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Femtocell Technology 1

1. INTRODUCTION

Can you hear me now? was a popular phrase for a while amongst

people who were mocking the poor sound and coverage of their mobilephones. Although it turned into something of a joke, its no laughingmatter when your cell phone suddenly loses its ability to allow you toenjoy clear communication. Unfortunately, this is often the case in homesand buildings where coverage decreases considerably as soon as you goindoors. Since more and more people are ditching their landlines in favorof mobile phones, as well as because of the simple fact that people wantto be able to talk on their cell phones wherever they are, it has becomenecessary to work on new technology that will facilitate calling coverage

both indoor and outdoor. Femtocell technology could be the answer. Inaddition to facilitating better indoor call coverage, this emergingtechnology reduces the drain that advanced mobile services (such asmobile broadband) are placing on the capacity offered by phonecompanies.

One of the solutions that people have started to use is femtocelltechnology. This technology may be better known to the user as anAccess Point Base Station, a small device which is installed in the home

or office in order to offer better support to mobile phones there. Thesebase stations can accommodate up to five cell phones which means thatyou can get increased coverage for your whole household. Essentially,you set up the femtocell technology in your home and it serves toenhance the cell phone signal that you receive indoors so that your callquality isnt decreased when youre talking indoors. Now many operatorssuch as AT&T, Sprint and Verizon in USA, Vodafone in UK are

providing Femtocell service.

Dept. of ECE Govt.Engg College, Sreekrishnapuram

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2. NETWORK ARCHITECTURE

Connecting femtocells to existing operator networks requires a network

architecture that addresses the security needs of operators and mobileusers, while supporting the scalable deployment of millions offemtocells. In addition, it must allow ordinary consumers to install themwith plug-and-play simplicity and ensure that critical services such asemergency calling are also supported with the same reliability andaccuracy as fixed-line emergency calling. The femtocell networkarchitecture describes the major nodes and connections in a femtocellnetwork, and how they achieve the objectives of mobile subscribers andoperators. The femtocell network architecture supports the following key

requirements:

Service Parity: Femtocells support the same voice and broadbanddata services that mobile users are currently receiving on themacrocell network. This includes circuit-switched services such astext messaging and various voice features, such as call forwarding,caller ID, voicemail and emergency calling.

Call Continuity: Femtocell networks are well-integrated with themacrocell network so that calls originating on either macrocell or

femtocell networks can continue when the user moves into or outof femtocell coverage. Femtocell network architecture needs toinclude the necessary connectivity between the femtocell andmacrocell networks to support such call continuity.

Security: Femtocells use the same over-the-air securitymechanisms that are used in macrocell radio networks. Butadditional security capabilities need to be supported to protectagainst threats that originate from the Internet or through tamperingwith the femtocell itself. Femtocell network architecture providesnetwork access security, and includes subscriber and femtocellauthentication and authorization procedures to protect againstfraud.

Self-Installation & Simple Operational Management:Femtocells are installed by end-users. Therefore, the femtocellnetwork architecture must support an extremely simple installation

procedure with automatic configuration of the femtocell andautomated operational management with zero-touch by the end-user.


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Scalability: Femtocell networks can have millions of access points. Therefore the femtocell network architecture must bescalable to grow into such large networks, while at the same timemaintaining reliability and manageability.

Figure 1: Deployment of Femtocell

Elements of the Femtocell Network Architecture

As shown in Figure 2 there are three network elements that are commonto 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 areentities that enable connectivity to the mobile operator core. Dependingon the specific architecture used for circuit switched calls, there can beeither a Femtocell Convergence Server (FCS) or a Femtocell NetworkGateway (FNG). This is also shown in Figure 1. For packet calls,depending on the airlink technology, there can be either a PDSN or xGSN(GGSN/SGSN) in the core. In most cases, the PDSN / xGSN are the same

as those used for macro networks.


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Figure 2: Common Components of Femtocell Network Architecture

Femtocell Access Point (FAP)

Femtocell Access Point is the primary node in a femtocell network thatresides in the user premises (e.g., home or office). The FAP implementsthe functions of the base station and base station controller and connectsto the operator network over a secure tunnel via the Internet.

