Introduction
Definition
Technological progress always brings new inventions to humanity, and femtocell is one of such innovative solutions. According to Shneyderman (2008), a femtocell is a solution “used to convert traffic to and from standard cellular handsets in close proximity (typically up to 100 meters) and carry it over IP” (p. 163). Accordingly, a femtocell is used predominantly for residential or small-scale business purposes.
Operating mode
Thus, a femtocell is a small-scale base station used in residential and enterprise buildings and characterized by radiated power it has in the operation of milliwatt range, simultaneous call capacity between four and ten units, backhaul carried out over broadband links of IP, and small range of approximately 100 meters (Shneyderman, 2008, p. 163). According to Chambers (2008, pp. 36 – 38), the femtocell can operate in both 2G and 3G modes in the regimes like Wi-Fi, CDMA, and GSM.
General benefits
Accordingly, the major benefits of using femtocells for ordinary end-users can be subdivided into three main categories referred to as usability, cost, and coverage in poor-coverage areas. The issue of usability is solved by femtocell as this base station allows handling both 2G and 3G calls in different areas with various coverage levels. At the same time, the use of femtocell can reduce cellular connection costs by specific pricing policies that femtocell providers offer. Finally, one of the main advantages of a femtocell is that it allows improving connection quality in poor coverage areas (Chambers, 2008, pp. 37 – 38; Shneyderman, 2008, p. 30).
Architectures
Home Node B
The architectures of a femtocell are numerous, and Home Node B is one of its basic elements. As Van de Velde (2007, pp. 48 – 49) argues, the Home Node B allows establishing and preserving the radio contact of the cell phone and the UE (User Entity) with the RAN (Radio Access Network), which is traditionally used with 3G femtocells. The Home Node B facilitates the greater mobility of femtocell users within the limits of the femtocell operating zone.
Cellular base station
The cellular base station is another element of femtocell architecture. According to scholars like Chambers (2008, p. 65) and Shneyderman (2008, p. 170) cellular base stations in this respect are divided into two subtypes. First, femtocell as such can be the cellular base station connected to the main station via broadband. Second, the femtocell can be used with the cellular base stations produced by different service providers, in which case the femtocell producers prefer to equip their devices with GPS navigators to track the mobility of the device and prevent users from using the femtocell in all locations possible.
Collapsed stack
Another notable architecture of femtocell is the so-called collapsed stack architecture. Its essence lies in the fact that femtocell of such an architecture operates through the integration of the work of UMA (Unlicensed Mobile Access), SIP (Session Initiation Protocol) bases, and VoIP networks (Van de Velde, 2007, p. 50; Seel, 2007, p. 161; Chambers, 2008, p. 87). Thus, the collapsed stack architecture provides better functionality to femtocell and increases its operating speed.
Collapsed stack with UMA backhaul
What is UMA?
Further on, femtocells can be based on the collapsed stack with the UMA backhaul. As stated above, UMA is defined as unlicensed mobile access (Seel, 2007, p. 31). The major idea behind the development of the UMA is the control over the unlicensed mobile traffic, which is carried out by the UMA Network Controller (UNC), which uses the IP network and controls the interchange of IP packets over the Wi-Fi networks (Seel, 2007, pp. 31 – 32; Shneyderman, 2008, p. 167).
Accordingly, the collapsed stack femtocell with UMA backhaul is similar to an ordinary collapsed stack device, to which the RNC (Radio Network Controller) function was added. The femtocell generates the calls while the UNC terminates their signals; RNC helps track the User Entity mobility around the Routing Area, also known as the set of cells, in which the user can freely operate his/her femtocell (Van de Velde, 2007, pp. 48 – 49).
SIP or IMS
The final issue regarding femtocell architecture is the choice between basing the device on either SIP (Session Initiation Protocol) or IMS (IP Multimedia Subsystem). Scholars like Van de Velde (2007) and Seel (2007) argue that SIP is a more advantageous femtocell solution among the two. This is explained by the better security that SIP provides, as well as increased mobility of femtocell users that adopt SIP solutions (Van de Velde, 2007, p. 41; Seel, 2007, p. 25).
Air Interfaces
The air interfaces range according to the time of their development and characteristics. Van de Velde (2007, p. 16) argues that femtocells can work with the OFDM or CDMA air interfaces, while Shneyderman (2008) considers the possibility of operating femtocells through the air interfaces like GAN or UMA/GAN (pp. 167 – 168). Finally, Chamber (2008, p. 85) considers IS95 A/B, CDMA2000 1X, and WCDMA as the most reliable and fitting air interfaces for femtocells.
