3 presents the proposed mac protocol design. chapter 4 describes the analytical ... figure 2.1 shows...

Adaptive-Reliable Medium Access Control

Protocol for Wireless Body Area Networks

By

Mr. Azizur Rahim

Registration Number: CIIT/SP11-REE-027/ISB

MS Thesis

In

Electrical Engineering

COMSATS Institute of Information Technology

Islamabad – PakistanSpring, 2012



A Thesis presented to


In partial fulfillment

of the requirement for the degree of

MS (Electrical Engineering)

By

Mr. Azizur Rahim

CIIT/SP11-REE-027/ISB

Spring, 2012


ii

Engineering).



A post Graduate Thesis submitted to Department of Electrical Engineering as

partial fulfillment of the requirement for the award of Degree of M.S

(Electrical

Supervisor:

Dr. Nadeem Javaid,

Assistant Professor,

Department of Electrical Engineering,

COMSATS Institute of Information Technology (CIIT)

Islamabad Campus

June, 2012

Name Registeration Number

Mr. Azizur Rahim CIIT/SP11-REE-027/ISB

iii

Final Approval

This thesis titled

Adaptive-Reliable MediumxAccessxControl

Protocol forxWirelessxBodyxAreaxNetworks

By

Mr. Azizur Rahim


Has been approved

For the COMSATS Institute of Information Technology, Islamabad

External Examiner: __________________________________

Supervisor: ________________________

Dr. Nadeem Javaid /Assistant professor

Department of Electrical Engineering

Islamabad Campus

Co-supervisor: ________________________

Dr. Safdar H.Bouk / Assistant professor


Islamabad Campus

HoD: ________________________

Dr. Shafayat Abrar / Associate professor


Islamabad Campus

iv

Declaration

I Mr. Azizur Rahim, CIIT/SP11-REE-027/ISB herebyxdeclare that I havexproduced

the workxpresented inxthis thesis, duringxthe scheduledxperiod of study. I also declare

that I havexnot taken anyxmaterial from anyxsource exceptxreferred toxwherever due

that amountxof plagiarism isxwithin acceptablexrange. If a violationxof HEC rulesxon

research hasxoccurred in thisxthesis, I shall be liablexto punishablexaction under the

plagiarismxrules of the HEC.

Date: ________________

________________

Mr. Azizur Rahim


v

Certificate

It is certified that Mr. Azizur Rahim, CIIT/SP11-REE-027/ISB hasxcarried out

allxthe work relatedxtoxthis thesisxunder myxsupervision at the Departmentxof

Electricalx Engineering COMSATSxInstitute ofxInformation Technology, xIslamabad

and thexwork fulfills thexrequirements for award of MSxdegree.

Date: _________________

Supervisor:____________________

Dr. Nadeem Javaid /Assistant professor


CIIT Islamabad Campus

Head of Department:

____________________________

Dr. Shafayat Abrar/Associate professor

HoD Electrical Engineering

vi

DEDICATION

Dedicated to my elder brother, Muhammad Rahim

vii

ACKNOWLEDGMENT

I am heartily grateful to my supervisor, Dr. Nadeem Javaid, whose patient

encouragement, guidance and insightful criticism from the beginning to the final level

enabled me have a deep understanding of the thesis.

Lastly, I offer my profound regard and blessing to everyone who supported me in

any respect during the completion of my thesis especially Dr. Safdar H.Bouk and my

friends in every way offered much assistance before, during and at completion

stage of this thesis work.

Mr. Azizur Rahim


viii

ABSTRACT

This thesis presents Adaptive-Reliable MediumxAccessxControl (AR-MAC)

protocolxfor WirelessxBody AreaxNetworks (WBANs). In WBANs, small battery-

operated on-body or implanted biomedical sensor nodes are used to monitor

physiological signs such as temperature, blood pressure, ECG, EEG etc. Proposed

protocol is based upon fixed topology of WBAN to use TimexDivisionxMultiple

Access (TDMA) approach for channel access with a novel scheme of synchronization.

All nodes remain in sleep mode until the time slot assigned by Central Node, to avoid

idle listening and overhearing. An adaptive guard band algorithm is used to avoid

collision due to clock drift of nodes. Simulationxresults showxthat proposed AR-MAC

outperformsxthan IEEE 802.15.4 inxterms of energyxconsumptionxand reliability.

ix

TABLE OF CONTENTS

1 Introduction 2

1.1 Wireless Body Area Networks (WBANs) . . . . . . . . . . . . . . . 2

1.2 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.3 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.4 Research methodology . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.5 Research Contribution . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.6 Thesis organization . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2 Introduction to WBANs 6

2.1 Wireless Sensor Networks . . . . . . . . . . . . . . . . . . . . . . . 6

2.1.1 Network Topology . . . . . . . . . . . . . . . . . . . . . . . 7

2.1.2 Transmission Media . . . . . . . . . . . . . . . . . . . . . . . 8

2.2 Wireless Body Area Networks . . . . . . . . . . . . . . . . . . . . . 8

2.3 Wireless Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.3.1 IEEE 802.15.1/Bluetooth . . . . . . . . . . . . . . . . . . . 10

2.3.2 IEEE 802.15.4 and ZigBee . . . . . . . . . . . . . . . . . . . 10

2.4 Comparison of wireless networking standard . . . . . . . . . . . . . 12

3 Related Work 14

3.1 WBANs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.2 WBAN Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.2.2 Design Requirements for WBANs . . . . . . . . . . . . . . . 16

3.2.2.1 Energy efficiency . . . . . . . . . . . . . . . . . . . 17

3.2.2.2 Reliability . . . . . . . . . . . . . . . . . . . . . . . 17

3.2.2.3 Scalability . . . . . . . . . . . . . . . . . . . . . . . 17

3.2.2.4 Quality of Service (QoS) . . . . . . . . . . . . . . . 17

3.3 Sources of Energy Dissipation in WBANs . . . . . . . . . . . . . . . 18

3.4 Classification of MAC protocols for WBANs . . . . . . . . . . . . . 19

3.4.1 Contention-Based MAC Protocols . . . . . . . . . . . . . . . 19

3.4.2 Contention-Free MAC Protocols . . . . . . . . . . . . . . . . 20

3.4.3 Low Power Listening (LPL) MAC Protocols . . . . . . . . . 21

3.5 MAC protocols for WBANs . . . . . . . . . . . . . . . . . . . . . . 23

3.5.1 IEEE 802.15.4 MAC protocol . . . . . . . . . . . . . . . . . 23

3.5.2 Battery-aware TDMA protocol . . . . . . . . . . . . . . . . 24

3.5.3 Priority guaranteed MAC protocol . . . . . . . . . . . . . . 24

3.5.4 Energy-Efficient Low Duty Cycle MAC Protocol . . . . . . . 25

x

3.5.5 A power-efficient MAC protocol for WBAN . . . . . . . . . 26

3.5.6 Energy Efficient Medium Access Protocol . . . . . . . . . . . 27

3.5.7 BodyMAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

3.5.8 MedMAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

3.5.9 Heartbeat-Driven MAC protocol . . . . . . . . . . . . . . . . 31

3.6 Discussion and Open Research Issues . . . . . . . . . . . . . . . . . 34

4 Proposed MAC Protocol 37

4.1 Protocol design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

4.1.1 Channel Selection . . . . . . . . . . . . . . . . . . . . . . . . 38

4.1.2 Time Slot Assignment . . . . . . . . . . . . . . . . . . . . . 38

4.1.3 Synchronization . . . . . . . . . . . . . . . . . . . . . . . . . 40

4.1.4 Frame Formate . . . . . . . . . . . . . . . . . . . . . . . . . 41

4.2 Energy Consumption Analysis . . . . . . . . . . . . . . . . . . . . . 42

4.2.1 Switching Energy . . . . . . . . . . . . . . . . . . . . . . . . 43

4.2.2 Transmission Energy . . . . . . . . . . . . . . . . . . . . . . 43

4.2.3 Receiving Energy . . . . . . . . . . . . . . . . . . . . . . . . 43

4.2.4 Time-Out Energy . . . . . . . . . . . . . . . . . . . . . . . . 44

4.3 Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

5 Conclusion 47

5.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

References 48

xi

LIST OF FIGURES

2.1 MICAz Sensor node . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.2 Architecture of Sensor node . . . . . . . . . . . . . . . . . . . . . . 7

2.3 WBAN with on-body sensor nodes . . . . . . . . . . . . . . . . . . 9

3.1 Communication Architecture of WBANs . . . . . . . . . . . . . . . 15

3.2 Algorithm of CSMA/CA . . . . . . . . . . . . . . . . . . . . . . . . 20

3.3 TDMA Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.4 Normalized Throughput Versus NC . . . . . . . . . . . . . . . . . . 24

3.5 TDMA Frame Structure . . . . . . . . . . . . . . . . . . . . . . . . 25

3.6 Superframe Structure of Priority-Guaranteed MAC . . . . . . . . . 25

3.7 TDMA Frame Structure . . . . . . . . . . . . . . . . . . . . . . . . 26

3.8 Superfame Structure . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.9 Power Compared to Sleep Time and Number of Retransmits . . . . 28

3.10 BodyMAC Frame Structure . . . . . . . . . . . . . . . . . . . . . . 29

3.11 Multi-Superframe Structure for MedMAC Protocol . . . . . . . . . 30

4.1 WBAN Topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

4.2 Channel Selection Procedure . . . . . . . . . . . . . . . . . . . . . . 38

4.3 Time Slots Assignment with Guard-band Time . . . . . . . . . . . . 39

4.4 MAC Layer Frame Formate . . . . . . . . . . . . . . . . . . . . . . 41

4.5 Energy consumption of AR-MAC and IEEE 802.15.4 for N = 1000 45

xii

LIST OF TABLES

1.1 Comparison of CSMA/CA and TDMA . . . . . . . . . . . . . . . . 3

2.1 IEEE 802.15.4 - Frequency bands and data rates . . . . . . . . . . 11

2.2 Comparison of Wireless Networking Standards . . . . . . . . . . . 12

3.1 Comparison of MAC protocols based on channel access mechanism . 22

3.2 Comparison of MAC Protocols . . . . . . . . . . . . . . . . . . . . . 32

3.3 Comparison of MAC Protocols . . . . . . . . . . . . . . . . . . . . . 33

4.1 Simulation Parameters Value . . . . . . . . . . . . . . . . . . . . . 44

xiii

Chapter 1

Introduction

1

1

Introduction

1.1 Wireless Body Area Networks (WBANs)

Pervasive and mobile healthcare are emerging technologies for long time pa-

tient monitoring using biomedical sensors. These biomedical sensors are small

in size and battery-operated devices with limited computational and communica-

tion capabilities. WBANs have enabled deployment of wearable and implantable

biomedical sensorsxto provide ubiquitous health monitoring services. Biomedical

sensorsxarexused toxmonitor the physiological parameters ofxhuman bodyxwith

throughput ranging fromxseveral bitsxper hourxup to 10xMbps. WBANs have

some similar demands and challenges like other wireless networks. Sensor nodes

in WBANs have small batteries because of size limitation. In most cases these

small batteries cannot be recharged or replaced. WBANs require energy efficient

mechanism for long time patient monitoring. Thus, energy efficiencyxis onexof

theximportant factors of the MAC design. Similarly, other requirements are min-

imum latency and fair bandwidth management.

