Greening Wireless Communications: A Top-Down Overview

Greening Wireless Communications: A Top-Down Overview

Pablo Serrano Dept. Ing. Telemática Univ. Carlos III de Madrid http://www.it.uc3m.es/pablo/

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Motivation: Green all the things

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Global warming CO2 emissions Cost reduction More efficient operation

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Motivation •  Cisco Visual Networking Index: Forecast of mobile data traffic

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Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Energy consumption decomposition

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Serrano, P., la Oliva, A., Patras, P., Mancuso, V., & Banchs, A. (2012). Greening wireless communications: Status and future directions. Computer Communications.

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Timescales

•  Usage pattern

•  Flow

•  Super-frame

•  Frame

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Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Timescale vs. Wireless tech

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Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Timescales

•  Usage pattern

•  Flow

•  Super-frame

•  Frame

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Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Resource on Demand schemes

•  Power on/off the infrastructure as required

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M. Ajmone Marsan, L. Chiaraviglio, D. Ciullo, M. Meo, A simple analytical model for the energy-efficient activation of access points in dense WLANs, in: Proceedings of the first International Conference on Energy-Efficient Computing and Networking, ACM, 2010, pp. 159–168.

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Powering on/off a device

From To Time OFF ON (3 W) 55 s ON OFF (0 W) 5 s IDLE ON < 1 s ON IDLE (1 W) < 1 s

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•  Linksys WRT54GL with OpenWRT 10.03.1

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

System Model: regenerative process

Nh+1 user

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Ton Nl users

≤ Nh sta (≤ K) ≤ 2 K sta

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

System Model

•  Three different chains (BW is shared)

•  Performance figures – Average delay – Power

consumption

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Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Results P = 3.5 W, 2K=10 sta, 0.1 arr/s, ts=10s

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Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Timescales

•  Usage pattern

•  Flow

•  Super-frame

•  Frame

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Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Generalizing the Perf. Anomaly solution

•  Performance Anomaly: a node far away reduces the overall performance

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6 Mbps

4.2 Mbps 0.6 W

4.2 Mbps 1.6 W

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Usual Solution

•  Opportunistic relaying can alleviate the issue, depending on the topology – Based on e.g. Wi-Fi Direct

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14.6 Mbps 1.26 W

7.3 Mbps 0.35 W

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Yet Another Solution

•  Degrees of freedom: the relay can decide how to spend its time: tx, relay, sleep

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4.2 Mbps 0.52 W

4.2 Mbps 0.21 W

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Problem Formulation

•  1 AP, legacy nodes, relay-capable nodes

•  Topology: paths used to reach the AP

•  Schedule: timing of the relays

•  For every topology, find the best schedule

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R R

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Problem Formulation

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•  Throughput •  Power

•  Maximize

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Finding a Solution

•  Scheduling: maximize a concave objective function under a convex set of constraints and thus admits a unique optimum.

•  Topology: combinatorial problem, and efficiently finding the optimal topology does not appear to be possible –  Search, closest, heuristic

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Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Results: 1 legacy, 2 relays

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Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Results: incremental deployment

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•  1 AP, 5 nodes •  Random relays

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Opportunistic Relaying: Challenges

•  Trade-off between throughput (performance) and cost (energy consumption) – Not that much explored – Heterogeneous settings

•  Works in practice, but – Estimate network cond. – Force re-associations, silence nodes

•  Enabler: Wi-Fi Direct? – Not immediate (~5 s)

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D Camps-Mur, A Garcia-Saavedra, P Serrano, “Device-to-device communications with Wi-Fi Direct: overview and experimentation” IEEE Wireless Communications, June 2013

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Timescales

•  Usage pattern

•  Flow

•  Super-frame

•  Frame

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Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Energy Efficiency of 802.11 MAC

•  Usual model – Transmission, Reception, Idle

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i

ii power

Throughput==

consumedenergy ttedly transmisuccessful bits

η

S. Chiaravalloti, F. Idzikowski, L. Budzisz, Power consumption of WLAN network elements, TKN Technical Report Series TKN-11-002, Telecommunication Networks Group, Technical University Berlin (Aug. 2011).

