Optimising DAS installations

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.

Cable selection

The first factor impacting TCO is the cable infrastructure the system uses. The most common choices are coaxial cable, Cat 5/6, or fibre. The medium you choose has a lot of impact not only on TCO, but also on the system’s performance.

Coaxial cabling was the first transport medium used for DAS installations. The older systems, as well as some of the newer ones, use a mixed infrastructure of fibre optic cable (generally used from the head end of the system to a closet-mounted remote unit) and a half inch diameter coax (the “last mile” from the remote unit to the passive antenna). When looking at material cost, a half inch coax is the most expensive of the various cable media typically used in a DAS solution.  From an installation standpoint, a half inch coax is problematic because it is heavy, has an extremely limited bend radius – which if exceeded will stop the “flow” of RF similar to a kink in a garden hose – and often requires special cable trays to support its weight. In addition, connectorising a half inch coax can be both time-consuming and costly.

When considering all of these factors, the use of a half inch coax can add around 25 percent to 35 percent to the cost of installation, and it doesn’t necessarily deliver the broadband capacity one would expect from such large cabling. In fact, RF signal attenuates as it travels over coax cabling, so there will be different output performance at different antennas, depending on the length of the cable run in each case. This makes system design and planning the antenna placement difficult and time-consuming. Note that a few DAS systems use thinner CATV (RG-6/U) cabling now, so the cable itself is easier to pull, but many of the same performance limitations still exist.


Figure 1: A half inch coaxial cabling.

 

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