For fair access of the shared medium, MAC protocols forxWireless SensorxNetworks

(WSNs) and other short range wireless technologies use TimexDivision Multi-

ple Accessx(TDMA) or CarrierxSense MultiplexAccess with Collision Avoidance

(CSMA/CA). Due to complex hardware and high computational power require-

ments, FrequencyxDivision Multiple Access (FDMA) and CodexDivision Multi-

plexAccess (CDMA) are not suitable approaches for medium access in sensor net-

works. CSMA/CA approach out performs in dynamic types networks. It is pre-

sumed that WBANs are not dynamic. TDMA approach is well suited for WBANs.

However, TDMA-based MAC protocols require extra energy consumption for syn-

chronization. Comparison of CSMA/CA and TDMA is shown in Table 1-1.

Packet collision, idle listening, overhearing, protocol overhead state switching,

etc are the major causes of energy dissipation in WSNs. Corrupted packets af-

ter collision are discarded and followed by retransmission. Re-transmission of

packets leads to extra energy consumption. Packet collision also increases latency.

Transceiver remains operational and continuously monitors medium for data pack-

2

ets during idle listening. In many sensor networks, nodes remain in idlexmode

forxmost ofxthe time, i.e., listening to receive data or control packets that are

not sent. In overhearingxnodes receivexpackets thatxare destinedxto other nodes.

Protocols with high control packet overhead, lead to complexity and high energy

consumption. However, frequent switching of transceiver to avoid idle listening

and overhearing is also energy consuming. Energy efficiency can be improved by

avoiding such wastage causes in efficient way. TDMA is the best approach to

avoid these major sources of energy dissipation. AR-MAC is based upon TDMA

approach to overcome these sources of energy waste. Adaptive assignment of time

slots and guard band improve efficiency of WBANs in terms of energy consumption

and bandwidth utilization.

Table 1.1: Comparison of CSMA/CA and TDMA

Feature CSMA/CA TDMA

Power Consumption High LowBandwidth utilization Low MaximumTraffic level support Low HighMobility(Dynamic) Good PoorSynchronization N/A Necessary

1.2 Motivation

Extensive energy is consumed by transceiver communication operation. Exist-

ing research on MAC layer focuses to maximize battery-powered sensor node’s life.

Bottleneck ofxMAC layer protocolxdesign for WBAN isxto achieve highxreliabilityxand

energy minimization. Majority of MAC protocols designed for WBANs are based

upon TDMA approach. However, a newxprotocol needs toxbe definedxto achieve

high energy efficiency, fairness and avoid extra energy consumption due to syn-

chronization.

1.3 Scope

The scope ofxthis research isxto define and developxa newxMAC layer protocol

for WBANs that is more energy efficient and can be implemented on the current

nodes.

3

1.4 Research methodology

An extensive study of the existing protocols and factors was done that influence

the performance of those protocols. A new protocol was designed taking into

consideration the common flaws and problems faced by those protocols. We use

MATLAB for performance evaluation of proposed protocol.

1.5 Research Contribution

We summarize our contribution in this thesis as follows:

• We describe the communication architecture of WBANs with major require-

ment and dominant sources of energy dissipation.

• Then we analyze the existing MAC protocols for WBANs with emphasis on

energy minimization at MAC layer.

• We discuss open research issues with direction for future research.

• Then propose Adaptive-Reliable Medium Access Control (AR-MAC) proto-

col

• Finally we evaluate the performance of AR-MAC with respect to IEEE

802.15.4 in termsxof energy consumptionxandxreliability

1.6 Thesis organization

We provide a detail discussion about the WBANs architecture with emphasis

on requirements, architecture and energy dissipation sources in chapter 2. Chapter

3 presents the proposed MAC protocol design. Chapter 4 describes the analytical

analysis of energy consumption with simulation results. We conclude our research

work in chapter 4 with performance analysis of proposed protocol with IEEE

802.15.4.

4

Chapter 2

Introduction to WBANs

5

2

Introduction to WBANs

2.1 Wireless Sensor Networks

Wireless Sensor Network was first introduced during the Cold War by US [4].

The acoustic sensors were placed in the bottom of ocean to detect the movement of

Soviet submarines. This system of acoustic sensors was called Sound Surveillance

System (SOSUS) [4]. During the same time US also used sensors for radars system.

Both of these networks were wired nature and having no constraint of bandwidth

or energy.

The modern sensor research was first started by Defense Advanced Research

Project Agency (DARPA) in early 1980’s. DARPA introduced Distributed Sensor

Networks (DSN) program, where a network is composed of many independent and

low cost nodes that are able to collaborate with each other. In the mid of 1980’s

the Massachusetts Institute of Technology (MIT) developed a DSN consisting of

acoustic sensors designed to detect and track low-flying aircrafts [4]. Figure 2.1

shows a MICAz node.

The four basic components of each and every node are power source, process-

ing unit, sensing unit and transceiver. Some sensor nodes also contain optional

components like location finding system (GPS), Mobilizer and power generator.

Figure 2.2 shows the basic components of a sensor node.

An optional power generator can be used to support the power unit; solar cells

can also be used for this purpose. The processing unit consists of a processor

and memory. This unit is responsible for managing the tasks of sensor unit. The

sensing unit is generally consistsxof axSensor and Analogue toxDigital Convertor

(ADC).xThe ADCxconverts the analogue data to digital data so that node can

process it before transmitting. The Transceiver connects the node to the network

either through Radio Frequency (RF) or optical communication such as infrared.

The optional location finding system may have a low power Global Positioning

System (GPS). Mobilizer is used to enable the node movement, if mobility is

required for a node to perform its task. All of these components must be fitted in

6

Figure 2.1: MICAz Sensor node

a smaller module like matchbox.

Figure 2.2: Architecture of Sensor node

2.1.1 Network Topology

In WSN network topology changes and maintenance can be viewed in three

phases i.e. deployment phase, post-deployment and re-deployment [9]. The initial

stage is the deployment phase, in which nodes are deployed in a certain territory

either by placing these nodes one by one or dropping from airplane. Topology

changes may occur due to nodes failure and mobility, the post deployment phase

7

are used here to manage such a situation. Sometimes additional nodes are deployed

in the network; this process is known as re-deployment.

2.1.2 Transmission Media

WSNs use wireless medium for RF communication. Most of the WSNs use the

IndustrialxScientific and Medicalx(ISM) frequency band for communication. ISM

frequency band is globally available, unlicensed and is centered around 2.4 GHz.

2.2 Wireless Body Area Networks

Number of small and smart devices increasing due to advancement in wireless

and storage technologies. These small devices are capable of long time health mon-

itoring with in hospital or outside. Wireless Body Area Networks (WBANs) enable

us to use portable, small and lightweight sensor nodes for long time health moni-

toring. Using sensing capabilities, these small energy constrained devices measure

human body parameters and communicate with some external monitoring sta-

tion for diagnose or prescription from a physician. Data streaming from human

body to monitoring station using wireless communication channel is an energy

consuming process. Low power signal processing and energy efficient communi-

cation mechanisms prolong lifespan of these small devices. For Low-Rate Wire-

lessxPersonal AreaxNetworks (LR-WPANs), IEEE 802.15.4 definesxspecification

for PhysicalxLayer and Data LinkxLayer.

In WBANs, sensor nodes of small size with low power and limited compu-

tational capabilities are attached or implanted to human body for measurement

of physiological signs. These physiological signs include; respiratory patterns,

heartbeat, temperature, posture, breathing rate, ElectroCardioGram (ECG), Elec-

troEncephaloGraphy (EEG) and many more. Transmission data rates for these

physiological parameters vary from 1Kbps to 1Mbps. Sensor nodes collect informa-

tion from human body and communicate with a central device called Coordinator.

2.3 Wireless Standards

In March 1999, the IEEE established the 802.15 working group as part ofxthe

IEEE ComputerxSociety’s 802 Localxand MetropolitanxArea NetworkxCommittee.

The 802.15 working group was established with the specific purpose of developing

8

Figure 2.3: WBAN with on-body sensor nodes

short range wireless networks, also known as Wireless Personal Area Networks

(WPANs).

Task Group 1 (802.15.1) defines a standard for WPANs based on Bluetooth

specification for physical and MAC layer. The goal of Task Group 2 (802.15.2) is

to develop axmodel for thexcoexistenceof WLAN (802.11) and WPAN (802.15).

