Femtocell in 3G (CDMA2000 and UMTS)

EE5517FEMTOCELLS IN 3G (CDMA2000 AND UMTS)Group Project

Mustari Laila (1029521/1)Oshiga Omotayo (0927755/1)Nasif Heba (0933793/1)Nur Abdimahad (0507413/2)GROUP 10

M.Sc. Wireless Communication SystemsSchool of Engineering & DesignBrunel University, UxbridgeUK

March 28, 2011 ABSTRACTIn this Group Project, A detailed report on Femtocells in 3G systems for CDMA2000 and UMTS is produced. In the first chapter, an introduction was provided which included the Aim and Objectives of this report, the introduction to Femtocell which gives a general overview of Femtocell, the benefits of using Femtocell to the User and the Network Operator. Then, examples of places where Femtocell has been deployed all over the world was given. In the second chapter, the Network Architecture of Femtocells which included detailed explanations and well-labelled diagrams were described. It explains the overall layout of the Femtocell Network which includes elements such as Femtocell Access points, Security gateway and Femtocell device management system. It also describes two main network models used to support circuit-switched services which are SIP/IMS and Legacy Network Models. It finally explains how Femtocells interwork with Packet Data Networks (PDN) and Local breakout which allows Femtocell to connect to their local home without traversing the Mobile operators network.Femtocell Radio Technology was described in chapter three, radio requirements for proper implementation of Femtocell was discussed. The interference scenarios, avoidance and mitigation techniques were explained. Femtocell access control also which prevents unauthorized access to the Femtocell network. And finally, seamless mobility and handover across Femtocell-Macrocell boundary was explained. In chapter four, other issues and challenges facing Femtocell were discussed which include Quality of Service, Security, Power and Health issues. Also Spectrum accuracy and synchronization were explained. Techniques and Measures were also provided.Finally, Real-life and Real-time applications for Femtocells were provided which includes the Bring life to home and life to mobile use of Femtocell which involves its use as an emergency support service, its green benefits, its Self Optimization and Femtocell as a payment tool.

Contents Page1. Introduction 11.1 Aim and Objectives of the Project 11.2 Introduction to Femtocell 11.3 Femtocell Benefits 21.4 Femtocell Deployment 5

2. Femtocell Network Architecture 62.1 Common Elements of the Femtocell Network Architecture 62.2 Architectural Models to Support Circuit-Switched services 92.2.1 SIP/IMS Network Model for Femtocell 102.2.2 Legacy Network Model for Femtocell 122.3 Interworking with Packet Data Networks 132.4 Local Breakout 14

3. Femtocell Radio Technology 153.1 Radio Requirements 153.2 Femtocell Interference 163.2.1 Interference Scenarios and Avoidance through Frequency Planning 163.2.2 Interference Mitigation in Co-Channel Femtocell Deployment 173.3 Femtocell Access Control 193.4 Seamless Mobility across Femtocell-Macrocell Boundaries 203.4.1 Mobility in Standby Mode 203.4.2 Handover 21

4. Other Issues Facing Femtocell 244.1 Quality of Service 244.2 Security issues 244.2.1 Security Vulnerabilities 254.2.2 Security Measures 254.3 Power and Health Issues 254.3.1 Femtocell Power Levels 254.3.2 Health Issues Research 264.4 Spectrum Synchronization and Accuracy 26

5. Application of Femtocell 295.1 Bringing Life Home and Bringing Life to Mobile 295.2 Green benefits of Femtocell 315.3 Self Optimizing Network 325.4 Femtocell as Payment Tool 33

6. Conclusions 34

7. References 35

1 INTRODUCTION 1.1 Aim and Objectives of the Project The aim of this project is to provide students with the opportunity to conduct a group assignment on a wireless communications related topic such as Femtocells in 3G systems (CDMA 2000 and UMTS). Objectives of the project are: To provide a detailed and well structured report on Femtocells in 3G systems. To develop team working, technical report writing and presentation skills. Experienced team working and peer assessment. Developed information gathering and Enhanced inter-personal gathering.1.2 Introduction to FemtocellFemtocells are low-power wireless access points which are of the order of 10 meters and operate in licensed spectrum to connect standard mobile devices to a mobile operators network. They are small cellular base stations that can be installed in residential or business environments either as single stand-alone items or in clusters to provide improved cellular coverage within a building. It is widely known that cellular coverage, especially for data transmission where good signal strengths are needed is not as good within buildings. By using a small internal base station Femtocell, the cellular performance can be improved along with the possible provision of additional services. In order to link the Femtocells with the main core network, the mobile backhaul scheme uses the user's using residential DSL or cable broadband (internet) connections. This provides a cost effective and widely available data link for the Femtocells that can be used as a standard for all applications. [1]

