We have all been there; While indoors you take out your phone to make a call, but you find that the network signal bars are down to zero and the call doesn’t connect. So, you start going to the nearest window or search for a network covered area. Since in the last few years more and more facilities and corporations became very network dependent having an area indoors with no coverage or reception is a major setback; That’s why IBS (In-Building Solutions) came to be.

“That’s great, but how does it work?” you might ask; IBS consists of a series of antennas and  signal repeaters inside the building that redirect the signal sent from network towers outside to reach maximum coverage area for said signal. That is achieved using Distributed Antenna Systems (DAS).

The main functions of DAS are the amplification of the radio frequency (RF) signals received from an outdoor antenna – when needed – and the broadcasting of the signals indoors. It can be passive or active, but what is the difference between them?

Passive DAS

Passive DAS  amplifies the signal and sends it through coaxial cables to a splitter that sends the signal to multiple antennas across the building, a single amplifier can have a coverage ranging from 5,000 to 100,000 sq ft and for buildings with a greater area it is not recommended to use a single amplifier since the signal will diminish as the cable length increases. Instead, multiple passive DAS units are hooked up to the outdoors antenna which is an advantage to have, another advantage of Passive DAS is that it covers all frequencies and carriers, also since the signal is sent directly without conversion it is less complicated to install and implement than Active DAS, and the most important advantage: It is 75% cheaper than Active DAS. 

Passive DAS is used in:

  1. Shopping malls
  2. Hotels
  3. Hospitals
  4. Private offices
  5. Residential flats (rarely)

Active DAS

Active DAS on the other hand takes the outdoors signal and sends it through coaxial cables to a Digital Conversion Unit (DCU) that converts it to an optical signal then, it is sent to a Remote Access Unit located (RAU) somewhere else in the building.The signal is converted back to RF by the RAU and is amplified before being distributed to the indoors antennas through coaxial cables.

Obviously, the Active DAS is more complicated to implement and to install and as complexity increases the price shoots through the roof. Another drawback is that it only supports one carrier frequency; and if more are needed then more sets of DCU and RAU are installed increasing the cost. But the use of these complicated components increases coverage and accessibility; using optical signals insures there is no data lost over long distances. Active DAS can be monitored remotely via Simple Network Management Protocol (SNMP) unlike Passive DAS.

Active DAS is most commonly used in:

  1. Stadiums
  2. Convention/Exhibition Centers

What do you think? for a large building would you implement an active or a passive DAS ?