Femtocells: Technologies, Standards and Applications

1 IEEE ComSoc Ft Worth & Dallas DLT© 2012 Mischa Dohler

Mischa DohlerCTTC, Spain

IEEE ComSoc Distinguished Lectureship TourFt Worth & Dallas ComSoc Chapters

19 November 2012Slide template is copyright of BeFEMTO. All rights reserved.

Femtocells: Technologies, Standards

and Applications


Drivers & Vision


Smartphones Cause Capacity Crunch

© Thierry Lestable, Sagemcom

home homeoffice

80% Indoors20% Outdoors


The Resulting Capacity Demand Prediction


Total worldwide mobile traffic by 2020: more than 127 exa-bytes (10^18) more than 30 times increase compared to today

Total mobile traffic (EB per year)

-

20.00

40.00

60.00

80.00

100.00

120.00

140.00

2010 2015 2020

Yea

rly

traf

fic in

EB Europe

Americas

Asia

Rest of the world

World

Source: IDATE


IMT-A 4G capacity targets [ITU-R M.2133]: 2.2b/s/Hz for downlink and 1.4b/s/Hz for uplink in urban deployment supported rate is thus maximal 100Mbps/km2 (500m cell size; 40MHz)

Capacity needs (reality check): peak density of 8,000 people/Km2 of which only 10% subscribe to the broadband service of which only 20% require access at the same time each requiring 5Mbps

4G requirements … … were short by a factor of 10 yesterday … are short by a factor of 50 today … will be short by a factor of 100 tomorrow

City Average People/Km2

Athens 5,400

Madrid 5,200

London 5,100

Barcelona 4,850

Warsaw 4,300

Naples 4,100

Berlin 3,750

Paris 3,550

Vienna 3,400

8,000 X 10% X 20% X 5Mbps = 800 Mbps/Km2

Are we prepared to meet this capacity demand?


Addressing Capacity Needs in the Past

Increase in capacity over past decades: Martin Cooper: doubled every 30 months over past 100 years overall: million-fold increase in capacity since 1957

Breakdown of these gains: 5 x PHY; 25 x spectrum; 1600 x reduced cells, 5 x rest

Breakdown of (estimated) cost:

Reduced Cells MHz

Reduced Cells MHz PHY

[HOT - TOP 3 IEEE DOWNLOAD IN APRIL 2011] Mischa Dohler, R.W. Heath Jr., A. Lozano, C. Papadias, R.A. Valenzuela, "Is the PHY Layer Dead?," IEEE Communications Magazine, vol 49, issue 4, April 2011, pp 159-165.

Ratio Gain/CostMost Important!

http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5741160


Trend confirms: Link-Layer won’t help

© Avneesh Agrawal, Qualcomm


Time for Major Design Changes

To facilitate the exponential capacityincrease, dramatic changes to how

we design cellular systems are needed!

… oh, and, yes, spectrum is not a problemand power efficiency neither …


Going 5G: Change in Design Paradigms

1. Differentiate clearly between outdoors and indoors design

20% of time 80% of time

Similar data experience outdoors & indoors important!



2. Put most efforts on architecture and management thereof



3. Acknowledge heterogeneous nature of wireless arena



4. Use absolute area capacity rather than spectral efficiencies

heterogeneous spectrum use users care about rates



5. Cost considerations must be taken into account at design phase


Outline of Talk (all very high-level!)

A. Indoors Femtocell B. Manage Through SON


A. Femtocells


The Small-Cell Solution Space

Only viable solution is via change in architecture & smaller cells: Remote Radio Head: “dumb” radio extension of BS; often RF/IF/BB-over-fiber Relay: wireless radio extension of BS; often limited intelligence Pico Cell: intelligent BS; owned, planned and placed by operator Femto Cell: intelligent BS; mostly owned and placed by consumer; no planning!

© Josep Vidal, UPC


Definition & Differentiation Of Femtocell

Femtocell Picocell WifiSite Rental customer operator customer

Installation customer operator customer

Electricity Bill customer operator customer

Radio Planning no (local) yes (prior & global) no

Backhaul Connection via customer dedicated via customer

Macrocell Interaction not (yet) yes not applicable

Transmission Power < 23dBm 23-30dBm 20dBm

Access Rights mainly closed public closed

Handover possible yes vertical

Photo

©Sagem, TID © bandaancha.eu© 3g.co.uk


The Femtocell Opportunity

)))