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Revisiting Channel Access

•  Bianchi-based:

•  With

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Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Homogeneous scenario: search * 10 stations

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4

4.5

5

5.5

6

6.5

7

7.5

8

0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4

Thro

ughp

ut (M

bps)

Efficiency (MbpJ)

Lucent WaveLAN SoketCom CF Intel PRO 2200 Max. Throughput

Max. E. Efficiency

P. Serrano, A. García, M. Höllick, A. Banchs, “On the Energy Efficiency of IEEE 802.11 WLANs”, European Wireless 2010

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Heterogeneous scenario * 2 stations -  Lucent WaveLAN -  SoketCom CF

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High-consuming station

Low-consuming station

But they can fall to extreme unfairness

The penalized station is the greener one!

This is the per-STA throughput for the «throughput» conf.

There are more efficient configurations

We search for the config. that Maximizes throughput

(same conf for all STAs)

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Timescales

•  Usage pattern

•  Flow

•  Super-frame

•  Frame

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Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Distributed Opportunistic Scheduling

•  Revisiting DOS

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Andres Garcia-Saavedra, Albert Banchs, Pablo Serrano, Joerg Widmer, “Distributed Opportunistic Scheduling: A Control Theoretic Approach” IEEE INFOCOM 2012, Orlando, USA, March 2012

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Green DOS

•  Like in the previous case, add the power consumption when probing, tx, etc.

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Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Review of existing mechanisms

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u  Typical savings achieved depending on network load for ~40 different mechanisms evaluated

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

1 Sa

ving

s "PAN"

"WLAN"

"WMAN"

Low Load

Medium Load

High Load

Serrano, P., la Oliva, A., Patras, P., Mancuso, V., & Banchs, A. (2012). Greening wireless communications: Status and future directions. Computer Communications.

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Open Challenges

•  Standardizing benchmarks – Otherwise, hard to compare – Understand trade-offs – Criterion?

•  More experimentation – For WMAN – But not only! IoD for 802.11? – And new findings

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A.P. Bianzino, A. K. Raju, D. Rossi, “Apples-to-apples: a framework analysis for energy-efficiency in networks”, ACM SIGMETRICS Perf. Ev. Review, Dec. 201

A. Garcia-Saavedra, P. Serrano, A. Banchs, M. Hollick, “Balancing Energy Efficiency and Throughput Fairness in IEEE 802.11 WLANs” Elsevier Pervasive and Mobile Computing, vol. 8, no. 5, October 2012.

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Time for experimentation

Try to put well in practice what you already know; and in so doing, you will in good time, discover the hidden things which you now inquire about.

Practice what you know, and it will help to make clear what now you do not know.

Rembrandt

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Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

What we wanted to do... •  Huge research efforts dedicated to improve energy efficiency •  We need to understand the power behavior of our devices

–  Per-state measurements of power consumption in e.g. laptops, cell phones…

34 A.Rice,  S.  Hay  “Measuring  mobile  phone  energy  consump:on  for  802.11  wireless  networking”    Pervasive  and  Mobile  compu:ng.  2010  

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

What we wanted to do... •  Huge research efforts dedicated to improve energy efficiency •  We need to understand the power behavior of our devices

–  Per-state measurements of power consumption in e.g. laptops, cell phones…

–  Fine-grained per-packet measurements in wireless interfaces only

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Rantala  et  al.  “Modeling  energy  efficiency  in  wireless  internet  communica:on”    ACM  Mobiheld,  2009  

Linksys  WRT54GL  WiFi  router  HW  

Wireless  interface  (WiFi  NIC)  

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

What we wanted to do... •  Huge research efforts dedicated to improve energy efficiency •  We need to understand the power behavior of our devices

–  Per-state measurements of power consumption in e.g. laptops, cell phones…

–  Fine-grained per-packet measurements in wireless interfaces only

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100%

Pow

er

Transmitting

Idle

Receiving

0% airtime (frame length, frame rate, MCS)

Sleep baseline

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

What we found out..

