Distributed Antenna System (DAS) Tutorial
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14 January 2015 - 17:04, by , in Blog, Comments off

What is DAS? DAS stands for Distributed Antenna System, which is a system that allows for the use of cell phones and other wireless devices in areas that do not have direct access to a cell tower or power source. DAS works by receiving power from a radio frequency (RF) source, and distributing it over a system of cables and antennas so that the signal reaches throughout a building or space. Though DAS is relatively new, the need for a DAS is increasing at a rapid rate. Here is an in-depth explanation of the “hows” and “whys” of DAS solutions:

Why Is There a Need For DAS?

Cell Phone UseAs technology has evolved over time, there has been a shift in how we use our wireless devices. Not too long ago, cell phones were just a convenient communication alternative for when you were outdoors, or away from a building with a landline. Remember when the first cell phones came out and we called them “car phones?” Now, over 70 percent of cell phone usage takes place indoors. Users want to stay connected at all times. Rather than having separate numbers for home, office and travel, they want one phone number they can use at all of their locations, whether it be at home, at the office, or wherever they may be. In addition to this shift, data usage is rising quickly, and is in demand in every location. With the demand for indoor cell phones and data on the rise, DAS solutions are quickly becoming a necessity for businesses and buildings with coverage challenges.

Passive, Active, and Hybrid DAS Solutions

The types of DAS solutions can be generally classified into three different categories: passive DAS, active DAS, and hybrid DAS. Coupling two DAS solutions together in a larger space is not recommended, because they could interfere with each other.

Passive DAS can be used for a smaller area, typically 125,000 square feet or less, and in a building that does not have a large amount of metal, masonry, or concrete wall materials blocking the RF signals. Passive DAS uses only coax cabling to distribute the signals. It is the smallest, simplest, and often the least expensive DAS solution to implement.

Active DAS is a solution used for larger spaces and spaces with more barrier materials that block the RF signals from traveling through the interior space. Active solutions use fiber optic cabling which changes the RF signals into light for distribution, and then back into usable signals at the desired locations.

A hybrid DAS solution employs a combination of both active and passive DAS.

Which solution is best for your building? The experts at Harris Communications can recommend a customized solution based on the unique communication challenges of your specific location.

The Basic Components of a DAS Solution

Whether a passive, active, or hybrid solution, each DAS system will consist of certain basic components. The first component is the donor antenna, which is usually located outdoors and above the tree line to directly receive RF signals from a cell tower or signal source. The donor antenna can receive multiple frequencies to meet emergency and large capacity needs. Once the signals are received by the donor antenna, they are transported to the head-end equipment room via coax cabling.

If the donor antenna is the eyes and ears of the DAS solution, the head-end equipment room is like the brain of the system. This is where the repeater, or bidirectional amplifier, collects the RF signals for redistribution. The bidirectional amplifier is a very important component in a DAS solution. Without it, the RF signals would continue to grow weaker as they traveled a farther distance from the donor antenna. With the bidirectional amplifier, the signal is increased, or amplified, as it travels, so that the RF signal stays strong throughout the system and site.

Depending on the type of system, the signals are transported via coax or fiber optic cables to remote antennas. These remote antennas are compact, and can be placed discretely in an indoor environment. Sometimes called antenna nodes, these antennas are the redistribution points of the DAS network. With the aid of the remote antennas, the RF signals are distributed to places they could not directly reach without the distributed antenna system.

Though each DAS solution has common components, it will be built to overcome the specific communication challenges in a particular location.

Implementing a Distributed Antenna System Solution

DAS SolutionWhen the expert DAS implementation team at Harris Communications builds a solution for a client, the team will first perform a site survey to gather preliminary information about the location and specific coverage needs. This site survey includes floor plan details such as public vs. private areas, and identifies all areas in need of coverage if the solution will be built for just part of a building. The team will gather information regarding the building’s construction materials (sheetrock, concrete, metal, etc.) which will affect a signal’s ability to travel. With preliminary information gathered, the implementation team evaluates the RF reception in each area, determines the locations for each component of the system, and plans the cable routes. In addition, the team considers the security needs of the DAS solution. Performing a detailed site survey will ensure that each component of the system is chosen and placed for successful communication in all targeted areas.

DAS Codes and Regulations

With the enactment of IFC510 in 2009, the new fire codes suggested RF coverage guidelines to ensure that first responders have constant radio communication. The suggestions included providing RF signal strength in 95% of all building areas. Several years later, the tragic events of 9/11 brought the need for first responders to have reliable radio coverage in large buildings to our nation’s attention. As a result, many states, cities and counties began reconsidering and changing the existing codes to ensure better coverage for public safety reasons. The codes and regulations for RF coverage are different in each region. You can be assured that the DAS experts at Harris Communications, who serve multiple states throughout the country, will build systems that meet all code requirements for your area.

DAS Applications and Benefits

There are many benefits to installing a DAS solution in your building. When you weigh the cost and benefits, DAS should be a high priority in coverage challenged locations. Here are some of the main benefits you can expect from DAS:

  • Coverage: There are many obvious benefits to providing reliable coverage including convenience, increased productivity, and added safety. Coverage is becoming a necessity in our society.
  • Capacity: DAS allows more users to use the signals.
  • Reduced Interference: A unified DAS solution reduces the interference between signals.
  • Scalability: DAS solutions are not “one size fits all.” Each solution can be customized to fit the site.
  • Extensibility: As technologies evolve and communications needs change, a DAS solution can be easily modified to meet the changing demands.

Who should consider a DAS solution? With the demand for cell phone and data service everywhere, as well the need for reliable communication during emergency situations, the need for a DAS solution in a coverage challenged location is fast becoming a necessity. Applications for DAS solutions include a wide variety of locations, such as hospitals, casinos, transits, stadiums, universities, convention centers, and office buildings. Any location where people want the convenience and safety of reliable communication is a candidate for DAS.

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