Energy

Security

Comfort

Health

Ethernet

WiFi

3G/LTE

FMC & Multimedia

Micro-generationMicro-generation

ADSL, FTTH, …

1. Smart Digital Home:

2. Reduces Customer Churn:

3. Allows Traffic Offload:

4. Energy Saver For All:


© Femto Forum, Thierry Lestable, Sagemcom

© Femto Forum, Thierry Lestable, Sagemcom

© Mobile VCE, D. Laurenson


Finding Femtocells Very Appealing

© Femto Forum


Femtocell Technology Providers

The ecosystem is now mature enough© Thierry Lestable, Sagemcom


Femtocell Rollouts & Deployments To-Date

36 commercial deployments in 23 countries15 roll-out commitments in 2012


Femtocells Business Model

In BeFEMTO, four business cases are investigated:

- One off fee: the user pays 50€ once, and the monthly payment does not change (35€/month)

- No fee: the user does not pay for the femtocell, and the monthly payment does not change (35€/month)

- Decrease: the user does not pay for the femtocell, and the monthly payment decreases by 5€ to 30€/month

- Increase: the user does not pay for the femtocell, and the monthly payment increases by 5€ to 40€/month

32$/month

159$ one off

250$ one off

5$/month

255$ one off+42$/month

free of charge

10$/month

180$ one off+1.5$/month

199€ one off10€/month15€/month

100€ one off+8€ /month

50£ one off+5£/month

© BeFEMTO


Femtocell Market Growth Forecast

© Informa Telecoms & Media© Thierry Lestable, Sagemcom


Related Fora & Standards Bodies

Small Cell Forum (before Femto Forum) not-for-profit, founded 2007, rebranded 2012 manufacturer-driven main driver behind femtocell uptake

3GPP IWLAN & EPC standards (for Non-3GPP Access & Mobility) H(e)NB standards (for Basic FemtoCells) LIPA & SIPTO standards (for Local Access & Offloading) ANDSF Standards (for Discovery, Selection & Policy) LIMONET (for LIPA Mobility), SaMOG(for Trusted WiFi), BBAI (for Broadband Network interworking)

IEEE/WFA/WBA Hot Spot 2.0 (Discovery & Seamless Access Control)

GSMA WLAN Task Force (2003?) WiFi Offload White Paper, April 2010 GSMA-WBA Joint Task Force –WiFi Roaming White Paper, Jan 2012

© Prabhakar Chitrapu, InterDigital


Femtocell Design Challenges

1. Low Device Cost: efficient, low-cost power amplifiers, highly sensitive receivers, flexible channel bandwidth, reliable RF

filters; low cost and low power implementation; etc.

2. System Interference Management: minimize interference to macro (and vice versa); minimize interference to adjacent femtos; coping with

unplanned rollouts; coverage estimation, interference cancellation; etc.

3. Femtocell Capacity Maximization: link and access management (handover, admission control, resource management, load balancing and

flow control); dynamic bandwidth allocation and sharing; etc.

4. Backhaul Issues: wired or wireless backhaul, reducing signaling load, QoS provisioning and traffic priorization, joint access

and backhaul design; etc.

5. Viable System Architecture: control & data planes, access control, authentication, local breakout, efficient forwarding, seamless

mobility, zero-config, etc.

© BeFEMTO


Problem Of Interference With Femtos

Source: Zubin Bharucha, DOCOMO Euro-Labs


Rel-10 ICIC In Heterogeneous Networks

To support femtocell deployment effectively, inter-cell interference coordination (ICIC) is necessary

Different from homogeneous network (macrocell deployments), o Low power nodes (femto eNBs) must mute (or reduce transmission

power) Named as “Protected resources” hereo High power nodes (macro eNBs) need not muteo Named as “Non-protected resources” here

Protected/Non-protected resources are multiplexed in frequency or time-domain Both ICIC techniques are effectively supported in Rel-10

Cell layer

Time

Frequency

Femto layerMacro layer

Frequency-domain ICIC

Car

rier

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Frequency

Time

Cell layer

Time-domain ICIC

Car

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1



LTE-A Control & Data Frame Structure

• data region interference mitigation (a lot of work with viable solutions)• control region interference mitigation (surprisingly little work given it is

the actual problem since no control means no data)Source: Zubin Bharucha, DOCOMO Euro-Labs


LTE-A Detailed Control Frame Structure

• The control region contains 3 control channels:– PCFICH: control frame indicator; occurs only on first OFDM symbol;

scattered in frequency domain; indicates size of control region– PDCCH: downlink control channel; spread in time and frequency;

carries scheduling information– PHICH: HARQ indicator channel; spread in time and frequency;

contains HARQ information• Focus on the performance of the first two because of differences in their

distribution patterns – the PCFICH has restricted positions in the time domain, whereas the PDCCH is dispersed in the time and frequency domains