A FAP can be introduced into a home in multiple ways. A standaloneFAP can be directly connected to the home router. In some applications,the FAP may also include a built-in router, which is useful in prioritizingFAP voice traffic over other Internet traffic in the home network. Moreadvanced FAPs include an Analog Terminal Adapter (ATA) to connect afixed-line phone. In some cases, FAPs are full-blown residentialgateways with built-in Wi-Fi and a broadband modem (xDSL, cable).


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Security Gateway

The security gateway is a network node that secures the Internetconnection between femtocell users and the mobile operator corenetwork. It uses standard Internet security protocols such as IPSec andIKEv2 to authenticate and authorize femtocells and provide encryptionsupport for all signaling and user traffic.The security gateway supports a large number of femtocells connecting tothe operators network. While similar to traditional VPN gateways usedin enterprises, femtocell security gateways are designed for use in carriernetworks and meet carrier-grade requirements such as scalability, highavailability, and network management.

Femtocell Device Management System

The femtocell management system, also located in the operator network, plays a critical role in the provisioning, activation and operationalmanagement of femtocells using industry standards. The managementsystem is perhaps the most critical node in ensuring the scalability of afemtocell network to millions of devices.

To ensure low-cost deployment and easy setup for subscribers, theactivation and provisioning of the femtocell must be plug-and-play with

no on-site assistance (sometimes called a truck roll) required from themobile operator.

FCS or FCG

The FCS or FNG enables femtocells to connect to the operator corenetwork. This is important for the operation of femtocells as this is whatallows femtocells to communicate with the core elements in theoperators networks and allow seamless service for the mobile. Forexample, basic call setup requires communicating with the MSC andPSTN of the operator core. The FCS or FNG allows this to happen.Depending on the specific architectural model used to support Circuit-

Switched Services the FCS /FNG can be used.

PDSN / xGSN


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The PDSN / xGSN enable femtocell users to receive packet data services

over the mobile operators core. In most cases, these will be the same asthose used by the mobile operators macro network.


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3. WORKING OF FEMTOCELL

Femtocells are sold by a Mobile Network Operator (MNO) to itsresidential end-users or enterprise customers. A femtocell is typicallythe size of a residential gateway or smaller, and connects into theend-user's broadband line. Integrated femtocells (which include botha DSL router and femtocell) also exist. Once plugged in, the femtocellconnects to the MNO's mobile network, and provides extra coveragein a range of typically 30 to 50 meters for residential femtocells

(depending on the existing coverage and output power usually20 mW which is five times less than a Wi-Fi router). From an end-users' perspective it isplugand play, there is no specific installationor technical knowledge required anyone can install a femtocell athome.

Femtocell device consists of a radio receiver and transmitter for theconnection between the mobile phone and Femtocell device.It alsohave an Application Specific Integrated Circuit or Digital SignalProcessor to handle the physical connectivity between handsets and

Femtocell and between thefemtocell and the mobile network. Chipmakers design the ASIC or DSP to work with the specific carriersnetwork.The Femtocell consists a host processor which supportssoftware based task such as security,encryption, and connectivity tothe broadband network via Internet Protocol, or technologies such asthe Dynamic Host Configuration Protocol.

The end-user must then declare which mobile phone numbers are allowedto connect to his/her femtocell, usually via a web interface provided by

the MNO. This only needs to be done once. When these mobile phonesarrive under coverage of the femtocell, they switch over from themacrocell (outdoor) to the femtocell automatically. Most MNOs providemeans for the end-user to know this has happened, for example by havinga different network name appear on the mobile phone. Allcommunications will then automatically go through the femtocell. Whenthe end-user leaves the femtocell coverage (whether in a call or not), his

phone hands over seamlessly to the macro network. Femtocells require

http://en.wikipedia.org/wiki/Mobile_Network_Operatorhttp://en.wikipedia.org/wiki/Residential_gatewayhttp://en.wikipedia.org/wiki/Broadbandhttp://en.wikipedia.org/wiki/WiFihttp://en.wikipedia.org/wiki/Plug_and_playhttp://en.wikipedia.org/wiki/Plug_and_playhttp://en.wikipedia.org/wiki/Plug_and_playhttp://en.wikipedia.org/wiki/Plug_and_playhttp://en.wikipedia.org/wiki/Macrocellhttp://en.wikipedia.org/wiki/Mobile_Network_Operatorhttp://en.wikipedia.org/wiki/Residential_gatewayhttp://en.wikipedia.org/wiki/Broadbandhttp://en.wikipedia.org/wiki/WiFihttp://en.wikipedia.org/wiki/Plug_and_playhttp://en.wikipedia.org/wiki/Macrocell

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specific hardware, so existing WiFi or DSL routers cannot be upgraded toa femtocell.