The Task Group 3 (802.15.3) is responsible to develop standards for high data

rate WPANs (20 Mbps or greater). The goal of Task Group 4 (802.15.4) is to

define a low data rate and less complex PHY and MAC layer standards that

will save energy and will achieve a battery life time of months to years. Task

Group 5 working in mesh networks with emphasis on interoperability, stability

and scalability. IEEE 802.15.6, TaskxGroup 6 works to define standards for BAN

xtechnologies.

Inxthe following section we will discuss the 802.15.1 and 802.15.4xstandards.

The 802.15.4 is especially important as it is aimed for sensors and other devices

needing long battery life.

9

2.3.1 IEEE 802.15.1/Bluetooth

Bluetooth was designed to replace the short range cable technology and pro-

vides communication between computer and its peripherals. Bluetooth isxa shortxrange

(10m), low power (1 to100 mW) and low cost device whose transceiver operate

in 2.4 GHz of ISMxband. Bluetooth uses FrequencyxHopping SpreadxSpectrum

(FHSS) with the hop rate of 1600 hops/s [12].

Bluetooth forms piconet, a small network of Bluetooth devices. A piconet can

have two to eight nodes. One of the nodesxact as a master whilexthe remaining

nodes are connected to it as slave. The limit of seven slaves is because of three

bit addressing scheme in piconet. Three bit allow eight different addresses in

which zero address is reserved for broadcasting, so a piconet can maximally have

seven slaves. The master clock is used for synchronization and all communication

within piconet is routed via master. When a node participates in more than one

network, scatternet is formed. A scatternet is a network ofxtwo orxmore piconets.

A node participating in more than one piconet is called gateway node and uses

Time Division Duplex (TDD) in order to be active in one piconet at a time.

Based on Bluetooth specificationxthe IEEE 802.15.1 definesxMAC and PHYxlayers

standard for WPANs. The radio layer of the Bluetooth protocol stack forms the

PHY layer of 802.15.1 while the Logical Link Control and Adaptation Protocol

(L2CAP), Link Management Protocol (LMP), and Baseband layers of Bluetooth

protocol stack form the 802.15.1 MAC layer. The PHY layer specifies the com-

munication band (2.4 GHz) while the MAC layer is responsible for the time syn-

chronization of the FHSS communication.

2.3.2 IEEE 802.15.4 and ZigBee

An Alliancexwas formed by an association of several companies in 2002, called

the ZigBee Alliance. The main goal of the Alliance was to develop monitoring

and controlling devices that are reliable, low power, low cost and are wirelessly

networked using an open global standard. The IEEE 802.15 task group four has

already started working on a standard for low data rate WPANs. The IEEE and

ZigBee Alliance joined and decided that ZigBee would be the commercial name of

the technology.

Some ofxthe applications ofxthe 802.15.4 standard include sensors, remote con-

trols, home automation, smart badges and interactive toys [13]. The standard use

three license free frequency bands with two Directed Sequence Spread Spectrum

10

(DSSS) PHY layers. One PHY layer operate at 868/915 MHz and uses the 868-870

MHz band with one channel and 902-928 MHz band with ten channels. This PHY

layer achieves a dataxrate of 20 kbps in 868-870 MHz frequency band and 40 kbps

in the 902-928 MHz band. The second PHY layer operates atx2.4 GHz and uses

the 2.4-2.4835 GHz band with sixteen channels and achieves a data rate of 250

kbps. The Table 2.2 summarizes the frequency band and data rates of 802.15.4

standardx.

Table 2.1: IEEE 802.15.4 - Frequency bands and data rates

PHY Band Channels ChipRate

Modulation BitRate

868/915 MHz868-870MHz

0 300Kchip/s

BPSK 20 kbps

902-928MHz

1 to 10 600Kchip/s

BPSK 40 kbps

2.4 GHz 2.4-2.4835GHz

11 to 26 2Mchip/s

O-QPSK 250 kbps

The IEEE 802.15.4 supportsxtwo addressing mechanism namelyx16bit short

and 64bit IEEE addressing. The PHY layer also has features for link quality

indication, receiver energy detection and clear channel assessment. MAC layer

support both contention free and contention based access with a maximum packet

size of 128 bytes, containing a payload of 104 bytes maximally. The MAC layer

uses full handshaking for reliability and uses CSMA/CA for carrier sensing.

ZigBee defines three software layers [10] (network, security and application)

on top of PHY and MAC 802.15.4 layers. Network layer supports three net-

workxtopologies namely star, mesh orxpeer-to-peer, andxcluster based topologies,

as shown in Figure 2.4. The 802.15.4 definesxtwo types of nodes i.e. Fully Func-

tionalxDevice (FFD) andxReduced Functional Device (RFD). An FFD canxroute

data while an RFD cannot, this standard also specify that a network must have

at least one FFD.

A start topology saves energy and increase network lifetime since every RFD is

directly connected with the coordinator. A mesh or p2p topology brings reliability

and scalability since all nodes are FFDs and directly interconnected so it introduces

multiple routing paths. The cluster tree topology combines both the start and

mesh topologies and trying to extend network lifetime with a reasonable reliability

and scalability [10].

11

2.4 Comparison of wireless networking standard

There are different standards defined for wireless networks. These standards

divide wireless networks into different categories based on factors like network

size, transmission range, data rate and network lifetime. Below table shows a

comparison of the three important wireless network standards.

Table 2.2: Comparison of Wireless Networking Standards

Market Name Wi-Fi Bluetooth ZigBeeStandard IEEE 802.11b IEEE 802.15.1 IEEE 802.15.4Type of Network WLAN WPAN WPANApplication Focus Web, email,

VideoCable Replace-ment

Monitoring andcontrol

System Resources 1MB+ 250KB+ 4KB-32KBBattery Life (days) 0.5 5 1-7 100 1,000+Network Size 32 7 255/65,000Data rate (kbps) 11,000+ 720 20-250TransmissionRange

1-100 (meters) 1 10+ (meters) 1-100+ (meters)

Success Metrics Speed, Flexibil-ity

Cost, Conve-nience

Reliability,Power, Cost

12

Chapter 3

Related Work

13

3

Related Work

3.1 WBANs

Number of small/smart devices increasing due to advancement in wireless and

storage technologies. These small devices are capable of long time health monitor-

ing with in hospital or outside. Wireless Body Area Networks (WBANs) enable

us to use portable, small and lightweight sensor nodes for long time health moni-

toring. Using sensing capabilities, these small energy constrained devices measure

human body parameters and communicate with some external monitoring sta-

tion for diagnose or prescription from a physician. Data streaming from human

body to monitoring station using wireless communication channel is an energy

consuming process. Low power signal processing and energy efficient communi-

cation mechanisms prolong lifespan of these small devices. ForxLow-Rate Wire-

lessxPersonal Area Networks (LR-WPANs), IEEEx802.15.4xdefines specification

for PhysicalxLayer and DataxLink Layer [1].

In WBANs, sensor nodes of small size with low power and limited compu-

tational capabilities are attached or implanted to human body for measurement

of physiological signs. These physiological signs include; respiratory patterns,

heartbeat, temperature, posture, breathing rate, ElectroCardioGram (ECG), Elec-

troEncephaloGraphy (EEG) and many more. Transmission data rates for these

physiological parameters vary from 1Kbps to 1Mbps. Sensor nodes collect informa-

tion from human body and communicate with a central device called Coordinator.

Energy efficiency is the mostximportant requirement of a goodxMAC proto-

colxfor WBANs. To improve energy efficiency of WBANs, a versatile MAC pro-

tocol should have the capabilities to reduce power dissipation due to collision of

packets, overhearing of nodes, idle listening to receive probable data packets and

control packet overhead of communication. Similarly Qualityxof Servicex(QoS) is

an important goal to achieve in WBANs. This includes latency, jitter, guaranteed

communication and security.

14

3.2 WBAN Architecture

In this section, we describe communication architecture of WBANs. Then

we describe the design requirements for WBANs. Finally, we briefly present the

energy dissipation sources in WBANs.

3.2.1 Overview

Figure 2.1 shows 3-level architecture of WBANs for non-medical and medical

applications. Lowest layer consists of small sensor nodes attached or implanted to

a human body for long time monitoring of physiological or biomedical signs or hu-

man body postures. Two types of nodes are used in WBANs: (1)Biosensors: used

to measure ElectroEencephalGgram (EEG), ElectroCardioGram (ECG), Heart-

beat, continues blood sugar, Human body temperature, Blood Pressure (BP); Bio-

kinetic Sensors: used to measure acceleration and human body mobility. These

on, in or around the body sensor nodes are organized in the most common star

topology for communication of sensed information to a central device. The cen-

tral device communicates the received information for diagnose and prescription

from health services provider. For communication, central node uses the existing

technology of Level 1 and Level 2 as shown in Figure 2-1. Communication pattern

in Level 1 is termed as IntraBAN. However, Level 2 and Level 3 communication

are termed as ExtraBAN communication.

WiFi

GPRS

Central Node

ECG

ECG

PH

Hearbeat

Motion

GSM/GPRS BTS

Aceess Point

Bluetooth

/ WiFi

Figure 3.1: Communication Architecture of WBANs

The number and nature of sensor nodes vary according to the application re-

quirements. In deployment of these nodes the human body structure and mobility

are kept in consideration for reliable communication. Human body tissues are

15

sensitive to the electromagnetic radiation of the transceiver. To avoid the harmful

effects, the transceiver power is adjusted to minimum level as possible. Sensor

nodes placed on head and torso do not observe mobility as compared to nodes

placed on head and legs. However, attached sensor nodes to legs and arms scru-

tinize high mobility. For data communication in Level 1, WBANs usexIndustrial,

Scientificxand Medical (ISM) frequency band, Ultra-WideBandx(UWB) andWire-

less MedicalxTelemetry Services (WMTS) frequency band. MICS (402-405 MHz)

and WMTS (14 MHz) are licensed frequency bands. However, ISM (2.4 MHz) is

an unlicensed frequency band. WMTS is highly secure and only authorized and

trained physicians/technicians can use this spectrum. However, WMTS cannot

support audio and video streaming. MICS is especially dedicated to implant com-

munication. The most common frequency band used in WBANs is ISM, WiFi,

Bluetooth and ZigBee [Sanaullah] also use this specific frequency band for wireless

communication.

