News

Femtocells "essential for ultimate mobile broadband" - Saunders

"LTE can revolutionise mobile broadband – and femtocells can play a role in helping it to deliver its potential” said Simon Saunders, Chairman of the Femto Forum, speaking at the LTE World Summit conference in Munich this week.

His statement comes at a time when mobile operators are (finally) facing up to the limitations of 3G broadband HSPA technology, which has been very popular.

But the number of users that can be supported simultaneously is not what original predictions led operators to believe. They have a choice of supporting fewer users, or reducing speeds, or both - with the dismal drawback of making the cost per bit transmitted disappointing.

User expectations in price or performance can be met, Saunders thinks, by moving to LTE (much higher bandwidth) and putting the LTE cells inside buildings, Saunders told his audience:

“By adopting femtocells, operators can roll out a much better performing Long Term Evolution (LTE) network than they could with macro base stations alone and at a lower cost and with less risk. All these factors are crucial in the current uncertain economic environment,"

Femtocells could provide the best possible LTE user experience, support new services, offer alternative rollout models and provide a critical improvement to the mobile broadband business case, he said.

The principal performance benefit femtocells bring to LTE is that they will ensure more users receive peak data rates more of the time, especially inside buildings where the vast majority of mobile broadband data is consumed and where the service quality is lower than outside.

Femtocells achieve this by maximising spectrum re-use and by ensuring power, and therefore network capacity, is not wasted by trying to penetrate buildings.

The Forum issued a summary statement today, pointing out that although most discussion to date of femtocells has focused on residential use, "the technology is also applicable to enterprises, public spaces or ‘metrozones’ and hot-spots. In this way, femtocells are an important complement to the more traditional macrocell deployment."

The Forum says there is also growing evidence that femtocells "are essential in order to deliver further improvements in mobile network design, and in the case of LTE, to ensure more subscribers receive peak data rates."

LTE is approaching the theoretical maximum information transfer rate (Shannon’s limit) and further improvements will only be possible by rolling out more, smaller cells, the Forum argues. "In fact, an analysis of Cooper’s law - which holds that wireless capacity doubles every 30 months – shows that the dominant factor in improvements to date has been the use of smaller cells as opposed to other methods such as revised modulation techniques, better coding or the use of more frequencies."

The problem of penetration into buildings can be partly addressed by re-using lower-frequency wireless. But this may not be cost effective in the market.

There are many plans to use sub 1GHz bands for LTE - but the Forum doesn't believe this will solve the overall problem. "Where LTE networks are deployed solely in the scarcer and more valuable sub-1Ghz bands, where in-building penetration is better, femtocells will still be required to provide the extra network capacity needed to deliver on the promise of high data rates for all subscribers,"  said the announcement today.

Where the Forum members believe the opportunity lies, in the imminent release of what it calls "an important quantity of new spectrum" which will be made available for LTE in the high frequency bands. These "do not penetrate buildings effectively but are ideal for femtocells," the Forum said.

And of course the crucial factor in LTE profitability is cutting the delivery cost per bit "through significant savings in cell site installation, maintenance and backhaul costs."

Media streaming is expected to drive the femtocell market. Next generation services enabled by LTE, will include some that are entirely internal to the subscriber's premises. Having a high-speed LTE femtocell could mean that some subscribers will stop using WiFi for internal networking in the home.

"LTE femtocells will provide the best possible environment for downloading and streaming media from the internet or between devices in the home without loading the mobile network at all," said the Forum today. "In the case of sharing media in the home, femtocells will not even require broadband backhaul and will therefore not be limited by throughput restrictions on the network - thereby capitalising on the full peak rates of LTE."

More controversially, there's the potential "presence" application. "Femtocells ‘know’ when a consumer is in the home thereby enabling presence-based applications that automatically trigger when a consumer enters, or leaves, the home," the Forum pointed out.

Finally, the report observes, "Operators can also use femtocells to lower the cost, and therefore the risk, of LTE rollout by adopting a different strategy to that employed in 2G and 3G networks."

It concedes: "Traditional macro base stations will still be essential to provide widespread surface coverage," but counters this with: "Operators can use both indoor and outdoor femtocells from the outset to carry substantial amounts of data traffic thereby realising major savings on backhaul and other associated capacity costs. Combining femtocells and macrocells in this way allows operators to build their LTE networks incrementally in line with demand and avoid the need to second guess user uptake."

The Femto Forum is preparing a detailed whitepaper on the case for LTE femtocells which will be released in the near future