Once installed in a specific location, most femtocells have protection

mechanisms so that a location change will be reported to the MNO.Whether the MNO allows femtocells to operate in a different locationdepends on the MNO's policy. International location change of afemtocell is not permitted because the femtocell transmits licensedfrequencies which belong to different network operators in differentcountries.

One of the key elements of the femtocell configuration occurs at the firststart up when the femtocell equipment is being installed. It is essentialthat this operates smoothly for the concept to gain acceptance by the user.

After acquiring a femtocell the customer should only need to plug thefemtocell into the power and connect it to the Internet connection to

provide the backhaul connection.

With power applied, the first element of the registration is for thefemtocell to register within the network. When a user makes a call insidethe range of Femtocell, the mobile phone uses its radio to connect to theFemtocell. The Femtocell will attempt to gain access to the core network

via the gateway. Femtocell is connected to the Security gateway viawired connection to the users broadband, typically DSL or cable. Toachieve this it will utilize the femtocell ID - a unique identifier given tothe each femtocell. Additionally the operator is likely to have obtainedthe address where the user will base the femtocell.

The connection between the femtocell and the femtocell host processoruses secure IP encryption (IPsec), which avoids interception. Additionalfunctions are also included such as some of the RNC (Radio NetworkController) processing, which would normally reside at the mobileswitching centre. Some femtocells also include core network element sothat data sessions can be managed locally without needing to flow backthrough the operators switching centre (local break out).

The extra capabilities of a femtocell demand it to be self-installing andself-configuring. This requires considerable extra software which scansthe environment to determine the available frequencies, power leveland/or scrambling codes to be used. This is a continuous process to adapt


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to changing radio conditions, for example if the French windows areopened in a room containing the femtocell.

Within the operators network, femtocell gateways aggregate large

numbers of femtocell connections (typically 100,000 to 300,000) whichare first securely connected through high capacity IP security firewalls.


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4. ADVANTAGES

Standalone or integrated femtocells

Early femtocell products look very much like Wi-Fi broadband modems,needing only two cables - one for power and one internet connection.

Several vendors such as Thomson, Netgear, Pirelli, Cisco and others haveintegrated the femtocell with other features such as DSL modem, Wi-Fi

and even IPTV into a single box. It is expected that in the longer term,most femtocells will be sold in this form.

Low power but high quality

Femtocells operate at very low radio power levels - less than cordlessphones, Wi-Fi or many other household equipment. This substantiallyincreases the battery life, both on standby and talk time. Since they are somuch closer to the handset or mobile device, call quality is excellent and

data devices can operate at full speed. Standard units can handle up to 3or 4 simultaneous calls from different users depending on the model.Larger femtocell designs intended for business (enterprise) use canhandle 8, 16 or even 32 concurrent call.

Secure and self-managing

The femtocell encrypts all voice and data sent and received from mobile phones and would normally not allow access to the home computernetwork, so external users cannot break into your computer.

In order to reduce cost, these units are self installing and use a variety ofclever tricks to sense which frequency to transmit on and power level touse.

Unlike outdoor mobile phone base stations (masts), femtocells don'trequire specialist RF planning engineers to design, calibrate or configurethemselves - minimizing the ongoing cost of maintaining them. They do


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have remote management from the network operator, who can upgradethe configuration and software as required.

Doesn't require special phones

They are compatible with existing standard mobile phones, although infuture some minor enhancements would allow clear indication of whenthe phone is using the local femtocell (and thus using a free callallowance) - currently this can be provided by tones at the start of eachcall.