The medical applications and consumer electronics applications depend on pro-

tocols design at Level 1. The small battery operated sensor nodes collect the crit-

ical and non-critical information from environment or human body. Traffic from

these nodes classified into; Normal traffic, Emergency traffic and On-demand traf-

fic. Normal traffic is generated periodically under normal conditions. Coordinator

or central node collects the normal traffic periodically. The on-body or implanted

sensor nodes initiate the emergency traffic whenever the measured value exceeds a

predefined threshold value. Emergency traffic is unpredictable and not generated

on regular basis. However, central node or coordinator originates on-demand traf-

fic to acquire some information needed by the physician or monitoring station for

treatment or network management. Overall performances of WBANs, especially

energy efficiency, reliability, robustness, wear ability and scalability is related to

Level 1. For energy efficiency and reliability of communication, design of MAC

layer protocols at Level 1 play a vital role. With a good MAC design at Level

1, high throughput, high energy efficiency and minimum delay can be archived.

A number of MAC protocols for WBANs are proposed so far, we discuss these

protocols with their pros and cons in Section IV.

3.2.2 Design Requirements for WBANs

In WBANs, sensor nodes collect the critical and non-critical information from

different parts of the patient body and communicate with coordinator. Latency

and transmission reliability are important requirements for effective patient health

monitoring systems. Similarly for long time monitoring, WBANs required high

16

energy efficiency and scalability at Level 1.

3.2.2.1 Energy efficiency

Energy efficiency is the first goal to achieve in WBANs since sensor nodes are

small and battery operated. For long time patient monitoring, it is an obligatory

goal to play down energy dissipation at Level 1 as much as possible. Multiple

and dynamic power management schemes can be used to prolong lifespan of sen-

sor nodes. In WBANs, sensor node’s transceiver is one of the dominant energy

dissipation sources. Optimization of PHYsical (PHY) and MAC layer processes

result in reduced power consumption of transceiver. PHY layer has some limita-

tion for power optimization. However, MAC layer provides higher level of energy

savings by introducing multiple transmission scheduling schemes, optimal packet

structure, smart signaling techniques and enhanced channel access techniques.

3.2.2.2 Reliability

Reliability of WBANs depends upon transmission delay of packets and packet

loss probability. Packet transmission procedures at MAC layer and Bit Error Rate

(BER) of channel influence packet loss probability. Appropriate channel access

techniques, packet re-transmission schemes, packet size, and enhanced scheduling

schemes at MAC layer improve reliability.

3.2.2.3 Scalability

Scalability is the essential requirement for WBANs. Number of nodes, to col-

lect life critical and non-critical information, varies according to patient monitor-

ing requirements. Easily configuration of WBANs by adding or removing sensor

nodes is required to support the scalability. MAC layer has the potential to achieve

scalability.

3.2.2.4 Quality of Service (QoS)

MAC layer play a vital role to achieve high QoS. Medium access techniques at

MAC layer like TDMA and polling put forward deterministic packet loss, packet

delay. However, contention based protocols like CSMA allocates the transmission

channel to node only when it is free and the node has data to transmit. Random

access techniques result in variable packet loss and delay. Adaptive sleep cycles in

17

contention based protocols enhance energy efficiency at the cost of increase latency

and packet drops.

3.3 Sources of Energy Dissipation in WBANs

Sensor nodes have small batteries with limited power capabilities. Replace-

ment or recharging of batteries by energy scavenging is not possible. Due to

limited energy resources the power consumption of sensor nodes needs to be con-

trolled tightly. Thus minimization of energy consumption is a major issue in

WBANs. Power consumption of sensor nodes can be decreased with low power

MAC protocols. Collision of packets, overhearing of nodes, idle listening to re-

ceive the possible data packets , communication control packet overhead, packet

forwarding and transceiver state switching are the foremost sources of energy dis-

sipation in Wireless Sensor Networks (WSNs). In [12] authors identify the first

four sources of energy dissipation.

Transmission ofxdata packets on single channel byxtwo or morexsensor nodes

simultaneously results in packet collision. Collision of the packets occurs at the

receiver end. These packets are dropped and sender nodes retransmit these pack-

ets. Re-transmission of the dropped packets results in extra energy dissipation. In

overhearing, sensor nodes receive the packetsxthat are destinedxfor otherxnodes.

Those received packets are dropped and energy is dissipated. In idle listening,

nodes listen to idle channel toxreceive the possiblexpackets transmitted by other

nodes which results in extra energy consumption. If the control packets used in

communication are maximumxeffective throughput decreases.xTransmission and

receptionxof these maximum control packets consume more energy. Energy is con-

sumed in packet forwarding, when router nodes consume energy to forward a data

packet from source to destination. However, energy consumption due to packet

forwarding is ignored in WBANs due to single-hop communication in star topol-

ogy. The last source is state switching, which occurs when a sensor node switch

its transceiver from sleep mode to active mode for data transmission and then

back to sl eep mode to avoid idle listening and overhearing. Frequent switching of

transceiver is also energy consuming. Energy efficiency can be improved by avoid-

ing such energy wastage sources in efficient way. In this chapter, we briefly discuss

the classification of MACxprotocols based upon medium access techniques. We

also discuss the existing proposed protocols in details with their pros and cons. A

comprehensive table of comparison of these protocols is given at the end of this

chapter.

18

3.4 Classification of MAC protocols for WBANs

For fair access of the shared medium, MACxprotocols developed forxWBANs

are classified intoxthree categories based on channel access mechanism; xContention-

Based, Contention-Free and Low Power Listening (LPL) or Polling. This section

provides brief description about these channel access mechanisms.

3.4.1 Contention-Based MAC Protocols

In contention-basedxchannel access mechanism, sensor nodes contend for shared

medium to communicate with other nodes or coordinator. There is no predefined

scheduled for the end nodes to communicate in contention-based mechanism re-

sulting in variable latency and packet loss. CSMA is a contention based mech-

anism to access the available shared medium for data transmission. However,

CSMA/CA is a modification of CSMA to avoid packet collision. In CSMA/CA

with no RTS/CTS exchange, before transmission of data packets, nodes listen to

shared medium/channel to find out whether the shared channel is idle or not.

In case of idle situation, node starts transmission of data packets. However, if

channelxis sensed busy, transmission is rescheduled for axrandom period of time.

Figure 2.2 shows the CSMA/CA simplified algorithm.

In some cases, we need a scheduled based contention channel access mecha-

nisms called scheduled-contention. A common schedule is used for data commu-

nication to ensure the reliability and collision avoidance. Scheduled-Contention

mechanisms required periodic synchronization. To maintain synchronization, sched-

ules are exchanged on regular basis leading to extra energy consumption. The

synchronization of nodes is highly sensitive to clock drift. Periodic sleep of nodes

in this mechanism reduces the idle listening and overhearing to improve the power

efficiency.

Contention-based mechanisms are well suited in dynamic and sealable net-

works. However, in WBANs such mechanisms do not provide reliable and efficient

communication due to high energy consumption for Clear Channel Assessment

(CCA) and poor handling capabilities for emergency and on-demand traffic.

19

START

Generate Data

Packet

Is the

Channel Idle?

Yes

NoWait for a

Random Backoff

Time

Transmit RTS

CTS Received?No

Transmit Data

Packet

END

--U

sin

g R

TS

/CT

S

Exch

an

ge

--

No

t u

sin

g R

TS

/CT

S

Exch

an

ge

Figure 3.2: Algorithm of CSMA/CA

3.4.2 Contention-Free MAC Protocols

InxContention-Free MAC protocols, sensor nodes are assigned Guaranteed

Time Slots (GTS) for data communication. These protocols provide determin-

istic delay with no packet loss due to communication in guaranteed time slots

with out contention period. TDMA is a Contention-Free channel access mecha-

nism where channelxis divided into multiple time slots of fixed orxvariable length.

These time slotsxare allocated to end nodes for communication. However, multiple

time slots can also be assigned to a single node depending upon the requirements

and data volume. Pre-defined and dedicated time slots in TDMA provide a col-

lision free environment for data communication. Synchronization is the key issue

in TDMA based MAC protocols. However, TDMA base MAC protocols are effi-

cient than CSMA/CA based protocols in terms of energy efficiency and bandwidth

utilization.

For limited number of sensor nodes in WBANs with fixed data rate, TDMA

is suitable. Sensor nodes only wakeup in specified time slots for communication

otherwise, they remain in sleep mode to avoid idle listening and overhearing.

Assigning time slots to sensor nodes with different data rates, non-periodic data

and scalability are the key issues in implementing TDMA in WBANs

20

TDMA Frame With N User Time Slots

Figure 3.3: TDMA Frame

PG-MAC protocol in [4] is based upon TDMA approach where dedicated time

slots or assigned to sensor nodes. Performance evaluation shows that proposed

protocol out performs than IEEE 802.15.4 with respect to power consumption.

3.4.3 Low Power Listening (LPL) MAC Protocols

In LPL mechanism, sensor nodes periodically listen to the channel. Nodes

go into sleep mode if channel is sensed idle, other wise keep the transceiver in

active mode to receive data packets. This mechanism is also known as Polling.

A long preamble is sent before the message to detect the pooling at receiver side.

LPL mechanisms avoid idle listening and overhearing. Synchronization is not

required here. Based on hardware complexity and listening of long preamble, LPL

mechanisms are not well suited in WBANs. LPL mechanisms support simplex

communication. However, WBANs required duplex channel communication to

accommodate periodic, on-demand and emergency traffic.

