Published in the November 2005 issue of Today’s Facility Manager
We live in a wireless world where business requires connectivity to function at the rapid pace that has become the norm. Cell phones have been a standard accessory for years, and now PDAs and hybrid devices like the BlackBerry are commonplace. Wireless Wide Area Network (or WAN) cards for laptops now allow people to connect to the Internet at high speeds from any place they can get a cell phone signal. This wireless revolution means that people can work, communicate, and collaborate almost anywhere…when the technology works.
Everyone has had the frustrating experience of a cell phone call being dropped in a dead zone. This occurrence can range from a minor inconvenience to a major disruption in business.
There are numerous reasons for the lack of good cell signal quality. Assuming the user is in a populated area that has reasonably good cell coverage, this problem can be related to either a coverage hole or structural interference.
One example of a coverage hole is illustrated in this recent problem encountered by a company whose offices were in the tallest building in their city. Cell phone tower antennas are directional and are aimed at the majority of customers, which, in this case, was from street level to just below the affected offices. This left occupants in the higher offices completely without cell phone or BlackBerry coverage. This was a major burden on the organization, keeping the employees either shackled to their desk phones or out of touch completely.
An example of structural interference occurred in an organization located in the lower level of an older office building which features heavy concrete and steel construction and a wide floor plate. Cell signal reception may be fine in the offices near the perimeter of the building, but it deteriorates quickly toward the center. This is simply a matter of physics: radio signals are thwarted by dense materials like concrete, steel, and soil, and the signal degrades in direct proportion to the amount of material it must pass through.
In both of these examples, the solution is the same: a cell phone repeater system. These systems are fairly simple to install and can quickly and economically solve cell signal problems.
There are two main components: an external receiver that mounts outside or in any area of good signal coverage, and an internal antenna. The system relays and boosts cell signals from inside to outside (and vice versa), eliminating signal quality issues. These systems range from fairly simple set ups with one exterior and one interior antenna all the way to distributed antenna systems, which use a cable that routes through the facility to act as a continuous antenna.
Many quality issues can easily be solved by installing a cell signal repeater, but some problems are more complex and require more detailed analysis. Cell signal propagation is affected by many different factors such as the density of walls and floors, signal reflection, and electromagnetic interference. Because identifying the cause is not always intuitive, some facility managers hire consultants to perform a wireless signal analysis. The consultants will walk through the facility with special receivers and produce a floor plan that shows signal strength throughout the building. This can give insight into how signals propagate through the facility and allows the facility manager to choose the best remedy for poor strength. It can also help to locate rogue signals and interference that might be causing problems.
My wireless team uses a product called AirMagnet that can detect signals from cell phones, wireless computer networks, and other sources to produce a color-coded map of the facility (see image). The different colors that result represent varying signal strengths measured at different locations in the facility. This allows facility managers to identify problem areas.
On the other hand, some facilities have great cell coverage, but do not always want such devices to be used. One major reason is the simple disruption caused by cell phones. After all, who hasn’t been in an important meeting where someone’s cell phone started to play some annoying jingle, disrupting the focus of the event?
Another reason to limit cell phone use is security; many would be surprised at how many people have transmitted confidential information out of a room just by using their cell phones. In this respect, the cell phone is no different than a hidden microphone and represents a clear threat to confidentiality.
Finally, cell phones can interfere with sensitive electronics in planes and hospitals. This has become less of a technological problem with today’s digital phones—which put out only a fraction of the energy of the old analog portable phones—but it is still a concern in these facilities.
There are two main ways to stop cell signals in a facility. One is a cell signal jammer, which actively broadcasts a signal that interferes with cell signals. This renders phones useless, often without interfering with adjacent signals that should not be disturbed.
A number of manufacturers make cell signal jamming systems for facilities, but these are not legal in the U.S., except when used by law enforcement agencies. However, these systems are becoming increasingly popular overseas, with France legalizing jammers in late 2004. Many organizations in the U.S., including churches and movie theaters, would like to use jammers to maintain a quiet environment, but concern over the inability to use cell phones during emergencies currently outweighs the desire for peace and quiet.
The other way to screen out cell signals is to create a “Faraday Cage” to shield a room. Named for physicist Michael Faraday, this cage uses the principle that any hollow, conductive object will not allow radio waves to enter or leave. By surrounding a room completely with a conductive material, facility managers can prevent any radio signals from entering the space.
This is a rather extreme technique I have only seen employed in high security government or military facilities, but it is very effective. There are many ways to achieve a Faraday Cage, including installing sheets of copper mesh behind the drywall, under the floor coverings, and above the ceilings. The copper mesh sheets are then connected together to form a single, conductive box.
This technique has other advantages as well; it prevents radio signals from inside the room from leaving, thwarting wireless listening devices. It is also effective in shielding sensitive electronics from interference, such as when computers are located near a main electrical distribution room.
There are a variety of products available to create a Faraday Cage, including wallpaper that contains a copper mesh. The size of the mesh is directly related to the signal frequencies that can be blocked, so facility managers need to choose these items wisely.
In dealing with cell phone signal issues—which can range from pesky to downright threatening—the technology available can help those in the facility to stay connected, or disconnected if that is more important.
Condon, a Facility Technologist and former facility manager, is a contributing author for BOMI Institute’s revised Technologies in Facility Management textbook. He works for System Development Integration, a Chicago, IL-based firm committed to improving the performance, quality, and reliability of client business through technology.