Distributed Antenna Systems (DAS). Active vs. Passive

Posted by Wave Wireless on Jun 22, 2015 10:46:00 AM

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RF signals degrade as they pass through the structural elements of buildings, contributing to the development of areas known as dead zones. These are areas where there is little or no wireless coverage what so ever. This means that developers and building owners must find ways to overcome this challenge and provide strong and reliable signal strength throughout the building and in turn maximize the performance of devices connected to the network. A good start would be determining exactly where the coverage is weak.

A distributed antenna system (DAS) offers a viable solution to fixing coverage deficiencies and capacity issues. A DAS is very scalable as it is based on the mobile network, a technology that is proven to be scalable. Two types of distributed antenna systems are:

Passive DAS:

Passive_DAS_System_1_r

A passive system is best suited for relatively small areas that were one or two mobile network operators need to be enhanced. It is the more cost effective solution but for this system to provide a reliable and uniform signal strength throughout the building, the RF power must be balanced among all the coverage antennas. The number of in-building antennae and coverage area is dependent on the output of the signal source. 

Active DAS:Active_DAS_InBuilding




These systems can be set up in large buildings and campuses by converting and transporting the radio frequencies over optical fiber. They may be deployed to cover large areas. They are best suited when there is a need to support multiple mobile network operators.  

In a properly designed active system, no re-engineering or rebelling of the original system is required when the system is expanding, thus meaning that they are flexible when adding 3G, 4G or LTE services. Furthermore, active systems utilizing optical fiber can provide coverage in areas up to 2km from the signal source making them ideal for campus environments.



To sum up, it is important to understand the difference between the two systems. A passive system does not require a powered antenna, it is not easily expanded and is relatively inexpensive. Active DAS requires powered antennas, is readily expandable and generally more expensive.

References: Images by radioaccess 

Topics: Cellular Blog Posts

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