Local Breakout

Femtocells also support a feature known as local breakout, which allowsa femtocell user to connect their mobile devices to the local home oroffice network without traversing the mobile operators core network.For traffic destined to the global Internet, local breakout also bypasses theoperator core network, thus reducing the network load.

Figure 3:block diagram of local break out

Emergency Services Support

One of the most important requirements for a femtocell is the support foremergency calling services, which is known in North America as e911.When the mobile user makes an emergency call, an emergency service isdispatched to users current location as soon as possible.


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Whether the call is made from a mobile handset or a fixed-line phone, thecall is directed to a Public Safety Answering Point (PSAP) that handlesthe 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 thataddress. When a call originates from a mobile phone, the location of theuser is inmost cases less certain. In North America, it has becomemandatory for mobile phones to support location identification for e911calls, so they can report the users location to the PSAP with a highdegree of accuracy. Other countries are adopting similar requirements foremergency calling from mobile devices.

To support emergency services, femtocells provide critical information tothe mobile operator core network, such as the location of the caller toidentify the nearest PSAP and a callback number to call the user in caseof a disconnection. Femtocells support emergency services even forthose users who are not authorized to use the femtocell.

Fixed Mobile Convergence

Fixed Mobile Convergence (FMC) is the trend towards seamlessconnectivity between fixed and wireless telecommunication networks. Ittries to provide optimum transmission of all data, voice and video

communication to and among users. Existing FMC services require dualmode (cellular/Wi-Fi) handsets that work with the unlicensed spectrumwireless access points. But Femtocell based FMC services are available atexisting handsets.


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5. CHALLENGES

Femtocell developers are facing several issues that require immediateattention such as,

Privacy and Security

Interference

Regulatory issues

Femtocell security risks and measuresThere are a number of concerns that exist about femtocell security. Bycategorizing the femtocell security concerns it is possible to address themand ensure that any risks are minimized.

User privacy: Since a variety of data bout the user, including thevoice calls and data themselves pass over the Internet. As a result itis necessary to provide security for these IP communications and

prevent any monitoring of the data. Fraud and service theft: This form of femtocell security

addresses the scenarios where unauthorized users connect to thefemtocell and use it in an unauthorized fashion. This may be doneto avoid being charged for calls, or to transfer the costs of the callsto the authorized femtocell user. This would clearly givesignificant adverse publicity which would not be wanted by theoperator

In 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 ismaintained across the Internet IPsec or IP security is used. TheIPsec standard is a widely used standard defined by the InternetEngineering Task Force (IETF).

Femtocell Secure Authentication: Authentication is required by both the service provider and operator to ensure that validfemtocells are connecting to the core network. Additionally


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femtocells need to be correctly identified within the network.Femtocell security procedures using SIM cards authentication orX.509 are used.

Wireless link security: The wireless link is an area where

femtocell security is needed to ensure that unauthorized users donot connect or take over the femtocell. Techniques includeensuring that the femtocll coverage area does not exceed the

physical area where the femtocell is to be used. EAP, Extensible Authentication Protocol: This form of

protocol is used in a number of wireless networks and its use hasbeen proposed for providing femtocell security.

Interference

Due to limited spectrum available to operators, macrocells andfemtocells may share at least one frequency in order to increaseefficiency of spectrum use, which will result in interference and noisein network. Closely placed Femtocells may also create interferencedue to unplanned deployment. In order to obtain better performance,interference mitigation methods has to be employed, such as

Adaptive pilot power control: In this system Femtocell detectthe signal from surrounding cells and dynamically adjust its

own transmitter power while still aiming to maintain itscoverage area.

Dynamic Femtocell receiver gain management: In order thatFemtocell can satisfactorily operate with mobiles, anappropriate form of automatic gain or attenuation control must

be installed. This will keep any increase in noise or interferenceminimum.

Regulatory issues

Since Femtocell work on a licensed spectrum, it requires regulatoryapproval before commercial roll out, which varies from country tocountry. Development of such related policies will decide the deploymentof Femtocell.


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6. COMPARISON WITH MACROCELL

Macrocell is a cell in a mobile phone network that provides radiocoverage served by a powerful cellularbase station (tower).The antennas for macrocells are mounted on ground-based masts,rooftops and other existing structures, at a height that provides a clearview over the surrounding buildings and terrain. Macrocell base stationshave power outputs of typically tens of watts.

