There are three basic types of DAS: active, passive and hybrid. Active systems digitize and encode RF and transport it along standard Category 5 or fiber optic cabling to the desired location, where they decode signal back to RF and shoot it out onto the antenna. Active systems have an advantage in that there's no signal loss during transport, which allows for very long runs over fiber and thus greater centralization. And, because signals are digitized, there's no interference among bands.
Disadvantages include cost and active components that could fail and the requirement for local power at the conversion point in the wiring closet. In addition, these systems are frequency-band-specific, meaning separate components will be required for 2.4 GHz (802.11b/g) and 5 GHz (802.11a and eventually 802.11n).
Passive systems use radiating coaxial cable, sometimes referred to as "leaky coax" because notches in the cable's protective sheath allow signal to bleed out. Generally broadband as opposed to narrow-band in nature, they operate from sub-1 GHz to sub-3 GHz. Because passive systems use copper for transport, signal loss is a concern. The advantage, of course, is that without active components there are no failures unless there's significant cable damage or a cut. Leaky-coax DAS is best for low-capacity usage because the signal is spread thinner around a wider area. And due to this characteristic, most leaky-coax DAS breaks location-tracking systems.
Hybrid systems use fiber for analog signal transport, which means an active component on the far end to modulate the RF onto the leaky coax.
The downside is that, for now, DAS for Wi-Fi alone cannot be cost-justified--Gartner estimates the cost at $0.50 to $2 per square foot. But if your location requires multiple wireless technologies--say, pager and cellular coverage--and/or you have relationships with multiple cellular providers, DAS may be a cost-effective choice, especially if your provider will subsidize the DAS setup.
