MIMO-aware Medium Access Control in IEEE 802.11 Networks by Abduladhim Mabruk Ashtaiwi A thesis submitted to the Department of Electrical and Computer Engineering in conformity with the requirements for the degree of Doctor of Philosophy Queen’s University Kingston, Ontario, Canada January 2009 Copyright c Abduladhim Mabruk Ashtaiwi, 2009 ISBN:978-0-494-48492-0 Abstract Wireless Mesh Networks (WMNs) are dynamically self-organized and self-configured, where the nodes in the network automatically establish an ad hoc network and main- tain mesh connectivity. These properties make WMNs a key technology for next- generation wireless networking. However, supporting Quality of Service (QoS) to enable multimedia services is still one of the major issues in next-generation WMNs. In distributed systems like WMNs, the Medium Access Control (MAC) layer is considered very important in the IEEE 802.11-based wireless networks, as it supports many crucial operational functions. Hence, QoS support in WMNs can be enhanced through the efficient cross-layer design of MAC protocols that utilizes advanced phys- ical layer technologies viz Multiple-Input Multiple-Output (MIMO) with its multiple spatial channels that are capable of simultaneous receive or transmit streams. MIMO has become a very attractive technology in providing support for different QoS re- quirements. In this thesis we propose a novel QoS MIMO-aware MAC Protocol (QMMP). QMMP is a MAC protocol framework that exploits the MIMO system gains to boost QoS support. The proposed MAC framework includes the following components. The first component enables concurrent sharing of the increased MIMO bandwidth, i.e., instead of allocating all the spatial channels to one connection, connections can i concurrently share the increase bandwidth via splitting the spatial channels. The second component reduces the medium access collisions problem. In distributed sys- tems like WMNs, medium access collisions have a noticeably negative impact on resource (bandwidth) utilization as they leave the bandwidth unutilized for a long time. To address this problem, we propose a spatial channels sharing scheme during medium contention period. The third component boosts the bandwidth utilization during data transmission. We propose resource management schemes that adapt the physical data rate and the aggregation frame length according to the instantaneous channel quality. Then we propose a QoS-aware bandwidth provisioning mechanism that performs effective bandwidth distribution to further boost QoS support. ii Dedication I wish to dedicate this thesis to the memory of my mother, Fatma. She was a constant source of inspiration in my life. Although she is not here to give me strength and support, I always feel her presence, urging me to strive to achieve my goals in life. May Almighty Allah reward her good deeds. To my father, Mabruk, who taught me that even the largest task can be accomplished if it is done one step at a time. To my wife, who stood beside me and encouraged me constantly. To my children, Saja, Sara, and Nada for giving me happiness. iii Acknowledgments First of all I would like to express my countless Praise to ALLAH for His graciousness and guidance, without which I could never have made it to the end. I would like to express my sincere gratitude to my supervisor Dr. Hossam S. Hassanein, for his patience and guidance throughout the course of this work. Special thanks to the external examiner, Dr. Wessam Ajib for his constructive and useful comments that helped improve the quality of this thesis. I would also like to thank the members of the examination committee, Dr. M. Ibnkahla, Dr. M.H. Rahman, Dr. P.K. Jain, and Dr. G.K. Takahara, for their valuable remarks and recommendations. Thanks are due to my colleagues Bader Manthari, Ashraf Ali Bourawy, Waleed Alsalih, Afzal Mawji, Khaled Ali, and Hassan Ahmad for their valuable collaboration and assistance during the course of this work. My deepest gratitude goes to my family for their unflagging love and support throughout my life. Finally, my sincere thanks to my friends and colleagues at the Telecommunication Research Lab (TRL) at Queen’s University for their guidance and friendship. I am also grateful to the numerous individuals who have directly or indirectly contributed to the completion of this work. iv Contents Abstract i Dedication iii Acknowledgments iv Contents v List of Tables viii List of Figures ix List of Acronyms xi List of Symbols xvi 1 Introduction 1 1.1 Motivation and Objectives . 3 1.2 Thesis Contributions . 6 1.2.1 QoS MIMO-aware MAC Protocol . 7 1.2.2 MIMO-aware Collision Avoidance Enhancements . 