The femtocell industry is young, but has already taken significant steps towards maturity. The continued growth of mobile services, especially for mobile broadband data, creates greater expectation for services, volume, quality and coverage for users and new challenges for operators. Femtocells represent a distinctive new class of device which can deliver economic and service benefits for operators and users alike. They are easy to install and use for the end-customer, while being fully managed by the operator and make full use of the operator’s existing spectrum and network assets.
Femtocells are expected to play a special role in next-generation mobile networks (NGMN), including LTE, WiMAX and any mobile network technology which qualifies under the ITU-R’s definition of IMT-Advanced services. The standards for NGMN are all expected to include femtocell features. The standards for NGMN are all expected to include femtocell features. Operators deploying NGMN will be able to incorporate femtocells into their NGMN strategy with a degree of integration fashion which has not been possible in 3G networks, where femtocells emerged well after initial deployments. User devices will incorporate features which specifically optimise their performance with femtocells and will deliver service capabilities that are specifically created with femtocells in mind.
femtocells fulfil the NGMN recommendations for self-organising networks (SON) regarding self-planning; self-configuration; self-optimisation and self-tuning; self-testing and self-healing. femtocells can be seen as the first commercial instance of a true SON, helping to build confidence and establish specific technical approaches which will be useful for the wider application of SON.
Femtocells are well suited to maximise the benefit associated with common next-generation air-interface features, such as high-order modulation schemes and multiple-input multiple-output (MIMO) antenna schemes, based on spatial processing. The high geometry factors associated with indoor cells enable the highest order modulation schemes to operate over almost the whole service area, ensuring that the peak data rate available is also representative of the typical user experience, in contrast to the macrocell environment, where only users close to the macrocell with excellent service quality gain such benefit. The rich three-dimensionalmultipath environment also provides a radio channel which maximises the ‘diversity order’ or ‘rank’ of the channel, enablingMIMO to maximise the data throughput and channel resilience. This advantageous propagation channel also permits the femtocell to incorporate the necessary multiple-element antenna structures for MIMO within very small volumes.
The interference management capabilities of femtocells could also allow spectrum to be used in new ways. For example, next-generation mobile networks will typically support both frequency-division (FDD) and time-division (TDD) modes. Given that user devices will often support both, operators can reuse spectrum which is usually intended for FDD use via femtocells and open up TDD bands which have been less widely used in third-generation systems. They might also be able to use portions of spectrum which were originally intended as guard bands, without creating harmful interference. Femtocells also enable next-generation mobile networks to benefit from several new deployment approaches, illustrated as follows;
1. Femto-centric NGMN deployment: femtocells can act as the first deployment of NGMN technology. Such deployments will complement rather than replace third-generation networks. Instead of upgrading thousands of macrocells with next-generation before launching a service, the operator can deliver initial NGMN services at an earlier stage and in the home and offices of those with the greatest needs and motivations for NGMN. Beyond these homes and offices multi-mode devices will fall back to third-generation networks, delivering a seamless IP-based user experience.
2. Quick-start packages: deployment of next-generation services has usually been slowed by the need to get enough user devices capable of next-generation operation into the population of users to make service launch viable. Operators can instead offer early adopters of nextgeneration technology a package comprising a next-generation femtocell and compatible devices. Such users will benefit from an enhanced user experience, help to road-test and optimise the delivery of new services and can also act as evangelists for the technology to other users, helping to build the user base and the operator business case for more extensive next-generation roll-out.
3. Match costs to revenues: femtocells can deliver next-generation services to the relevant users and locations with surgical precision. Operators avoid a ‘build-it and they will come’ approach, where the costs of network upgrade are incurred and user demand fails to emerge as soon and as extensively as envisaged. They can both accelerate and retard roll-out in response to changes in demand with very little delay, in contrast to response times of order 1–3 years with macrocells. Thus costs can be matched very closely to variations in the associated revenues, reducing the financial risks and increasing the overall value associated with next-generation roll-outs. This reduction in risk helps the case for the wider roll-out, even beyond the femtocell element of service
Finally, the high bit rates available on femtocells in the home and office, combined with the offload capabilities of direct IP access, enable femtocells to be used for local area networking in ways which would not previously have been contemplated. This would allow, for example, the distribution of high-definition video content around home devices, enabling the home or office networking, which has so far been delivered using Wi-Fi, to be combined with the benefits of resilience and QoS associated with licensed spectrum.
