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Femtocells: Introduction

and Research Issues

By

Dharma P. Agrawal

Ohio Board of Regents Distinguished Professor of Computer ScienceOhio Board of Regents Distinguished Professor of Computer Science

Director, Center for Distributed and Mobile ComputingDirector, Center for Distributed and Mobile Computing

Computer Science DepartmentComputer Science Department

University of Cincinnati, Cincinnati, OH, 45221University of Cincinnati, Cincinnati, OH, 45221--00300030

Tel: 513Tel: 513--556556--47564756

EE--mail:mail: [email protected]

[email protected],, www.cs.uc.edu/www

.cs.uc.edu/~dpa
mailto:[email protected]:[email protected]://www.cs.uc.edu/~dpahttp://www.cs.uc.edu/~dpahttp://www.cs.uc.edu/~dpahttp://www.cs.uc.edu/~dpahttp://www.cs.uc.edu/mailto:[email protected]:[email protected]


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Outline

n PART I: Introduction to Femtocells

n PART II: Research Topics

n PART III: Conclusions

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Background

n More people choose mobile handset for all voicecommunication

n More than 50% of voice call and

More than 70% of data traffic

from indoor environment

n Poor voice quality and slow data rates, even withoutany signal inside buildings because of high frequencyradio signals penetrating problem

All traffic Distribution

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What are Femtocells?

n Femtocells, short for femtocell base stations, are

low-power, short-range, low-cost indoor cellular basestation for better coverage and capacity

It is different than Access Point

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What are Femtocells

n The femto in femtocell means 10-15 . Femtocellsacquired the name because they are much smallerthan the standard Macrocell cellular towers

n Each of Femtocells works with the major wirelesstelecommunications standard and connects users

with cellular provider via broadband Internet links

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6

Telephone Core Network

difference


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Femtocell Interfaces

n Air In terface

UMTS

CDMA2000WiMax

LTE (Long Term Evolution basedon 3GPP) ("Home eNode B")

n Internet InterfaceDSL

Cable

Vodafone Gateway

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Femtocells Architecture

Another alternative architecture8One alternative architecture


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Why Femtocells?

Benefits For Cellular Users

n Better coverage

n Higher capacity

n Lower transmit power

n Prolong handset battery life

n Higher signal-to-interference-plus-noise ratio (SINR)

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Why Femtocells?

Benefits for Cellular Providers

n Improved Macrocell BSs reliability

n Offload data traffic from the Macrocell BSs

n Increasing the area spectral efficiency

(total number of active users per Hertz per unit area)n Operating Cost benefits

n But, no additional revenue

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Femtocell Development

n In 2002, a group of Motorola engineers introduced aHome Base Station technology

n In 2007, vendors formed the Femto Forum topromote femtocell use

n In 2008, Sprint Nextel released home-based 2Gfemtocell built by Samsung Electronics that workswith any Sprint handset

n In 2009, Verizon and Vodafone rolled out theirfemtocell network service with 3G standard

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Technology Comparisons

n

Femtocell VS Macrocell

n Femtocell VS WLAN

n Femtocell VS UMA(Unlicensed Mobile Access)

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Femtocell VS Macrocell

Femtocell Macrocell

Air interface Telecommunicationstandard

Telecommunicationstandard

Backhaul Broadband Internet Telephony network

Cost* $200/year $60,000/year

Cell phone

Power consumption

low high

Radio Range 10-50 meters 300-2000 meters

*Analysis, Http://research.analysis.com 13
http://research.analysis.com/http://research.analysis.com/


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Femtocell VS WLAN

Femtocell WLAN (AP)

Spectrum Licensed Unlicensed

MAC layer Conflict-free Contention-based

Backhaul Cable/DSL Cable/DSL

Air interface Cellular standard 802.11a/b/g/n

Range 10-50m 35-70m

Service Primarily voice Primarily data

Current Cost $200-$250 $50-$100

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Femtocell V/S UMA

n Unlicensed Mobile Access(UMA), an IP-based 3GPPstandard for connecting to

mobile networks viabroadband IP networks

n UMA provides access tomobile voice and dataservices over unlicensed-spectrum technologiessuch as WLAN

Femtocell UMA

Spectrum licensed unlicensed

Phone Mode Single mode Dual mode

Air interface Cellulartechnology

WLAN

technology

Backhaul Broadband

Internet

Broadband

Internet

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Outline

n PART I: Introduction to Femtocells

n PART II: Research Topics

n PART III: Conclusions

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Interference Between?

n Femtocell Macrocell (cross-tier)

n Femtocell - Femtocell

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Interference

n In CDMA systemInterference avoidance through time hopping and directional

antennas*

n In the LTE (Long Term Evolut ion based on3GPP) and Mobile W iMax system

Pow er control

Frequency assignment

*Vikram C. and Jeffrey G. A., Uplink capacity and interference avoidance for two-tier Femtocell networks

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Quality of service (VoIP)

n Existing Macrocell networks provide latencyguarantees

n Femtocell backhaul needs QoS for delay-sensitivetraffic and provides enough capacity

n Cellular provider can not control voice data priorityunless internet backhaul belongs to the same

company

n Dont forget! Originally, broadband internet is forWLAN traffic

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Handover???

n Femtocell to Macrocell

n Macrocell to Femtocell

n Femtocell to Femtocell

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Handover

n Frequent and unnecessary Handover

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Synchronization

n Synchronization is for:- Handover- Minimizing multi-access interference- Ensuring a tolerable carrier offset

n Proposed Solution:- Precision timing protocol over IP

- GPS- High-precision crystal oscillators

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Access control

n Open access

Provide service to anyone who pass nearbyn Closed access

A fixed set of home users are licensed to use femto

n Hybrid access

resources are reserved for registered family usersand others are open for roamers

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Self-Configuration & Self-operation

n Femtocell should be a plug-and-play device that canintegrate itself into mobile network

n A configuration function should be capable ofadjusting parameters under various environments

n Self-operation is needed in WiMax network. Forexample, Handover and radio resource management(RRM) are directly controlled by Macrocell BS andFemtocell BS

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Current Deployments

n Sprint started in 3Q/2007 as a limited rollout(Denver and Indianapolis)

n Starhub put in November 2008

n Verizon did in January of 2009

n Vodafone released in July of 2009

n

More operators in 2008: O2, Softbank,TeliaSonera, and Vodafone

n AT&T announced testing in Raleigh andCharlotte as of 28 October 2009

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Limitations

n Currently MIMO Femtocells

MIMO Femtocells can switch between providing

high data rates and robust transmission

n Security problem

Femtocells backhaul are local ISP networks, whichare different from cellular network and can be

accessed by anyone, including hackers

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Other Issues

n Adaptive power control

Sprints AIRAVE femtocell uses adaptive power

control for cross-tier interference

n Emergency Call & Location Tracking

Government required 911 call service with location

informationn GPS inside femtocells

n Location information over backhaul

n Pay for Femtocell provider as well asInternet service provider

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References

n Journal and Conference Papers

n

http://www.femtoforum.orgn http://www.airwalkcom.com/

nVodafone Homepage

n Sprint Homepage

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http://www.femtoforum.org/http://www.airwalkcom.com/http://www.airwalkcom.com/http://www.femtoforum.org/


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Conclusions

n Observation: Femtocell provides goodindoor access and fills the voids, but no

additional revenue to service providern How to minimize interference?

n How to control the access?

n How to provide effective Handover?n How do you ensure security?

n How to charge more money to

customers??29


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Any [email protected]

Future of 4-G???
mailto:[email protected]:[email protected]

Documents

Femtocell 1