8 1.2.3 MIMO-aware Bandwidth Utilization and QoS Support . 8 1.3 Thesis outline . 9 2 Background and Framework Overview 10 2.1 IEEE 802.11 Standard–Wireless Local Area Networks . 11 2.2 IEEE 802.11 Amendment Activities . 13 2.3 IEEE 802.11e–MAC Quality of Service Enhancements . 15 2.4 Multiple Input Multiple Output (MIMO) . 17 2.5 IEEE 802.11n–Enhancements for Higher Throughput . 18 2.6 IEEE 802.11s–Wireless Mesh Networks . 20 2.7 Proposed Framework and Related Work . 22 v 2.7.1 MIMO-aware MAC Protocol . 23 2.7.2 MIMO-aware Collision Avoidance . 28 2.7.3 MIMO-aware Bandwidth Utilization . 33 2.8 Summary . 35 3 QoS MIMO-aware MAC Protocol 37 3.1 Introduction . 37 3.2 Motivation and Problem Formulation . 38 3.3 MIMO Channel Interference Model . 40 3.4 QoS MIMO-aware MAC Protocol (QMMP) . 44 3.4.1 TXOP Scheduling and Broadcasting . 51 3.5 QMMP Properties . 58 3.6 Discussion of other QMMP Advantages . 60 3.7 Performance Evaluation . 66 3.7.1 Simulation Model . 66 3.7.2 Traffic Model . 69 3.7.3 Simulation Parameters . 69 3.7.4 Performance Metrics . 70 3.7.5 Simulation Results . 70 3.8 Summary . 78 4 MIMO-aware Medium Access Collision Avoidance 80 4.1 Introduction . 80 4.2 Enhancements to the IEEE 802.11e EDCF Collision Avoidance Mech- anism . 82 4.3 Performance Evaluation . 91 4.3.1 Simulation Model . 91 4.3.2 Network Topology . 92 4.3.3 Simulation Parameters . 92 4.3.4 Performance Metrics . 93 4.4 Simulation Results–Single-hop Network . 93 4.5 Adaptive γ ................................ 99 4.6 Simulation Results–Multi-hop network . 110 4.7 Summary . 112 5 MIMO-aware Bandwidth Utilization 114 5.1 Introduction . 114 5.2 IEEE 802.11n MAC-Layer Frames . 116 5.2.1 A-MSDU Aggregation Frame Structure . 116 5.2.2 A-MPDU Aggregation Frame Structure . 117 5.2.3 A-MSDU and A-MPDU Two-level Frame Aggregation Structure 118 vi 5.3 Exploiting 802.11n Capabilities to Support QoS in IEEE 802.11s . 119 5.3.1 Link Adaptation . 120 5.3.2 Aggregation Frame Length Adaptation . 122 5.3.3 Bandwidth Provisioning Scheme . 124 5.4 Performance Evaluation . 126 5.4.1 Simulation Model . 126 5.4.2 Network Topology . 127 5.4.3 Traffic Model . 128 5.4.4 Performance Metrics . 128 5.4.5 Simulation Results . 129 5.5 Summary . 136 6 Conclusions and Future Work 138 6.1 Summary of Contributions . 139 6.2 Future Research Directions . 143 Bibliography 146 vii List of Tables 2.1 VoIP Codecs . 23 3.1 The physical and MAC configuration attributes of the IEEE 802.11n and traffic specifications . 39 3.2 IEEE 802.11n configurations . 69 5.1 Channel modulation parameters . 121 5.2 Traffic specifications . 128 viii List of Figures 1.1 Wireless mesh network evolution . 2 2.1 Snapshot of 802.11 physical and MAC standardization activities . 14 2.2 The structure of the sounding frame . 20 2.3 Wireless mesh network’s components and hierarchy structure . 21 2.4 The basic structure and operation of the proposed MAC in [50] . 25 3.1 Average medium access delay versus transmission delay comparison of different access classes. 40 3.2 Interference channel model . 41 3.3 Stage 1: depiction of the QMMP main phases, deferral, and concurrent transmissions . 46 3.4 Stage 2: depiction of the QMMP main phases, deferral, and concurrent transmissions . 47 3.5 The QMMP scheme under hidden node problem . 49 3.6 Finding a slot in case there exist previously reserved slots . 54 3.7 Some functional aspects of the QMMP MAC protocol . 63 3.8 Instantaneous signal decode-ability with ϕ=4 . 68 3.10 Achievable throughput as a function of communication and interference distance . 72 3.11 Medium access delay for different ranges . 73 3.12 Throughput for different ranges of requested rates . 74 3.13 Medium access delay for different values of D . 75 3.14 Throughput for different values of D . 75 3.15 Wireless mesh network model . 76 3.16 performance comparison between the IEEE 802.11 DCF and QMMP MAC protocol . 77 3.17 Comparison of requested and achieved rates . 78 4.1 The sounding frames transmission window . 83 4.2 The synchronization of the sounding frames transmission windows . 85 4.3 Medium contention at transmitters . 87 ix 4.4 Medium contention at receivers . 90 4.5 Hidden node network topology . 92 4.6 Mean number of attempts per packet for different γ and network loads. 94 4.7 M-EDCF MAC delay for different γ and network loads. 95 4.8 Channel utilization for different γ and network loads. 96 4.9 Throughput for different γ and network loads. 97 4.10 Actuating versus silencing the selection and termination properties . 98 4.11 The effect of changing γ ......................... 100 4.12 Virtual transmission period. 103 4.13 γ variability . 104 4.14 The success probability as function of different values of γ and β .