21

Table

3.1:ComparisonofMAC

protocols

basedonchannel

accessmechanism

MAC

Featu

res

Contention-B

ased

MAC

pro

toco

lsContention-Free

MAC

Pro

toco

lsLow

Power

Listening

MAC

Pro

toco

lsNetwork

Scala-

bility

Highly

Scalable

Poor

Scalability

Goodbutlimited

bydelay

Packetdelay

Variable,dep

endson

traffi

cLoad,priorityan

dap

plica-

tion

Deterministic

Deterministic

but

varies

withTrafficload

Packetloss

Variable,dep

endson

traffi

cLoad,priorityan

dap

plica-

tion

Deterministic

Deterministic

but

varies

withTrafficload

Energy

Effi-

cien

cyCCA

inhightraffi

cendsup

withhighenergy

consump-

tion

Guaran

teed

time

Enab

lecollisions

free

communica-

tion

and

periodic

sleep

whichim

provesenergy

effi-

ciency

HighEnergy

efficiency

TrafficHan

dling

Han

dle

periodic,

non

-periodic

and

ondem

and

traffi

c

Han

dle

periodic

traffi

cHan

dle

periodic

traffi

cwith

capab

ilitiesfornon

-periodic

Throu

ghpu

tLow

Excellent

Good

Syn

chronization

Synchronou

sSynchronizationisrequired

NA

Sen

sitivity

toclockdrift

Sensitive

toclock

drift

Highly

Sensitive

toclock

drift

NA

22

3.5 MAC protocols for WBANs

Inxthis section wexdiscuss some of well known existing MAC protocols pro-

posed for WBANs. This discussion covers the pros and cons of these proposed

protocols in context of energy minimization and resource utilization. The fol-

lowing subsections provide detail operation of these protocols with emphasize on

energy consumption. We also discuss, how these protocols tackle energy ineffi-

ciency sources like collision, idlexlistening,xoverhearing and controlxpacket over-

headxwhich are widely addressed in literature.

3.5.1 IEEE 802.15.4 MAC protocol

IEEE 802.15.4 is designed for low data rate wireless applications [1]. This

protocol operates in threexfrequency bands: 868 MHz,x915 MHz andx2.4 GHz

frequency bands. These frequency bands are further divided into 27 sub-channels

i.e., 2.4 GHz frequencyxband is divided into 16 sub-channels, 915 MHs frequency

band into 9 sub-channels and onexsub channel in 868 MHz frequency band. Two

operational modesxare defined for IEEE 802.15.4: beaconxenabled mode and non-

beaconxenabled mode.

In beaconxenabled mode, coordinator controls device synchronization, associ-

ation and data transmission using periodic beacons. Beacon enabled mode use

a super frame. Thisxsuper frame consists of active and inactive periodsx. Ac-

tive period of super frame isxdivided into three parts: Contention Access Period

(CAP) using slotted CSMA/CA, beacon and a Contention Free Period (CFP). A

maximum ofxseven Guaranteed Time Slots (GTS) are assigned to end nodes to

accommodate time critical data in CFP. This mode of operation ofxIEEE 802.15.4

is not suitable for WBANs due to its asymmetric transmission support.

Non-beaconxenabled mode ofxIEEE 802.15.4 uses un-slotted CSMA/CA. Au-

thors in [2], analyze slotted and un-slotted CSMA/CA and presented their re-

sults. These results show that un-slotted mechanism out performs well in terms

of bandwidth utilization and latency as shown is Figure 2.4. However, inxnon-

beacon enabled mode the Clear ChannelxAssessment (CCA) leads to high energy

consumption.

23

Figure 3.4: Normalized Throughput Versus NC

3.5.2 Battery-aware TDMA protocol

In [3], authors propose a battery-aware TDMA based MAC protocol with

cross-layer design to maximize the network life. This protocol takes the following

parameters into account for medium access: electrochemicalxproperties of battery,

time-varying wirelessxfading channel, and packetxqueuing characteristics. The

operation of this protocolxis similar toxIEEE 802.15.4 beacon enabled mode, where

the modes listen periodically to beacons from coordinator. The time axis is divided

into three parts; beaconxslot, active time slots andxinactive period as shown in

the Figure 2.5 [3]. The frame length is adaptive and can be changed according

to application requirements. Sensor nodes wake up at the beginning of beacon

period. Each node has its own distinct time slot Ts to transmit data in active

period after receiving the beacon. To avoid extra energy consumption, nodes

remain in sleep mode for the inactive time. This protocol prolongs the lifespanxof

wireless sensorxnodes.xReliable and timelyxdelivery of packets is achieved using

GTS. However, there is no mechanism defined for emergency data. Similarly

holding of packets in buffer for long time, leads to high average delay and packet

drop rate.

3.5.3 Priority guaranteed MAC protocol

In [4], authors propose a priority-guaranteedxMAC protocol. This protocol

uses a new superframe structure as shown in Figure 2.6. The activexperiod is di-

videdxinto five parts; a beacon, Control Channel AC1, Control Channel AC2,

Time SlotxReserved for Periodic (TSRP) traffic, and Time Slot Reservedxfor

24

Figure 3.5: TDMA Frame Structure

Bursty (TSRB) traffic. AC1 is used for uplinkxcontrol of life-critical medical

application while AC2 is used for uplinkxcontrol of Consumer Electronics (CE)

applications. Randomized ALOHA is used for these two control channels. Pro-

posed protocol is based upon TDMA approach to assign Guaranteed Time Slots

(GTS) within twoxdata channels TSRP and TSRB. These time slots are allocated

on-demand to using the control channels. As shown in simulation results [4],

this protocol outxperforms than IEEE 802.15.4 inxterms of energyxconsumption.

However, complexxsuperframe structure and inadaptability to emergencyxtraffic

are major drawbacks of this protocol.

Figure 3.6: Superframe Structure of Priority-Guaranteed MAC

3.5.4 Energy-Efficient Low Duty Cycle MAC Protocol

Authorsxpropose a new MAC protocol based upon the static nature of BAN

[5]. TDMA approach is used for streamingxlarge amount ofxdata. The Static

nature and TDMA approach are being utilized efficiently to maximize the network

life. In target topology a Master Node (MN) collects data from on body nodes

and communicates with a Monitoring Station (MS). The received data is being

analyzed by MS while the on-body network coordination and synchronization is

being performed by MN. As shown in Figure 2.7, the total frame is dividedxinto

multiplextime slots. Timexslots S1 to Sn are allocated to sensor nodes while

time slots RS1 to RS2 are reserved which are being assigned when requested.

25

The number of these extra time slots depends upon the targeted packet drop,

packetxerror rate and numberxof sensor nodes.

Figure 3.7: TDMA Frame Structure

To avoid the collision/overlapping of packets transmission due to clock drifts,

guard band time is inserted between two consecutive time slots. Two types of

communication models are being discussed in the paper. First, the MN has one

transceiver. In this case, enough time is reserved for communication of MN with

MS. In second case, where the MN has two transceivers, simultaneously commu-

nication of MN with MS and sensor nodes is possible. The communication uses

the different physical layer communication models for transparency. From energy

consumption analysis in [5], proposed protocol out performs in term of energy for

high communication data rates as well as for short burst of data. However, this

protocol uses a Network Control (NC) packet for periodic synchronization after

N number of time frames which leads to an extra consumption of energy. Other

shortcoming includes; fixed frame structure based on pure TDMA, no CAP to

accommodate small burst of data, and no mechanism is defined for on-demand

traffic.

3.5.5 A power-efficient MAC protocol for WBAN

In [6], authors propose a new mechanism at MAC layer to accommodate nor-

mal, emergency,xand on-demand traffic.xFor reliable transmission twoxwakeup

mechanisms are defined: traffic-based wakeupxmechanism for transmission of nor-

mal traffic and wakeupxradio mechanism for emergency/on-demandxdata trans-

mission. Normal traffic is generated periodically by sensor nodes to monitor rou-

tine physiological parameters. The unpredictable emergencyxtraffic is initiated by

26

on-body sensor nodes in emergency situation. However, the coordinator generates

on-demand traffic to acquire information from sensor nodes. A new superframe

structure is defined where the time axis is divided intoxthree parts: axbeacon mes-

sage, a Configurable ContentionxAccess Period (CCAP) to accommodate short

burst of data, and axContention Free Period (CFP) where Guaranteed Time Slots

(GTS) are assigned to end nodes for collision free communication. In CCAP,

proposed protocol uses slotted ALOHA. Superframe structure for this protocol is

shownxin Figure 2.8 [6].

Figure 3.8: Superfame Structure

Coordinator organizes the traffic-based wakeup table according to application.

Periodic sleep/wakeup mode avoids the unnecessary energy dissipation due to

idle listening and overhearing. To compensate the clocks drift at coordinator

and sensor nodes, sensor nodes wake up in advance for a time period of TK =

2θTW where TW is the beacon period. For emergency traffic sensor nodes send

wake up radio signal to coordinator while coordinator sends a wake up signal to

sensor nodes for on demand traffic. Simulation results based upon Monte Carlo

method for poisson and deterministic traffic. Performance of proposed protocol

in terms of energy and delay are compared with that of WiseMAC [7], where it

performs better. However, use of Low Power Listening (LPL) is not an optimal

choice for implanted and on-body sensor nodes communication due to strict power

capabilities.

3.5.6 Energy Efficient Medium Access Protocol

In [8], authors propose a new MAC protocol based upon centrally controlled

wakeup and sleep mechanisms to maximize energy efficiency. Some upper layer

functionalities are incorporated to reduce power dissipation due to overhead. This

protocol is based upon basic assumption of sensor nodes with a star topology

where a central node (master node) coordinates with on-body/implanted sensor

27

nodes (Slave nodes). Maximum number of slave nodes for a single master nodes is

defined to be 8. Due to high power and computational capabilities, more activities

and processes are assigned to central node.

Basic operation of this MAC protocol involves three processes. First one is

link establishment, where a slave node wants to join a cluster. After success-

ful link establishment, each nodexis assigned with a unique sleep time to avoid

idle listening and overhearing. Second one is the wakeupxservice process, where

master and slave nodes communicate. Exception process, also called an Alarm

process is initiated by slave node to communicate with master node for emergency

data. For guaranteed and reliable communication, a novelxconcept of Wakeup

FallbackxTime (WFT) is introduced. In case of failure in assigned wakeup pro-

cess, sensor node enters into sleep mode for a specific time interval calculated by

WFT. During this sleep time, senors node buffers data packets for future commu-

nication. Similarly, master node also goes into sleep mode set by WFT if it fails

to communicate with slave nodes. Overlapping of time slots is being avoided by

this mechanism.