Challenges & problems
Interference
However, even despite the scholarly discussed advantages of femtocells, there are considerable drawbacks, or at least issues that lack sufficient research, regarding the use of these devices in residential and enterprise areas. Interference, i. e. “receiving two signals with the same frequency from two transmitters” (Van de Velde, 2007, p. 64), is one of the main challenges faced by femtocell users. The point here is that femtocells installed at residential buildings are hardly ever put in conformance with basic cell units, and this provides the grounds for developing femtocells functioning at frequencies similar to the ones at which either their services providers or other private femtocells function. Accordingly, when such interferences occur, neither of the signals is perceived properly and the potential for eavesdropping grows (Shneyderman, 2008, p. 170).
Spectrum
Spectrum accuracy
Another important challenge in the development of femtocells is the controversy of spectrum use, its accuracy, the borderline between the licensed and unlicensed spectrum use, and the ways to control and regulate both. Thus, Seel (2007, pp. 170 – 171) defines spectrum as the environment in which various radio and mobile connection operators’ function. Accordingly, the spectrum accuracy can be viewed as the ability of every single operator and end-user to match the limits of the spectrum and use only the licensed one. Apart from legal issues provoked by the use of unlicensed spectrum, Shneyderman (2008, p. 168) argues that unlicensed spectrum use facilitates the development of interferences when the unlicensed users tune in to the same frequency as licensed ones do. Accordingly, licensed use of spectrum and its accuracy are vital challenges that femtocell producers are currently unable to handle.
Access control
Access control is another challenge faced by femtocell producers and end-users as, according to Van de Velde (2007, p. 62) and Seel (2007, p. 162), it is still practically not proven that a femtocell user can control the access of other people living in the Routing Area of his device to the content he transmits through the unit and to the services presented by the femtocell operator.
Security
The issue of security is one of the basics for femtocell producers and users. Chambers (2008), for instance, argues that the first security challenge faced by a femtocell user is the secure setup installation, which often requires reconfiguring each unit to which the femtocell is connected. Another point in this challenge is the lack of adequate security updates that one might face (Chambers, 2008, p. 33). Further on, Shneyderman (2008, p. 175) identifies the issues of authorization and authentication as two major security issues of femtocells. Finally, Seel (2007, p. 162) considers it necessary that femtocell producers should develop specific data encryption systems that would provide security for femtocell user content.
Equipment location
The location of the femtocell equipment is also one of the basic challenges. Governmental rules might require only licensed femtocells to be used only in registered areas, while taking a femtocell to another area would involve a fine or additional charge made by the operator. This challenge is made more complicated by the fact that not all femtocells can work in all areas, but all of them are equipped with GPS that allows tracing their movement and blocking them in case of necessity (Chambers, 2008, pp. 55 – 56).
Emergency calls and Quality of service
Emergency calls are also essential in determining the quality of femtocells. According to Chambers (2008), every femtocell must support emergency calls function and must be equipped with alternative power sources for this purpose (p. 93). The same can be said about the quality of service. On the whole, the ability of the user to receive services is the first marker of the latter’s quality. Improved coverage and increased bandwidth are ways that Shneyderman (2008, p. 31) and Van de Velde (2007, p. 35) see to cope with the emergency call and service quality challenges.
Handover
The problem of handover is also essential for femtocells. The first point of this problem is the impossibility of software handover. At the same time, “hard handover” is possible, as Chambers (2008, p. 35) argues, because femtocells can switch between the internal and external network operations, as well as between 2G and 3G if both connection types are supported by a similar operation mode like CDMA, UMTS, or others (Chambers, 2008, p. 35).
Controversy and Marketing
Thus, it is obvious that the use of femtocells is still surrounded by considerable controversy. Requiring almost no costs from their producers, femtocells impose expenses on their users in association with installment, maintenance, software updates, hardware handovers, and mobility concerns discussed above. Not surprisingly, this controversy is reflected in the marketing and deployment of femtocells, which are rather limited and regionally-based. However, the recent development in the femtocells market shows the increase of demand for them for about 40%, while Chambers (2008, pp. 65, 76, 105) considers at least a dozen femtocells manufacturers that acquire greater influence in the market, including ZTE, Airvana, Motorola, Connected Home, etc. These recent developments allow predicting the potentially bright future for femtocells technology in the telecommunications market.
Works Cited
Chambers, David. Femtocell Primer. Lulu.com, 2008. Print.
Seel, Nigel. Business strategies for the next-generation network. CRC Press, 2007. Print.
Shneyderman, Alex. Fixed mobile convergence: voice over Wi-Fi, IMS, UMA/GAN, femtocells, and other enablers. McGraw-Hill Professional, 2008. Print.
Van de Velde, Thierry. Value-Added Services for Next Generation Networks. CRC Press, 2007. Print.