Study concludes that interference is not a barrier to femtocell deployment
Manufacturers find ways to mitigate potential femtocell interference.
The research has also found workarounds for potential interference issues between femtocells and macrocells.
The study looked at femtocells using a separate carrier to the surrounding macro network, and those using the same carrier, which greatest interference threat bur also offer the greatest opportunity for increased spectrum efficiency. Although femtocells using a separate carrier provide a simple way to reduce interference, many 3G operators do not have the spare spectrum to make this possible.
Possible solutions to interference issues include adaptive power control, in which the femtocell dynamically adjusts its transmit power to the current level of signals from surrounding cells and the desired coverage area, and better testing of femtocells' dynamic range, to ensure they can work reliably even in the presence of a high-power mobile phone connection to the macro network. The Forum study also identified capping the power of mobile phones' transmit circuits when near femtocells, and automatic gain control on femtocell receiver circuits.
These techniques are already being developed for pre-standard femtocell solutions, and Femto Forum members are working to make them part of the standards framework.
“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, chairman of the Femto Forum. "By using interference management techniques, femtocells offer operators an effective method to increase capacity and coverage within their existing networks through dense cell deployments."
The research builds upon work done within 3GPP by putting femtocells through a more extreme series of interference tests. The full results can be found in a white paper available on the Femto Forum web site (www.femtoforum.org).