The principal performance benefit femtocells bring to LTE is to ensure more users receive peak data rates more of the time, especially inside buildings where the most 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.
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.
There is also growing evidence that femtocells are essential 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.
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.
Maximising spectrum efficiency
Femtocells also allow operators to make the best use of their LTE spectrum. An important quantity of new spectrum will be made available for LTE in the high frequency bands that do not penetrate buildings effectively but are ideal for femtocells.
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.
Business case
Femtocells also allow operators to create a more compelling mobile broadband business case. Femtocells can lower considerably the delivery cost per bit through significant savings in cell site installation, maintenance and backhaul costs.
LTE can revolutionise mobile broadband – and femtocells can play a role in helping it to deliver its potential. By adopting femtocells operators can roll out a much better performing 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.”
New services
Femtocells are also designed to power the kinds of next generation services that are expected to epitomise LTE. 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.
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. Additionally 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.
New roll-out strategies
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. Although traditional macro base stations will still be essential to provide widespread surface coverage, 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.
