Reader Forum: Femtocells are growing up

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Carriers around the world are now deploying femtocells in large numbers. While the biggest deployments are aimed at the consumer market, increasingly carriers are looking to extend femtocells to business customers and high-traffic indoor (and even outdoor) locations such as shopping malls and railway stations. These deployment models introduce new challenges in the way femtocells are provisioned and managed. However, public access femtocells offer significant benefits, not only in delivering improved service quality, but also in offloading data traffic from the carriers’ overloaded macro networks.
By far the largest volume is in residential femtocells, with AT&T Mobility, Vodafone Group plc and Sprint Nextel Corp. in the vanguard. The key motivation for these femtocell offerings is simply to improve the quality of cellphone service in the home with better voice quality, fewer call drops and faster 3G data speeds. The carriers hope that improved service will make for happier (and more loyal) customers – a premise consistent with the largest survey on consumer attitudes to femtocells, carried out by Parks Associates on behalf of the Femto Forum. The survey of more than 6,000 consumers in six countries revealed that femtocells could prevent up to 42% of churn caused by poor quality in-building cellphone service, which is the single most important criteria by which consumers rate their mobile network provider.
Some have accused the carriers of making their subscribers pay for femtocells as a way to patch holes in their networks, but this overlooks the fact that femtocells provide a personal cell for the subscriber’s family and friends only. One exception is SoftBank in Japan, whose femtocells are deployed in open access mode so that any SoftBank subscriber in the neighborhood of a femtocell benefits from improved cellphone reception. SoftBank justifies its femto proposition by giving away the femtocell access point, and providing a free broadband connection – the subscriber only provides house space.
In fact, many other operators are also giving away femtocells, at least to select, high-value subscribers. In addition to reducing churn, there are other motivations, such as capturing new subscribers and selling add-on services. According to the Parks Associates survey, 18% of consumers are willing to switch to an operator offering femtocells and 36% of consumers in multicarrier households might switch carriers in order to consolidate with a single femtocell provider. Some carriers also offer add-on subscription services, including homezone tariffs (providing free cellphone use on the femtocell) and presence-based services, such as alerts to notify busy parents when their children arrive safely at home.
The ability to greatly improve in-building coverage is driving many operators to deploy femtocells beyond the home, in enterprises and public hotspots. And as femtocells move out of the home and into more public environments, a new business driver emerges – data offload. Today’s femtocell (and picocell) networks offer a cost-effective way for carriers to reduce the growing traffic burden on their macro networks.
Indoor users consume more than their fair share of the cell’s resources because the radio waves must pass through signal-absorbing walls to reach them. If these subscribers are served via femtocells instead, outdoor users also benefit from improved quality of service – in fact, the capacity of the macro network improves out of all proportion to the number of subscribers who have been removed from the cell. Considering that the majority of mobile data is consumed indoors, even a relatively sparse population of femtocells can make a difference.
Furthermore, femtocells help solve radio network performance issues caused by interference from a dense population of smartphones. A cellphone communicating with a nearby femtocell transmits at a much lower power than if it were signaling to a cell tower, thereby reducing the uplink interference it creates. Reducing interference in this way improves service quality and data speeds – not only for the femtocell user, but also for all other cellphone users in the area. According to Gordon Mansfield, AT&T’s Executive Director of RAN Delivery, “The more femtocells you deploy, the more uplink interference is reduced.”
Congestion issues on the macro network are compounded by smartphone applications, which cause a heavy signaling load on the radio network controllers that manage radio resources on the mobile network. The problem is that “always-on” applications are constantly making brief connections to the network to retrieve updates (e-mail, weather, stock quotes, etc). As a result, the RNCs become a bottleneck and slow down network performance for all users. With a femtocell, the RNC is incorporated within the unit itself, and the traffic is routed away from the bottleneck, reducing the load on the network RNCs and improving service for all cellphone users.
Residential femtocells have hit the market with a proposition that includes self-provisioning capabilities that offer something new and valuable and have, at times, been held up as an all-encompassing solution. However, the assumption that a femtocell’s self-organizing and managing functionality can easily be transferred to larger cell sizes, and that this is always a good thing, is questionable because the user and operator requirements for small cells change substantially from the home to the office to public access deployments. It is not simply a case of scaling up the consumer femto proposition to larger and larger cells. Rather, there is a more complex equation to be made based around cost, transmit power (range), capacity, access mode, handover configuration and management.
For example, open access femtocells (in actuality picocells) with a range of 100 meters or so in a public environment need a much higher capacity than a residential femtocell – typically up to 16 simultaneous calls. They must also support two-way handover with the neighboring macro cells, which necessarily involves some degree of cell planning by the carrier. Another difference from residential femtocells is the need to support real-time alarms for signaling faults to the network operations center. Fortunately, these differences can be readily accommodated without diminishing the cost-effectiveness of the femto/picocell approach.
Eventually, these “small cells” will inevitably become a key plank in all carriers’ network strategies. As subscribers’ expectations for high-speed data continue to grow, the need to reuse spectrum more efficiently in smaller and smaller cells becomes paramount. Ultimately there is no viable alternative to the femtocell.