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A look back and forth – 2008 and 2009 in a nutshell

2008 was a year of overcoming barriers.  Within the Femto Forum there was a definite sense of awe at the scale of the challenge back in January 2008. The femtocell industry was fragmented with numerous different approaches to network integration and device management. None of the standards bodies had fully committed femtocell projects. Various naysayers were adamant that the whole femtocell proposition was flawed due to difficulties surrounding interference. Yet as the year closed, 3GPP was in the process of completing its femtocell standard, with lots of activity in 3GPP2 and the WiMAX Forum too. The industry reached consensus around the use of the Broadband Forum’s TR-069 protocol for femtocell management. The Femto Forum announced that, following an exhaustive study of interference management issues we have a series of techniques that successfully mitigate interference and deliver improved performance in the process. The Forum also undertook to prepare the wider industry for femtocells by speaking to regulators and industry bodies – we ended up with alliances with the 3GPP, 3GPP2, Broadband Forum, GSMA and NGMN Alliance and considerable recognition of femtocells by international regulators.

2009 will be about enabling scale.  This year we’re going to see more operators moving out of trials into commercial deployments. If mass deployment is really to take place in 2010 then there is plenty of work to be done. As standards activity matures, the Forum will be working to ensure that femtocells and gateways from different vendors are fully interoperable. We'll also be supporting the 3GPP’s Release 9 specification with its ongoing evolution of the WCDMA and LTE femtocell standards. In preparation for mounting femtocell deployments the Forum commissioned research into the operator business case and we’ll be communicating what we learned shortly. Last year it became clear that operators were interested in extending femtocells beyond the home and into the enterprise so the Forum will also be working to facilitate this evolution. Finally, there will be a focus on developing ‘Connected Home ’ and ‘femtozone’ services’, creating new mobile applications that make the most of the femtocell’s unification of the broadband internet, the home network and the mobile phone.

Part of the excitement fuelling the industry is that far-reaching possibilities can emanate from the basic femtocell concept. It is no longer just improving indoor coverage. Yet we must keep in mind that new technologies adhere to curious evolutionary laws – the best ones don’t always come out on top, they don’t always reach their potential. Right now femtocells are well placed to succeed – even the dire economic climate might be more opportunity that threat.  But it is incumbent upon all of us to keep up the momentum and to continue to collaborate to meet the forthcoming challenges.

Taking the fear out of interference

In December the Forum completed its long awaited interference study and concluded that although the challenge is great there are a series of techniques that successfully mitigate the issue. On the flip side, the study also found that dense deployments of femtocells can increase overall network capacity by an order of magnitude.

“At a time when mobile operators are seeing data usage rocket, femtocells offer an economic and effective way to deal with demand. 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."
Professor Simon Saunders, Femto Forum Chairman

whitepaperIt has escaped nobody’s attention that one of the greatest challenges facing femtocells is to prevent interference with both the macro network and other femtos.  With the relatively small number of macro base stations in any operator network requiring intensive radio planning, the prospect of subscribers self deploying thousands, potentially millions, of femtocells with no prior planning would until recently have sounded like pure science fiction.

The study 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. It looked at both femtocells using a separate carrier to the surrounding macro network and those using the same carrier – which poses the greatest interference challenge, but also the greatest opportunity for increased spectrum efficiency. This study relates to WCDMA but similar studies are underway in the Forum for other air interfaces.

Although femtocells using a separate carrier and appropriate RF parameters were demonstrated to provide a simple means to essentially eliminate interference, clearly this is impractical for many 3G operators who don’t have enough spectrum for a dedicated femtocell carrier. The study therefore looked for technological solutions that mitigate the potential interference where femtocells share the same carrier as the macro network. The key solutions were found to be:

  • 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.
But with the interference mitigated, the study found that dense femtocell deployments have an enormous effect on network capacity.  In fact the study found network capacity increased by at least 10 times. This supports the assertion by Paul Jacobs, Qualcomm’s CEO, that the gains in throughput available to femtocell users are “equivalent to that brought by the cell phone's shift from analog to digital.” The full results can be found in a white paper available on the Femto Forum web site HERE.

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