Optimising DAS installations: Page 2 of 5

April 20, 2016 //By John Spindler, Zinwave
Given that installation costs can amount to 50 or 60 percent of the total cost of a distributed antenna system (DAS) deployment, it’s important to select systems and cabling that minimise total cost of ownership (TCO). This article will take a look at three key factors in DAS installations that can impact TCO, which includes cable selection, future proofing, and facilities use.

Another point to be considered regarding coax cabling is that if the DAS deployment demands use of multiple input/multiple output (MIMO) technology. This will require two antennas at each remote location and, therefore, two separate coax cable runs. MIMO is increasingly popular in DAS deployments because it delivers greater capacity than single input/single output (SISO) implementations (which have been the norm until recently), particularly for those applications where there is either a high user density, such as a stadium or airport, or a significant amount of wireless data use. But using MIMO means that installers must pull twice as much coax to support such an architecture, thereby doubling the material cost and greatly increasing the installation cost.

Cat 5/6 Ethernet cabling has been used by a number of DAS solutions, but many of these systems were introduced a number of years ago, prior to the proliferation of available mobile frequencies. This cable type is inherently a narrowband medium, so it’s constrained in the amount of frequency it can practically support. In one system, for example, the vendor was only able to support a maximum of 37 MHz of bandwidth on a single Cat 5/6 cable.  This is problematic in today’s mobile-centric world, as some spectrum bands come in much broader swaths than that. So supporting a relatively meager 37 MHz of bandwidth only allows you to support a single mobile band or frequency (and in some instances only a portion of that band). Meeting today’s frequency support requirements (which can require support of as many as 6-8 bands) would require independent layers of equipment and cabling for each band supported. Clearly, this kind of solution would radically impact the total cost.

The other limitation with Cat 5/6 which must be considered is run length. The distance is limited to only about 100 metres, so some installations, particularly those in larger venues, won’t be possible with Cat 5/6 cable.

In contrast, fibre is a broadband transport medium that is thin, light, flexible, and can support many frequencies. While a few solutions can use either multi-mode or single mode fibre, single mode fibre is most commonly used in DAS systems.  Given the broadband nature of fibre transport, some DAS systems which use fibre transport end-to-end – effectively from the headend to the antenna – can support mobile, public safety, and Gigabit Ethernet services on the same cable.

Fibre is also commonplace in any Class A building. Contractors put in bundles (generally speaking, using a minimum 12-strand fibre in a single bundle) in order to accommodate current and future services, so there may be existing fibre that can be leveraged for a DAS deployment in a building, thereby reducing the turnkey cost of the solution.

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