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Femtocells are low power wireless access points or base stations that operate in cellular bands to connect mobile devices to operator's network through residential DSL, Cable broadband connection or Fiber. They are so small and inexpensive that they can be placed in individual homes and use DSL as a backhaul to operator's network. They offer excellent coverage inside home and office for both voice and data. The most apparent reason for deployment of femtocells is the excellent coverage and capacity and there are number of ways it helps operator and users to deploy this small base station inside home and enterprise environment. according to studies 70% of the mobile and internet usage is inside homes so when we talk to about WiMax the frequency bands in which it operates is 2.5Ghz and more so when WiMax singal penetrates through walls to serve indoor it gets attenuated and a significant amount of power in dB is lost which eventually affects the services and user experience in indoor environment.
Femtocell is expected to provide a high quality, high speed signal & better indoor coverage in residential or small business premises, it will more likely provide quality of voice calls, fast downloading and video applications as compared to wifi. Unlike wifi, femtocells are low power wireless access points that operate in licensed spectrum to connect standard devices to a service provider's network using residential DSL or cable broadband connections. Apart from improving indoor coverage femtocell also enhances system capacity.
Femtocells are expected to play an important role in terms of cost-effective delivery of new services, such as multimedia, gaming, social networking, and other demanding applications with the high quality of service (QoS) level expected by users in an indoor environment.
2.2 How does femtocell work?
As already described femtocells are small base stations, so a femtocell appears to the standard 3G phone as an other macro cell site from the cellular operator.
The mobile operator's MSC and data switch (SGSN) also operates and communicates to the femtocell in the same way as for the other mobile calls. Therefore the rest of the services like phone numbers, call diversion, voice mail etc also operate in the same and appear the same to the customer.
Secure IP encryption is used between femtocell controller and femtocell connection which helps to avoid interception and there is also authentication of femtocell itself to ensure it is a valid access point.
Femtocell includes complete working of a base station inside in it. Some of the additional functionalities are also included for instance RNC (Radio Network Controller) processing which would normally be put at the mobile switching center. In order to manage data session locally some femtocells also include core network elements so that there would be no need to flow back to the operator's switching centers.
Femtocell Architecture Overview
Inside the femtocell there is a single chip like PC302 from picoChip or the PRC6500 from Percello on which main functions are integrated. Femtocells are subject to some unique extra capabilities that they should be self-installing and self-configuring and to achieve these capabilities some extra software programs are required which scan the environment to sense the available frequencies, power level and scrambling codes to be used and this is a continuous process to adapt to changing radio conditions.
2.3 WiMax femtocell:
WiMax technology is based on IEEE 802..16 standard and provides strong mobility to support high speed broadband services. In addition it's also a source to deliver a wireless solution for last mile broadband connectivity.
With the diffusion of WiMax networks the operators realize that like all other high frequency spectrum networks, WiMax networks also suffer from poor indoor coverage inside homes and office environments. Femtocells or home base station are the important in solving the indoor coverage issues. WiMax femtocells help in providing excellent coverage and reduce macro network deployment costs.
Fig: Depicting typical femtocell network
As WiMax suffers from poor indoor coverage, this results in slow speed data downloading and eventually affects the quality and and provides poor user experience. This also affects the adoption of data services that WiMax is supposed to boost. Poor quality of service, long time waits to downloading videos and other user applications will eventually be affected which in turn will have a direct impact on operator's revenues.
Hence, there is a serious requirement for a solution that can significantly improve indoor coverage without increasing the costs of operator's expenditures of macrocell site deployments, a solution that can help to support and operate as an extension to an operator's existing network and use the same frequency spectrum as used by operator's rest of the network. WiMax femtocells are the cost effective solution to improve coverage inside building.
2.4 Femtocell standard:
WiMax forum and femto forum have jointly announced the WiMax femtocell standards which will allow vendors to take step into the development of standardized femtocells and its associated network equipments based on the IEEE 802.16e radio interface and profiles, and it is expected that WiMax forum will start to certify compatible products in early 2011. A security framework has been incorporated that allows WiMax networks to support a large number of access points via standard commercial IPSec based security gateways. The standardized phase of specifications also contains simple Self Organizing Network (SON ) capabilities in order to allow automatic configuration of large number of femtocells. The coming future versions will further improve the existing SON capabilities to standardize automatic interference management between femtocells and macro base stations.
The standard also incorporates support for three usage models to support different deployment scenarios such as residential, enterprise and outdoor environments. The 'Open Model' allows the femtocell to operate like a normal WiMAX base station by allowing anyone to use the service; 'Closed Subscriber Group (CSG) Closed' allows a limited number of pre-allocated subscribers to use the femtocell. The 'Closed Subscriber Group (CSG) Open' extends the previous model to allow the subscriber to add users themselves.
The standard will impact all elements of the WiMAX femtocell network including: the MS (Mobile Station), WFAP (WiMAX Femtocell Access Point), Security Gateway, Femto Gateway, SON Server, AAA Server, WFAP Management Server and other Core Service Network (CSN) functions.
2.5 Femtocell and Health:
Consumer health is always a top concern for the mobile industry. Femtocells emit very low levels of radio waves (also known as radiofrequency (RF) electromagnetic fields) when being used. The safety of radio waves has been extensively studied for more than 50 years. Numerous independent scientific expert panels, health agencies and standard-setting organizations around the world regularly review this large growing body of research.
These organizations have agreed upon a general provision that there are no specific health concerns from the radio frequency waves below the limit applicable to wireless communication systems.
Femtocells must comply to the safety limits that are equally applicable to all the other wireless systems and devices like cell phones etc. These safety standards and limits have been setup by International Commission on Non-Ionizing Radiation Protection (ICNIRP), so femtocells are designed and tested to ensure that they comply to both internationally established safety limits, and to the regulations practiced by governments around the world.