Figure 1: Overview of a Femtocell network [1] 1.3 Femtocell BenefitsFemtocells overcome the issue of providing effective indoor coverage from the 3G macro layer by their placement in the end-users homes. Once installed in an end-users home a Femtocell will enable the Operator to provide higher-quality and higher-performance wireless voice and 3G data services in and around the immediate vicinity of the home environment.There are many benefits for the deployment of Femtocells to both the user and the mobile network operator. Its clear more and more consumers want to use mobile phones in the home, even when theres a fixed line available. Friends and family usually call a mobile number first, and its where messages and contact lists are stored. However, it is often the case that providing full or even adequate mobile residential coverage is a significant challenge for operators. [1]For the user, the use of a femto cell within the home enables far better coverage to be enjoyed along with the possible provision of additional services, possible cost benefits, and the use of a single number for both home and mobile applications. Improving user experience in the home is also essential for reducing churn and gaining market share and new revenues. For the network operator, the use of Femtocells provides a very cost effective means of improving coverage, along with linking users to their network, and providing additional revenue from the provision of additional services. Femtocells are important because mobile operators need to seize residential minutes from fixed providers, and respond to emerging VoIP and Wi-Fi offerings. Using Femtocells solves these problems with a device that employs power and backhaul via the users existing resources. It also enables capacity equivalent to a full 3G network sector at very low transmit powers, dramatically increasing battery life of existing phones, without needing to introduce Wi-Fi enabled handsets. [2]Accordingly, Femtocells must fulfill the below criteria to provide the above benefits:Low-impact: Space may be limited for some households. As a result Femtocells must be physically small, ideally aesthetically pleasing and easy to position. Furthermore, they should also be silent in operation, generate low levels of heat output and inexpensive to run in terms of on-going [electricity] costs.Low RF power: The transmit RF power output of Femtocells is low; between 10 and 100 milli-watts. Put in perspective, this is a lower power level than many Wi-Fi access points, which can be specified up to 1 Watt of output power. Additionally, by being close to the Femtocell the 3G handset is itself able to transmit at lower power levels than it might otherwise have to when on the macro network.Capacity: Femtocells are aimed at delivering dedicated 3G coverage to a household and in doing so can provide a very good end-user experience within the home environment. As a result, Femtocells have a design capacity of up to 6 end-users.Low-cost: There is significant competition for access solutions in the home space. Wi-Fi is commonplace, easy to install/configure, provide a very good benchmark in terms of performance, and are highly cost effective. Femtocells will be offered for purchase via their Operators. This may be direct or through resellers. Energy offset - Low-power consumption Clearly if the end-user is to foot the bill for the electrical energy consumed by the Femtocell base-station then this figure must be low enough not to raise concerns as to its impact on the fuel bill. That said, from an Operators perspective, this OPEX is effectively offloaded, which makes the business case for Femtocells even more attractive.Easy end-user installation: Like cable modems and DSL routers, Femtocells will be installed by consumers and activated through service providers. This means that the Operator no longer has to employ installation teams or have a truck-roll every time a new Femtocell is deployed. From the end-user perspective the unit must be a simple plug and play installation with a minimal amount of intervention required.Backhaul via broadband: Femtocells utilize Internet protocol (IP) and flat base-station architectures. Backhaul connection to Operator networks will be through wired broadband Internet service existing in the home such as DSL, cable, or fiber optics as available. There are no connections required to the wider cellular network other than through the IP core. This will benefit Operators by effectively offloading traffic that would otherwise be on the macro-layer directly onto the internet from the Femtocell; this not only reduces the load on the core network but also lowers the cost of delivering wireless traffic when compared to the macro network.Interference: The use of Femtocells in spectrum also currently used by the macro layer may, if not managed correctly, give rise to issues with interference between cells; macro with Femtocell and in the instance of close proximity of two or more units, Femtocell with Femtocell. Operators will likely want to launch Femtocells on the same channel as their macro cell network for capacity reasons.Handovers: Current macro RF planning techniques are inappropriate for Femtocells. Not least because of the sheer potential numbers of Femtocells and managing the neighbor lists that would be necessary. Also the potential to ping-pong between layers, especially as an end-user moves around the home and enters into areas where the signal strength from the macro-cell is greater than that of the Femtocell, must be considered very carefully to ensure that the networks provide the best overall coverage without issue. Security: Given the requirements for low-cost and easy installation, the use of the broadband internet as the network interface becomes very easy to understand. However this raises security risks in that broadband internet has open access. There are various approaches to address this issue including the embedding of the Iub interface within the IP signaling itself while network security is managed by the IP security (IPSec) protocol. Operation (transmit/receive) in Operator-owned spectrum: Femtocells operate in licensed spectrum owned by Operators and may share the same spectrum (currently the 2100MHz frequency band) with the macro network.Operator controlled: Femtocells operate in licensed spectrum and as such Operators must ensure that they comply with the conditions of that license and any other controls enforced by a regulator. To these ends Femtocells feature client software that enables remote configuration and monitoring via an Operations, Administration, Maintenance and Provisioning (OAM&P) system in a similar manner to that used by the macro network.Service Assurance: Remote Management to enable an operator to provide the end-user quality of service at the edge of the network. [1]

1.4 Femtocell DeploymentAccording to market Research firm Informa and the Femto Forum,as of December, 2010 18 operators have launched commercial Femtocell services, with a total of 30 committed to deployment. Femtocell shipments are estimated to have reached almost 2 million at the end of 2010. Research firm Berg Insight estimates that the shipments will grow to 12 million units worldwide in 2014.Within the United States, the most significant deployments up to December 2010 are byVerizon WirelessandAT&T Wireless. In January 2009 Verizon rolled out its Wireless Network Extender.In late March 2010, AT&T announced nationwide roll-out of its 3G MicroCell, which commenced in April. The equipment is made byCisco Systemsand was the first 3G Femtocell in US, supporting both voice and dataHSPA. Verizon upgraded to 3G CDMA Femtocells during 2010, with capacity for more concurrent calls and much higher data rates.In Asia, several service providers have rolled out Femtocell networks. In Japan,Softbanklaunched its residential 3G Femtocell service in January 2009with devices provided by Ubiquisys. In the same year the operator launched a project to deploy Femtocells to deliver outdoor services in rural environments where existing coverage is limited. In May 2010, SoftBank Mobile launched the first free Femtocell offer, providing open access Femtocells free of charge to its residential and business customers. In Singapore, Starhub rolled out its first nation-wide commercial 3G Femtocell services with devices provided byHuawei Technologies, though the uptake is low. In 2009, China Unicom announced its own Femtocell network. NTT DoCoMo in Japan launched their Femtocell service on the 10th November 2009. [3]

2 FEMTOCELL NETWORK ARCHITECTUREThe Femtocell network architecture describes the main nodes and connections in a Femtocell network, and how they achieve the objectives of mobile subscribers and operators.The Femtocell network architecture supports the following key requirements: Service Parity: Femtocells support the same voice and broadband data services that mobile users are currently receiving on the Macrocell network. This includes circuit-switched services such as text messaging and various voice features. Call Continuity: Femtocell networks are well-designed with the Macrocell network so that calls originating on either Macrocell or Femtocell networks can carry on when the user moves into or out of Femtocell coverage. Femtocell network architecture requirements include the necessary connectivity between the Femtocell and Macrocell networks to support such call continuity. Security: Femtocells use the same over-the-air security mechanisms that are used in Macrocell radio networks. But extra security capabilities need to be supported to guard against threats that originate from the Internet or through tampering with the Femtocell itself. Femtocell network architecture provides network access security, and includes subscriber and Femtocell authentication and authorization procedures to protect against fraud. Self-Installation & Simple Operational Management: Femtocells are installed by end-users. However, the Femtocell network architecture must support an extremely simple installation procedure with automatic configuration of the Femtocell and automated operational management with zero-touch by the end-user. Scalability: Femtocell networks can have millions of access points. However, the Femtocell network architecture must be scalable to rise into such large networks, whereas at the same time maintaining reliability and manageability. [4]

2.1 Common Elements of the Femtocell Network Architecture As shown in Figure 2.1 there are three network elements that are common to any Femtocell network architecture. These are: Femtocell Access Point (FAP) Security Gateway (SeGW) Femtocell Device Management System (FMS) Two other elements that are in all Femtocell network architectures are entities that permit connectivity to the mobile operator core. Depending on the precise architecture used for circuit switched calls, there can be whether a Femtocell Convergence Server (FCS) or a Femtocell Network Gateway (FNG).This is also shown in Figure 2.1. For packet calls, depending on the air-link technology, there can be either a PDSN or xGSN (GGSN/SGSN) in the core. In many cases, the PDSN / xGSN are the same as those used for macro networks.

