A COMMUNICATION PROTOCOL FOR WIRELESS SENSOR NETWORKS by Edgar H. Callaway, Jr. A Thesis Submitted to the Faculty of the College of Engineering in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Florida Atlantic University Boca Raton, Florida August 2002 Copyright by Edgar H. Callaway, Jr. 2002 ii A COMMUNICATION PROTOCOL FOR WIRELESS SENSOR NETWORKS by Edgar H. Callaway, Jr. This dissertation was prepared under the direction of the candidate's dissertation advisor, Dr. Ravi Shankar, Department of Computer Science and Engineering, and has been approved by the members of his supervisory committee. It was submitted to the faculty of the College of Engineering and was accepted in partial fulfillment of the requirements for the degree of Doctor of Philosophy. SUPERVISORY COMMITTEE: Chairman Chairman, Department of Computer Science and En~ ·ng Vice Provost Date lll Acknowledgements I thank the chairman of my committee, Dr. Ravi Shankar, for his guidance and optimism. If, as Newton said, a body remains at rest until acted upon by an external force, his was the force that moved me to return to school and complete my education. I also thank the other members of my committee, Dr. Valentine Aalo, Dr. Raymond Barrett, Dr. Borko Furht, Dr. Sam Hsu, and Dr. Fred Martin, for consenting to serve on the committee and their constructive criticism of this text. This research was done while I was employed at the Florida Communication Research Laboratory, Motorola Labs. I am indebted to the laboratory director, Dr. Larry Dworsky, and my immediate superior, Dr. Bob O'Dea, for their support, which went far beyond Corporate SOP. I also benefited from many useful technical discussions with my coworkers, including Anthony Allen, Monique Bourgeois, Priscilla Chen, Dr. Neiyer Correal, Dr. Lance Hester, Dr. Jian Huang, Dr. Y an Huang, Masahiro Maeda, Qicai Shi, and especially Paul Gorday, Sumit Talwalkar, and David Taubenheim for SPW consultations. I also thank Clint Powell, for supporting my return to school (and overlooking my many forced absences). iv My parents, Pat and Ed, deserve special thanks for emphasizing the value of education to a young man more often interested in other things. I also recognize my greatest debt of gratitude: to my wife, Jan. Without her support and understanding, this work would not have been possible. v ABSTRACT Author: Edgar H. Callaway, Jr. Title: A Communication Protocol for Wireless Sensor Networks Institution: Florida Atlantic University Dissertation Advisor: Dr. Ravi Shankar Degree: Doctor of Philosophy Year: 2002 Many wireless network applications, such as wireless computing on local area networks, employ data throughput as a primary perfonnance metric. The data throughput on such networks has therefore been increasing in recent years. However, there are other potential wireless network applications, such as industrial monitoring and control, consumer home automation, and military remote sensing, that have relaxed throughput requirements, often measured in bits/day. Such networks have power consumption and cost as primary performance metrics, rather than data throughput, and have been called wireless sensor networks. This work describes a physical layer, a data link layer, and a network layer design suitable for use in wireless sensor networks. To minimize node duty cycle and therefore average power consumption, while minimizing the symbol rate, the proposed physical layer employs a form of orthogonal vi multilevel signaling in a direct sequence spread spectrum format. Results of Signal Processing Worksystem (SPW, Cadence, Inc.) simulations are presented showing a 4-dB sensitivity advantage of the proposed modulation method compared to binary signaling, in agreement with theory. Since the proposed band of operation is the 2.4 GHz unlicensed band, interference from other services is possible; to address this, SPW simulations of the proposed modulation method in the presence of Bluetooth interference are presented. The processing gain inherent in the proposed spread spectrum scheme is shown to require the interferer to be significantly stronger than the desired signal before materially affecting the received bit error rate. The proposed data link layer employs a novel distributed mediation device (MD) technique to enable networked nodes to synchronize to each other, even when the node duty cycle is arbitrarily low (e.g., < 0.1 %). This technique enables low-cost devices, which may employ only low-stability time bases, to remain asynchronous to one another, becoming synchronized only when communication is necessary between them. Finally, a wireless sensor network design is presented. A cluster-type architecture is chosen; the clusters are organized in a hierarchical tree to simplify the routing algorithm. Results of several network performance metrics simulations, including the effects of the distributed MD dynamic synchronization scheme, are presented, including the average message latency, node duty cycle, and data throughput. The architecture is shown to represent a practical alternative for the design of wireless sensor networks. VII To Jan Table of Contents Chapter I: Introduction to Wireless Sensor Networks . 