Seminario fine secondo anno di dottorato

Flavia Martelli

flavia.martelli@unibo.it

Research context

Tutor: Prof. Oreste Andrisano

Co-Tutor: Prof. Roberto Verdone

Reasearch activity performed in the framework of:

• European Integrated Project WiserBAN

• Cost Actions:

- 2100

- IC1004

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Introduction

WBAN = Wireless Body Area Network

Collection of nodes placed on, or optionally inside, the human body

Sensing and communication capabilities

Applications

• Medical: monitoring vital parameters, drug delivery, implants, hearing aids

• Sport/Fitness: rehabilitation, motion capture, monitoring parameters

• Entertainment: consumer electronics (audio/video streaming, interactive gaming), personal item tracking

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WBAN applications: WiserBAN Use Cases

Audio streaming Binaural audio link

Remote control

« behind-the-ear » to « in-the-ear »

Hearing aids

Cardiac Implants

Implantedpart

FMT Floating Mass Transducer

or Cochlear Implant multi-channel electrode

Digital Audio

Audio Streaming

Telephony

Clinical Fitting

Remote control

Cochlear Implant

Glucometer

Insulin pump

PC

Internet

Remote control

Insulin Pumps 4 Flavia Martelli

Research interests

Link Adaptation in WBANs

Performance evaluation of standards for WBANs:

• IEEE 802.15.4

• IEEE 802.15.6

Coexistence studies

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Coexistence issues for Wireless Body Area Networks

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Motivation

2.4 GHz ISM band

• envisaged for WBAN

• already used by several wireless devices

- standard: IEEE 802.11 (Wi-Fi), Bluetooth, IEEE 802.15.4 (Zigbee)

- proprietary

WBAN should be used everywhere in the daily life

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Right Hip

Heart

Right Ear

RC

Left Ear

Right Hand

Reference WBAN Scenario

Coordinator (RC) held in the right hand

Star topology

Query-based traffic

- One packet per node per query

- Packet has to be sent before next query

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WBAN Protocol Architecture (1/2)

Physical layer:

1. IEEE 802.15.4 - compliant PHY

(MSK with spreading, Rb = 250 kbit/s)

2. MSK without spreading

(Rb = 2 Mbit/s)

3. Bluetooth Low Energy (BT-LE) - compliant PHY

(GMSK, Rb = 1 Mbit/s)

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WBAN Protocol Architecture (2/2)

MAC layer:

• The network is managed by a Coordinator

• A superframe structure is established when needed for the communication

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Superframe

802.15.6 CSMA/CA

BEACO

N

BEACO

N

t

CAP

CFP Ind ACK Inactive 802.15.4 CSMA/CA

Methodology

Measurements

WBAN Simulator f

Power Spectral Density

KNOWN FROM STANDARD

WBAN Performance

t

Generated traffic

Methodology

Interference characterization Performance evaluation

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Two different sources of interference:

• IEEE 802.11 (Wi-Fi)

• IEEE 802.15.4 (Zigbee)

Time domain characterization

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Frequency domain characterization

WBAN channels 𝑓𝑐 = 2405 + 𝑖 ∙ 5 [MHz], 𝑖 = 0,… , 15

𝐵 = 5 [MHz] (PHY1,2) or 𝐵 = 2 [MHz] (PHY3)

𝑃𝑖𝑛𝑡 = 𝑊𝑚𝑗(𝑓) ∙ 𝐻𝑟𝑖(𝑓)

2ⅆ𝑓

𝐵𝑖

𝐶

𝐼=? 𝐼 =

𝑃𝑖𝑛𝑡

𝐴(𝑑𝑗) 𝐴 ⅆ =

4𝜋

λ

2∙ ⅆ3 𝐶 =

𝑃𝑡𝑥

𝐴𝑜𝑛−𝑏𝑜𝑑𝑦

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IEEE 802.11

(Wi-Fi)

IEEE 802.15.4

(Zigbee)

