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General Information
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July 17, 2009
• Vol.31 Issue 19
Page(s) 32 in print issue
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Femtocells & Wireless LANs
Are The Technologies Complementary Or Competitive?
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| Key Points
• Resembling a Wi-Fi access point, femtocells are small, self-configuring appliances that use a telecom carrier’s licensed frequencies to extend and enhance cellular coverage within a building; they use a broadband WAN circuit to backhaul cellular voice and data traffic to the telco’s network.
• Initially targeted at consumers, SMEs can use femtocells to extend smartphone voice and data to the office.
• Femtocell technology is rapidly evolving to solve a number of technical challenges, so most enterprises are advised to monitor the market and defer trials and tests until next year. | Sounding something like a microorganism, a femtocell has nothing to do with biology, but it could well become part of the IT lexicon within a few years. Femtocells are very small cellular base stations that provide localized coverage, usually within a home or small office, using a wireless carrier’s licensed frequencies.
As David Passmore, research director for Burton Group, puts it, “The femtocell operates just like a large cellular base station (typically located on a cell tower) but enables wireless communications—voice phone calls and data transmission—with mobile phones located primarily within the home or small-business location.” Because femtocells are tiny, self-configuring appliances supporting 3G cellular data networks, they bear striking resemblance to a Wi-Fi access point. In fact, as femtocells require a wired broadband connection for backhaul to the carrier’s network, David Chambers of the consultancy ThinkFemtocell says, “Some vendors are planning to incorporate all three features into a single box (Wi-Fi, DSL, and mobile).”
Unlike Wi-Fi APs, femtocells use licensed radio spectrum, so the technology is largely driven and controlled by the major telecom carriers. According to John Spindler, vice president of product marketing at ADC (www.adc.com), femtocells, by eliminating cellular dead spots, were originally envisioned as a way to facilitate wire line phone displacement in the home; however, with the rise of smartphones and 3G networks, femtocells may play an important role in converged mobile voice and data networks.
Femtocells have become a beachhead in the cell phone’s larger campaign to obsolete traditional wired telephony—a battle that Passmore sees progressing along two fronts: fixed-mobile convergence (aka unified communications) and fixed-mobile substitution. He adds, “Because femtocells can work with most existing mobile phones, they are likely to emerge as a far more popular alternative to Unlicensed Mobile Access or other fixed mobile convergence solutions that make use of WLANs for voice communications.”
 How Femtocells Work
From a carrier’s perspective, “Femtocells are a completely new way of looking at mobile networks,” says Aditya Kaul, senior analyst of mobile networks for ABI Research. They enable a bottom-up, distributed architecture with many small base stations complementing traditional arrays of cell towers, each covering a broad geography. According to Chambers, “Inside the femtocell are the complete workings of a mobile phone base station, [and it] appears to the standard 3G phone as just another cell site from the host mobile operator and can be used by almost any phone, including roamers visiting from other countries.” Yet, Passmore notes that the femtocell’s technological immaturity and use of licensed spectrum tied to a specific carrier means that roaming between networks is problematic at best and impossible between carriers and phones using different mobile telephony standards (such as Verizon with CDMA vs. AT&T with GSM).
From an IT standpoint, the femtocell architecture looks much like a WLAN, with each station providing coverage for several thousand square feet. Belying their roots in voice networks, femtocells offer dedicated capacity for several simultaneous channels, a differentiating feature from various voice-over-Wi-Fi solutions that must share bandwidth among all voice and data users. Therefore, where the femtocell emerged as a more robust alternative for cellular dead zones than signal repeaters, Kaul believes their addition of dedicated network capacity becomes a more important attribute as smartphone users increasingly rely upon wireless data applications.
Although femtocells are self-installing and designed to work “out of the box,” Kaul notes that their reliance on licensed spectrum means carriers maintain substantial operational and deployment control. That said, femtocells do provide local configuration of the users and phones allowed to access the network.
Femtocells In The Enterprise
The smartphone’s ubiquity as an information appliance, juxtaposed with the emergence of dual-mode Wi-Fi phones providing voice communication over WLAN data networks, heralds a likely collision of technologies. Yet Spindler sees the two as complimentary, not competitive. He notes that while voice over Wi-Fi is serviceable, problems with traffic prioritization and call handoff (between APs or between an AP and cellular network) mean it’s tricky to make seamless and reliable. Passmore agrees that the two will coexist, particularly because the increased capacity and bandwidth of 802.11n-based WLANs mean many enterprises are contemplating replacing existing wired Ethernets with wireless. However, he adds that with employees accessing enterprise applications and data via 3G-tethered smartphones or netbooks, femtocells still have a place in the wireless office.
For enterprises, Passmore sees femtocells providing five key benefits: improved local coverage with better voice/data service quality, improved mobile phone battery life, potential cost savings on mobile service plans, compatibility with existing mobile phones, and reduced density of necessary WLAN APs by offloading VoIP traffic.
A major obstacle to enterprise femtocell deployment is its current focus on the consumer market, with the consequent limitations on areal coverage and number of concurrent users. Kaul says the technical limitations of existing products means deploying multiple femtocells in a large office is challenging. Significant hurdles include radio interference and call handoff between multiple base stations.
An example of the femtocell’s adaptation to enterprise requirements is the emergence of super-femtocells, which add capacity for 8 to 16 simultaneous channels and which Kaul says should easily suffice for SMEs with 50 or 100 employees. While at least one super-femtocell product has been announced, Passmore doesn’t expect to see widespread availability until next year, with Kaul estimating the market topping 500,000 units by 2013.
State Of The Technology & Recommendations
Still, femtocells are largely a consumer-oriented solution with most experts seeing their enterprise use limited to early adopters in small or branch offices. Although Wi-Fi phones have become less exotic, using femtocells with standard cellular phones is easier than running voice traffic over an existing WLAN. Yet enterprise femtocells are hardly mainstream. As Kaul points out, the technology is still scaling an array of technical hurdles, hasn’t achieved economies of scale, and thus can’t challenge the aggressive pricing of Wi-Fi access points. Therefore, while enterprises shouldn’t rush deployments, femtocells certainly warrant consideration as an alternative to equally problematic wireless VoIP phone solutions. 
by Kurt Marko
Femtocell Alternatives
Femtocells aren’t the only way for residential consumers or enterprises to improve their indoor reception of wireless cellular signals, nor are femtocells the only choice for mobile phone users who want to redirect their calls over some other network to reduce cellular network usage and related fees. Here are the technologies, techniques, and configurations that might be considered femtocell alternatives.
UMA (Unlicensed Mobile Access) Voice over WLAN: dual-mode (cellular, Wi-Fi) phones (for example, T-Mobile HotSpot@Home)
Enterprise client/server Voice over WLAN with FMC (fixed-mobile convergence): essentially a mobile phone that roams between a cellular network and enterprise VoIP PBX (private branch exchange)
Enterprise picocells: a small cellular base station placed at a customer’s location but managed by the mobile operator
Cellular radio repeaters: a radio repeater for improving signal strength in a building using an outdoor antenna; data is not backhauled over the WAN, but directly through the wireless cellular network
Wi-Fi-only phones with VoIP services: use of a dedicated VoIP phone or dual-mode smartphone with VoIP software and networks such as Fring, Skype, or Truphone to completely bypass the cellular network
SOURCES: “MOBILE PHONE SERVICE FUTURES: FEMTOCELLS OR WIRELESS LANS?”; BURTON GROUP RESEARCH REPORT BY DAVID PASSMORE; APRIL 14, 2009. |
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