Figure 2.1: Common Components of Femtocell Network Architecture [4]Femtocell Access Point (FAP): Femtocell Access Point is the primary node in a Femtocell network that resides in the user location (e.g., home or office). The FAP performs the functions of the base station and base station controller and connects to the operator network over a secure tunnel through the Internet. A FAP can be introduced into a home in multiple ways. A separate FAP can be directly connected to the home router. In some cases, the FAP may also include a built-in router, which is useful in prioritizing FAP voice traffic over other Internet traffic in the home network. More highly developed FAPs include an Analog Terminal Adapter (ATA) to connect a fixed-line phone. In other cases, FAPs are full-blown residential gateways with built-in Wi-Fi and a broadband modem (xDSL, cable). Note, the 3GPP refers to 3G Femtocells as Home Node Bs (HNBs)Security Gateway: The security gateway is a network node that secures the Internet connection between Femtocell users and the mobile operator core network. It uses standard Internet security protocols such as IPSec and IKEv2 to authenticate and authorize Femtocells and provides encryption support for all signaling and user traffic. The security gateway supports a large number of Femtocells connecting to the operators network. While like to traditional VPN gateways used in enterprises, Femtocell security gateways are designed for use in carrier networks and meet carrier-grade requirements for instance scalability, high availability, and network management.Femtocell Device Management System: The Femtocell management system, also placed in the operator network, plays a significant role in the activation and operational management of Femtocells using industry standards such as TR-069. The management system is probably the most critical node in ensuring the scalability of a Femtocell network to millions of devices. To ensure low-cost deployment and easy setup for subscribers, the activation and provisioning of the Femtocell must be plug-and-play with no on-site assistance (sometimes called a truck roll) required from the mobile operator. Different standards bodies state the use of the TR-069 family of standards as the base device management framework for Femtocells. This protocol is widely used in DSL modem and residential gateway deployments, and uses a proven web-based architecture that can scale to support millions of devices. Femtocell Service Manager (FSM) is a comprehensive TR-069-based Femtocell management system that supports efficient management of large numbers of Femtocells using a clustering and load balancing architecture. The FSM contains two primary elements, the Device Manager application and the Automatic Network Planner application. The Device Manager implements Functions such as remote configuration, remote diagnostics, fault management, software upgrade, performance data collection and device authentication. The Automatic Network Planner adds RF planning algorithms, RF configuration and a northbound interface to Operational Support Systems (OSS). [5]

Figure 2.2: Femtocell Service Manger [4]

FCS or FNG: The FCS or FNG enables Femtocells to connect to the operator core network. This is important for the operation of Femtocells as this is what allows Femtocells to communicate with the core elements in the operators networks and allow seamless service for the mobile. For example, basic call setup requires communicating with the MSC and PSTN of the operator core. The FCS or FNG allows this to happen. As will be shown below, depending on the specific architectural model used to support Circuit-Switched Services the FCS /FNG can be used. PDSN /xGSN: The PDSN / xGSN enable Femtocell users to receive packet data services over the mobile operators core. In most cases, these will be the same as those used by the mobile operators macro network.

2.2 Architectural Models to Support Circuit-Switched ServicesMacrocell networks consist of a radio network and a core network. The radio network is made up of base stations, base station controllers (BSCs) and a radio network management system. The core network includes the Mobile Switching Centre (MSC), mobile data node such as Packet Data Serving Node (PDSN) in CDMA and Serving/Gateway GPRS Serving Nodes (SGSN/GGSN) in UMTS, subscriber data bases, such as the Home Location Register (HLR), and various billing systems.Femtocells connect to a mobile operator core network to deliver both circuit-switched and packet data services. Broadly speaking, there are two distinct architectural models for supporting circuit-switched services in Femtocells. In the SIP/IMS model, Femtocells connect into an overlay SIP/IMS core network. In the alternate so-called legacy model, Femtocells connect directly into the mobile operators legacy core network (MSC). In the remainder of this section, we will review these models in detail. [5]

Figure 2.3: Femtocell Network Architectures for Supporting Voice (Circuit Switched Services) [4]

2.2.1 SIP/IMS Network Model for Femtocells In this model, the Femtocell connects to a new core network of the mobile operator that is based on the SIP/IMS architecture. This is achieved by having the Femtocells behave towards the SIP/IMS network like a SIP/IMS client by converting the circuit-switched 3G signalling to SIP/IMS signalling, and by transporting the voice traffic over RTP as defined in the IETF standards. To support Femtocells, a new network node called a Femtocell Convergence Server (FCS) is added to the SIP/IMS network. The FCS also attaches to the legacy mobile core network by acting like an MSC towards the legacy core network, the FCS helps support handoffs between Femtocell and Macrocell networks, accesses subscriber databases such as HLRs and provides the supplementary services required for feature parity. 3GPP2 standards for CDMA Femtocells use the SIP/IMS Model, and the description that follows mirrors the use of this architecture in CDMA Femtocells.The following figure shows the detailed diagram for the SIP/IMS Femtocell network for CDMA Femtocells. As can be seen, the CDMA Femtocell connects to a SIP/IMS core network which in turn has a signalling connection to the legacy CDMA core network, whose interfaces are defined in the TIA IS-41 standard. The SIP/IMS network is used for the call control and media routing while the legacy core network is used to retrieve subscriber data stored on the legacy network and to support handoffs to/from the Macrocell network, which exclusively uses the legacy core network. [5]

Figure 2.4: SIP/IMS Network Model [4]The main components in the SIP/IMS architecture are as follows: Femtocell Access Point with SIP/IMS Client SIP/IMS Core Network Femtocell Convergence Server (FCS) The SIP/IMS core network can be a full-blown IMS network or it can be a basic SIP-based VoIP network. An IMS core network would have the IMS nodes, such as the Call Signalling Control Function (CSCF) nodes for call control, Home Subscriber System (HSS) to manage subscriber data, and Media Gateway (MGW)/Media Gateway Control Function (MGCF) nodes to connect to the Public Telephone Network (PSTN). In a more basic SIP network, the functionality of the CSCF and MGCF functions may be integrated into a SIP soft switch, and the HSS function may be handled by a Radius server. FCS is the key component in this architecture. It fits into an IMS core network as an Application Server (AS) that connects to the CSCFs using the standard ISC interface. FCS connects to the legacy core network like an MSC using standard IS-41 network interfaces.The SIP/IMS model is a forward-looking approach for delivering services over Femtocells. It offers not only a scalable approach for delivering services, but can also be used to offer converged fixed-mobile services to both mobile devices and fixed-line phones. In the SIP/IMS model, support of active handoff is done through the FCS. As the FCS essentially acts as a peer MSC in the mobile core network, the handoff uses the well known inter-MSC active handoff mechanisms using existing core network interfaces, as defined in IS-41. When a user moves from Femtocell coverage to macro network coverage, the Femtocell sends and receives messages that correspond to the handoff request messages sent in the macro network in handoff scenarios. [5]

