In -building
it distributes the wireless signal through a se- ries of managed expansion hubs, remote access units, and antennas.T is system aggregates all capacity and simulcasts the signal to each an- tenna location. Because the signal is amplifi ed at the re-
DAS antennas fi t unobtrusively in ceilings and can carry whichever frequencies the base station puts out. Once deployed, the indoor system is virtually transparent to the network and is largely trouble-free
ute radio signals is inherently capable of sup- porting multiple carrier frequencies. While passive systems are thereby viewed as
simpler, one-stop solutions for indoor wireless coverage, there is a great risk of signal interfer- ence. Multiple bands may ‘mix’ and produce noise on the network. In a passive system, the signal degrades with
the length of the cable in any particular run. As a result, passive systems are not well suited to large sites with long or complex cable runs, or those that require high call capacity or high sig- nal strength. Signal quality degrades the further you are from the RF source. Passive systems do not off er end-to-end
monitoring and management. T e signal is simply pushed out over copper cabling, and so service providers and building owners never know if a particular antenna has failed until us- ers start complaining. Finally, passive systems are more diffi cult
and expensive to install because their heavy, rigid cabling requires special expertise and of- ten special cable raceways or hangers. Since the cabling is not as fl exible, it is also more diffi cult to deploy in tight spaces. Active systems: active DAS use managed
hubs and standard building cabling (i.e., single- or multi-mode fi bre and CATV cabling), much like an ethernet LAN. In an active DAS, the main hub is deployed next to the base station or repeater in the building’s equipment room, and
motes, active DAS deliver strong and consist- ent signals at every antenna, no matter how far away it is from the base station and main hub. In the largest airports or multi-facility deploy- ments such as major hotels on the Las Vegas Strip, some active DAS extend for miles. Since every antenna has predictable signal strength and coverage, it is far easier to plan the antenna placement in an active system. With their double-star architecture, active
DAS can be expanded indefi nitely through deployment of additional hubs and antennas. T e distributed hub architecture of an active system mirrors the design of ethernet LANs – it scales easily through addition of new anten- nas and hubs, and the hub electronics can be upgraded to support new services as they come on line. T is leaves the most expensive part of the system – the cabling and antenna plant – untouched. Active systems usually support SNMP alarms as well, so a company’s IT staff can monitor the status of all remote antennas in the network using the same network manage- ment tools used for the LAN.
Installation Active DAS can be less expensive and are less disruptive to deploy because their standard ca- bling is inexpensive, and the job can be handled by IT cabling contractors or electricians rather than specialized technicians. Standard cabling can be run across suspended ceilings and in tight spaces like conduit just as easily as LAN cabling. In many cases, an active system can use exist-
ing, unused fi bre that runs up a multi-storey building’s utility riser to link a main hub with expansion hubs, and then use new CATV cabling to connect each expansion hub to its RAUs and antennas. While multiple sets of electronics may be re-
Olympic data traffi c could leave cellular networks paralysed
New forecasts from Ericsson indicate that mobile data traffi c is likely to grow tenfold by 2016, and that smartphone traffi c will have tripled during 2011 alone. Steven Glapa, of the Wi-Fi systems manu-
facturer Ruckus Wireless, comments that mobile phone networks will struggle to ac- commodate these monstrous volumes of data traffi c. And as the UK prepares for an infl ux of tourists in the run up to the Olympics, he warns that network operators must act to en- sure that they are able to deliver the level of
LAND mobile November 2011
service that subscribers have come to expect. “Cellular networks were initially designed
for voice traffi c, so unless steps are taken to address the unprecedented growth in mobile data traffi c, the UK’s networks are at risk of failing millions of customers during the Olym- pic Games”, Glapa says. “To avoid this, operators should be looking
to deploy solutions that bolster their macro cellular networks and help to ease the pres- sure, especially in places such as stadiums, where data traffi c is likely to be particularly
high. Options include Wi-Fi offl oad, ideal in areas where 3G/4G subscriber density and usage is high as well as small cell underlays to address high capacity density. “Although traditionally competing solutions,
Wi-Fi offl oad and small cell underlays are increasingly being considered in tandem to improve overall network utilization, allowing traffi c to be successfully managed.
It’s a
winning partnership that looks to deliver big time benefi ts – and is sure to keep London connected during the Games.”
23
Equipment in an active DAS installation
quired to support all service providers (depend- ing on the service providers’ requirements), the cost of cable runs is a larger factor in the overall price of a system in all but the smallest facilities. With the coming of LTE and its enormous
new requirements for capacity in the network, DAS will be the most cost-eff ective and fl exible means of providing that capacity. We can ex- pect to see a signifi cant increase in DAS deploy- ments in many enterprise and public buildings.
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