The good news for service providers is that despite the fact that femtocells could potentially have a massive impact on the way services are provided and become as familiar as Wi-Fi routers-with which they will compete-the gadgets lend themselves to smooth integration. For one thing, the entire network need not be upgraded at once. It's possible for carriers to employ femtocells that target, for instance, bandwidth hogs using a disproportionate amount of network capacity. It also is possible to run pre-standard femtocells-the type available in today's quiet offerings-alongside the standards-based devices to come, says Femto Forum Chairman Simon Saunders.
"The entry level for carriers really is quite small and evolutionary," Saunders says. You do not need to deploy across your entire base. You can select. You can target a particular customer segment and use the kind of laser precision that will benefit [the target subscribers] and the operator itself."
Two Interference Threats
The key technical concerns focus on two types of interference. One is between femtocells themselves and the other is between the femtocell and the macro base stations. The most elegant solution is to put the macro base stations and the femtocells on different frequencies. This is an expensive approach, however, since it entails real estate in two different licensed frequency bands. EJL Wireless Research principal Earl Lum says that a big issue in such scenarios is the transfer of sessions-calls or data transfers-between frequencies.
"The data points to the fact that you can't at this point have a plug-and-play scenario if you plan to use the same frequency channels," he says. "If you are on the same channel with the macro and femto, you will experience interference. The question is how much one degrades versus the other."
Engineers plotting the relationship between different pieces of gear vying for a slice of the same bandwidth like to eliminate as many variables as possible. Unfortunately, there is a relatively high level of uncertainty and more than one variable in the femto-verse. Unlike the constellation of macro base stations, which essentially are fixed, femtocells are a consumer product. Thus, the number of devices queuing up for a sliver of the bandwidth pie constantly is shifting. In short, interference parameters change as femtocells are added and removed and as their utilization by subscribers waxes and wanes.
Keith Day, the vice president of marketing for Ubiquisys, says there are three ways to approach this issue. One is to scan the environment at deployment and to leave enough of a buffer to accommodate likely changes. The second is to program the femtocells to periodically scan the environment and report interference problems to the service provider. The third option, which Day says is only available from Ubiquisys, is to continually monitor the network with what it calls a "cognitive radio" system that identifies and solves problems as they materialize.
There will not just be one deployment of femtocells. Baines says that the new technology likely will emerge in three waves: The first-the one that is likely to get going in earnest next year-will focus on voice. The second will combine voice and data, and the third will feature applications developed to take advantage of the networking opportunities presented by the presence of an addressable widget in the premises. The Femto Forum's Saunders says that an applications working group aimed at exploiting femtocells' networking capabilities has been created.
The work to date on femtocells has been in the 2.5G and 3G realm. The coming of 4G-Long Term Evolution and WiMax-will make the need for femtocells even greater for two reasons. For one thing, 4G runs at even higher frequencies than 3G. The other is that the growth of data traffic will continue unabated and the ability to offload data to a parallel DSL- or modem-based network will be vital.
Femtocell-based services are likely to become big news in the consumer sector next year. Like all overnight sensations, the reality is that the success or failure of the projects will be based upon how well the groundwork was done beforehand. The good news-for carriers and their subscribers-is that experts are unanimous in their opinion that the telecommunications industry is preparing the transition very carefully.