2.2.2 Legacy Network Model for FemtocellsIn the legacy network model, the Femtocell connects directly to the existing mobile operator core network. A network node called a femto network gateway sits between the Femtocell and the legacy core network and performs the necessary translations to ensure the Femtocells appear as a radio network controller to existing MSCs. 3GPP standards for UMTS Femtocells use the Legacy Core Network Model, so the description that follows largely mirrors the use of this architecture in UMTS Femtocells. The main components of the legacy network model are: Femtocell Access Point Femtocell Network Gateway (FNG) Security Gateway The FNG is responsible for connecting the Femtocell to the MSCs in the legacy core network. Using the standardized UMTS interface known as Iu, the FNG behaves like a Macrocell Radio Network Controller (RNC) and as such requires no modifications to existing MSCs to support Femtocells. Towards Femtocells, the FNG uses a variant of the Iu interface, known as Iub, which has been standardized in 3GPP. The legacy network architecture is easier to deploy when a SIP/IMS network is not already in place, since it allows the operator to reuse the existing mobile core network. Using the existing core network implies 100% compatibility with many service features and avoids the need to replicate these features on a new SIP/IMS network. In this model support of active handoff is done through the legacy MSC. As the FNG essentially acts as an RNC in the core network, the handoff is implemented using the well known Iu interface between the RNC and MSC/SGSN. When a user moves from Femtocell coverage to macro network coverage, the Femtocell sends and receives messages that correspond to the handoff request messages sent in the macro network in handoff scenarios. [5]

Figure 2.5: Legacy Network Model for UMTS [4]Although the legacy network model is currently not supported in CDMA Femtocell standards, it is supported by CDMA Femtocell. As shown in Figure 2.6, in this architecture the FNG uses the 3GPP2 standard A1p/A2p interfaces to connect to the MSC in the legacy network and a SIP-based interface to connect Femtocells to the FNG. Using the SIP-based interface between the Femtocell and the FNG makes the FNG more scalable and also creates a natural migration path from the legacy model to the SIP/IMS model.

Figure 2.6: Legacy Network Model for CDMA [4]

2.3 Interworking with Packet Data Networks Femtocells connect to the mobile core packet data network through existing packet data network nodes, such as SGSN/GGSNs in UMTS and PDSNs in CDMA. In CDMA networks, Femtocells can connect to the PDSN directly via the security gateway. This is possible because existing PDSNs can generally handle a very large number of Femtocells without any modifications. In UMTS networks on the other hand, the femto network gateway acts as an intermediary between the SGSN/GGSN and the Femtocell makes the data traffic from these devices appear as if it is coming from an RNC.

2.4 Local Breakout Femtocells also support a feature known as local breakout, which allows a Femtocell user to connect their mobile devices to the local home or office network without traversing the mobile operators core network. For traffic destined to the global Internet, local breakout also bypasses the operator core network, thus reducing the network load. This is shown conceptually in figure 2.7. [5]

Figure 2.7: Local Breakout [4]

3 FEMTOCELL RADIO TECHNOLOGY Femtocells are intelligent cellular access points that support any mobile device using standard air interfaces such as CDMA2000, UMTS and LTE. They have cellular radios that are tightly integrated with the existing Macrocellular radio network and thus create a seamless roaming for users as they move in and out of the Femtocell coverage, whether in an active call or standby mode. Femtocells obtain information about the radio frequency of their surroundings and use this information to self-organize their operation. Femtocells use their RF awareness to control interference between themselves and between Femtocells and Macrocells. This is done without making any change to the bilions of mobile devices all ready in use. They also support access control where only the authorized users are allowed to access or use it and finally handover procedure to enable call continuity and seamless roaming between Femtocell and Macrocell networks.

3.1 Radio RequirementsFrom the 3GPP2, the following radio frequency requirement was proposed for Femto cell. Femto cell systems include mechanisms to control and minimize interference with the Macrocellular system. Also, Femto cell systems include mechanisms to control and minimize interference between femto cell devices.Femto cell systems are capable of supporting one or more of the various types cdma2000 air interfaces (1x and EV-DO). Femto cell systems shall support one or more of the band classes defined for cdma2000 radio technologies. UMTS Femtocell provide the full capacity of the UMTS carrier in a limited cell size and handles users while delivering full HSDPA, HSUPA and HSPA+ performance. Femto cell systems supports existing terminal devices that employ any radio interface supported by the femto cell. Femto cell systems are capable of operating and co-existing with the Macrocellular system in the same channel. They are also capable of operating and co-existing with the Macrocellular system when the Macrocellular system is operating in different channels or bands than the femto cell system. A Femto BS shall support a single carrier frequency in a licensed band for the supported air interface specification(s).[7]

3.2 Femtocell InterferenceInterference is a key issue associated with Femtocell development. There are number of interference issues which have been investigated and solutions found to ensure that the deployment of any Femtocell will successfully take place. The issues arise from the fact that Femtocells create tiny cells which typically lie inside larger cells served by nearby Macrocell base stations and they will utilize the spectrum already allocated for macro cellular systems. As a result of this, there is every possibility that interference will arise which would lead to poor network performance being achieved in all the cellular systems (macro and femto). While Femtocells can give major advantages in terms of coverage improvements for a comparatively low cost, these benefits could be negated if the overall performance of the network was reduced. To operate such an underlay network reliably, Femtocells need to prevent and strongly mitigate any form of interference with Macrocells and provide seamless roaming to users as they move in and out of their coverage. As a result an amount of work has to be done to ensure that Femtocell interference issues do not arise and prevent their widespread deployment. There are a number of methods that have been developed to ensure the easy minimization of interference so that Femtocells can be installed by users without the need to worry about any technical issues. [8] Femtocells implement various layers of interference management to optimize user experience across both Femtocell and Macrocell networks.3.2.1 Interference Scenarios and Avoidance through Frequency PlanningA mobile operator has three basic options for allocating frequency in Femtocell deployments. These are shown by the scenarios A, B and C in Figure 3.1.Scenario A represents a dedicated radio channel Femtocell deployment that provides different Macrocell and Femtocell radio channels. This helps to minimize interference between the two networks and simplifies initial deployment of Femtocells. This is usually suitable in rural areas where the operator has unused radio channels.Scenario C shares all available radio channels between the Macrocell and Femtocell networks. This has the pros of adding more freedom to manage interference between Femtocells, mostly in dense urban deployments, but also requires the highest degree of interference management to ensure minimal impact on the macro network from co-channel Femtocells.Scenario B represents a compromise between scenario A and C in which some radio channels are shared between Macrocell and Femtocell networks and other radio channels are observed for Macrocell network only. In this scenario, the Macrocell can redirect the mobile devices it is serving on a shared radio channel to a dedicated Macrocell radio channel as they approach a Femtocell. Since mobile operators do not have dedicated radio channels to Femtocells in many of their markets. Therefore, Femtocells need to be designed with advanced interference mitigation techniques that allow reliable operation when Femtocells and Macrocells networks share the same radio channels as in scenario C. [6]

