i Analysis of Hybrid CSMA/CA-TDMA Channel Access Schemes with Application to Wireless Sensor Networks by Bharat Shrestha A Thesis submitted to the Faculty of Graduate Studies of The University of Manitoba in Partial Fulfilment of the Requirements for the degree of Doctor of Philosophy Department of Electrical and Computer Engineering University of Manitoba Winnipeg c 2013 by Bharat Shrestha ii Supervisor: Prof. E. Hossain ABSTRACT A wireless sensor network consists of a number of sensor devices and coordinator(s) or sink(s). A coordinator collects the sensed data from the sensor devices for further processing. In such networks, sensor devices are generally powered by batteries. Since wireless transmission of packets consumes significant amount of energy, it is important for a network to adopt a medium access control (MAC) technology which is energy efficient and satisfies the communication performance requirements. Carrier sense multiple access with collision avoidance (CSMA/CA), which is a popular access technique because of its simplicity, flexibility and robustness, suffers poor throughput and energy inefficiency performance in wireless sensor networks. On the other hand, time division multiple access (TDMA) is a collision free and delay bounded access technique but suffers from the scalability problem. For this reason, this thesis focuses on design and analysis of hybrid channel access schemes which combine the strengths of both the CSMA/CA and TDMA schemes. In a hybrid CSMA/CA-TDMA scheme, the use of the CSMA/CA period and the TDMA period can be optimized to enhance the communication performance in the network. If such a hybrid channel access scheme is not designed properly, high congestion during the CSMA/CA period and wastage of bandwidth during the TDMA period result in poor communication performance in terms of throughput and energy efficiency. To address this issue, distributed and centralized channel access schemes are proposed to regulate the activities (such as transmitting, receiving, idling and going into low power mode) of the sensor devices. This regulation during the CSMA/CA period and allocation of TDMA slots reduce traffic congestion and thus improve the network performance. In this thesis work, time slot allocation methods in hybrid CSMA/CA-TDMA schemes are also proposed and analyzed to improve the network performance. Finally, such hybrid CSMA/CA-TDMA schemes are used in a cellular layout model for the multihop wireless sensor network to mitigate the hidden terminal collision problem. iii Acknowledgment First and foremost, I would like to thank my advisor Professor Ekram Hossain for his constant support, guidelines, comments and direction to this work. His comments were always motivational to me. I would like to express my sincere thanks to Dr. Sergio Camorlinga for his support and helpful comments. It has been a great experience for me to work with him at TRLabs Winnipeg. I am very thankful towards TRLabs Winnipeg for providing research facilities and financial support. Also, it was an honor for me to receive grants from NSERC to support this work financially. I am grateful to InfoMagnetics Technologies Corporation Winnipeg for the sponsorship of the project at TRLabs Winnipeg. I am also thankful to Dr. Kaewon Choi for his suggestions, insightful comments and guidance. I would like to thank Dr. Dusit Niyato for his support and sugges- tions. I would like to thank my friends Dr. Phond Phunchongharn, Dr. Khajonpong Akkarajitsakul and Dr. Surachai Chieochan for their support and suggestions to make my study at the University of Manitoba beautiful. I would also like to thank all my friends at the University of Manitoba for their moral support. I am also grateful to our Nepali friends and Nepali community for making my stay in Winnipeg enjoyable. Finally, I am happy to dedicate this work to my parents, my wife and family members because their support and encouragement brought me to this point. iv To My Family v Table of Contents Abstract ii Acknowledgment iii Dedication iv Table of Contents v List of Tables x List of Figures xi 1 Introduction 1 1.1 Wireless Sensor Networks . 1 1.2 Wireless Body Area Sensor Networks . 3 1.3 Medium Access Control (MAC) Protocols . 5 1.3.1 Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) 7 1.3.2 Time Division Multiple Access (TDMA) . 9 1.3.3 Hybrid CSMA/CA-TDMA . 10 1.4 Wireless Communications Standards . 11 1.4.1 ZigBee Using IEEE 802.15.4 . 