A large deployment of femtocells is expected in 2012 as ilustrated below (Data from www.wirelessweek.com showing Global femto base station infrastructure equipment market forecast), but why is this small thing important? The Femtocell is very important for the following reasons:
v It can provide indoor coverage for places where macrocells cannot.
v It can offload traffic from the macrocell layer and improve macrocell capacity (in the case of using macrocells to provide indoor coverage, more power from the base station will be needed to compensate for high penetration loss, resulting in a decrease inmacrocell capacity).
v Assume that good isolation (hence, the signal leakage from indoor to outdoor will be small) can be achieved, the addition of a femtocell layer will significantly improve the total network capacity by reusing radio spectrum indoors.
v There is a growing demand for higher and higher data rates. Due to the high penetration loss, high data rate services can not be provided to indoors apart from those areas near windows that are facing a macrocell site. This is because high data rate requires high performance RF links. High data rate services such as those facilitated by HSDPA are the key drive of femtocells.
v Femtocells can provide significant power saving to UEs. The path loss to indoor FAP is much smaller than that to the outdoor macrocell base station, and so is the required transmitting power from UE to the FAP. Battery life is one of the biggest bottlenecks for providing high speed data services to mobile terminals.
v As FAPs only need to be switched on when the users are at home (for home femtocells) or at work (for enterprise femtocells), the use of femtocell is ‘greener’ than macrocells. The power consumption of base stations accounts for a considerable amount of an operator’s OPEX. In the UK, the power to run base stations is over 3 watts per subscriber. In some developing countries, the power consumption accounts for some two thirds of the OPEX. A base station consumes far more power than that is used for transmitting and receiving signals. This is caused by a number of factors: first, the efficiency of the amplifiers is very low (typically 10–15%) as they work at the linear rather than the saturation region as the sophisticated modulation techniques used in 3G and beyond systems require linear amplification; second, a base station requires an air-conditioning system in order to keep running at atmospheric temperature; third, a backup system is also needed to account for loss of power supply. The base station power consumption problem leads to a high demand on the so-called ‘green communications systems’ or ‘green radio’.
v Femtocell provides an ideal solution for FMC (Fixed Mobile Convergence).
v Femtocell plays an important role in mobile broadband and ubiquitous communications.
v Femtocell represents a major paradigm shift. Users will pay to install femtocells. Hence, the first phase of the rollout of high data rate networks such as LTE can start from indoor where high data rates are needed most. As future terminals will support GSM, WCDMA (or other 3G technologies) and LTE, the rollouts of LTE can be very different from the rollouts of GSM and UMTS. This is really an important paradigm shift as far as future mobile communications network rollouts are concerned.
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