Figure 3.1: Deployment Scenarios for Sharing Radio Channels between Macrocells and Femtocells Networks

3.2.2 Interference Mitigation in Co-Channel Femtocell Deployments Finding a way to share all available spectrums between Femtocell and Macrocell networks leads to the most efficient use of the available spectrum, provided proper interference mitigation techniques are employed. We will separately consider interference on the Downlink (DL) (from the base station to the mobile device) and interference on the Uplink (UL) (from the mobile device towards the base station) and also separately interference affecting users of the Femtocell and users of Macrocell. Downlink Interference Mitigation: A Femtocell must set its DL transmission power high enough to overcome the interfering Macrocell signal within the Femtocells target coverage area. But the Femtocell cannot arbitrarily increase its transmission power, as this would generate interference to mobile devices nearby that are operating on the same radio channel but are being served by a Macrocell base station or another Femtocell. To deal with this situation Femtocells set their transmission power adaptively. They measure the strength of the signals received from nearby Macrocells and other Femtocells and set the DL transmission power level just high enough to achieve acceptable SNR inside the target coverage area. A Femtocell transmitting at too high a power level creates interference to a nearby mobile device that is being served on the same radio channel by a far away Macrocell. This can create a dead zone where even basic voice communication with the Macrocell base station may become impossible. Femtocells avoid this scenario by either pushing these mobile devices away to another radio channel on the Macrocell network while they are still in standby mode or by allowing them to park on the Femtocell in standby mode, and handing them out to a different radio channel on the Macrocell network whenever they turn active for a voice or data call. This way all Macrocell calls in the close vicinity of the Femtocell always take place on a different radio channel and thus avoid any interference from the Femtocell. [6]

Uplink Interference Mitigation: Macrocell base stations maintain system stability on the UL by controlling the total received UL power. The transmission power of mobile devices that are being served by the Macrocell base station are controlled in such a way that the rise in total received power over the equivalent thermal noise level is maintained at or below a pre-determined threshold. This threshold known as the Rise-Over-Thermal (RoT) is set between 5 and 10 dB. Power control ensures the strength of signals being received from mobile devices that are at different distances from the base station is equal, and thereby maintains system stability. Soft handoff procedures also allow multiple base stations to control the transmission power of the mobile device located at a cell boundary. Mobile devices that are being served by Macrocells will set their transmission power in a way that is oblivious to the presence of Femtocells. Because the distance between a mobile device and a Macrocell is typically larger than that between the device and a nearby Femtocell, the UL signal received by the Femtocell from such a device can be very high, raising the interference level up to 30 or 40 dB above levels typically seen in Macrocell base station receivers. The Femtocell receiver hardware is designed to handle high levels of interference from nearby mobile devices, without suffering from any saturation effects. The Femtocell will inform the mobile devices it is serving to increase their transmission power to overcome the interference from nearby mobile devices being served by a Macrocell base station, using a variation of the power control algorithm used in Macrocell base stations. The increase in transmission power poses no problem for the mobile device being served by the Femtocell because its transmitter is designed for operation with distant Macrocell base stations. It generally has plenty of power available to reliably communicate with a nearby Femtocell, even in presence of interference from other nearby mobile devices transmitting to a Macrocell at a high power. In fact, in the absence of any interference from other mobile devices, a mobile device being served by a Femtocell uses very little transmission power relative to what it uses on a Macrocell network, which leads to longer battery life (talk time) and avoids UL interference to nearby Macrocell base stations. However in the scenario where a mobile device being served by Femtocell has to raise its transmission power in response to interference being caused by a mobile device being served by a far away Macrocell base station, elevated interference levels can occur in the Macrocell base station. As Macrocell base stations are designed to operate in a power-controlled environment, unplanned interference from such a mobile device can cause mobile users being served by the Macrocell near the cell edge to experience lower data throughput and call drops. Femtocells avoid this phenomenon by constantly evaluating the interference its mobile devices are causing to nearby Macrocell base stations, and ensure that such interference does not reach levels where they affect Macrocell user experience. This is done by using measurement reports from mobile devices to evaluate their path loss to the nearest Macrocell base station, and by limiting their transmission power using power control algorithms. [6]

3.3 Femtocell Access ControlIn restricted access, the Femtocell owner can restrict Femtocell usage to members of the household and frequent visitors and avoid sharing Internet backhaul with others. CDMA Femtocells implement restricted access by having its beacon redirect only authorized mobile devices, thus leaving unauthorized mobile devices to continue operating normally on other radio channels and attached to the Macrocell. Unauthorized mobile devices on the same radio channel as the Femtocell who detect the Femtocell may be allowed to camp on the Femtocell and when they turn active they are handed out to the Macrocell on a different radio channel. This ensures that no unauthorized active user is allowed to use the Femtocell and they are moved away from the Femtocell radio channel to avoid interference. UMTS Femtocells implement access control by sending an appropriate rejection message, which causes the mobile device to switch to another radio channel on the Macrocell network. Mobile operators may choose to provide commercial incentives to Femtocell owners to have them configure their Femtocells in open access mode, where any mobile device can receive service from the Femtocell. Open access not only makes the Femtocell experience available to more users, it also avoids many of the interference scenarios discussed in the previous section. In open access, the Femtocell beacon will redirect all mobile devices within its coverage area to the Femtocell radio channel. Hybrid access is similar to open access except here certain mobile devices selected by the Femtocell owner are given preferential treatment over other mobile devices that can use the Femtocell on a best-effort basis. [6]

3.4 Seamless Mobility across Femtocell-Macrocell Boundaries 3.4.1 Mobility in Standby ModeA mobile device in standby mode changes the cell that it is camped on as it moves across cell boundaries. This process is helped by parameters broadcast by the cell sites. It is desirable for a mobile device to switch to a Femtocell when the received signal strength from the Femtocell is strong enough to support reliable service. This still needs to occur even when the Macrocell network can provide reliable service, due to the Femtocell been able to improve the mobile user experience and ensure they take advantage of any subscribed flat rate femtozone calling rate.In either CDMA or UMTS, the mobile device will switch to a new cell on the same radio channel based on continuous measurement of pilot signals from neighbouring cells. But mobile operators use multiple radio channels and switching to a cell on a different radio channel has more stringent requirements. To increase battery standby time the mobile device scans other radio channels only when the signal-to-noise ratio of the current cell is lower than a certain threshold. In UMTS systems, this threshold is determined by a system parameter called SIntersearch. Setting SIntersearch to a higher value can force all mobile devices to perform inter-frequency searches under more circumstances, thus increasing their battery drainage. On the other hand, if SIntersearch is set to a lower value, the inter-frequency scans required to detect the Femtocell may not be triggered if the signal received from the Macrocell base station is strong and a mobile device may never switch to the Femtocell. Thus operator must optimize how they set SIntersearch. CDMA2000 Femtocells solve this problem by including a special transmitter called a beacon, which makes the Femtocells presence known on all Macrocell radio channels except the one used by the Femtocell. The beacon is a special signal that consists essentially of a low-power pilot signal along with a broadcast signal that forces mobile devices to camp on the Femtocell radio channel. In CDMA a command is sent to all mobile devices or only to those devices authorized to use the Femtocell. Since most CDMA2000 devices support both CDMA2000 1x and EV-DO, a mobile device needs to camp on the Femtocell in both 1x and EV-DO systems simultaneously. CDMA Femtocells implement a unique beacon solution to allow a device entering Femtocell coverage area to attach and remain attached to both systems. The overall Femtocell user experience will be best when the beacon range is somewhat smaller than the service range most of the time and occasionally equal to the service range, as illustrated in Figure 3.2. [6]

