A Distributed Antenna System, often called a DAS for short, takes mobile phone signals to & from Mobile Network Operators’ (O2, EE, Vodafone & Three in the UK) radio equipment, typically Base Stations just like the ones use for the Mobile Phone Mast you see outside, and distributes those signals inside buildings using low RF power (i.e. safe 0.2Watts) antennas distributed about 30-40metres apart throughout the building connected together in various ways (see below).
A DAS connected to a Base Station will provide sufficient coverage and voice call & data capacity for 1,000 – 10,000 building occupants and is typically deployed in large Office Blocks, Railway Stations, Shopping Centres, Airports and even Stadiums (e.g. Tottenham Hotspurs’).
There are two types of DAS; a Passive DAS where a Base Stations’ high power (40Watts) RF signals are split across many 10’s of low RF power antennas using RF power dividers and couplers connected together using thick coaxial cables, and an Active DAS where the Base Stations’ high power (40Watts) RF signals are converted into digital or analogue signals and transported over optical fibre &/or copper (e.g. Cat6a) data cables to Remote Radio Units (RUs for short) which converts these into low RF power signals radiating over a 15m to 20m radius.
It is also possible to use Ofcom License Exempt “Off-Air” Repeaters (often called Boosters) for each Mobile Network Operator (MNO) to receive & transmit the mobile signals outside the building and feed them inside using Passive or Active DAS, provided there are no more than 150-180 Users on each network inside and outside network is not already at full capacity. A Repeater is required for each MNO and they must repeat (sometimes called boost or boosting) 3G signals so Users can make 999 (or 111) emergency services calls inside the building. Herbert In-Building Wireless Ltd will not offer or install a Repeater based in-building coverage solution without gaining agreement from the relevant MNOs.
Some UK Mobile Network Operators provide Pico Cells which can be connected to Active DAS systems to provide coverage for up to 500 Users on their particular network.
A Passive DAS has the following Pros & Cons:
Passive DAS Pros
Passive DAS Cons
It’s the lowest cost single Operator (e.g. O2 or EE or Vodafone or Three) DAS
It can only distribute signals from one Mobile Network Operator (O2, EE, Vodafone or Three)
It has a maximum limit (typ. 200,00sqft) on the floor area and therefore Users it can cover.
The coaxial cables, couplers & splitters require their own dedicated containment as they are bulky & heavy
Can’t monitor the health/state of the system; have to rely on User complaints and annual coverage walk tests
Active DAS have the following Pros & Cons:
Active DAS Pros
Active DAS Cons
They can distribute signals from multiple Mobile Network Operator (O2, EE, Vodafone or Three)
They are expensive for single Operator (e.g. O2 or EE or Vodafone or Three) DAS deployments
There is no maximum limit on the floor area and therefore Users they can cover.
They require Rack Space in the ICT rooms for Hubs
The fibre &/or Cat6 cables can be run over existing containment.
Can monitor the health/state of the system, often with automatic alerts & remote diagnostics