1 1.1: Motivation and Objectives . 1 1.1.1 : Low Power Consumption . 2 1.1.2: Low Cost . 3 1.1.3: Worldwide Availability 5 1.1.4: Network Type 6 1.1.5: Data Throughput . 6 1.1.6: Message Latency 7 1.1.7: Mobility . ..... 7 1.2: Contributions of this Research . 8 1.3: Organization of the Dissertation . 8 Chapter 2: Related Work . 10 2.1: Early Wireless Networks . 10 2.2: Wireless Data Networks . 21 2.2.1: The ALOHA System . 21 2.2.2: The PRNET System . 22 2.2.3: Amateur Packet Radio Networks . 23 2.2.4: Wireless Local Area Networks (WLANs). 24 2.2.5: Wireless Personal Area Networks (WPANs) 25 2.3: Wireless Sensor and Related Networks . 27 2.3.1: WINS . 27 2.3.2: PicoRadio . 28 2.3 .3: J.1AMPS . 30 2.3.4: Tenninodes, MANET, and Other Mobile Ad Hoc Networks. 30 2.3.5: Underwater Acoustic and Deep Space Networks 31 2.4: Conclusion . 31 Chapter 3: Physical Layer . 33 3.1: Introduction . 33 3.2: Related Work . 34 3 .2.1 : Bluetooth . 35 3.2.2: IEEE 802.llb . 36 3.2.3: Wireless Sensor Networks . 37 viii Pi co Radio 38 WINS .. 38 JlAMPS . 38 3.3: This work 39 3.3.1: Cost . 39 3.3 .2: Power 43 Power Source 44 Power Consumption 45 3.4: Simulations and Results 52 3.4.1: Simulations 52 3.4.2: Results 54 3.5: Conclusion . 61 Chapter 4: Data Link Layer 62 4.1: Introduction . .. 62 4.2: Related work . 65 4.2.1: ALOHA . 65 4.2.2: Carrier Sense Multiple Access . 66 4.2.3: Access Techniques in Wireless Sensor Networks 69 WINS . 70 Pi co Radio 70 Others 71 4.3 The Mediation Device 72 4.3.1: The Mediation Device Protocol 72 4.3.2: The Distributed MD Protocol 76 4.3.3: "Emergency" Mode 80 4.3.4: Channel Access 81 4.4: System Analysis and Simulation 82 4.4.1 : Duty Cycle 82 4.4.2: Latency 83 4.5: Conclusion 86 Chapter 5: Network Layer 88 5.1: Introduction 88 5.2: Related Work 89 5.2.1: Structure 89 5.2.2: Routing 93 5.3: This Work . 100 5.3.1: Network Design . 100 5.3.2: Network Association . 103 5.3.3: Network Maintenance . 105 5.3.4: Routing . 107 5.4: Simulations . 108 5.5: Results . 116 ix 5.5.1: Throughput (Cumulative Percentage of Messages Arriving at the DD vs. Time) . 116 5.5.2: Throughput (Cumulative Percentage of Messages Arriving at the DD vs. Node Level) . 117 5.5.3: Average Message Transmission Time . 118 5.5.4: Average Message Latency vs. Node Level . 119 5.5.5: Packet Collisions vs. Time . 120 5.5.6: Duty Cycle . 121 5.5. 7: Duty Cycle vs. Level . 122 5.5.8: Message Latency vs. MD Period . 124 5.5.9: Maximum Network Throughput vs. MD Period 125 5.5.1 0: Maximum Network Throughput vs. Node Density 126 5.6: Conclusion . 127 Chapter 6: Summary and Future Work . 129 6. 1: Summary . 129 6.2: Future work . 132 Appendix A: SPW . 136 Appendix 8: WinneuRFon . 137 8.1: Motivation . 137 8.2: System Requirements . 138 8.3: Supported Features . 140 8.4: Current Status and Achievement • . 140 8.5: Simulation Method and More Potential Functionalities . 143 8.6: Proposal for Future Work . 146 8.7: Summary . 146 Reference Bibliography . 147 X List of Tables Table 5.3.1: Sample routing table for node 7, cluster 1 . 106 Table 5.4.1: Network simulation parameters for wireless thermostat application . 114 Table 5.4.2: Network simulation parameters for supermarket price tag application . • . 114 Table 5.4.3: Network simulation parameters for consumer electronic application . 115 xi List of Illustrations Figure 2.1.1: The Army Amateur Radio System (1925) . 13 Figure 2.1.2: Organization of the National Traffic System, Central Area 18 Figure 3.3.1: Code position modulation so Figure 3 .4.1: Code position modulation simulation in SPW . 55 Figure 3.4.2: SPW simulation ofCPM modulator . 56 Figure 3.4.3: SPW simulation ofCPM demodulator . 57 Figure 3.4.4: SPW simulation ofBluetooth interference scenario 58 Figure 3.4.5: BER performance of code position modulation vs. Et/No 60 Figure 3.4.6: BER performance of code position modulation in the presence of Bluetooth interference . 6 0 Figure 4.2.1: The hidden and exposed terminal problems . 6 a Figure 4.3.1: Mediation Device operation . 73 Figure 4.3.2: Timing schedule for the Mediation Device protocol . 7 6 Figure 4.3.3: Timing schedule for the distributed Mediation Device protocol 78 Figure 4.4.1: A typical timing schedule for a node employing the distributed Mediation Device protocol .