Simulation scenario

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Room of 3x3.5m

Person wearing a WBAN walking in the room

IEEE 802.11 (Wi-Fi)

interference IEEE 802.15.4 (Zigbee)

interference

Case 1: Pint = -15 dBm

Case 2: Pint = +14 dBm

Case 1: only ZC and ZR3

Case 2: all nodes

WBAN Channel model: on-body

0 0.5 1 1.5 2 2.5-65

-60

-55

-50

-45Indoor - Rx Right Hand

Time [s]

Channel G

ain

[dB

]

Right Ear Tx

Left Ear Tx

Heart Tx

Hip Tx

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Right Hip

Heart

Right Ear

RC

Left Ear

Right Hand

Results

Performance metrics

generated packets

lost packets

N

NPLR

Packet correctly received at the coordinator

DELAY

Superframe 40 ms

CSMA/CA BEACO

N

BEACO

N

Nodes start accessing the channel

t

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Evaluation through simulations

oPacket Loss Rate

- Possible causes for packet losses:

• Connectivity

• Collisions

• End of Superframe

oDelay

oEnergy consumption

Results: PLR, PHY1

0 50 100 150 20010

-3

10-2

10-1

100

MAC payload [byte]

PLR

IEEE 802.15.4 CSMA/CAMSK with spreading (15.4-like) PHY - 250 kbit/s

802.11 Interference - case 2

802.11 Interference - case 1

802.15.4 Interference - case 2

802.15.4 Interference - case 1

No Interference

0 50 100 150 20010

-3

10-2

10-1

100

MAC payload [byte]

PLR

IEEE 802.15.6 CSMA/CAMSK with spreading (15.4-like) PHY - 250 kbit/s

802.11 Interference - case 2

802.11 Interference - case 1

802.15.4 Interference - case 2

802.15.4 Interference - case 1

No Interference

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IEEE 802.15.4 CSMA/CA IEEE 802.15.6 CSMA/CA

Results: PLR, PHY2

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0 50 100 150 20010

-3

10-2

10-1

100

MAC payload [byte]

PLR

IEEE 802.15.6 CSMA/CAMSK without spreading PHY - 2 Mbit/s

802.11 Interference - case 2

802.11 Interference - case 1

802.15.4 Interference - case 2

802.15.4 Interference - case 1

No Interference

Results: PLR, PHY3

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0 50 100 150 20010

-3

10-2

10-1

100

MAC payload [byte]

PLR

IEEE 802.15.6 CSMA/CABT-LE PHY (GMSK) - 1Mbit/s

802.11 Interference - case 2

802.11 Interference - case 1

802.15.4 Interference - case 2

802.15.4 Interference - case 1

No Interference

Energy consumption

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Current consumption

• TX/RX on: 10 mA

• stand-by: 1.6 mA

Supply voltage: 1.2 V

0 50 100 150 2000

50

100

150

200

250

MAC payload [byte]

Energ

y [J]

MSK with spreading (15.4-like) PHY - 250 kbit/s

802.11 Interference - case 2

802.11 Interference - case 1

No interference

15.4 CSMA/CA

15.6 CSMA/CA

Conclusions

Study on WBAN coexistence issues at 2.45 GHz

• Different PHYs

• Different channel access protocols

Results:

• Newly investigated topic

• In the mainframe of WiserBAN: helpful in MAC protocol selection

Future PhD research topic:

• Body-to-Body communications

Network layer oriented study

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Publications

Chiara Buratti, Raffaele D'Errico, Mickael Maman, Flavia Martelli, Ramona Rosini, Roberto Verdone, Simon Huettinger, "Design of a Body Area Network for Medical Applications: the WiserBAN Project", ACM ISABEL 2011, Barcelona, October 2011

Flavia Martelli, Roberto Verdone, Chiara Buratti, "Link Adaptation in Wireless Body Area Networks", IEEE VTC 2011 Spring, Budapest, May 2011

Flavia Martelli, Chiara Buratti, Roberto Verdone, "On the performance of an IEEE 802.15.6 Wireless Body Area Network", EW 2011, Vienna, April 2011