To be broadly successful, Femtocells need to perform the same functionmeasured in capacity per square meteras a macro cell. So, to besuccessful as a replacement technology, our femtocell would need todeliver the same capacity (voice calls or data bits) per square mile for thesame cost. Using a simple example where we only look at basic costs(ignoring other lifecycle costs, such as operation and maintenance), itfound that a femtocell could be slightly more cost efficient than amacrocellular network, if it delivered.The advanced femtocells do already provide a cell size of 100 m radius

about the same coverage as modern Wi-Fi. Super femtocells are beingdesigned to provide the higher capacity solution that was needed to servemore than just the Home market.

Parameters FFemtocell MacrocellAir interface Telecommunication

standardTelecommunicationstandard

backhaul Broadband internet Telephony network

cost $200/year $60000/year

Cell phone powerconsumption

Low High

Radio range 30-50 meters 300-2000 metersSize small large

Table 1: comparison between femtocell and macrocell

The figure 4 shows the probability of achieving a given data rate inindoor for Femtocells and for Macro network. The horizontal axis shows

http://en.wikipedia.org/wiki/Mobile_Phonehttp://en.wikipedia.org/wiki/Mobile_Phone

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the air link data rate and the vertical axis represents the probability thatthe requested data rate exceeds the value in the horizontal axis. Eachcurve represents thousands of measurement points.

The figure demonstrates that Femtocell provide high indoor data rate withsignificantly greater consistency than do Macrocell. It also shows that therelative improvement in performance and in coverage within the home forFemtocell over Macrocell. The probability of achieving high speedthroughput within the home drops precipitously for Macrocell coverage.

Figure 4: indoor data rate comparison between Femtocell and Macrocell

For example, femtocell provides effective air link indoor data rate of 1

Mbps in over 95% cases, while Macrocell provides fewer than 5% cases.


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7. APPLICATION

1. The Domestic applications of FEMTOCELL technology in a

condensed residential area.

The same characteristics as a crowded shopping centre or CBD may beapplied here. Due to condensed living spaces, the demand for cellularnetwork connections and data transfer (for internet etc) is constantlyincreasing.

One cellular tower may be able to handle the majority of the traffic butduring peak times it may lag or slow dramatically. Then you also have

problems with connecting in some poor coverage areas. This may be dueto objects or structures decreasing the signal strength.

3G networks supply high speed internet connections to those using it. Italso improves the quality of voice calls over a mobile phone. With theassistance of a cellular provider or an ISP, a Femtocell router or two can

be placed in appropriate spots where the load is significantly more.

This connection can be paid for through either the strata or TelcoCompany providing the connection. These routers could easily take thedemand and as the cost to purchase and install one is about the same as adomestic wireless router.

Condensed living always present problems for telecommunications but itcan be overcome by practically apply domestic level products to areaswhere it is needed the most. This would save the cost of both your back

pocket and health of having a second communications tower installed in

an attempt to cover the black spots.

2. Poor coverage areas and the application of FEMTOCELL to take

the load.

As it says, applying FEMTOCELL to areas such as behind hills,mountain valleys or gullies and areas where a signal would be less thannormal. Mountains, gullies and other poor coverage areas could be taken


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advantage of and with only one or two FEMTOCELL routers could havethe same connection quality as an inner city CBD.

Smaller remote towns will benefit from this technology if Telcocompanies choose not to install cell towers in poor coverage areas.Examples can include small remote town businesses or groups of

businesses, cattle stations, truck stops and remote highway outlets. Asyou can see with a landline internet connection any location can becomea small domestic cell tower.


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9. REFERENCES

1. Wireless Industry Begins to Embrace Femtocells-SixtoOrtiz Jr.,IEEE Computer Magazine, July 2008

2. A Self Organized Femtocell for IEEE 802.16e System-Published by IEEE Communication Society,2009

3. Performance Analysis of UMTS Femtocells-MehmetYuvuz,FarhadMeshkati and SanjivNanda,IEEEcommunication society, September 2009

4. Interference Management in UMTS Femtocells Publishedby Femto Forum , February 2010


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