Femtocells: Spectrum Efficiency Improved | Radisys

Technology Article

Femtocells: By Manish Singh, Spectrum Efficiency CTO Improved

One of the most limited resources in telecom is wireless spectrum; therefore, it is not surprising that carriers are paying premium licensing fees for spectrum acquisition. For example, the recent 700 MHz spectrum auction in the U.S. had an aggregate bid value of $19.6 billion. Since acquisition of wireless spectrum is limited, it is advantageous for wireless carriers to use the spectrum efficiently in both outdoor and indoor environments.

From a radio frequency (RF) propagation perspective, buildings and walls have never been friends to a radio signal. Physical structures cause RF signal attenuation because of reflection, diffraction, scattering, and multi-pathsignal fading, all resulting in poor radio signal reception in an indoor environment. In some cases, virtual dead spots can occur inside buildings, even though there is great coverage outside. Walls can attenuate signals by 10 to 20 dB depending on the type of construction. At the same time, studies have shown that an average consumer spends 50 to 60% of his or her time in an indoor environment, and that 70% of wireless calls originate and terminate indoors. All things considered, this poses the question: Are wireless carriers using their spectrum efficiently in indoor environments? Femtocells: Spectrum Efficiency Improved 2

Market Drivers For Femtocells become their friend as they attenuate RF femtocells are widely available. One silicon signal propagation out of the home from part, integrating the required compute, digital From an engineering standpoint, wireless the femtocell, thereby minimizing radio signal processing, encryption and various system spectral efficiency is measured in interference with an existing macro-cellular other key features for a small wireless base bps/Hz/cell. From a carrier standpoint, this network or another nearby femtocell. In fact, station, is key to drive the bill of materials translates into the number of simultaneous femtocells not only provide excellent indoor (BOM) cost down for a commercially viable subscribers that can be supported in one coverage, but also, by virtue of creating a femtocell deployment. Lastly, with more than cell site (i.e., network capacity). From a small indoor cell-site, they free up capacity 2.5 billion wireless subscribers worldwide, consumer standpoint, this all translates into in the macro-cellular network. In other the economy of scale to justify femtocell quality of voice and video, dropped calls, words, indoor subscribers’ cell phone traffic deployment is finally in place. and high-speed packet access (HSPA) data is parked on a femtocell as opposed to on rates. Poor indoor RF signal penetration has a macrocell. Femtocells eliminate the need adverse effects on the link spectral efficiency, Femtocell In The Enterprise for dual-mode handsets as virtually any which has a direct impact on system spectral The business case for femtocell rollout is existing wireless handset should seamlessly efficiency. Simply put, carriers lose revenue as straightforward and can be summarized work with a femtocell. And last but not mobile minutes are lost to landline minutes in three key parts. First, consumers today least, one femtocell can support four to six when consumers experience dropped calls, are paying for landline connections. These simultaneous voice calls, which means that poor quality of voice, and lower data rates landline minutes and Average Revenue each member of a family of four can talk when indoors. When considered in aggregate, Per User (ARPU) are up for grabs due to simultaneously as if they had four virtual one can easily see the underlying market competition, but only if wireless carriers landlines for the price of one. drivers for femtocells. can provide reliable indoor coverage. In the Why Has It Taken So Long? U.S., the number of cell phone-only homes exceeded the number of landline-only So, if femtocells enhance coverage, increase homes in 2007, and household cell phone network capacity, and improve spectral spending has exceeded landline spending. efficiency, then why have they not been widely With femtocells, carriers can provide a deployed before now? In fact, the femtocell robust wireless alternative to landlines is not a new idea. It has been around for and accelerate this social phenomenon of a long time, yet the catalyst for driving a consumers replacing their landlines. commercially viable rollout for femtocells has only fallen into place very recently. In the Second, the demand for mobile broadband earlier days, backhaul costs were a barrier is on the rise, as fueled by the YouTubes for mass deployment, but today the wide and Facebooks of the world. Femtocells add proliferation of IP broadband connections network capacity and make it possible to (fiber, DSL, or cable) means that the backhaul deliver 7.2 Mb/s and 14.4 Mb/s HSDPA data infrastructure already exists. In the U.S. rates to consumers in indoor environments — alone, more than 52% of homes now have thereby fulfilling market demand for wireless What Is A Femtocell? broadband connections, and the figure is broadband access. growing. Femtocells leverage a consumer’s A femtocell is essentially a small wireless IP broadband connection to backhaul voice, Thirdly, femtocells deliver capital and base station that resides in the consumer’s video, SMS, and data traffic from millions of operational expenditure savings. Adding home or office. Femtocells transmit at very homes into an existing wireless core network. a new macro base station costs roughly low power, yet create almost ideal indoor $600,000, depending on site geography, radio conditions. For backhaul, femtocells Furthermore, thanks to Moore’s Law — which technology, supplier cost model, etc. Add use an IP broadband connection (e.g., states that silicon performance doubles to this approximately $15,000 per month fiber/DSL/cable). The very walls which every 18 months — we are now at the point for operation costs, such as leased lines, are a radio signal’s adversary actually where integrated custom silicon parts for electricity, and cooling, etc. For the cost of Femtocells: Spectrum Efficiency Improved 3

