Femto Firms Counter Interference Flak

BARCELONA -- Mobile World Congress -- Femtocells, the mini base stations designed to provide better mobile voice and data coverage in homes and offices, have been a hot topic of debate in Barcelona again this year, with some operational concerns being raised as major operators begin trials and vendors move closer to commercial deals and customer rollouts.

As news of various carrier trials were going the rounds in MWC’s eight halls, Qualcomm Inc. (Nasdaq: QCOM) CEO Paul Jacobs was issuing a warning, during a keynote address, about the potential impact on mobile networks of adding femtocells into the mix. (See Femtocells Go Big Time in Barcelona.)

”Femtocells are going to cause management and interference problems,” stated the Qualcomm man. “They may jam other access points or create jams or gaps in macro coverage. It’s a challenge for the technology world to make this work properly.”

So, was Jacobs scaremongering somewhat, or was he raising a serious point that needs addressing? As one delegate here told Light Reading on background, mobile operators are constantly addressing network planning challenges as their subscriber numbers grow and they add new cell sites to their networks, and having potentially tens of thousands more mini base stations could cause some operational nightmares.

"It’s not scaremongering -- it is an issue," concedes Keith Day, VP of marketing at Ubiquisys Ltd. , one of the most prominent femtocell startups and a Light Reading Top 10 Startup. (See Vodafone, O2 Test Femtocells, Netgear Gateway Goes Femto, and Yahoo Music Videos Facebook App.)

"But we’ve been looking at this for two years and done studies of dense femto environments to look at the interference issues. We think we’ve cracked it."

Day notes that UbiquiSys has been producing femtocells commercially for four months. "The femtocell scans for neighboring femtos and macro sites and gauges the strengths of the other signals, and creates a view of the RF [radio frequency] environment. Then it chooses the right frequency, scrambling code, and power on a continuous basis. So if, for example, there’s a re-plan of the macro network, the femtos will automatically adjust."

It's much the same story over at another of the femtocell world's leading specialists, ip.access Ltd. . (See Cisco Invests in ip.access, ip.access, Mavenir Team, Thomson, IP.access Team, and Sonus, IP.access Partner.)

There, marketing manager Chris Cox notes that the Femto Forum Ltd. has four working groups, and that Working Group 2 looks at the interference issues, among other things. (See Operators Flock to Femto Forum, Industry Forms Femto Forum, and IP.access Joins Femto Forum.)

"That group is headed up by our CTO, Nick Johnson," says Cox. "We are establishing best practice in this, and most on the vendor side believe this [interference issue] has been sorted out."

Cox notes that there are different types of interference. Femto-to-femto is the least troublesome, he says, as that sort of interference can be dealt with by reducing the power of the signal.

With femto-to-macro interference, you have the possibility of creating noise in the macro cells that cause "dead spots," where users connected to the macro wireless cell lose coverage. Macro-to-femto interference, meanwhile, raises the possibility of the femto’s coverage being swamped by the macro base station's signal.

"We have a ‘listen’ function in our platform, and the modeling we have done has given us a good understanding of the issues. Also, handsets are well designed to deal with noise issues, so that’s another way to help counter the problem."

But he's waiting on how things go with the carriers, as that'll be the real test. "We've done the modeling, and we have the solutions, but we really need trials to sort this out," says Cox, who adds that he still can't talk about the operators that ip.access is involved with in terms of femtocell trials.

— Ray Le Maistre, International News Editor, Light Reading