As mobile data traffic continues to increase, with more generated by home users, operators are under pressure to adopt either UMA (Unlicensed Mobile Access) or femtocells, both of which have a lot going for them, according to their respective proponents.

Mobile traffic generated from homes was estimated at 40 percent of the total of such traffic in 2007, and by 2013 it is expected to reach 58 percent, according to Informa Telecoms & Media.

At the same time, data traffic from users is increasing fast, forcing operators to upgrade their backhaul networks at great expense. Those networks connect base stations to the rest of the network and the Internet. "Operators will be under increasing pressure to adopt some kind of mobile access at home -- if traffic continues to triple over the next year or two they will have to react to that," said Malik Kamal-Saadi, principal analyst at Informa.

To offload their networks and lower both capital and operating expenditures while at the same time improving coverage at home, operators worldwide are looking at or already offering mobile access to homes, according to Kamal-Saadi.

The main alternatives for homes are UMA using dual-mode phones, which use Wi-Fi, and femtocells, which are small cellular base stations that exclusively use mobile network technology but send traffic via the femtocell and a fixed broadband connection.

The most immediate difference between the technologies is that femtocells don't need a specific phone, while UMA requires a special application on the phone, which has limited the number of phones customers can choose between. Users get more flexibility when choosing a device with femtocells; they are not locked into UMA phones, according to Kamal-Saadi.

It's also an alluring promise to operators. "That difference makes femtocells an interesting alternative," said Claes Nycander, acting CTO and senior vice president for Mobility Services at TeliaSonera, which is currently offering a UMA service based on GSM (Global System for Mobile Communications), but is also evaluating femtocells.

"It's a question of what comes first. If we get more UMA phones very fast, or if femto matures next year. That is something we have to consider," Nycander said.

But not everyone sees the number of phones as a big problem. Phone support for UMA is about to increase, according to Georges Penalver, executive vice president of group strategic marketing at Orange.

"The market is moving fast, what is important to know is that the main chipset manufacturers, like Qualcomm, have already integrated or decided to integrate the UMA stack in their chipsets. This is a very important sign, and the handset manufacturers are following. Every quarter we have another handset manufacturer joining the UMA club," said Penalver.

Orange recently announced it will launch a 3G (third-generation) version of its UMA-based Unik service. The service will initially be available in France this month (with only one phone, according to a spokesman), followed by Poland, the U.K. and Spain.

A second sticking point is the frequencies over which the two technologies send data and voice. UMA use Wi-Fi frequencies and femtocells use mobile network bands, which, depending on whom you ask, is either good or bad.

Using the same frequency as the mobile networks is a boon for femtocells when it comes to the number of devices, but it also poses challenges for operators.

Managing the spectrum for femtocells in dense areas is a huge challenge, according to Orange, which says it has done some experimentation. "You must dedicate a frequency to the femtocells. In 2G it's easy, because you have a large number of carriers. But in 3G you don't have that; you have three or four in a best case scenario. If you dedicate one for femtocells, it's a huge part of what we have paid for our spectrum," Penalver said.

That makes femtocells unsuitable for use in dense areas, but it could technically work in scarcely populated areas, according to Penalver.

TeliaSonera is more upbeat, contending that issues with frequency interference when using femtocells can be solved.

At the same time, proponents of femtocells contend that using mobile network spectrum is a better alternative. "Wi-Fi works in unlicensed spectrum, where anybody can deploy anything, so you are contending with a lot of things. Working in that spectrum is increasingly not scalable, the more success you have, the more problems you have with interference," said Simon Saunders, chairman of the Femto Forum.

With licensed spectrum, which femtocells use, that isn't the case. "Each and every femtocell is under the full control of the operator. No interference is actually possible without the operator being in full control of managing that," Saunders said.

The IDG News Service is a Network World affiliate.