The Femto Forum, the independent industry and operator association that supports femtocell deployment worldwide, has announced the results of its femtocell radio study. The study found that femtocells have the potential to deliver an order of magnitude more capacity than the macro network alone when used in dense deployments, even when occupying the same radio channel as the macrocells. It also identified numerous technological solutions that mitigate potential interference with the macro network to remove barriers to wide-scale deployment and maximize the capacity benefits.
The research assessed the impact of femtocells on a mobile network in a wide
range of deployment scenarios in order to explore co-existence issues
including interference.
The study looked at both femtocells using a separate carrier to the
surrounding macro network and those using the same carrier – which pose the
greatest interference challenge, but also the greatest opportunity for
increased spectrum efficiency.
Although femtocells using a separate carrier were demonstrated to provide a
simple means to essentially eliminate interference, many 3G operators do not
have enough spectrum for this to be practical. The Femto Forum therefore
identified technological solutions that mitigate the potential interference
where femtocells share the same carrier as the macro network. These methods
are already being developed for pre-standard femtocell solutions, and Femto
Forum members are working to bring them within the standards framework.
The key solutions are:
. Adaptive Pilot Power Control, whereby the femtocell dynamically
adjusts its transmit power in response to the current level of signals from
surrounding cells and the desired coverage area.
. Extended Tests for Dynamic Range, to ensure that femtocell designs
are able to operate reliably even in the presence of nearby high power
mobile phones connected to the macro network (this test has already been
incorporated into the latest 3GPP Release 8 25.104 specification).
. Uplink power capping of the mobile phone when operating in the
femtocell environment, ensuring that, even in difficult radio conditions,
the phone hands-off to the macro network before its transmit power increases
to the point where macro noise rise is a problem.
. Dynamic receiver gain management in the femtocell (Automatic Gain
Control or adaptive attenuation), to ensure that femtocells can offer good
service to both near and far mobile phones without unnecessarily increasing
the phone transmit power, therefore keeping the noise rise to a minimum.
This particular study relates to WCDMA, but the Femto Forum represents the
full range of radio standards and similar studies are underway for other air
interfaces.
"At a time when mobile operators are seeing data usage rocket, femtocells
offer an economic and effective way to deal with demand," said Professor
Simon Saunders, the Femto Forum's Chairman. "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."