Femto backers sort out interference

Femtocell supporters announced Tuesday a number of methods designed to reduce interference between the domestic bits of kit and the surrounding macro network.

The Femto Forum recently conducted research to assess the impact of femtocells on a mobile network in a wide range of deployment scenarios in order to explore co-existence issues including interference.

Femtocells are low power wireless access points that operate in licensed spectrum to connect standard mobile devices to a mobile operator’s network using residential DSL or cable broadband connections. Femtcells are more targeted at the domestic market than picocells, they are intended to be used in the home and will typically be connected to the consumer’s fixed internet connection.

Although femtocells using a separate carrier, or different swathe of spectrum to the surrounding macro network, were the most simple way of eliminating interference, many 3G operators do not have enough spectrum for this to be practical.

As a result, femto backers are looking at ways of mitigating the potential interference where femtocells share the same carrier as the macro network.

These proposals include, Adaptive Pilot Power Control, whereby the femtocell dynamically adjusts its transmit power in response to the current level of signals from surrounding cells; Extended Tests for Dynamic Range, to ensure that femtocells are able to operate in the presence of nearby high power mobile phones connected to the macro network; Uplink power capping of the mobile phone when operating in a femtocell to ensure that the phone hands-off to the macro network before its transmit power increases to the point where macro noise rise is a problem; and dynamic receiver gain management in the femtocell, to ensure that femtocells can offer good service to both near and far mobile phones without unnecessarily increasing the phone transmit power.

“At a time when mobile operators are seeing data usage rocket, femtocells offer an economic and effective way to deal with demand,” said Simon Saunders, chairman of the Femto Forum. “By utilizing the identified interference management techniques it has been shown that femtocells offer operators an effective method to increase capacity and coverage within their existing networks through dense cell deployments.”

Last week, Singaporean operator StarHub announced the limited availability of its own commercial 3G femtocell service. The operator has made 200 MaxOnline-enabled routers available on a first come first served basis.

Subscribers to the femto service will get all local outgoing voice, video calls and SMS included for a monthly subscription of S$30.