Femtocells: Introduction and Research Issues

ByDharma P. Agrawal

Ohio Board of Regents Distinguished Professor of Computer ScienceOhio Board of Regents Distinguished Professor of Computer ScienceDirector, Center for Distributed and Mobile ComputingDirector, Center for Distributed and Mobile Computing

Computer Science DepartmentComputer Science DepartmentUniversity of Cincinnati, Cincinnati, OH, 45221University of Cincinnati, Cincinnati, OH, 45221--00300030

Tel: 513Tel: 513--556556--47564756EE--mail: mail: dpa@cs.uc.edudpa@cs.uc.edu, , www.cs.uc.edu/www.cs.uc.edu/~dpa

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 voice communication

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 without any signal inside buildings because of high frequency radio 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 base station 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 . Femtocells acquired the name because they are much smaller than the standard Macrocell cellular towers

n Each of Femtocells works with the major wireless telecommunications standard and connects users with cellular provider via broadband Internet links

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Telephone Core Network

difference

Femtocell Interfaces

n Air InterfaceUMTSCDMA2000WiMax LTE (Long Term Evolution based on 3GPP) ("Home eNode B")

n Internet InterfaceDSLCable

Vodafone Gateway

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Femtocells Architecture

Another alternative architecture 8One alternative architecture

Why Femtocells?

Benefits For Cellular Users

n Better coveragen Higher capacityn Lower transmit powern Prolong handset battery lifen Higher signal-to-interference-plus-noise ratio (SINR)

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Why Femtocells?

Benefits for Cellular Providers

n Improved Macrocell BSs reliabilityn 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 benefitsn But, no additional revenue

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Femtocell Development

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

n In 2007, vendors formed the Femto Forum to promote femtocell use

n In 2008, Sprint Nextel released home-based 2G femtocell built by Samsung Electronics that works with any Sprint handset

n In 2009, Verizon and Vodafone rolled out their femtocell 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 MacrocellAir interface Telecommunication

standardTelecommunication

standard

Backhaul Broadband Internet Telephony network

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

Cell phonePower consumption

low high

Radio Range 10-50 meters 300-2000 meters

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

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 via broadband IP networks

n UMA provides access to mobile voice and data services over unlicensed-spectrum technologies such as WLAN

Femtocell UMA

Spectrum licensed unlicensed

Phone Mode Single mode Dual mode

Air interface Cellular technology

WLANtechnology

Backhaul Broadband Internet

BroadbandInternet

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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 Evolution based on 3GPP) and Mobile WiMax system

Power controlFrequency 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 latency guarantees

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

n Cellular provider can not control voice data priority unless internet backhaul belongs to the same company

n Don’t forget! Originally, broadband internet is for WLAN 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 accessProvide service to anyone who pass nearby

n Closed accessA fixed set of home users are licensed to use femto

n Hybrid accessresources are reserved for registered family users

and others are open for roamers

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Self-Configuration & Self-operation

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

n A configuration function should be capable of adjusting parameters under various environments

n Self-operation is needed in WiMax network. For example, Handover and radio resource management (RRM) are directly controlled by Macrocell BS and Femtocell 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 2008n Verizon did in January of 2009n Vodafone released in July of 2009n More operators in 2008: O2, Softbank,

TeliaSonera, and Vodafonen AT&T announced testing in Raleigh and

Charlotte as of 28 October 200925

Limitations

n Currently MIMO Femtocells

MIMO Femtocells can switch between providing high data rates and robust transmission

n Security problemFemtocells backhaul are local ISP networks, which

are different from cellular network and can be accessed by anyone, including hackers

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Other Issues

n Adaptive power control

Sprint’s AIRAVE femtocell uses adaptive power control for cross-tier interference

n Emergency Call & Location Tracking

Government required 911 call service with location information

n GPS inside femtocellsn Location information over backhaul

n Pay for Femtocell provider as well as Internet service provider

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References

n Journal and Conference Papersn http://www.femtoforum.orgn http://www.airwalkcom.com/n Vodafone Homepagen Sprint Homepage

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Conclusions

n Observation: Femtocell provides good indoor access and fills the voids, but no additional revenue to service provider

n 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 Questions??dpa@cs.uc.edu

Future of 4-G???