Flavia Martelli, Roberto Verdone, Chiara Buratti, "Link Adaptation in IEEE 802.15.4-Based Wireless Body Area Networks", IEEE PIMRC 2010 International Workshop on Body Area Networks, Istanbul, September 2010

Flavia Martelli, Leonardo Goratti, Jussi Haapola, "Performance of Sensor MAC Protocols for Medical ICT using IR-UWB Technology", HealthInf2010, Valencia, January 2010

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Credits

“L’Ingegnere delle Telecomunicazioni in azienda M”, Academic Course, UNIBO (30)

“Trends in Communications M”, Academic Course, UNIBO (30)

English course, level C1, CILTA (30)

“B-Aware” Summer School, EPFL Lausanne (27)

“Short-Range Positioning Systems: Fundamentals and Advanced Research Results with Case Studies”, PhD short course, UNIBO (8)

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Thank you for your attention

Questions?

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Parameter Value

WBAN transmit power 0 dBm

Receiver sensitivity (PHY1) - 96 dBm

Receiver sensitivity (PHY2) - 87 dBm

Receiver sensitivity (PHY3) - 90 dBm

Noise power - 101 dBm

Antenna gain, RC - 3 dB

Antenna gain, node - 15 dB

802.15.4 transmit power 0 dBm

802.11 transmit power 20 dBm

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Simulation settings

t

t

IEEE 802.15.6 CSMA/CA Algorithm

CSMA Slot

125 µs pSIFS pSIFS

BC = 1 BC = 1

pSIFS 50 µs

CW = CWmin = 8 BC = random(CW) = 2

Data arrives

Sensi

ng

Sensi

ng

Sensi

ng

Sensi

ng

Sensi

ng

Idle

Channel

Busy Idle

BC = 1 BC = 0

Tx

Tx fails CW = 8 (s.a.b.)

BC = random(CW) = 1

BC = 0

Sensi

ng

Busy Idle

Tx fails CW = 16 (doubled)

BC = random(CW) = 4

BC = 4

Busy Idle

Sensi

ng

Sensi

ng

Sensi

ng

Sensi

ng

Tx

BC = 3 BC = 2

Busy

Sensi

ng

BC = 1

Sensi

ng

Tx succeeds CW = CWmin

BC = 1 BC = 0

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BC decrements

Tx

t

t

Slot

320 µs

IEEE 802.15.4 CSMA/CA Algorithm

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Slot

320 µs

Data arrives CW = 2 NB = 0

BE = BEmin = 3 x = random(2BE - 1) = 3

Back

off

Back

off

Back

off

Sensi

ng

Idle Busy

Sensi

ng

Idle

Tx

Busy

Tx succeeds

Channel

CW = 2 NB = 1 BE = 4

x = random(2BE - 1) = 5

Back

off

Back

off

Back

off

Back

off

Back

off

Sensi

ng

Sensi

ng

CW = 1 CW = 0

3. Overall PER (Packet Error Rate)

4. Considering X as a uniformly distributed random variable in [0 1] drawn for each packet:

if (X ≥ PER) packet correctly received

else packet lost

Packet capture model

1. C/I (Signal-to-Interference Ratio) values computed according to current transmission and interference variations

2. BER (Bit Error Rate) for every packet portion i

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7.0

2

1

iI

C

i eBER

N

i

N

iibit

BERPER1

)1(1N : number of packet portions

Nbiti : number of bits in the

portion i

Delay

0 50 100 150 2000

2

4

6

8

10

12

14

16

18

20

MAC payload [byte]

Dela

y [

ms]

MSK with spreading (15.4-like) PHY - 250 kbit/s

802.11 Interference - case 2

802.11 Interference - case 1

No interference

15.4 CSMA/CA

15.6 CSMA/CA

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WBAN Channel model: off-body

1 2 3 4-70

-65

-60

-55

-50

-45

-40

d [m]

Channel gain

[dB

]

Goff

Ear LOS

Heart LOS

Hip LOS

Ear NLOS

Heart NLOS

Hip NLOS

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Right Hip

Heart

Right Ear

𝐺off ⅆ =4𝜋

λ

−2

∙ ⅆ−3