LTE-A Control Interference - Current Approaches

(a) •No coordination

Heavy interference on 2 OFDM symbols

(b)• Femto control channel sparseness

Interference to first OFDM symbol is lowered

(c) •Almost blank subframe

Only interference from reference symbol

Femto data transmission is not allowedSource: Zubin Bharucha, DOCOMO Euro-Labs


Novel Femto-Macro ICIC Approach [1/4]

The proposal from DoCoMo Euro-Labs advocates carefully selecting the Physical Cell Identifier (PCI) of HeNBs at start-up, such that any interference caused by their control channels to the PCFICH of any trapped macro UEs is avoided.o In order for this to be possible, the HeNB needs to identify the eNB that it is

closest to. Identifying the eNB means that the HeNB must be aware of the PCI of the eNB

(decoded using synchronization procedure).

Illustration onlySource: Zubin Bharucha, DOCOMO Euro-Labs


Qualcomm Proposition in BeFEMTO for Resource Partitioning in Space for Femto-Macro Interference Mitigation:

Problem Statement: proper resource partitioning is a must to handle femto-macro interference beam selection in MIMO-enabled femto BS equipment could be made use of

Innovative Proposition: design of suitable coordinated beam selection algorithm following LTE codebook designs comparative study between different restriction and codebook policies study outcomes: codebook restrictions yields gains to macro users at low femto capacity loss

Novel Femto-Macro ICIC Approach [4/4]

50% improvement @ macro

5% deterioration @ femtoSource: Qualcomm, BeFEMTO


B. Self-Organizing Networking

34© 2012 Mischa Dohler IEEE ComSoc Ft Worth & Dallas DLT

Capacity-Optimal Schedule?

With femtocells, the degrees-of-freedom (DOF) increase significantly – and with it complexity! [presented by Interdigital: Globecom’11 – IWM2M, Houston]


System Degrees of Freedom

High number of femtos/users/resources/etc + interference constraints -> Problem of DOF

Degrees of Freedom (DOF) / Area: new system DOF = old system DOF x 20-30 new system density = old system density x 4 new DOF/km2 = old DOF/km2 x 100


SON Is The Only Solution

SON Helps For Previously Manual Processes: reduce manual intervention for deployment savings automate repetitive processes examples: automatic planning & self-configuration

SON Helps For Too Fast/Complex Processes: improve run-time operation based on real-time data automate optimization of critical network elements example: self-optimization & self-healing

Among the many possible approaches, we deal with cognitive/docitive RRM to facilitate SON.


SON In Cellular Networks


Important SON Tradeoffs


From cognitive to docitive networking paradigms: cognition: “system which is working under conditions it was not designed for” docition: “teaching” between expert nodes to accelerate learning/cognition result: truly autonomous SON with quick convergence

SON Through Cognition/Docition


Cognitive Approach – Q-Learning

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),( 12 asQ ),( 2 lasQ

),( 1asQ k ),( lk asQ

...v ),( 1avQ ),( lavQ

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FOR each (s, a) DO

Initialize table entry: Observe current state s

WHILE (true) DO

Select action a and execute it

Receive immediate cost c

Observe new state v

Update table entry for Q(s,a) as

follows

State transition from s to v

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Nodes operate in a distributed and autonomous fashion but exchange suitable parts of their Q-Table:

Docition Approach – Exchange of Q-Entries

Input State

Output Action

pxy

Startup Docition. Docitive femto BSs teach their policies to newcomers joining the network.

IQ-Driven Docition. Docitive radios periodically share part of their policies with less expert nodes with similar gradient.


Macrocell capacity as function of femtocell density:

Performance – Superior Capacity


CCDF of average SINR at macrouser for a 50 % occupation ratio:

Performance – Superior Convergence Precision


Convergence speed improves by order of magnitude from 20,000 (cognitive) to 4,000 (docitive) iterations:

Performance – Superior Convergence Speed


C. Future Challenges


Conclusions on Femto Cells

Heterogeneity Is Quickly Increasing:femtos, networked femtos, wifi, m2m, etc, etcfuture use outdoors, mobile, in relay formallow for viable QoS/QoE delivery

Self-Organizing Networking Will Be Key:distributed localized SON (important for signaling) standards compliant SON approaches for industry uptaketake energy constraints into account

Business Models subscriber models FON-like approaches


Conclusions on Femto Cells

Data Traffic: 40% @Home 35% On the Move 25% Work

© BeFEMTO & Thierry Lestable, Sagemcom

Femtocell rollouts of the future:

Documents

Femtocells: Technologies, Standards and Applications