DAS, or distributed antenna systems, are creative means of effectively dealing with areas in which telecommunications coverage is poor, especially inside of urban buildings. This is accomplished by boosting an in-building wireless signal via a series of unobtrusive antenna-repeaters that are located around the facility.
Such antennas are physically wired to central controllers. These centralized controllers are then connected with the base stations of each carrier’s wireless network. In fact it is necessary to work with one or more of the wireless carriers on such a project, as the antenna systems that re-distribute the signal are operating on the wireless carrier licensed RF spectrums.
These distributed antenna systems may be active or passive. Active system layouts take the signal from a roof antenna and relay it via fiber cables to hot spots within the structure. The signals are amplified and boosted as necessary along the way. With the passive approach, the signal is also grabbed from rooftop antennas and then run through “leaky” feeder cables located around a building. The signal is actually distributed through signal leakage in this approach.
Why DAS Is Needed
DAS becomes necessary partially because of the effects of modern construction designs and materials on wireless signals. Many newer buildings find that their interior cell reception is blocked or at least degraded. These DAS setups were created counteract the problem so that cell phones and radios are able to function effectively in every corner of the building.
It’s not just the annoyance of a blocked cell signal; indoor radio reception has become a dilemma for first responders. Building occupants’ safety could well rely on uninterrupted communications in an emergency.
What’s the Problem?
“Green” buildings have been well designed to serve the needs of the environment with many energy and CO2-saving advantages. Unfortunately, the advanced materials can also destroy the integrity of cell phone signals. As many as 80% of all cell phone carried calls start or conclude within a building. The main culprit is the Low-e glass used in the outer shell of many newer high-rises. They’re great for blocking out UV rays and providing needed insulation, but they also wreak havoc on cell and radio signals propagating into and out of the walls.
This is why DAS is utilized to address these problems and to provide greater value for the building tenants and occupants as well as their employees via improving the mobile device experience around the building. One DAS is able to support a number of wireless carriers at the same time and to even boost phone battery life. DAS similarly helps with the stronger signals needed for transferring data on and off of mobile devices. It assures that the rates of data transfer will be sufficient for the constantly changing needs of advancing cell phone technology.
Isn’t this my Wireless Carrier’s Problem?
No. RF Connect, a Michigan wireless networking company, shares their findings:
“The wireless service providers’ (WSP) macro systems provide sufficient outdoor coverage and capacity for the most part, but building materials can significantly compromise the signal, especially if the building uses modern low-emission glass to achieve LEED certification. In areas where there are dense structural footprints, it is getting harder and harder to manage consistent cell phone coverage within structures. Unlike landlines, where it is common practice for the phone company to accept responsibility for providing the service, indoor coverage and capacity for mobile devices only gets carrier funding if it is strategic to the carrier’s interest. Most individual, commercial, residential and office buildings are not considered to be of strategic interest, so the burden of providing coverage and capacity in the building becomes the owner’s or tenant’s problem, as it is in Public Safety Radio amplification.”
How It Works
DAS relies on a strong signal from a base station. Remote antennas take this base station signal and re-broadcast it out to the area that is to be served in a building or obstructed area that still may need cell and first responder radio coverage. DAS then provides consistent and improved coverage at a faster rate for the entire area that it services.
There are large-scale DAS projects in existence that operate over miles and assist literally thousands of subscribers with better coverage and service. The remote antennas may be invisible or at least discreet as they can be located atop telephone poles, lamp posts, street furniture, or street cabinets. The re-broadcast of phone and Internet coverage from these antennas is totally transparent to all mobile devices and delivers comparable data and voice services to any and all mobile devices as would any cell phone network tower.
A DAS network will require either active repeater amplifiers or passive feeders and splitters. Antennas are heavily relied upon, as are the receivers in the base station that receive the signal to re-broadcast.
Building Code Issues
So far, more than 30 states have either adopted codes or will adopt soon such codes to require DAS systems that boost communications systems’ coverage for first responders. Fire codes were updated in 2009 via IFC 510 to require guidelines be implemented for emergency and first responder radio communications coverage. This has included such mandates as all newly built buildings should be set up for improved radio coverage to first responders and the strength of radio signals has to be achieved at 95% in every floor for all areas in the building. It also mandates that existing buildings must provide effective radio communications coverage around the building and should retrofit their buildings as needed so that the present wired systems will provide adequate coverage.
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