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Dense deployment of femtocells will offload large amounts of tra Content type: Research. Published on: 7 January
The Journal of Applied Research and Technology JART is a bimonthly open access journal that publishes papers on innovative applications, development of new technologies and efficient solutions in engineering, computing and scientific research.
JART publishes manuscripts describing original research, with significant results based on experimental, theoretical and numerical work. The journal does not charge for submission, processing, publication of manuscripts or for color reproduction of photographs. JART classifies research into the following main fields: Material Science Biomaterials, carbon, ceramics, composite, metals, polymers, thin films, functional materials and semiconductors.
Computer Science Computer graphics and visualization, programming, human-computer interaction, neural networks, image processing and software engineering. Industrial Engineering Operations research, systems engineering, management science, complex systems and cybernetics applications and information technologies Electronic Engineering Solid-state physics, radio engineering, telecommunications, control systems, signal processing, power electronics, electronic devices and circuits and automation.
Instrumentation engineering and science Measurement devices pressure, temperature, flow, voltage, frequency etc. Femtocell networks are considered to be a viable option that can fulfill the demands of high speed voice and data traffic for the indoor users.
It uses the services of the existing broadband connection to connect to the operator core network. The cellular network operators need to modify the existing single tier macrocell network in order to provide the services of femtocells to its users. In this paper, we present a survey on femtocell deployment. Various aspects of femtocell networks in a diverse domain are discussed.
A detailed analysis of the previous approaches is given to highlight their pros and the cons.. Since mids, the mobile cellular communication industry has been enjoying its fastest growth. Today's wireless communication technology is the refined and mature version of what we called the new technology during the seventies. The worldwide success of wireless communication demonstrated that it is a workable medium for multimedia communication causing new wireless systems and standards being introduced for other types of telecommunication traffic besides voice and data service.
With the maturity in mobile communication technology, operators are deploying it both indoors and outdoors. There is a continuously increasing trend in the demands of high speed data services among end users. It has been estimated that between the year and , there will be 10 to 30 times increase in mobile phone data traffic . The demand of multimedia traffic is high and the existing cellular network system cannot meet the required demands as its coverage area and capacity is not sufficient.
Providing these high speed data services to the dense urban areas is quite challenging. Especially in case of indoor environments, where penetration losses and high interferences makes the macrocell antenna's coverage very poor  and cellular users feel lot of difficulties in receiving high speed services in the indoor environment. The problems faced by the indoor mobile users can be alleviated by employing femtocells.
IEEE They are low power, short range, low cost small Base stations that operate in a licensed spectrum. Femtocells provide strengthened cellular signals for indoor users. It usually has coverage of 30—40 meters and is placed indoors for stationary or less mobile users.
The femtocell communicates with the cellular operators' network over a broadband connection such as digital subscriber line DSL , cable modem or a separate radio frequency backhaul channel . Introduction of femtocells in the existing macrocell forms a two tier hierarchical cell network. Macrocell being the first tier primary user and femtocell, the second tier secondary user.
Both the femtocell user and the operator can potentially benefit from deployment of femtocells. The users experience better signal quality while the operators achieve greater network capacity and spectral efficiency. Like every other technology, femtocells also have some drawbacks that give rise to some major concern on part of the end users. In this paper, we presented a detailed survey on femtocells deployment. Various aspects of femtocells are studied along with a detailed analysis of the research done in past to figure out various cons and pros of femtocell deployment mechanisms in diverse environmental scenarios.
This paper is structured as follows. In Section 2, we present various architectures proposed for femtocell networks. Section 3 provides the access control modes. In Section 4, different frequency reuse and resource allocation schemes are presented. Coverage quality is discussed in Section 5. Similarly in Section 6, various schemes for securing femtocells are given. Handover algorithms are introduced in Section 7, while different interference management schemes are presented in Section 8.
Finally in Section 9, we conclude the paper. To provide services to the end users having a femtocell base station, it is necessary for the operators to define the architecture for a femtocell based on the type of cellular network.
Generally, a mobile phone user can switch itself to the core network either by connecting itself to the femtocell or macrocell.
Researchers have presented architectures for various femtocell networks. As shown in Figure 1 , the design of femtocell network is such that data traffic uses the public internet while the voice traffic goes through the IMS IP Multimedia Subsystem network .
A general femtocell deployment architecture. It must be kept in mind that IMS can handle only voice traffic; however it can be connected to several femtocells. Since data does not go through the IMS network, the subscribers can avail various services at lower cost. There is also another architectural fact, in which conventional cellular deployment has been modified and IP-like architecture is proposed [ 7 , 8 ], with mobility enhancement  , and also paging mechanisms are introduced for distributed environments .
Initially femtocells were designed just for residential use, but by observing its competency and consistency, its self-optimization and coverage principles, can be extended further to include enterprises, campus, and even metropolitan zones. The standard architecture of CDMA 1x is shown in the Figure 2 of femtocell integrated network defined in . The Femtocell integrated architecture can be divided into two modes . In Figure 2 , it is visible that in legacy mode the femtocell is connected to radio access network, while in the flat mode, the femtocell is directly connected to the mobile core network.
The flat mode can reduce load on the radio access network. IMS is used on behalf of session management for voice communication. During the IMS session establishment process the SIP signaling delay can be analyzed as the performance indicator .
Three integrated architectures based on the coverage of macrocell network and on the availability of broadband connection are presented in . The proposed configurations are single stand-alone femtocell, network-alone femtocell and femtocell network integrated with a macro-cellular infrastructure. The single stand-alone femtocell provides coverage to areas with no or poor macrocell signals and neighboring femtocells are avoided in such areas.
