Femtocells may be stymied by handsets that can't make best use of them, even though an industry agreement has been signed which should make the indoor base stations a fundamental part of future wireless networks including WiMax and LTE.

Femtocells are low-power cellular base stations placed indoors or built into a home gateway to improve indoor coverage using the customer's broadband to connect over the Internet to the phone network. Both sides of the femto story emerged at the Femtocells Europe 2008 event in London this week.

The devices could do useful jobs such as handling large media files on phones, but these applications won't work well unless the phone has a reliable way of knowing whether it is on the femto or the "macro" network, said Dean Bubley of Disruptive Analysis. Unfortunately, vendors' efforts to make femtocells work seamlessly with all existing phones has resulted in a definition which makes the femto look exactly like a macrocell, to the handset.

"If femtos change user behavior you will need to change the handsets," said Bubley of Disruptive Analysis, who warns in a report that femto-aware handsets will be required.

Femto-aware handsets will be important after 2010, said Vedat Eyuboglu, chief technology officer at femto maker Airvana, which supplies silicon modules to Thomson, a maker of home gateways including BT's Home Hub.

However, Bubley warned that the actual phones might get forgotten, or take too long to develop: "The debate around femto-aware phones may get mired in discussions about interference management and 3GPP R8 tweaks to the interfaces involved," he said. "It takes two years to alter protocol stacks and hardware - we won't have femto-optimized phones until at least the end of 2010."

The handset issue could be addressed by industry body the Femto Forum, said Forum chair Simon Saunders, announcing the Forum's new relationship with the Next Generation Mobile Network Alliance (NGMNA), a body helping specify requirements for WiMax and LTE systems.

"As well as phones, femtocells will be used by devices including dongles and ultra-mobile PCs," said Saunders. "They do not have such long development cycles as mobile phones."

The NGMNA is developing recommendations for a cost-optimized indoor node, and for self-organizing networks, both of which can be met by femtocell designs that the Femto Forum will help develop. The two bodies will promote joint solutions and submit them to standards bodies.