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Passive Vs Active Small Cell DAS

January 3, 2017

 

What is a Passive DAS?

 

A passive distributed antenna system (DAS) uses dedicated backhaul (leased line) per operator connected to a signal source AKA base station (3G, 4G etc), the signal of which is blasted with very high power via thick COAX cable direct to radio antennas. Passive DAS is very cheap as there are no active components, just COAX cable and antennas. However, they are suitable to a very limited size of building because the further the antenna is from the signal source, the weaker the signal becomes meaning it wouldn’t be suitable for a large building.

 

Each mobile operator has to fund the backhaul and base station which costs them around £50K each, meaning if there's less than a 2,000 person occupancy in the building, they're unlikely to fund this element as there's no return on investment for them. The whole reason operators provide in-building mobile coverage is to increase traffic and users on their network.

 

So, although passive DAS is very cheap, there are two issues with the deployment being viable; the system is only suitable for small buildings, however, if the occupancy is less than 2,000 per day, the networks are unlikely to fund a base station and backhaul.

 

What is Active DAS?

 

Traditionally, an active distributed antenna system (DAS) uses dedicated backhaul per operator and a base station in the same way a passive DAS does, however, it uses a DAS ‘head end’ or ‘hub’ which distributes the signal of the base station via a fibre optic cable to ‘radio remote units’ connected to radio antennas. This type of solution is suited to much larger deployments because we use fibre optic cable instead of COAX allowing us to send the signal of the base station up to 8km in distance without the weakening effect that comes with COAX and passive systems.

 

An active DAS is more expensive than passive DAS due to the amount of components it uses and again, traditionally would only be suitable for buildings with 2,000+ occupancy per day because the networks still have to fund a base station and backhaul. However, Spectrum Infrastructure are pioneering the use of small cells with DAS. A small cell is a scaled down base station which costs around £2,000 and can use shared backhaul, all of which can be funded by the building owner, meaning there's now no investment required from the mobile operators which in turn means an active DAS is now suitable to a building of ANY size. This is a revelation in the mobile coverage world because there are so many buildings that require mobile signal, for instance in a four floor building with a 400 person occupancy where a low cost passive DAS wouldn’t be viable from the mobile operators perspective.

 

There are a huge host of benefits that come with active DAS from pro-active monitoring, hardware fault isolation, power consumption, faster installation and minimal building disruption.

 

If you would like to know more, please call Spectrum Infrastructure on 02393 874 720 or complete the form (bottom right) and we will contact you soon.

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