Figure 3.2: Illustration of beacon and service coverage areas [6]

3.4.2 Handover/HandoffFemtocell handover or handoff techniques need to ensure that seamless coverage is perceived and call continuity is maintained by the user when moving onto or off a Femtocell. Femtocell handover is more challenging than normal Macrocell cellular handover because the backhaul network is different and there is also little possibility of direct communication between the Femtocell and the Macrocell. Femtocell handover (handoff) to and from Femtocells is obviously an essential element of the technology. It is essential that users do not see any problems with the handover process; otherwise this would provide a basic distrust of the system and lead to their use being avoided. [9]These are the three ways in which Femtocell handover (handoff) occurs: Hand-in This is where handover occurs from the macro-cell or standard cellular network to the Femtocell. Hand-out: This is where a handover occurs from the Femtocell to the Macrocell or standard cellular network. Femtocell to Femtocell: There will be situations where handover will occur between one Femtocell and another close by. This will be commonplace in offices that may have a number of Femtocells to give continuous coverage within a building.

Figure 3.3 Simplified CDMA2000 1x Circuit-switched Services Femtocell Architecture [6]Hand-out can be supported with relative ease without any form of changes to the existing Macrocell network or to the mobile devices. This is achieved by making the Femtocell network behave like a Macrocell network towards the Macrocell mobile switching center, thereby making the legacy equipment think that it is handling a handoff between two Macrocell networks, except when the Femtocell and Macrocell networks are sharing a single available radio channel, hand out is generally performed to a Macrocell radio channel that is different from the Femtocell radio channel.Hand-in on the other hand is more difficult because there is no simple mechanism for the Macrocell network to determine the identity of the target Femtocell from the measurement reports sent by the mobile device approaching the Femtocell. In CDMA2000 systems, the measurement report includes the strength of pilot signals seen by the mobile device and uses the PN offset to identify the target cell. However, target Femtocells cannot be identified without ambiguity based only on PN offset report because out of the available 512 distinct PN offsets only a small number will be allocated to Femtocells and these are re-used among them. Thus with possibly hundreds of Femtocells per Macrocell it is not possible to uniquely identify the handoff target with the PN offset. CDMA Femtocells can solve this problem by measuring the UL signal of the approaching mobile device. First, using cdma2000 1x signaling protocols the Base Station Controller (BSC) in the Macrocell network triggers the handoff and forwards the mobile devices UL scrambling code information and the target PN offset to the Femtocell Convergence Server (FCS) via the MSC. Based on this and other available information, the FCS then requests a subset of the Femtocells it is serving to listen for the mobile device based on the UL scrambling code. All Femtocells with the same target PN offset then report back the mobile devices UL signal quality together with the Femtocells DL pilot transmission power level. Based on the reports from the various Femtocells, the FCS determines the correct target Femtocell and signals the Macrocell BSC to order the mobile device to handoff to the Femtocell. The same Femtocell identification issue occurs in UMTS Femtocells. A scalable hand-in solution requires changes to existing standards, thus can work with only future devices that will be compliant with these new standards. A proposed 3GPP standard solution is based on autonomous gaps which allows the mobile device in a call to break from the call for a sufficiently long period of time to allow it to search for a Femtocell on a different radio channel and decode its broadcast channel. Based on the cell identity and the measurements, the Macrocell network can trigger a hand-in to the Femtocell. [6]

4 OTHER ISSUES FACING FEMTOCELL4.1 Quality of serviceWhen using an ADSL home backhaul connection, an Access Point Base Station must either share the backhaul bandwidth with other services, such as Internet browsing, gaming consoles, set-top boxes and triple-play equipment in general, or alternatively directly replace these functions within an integrated unit. In shared-bandwidth approaches, which are the majority of designs currently being developed, the effect on Quality of Service may be an issue.The uptake of Femtocell services will depend on the reliability and quality of both the cellular operators network and the third-party broadband connection, and the broadband connection's subscriber understanding the concept of bandwidth utilization by different applications a subscriber may use. When things go wrong, subscribers will turn to cellular operators for support even if the root cause of the problem lies with the broadband connection to the home or workplace. Hence, the effects of any third-party ISP broadband network issues or traffic management policies need to be very closely monitored and the ramifications quickly communicated to subscribers.A key issue recently identified is active Traffic shaping by many ISPs on the underlying transport protocol IPSec. UK-based Femtocell authority Epitiro have recently provided significant publicly available research and insight into many of these IP-focused QoS issues. [3]4.2 Security IssuesThere are a number of concerns that exist about Femtocell security. User privacy: Since a variety of data about the user, voice calls and data and IP. Denial of service and general service availability: Major concerns on the link between the Femtocell and the cellular core network are across the Internet and it is IP based. Fraud and service theft: This form of Femtocell security addresses the scenarios where unauthorised users connect to the Femtocell.It is therefore essential, that from the first deployment phase for Femtocells, to the maintenance phases, operators keep sufficient security measures in place and upgrade them to counter any new techniques that are developed.4.2.1 Security VulnerabilitiesThere are a number of areas where there are possible security risks within the overall Femtocell system. It is assumed that the cellular core network is safe from attack. This is a safe assumption as the core network is under the control of the operator. The main areas of Femtocell security vulnerabilities are given below: Wireless link into the Femtocell: Here there is a possible for external wireless transmissions to gain access to the Femtocell. The Femtocell itself: It is possible that hackers could gain access into the Femtocell and control it for their own use. Internet link: This is the backhaul link used between the Femtocell and the Femtocell gateway into the service provider's core network. 4.2.2 Security MeasuresIn order to prevent Femtocell security attacks from succeeding, there are several areas that can be addressed: Use of IPSec: In order to ensure that the Femtocell security is maintained across the Internet IPSec or IP security is used. Femtocell Secure Authentication: Authentication is required by either the service provider or operator to ensure that valid Femtocells are connecting to the core network. Wireless link security: The wireless link is an area where Femtocell security is needed to ensure that unauthorised users do not connect or take over the Femtocell. EAP, Extensible Authentication Protocol: This form of protocol is used in a number of wireless networks and its use has been proposed for providing Femtocell security. [10]