Figure 3.9: Power Compared to Sleep Time and Number of Retransmits

From simulation results for different applications such as glucose monitoring,

human body temperature, EEG, and ECG, power consumption depends on sleep

28

interval and number of retransmissions as shown in Figure 2.9. The centrally

controlled process reduces efficiently the extra energy consumptionxdue to idle

listeningxand overhearing. However, implementation of this protocol is highly

complex and has no proper mechanism to handle on-demand traffic. Other draw-

backs include: limitation of nodes in one cluster, communication is only initiated

by mater node and only one node goes into link establishment process at a time.

3.5.7 BodyMAC

In [9], authors propose a TDMA-based MAC protocol where they define uplink

and downlink subframes to facilitate sleep mode with emphasize on energy min-

imization. Nodes remain in sleep modexwhen they havexno data to send.xSleep

mode performs well for low duty cycle sensor nodes. Different data communica-

tion models are accommodated using 3 bandwidth management procedures; Burst

Bandwidth procedure, Periodic Bandwidth procedure and Adjust Bandwidth proce-

dure. This efficient and flexible bandwidth management procedure improves the

network stability and improves transmission of control packets.

Figure 3.10: BodyMAC Frame Structure

As shown in Figure 2.10 [9], the MAC frame isxdivided intoxthree parts; a

beacon, a downlink and uplink. Synchronization is archived by beacon. To ac-

commodate on demand traffic, downlink is used for data communication from

coordinator node to sensor nodes. However, the uplink frame isxdivided into Con-

tention Access Period (CAP) and Contention Free Period (CFP). CAP is based

on CSMA/CA, where nodes compete to send control packets to coordinator for

Guaranteed Time Slots (GTS). However, nodes can also communicate for small

data packets during CAP. Coordinator assigns GTS to sensor nodes in CFP to

avoid collision. Communication using CFP improves energy effecting. However,

for uplink frame in CAP, CSMA/CA ends up with high energy consumption due

to Clear Channel Assessment (CCA) and collision issues.

29

3.5.8 MedMAC

In [10], authors propose Medical Medium Access Control (MedMAC) protocol

for WBANs to improve channel access mechanism and reduce energy dissipation.

MedMAC using TDMA approach for time slots assignments to end nodes for data

communication. However, these assigned time slots are of variable length and

vary according to sensor nodes requirements. A novel scheme is introduced for

synchronization. MedMAC uses multi-superframe structure, where beacons are

used for synchronization as shown in Figure 2.11 [10]. For network initialization,

emergency traffic, and low data communication it uses an optimal contention

period.

Figure 3.11: Multi-Superframe Structure for MedMAC Protocol

To maintain clock synchronization of nodes and coordinator, MedMAC uses

timestamp scavenging with Adaptive Guard Band Algorithm (AGBA). Collision

of data packets is avoided using unique GTS for each sensor node. Similarly AGBA

maintain the synchronization of devices to avoid collision due to clocks drift. Us-

ing AGBA guard band time is inserted between two consecutive time slots. This

guard band time is adjustable and based on clock drift of devices. Drift Adjust-

ment Factor (DAF) monitors the guard band and avoid waste of bandwidth using

extra guard bands.

Authors use OPNET for simulation. They comparexthe performancexof Med-

MAC with thatxof IEEE 802.15.4 with respect to power dissipation. For applica-

tions with low data rates like pulse (8 bps),respiration (640 bps), and temperature

(16 bps), and medium data like ECG, simulation are performed. From the simu-

30

lation results in [25], it is concluded that it out performs than IEEE 802.15.4 with

respect to energyxconsumption. Collision is being avoided using GTS. However,

MedMAC takes low data traffic into consideration which is not suited in WBANs

where date rates for wearable and implanted sensors may be high.

3.5.9 Heartbeat-Driven MAC protocol

In [11], authors propose a TDMA based protocol for WBANs with utilization

of Heartbeat-Rhythm for synchronization. Network topology for proposed pro-

tocol is star topology where a central node coordinates the network. To avoid

collision, H-MAC assigns dedicated time slots to sensor nodes for communica-

tion. Using Heartbeat Rhythm, H-MAC maintains the synchronization required

for TDMA approach without using periodic control messages. This mechanism

leads to minimize overall energy consumption. Each biosensor extracts Heartbeat

Rhythm information from its sensory data. For detection of peaks in the heart-

beat rhythm, authors use the algorithms proposed in [12,13]. Synchronization is

archived by these peaks. H-MAC uses the peek intervals for data communication.

Time slots assignment and frame cycles for synchronization are calculated by co-

ordinator. The coordinator also utilizes Heartbeat Rhythm information from its

own sensory data.

From simulation results, H-MAC prolongs the networks life as compared to

Lightweight MAC (L-MAC) [14] and Sensor MAC (S-MAC) [15]. This efficiency

is achieved by TDMA approach, where collisions are avoided by dedicated time

slots and reduced idle listening. Replacement of traditional synchronization with

Heartbeat Rhythm pattern also reduces the energy consumption. However, Heart-

beat Rhythm is not accessible by all sensors like accelerometer. In such cases

devices can not by synchronized. Integration of accelerometer with other sensors

or facilitating accelerometer to access the heartbeat leads to complexity. Similarly

the insertion of guard band time to avoid collisions leads to minimize bandwidth

utilization.

31

Table

3.2:ComparisonofMAC

Protocols

MAC

Protocol

Access

Tech-

nique

Energy

Efficiency

Mech-

anism

Synchronization

Perform

ance

Com

pari-

son

Rem

arks

IEEE

802.15.4

Beacon

Enab

led

[1]

Slotted

CSMA/C

ANA

Transm

itBeacons

NA

Beaconenab

ledis

not

suitab

leforlongtime

mon

itoring

Battery-aware

TDMA

protocol

[3]

TDMA

Periodic

Sleep

mode

Using

beacons

like

IEEE802.15.4

IEEE

802.15.4

and

Blue-

tooth

No

Mechan

ism

for

Emergency

Traffic.

Has

highpacketdelay

Priority

guaran

-teed

MAC

pro-

tocol[4]

Ran

dom

ized

ALOHA

and

TDMA

Differentiating

control

and

data

chan

nels

and

introducing

periodic

sleepmode

Beaconsareused

for

dow

nlinksynchroniza-

tion

IEEE

802.15.4

Com

plex

Super

fram

eStructure

and

inad

aptability

toem

ergency

Traffic

Energy

-Efficient

Low

Duty

Cycle

MAC

Protocol

[5]

TDMA

Low

duty

cyclean

dlong

sleep

time

toreduce

pow

erconsumption

Periodic

synchroniza-

tion

afterN

cycles

us-

ing

Network

Con

trol

Packet

FlexiM

AC

[16]

No

mechan

ism

isde-

fined

for

on-dem

and

traffi

c,Periodic

syn-

chronizationis

energy

consuming

Apow

er-efficient

MAC

protocol

forW

BAN

[6]

Low

Pow

erLis-

tening

(LPL)&

slottedALOHA

Using

Guarented

time

slots

for

communiation

toavoid

collisions,

idle

listening

and

overhear-

ingareavoided

byperiod

sleep

Early

wakeup

mech-

anism

tocompensate

clock

drift

B-M

AC,

X-M

AC,

WiseM

AC

and

Zig-

Bee

Low

Pow

erListening

(LPL)is

not

anop

-timal

choice

for

im-

plantedan

don

-body

32

Table

3.3:ComparisonofMAC

Protocols

MAC

Protocol

Access

Tech-

nique

Energy

Efficiency

Mech-

anism

Synchronization

Perform

ance

Com

pari-

son

Rem

arks

IEEE

802.15.4

Non

-Beacon

Enab

led[1]

Unslotted

CSMA/C

ANA

NA

NA

High

through

put

,Low

latency

andhigh

pow

erconsumption

Energy

Efficient

Medium

Access

Protocol[7]

CCA

based

onListen

Before

Transm

it(LBT)

centrally

controlled

pro-

cess

reduces

efficiently

the

extra

energy

con-

sumption

dueto

idle

lis-

teningan

doverhearing

Duringeverycommu-

nication

master

ans

slavenodesharetheir

clocksinform

ations

Zigbee,

Bluetooth

and

IEEE

802.11

highly

complexim

ple-

mentation

and

have

noproper

mechan

ism

tohan

dle

on-dem

and

traffi

cBodyMAC

[8]

TDMA

and

CSMA/C

AIdles

listeing

and

over-

hearing

are

avoided

by

periodic

sleep

Beacon

messages

are

used

forsynchroniza-

tion

IEEE

802.15.4

CCA

inuplink

lead

sto

high

energy

con-

sumption

MedMAC

[10]

TDMA

Dynam

icad

justment

ofresources

forQoS

multi-superfram

estructure

isused

for

synchronization

IEEE

802.15.4

Efficientforlow

data

rate

Heartbeat-

Driven

MAC

protocol[11]

TDMA

UsingTDMA

approach,

dedicated

timeslotsfor

sonsornodes

utilization

ofHeartbeat-Rhythm

forsynchronization.

Lightw

eigh

tMAC

(L-

MAC)[14]

and

Sen-

sor

MAC

(S-M

AC)

[15]

Insertion

ofGuard

ban

dreduces

ban

d-

width

utilization

33

3.6 Discussion and Open Research Issues

Energy efficiency is one of the main goal to achieve in WBANs for mobile

and ubiquitous health monitoring with critical and non-critical conditions. Cur-

rent research work for energy minimization is focused at MAC layer. However,

other areas such as network layer and cross layer design need to be consider for

energy minimization. In cross layer design we can improve the energy efficiency

by integrating two or more protocol layers from communication protocol stack.

