femtocell in 3g systems

Femtocell in 3G (CDMA2000 and UMTS)

EE5517

FEMTOCELLS IN 3G (CDMA2000 AND UMTS)

March 28, 2011

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ABSTRACT

In 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 operator’s 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.

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Contents Page

1. Introduction 1

1.1 Aim and Objectives of the Project 1

1.2 Introduction to Femtocell 1

1.3 Femtocell Benefits 2

1.4 Femtocell Deployment 5

2. Femtocell Network Architecture 6

2.1 Common Elements of the Femtocell Network Architecture 6

2.2 Architectural Models to Support Circuit-Switched services 9

2.2.1 SIP/IMS Network Model for Femtocell 10

2.2.2 Legacy Network Model for Femtocell 12

2.3 Interworking with Packet Data Networks 13

2.4 Local Breakout 14

3. Femtocell Radio Technology 15

3.1 Radio Requirements 15

3.2 Femtocell Interference 16

3.2.1 Interference Scenarios and Avoidance through Frequency

Planning 16

3.2.2 Interference Mitigation in Co-Channel Femtocell

Deployment 17

3.3 Femtocell Access Control 19

3.4 Seamless Mobility across Femtocell-Macrocell Boundaries 20

3.4.1 Mobility in Standby Mode 20

3.4.2 Handover 21

4. Other Issues Facing Femtocell 24

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4.1 Quality of Service 24

4.2 Security issues 24

4.2.1 Security Vulnerabilities 25

4.2.2 Security Measures 25

4.3 Power and Health Issues 25

4.3.1 Femtocell Power Levels 25

4.3.2 Health Issues Research 26

4.4 Spectrum Synchronization and Accuracy 26

5. Application of Femtocell 29

5.1 Bringing Life Home and Bringing Life to Mobile 29

5.2 Green benefits of Femtocell 31

5.3 Self Optimizing Network 32

5.4 Femtocell as Payment Tool 33

6. Conclusions 34

7. References 35

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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 Femtocell

Femtocells 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 operator’s 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]

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Figure 1: Overview of a Femtocell network [1]

1.3 Femtocell Benefits

Femtocells 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-user’s 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. It’s clear more and more consumers want to use mobile phones in the home,

even when there’s a fixed line available. Friends and family usually call a mobile number first, and

it’s 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 user’s 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]

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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 Operator’s

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

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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.

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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 Deployment

According 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

by Verizon Wireless and AT&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 by Cisco Systems and was the first 3G Femtocell in US,

supporting both voice and data HSPA. 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, Softbank launched

its residential 3G Femtocell service in January 2009 with 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 by Huawei 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]

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2 FEMTOCELL NETWORK ARCHITECTURE

The 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.

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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

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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 FAP’s include an Analog Terminal Adapter (ATA) to connect a fixed-line phone. In

other cases, FAP’s 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 operator’s 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

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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 operator’s 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 operator’s core. In most cases, these will be the same as those used by the mobile

operator’s macro network.

2.2 Architectural Models to Support Circuit-Switched Services

Macrocell networks consist of a radio network and a core network. The radio network is

made up of base stations, base station controllers (BSC’s) 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.

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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

operator’s 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 HLR’s 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

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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 CSCF’s 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

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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 Femtocells

In 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 MSC’s. 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 MSC’s 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 MSC’s 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]

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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/GGSN’s in UMTS and PDSN’s in CDMA. In CDMA networks, Femtocells

can connect to the PDSN directly via the security gateway. This is possible because existing PDSN’s

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

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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

operator’s 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]

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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 Requirements

From 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]

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3.2 Femtocell Interference

Interference 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 Planning

A 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.

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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

21


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

22


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 Control

In 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

23


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 Mode

A 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

24


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/Handoff

Femtocell 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

25


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.

26


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 device’s 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

device’s 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]

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4 OTHER ISSUES FACING FEMTOCELL

4.1 Quality of service

When 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 operator’s 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 Issues

There 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.

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4.2.1 Security Vulnerabilities

There 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 Measures

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 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 Issues

There 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 levels

The 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

29


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 Research

A 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 Accuracy

There 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.

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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]

31


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]

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5 APPLICATION OF FEMTOCELL

5.1 Bringing Mobile Life Home, Bringing Home Life to Mobile

Femtocells are strategically located in the home and they are the only devices that are part

of both the home network and the operator’s 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.