While in network-alone femtocell, multiple neighboring femtocells are available. In a femtocell network integrated with a macrocell infrastructure there is an overlapping coverage of both the femtocell and the macrocell thus forming a two tier hierarchical network.
In  and  , the cognitive femtocell network architecture is presented. In  , cognitive femtocell sub-network CFS provides services like profile management, user rights and services provision. CFBS controls interference between the femtocell and macrocell. The whole architecture is shown in Figure 3.
Cognitive femtocell network architecture. Architecture for femtocells in a UMTS network is presented in . User equipment can access the services provided by the UMTS network. Core network performs location management, handovers, and gateways to other networks. Figure 4 shows the proposed UMTS network. In the Figure Home Node-B is the femtocell, which is connected to the internet. Proposed UMTS network architecture. In some other researches, such as in  , hierarchical overlay network in which femtocells deployed in a macrocell is presented.
Similarly standardization of femtocells in 3GPP2 is presented in  and the CDMA femtocell architecture for a legacy network is demonstrated. Femtocell base stations have a list of its users in order to limit and prevent the usage of femtocells against illegal subscribers.
Three types of access control methods in which femtocells can be configured to allow or block the users are thoroughly proposed. The open type access control is similar to a typical macrocell, i.
It can be used for general public users in malls, restaurants, and airports etc. In case of closed access method, the femtocell services can be availed by limited number of subscribers subscribed to the given base station. This case can be used for private usage such as in homes and offices etc. There is also an adaptive femtocell access policy, called hybrid access method, which takes the specific accounts of the instantaneous loads on the network.
It can lead to improved performance over the completely open, or completely closed approach suggested earlier . In hybrid access mode, the subscribed users get the preferential charging in comparison with the non-subscribed users to the cell to avail the services .
The three different access control modes are illustrated in Figure 5. There are security concerns regarding access control to block unauthorized users and allow authorized users.
It is also important because without the knowledge of the owner its neighbors may use its services and can lead to the potential network intrusions and hacking.
In closed access method only authorized subscribers can establish connection and communicate. While in hybrid access mode the non-subscribers have limited access of the femtocell resources. The CSG Closed Subscriber Group list can be managed by the femtocell owner through a protected web page, where the owner can login and add or remove users by entering their mobile numbers . The network capacity can be improved by using the open access method  because, wherever the macrocell coverage decreases, the users can connect to the nearby femtocell.
As in this method the outdoor users can connect to the indoor femtocells, therefore, it can also avoid femtocells behaving as interferers to their neighbors. The negative aspect of open access is the increase in number of handoff and signaling causing certain security issues.
In addition a recent survey shows that open access is also exigent to the operators commercially as well, because the non-subscribers are able to avail the services as users of their own femtocells without any returns. This issue of open access can be handled by the closed access method, in which only the subscribers can avail the femtocell services in a home or small enterprise.
Power leakage through the doors and windows can be sensed as interference by the passing macrocell users, and consequently the signal quality attenuates, because if the distance between the subscriber and Femtocell Access Point FAP is more and if asked to increase their strength level will result in a very high level of interference not only with the neighboring femtocells but possibly with the macrocell.
However, to some extent, this problem can be resolved by OFDMA sub-channel algorithm, which uses frequency sub channel allocation technique which utilizes the frequency reuse approach and consequently maximizes the cell throughput. In the Hybrid case they can also use the OFDMA sub channel technique which allows the non-subscribers to communicate through, but with certain restrictions.
The Journal of Applied Research and Technology JART is a bimonthly open access journal that publishes papers on innovative applications, development of new technologies and efficient solutions in engineering, computing and scientific research. JART publishes manuscripts describing original research, with significant results based on experimental, theoretical and numerical work. The journal does not charge for submission, processing, publication of manuscripts or for color reproduction of photographs. JART classifies research into the following main fields: Material Science Biomaterials, carbon, ceramics, composite, metals, polymers, thin films, functional materials and semiconductors. Computer Science Computer graphics and visualization, programming, human-computer interaction, neural networks, image processing and software engineering. Industrial Engineering Operations research, systems engineering, management science, complex systems and cybernetics applications and information technologies Electronic Engineering Solid-state physics, radio engineering, telecommunications, control systems, signal processing, power electronics, electronic devices and circuits and automation. Instrumentation engineering and science Measurement devices pressure, temperature, flow, voltage, frequency etc.
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Modern, advanced mobile radio networks have billions of users and an increasing amount is using the mobile networks indoors. Smartphones are designed for data consumption and thus the demand is for higher and higher throughput rates. At the same time the users and operators of mobile radio networks encounter difficulties with coverage gaps, especially indoors. Femtocells are a new concept that aims for ease of use, low cost and high performance in providing coverage and capacity for indoor users. This paper presents measurement results for an arbitrary, large-scale, indoor femtocell deployment. The measurements revealed clear promise in the technology, but at the same time difficulties with interference in such a high density femtocell environment. Power management is increasingly important in femtocell deployments as the placement is uncontrolled by the operator.
Claussen, D. Ho, R. Razavi, S. Chu, D. Laselva, D.
Haynes ManualsThe Haynes Author : Jie Zhang, Guillaume la de Roche Description:This book provides an in-depth guide to femtocell technologiesIn this book, the authors provide a comprehensive and organized explanation of the femtocell concepts, architecture, air interface technologies, and challenging issues arising from the deployment of femtocells, such as interference, mobility management and self-organization. The book details a system level simulation based methodology addressing the key concerns of femtocell deployment such as interference between femto and macrocells, and the performance of both femto and macrocell layers.
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