Carriers and enterprises looking to extend mobile wireless coverage inside buildings typically consider the technical capabilities of various systems when evaluating which one to deploy. Certainly, no system is worthwhile if it doesn't properly support the wireless frequencies required for specific carrier services (i.e., 800, 850, 900 or 1900 MHz), and the complexity and placement of varying equipment platforms does play a role in such decisions.
The reality is, however, that every competing system supports every mobile carrier service. The real decision often comes down to installation costs, which can account for 60% of the project's price. As it happens, the transport networks that are used to link distributed antennae with equipment platforms -- and the cost and complexity of installing those transport networks -- are where the real differences lie. These differences are significantly affected by the type of in-building system.
Active versus passive systemsThe majority of in-building wireless systems use distributed antennae to propagate the signal, but there are two main ways to achieve this: via passive or active systems.
Passive systems use rigid coaxial cable (1/2 to 7/8" in diameter) to distribute the wireless signal from a repeater or base station to the distributed antennae. These systems are passive because the distributed antenna system (DAS) itself uses no electronic components.
Active in-building systems take an approach that more closely mirrors standard LAN architecture. These systems use managed hubs and standard building cabling such as fiber and Cat 5 to distribute the signal from the RF source to the antennae.
Passive systems often appear simpler because they have fewer electronic components, and people typically associate electronics with high costs when compared with the cabling that links the components of a network. But buyers should look at the total cost of the system (components and deployment), along with the cost of any changes or upgrades.
Cost issuesHere's how differences in technology affect the total cost of a system.
- Deployment costs: There is a big difference in installation costs between coaxial cabling in a passive system and the standard fiber and Cat-5 cabling in an active system. Coaxial cabling can cost up to $4.50 per foot for materials and installation because it requires specialized expertise. It is difficult to install because it's heavy and does not bend easily. On the other hand, standard cabling (fiber & Cat 5) costs about $1 to $2 per foot, including installation.
- Signal strength: The electronics in active systems, which don't use coaxial cabling, ensure that each antenna distributes the same signal strength, no matter where it's located. In contrast, the coaxial cabling in a passive system is lossy – the farther the cable runs, the weaker the signal. To support long runs, passive-system users must install signal repeaters along the way at additional cost.
- Cost per square foot: The previous two factors create sharply different cost equations for the two types of wireless systems. In almost any other type of building improvement (LAN, carpeting, lighting, and so on), the total cost per square foot should drop as the building size increases, and this is the case with an active in-building system. With a passive system, however, the per-foot cost actually increases with building size.
- Local labor rates: The cost of labor will naturally be a key factor in the overall deployment. Labor costs are much lower in the third world, so the difference between the costs of installing passive and active systems will be less. But in industrialized nations, labor costs will almost certainly ensure that active systems will be less expensive overall.
- Installation time: The difficulty of installing coaxial cabling is another issue that affects costs because it increases deployment time. Installing any such system can be disruptive to the ongoing operations of the business or venue, so customers always prefer shorter deployment periods when they have a choice. This is less of an issue in new construction, but it can be a major factor in buildings such as hospitals, manufacturing facilities, transportation hubs, and resorts, where daytime access is difficult. In some situations, the installers may need special escorts for security and safety reasons, and this adds even more to the cost of deployment.
- Code requirements: Local building and fire codes can also affect the cost of deployment. Codes requiring placement of cabling in conduit or mandating asbestos abatement can greatly affect the overall cost of a project, and must be identified up front.
- Change orders: It's not uncommon for users to discover the need for additional antennae during or after the initial installation or to want to upgrade the system to handle new frequencies or services over time. Buyers should carefully consider the cost of such changes. Passive systems must often be significantly re-engineered to handle new antenna placements, leading to some truly hair-raising change order costs. Active systems, on the other hand, can usually handle new antennae or service changes without re-engineering. In most cases, expanding an active system simply involves adding antennae.
So there's more to in-building wireless than deciding which cellular frequencies to support. When evaluating in-building wireless systems, cost-related issues should prompt some searching questions for prospective vendors, helping buyers to make the right choices.
This was first published in April 2006