UMTS Femtocell Wireless Gateway

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UMTS Femtocell as

Wireless Residential Gateway


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CONTENTS

1. Abstract 4

2. Introduction 4

3. Key Business Drivers for UMTS Femtocell 4

4. Networks Integration Models 5

5. Key Challenges 6

6. Competition and Threats 7

7. Aricent Edge 7

8. Summary 8

9. References 8


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1. ABSTRACT

Mobile operators today are trying hard to overcome the challenges

posed by intense competition in the wireless communication space.

There is an ever-increasing demand from operators to increase

ARPU while decreasing cost. New competitors entering the market

are posing a big threat to existing players apart from the alternative

technologies such as Voice over WiFi. Vendors are under intense

pressure to come up with innovative solutions for providing better

quality and coverage to mobile subscribers at lower cost.

The discussion about UMTS based Femtocell (also called 3G

Access Point`) that is doing rounds for quite sometime to counter

the challenge posed by unlicensed access technologies like WiFi

and WiMAX. The concept is of a UMTS Femtocell is to make a

UMTS NodeB cheap enough to be deployed for residential use by a

very limited number of users. This NodeB is connected to the

backhaul network via subscribers broadband connection and is

deployed in huge volumes. This would deliver the same services to

a subscriber as other alternative technologies and, most importantly,

would use the existing UMTS handset, with no need to upgrade to a

dual-mode handset.

While there are several challenges faced by vendors in making sucha system like network integration, security, provisioning, radio

interference and cost; solutions to these problems exist enabling the

vendors and operators to build a strong and viable business case for

low cost UMTS Femtocell. The subscriber gets a benefit of reduced

call costs, increased quality and convenience of using an existing

UMTS handheld device. The operator benefits by increase in ARPU

and customer loyalty.

This paper takes a closer look at the key business drivers in this

space as well as advantages/opportunities available with the

operators and vendors in this nascent market. The paper also

captures the key challenges that need to be focused on for

developing a Femtocell solution viable for mass-market deployment

and the various network integration models for the Femtocell.

2. INTRODUCTION

WCDMA is an interference-limited technology, in which the cell

capacity is limited by the interference caused by transmission from

each user in the cell. To increase cell capacity, all transmissions

(from base station as wellhandsets) are kept at minimum transmit

power. However, in the in-building coverage area, there is significant

attenuation of the radio signal from the macro cells, which results in

the lower voice quality and higher call drops for CS services and

lower user data rate for PS services. To maintain the QoS, UMTS

indoor users causing significant interference to the outdoor users,

thereby further reducing the macro cell capacity.

UMTS operators believe that the killer applications for their networks

in future would be the high bandwidth streaming applications like

IPTV, video telephony, movie-on-demand. Studies indicate that

majority of usage of these applications would be when the user is

indoors. Clearly, there is a compelling requirement for mobile

network operators for providing an effective coverage for these

applications where it is needed the most inside the buildings.

Using a UMTS femtocell in the home environment will help

minimizing the transmit power levels both for the femtocell and the

UE as there would be a significant decrease in the signal

attenuation. The lower output power from the UE will reduce the

interference generated while decreasing the drain on battery. High

signal attenuation through walls further reduces the impact of

interference of the indoor traffic on the outdoor environment.

A few years ago, an indoor base station would have seemed

impossible especially because of the lack of appropriate hardware

and also considering the impression of a typical base station. Todaythe reality is different, with different companies thinking seriously

about developing an extremely low-power femtocell (home base

station), of size comparable to an existing WiFi access point and a

price of less than $200. It is predicted that there will be 102 million

worldwide users on 32 million home base stations by 2011 [1].

Overall, UMTS has a tremendous potential to take up a significant

share of this indoor wireless access market.

3. KEY BUSINESS DRIVERS FOR UMTS FEMTOCELL

What are the business drivers for this kind of solution? To answerthis, consider the following points:

. Competiion: Mobile Operators today are under tremendous

pressure of balancing the relentless technology advances and

new services with increasing costs, reducing revenues and

growing competition from other service providers. As mobile and

fixed-line markets become saturated and voice revenues decline,

the home is the primary focus for capturing market share by

offering attractive service bundles: voice, data and television as

the so-called triple play. Mobile access adds another dimension for

some

. Backward Compatbility: This solution does not require the

subscriber to purchase an expensive dual-mode handset for

getting indoor and outdoor coverage from a single handheld

device


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. Threat from voice over IP, voice-over-WiFi: The threat from

unlicensed technologies, which are currently eating up the

revenue share of licensed spectrum operators, will get reduced if

cheaper wireless coverage can be provided indoors

. Threat from wireless technologies like WiMax: WiMax based

solutions, which are able to provide higher data rates than UMTS

are also gaining ground for indoor wireless access market but

UMTS have some clear advantages over WiMax. Apart from being

able to work without requiring a dual-mode handset, UMTS would

be able to provide better security on the radio interface and a

unified billing solution to the subscriber for outdoor and indoor

access

. Increased Network Coverage and Capacity: Providing high QoS

in indoor coverage from macro/micro cells has inherent limitations

due to a significant radio signal path loss that happens while

permeating walls. The indoor solution will be much better

equipped to provide a better coverage and high QoS (due to

reduced path loss). At the same time, if the UMTS Femtocell takes

care of the bulk of traffic generated by indoor users, the load on

macro network will get eased significantly. This would simplify the

RF Planning issues and increase cell capacity for the UMTS

macro network. Increased Customer Loyalty: A customer that purchases a

femtocell will not abandon the operators service so easily. Apart

from creating a psychological barrier, there are other benefits to

the customer, such as improved in-home coverage, improved

in-home data rates, and cheap or maybe free calls. If a femtocell

can deliver on these benefits, the probability of a subscriber

switching the service provider will reduce significantly

4. NETWORK INTEGRATION MODELS

An operators Femtocell network must be connected into its mobile

core to interconnect the Femtocell user to the PSTN and people on

the operators macro network. Several options are available for

network integration. Each option comes with a tradeoff in terms of

scale (proprietary gateways and UMA) and/or time to market (IP Iub

and IMS). The best option will depend on an operators existing

network capabilities and their network evolution roadmap. Some of

the network integration models possible have been described here:

. Iub over public IP: This architecture is quite similar to the existing

3G-network architecture where each femtocell (equivalent of

NodeB) is connected to the RNC over an IP interface as shown in

figure below. The Iub signaling takes place over an IP network.

Network security can be handled by the IP security (IPsec)

protocol between the femtocell and the security gateway node.

This architecture is suitable for operators who have an existing

UMTS infrastructure deployed and are looking for a fast

integration of femtocell into this existing infrastructure

Illustration 1: Iub over public IP

. IP Concentrator with standard RNC:An alternative architecture

is possible that uses an aggregator node to connect multiple

femtocells to the existing RNC. The Concentrator node is

connected to the RNC over the standard Iub interface and looks

like a normal Node B

. UMA based network with modified UTRAN architecture: TheUMA approach provides an option of using the existing Core

Network infrastructure while re-architecting the UTRAN to support

the unlicensed spectrum deployment [2]. The interface to the

existing Core Network is through the UMA Network Controller

(UNC), which is the equivalent to an RNC. This concept can be

extended to support a UMTS femtocell through the UNC [3]. The

UMA client function moves into the femtocell allowing any

standard UMTS handset to communicate with the network through

the UMA network. The advantage in this architecture is that it uses

most of the existing network elements and will be able to support

integration of a large number of end-user devices into the mobile

network

Illustration 2: UMA based on modified UTRAN architecture

Mobile Operators Network

ADSLlub over

secured IP

SecurityGateway

lub

Tunneling

RNC

Femtocell

ADSL

Femtocell

luPS SGSN

MSC

Femtocell

Femtocell

luCS

ADSL

Femtocell

Femtocell

ADSL

ADSL

ADSL

ISPNetwork

ISPNetwork

Mobile Operators Network

ADSLUMA

Signalling

UNC

UMTS

Femtocell

UMTS Femtocell

UMTS Femtocell

UMTS Femtocell

UMTS Femtocell

UMTS Femtocell

ADSL

luPS SGSN

MSCluCS

ADSL

ADSL

ADSL

ADSL

ISP

Network

ISP

Network


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. IMS core based with Integrated RNC, SGSN and GGSN:

Illustration 3 shows another approach that moves away from the

existing network architecture completely to an all-IP network

defined in 3GPP IP Multimedia Subsystem (IMS). The voice is

carried using Voice over IP (VoIP) protocol using Session Initiated

Protocol (SIP). The RNC and packet core functionality is now fully

integrated into the femtocell and the Gateway node, which

enables proper interworking with the IMS or a pre-IMS core

network. The SIP signalling can happen directly between the IMS

core and IMS enabled handset in which case the UMTS Femtocell

just provides the UTRAN and packet core functionality. In case UE

is not SIP enabled, the Femtocell shall additionally function as an

IMS client and terminate the SIP signalling on behalf of UE. The

Femtocell shall then interwork the IMS session towards the IMS

core to a standard CS Call on the Radio side towards the UE. The

main advantage of using this architecture is that it doesnt need

the packet core infrastructure, which might get congested in an

eventual large-scale deployment of femtocells. This approach is

more suitable as a long-term strategy in the femtocell evolution

path

Illustration 3: IMS based architecture

5. KEY CHALLENGES

Like any new technology, the femtocell space is also facing a

number of challenges. The ones that are concerning operators and

vendors the most for a successful commercial deployment of

femtocell, are discussed below:

. Subscriber BoM cost: Pricing of the femtocell needs to be kept in

the range of $200 or even lesser to make it a viable FMC solution.

This is not going to be an easy task considering its typical

performance requirements (4 HSPDA/HSUPA users with

cumulative data rate above 1 Mbps).

. Network Integration Model: The network integration model

adopted for femtocell (some models shown above) will also play a

key role in enabling easier integration with existing network

infrastructure while at the same time being able to meet the end

user requirements.

. Upgrades: With the new technologies like HSUPA evolving over a

period of time, a femtocell has to be made upgradeable to support

these new requirements. This can be achieved by relying on

software-defined radio or DSP based solutions but it has cost

implications associated with it.

. Access Control: The radio access cannot be open to everyone in

the coverage area of a femtocell. The subscriber would pay for the

femtocell installation and backhaul (lets say DSL) access charges,

therefore the subscriber would need to have an option to control

the set of users (UEs) authorized to make or receive calls through

that femtocell. Anyone else should be barred from using the

services of that femtocell. This kind of access restriction

mechanism is not provided by the standard UMTS protocols and

therefore some innovation is required to make this happen.

. RF Planning: The RF planning needs to be done very carefully for

deriving the desired benefits from femtocell environment. While aseparate carrier for the femto environment may help mitigate

interference with the macro network, this option may not be

available with operators who are tight on the allocated spectrum

and want to maximize the capacity by frequency reuse. Other

consideration could be the use of such scrambling codes that are

not in use in the neighboring cells. Configuration of scrambling

codes from the operator could be a problem because of the

ad-hoc nature of femtocell deployment. The femtocell could

emulate the UE behavior to listen the neighbor cell environment

and read the primary scrambling codes of the cells around to

select a scrambling code that is not in use

. Network Planning: Network configuration with respect to

allocation of cell identifiers, location and routing area identifiers

etc. to the femtocell needs to be done in such a way that it does

not create integration issues with the core network. Careful

planning is also needed for providing seamless handover and

mobility between the femtocell and macro network. These

aspects, if not taken care properly, can create operational issues

or the UMTS network operator

. Radio Resource Management: The radio resource management

strategy and algorithms need to be developed specifically for the

indoor deployment model. Smart algorithms need to be defined

which enable high radio resource utilization and better service

(lower call drops, higher QoS, seamless handovers) while

minimizing the interference to the neighboring environment

ADSL

SIP Enabled UE

SIP Signalling

Gateway

UMTSFemtocell

UMTS Femtocell

UMTS Femtocell

ADSL

UMTS Femtocell

ADSL

ADSL

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. Radio Emission Aspects: Radio Emission levels in the indoor

environment needs to be kept much lower to avoid any

undesirable impact on human beings. This is achievable due to

much lesser signal attenuation in the indoor environment, which

requires both the UE and the femtocell to transmit at very low

power for achieving good signal strength on the receiver side. This

actually leads to a safer radio environment as compared to macro

network environment and there is a need for educating the end

users for whom the idea of an indoor base station might create

some amount of fear.

. Automatic Configuration: It will be necessary for the femtocell to

get configured, seamlessly connected with the subscribers ISP

network and operators core without requiring much manual

intervention either from the subscriber or from the operator. This

plug-and-play feature is needed firstly to enable the subscriber to

install a femtocell in his/her home independently without any

hassles and secondly for lowering the operators customer support

cost.

. Customer Support Model: Though the customer expectations of

providing support for a residential access point have been

minimized by WiFi access points, still there would be some

requirement for diagnosing the problems that could occur in afemtocell. Network monitoring tools need to be put in place to

ensure that a femtocell is able to deliver good coverage and

reliable service to the end user without which the operator will not

be able to get the maximum value from such deployment.

