Published: 10 Jan 2011
Developing a strategic plan for enterprise Wi-Fi coverage will likely include a hybrid approach, combining aspects of DAS, femtocell and FMC.
Given broader Wi-Fi deployment, many enterprises are now rethinking use of both wired LAN and wireless cellular technology. But how can companies leverage their investment in increasing and improving enterprise Wi-Fi coverage that leverages existing Wi-Fi investments, minimizes costs and improves coverage? Let's look at a few options for extending cellular coverage and how Wi-Fi can help.
Distributed antenna systems
Many workers and their employers would like to eliminate desk phones, shifting all business calls onto mobile handsets -- especially dual-mode smartphones. This shift could greatly improve worker reachability and productivity while cutting costs by consolidating communications infrastructure, fees and maintenance.
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However, one major challenge preventing this shift is poor indoor cellular penetration. In a mobile-only scenario, a high percentage of missed, dropped or poor quality cellular phone calls simply cannot be tolerated. One way to improve in-building cellular reception is by using a distributed antenna system (DAS).
A DAS is a network of spatially separated antennas that connect back to a single source (e.g., outdoor cell tower) and together deliver wireless service within a given location (e.g., an office building or campus). A DAS avoids physical barriers that often impede indoor wireless propagation -- walls, doors, elevator shafts -- by positioning relatively small "repeater" antennas throughout a coverage area. Instead of having to stand near a window to get decent reception, users' handsets need only be within reach of any DAS antenna.
But with DAS, the devil lies in the details. Federal, state and local regulations determine who can deploy a DAS and where and how it can be deployed. According to the DAS Forum, "DAS operators must navigate through a complex maze of regulatory entitlements and approvals in advance of construction. This adds uncertainty to the DAS permitting process." In short, DAS isn't a quick DIY solution for enterprises to extend their own indoor cellular coverage. To learn more about DAS deployment, read this tip about in-building wireless solutions.
Another way to improve indoor cellular reception is by backhauling cellular traffic across another network that already exists and is relatively ubiquitous: the Internet. This can be accomplished by deploying your own little indoor cell tower: a femtocell. Click here for more information on mobile backhauling.
A femtocell is a small cellular base station with typical range of 50 to 200 meters, supporting anywhere from four to 16 simultaneous calls. Femtocells are plug-and-play devices, purchased or leased from a single cellular network operator. Simply plug the femtocell into a home or business LAN with Internet access and register authorized handsets. Thereafter, any authorized handset experiencing weak signal from an outdoor cell tower may get better service indoors by roaming transparently to the femtocell.
Femtocells are starting to become more popular for residential use. For example, AT&T's 3G MicroCell ($150) appeals to many iPhone subscribers with weak signals at home. Sprint's AIRAVE ($100, plus $5 per month) can be combined with $10 to $20 per month unlimited calling plans as a lower-cost alternative to landline phone or metered cellular services.
Business-grade femtocells are also available, but femtocells are often only appropriate for small offices where the desired coverage area and total number of handsets are modest. Those that need to extend indoor coverage for more than one cellular network -- for example, T-Mobile and Verizon Wireless -- must purchase two different femtocells. These factors have historically combined to limit femtocell appeal to larger enterprises. To learn more, read this tip about what to consider when purchasing a femtocell.
Fixed mobile convergence
DAS and femtocell both improve indoor voice service by strengthening cellular signal. However, cellular isn't the only indoor wireless technology. Increasingly, homes, offices, large enterprises and even entire campuses are being blanketed by Wi-Fi, and a growing percentage of mobile handsets are now dual-mode (3G + Wi-Fi) phones. Combine these trends and you have a fantastic foundation for fixed-mobile convergence (FMC).
Specifically, indoor calls can be relayed back to your cellular operator's network using an existing wireless (and perhaps wired) LAN. This approach leverages private LAN assets to improve indoor voice coverage by letting dual-mode handsets roam between cellular and Wi-Fi. ABI Research predicts that FMC handset voice connections for business customers will grow from 6.3 million in 2009 to over 27 million by 2014.
One such solution is Unlicensed Mobile Access (UMA) -- also called Generic Access Network (GAN), a 3GPP standard for handing off cellular calls to “unlicensed” networks, including office, home and hotspot WLANs. In UMA, the operator’s network controller decides if and when to re-route cellular calls. Alternatively, enterprises can host their own mobility controller or unified communications server to transition calls -- for example, directing a handset-resident agent to establish a cellular call just before Wi-Fi connectivity is lost.
To learn more about FMC deployment alternatives, these tips on buying femtocells are helpful. FMC can improve indoor performance where enterprise Wi-Fi coverage is available, while cutting cellular network load and metered usage fees. However, note that it's still necessary to create that ubiquitous indoor Wi-Fi network. That's where new hybrid approaches can help.
Traditional DAS solutions have the benefit of being multi-operator, while femtocells have the advantage of being easily deployed. Fixed-mobile convergence (FMC) appeals to those who want to use shared infrastructure to support multiple services. Vendors chasing the indoor cellular market have been searching for innovative approaches that combine these attributes.
For example, MobileAccess recently announced an "indoor coverage" system that extends the DAS concept to support cellular voice and Wi-Fi data over shared, in-building infrastructures. MobileAccessVE reuses CAT-5/6 Ethernet cables for cellular signal distribution throughout a building, without disrupting wired or wireless LAN operation. 2G/3G/4G traffic, potentially sourced from multiple operators, coexists with Ethernet data frames until it reaches the LAN edge. There, cellular and Wi-Fi signals are sent over the air using the same multiple-input, multiple-output (MIMO) antennas. In addition to cellular and Wi-Fi, public safety, WMTS and 900 MHz services can share the same infrastructure.
The growing need for enterprise Wi-Fi coverage will prompt other new hybrid approaches to emerge, combining aspects of DAS, femtocell and FMC. For example, a DAS may source traffic from several femtocells to simplify operator interfacing and speed deployment. By making your indoor network infrastructure investments do more, you may well be able to improve indoor coverage for many wireless services at a reduced total cost.
About the author:
Lisa Phifer is president and co-owner of Core Competence, a consulting firm focused on business use of emerging network and security technologies. At Core Competence, Lisa draws upon her 27 years of network design, implementation and testing experience to provide a range of services, from vulnerability assessment and product evaluation to user education and white paper development.
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