•  Non-card operations can dominate –  This questions previous schema’s real performance –  Opens the door to new designs

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Card App O.S.

Device

Non-card operations Card operations

Andres Garcia-Saavedra, Pablo Serrano, Albert Banchs, Giuseppe Bianchi, “Energy consumption anatomy of 802.11 devices and its implication on modeling and design” ACM CoNEXT 2012, Nice, France, December 2012

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Experimental characterization

•  Experimental characterization in several devices •  Power generator/Power meter

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Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

TX characterization *Soekris, UDP, no acks

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Base  (idle)  consump:on   «classical»  consump:on    

There  is  an  extra  power  cost!  

3.25

3.75

4.25

4.75

5.25

5.75

6.25

0 10 20 30 40 50 60 70 80 90 100

Pow

er (W

atts

)

airtime (%)

3.25

3.75

4.25

4.75

5.25

5.75

6.25

0 10 20 30 40 50 60 70 80 90 100

Pow

er (W

atts

)

airtime (%)

6Mbps,  400fps,  15dBm  

3.25

3.75

4.25

4.75

5.25

5.75

6.25

0 10 20 30 40 50 60 70 80 90 100

Pow

er (W

atts

)

airtime (%)

6Mbps,  400fps,  5dBm  

3.25

3.75

4.25

4.75

5.25

5.75

6.25

0 10 20 30 40 50 60 70 80 90 100

Pow

er (W

atts

)

airtime (%)

24Mbps,  400fps,  15dBm  

3.25

3.75

4.25

4.75

5.25

5.75

6.25

0 10 20 30 40 50 60 70 80 90 100

Pow

er (W

atts

)

airtime (%)

24Mbps,  1200fps,  15dBm  

3.25

3.75

4.25

4.75

5.25

5.75

6.25

0 10 20 30 40 50 60 70 80 90 100

Pow

er (W

atts

)

airtime (%)

3.25

3.75

4.25

4.75

5.25

5.75

6.25

0 10 20 30 40 50 60 70 80 90 100

Pow

er (W

atts

)

airtime (%)

+0.4 W

+1.2 W

6Mbps,  400fps,  15dBm  

3.25

3.75

4.25

4.75

5.25

5.75

6.25

0 10 20 30 40 50 60 70 80 90 100

Pow

er (W

atts

)

airtime (%)

L  =  1400  B  

L  =  100  B  

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

0

0.5

1

1.5

2

0 500 1000 1500 2000

Δ B

ase

Pow

er (o

ffset

)

λg (fps)

6Mbps, 15dBm 12Mbps, 15dBm 24Mbps, 15dBm 48Mbps, 15dBm 6Mbps, 12dBm 12Mbps, 12dBm 24Mbps, 12dBm 48Mbps, 12dBm 6Mbps, 9dBm 12Mbps, 9dBm 24Mbps, 9dBm 48Mbps, 9dBm

0

0.5

1

1.5

2

0 500 1000 1500 2000

Δ B

ase

Pow

er (o

ffset

)

λg (fps)

6Mbps, 15dBm 12Mbps, 15dBm 24Mbps, 15dBm 48Mbps, 15dBm 6Mbps, 12dBm 12Mbps, 12dBm 24Mbps, 12dBm 48Mbps, 12dBm 6Mbps, 9dBm 12Mbps, 9dBm 24Mbps, 9dBm 48Mbps, 9dBm

Energy consumption anatomy

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Base  (idle)  consump:on   «classical»  consump:on    Cross-­‐factor  (mJ/frame)  

 Cross-­‐factor  (mJ/frame):    •  0.93  (Soekris/Linux  Gentoo)  •  1.27  (Soekris/OpenBSD)    •  0.46  (Linksys/Linux  Ubuntu)  •  0.11  (Alix/OpenWRT)  

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Energy consumption anatomy

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“cross-factor” Transmission

3.25

3.75

4.25

4.75

5.25

5.75

6.25

0 20 40 60 80 100

Pow

er (W

atts

)

airtime (%)