. Security Aspects: Registration and authentication of the

femtocell need to be carried out in some way to provide a secure

connection with the core network through subscribers ISP

network. This could be achieved by including a SIM in the

femtocell, which will store the subscriber identity and subscription

preferences. Authentication can take place when the femtocell is

powered on and tries to connect with the backhaul network. There

could be other ways of achieving the same results depending

upon the operators deployment scenario

. Regulatory Restrictions: Mechanism needs to be provided in the

femtocell to adhere to regulatory restrictions imposed in a

geographical location/country For example, before the femtocell

starts radio transmission, it needs to ensure that the carrier

frequency/band could be used in that geographical location. The

location where the end user purchases the femtocell cannot be

used for this purpose since the user can easily carry the femtocell

to a distant location/country and try to install the device in that

location

. Synchronization: There is a requirement of timing accuracy of

0.1 parts per million (ppm) for picocells as per the 3GPP Release

6 specifications [7] . A severe synchronization and accuracy

requirements, such as this, can make the equipment costly and

therefore, unviable. Some innovative mechanism for providing

synchronization needs to be in place until there is a relaxation for

picocells in future versions of the 3GPP standards or an operator

specific relaxation is provided.

6. COMPETITION AND THREATS

The competition to the UMTS Femtocell market from other

technologies like Voice over WiFi, WiMAX, UMA is for real.

. Time-to-Market: The existing WiFi based solutions have got a

major head start in terms of product development, trials, marketing

etc. Potential Femtocell vendors need to start with an aggressive

development plan and a marketing campaign to overcome this

lead and position their product credibly with a fast

Ztime-to-market.

. High Speed Packet Data Services: WiMax, which uses a

much-advanced radio interface with higher spectral efficiency,

poses a big threat to the UMTS space for the residential market as

well. WiMax technology, although theoretically boasting of

supporting up to 75 Mbps of peak data rate per 20 MHz channel,

might be able to provide a real world performance of around 45

Mbps in some fixed broadband applications [8] . The introduction

of HSDPA and HSUPA channels in UMTS is

trying to overcome this threat to some extent but the data rates

achievable in WiMax still remain much higher as compared to

UMTS.

7. ARICENT EDGE

Aricent has more than 20,000 man years of telecom experience and

expertise in different wireless systems to help vendors in

architecting and developing femtocell solutions that have viable

deployment scenario and a faster time-to-market. Aricent has

developed a strong partnership with different eco-system vendors to

keep ahead of the evolving standards and provide quicker solutions

to OEMs.

Aricent service offerings in the Femtocell space includes:

. Technical consulting - Migration to newer technologies, Defining

and selecting right architectures

. defining system architecture including system module definition,

interface definition, definition for MIB, fault management,

performance management, system dynamic behavior for a high

availability solution.

. designing high-level and low-level architectures for call control,

resource management, user plane protocols and applications


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. Product development Compltete end-to-end software

development, feature development

. development of high availability, carrier grade solutions for

UMTS Access Network nodes

. Testing Test automation, system integration, interop testing

. Integration of Femtocell with 3rd party UE (both Test UE & actual

UE) to execute functional test scenarios

Extensive Load, Soak & Performance Testing experience in the

UMTS domain

Aricent IPRs in the Femtocell space include:

. Control Plane Stacks RANAP, RNSAP, NBAP, RRC,RLC,

MAC, MAC-es, MAC-hs, MAC-e

. Transport Place Stacks SS7 stacks- SCCP, MTP3-

B/SAAL-NNI, M3UA/SCIP, ALCAP, SAAL-UNI

. User Plane Stacks Iu-UP, Iub-FP, Iur-FP, GTP-U, PDCP

8. SUMMARY

Every solution being conceived or developed will bring its own

complexity and challenges. A mature solution to meet these

challenges is evolving and industry experts are expecting the UMTS

to come as a front-runner in the indoor solution.

9. REFERENCES

. http://www.telecomredux.com/index.php?option=com_content&

task=view&id=3478&Itemid=35

. Kineto Wireless, The Role of UMA in Mobile Network Evolution,

White Paper, August 2006

. Kineto Wireless, The Case for UMA-Enabled Femtocells, White

Paper, August 2006

. 3GPP TS 25.104,Base Station (BS) radio transmission and

reception (FDD)

. http://www.wimax.com/education/faq/faq38

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UMTS Femtocell Wireless Gateway

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