Introduction to Wireless Sensor Networks

Anna Förster is a Professor and Head of the Sustainable Communication Networks Group at the University of Bremen, Germany. She earned her MSc in Computer Science and Aerospace Engineering from the Free University of Berlin and her PhD from the University of Lugano, Switzerland. Her main research interests lie in the area of sustainable communication networks and their applications to sustainability. Her passion is teaching these topics, both to students and the general public.

How to Use This Book xiii

1 What are Wireless Sensor Networks? 1

1.1 Wireless Sensor Networks 1

1.2 Sample Applications Around the World 3

1.3 Types of Wireless Sensor Networks 7

Summary 10

Further Reading 10

2 Anatomy of a Sensor Node 11

2.1 Hardware Components 11

2.2 Power Consumption 13

2.3 Operating Systems and Concepts 15

2.3.1 Memory Management 17

2.3.2 Interrupts 23

2.3.3 Tasks Threads and Events 24

2.4 Simulators 26

2.5 Communication Stack 28

2.5.1 Sensor Network Communication Stack 28

2.5.2 Protocols and Algorithms 30

Anatomy of a Sensor Node: Summary 30

Further Reading 30

3 Radio Communications 33

3.1 Radio Waves and Modulation/Demodulation 33

3.2 Properties of Wireless Communications 36

3.2.1 Interference and Noise 37

3.2.2 Hidden Terminal Problem 38

3.2.3 Exposed Terminal Problem 39

3.3 Medium Access Protocols 39

3.3.1 Design Criteria for Medium Access Protocols 41

3.3.2 Time Division Multiple Access 42

3.3.3 Carrier Sense Multiple Access 45

3.3.4 Sensor MAC 48

3.3.5 Berkeley MAC 50

3.3.6 Optimizations of B-MAC 51

3.3.7 Other Protocols and Trends 51

Radio Communications: Summary 53

Questions and Exercises 53

Further Reading 54

4 Link Management 57

4.1 Wireless Links Introduction 57

4.2 Properties of Wireless Links 59

4.2.1 Links and Geographic Distance 59

4.2.2 Asymmetric Links 60

4.2.3 Link Stability and Burstiness 61

4.3 Error Control 62

4.3.1 Backward Error Control 62

4.3.2 Forward Error Control 63

4.4 Naming and Addressing 64

4.4.1 Naming 64

4.4.2 Addressing 65

4.4.3 Assignment of Addresses and Names 65

4.4.4 Using Names and Addresses 66

4.5 Link Estimation Protocols 66

4.5.1 Design Criteria 66

4.5.2 Link Quality Based 67

4.5.3 Delivery Rate Based 68

4.5.4 Passive and Active Estimators 69

4.5.5 Collection Tree Protocol 69

4.6 Topology Control 71

4.6.1 Centralized Topology Control 71

4.6.2 Distributed Topology Control 72

Link Management: Summary 73

Questions and Exercises 73

Further Reading 74

5 Multi-Hop Communications 77

5.1 Routing Basics 77

5.2 Routing Metrics 80

5.2.1 Location and Geographic Vicinity 80

5.2.2 Hops 81

5.2.3 Number of Retransmissions 82

5.2.4 Delivery Delay 83

5.3 Routing Protocols 84

5.3.1 Full-Network Broadcast 85

5.3.2 Location-Based Routing 87

5.3.3 Directed Diffusion 90

5.3.4 Collection Tree Protocol 92

5.3.5 Zigbee 94

Multi-Hop Communications: Summary 95

Questions and Exercises 96

Further Reading 96

6 Data Aggregation and Clustering 99

6.1 Clustering Techniques 99

6.1.1 Random Clustering 101

6.1.2 Nearest Sink 102

6.1.3 Geographic Clustering 103

6.1.4 Clustering Summary 104

6.2 In-Network Processing and Data Aggregation 104

6.2.1 Compression 104

6.2.2 Statistical Techniques 107

6.3 Compressive Sampling 109

Data Aggregation and Clustering: Summary 110

Questions and Exercises 111

Further Reading 111

7 Time Synchronization 113

7.1 Clocks and Delay Sources 113

7.2 Requirements and Challenges 114

7.3 Time Synchronization Protocols 117

7.3.1 Lightweight Tree Synchronization 117

7.3.2 Reference Broadcast Synchronization 118

7.3.3 NoTime Protocol 118

Time Synchronization: Summary 120

Questions and Exercises 121

Further Reading 121

8 Localization Techniques 123

8.1 Localization Challenges and Properties 123

8.1.1 Types of Location Information 124

8.1.2 Precision Against Accuracy 125

8.1.3 Costs 125

8.2 Pre-Deployment Schemes 126

8.3 Proximity Schemes 126

8.4 Ranging Schemes 128

8.4.1 Triangulation 129

8.4.2 Trilateration 129

8.5 Range-Based Localization 129

8.6 Range-Free Localization 130

8.6.1 Hop-Based Localization 130

8.6.2 Point in Triangle (PIT) 131

Localization: Summary 132

Questions and Exercises 133

Further Reading 133

9 Sensing Techniques 135

9.1 Types of Sensors 135

9.2 Sensing Coverage 136

9.3 High-Level Sensors 137

9.4 Special Case: The Human As a Sensor 138

9.5 Actuators 138

9.6 Sensor Calibration 139

9.7 Detecting Errors 140

Sensing Techniques: Summary 141

Questions and Exercises 141

10 Designing and Deploying WSN Applications 143

10.1 Early WSN Deployments 143

10.1.1 Murphy Loves Potatoes 144

10.1.2 Great Duck Island 144

10.2 General Problems 145

10.2.1 Node Problems 146

10.2.2 Link/Path Problems 147

10.2.3 Global Problems 148

10.3 General Testing and Validation 149

10.4 Requirements Analysis 151

10.4.1 Analyzing the Environment 151

10.4.2 Analyzing Lifetime and Energy Requirements 153

10.4.3 Analyzing Required Data 153

10.4.4 Analyzing User Expectations 154

10.5 The Top-Down Design Process 154

10.5.1 The Network 154

10.5.2 The Node Neighborhood 155

10.5.3 The Node 156

10.5.4 Individual Components of the Node 156

10.6 Bottom-Up Implementation Process 157

10.6.1 Individual Node-Level Modules 158

10.6.2 The Node As an Entity 159

10.6.3 The Network As an Entity 159

Designing and Deploying WSN Applications: Summary 160

Further Reading 160

11 Summary and Outlook 163

Index 167