4.3 Power and Health IssuesThere is a large concern on health issues regarding Femtocells, which is the health issues related with the use of radio frequency radiation. Many companies show that Femtocells are not threats to health, currently the standards for radio frequency radiation are set to levels that allow radio transmissions of different forms to be used, but current research shows that there are no unreasonable risks.4.3.1 Femtocell power levelsThe Femtocells power levels are quite low and low power access point used for short range communications. They provide improved coverage and capacity and use the same signal formats that are used by other cellular base stations and phones. Power levels are about the same as the power levels used by ordinary wireless access points for Wi-Fi. Phones using the Femtocell will have low level power likely to be within easy radio-range, its power levels will be reduced to only the required level needed to give reliable communications. In this way the overall level of radio signal may be reduced.4.3.2 Health Issues ResearchA very large amount of research has been undertaken into discovering any links between low level radio frequency radiation and health issues for 50 years. Although no direct links to health have been found, it is a recognized fact that radio frequency radiation does heat up local tissue like microwave oven works, although the power levels for microwave ovens are much higher. As a result a fact known as "hot ear" can occur when a cell phone held close to the ear is used for an extended period of time. It is therefore recommended that cell phones are not used for extended periods of the day. However, it is current thinking that in view of the 1/d^2 law where power reduces as the square of the distance, means that Femtocells should not pose any form of risk.In order that those who design radio equipment are able to design to a common agreed safe standard, Femtocells are deigned to the same safety limits that are applied to all wireless equipment including mobile phones, Wi-Fi access points Bluetooth devices, etc. [11]

4.4 Spectrum Synchronization and AccuracyThere areas of Femtocell operation that require synchronization and accuracy are follows: Supply frequency information to handsets: It is not possible for user equipments to achieve the level of frequency accuracy like base stations. So handsets synchronize to base stations. Ensure reliable handover: If the Femtocell is not synchronized to the network, handovers will fail. Interference reduction: All base stations should be synchronised to reduce interference. High levels of interference can reduce call quality and capacity. Ensures Femtocell to be aware of adjacent cell sites: If Femtocell is accurately synchronized to all network it can detect other cells more quickly and improve the operation of the Femtocell. Accuracy levels are defined in many standards for different types of cell. These tend to vary according to the type of cell which the base station is serving.Base station type Frequency accuracy (ppb)

Wide area 50

Local area 100

Home - Femtocell 250

It would be possible to utilize a very high stability standard to produce the required level of accuracy and hence Femtocell synchronization. However cost can be an issue and therefore other methods of obtaining the required level of Femtocell synchronization and frequency accuracy may be more effective.Crystal oscillators are generally at the heart of any clock system used to provide a timing and frequency reference. Different types of crystal oscillator may be used, but these have cost implications. TCXO OCXO Hybrid

Price Lower Higher Medium

Accuracy Lower Higher Medium

NB: TCXO = Temperature compensated crystal oscillator, OCXO = Oven controlled crystal oscillator.It can be seen that the accuracy is broadly reflected in the cost. As OCXOs can be particularly expensive, and often relatively large, other ways are normally sought of gaining he required level of stability. As the cost of both the OCXO and hybrid solutions are normally too high for the maximum manufacturing costs that are viable for Femtocell production, and therefore a TCXO combined with another form of external Femtocell synchronization. [10]

There are a number of ways in which Femtocell synchronization can be achieved. There are several sources of time information that can be used. The major time synchronization sources that are used are:Internet timing for Femtocell synchronization: Using this method, the Femtocell access point can use the backhaul connection to access the clock of the clock on the network of the operator. There are problems with this method because this form of Femtocell synchronization can suffer delays resulting from the varying delays introduced by the Internet. The use of the Internet connection to provide timing suffers from two main disadvantages: Variable delays of packets and timing information which reduces the Femtocell synchronization. This becomes more pronounced the further the Femtocell is located from the clock. Bandwidth required can be significant, especially if the precision is low because the synchronization process has to be performed on a more regular basis.GPS timing for Femtocell synchronization: GPS is now widely used, not only for navigation but also as a very accurate source of timing. GPS receivers for timing applications are widespread and cheap to include in Femtocells. However GPS has the disadvantage that when used within buildings the signal suffers significant levels of attenuation and may often not operate.To overcome the Femtocell could be located by a window, or it may be possible to install and external antenna, but this makes installation more complicated and expensive.TV transmitters for Femtocell synchronization: In many countries are able to receive terrestrial television transmissions at good strength. Also as they are broadcast at frequencies below 1GHz, they are able to penetrate buildings well. Accordingly many of these transmissions can be used to provide a reference source for the Femtocell synchronization.Television receivers suitable for providing Femtocell synchronization can be built into Femtocells quite cheaply, and in fact cost less than a GPS receiver. As a result they can represent a very cost effective solution. [12]