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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: Ability of 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 user’s 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 user’s 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 user’s

location to the PSAP with a high degree of accuracy. Other countries are adopting similar

34


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 consumption per 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

can increase when 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]

35


Figure 5.1: energy consumption comparison between Femtocell and Macrocell

5.3 Self Optimizing Network

Increasingly 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 as Femtocells and

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]

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5.4 Femtocell as Payment Tool

By 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

handset’s 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 what’s 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]

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6 CONCLUSION

Femtocells 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.

38


7 REFERENCES

[1] Femto Forum, “About Femtocells: what is Femtocell,” Femto Forum, 2010. [Online]. Available:

http://www.femtoforum.org/femto/aboutFemtocells.php [Accessed: Mar 20, 2011].

[2] Ian Poole, “Femtocell Tutorial Basics” Jan 2010. [Online]. Available: http://www.radio-

electronics.com/info/cellulartelecomms/Femtocells/femto-cells-tutorial-basics.php [Accessed: Mar

20, 2011].

[3] Geralds, “Femtocell”, Wikipedia.com, last para, Mar 17, 2011. [Online]. Available:

http://en.wikipedia.org/wiki/Femtocell [Accessed: Mar 22, 2011].

[4] Woojune Kim, “Femtocell Network Architecture,” Airvana Corp., Chelmsford, MA, USA, May

2010. [Online]. Available:http://www.airvana.com/technology/Femtocell-network-architecture

[5] Ian Poole, “Femtocell Network Architecture” Jan 2010. [Online]. Available: http://www.radio-

electronics.com/info/cellulartelecomms/Femtocells/femto-cells-network-architecture.php

[Accessed: Mar 21, 2011].

[6] Pierre Humblet and Andy Richardson, “Femtocell Radio Technology,” Airvana Corp., Chelmsford,

MA, USA, May 2010. [Online]. Available: http://www.airvana.com/technology/Femtocell-radio-

technology

[7] 3rd Generation Partnership Project, “Pico- and Femto cell System Requirements,” 3GGP, 2010.

3GPP2 S10-20070913-002r1 [Accessed: Mar 19, 2011].

[8] Ian Poole, “Femtocell Interference” Jan 2010. [Online]. Available: http://www.radio-

electronics.com/info/cellulartelecomms/Femtocells/femto-cells-interference.php [Accessed: Mar

19, 2011].

[9] Ian Poole, “Femtocell Handover/handoff” Jan 2010. [Online]. Available: http://www.radio-

electronics.com/info/cellulartelecomms/Femtocells/femto-cells-handover-handoff.php [Accessed:

Mar 21, 2011].

[10] Ian Poole, “Femtocell Security” Jan 2010. [Online]. Available: http://www.radio-

electronics.com/info/cellulartelecomms/Femtocells/femto-cells-security.php [Accessed: Mar 19,

2011].

[11] Ian Poole, “Femtocell Public Health Issues” Jan 2010. [Online]. http://www.radio-

electronics.com/info/cellulartelecomms/Femtocells/femto-cells-health-issues.php [Accessed: Mar

20, 2011].

39


[12] Ian Poole, “Femtocell Synchronization and Spectrum Accuracy” Jan 2010. [Online]. Available:

http://www.radio-electronics.com/info/cellulartelecomms/Femtocells/femto-cells-synchronization-

synchronisation.php [Accessed: Mar 19, 2011].

[13] Pierre Humblet, “Femtocell Radio Technology,” Airvana Corp., Chelmsford, MA, USA, May

2010. [Online]. http://www.airvana.com/technology/femtozone-applications/

[14] www.nttdocomo.co.jp/english/binary/pdf/.../rd/.../vol11_4_019en.pdf

[15] Alcatel-lucent, “Femtocells combat climate change – and reduce the bottom line,” Feb, 2011.

[Online]. Available: http://www.wilson-street.com/2011/02/Femtocells-combat-climate-

change-%E2%80%93-and-reduce-the-bottom-line/

[16] Alcatel-lucent, “How small cells can be good citizens with self organisation,” Feb, 2011.

http://www.wilson-street.com/2010/02/how-small-cells-can-be-good-citizens-with-self-

organisation/

[17] Alcatel-lucent, “Who needs NFC when femtos can do cashless payments?,” Feb, 2011.

http://www.wilson-street.com/2011/02/who-needs-nfc-when-femtos-can-do-cashless-

payments/

40

femtocell in 3g systems

Documents

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