Therefore, research work using cross layer approach will be prominent field to

minimize energy consumption. Similarly Radio Frequency (RF) communication,

antenna design, and propagation modules effect performance of WBANs. Other

issues for researcher to be consider includes mobility of on, in or around human

body sensor nodes, transparency at MAC layer, interoperability, security and QoS.

A comparison of discussed MAC protocols is presented in Table III.

CDMA, FDMA, CSMA, and TDMA are multiple approaches for medium ac-

cess. However, each of them has some advantages and disadvantages. Collision free

communication is achieved by CDMA, but high computational and power require-

ments are major obstacles for implementation in WBANs where sensor nodes have

limited computational capabilities with constrained power. Hardware complexity

required for FDMA, to achieve collision free channel access, makes FDMA an

inappropriate solution for WBANs. CSMA based MAC protocols provide promis-

ing results such as low delay, reliable communication, and simple implementation

procedure in small dynamic networks. However, additional energy consumption

for collision detection or collision avoidance, and protocol overhead are major

shortcomings of CSMA. TDMA-based MAC protocols are contention free, nodes

transmit data in predefined time slots to avoid packet collision. For small networks

with low mobility and small number of sensor nodes and periodic data generation,

TDMA is the best approach for medium access. However, strict synchronization

requirement, non-adaptability and scalability are some issues faced by TDMA.

Based on topology and limited number of nodes in WBANs, TDMA could be

considered most suitable solution for medium access in WBANs.

Energyxefficiency is of utmost importance in WBANs. For high energy ef-

ficiency, a number of protocols have been proposed. However, MAC protocols

specifically for WBANs need to be developed. The aim of these protocols would

be to avoid energy dissipation due to collision, overhearing and idle listening with

reduced control packet overhead and implementation complexities. Fairness at

MAC layer, high bandwidth utilization, reliable communication, minimum delay,

and reduced synchronization cost are other objectives for multipurpose efficient

34

MAC protocol. The proposed protocol should have capabilities toxaccommodate

communication of normal,xemergency, andxon-demand traffic. However, selection

of MAC protocols is application and hardware dependent. This may be one of the

reasons that no proposed protocol is accepted as a standard for WBANs so far.

35

Chapter 4

Proposed MAC Protocol

36

4

Proposed MAC Protocol

4.1 Protocol design

Proposed MAC protocol, AR-MAC is based upon TDMA approach to min-

imize energy consumption. AR-MAC assigns Guaranteed Times Slot (GTS) to

each sensor node for communication based upon the requirements of sensor node .

To reduce overhearing and idle listening, proposed system uses periodic sleep and

wakeup according to node requirements. We assume a star topology; a Central

Node (CN) collects data from sensor nodes and communicates with a Monitoring

Station (MS), direct or through an Access Point (AP) as shown in the Figure 1.1.

Figure 4.1: WBAN Topology

CN is usually equipped with larger batteries and higher computational power.

One or two transceivers may be used within a single CN. In case of two transceivers

total time frame T Frame is allocated for communication with sensor nodes. We

assume CN with single transceiver where T Frame is divided into three parts: Con-

tention Free Period (CFP) for communication with sensors, Contention Access

Period (CAP) to accommodate emergency or on-demand traffic and time TMS

37

Start

Scans RF Channel

Wait For

Time TCP

Switch to another one Send ACK Send Channel Packet

Scans RF Channel

Start

Yes

Yes

Free

CP

Recieved Free

NoNo

No

Sensor Node Central Node

Yes

Figure 4.2: Channel Selection Procedure

for communicating sensor nodes’ data to MS. Following subsections describe AR-

MAC from its Channel Selection, Time Slots Assignment, Synchronization and

Frame Format.

4.1.1 Channel Selection

Initially, CN starts scanning for available free Radio Frequency (RF) channels.

If the current RF Channel is busy, CN switches to another RF Channel. CN selects

a free RF channel for communication. After successful selection of RF Channel,

CN broadcasts the Channel Packet with address and channel information to sensor

nodes. On the other side end nodes scan RF channels for Channel Packet from

CN. Sensor node scans the RF channel if it is free it switches to another RF

channel. If the channel is busy it waits for time TCP to listen Channel Packet. If

sensor node does not receive the Channel Packet, it switches again to next channel.

After successful reception of Channel Packet, node starts transmission and sends

an acknowledgment (ACK) packet to CN, as shown in Figure 2.2.

4.1.2 Time Slot Assignment

Once sensor node selects a proper RF Channel after receiving Channel Packet

from CN, sensor node sends out a Time Slot Request (TSR) packet to CN. TSR

packet includes sensor node’s data rate and required time slot information. Au-

thors in [6], propose time slots of fixed length with fixed guard band time. Biomed-

ical sensors in-body and on-body have different data rates and sampling intervals

with different clock drifts. Assigning time slots of equal length for unequal require-

ments is wastage of resources. AR-MAC uses an adaptive scheme for Time Slot

(TS) and GBT time. Based on traffic pattern of nodes, CN assigns time slot and

38

sends Time Slot Request Reply (TSRR). These time slots are of variable length

depend upon the requirements of sensor nodes. Assigned time slot can easily ac-

commodate the transmission of data packet, reception of ACK packet and some

acceptable delay, based on the communication model. A guard band time TGB

is inserted between the two successive time slots to avoid the interference due to

clock drift of node and CN as shown in Figure 2.3.

TS1 TSn------------------ CAP TMS

Guard Time Contention Access Period

Communication with MSGuaranteed Time Slot

Figure 4.3: Time Slots Assignment with Guard-band Time

Value of TGB depends upon length of the successive time slots. Adaptive guard

band avoids possibilities of collision and interference due to clock drift. We use

the following equation to calculate TGB .

TGBn,n+1 =

F

100× 1

2[TSn + TSn+1] (4.1)

TGB1 =

F × TS1

100(4.2)

TGBn =

F × TSn

100(4.3)

where F is guard band factor, depends upon the average drift value. However

guard band time TGB1 is inserted before first time slot and similarly guard band

time TGBn is placed after N time slot. After successful time slot assignment, sensor

nodes enter into sleep mode and wakeup only to send data to CN in allocated

time slots. Periodic sleep reduces energy consumption due to idle listening and

Overhearing. Allocated time slots in CFP are completely collision free thus reduce

the energy consumption and make the communication reliable.

39

4.1.3 Synchronization

TDMA schemes require extra energy cost for periodic synchronization [8]. Syn-

chronization of nodes after N number of cycles is energy consuming process. AR-

MAC uses a novel synchronization mechanism to avoid collision and energy con-

sumption. After successful assignment of time slots to nodes, CN listens to data

packet within expected time slot. Upon arrival of data packet, CN compares cur-

rent arrival time of the packet and expected arrival time with acceptable delay

(D). Based on the difference of current arrival time and expected arrival time a

Drift Value (DV ) is calculated. This DV is transmitted to node within ACKnowl-

edgment (ACK) packet to adjust time slot for future communication. However,

this value depends upon acceptable delay and F . If the difference between the

expected arrival time and current arrival is greater than D, CN sends DV with

in SYNChronization ACKnowledgment (SYNC-ACK) packet for future synchro-

nization to sensor nodes otherwise, CN sends simple ACK packet for received data

packet. For communication of data in future, sensor node adjusts its wakeup time

schedule according toDV . Using this scheme of synchronization a node can go into

sleep mode without loosing synchronization for N number of cycles. Acceptable

delay D is linked with guard band factor F as under:

D = Min(TS1......TSn)×F

100(4.4)

For future synchronization, decision of sending DV to end nodes is based upon

the difference of current arrival time and expected arrival time of data packet.

△T represents this difference.

△T = ExpectedArrivalT ime− CurrentArrivalT ime (4.5)

DV =

{0 if | △T |< D

△T if | △T |> D(4.6)

40

4.1.4 Frame Formate

Proposed AR-MAC uses two types of packets: Data Packets and Control Pack-

ets. In data packet sensor node sends its periodic data in allocated time slot. For

emergency data, node uses CAP. Control Packets are:

1. Channel Packet: After channel selection Central Node advertises channel

information and its unique address in Channel Packet.

2. Time Slot Request (TSR) Packet: Sensor node TSR packet to Central Node

for Guaranteed Time Slot (GTS) assignment for data communication

3. Time Slot Request Reply (TSRR) Packet: Central node sends Guaranteed

Time Slot information with CAP information to node in Time Slot Request

Reply packet

4. Synchronization-Acknowledgment (SYNC-ACK) Packet: For synchroniza-

tion, Central Node sends the required Drift Value to end node with ACK

of previously received data packet in Synchronization Packet to compensate

the clock drift and maintain the synchronization

5. Data Request (DR) Packet: For on demand traffic/information, Central

Node sends Data Request Packet to end nodes

6. Acknowledgment (ACK) Packet: Each data packet is acknowledged using

Acknowledgment Packet

Preamble Sync Frame Len MPDU

Control Address Other Payload (Variable ) CRC

Packet Type ACK ODT

Figure 4.4: MAC Layer Frame Formate

The MAC Protocol Data Unit (MPDU) stars with 3 octets of overhead. First

octet carries information about packet type. Preceding two octets carry address

41

information. In case of emergency traffic sensor node waits for CAP. Upon suc-

cessful Clear Channel Assessment (CCA), sensor node starts communication with

CN. However, in case of on-demand traffic CN sets On-Demand Traffic (ODT)

field in ACK or SYNC-ACK packet to 1. After receiving this packet sensor node

wakes up in CAP to listen data request from CN. After receiving data request

from CN, sensor node sends requested data packets and waits for ACK packet.

Sensor node enters into sleep mode after successful reception of ACK.

4.2 Energy Consumption Analysis

In order to model energy consumption, we consider the energy consumption

related to transceiver. In this study, we assume energy consumption of sensing and

processing units to be constant. We assume periodic traffic pattern, i.e., sensor

nodes send periodic data to CN in assigned time slots. Most of the time sensor

nodes remain in sleep mode. During allocated time slots, they wakeup to send

data. We use the following equation to measure the energy consumption for N

number of cycles.

