Monday 29 December 2008

Femtocell interference by macro network is now addressed

It is widely accepted that the deployment of femtocells will be a significant factor in driving the future uptake of mobile broadband services. There has been concern however over potential issues of interference between femtocells and the micro/macro networks. These concerns have been largely allayed by a femtocell radio study carried out by The Femto Forum.

If one understand the basic concept of femtocells that the concern for interference is obvious. The femtocells and macrocell network share the same carrier and hence the cause for interference. The simplest way to avoid interference is for the femtocell to utilise a different carrier than the surrounding macro network. But I think this will be like running away from the problem instead of solving it. Also this not very much feasible or practical solution either because majority of 3G operators do not have sufficient spectrum.

This issue was really serious and as expected whoever involved with the femtocell deployment specially the Femto Forum got involved into the research to answers the queries regarding the interference.

The Femto Forum study therefore focused on finding technological solutions for mitigating interference when both the femtocell and macrocell networks share the same carrier. 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 main objective of the study was to identify a number of solutions that will mitigate any potential interference of the macro network by the femtocells.

The first really good news is that the study found femtocells have the potential to deliver an order of magnitude of more capacity than the macro network alone when used in dense deployments, even when occupying the same radio channel as the macrocell.

Effectively what it’s been suggested is that any interference related barriers to wide scale femtocell deployment have been removed so operators will be able to maximise the capacity benefits offered by femtocells.

Following are the key solutions suggested for interference mitigation considering that femtocell and macro cell using the same carrier:
  • Adaptive Pilot Power Control: In this case the femtocell dynamicallyadjusts its transmit power in response to the current level of signals fromsurrounding cells and the desired coverage area.
  • Extended Tests for Dynamic Range: This will ensure that femtocell designsare able to operate reliably even in the presence of nearby high powermobile phones connected to the macro network (this test has already beenincorporated into the latest 3GPP Release 8, 25.104 specification).
  • Uplink power capping: This technique specify that the uplink power of the mobile phone is capped when operating in the femtocell environment thus ensuring that even in difficult radio conditions,the phone hands-off to the macro network before its transmit power increasesto the point where macro noise rise is a problem.
  • Dynamic receiver gain management: Automatic gain or adaptive attenuation in the femtocell will 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.

At a time when mobile operators are seeing data usage rocket, femtocells offer an economic and effective way to deal with demand. This therefore makes it very important for the femtocell technology to sort out any niggling issues.

There is no doubt that by utilizing the identified interference management techniques femtocells can offer operators an effective method to increase capacity and coverage within theirexisting networks through dense cell deployments.

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