11 1.4.2 WiFi Using IEEE 802.11 . 12 1.4.3 Bluetooth Using IEEE 802.15.1 . 13 1.5 Overview of IEEE 802.15.4 Medium Access Control Protocol . 13 1.6 Design Issues for Hybrid CSMA/CA-TDMA Scheme . 16 1.6.1 Sizes of CSMA/CA and TDMA Periods . 16 1.6.2 Allocation of TDMA Slots . 17 1.6.3 Support for Multihop Networks . 17 vi 1.7 Contributions of the Thesis . 17 1.7.1 Balanced Use of Contention Access Period and Contention- Free Period . 18 1.7.2 Analytical Modeling of the IEEE 802.15.4-Based Hybrid CSMA/CA- TDMA Scheme . 19 1.7.3 Improving Performance of the IEEE 802.15.4-Based Hybrid CSMA/CA-TDMA Scheme . 20 1.7.4 Improving Performance of the Sensor Devices Under Uncer- tainty in the Queue Length in the Hybrid CSMA/CA-TDMA Scheme . 20 1.7.5 Mitigating the Hidden Node Collision Using the Hybrid CSMA/CA- TDMA Scheme . 21 2 Distributed and Centralized Channel Access Schemes 22 2.1 Introduction . 22 2.2 Related Work . 25 2.3 System Model, Assumptions, and the Hybrid CSMA/CA-TDMA Schemes 27 2.3.1 Network Model . 27 2.3.2 Traffic Model . 28 2.3.3 Operation of Nodes . 29 2.3.3.1 MDCA scheme . 29 2.3.3.2 MCCA scheme . 31 2.3.4 Beacon Loss and Change in Network Size . 32 2.3.5 An Analytical Model of Slotted CSMA/CA . 32 2.3.6 Compatibility to the IEEE 802.15.4 Standard . 34 2.4 MDP-Based Distributed Channel Access (MDCA) Model . 36 2.4.1 Reward . 37 2.4.2 State Transition Probability . 38 2.4.3 MDP Solution . 39 2.5 MDP-Based Centralized Channel Access (MCCA) Model . 40 2.5.1 MDP Formulation . 40 2.5.2 Complexity of Solving the MDP Problem . 41 2.5.3 Approximate Solution . 41 vii 2.6 Extension of the Models Considering Channel Fading . 43 2.7 Performance Evaluation . 46 2.7.1 Performance Metrics and Simulation Parameters . 46 2.7.2 Simulation Results . 47 2.7.2.1 Comparison . 47 2.7.2.2 Performance of the MDCA scheme . 48 2.7.2.3 Performance of the MCCA scheme . 50 2.7.2.4 Effect of number of time slots on the performance of MCCA scheme . 51 2.7.2.5 Effect of probability of outage on the performance of MDCA and MCCA schemes . 51 2.7.2.6 Effect of network size on the performance of MDCA and MCCA schemes . 52 2.7.2.7 Performances of MDCA and MCCA schemes under heterogeneous traffic . 53 2.8 Chapter Summary . 54 3 Analytical Modeling of Guaranteed Time Slot Transmission by Het- erogeneous Devices 59 3.1 Introduction . 59 3.2 Related Work . 63 3.3 System Model and Assumptions . 65 3.4 Markov Chain Model . 68 3.5 Analysis of MAC Layer Service Time . 73 3.6 Wireless Propagation Model and Outage Probability . 75 3.7 Performance Evaluation . 77 3.7.1 Ideal Channel Case . 78 3.7.2 Non-Ideal Channel Case . 80 3.8 Chapter Summary . 82 4 An Optimization-Based Guaranteed Time Slot Allocation Scheme 85 4.1 Introduction . 85 4.2 Related Work . 86 viii 4.3 WiBASE-Net Model and Knapsack Problem Formulation . 87 4.3.1 IEEE 802.15.4-Based WiBASE-Net Model . 87 4.3.2 Knapsack Problem Formulation . 89 4.4 Proposed Algorithm . 90 4.5 Simulation Setup and Performance Evaluation . 93 4.5.1 Simulation Setup . 93 4.5.2 Performance Evaluation . 94 4.6 Chapter Summary . 96 5 A Dynamic Time Slot Allocation Scheme 97 5.1 Introduction . 97 5.2 System Model and Assumptions . 98 5.2.1 Network Model and Superframe Structure . 98 5.2.2 Data Traffic Model . 99 5.2.3 Node Operation . 100 5.2.4 Random Access During CSMA Period . 101 5.3 Dynamic Time Slot Allocation Scheme . 104 5.3.1 Queue Length Distribution . 104 5.3.2 Formulation of a Utilization Maximization Problem . 105 5.3.3 Greedy Algorithm for Solving Utilization Maximization Problem106 5.4 Performance Evaluation . 108 5.5 Chapter Summary . 110 6 Hidden Node Collision Mitigated Multihop Wireless Sensor Net- works 111 6.1 Introduction . 111 6.2 Related Work . 113 6.3 A Cellular Layout for CSMA/CA-based Multihop Wireless Sensor Networks . 114 6.3.1 Network Model . 114 6.3.2 Node Mobility . 114 6.3.3 Hidden Node Collision (HNC) Mitigation . 115 6.3.4 Selection of Next Hop Nodes . 116 ix 6.4 Application of the Model to the IEEE 802.15.4-Based Networks . 120 6.4.1 IEEE 802.15.4-Based Multihop Sensor Networks . 120 6.4.2 Scheduling of Cells . 120 6.5 Analysis of Network Size . 121 6.6 Performance Evaluation . 122 6.7 Chapter Summary . 124 7 Summary and Discussions 127 7.1 Summary of Contributions . 127 7.2 Future Work . 129 Bibliography 132 Appendix A Proof of uniqueness of solution of the equations (3.10) and (3.11) 141 Appendix B Derivation of total backoff 143 x List of Tables Table 2.1 List of notations .