ETotal =N∑k=1

ESleepk +N∑k=1

EActivek (4.7)

Energy consumption is a function of time and current drawing from voltage

source for a specific task. When nodes enter into sleep mode they still consume

energy. The sleep mode duration can be calculated from total time frame length

and time for which the node is in active mode.

TSleep = TFrame − TActive (4.8)

ESleep = TSleep × ISleep × V (4.9)

ISleep is the current drawing from voltage source V during sleep mode. In

TActive the nodes receive, transmit and wait for Acknowledgment. Energy is also

consumed in switching, from sleep to active and active to sleep mode. The energy

consumed for all these tasks will be considered as energy in TActive.

42

EActive = 2× ESw + ETrans + ERec + ETOut (4.10)

where, ESw is Switching energy, ETrans Transmission energy, ERec is Receiving

energy and ETOut is Time-Out energy. We describe these terms in details in the

following subsections.

4.2.1 Switching Energy

Most of the time, sensor nodes remain in sleep mode. Sensor nodes turn

on its transceiver in wakeup mode for communication. Switching energy is the

consumed energy for switching transceiver between states; sleep mode and wakeup

mode. Frequently switching of transceiver between states leads to high energy

consumption. Energy consumed for switching the transceiver is determined by

the following equation.

ESw = TSwitch × ISwitch × V (4.11)

where TSwitch is the required for the transceiver to switch between sleep and wakup

mode and ISwitch is the required current.

4.2.2 Transmission Energy

Transmission energy is the energy consumed for transmission of Data or Con-

trol packet of length P . Following equation links the transmission energy with

length of packet P , time required for transmission of single byte TByte, current

draw during transmission ITrans and a voltage source V.

ETrans = P × TByte × ITrans × V (4.12)

4.2.3 Receiving Energy

Receiving Energy is the consumed energy while receiving packets and their

associated overhead. Receiving energy is expressed as:

43

ERec = P × TByte × IRec × V (4.13)

where, IRec is the Current during reception, TByte is the time for single byte, P is

the length of packet and V is the voltage source.

4.2.4 Time-Out Energy

The energy consumed after transmission and before reception of an ACK

packet is termed as Time-Out energy. For time TTOut, current ITOut and voltage

source V , we used the equation given below to calculate the energy consumption

during Time-Out.

ET−Out = TTOut × ITOut × V (4.14)

4.3 Simulation Results

We use MATLAB to measure and compare the energy efficiency of the AR-

MAC with that of IEEE 802.15.4. In energy consumption comparison, we consider

the energy consumption of RF transceiver. We use the energy consumption model

from Crossbow MICAz data sheet as shown in Table II. Packets are dropped

randomly with average Packet Error Rate probability from 1% to 20%. Time

frame size used in simulations is T Frame = 1 Second. We used packets format as

shown in Fig.4. Simulation has been carried out for 10 Sensor Nodes.

Table 4.1: Simulation Parameters Value

Parameter Value

Time frame( T Frame) 1 SecondVoltage Source 3 voltsCurrent Draw in Receive Mode 19.7 mACurrent Draw in Transmit Mode 17.4 mACurrent Draw in Idle Mode 20.0 mACurrent Draw in Sleep Mode 1 micro-ANumber of Sensor Nodes 10Number of Cycles N 1000

44

2 4 6 8 10 12 14 16 18 209.25

9.3

9.35

9.4

9.45

9.5

9.55

9.6

Packet Error Rate[%]

Ene

rgy

Con

sum

ptio

n [J

oule

]

802.15.4AR−MAC

Figure 4.5: Energy consumption of AR-MAC and IEEE 802.15.4 for N = 1000

We used Eq. 7 to calculate the energy consumption for N = 1000. Figure 5

shows the energy comparison of the AR-MAC with IEEE 802.15.4. The graph in

Figure 5 shows that energy consumption of IEEE 802.15.4 increases with increase

in probability of Packet Error Rate. This increase in energy consumption is due to

extra energy requirement of CSMA/CA operation in IEEE 802.15.4. The energy

consumption of AR-MAC increases with a minor variation due its adaptive time

allocation and adaptive guard band mechanism. AR-MAC assignees guaranteed

time slots to sensor nodes for communication, to overcome the packet collision

and overhearing.

45

Chapter 5

Conclusion

46

5

Conclusion

5.1 Conclusion

Aim of this research work is to analyze the existing MAC protocols for WBANs

with emphasis on energy minimization. These protocols are being developed to

prolong the lifespan of WBANs, reliable communication, flexibility, fair manage-

ment, and QoS. However, MAC protocols based on random access and LPL are

unable to accommodate the emergency and on-demand traffic. On the other hand,

TDMA is a vital approach for medium access to be used in WBANs. Majority of

the existing MAC protocols based on TDMA approach. Each of them has some

advantages and disadvantages discussed above. Due to diverse application require-

ment and hardware constrains, no one protocol is being accepted as a standard.

A new protocol needs to be developed to achieve requirements of WBANs like

energy efficiency, scalability, fairness, reduced implementation complexity, sup-

port for divers application, interoperability, reduced synchronization overhead,

and QoS.

In this thesis we proposed AR-MAC, a new MAC protocol for WBANs. AR-

MAC assigns guaranteed time slots in adaptive manner and makes the communica-

tion reliable by introducing adaptive guard band to avoid collisions. Synchroniza-

tion is achieved by introducing a smart mechanism to compensate drift of sensor

node’s clock. By simulation, we compared the performance of AR-MAC with that

of IEEE 802.15.4 in terms of energy consumption. Simulation results show supe-

rior performance. Future work will be carried out to implement proposed protocol

including all Control and Data Packets in real time scenario.

47

References

48

References

[1] IEEE Std.802.15.4, Wireless medium accesses control (MAC) and physical

layer (PHY) specif ications for low data rate wireless personal area networks

(WPAN). IEEE: Piscataway, USA, 2006

[2] Changle, L., Huan-Bang, L., and Kohno, R., “Performance evaluation of IEEE

802.15.4 for Wireless Body Area Network (WBAN),” in the Proc. of IEEE In-

ternational Conference on Communications Workshops (ICC Workshops 2009)

pp. 1-5, 2009.

[3] Su, H., and Zhang, X., “Battery-dynamics driven TDMA MAC protocols for

wireless body-area monitoring networks in healthcare applications,” IEEE J.

Sel. Areas Commun. 27(4):424-434, 2009.

[4] Zhang, Y., and Dolmans, G., “A new priority-guaranteed MAC protocol for

emerging body area networks,” in the Proc. of Fifth International Conference

on Wireless and Mobile Communications (ICWMC 2009), pp.140-145, 2009.

[5] Marinkovi, S. J., Popovici, E. M., Spagnol, C., Faul, S., and Marnane, W.

P., “Energy-efficient low duty cycle MAC protocol for wireless body area net-

works,” IEEE Trans. Inf. Technol. Biomed. 13(6):915925, 2009.

[6] Kwak, K. S., Ullah, S., Kwak, D. H., Lee, C. H., and Lee., H. S., “A power-

efficient MAC protocol for WBAN,” Journal of Korean Institute of Intelligent

Transport Systems 8(6):131140, 2009.

[7] A. El-Hoiydi et al., “WiseMAC: An Ultra Low Power MAC Protocol for the

WiseNET Wireless Sensor Network,” Proc. 1st ACM SenSys Conf., ACM

Press, 2003, pp. 302-303.

[8] O. Omeni, A. C. W. Wong, A. J. Burdett, and C. Toumazou, “Energy efficient

medium access protocol for wireless medical body area sensor networks,” IEEE

Transactions on Biomedical Circuits and Systems. vol. 2, no. 4, pp. 251-259,

Dec. 2008.

49

[9] G. Fang and E. Dutkiewicz, “BodyMAC: Energy efficient TDMA-based MAC

protocol for wireless body area networks,” 9th International Symposium on

Communications and Information Technology, ISCIT, pp. 1455-1459, 2009.

[10] N.F. Timmons and W.G. Scanlon, “An adaptive energy efficient MAC pro-

tocol for the medical body area networks,” 1st International Conference on

Wireless communication VITAE, pp. 587-593, 2009.

[11] Huaming L., and Jindong T., “Heartbeat-Driven Medium-Access Control

for Body Sensor Networks,” IEEE TRANSACTIONS ON INFORMATION

TECHNOLOGY IN BIOMEDICINE, VOL. 14, NO. 1, JANUARY 2010

[12] H. Li and J. Tan, “Body sensor network based context aware QRS detection,”

in Proc. 28th IEEE EMBS Annu. Int. Conf., Aug. 2006, pp. 32663269.

[13] M. Aboy, J. McNames, T. Thong, D. Tsunami, M. S. Ellenby, and B. Gold-

stein,“ An automatic beat detection algorithm for pressure signals,” IEEE

Trans. Biomed. Eng., vol. 52, no. 10, pp. 16621670, Oct. 2005.

[14] L. van Hoesel and P. Havinga, “A lightweight medium access protocol

(LMAC) for wireless sensor networks,” presented at the 1st Int. Workshop

Netw. Sens. Syst. (INSS 2004), Tokyo, Japan, 2004.

[15] W. Ye, J. Heidemann, and D. Estrin, “An energy-efficientmac protocol for

wireless sensor networks,” in Proc. IEEE Infocom, 2002, pp. 15671576.

[16] W. L. Lee, A. Datta, andR.Cardell-Oliver, “FlexiMAC:Aflexible

TDMAbasedMAC Protocol for fault-tolerant and energy-efficientwireless

sensor networks,” in Proc. 14th IEEE Int. Conf.Netw. (ICON 2006), Sep., pp.

16.

50

3 presents the proposed mac protocol design. chapter 4 describes the analytical ... figure 2.1 shows...

Documents