one macrocell site, a network operator could existing carrier’s macro network. Traditional 3G networks simply do not scale for potentially cover 6,000 homes, assuming RF planning tools used to plan macro femtocells. The Broadband Forum already a cost of $150 femtocell price per unit and cellular networks will not work for femtocell has developed the TR-069 standard for operator subsidies of $100 per unit. For deployments. Instead, femtocells will need remote customer premise equipment (CPE) $600,000, assuming 7.2 Mb/s HSDPA rate, the ability to scan the dynamically changing device management. This standard needs to one macrocell site would add an aggregated RF environment and configure themselves be further extended to support femtocells’ 7.2 Mb/s bandwidth capacity, as opposed with frequency bands, scrambling codes and data models and deployment models. With to 43 Gb/s with 6,000 femtocells. This is a transmit power levels. TR-069, carriers can re-use their existing huge difference — especially if revenue is CPE device management infrastructure accumulated on a usage basis. Femtocells take security challenges by just extending it to include femtocells. to another level. Since the traffic from Likewise, to support E911 regulations, Carrier Benefits femtocells can be carried over a public IP carriers will need the exact location network, the traffic needs to be encrypted The carriers that roll out femtocells first will information of femtocells to effectively route to avoid eavesdropping. Potential solutions benefit from reduced churn as subscribers emergency calls to the nearest public safety include establishing IPSec tunnels, SRTP, will not struggle with dropped calls. The answering point (PSAP). Femtocell location or TLS for securing the traffic. Carriers also quality of the consumer’s experience will information could potentially be obtained need to secure their existing core network improve significantly as clear voice and HSPA using global positioning system (GPS) infrastructure from any Denial of Service data rates are delivered. Most importantly, technology; however, GPS itself does not (DoS) attacks — hence the need for a the carriers that initiate the charge will function very well in indoor environments. Security Gateway between femtocells and benefit from “reverse-churn” as femtocells Another alternative could be mapping a the core network. enable home-zone “family tariff plans” which static IP address to a femtocell’s physical location. All of these challenges will need to will entice all family members to switch to Quality of Service (QoS) is another challenge be addressed before widespread femtocell one carrier in order to take advantage of that needs to be addressed. The best effort deployment becomes a reality. packaged bulk service benefits. of an IP network is just not good enough Challenges Of Femtocell to carry real-time voice which might be What Lies Ahead? Rollouts vying for bandwidth on a shared IP link with peer-to-peer (P2P) and other data traffic. Looking further into the future, femtocells While the economics for femtocells are In certain deployment scenarios, the DSL will be more than just access points. The compelling, there are many technical uplink bandwidth can be as low as 200 Kb/s market will see more converged CPE devices challenges that need to be addressed. and pack four simultaneous voice calls. In with femtocell functionality embedded into Utilizing femtocell means that a wireless this environment, not losing a consumer’s a residential gateway — an IPTV set top box base station essentially moves into the VPN connection on his or her PC will be or a cable/DSL modem. For example, Netgear consumer’s home, and along with that comes difficult. As a result, classifying, marking, has already announced the availability of a the challenge of integrating millions of and prioritizing IP packets based on class of Residential Gateway incorporating femtocell femtocells with an existing 3G wireless core service becomes a key requirement. Potential technology. These converged CPE devices infrastructure. Many different architecture QoS solutions include static Diffserv-based will enable carriers to deploy true quad- options, like Tunneled Iub, Tunneled Iu, and solutions as well as Signaled QoS solutions play services — voice, video, data, and SIP/IMS are under consideration, and much based on RSVP or SIP. mobility — all out of one box. And let’s not more work is needed in order to reduce these forget that 3G Long Term Evolution (LTE), or choices to only one or two. TR-069 Standard “4G,” standardization work is already being influenced architecturally as eNodeBs are Femtocells also bring up the challenge of Management of millions of femtocells also expected to be deployed as home base managing RF interference. RF interference requires unique solutions. Traditional stations, i.e., Home eNodeBs (HeNB). Carriers between femto-femto and femto-macro Element Management Systems (EMS) that that have already secured CPE real estate in can create virtual dead spots as well as the are used to manage NodeBs and Radio consumers’ homes will continue to have an potential of degrading the performance of an Network Controllers (RNCs) in today’s advantage long into the next decade. Femtocells: Spectrum Efficiency Improved 4

Conclusion Carriers and consumers will both benefit by femtocell rollouts. Carriers will accelerate return on investment (ROI) on spectrum acquisition by efficiently using this scarce and costly resource in indoor environments, while at the same time monetizing mobile minutes substituting for landline minutes; thereby, creating pull for new customer acquisitions through family tariff plans and aggressively growing the data ARPU. Consumers will benefit as they jettison their landlines and become accustomed to their existing cell phones working seamlessly with femtocells while enjoying better coverage, HSPA data rates, zero dropped calls and multiple virtual connections. And this is all just the beginning. In the future, femtocells are poised to play a key role in delivering converged services via IP Multimedia Subsystem (IMS) — a topic for another day and another article.

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