difficulties in maintaining a continuous call when switching from a Wi-Fi network to the cell network and limited availability of public Wi-Fi hotspots.