3.25

3.75

4.25

4.75

5.25

5.75

6.25

0 20 40 60 80 100

Pow

er (W

atts

)

airtime (%)

(a) App.: discarded before OS (b) TCP/IP: discarded after TCP/IP (c) Driver: discarded after driver Total: Full transmission (w/o ACKs)

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Energy consumption anatomy

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2.6 2.4 2.2

≈ ≈ 48 Mbps 100 B/Pkt 300 fps

48 Mbps 100 B/Pkt 1200 fps

2.6 2.4 2.2

≈ ≈ 48 Mbps 100 B/Pkt 300 fps

48 Mbps 100 B/Pkt 1200 fps

48 Mbps 750 B/Pkt 1200 fps

48 Mbps 1400 B/Pkt 1200 fps

2.6 2.4 2.2

≈ ≈

48 Mbps 100 B/Pkt 300 fps

48 Mbps 100 B/Pkt 1200 fps

48 Mbps 750 B/Pkt 1200 fps

48 Mbps 1400 B/Pkt 1200 fps

6 Mbps 1400 B/Pkt

400 fps

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

The cross-factor

•  Cross-factor: energy «toll» to process a frame –  ~ independent of frame size –  Total Power > base power + card power

•  Consumption weights (soekris)

•  This packet processing cost is not negligible –  Soekris: 37%-97% energy/frame

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App TCP/IP Driver NIC 24% 33% 21% 22%

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

The cross-factor

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Soekris (Linux) Alix Linksys

Soekris (BSD)

HTC Legend

Samsung Galaxy

Note 10.1 Raspberri

Pi

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Several other experiments

•  Retransmissions – No X-Factor

•  ACKs – No X-Factor – Very small impact (as expected)

•  Reception – There is X-Factor

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Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Model

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Baseline   Data  transmission   Data  recep:on   Ack  rx/tx  

Driver  sta:s:cs    available  info!  

Baseline  

TX  air:me  

RX  air:me  

Packet  processing  

Parametriza:on  

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Implications

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What about those mechamisms that do not consider this?

Driver App.

•  Packet relaying •  Relay & compress •  Multicasting

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Implications – e.g. relaying * Soekris, 15 dBm

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10.7 10.8 10.9

11 11.1 11.2 11.3 11.4 11.5 11.6

0 250 500 750 1000 1250 1500

Pow

er (W

atts

)

Packet size (B)

1 hop (6 Mbps)

2 hops (48 - 48 Mbps)

Old  

AP  

STA  1  

STA  2  

6Mbps  

48Mbps  48Mbps  

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Implications – e.g. relaying * Soekris, 15 dBm

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10.7 10.8 10.9

11 11.1 11.2 11.3 11.4 11.5 11.6

0 250 500 750 1000 1250 1500

Pow

er (W

atts

)

Packet size (B)

1 hop (6 Mbps)

2 hops (48 - 48 Mbps)

11

11.4

11.8

12.2

12.6

0 250 500 750 1000 1250 1500

Pow

er (W

atts

)

Packet size (B)

1 hop (6 Mbps) 2 hops (48 - 48 Mbps) Measurement

New  

AP  

STA  1  

STA  2  

6Mbps  

48Mbps  48Mbps  

Fwd.

iface iface

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Implications

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Can we exploit this knowledge?

App iface TCP

•  «raw» sockets •  Packet batching

Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Implications – e.g. batching * Soekris, 100B, 48 Mbps

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Pablo Serrano – Greening Wireless… University of Edinburgh, March 7th, 2014

Conclusions and Future Directions, pt. 2

•  Much effort has been devoted to reducing the energy consumption of wireless devices

•  Most of the efforts conducted so far –  Switching devices off –  Reducing the consumption of the wireless card

•  But ≥ 50% of the per-frame energy is consumed by the packet processing of the protocol stack –  Need to revisit previous models –  Explore new approaches to save energy

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Many Thanks!

Pablo Serrano Yáñez-Mingot pablo@it.uc3m.es

Greening Wireless Communications: A Top-Down Overview