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© The University of Sheffield, Professor T. O’Farrell 31/05/15

Energy Metrics and Figures of Merit for Planning EE Communication Networks

Professor Timothy O’Farrell Chair of Wireless Communications Department of Electronic and Electrical Engineering The University of Sheffield, UK

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Third ETSI Workshop on ICT Energy Efficiency and Environmental Sustainability, 3-5 June 2015, Sophia-Antipolis, France.

Presentation Outline •  Introduction •  Remarks on current EE framework •  A new EE framework – Figures of Merit & Metrics •  Radio Access Network case studies

•  Macrocell densification •  Microcell densification •  HetNets vs. Small Cells

•  Conclusions

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Introduction •  Energy consumption is a concern in communication

networks, in particular in cellular mobile radio networks. •  Despite intense global research since 2009, there still

isn’t a consistent evaluation framework for unambiguously comparing the EE of different network topologies for network planning purposes.

•  For example, a question pertinent to 5G – “For best EE should only small cells be deployed or HetNets?” largely remains an open question!

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Current EE Framework Essentially, one joint “EE metric and figure of merit (FoM)” has emerged – the Energy Consumption Ratio (ECR). E is energy consumed, M is data volume The rational being EE relates useful output (bits) to energy consumed (J). Then, EE is measured in various forms:

ECR ! E

MJ Bit−1 EE = 1

ECR= ME

Bit J−1

EE = M /TE /T

= SP= Throughput

Power

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Remarks •  Initially, E was the transmitted signal energy; later total

energy to account for the equipment overhead energy. •  T is a common observation or coherence period. •  The EE calculated depends on how S and P are defined

and where and when they are measured. •  Some concerns when comparing networks:

•  As E is total energy, E(M) = ECR x M is problematic (e.g. M = 0); •  Between two network topologies, does the network with the

largest EE consume the least energy if the data volumes differ (i.e. M2 ≠ M1)

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New EE Framework

RAN1

RAN2

E1

E2

{E1{o} M1 T | T1, P1, A1, n1, α1, C1}

{E2{o} M2 T | T2, P2, A2, n2, α2, C2}

O/P

Ene

rgy

I/P E

nerg

y

Dat

a vo

lum

e

Obs

erva

tion

Tim

e

BTS

Tx

dura

tion

BTS

cov

erag

e ar

ea

Num

ber o

f BTS

s

Tota

l BTS

Pow

er

BTS

Loa

d fa

ctor

BTS

mea

n ca

paci

ty

α i = Ti T {i = 1,2}

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Figures of Merit (FoM) •  Consider a FoM based on the ratio ECR1:ECR2

•  This suggests three essential FoMs

ECR1ECR2

= EE2EE1

= E1 M1

E2 M 2

= E1E2

× M 2

M1

Energy Ratio ER = E1

E2

, Throughput Ratio TR = M 2

M1

Joint Energy Throughput Ratio ETR = ER ×TR = E1

E2

× M 2

M1

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Remarks on FoM •  ER compares energy consumption definitively. •  TR compares data volumes definitively. •  ETR is a joint FoM which compares energy consumption

if and only if TR = 1 (i.e. M2 = M1) since for this condition ETR = ER.

•  Therefore, comparing network designs based only on EE defined in terms of ECR is problematic.

•  We now require metrics for ER, TR and ETR.

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Metrics (Homogeneous, 1-sector cell plan) •  For ETR:

•  For TR:

since •  For ER:

T = M1 n1α1C1

= M 2 n2α 2C2

⇒ TR = M 2

M1

≡ S2 A2S1 A1

Si =α iCi {i = 1,2} and n2 n1 = A1 A2

ER = ETRTR

= E1E2

≡ P1 A1P2 A2

ETR = ECR1ECR2

≡ P1 S1P2 S2

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Metrics

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RAN Case Studies

Poh = Pac + Pbh + ns ⋅ Pps + Ppu{ }

Pbts =αPrh + Poh 0 ≤α ≤1

Prh = ns ⋅na Ptrx +Ptx

ηpa ⋅ηcl

⎧⎨⎪

⎩⎪

⎫⎬⎪

⎭⎪

C = B log2 1+1

αSIRmin

+ mkdγ N

GPtx

⎛

⎝

⎜⎜⎜⎜

⎞

⎠

⎟⎟⎟⎟

Cbts =1A

CdAA∫

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Macrocell Densification

Macrocell Baseline

ER TR ETR

RA

N E

R

RA

N T

R

RA

N E

TR

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Microcell Densification

Macrocell Baseline

ER TR ETR

RA

N E

R

RA

N T

R

RA

N E

TR

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Small cells vs HetNets

HN1 = Macro + Micro HN2 = Macro + Pico HN3 = Micro + Pico 10 MHz Macrocell benchmark

ER

TR

ETR

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Conclusions •  Designing for EE RANs requires at least three FoMs (ER, TR and ETR) as

determined by three metrics (P/A, S/A and P/S). •  Having an accurate power consumption model of the network equipment

(including backhaul) is essential to the design process. •  IMEC/Greentouch power models (www.imec.be/powermodel) released 18 June 2015 -

Power model for today's and future base stations.

•  And of HetNets vs. small cells? •  HetNets (as in adding small cells to existing macrocell infrastructure) is more about

increasing capacity rather than reducing energy consumption. •  Replacing macrocells with small cells can reduce energy consumption (up to a point) as well

as increase capacity.

•  Some next steps: •  Combining our analysis with ETSI ES 203228 in a Switzerland case study; •  Adding cost km-2 as an additional FoM and metric.

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Thank you Questions? Acknowledgements: 1.  Simon Fletcher, NEC Telecom MODUS, Leatherhead, Surrey, UK. 2.  Konstantinos Samdanis, NEC Laboratories Europe, Heidelberg, Germany. [1] T. O’Farrell and S. Fletcher, “Green Communication Concepts, Energy

Metrics and Throughput Efficiency for Wireless Systems,” Green Communications: Principles, Concepts and Practice, First Edition, Edited by Konstantinos Samdanis, Peter Rost, Andreas Maeder, Michela Meo and Christos Verikoukis. © 2015 John Wiley & Sons, Ltd. Published 2015 by John Wiley & Sons, Ltd. (in print)

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