5 APPLICATION OF FEMTOCELL5.1 Bringing Mobile Life Home, Bringing Home Life to MobileFemtocells are strategically located in the home and they are the only devices that are part of both the home network and the operators network. As such, they can play a crucial role in the home by bridging mobile and home devices and enabling a new class of tightly-converged services.In this respect, Femtocells have the potential to become game-changing devices. And they can change the big game, namely that of the connected digital home. In fact, in the fierce battle to determine which device will be the center of the digital living room of tomorrow, Femtocells has several advantages over other contenders such as the PC, the set-top box, the router/home gateway, and the media gateway.Specifically, Femtocells have seven characteristics that set them apart from all other devices in the home. Because of these characteristics, Femtocells have the potential of becoming the center of the digital home user experience. By providing the most natural bridge between mobile and wired worlds both at home and away, Femtocells can deliver user experiences in the home that are intrinsically and seamlessly mobile. [13]The new class of femtozone services takes advantage of these unique enablers provided by the Femtocell. In addition to creating new services, it is possible to smoothly integrate the Femtocell with existing mobile and fixed-line service platforms, so that its presence in the home can be used to also enhance existing services. Different service can be provide at home mobile by Femtocell Family Alert Service:When a family member arrives home or leaves, the Femtocell automatically sends an SMS message. For example, a parent at work can be notified that their child has arrived home from school. Virtual Home Number:A home phone number that rings on all the handsets at home when a call comes in to that number. Media Synchronization: Ability to synchronize music tracks and video clips automatically between a mobile handset and a home PC. Photo Upload:Ability to upload photos automatically from the handset to a home PC when handset arrives home and display the photos to a digital picture frame. Contact/Calendar Synchronization:Ability to synchronize handset calendar or contacts with home personal and family calendars/contacts every time the handset arrives home. Remote Control:Abilityof the mobile phone to function as a remote control for home devices (DVR, DVD, TV) when it is in the home. Mobile Video:Ability to stream videos from DVR/DVD player directly to your mobile phone. Family Tablet:Ability to enable a group of family communication features on an in-home display to show the geographic locations of household members, display household calendar and reminder messages, access voicemail and text messages, and store and display pictures from the mobile phone. Point-of-Sale promotion:Femtocells in retail spaces allow merchants to detect customers presence and provide welcome messages, coupons, and store directory services. Virtual PBX:In an office setting, the Femtocell combined with IP-PBX software on the corporate network can make mobile phones into virtual extensions on the office phone system. Service integrating Electrical Home Appliances: It will be possible to control electrical home appliance utilizing registered users presence notification. [14] Emergency Services Support One of the most important requirements for a Femtocell is the support for emergency calling services, which is known in North America as e911. When the mobile user makes an emergency call, an emergency service is dispatched to users current location as soon as possible. Whether the call is made from a mobile handset or a fixed-line phone, the call is directed to a Public Safety Answering Point (PSAP) that handles the geographic region in which the call was initiated. For a fixed-line call, in most cases, the street address of the fixed-line phone is known, so an emergency dispatch (e.g. police) is sent immediately to that address. When a call originates from a mobile phone, the location of the user is in most cases less certain. In North America, it has become mandatory for mobile phones to support location identification for e911 calls, so they can report the users location to the PSAP with a high degree of accuracy. Other countries are adopting similar requirements for emergency calling from mobile devices. To support emergency services, Femtocells provide critical information to the mobile operator core network, such as the location of the caller to identify the nearest PSAP and a call back number to call the user in case of a disconnection. Femtocells support emergency services even for those users who are not authorized to use the Femtocell. [4]

5.2 Green Benefits of Femtocell Operators are to meet the growing demand for mobile data, the only way they will be able to achieve this in an environmentally-sustainable manner will be to use Femtocells. This is because Femtocells typically consume less power per user both in terms of their manufacture and their operation. Energy efficiency is not just important for corporate social responsibility. By deploying Femtocells in the right place, operators can save millions of dollars on their energy bills. Energy efficiency depends on the population density and subscriber density. The Mobile VCE found that in most scenarios, the introduction of Femtocells reduces the power consumptionper user. For instance, if a macro cell supports just 30 users (e.g. a rural setting); the average power consumption per user is 4.4 watts. If they complement this macro with Femtocells, the power consumption drops.If 10% of customers within the Macrocells footprint had a Femtocell, the overall power consumption would drop to 3.6 watts per user. If 70% or more have Femtocells, the average power consumption over all users falls to 2.8 watts.This modeling does not presume that Femtocells are a direct replacement for Macrocells. In fact, as more Femtocells are added, the Macrocell must remain on, radiating power, to support users that cannot be connected to a Femtocell (such as those that a driving).A similar curve, though less steep, exists for a Macrocell with 60 users (3.4 watts per user when provided by macro only). It becomes more energy efficient (2.8 watts) when there are upwards of 40% of users with Femtocells.In really dense areas, such as 240 users per macro cell, the energy efficiency canincreasewhen more Femtocells are used. A small number of Femtocells results in drop in energy consumption, while a large proportion of Femtocells see a small rise in total energy consumption. [15]

Figure 5.1: energy consumption comparison between Femtocell and Macrocell5.3 Self Optimizing NetworkIncreasingly complex networks require increasingly sophisticated management. The development of self optimizing network technology addresses many of the issues created by explosive growth in mobile data traffic by enabling networks to think for themselves.A self optimizing network (SON) is a network that automatically configures and optimizes itself during operation, reducing the need for manual intervention. Each base station or node effectively works out its own response to changes in demand and environmental conditions and new base stations are configured in a plug and play manner.There are several reasons why operators are excited about the potential of SONs: Installing or upgrading a network is a time consuming process. Customers will use a wide variety of technologies (small cells such asFemtocellsand picocells as well as Wi-Fi) to access network services, which makes it difficult to get a complete picture of how the network is performing and manage demand accordingly. Operational costs account for about three-quarters of the total cost of maintaining a network. SONs allows operators to roll out new networks much more quickly, bringing the economic and social benefits of modern communications to markets that would previously have been too expensive to address and because so many of the processes no longer require physical intervention from engineering staff, the environmental footprint of the network is massively reduced. [16]5.4 Femtocell as Payment ToolBy using Femtocell one can use his mobile as an electronic wallet. The idea of using mobile to pay for low value items (under 20.00) without having to key in a PIN (Personal identity Number) is appealing. A Femtocell ratcheted down to this level could be an ideal way of authenticating a mobile payment. When a mobile is touched onto the Femtocells payment pad, the handset would see the femto as the strongest signal, and it would be handed over from the macro network. As soon as this has happened, presence information is sent to the presence server, which contains the handsets unique IMEI identity. When authenticated, the Femtocell then sends the payment request to the merchant clearinghouse or to an operator-run prepaid account. Because there is only one channel, only one handset can make a payment at any one time.The distinct advantage of this approach is that anyone with a 3G phone could make the mobile payment. Secure entry: The same technology would also be ideal for providing secure authentication to access buildings or events. For instance, consider a theatre company with a number of venues. Instead the audience buying tickets online, printing them off, and staff at the theatre having checking each ticket by hand, a handset could be used to authenticate attendees.A Femtocell at the entrance door or turnstile would request the information via the web-based APIs to identify the mobile number. It matches this information with its own database of ticket purchases (and the mobile number associated with the purchase) and allows the gate to open. As such, it is not being used for payment; it is being used for secure access. No printing of tickets, no barcode scanners and whats more one will know who comes into the building because it will recorded the time of when they enter and their mobile number. That will allow the event promoters to send them an exclusive invitation to a VIP room or to meet the stars of the show.This same authentication process could provide secure entry into buildings or campuses. And if anyone wants a second level of authentication for restricted areas, a small app on the handset could match the PIN or, in future, a biometric application.Alternatively, a Femtocell payment pad could be built into a parking meter. Rather than the cumbersome SMS payments or calling an IVR and having to key in your credit card, femto payment would the ultimate in convenience, even better than carrying around a bag of loose change. [17]

6 CONCLUSIONFemtocells are now an integral part of the development strategy for cellular telecommunications operators. Not only do Femtocells provide additional advantages for users in terms of improved performance within the home, or business office, but they also provide the possibility for additional services and the promise of lower charges. They also offer the change of convergence where a single phone can be used instead of the landline as well as for roaming. For operators they provide a cost effective manner in which they can improve their coverage and gain extra revenue by the provision of additional services. Accordingly the use of Femtocells will become a mainstay in the cellular telecommunications roadmap for the future.

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