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Performance Enhancement Optimizing Contention Window in IEEE 802.11 Wireless Local Area Networks

Performance Enhancement Optimizing Contention Window in IEEE 802.11 Wireless Local Area Networks

초록/요약

IEEE 802.11 Wireless LANs are becoming the most popular and widely deployed networks, and a tremendous growth has been noticed in wireless connected devices, and this upward trend will continue for the coming years. By 2020, the number of wireless devices are expected to reach over 40 billion. However, the efficiency of the IEEE 802.11 MAC protocol is a challenging task when the network is deployed in dense environment. This thesis focuses on the enhancement of IEEE 802.11 MAC protocol in a dense and widely fluctuating network loads. Firstly, we observe that the high data rates of PHY layer do not necessarily translate into corresponding increase in MAC layer throughput due to the contention of the random backoff algorithm based MAC layer. To reduce the contention among contender stations, we propose an adaptive backoff algorithm for MAC layer that maximizes the system throughput, reduces the collision probability, and maintains a high fairness for the IEEE 802.11 DCF under dense network conditions. Secondly, we investigate the Quality of service (QoS) for MAC layer, which is one of the critical aspects for real-time applications in wireless LANs. To improve the QoS for the MAC layer in terms of delay and throughput. We propose an extensive analytical model for the adaptive backoff algorithm for the IEEE 802.11e EDCA networks and derived an explicit expression for the mean frame delay, collision probability, and network throughput. The main objective of this work is to find the optimal CW parameters for each AC in order to achieve maximum throughput and small mean frame delay under saturated network condition. Thirdly, we investigate the performance of Restricted Access Window within TIM group in dense network environment. The efficiency for the restricted access window mechanism in term of collision rate and throughput reduces when the number of contender stations increase within the TIM group. To improve the efficiency of the restricted access window mechanism for the TIM group in a dense environment, we adopt an adaptive backoff mechanism for the contention among TIM group’s stations. The simulation results confirmed that the adaptive backoff mechanism achieves better network throughput and low collision rate compared with the IEEE 802.11ah RAW mechanism.

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목차

Chapter 1 INTRODUCTION 1
1.1 IEEE 802.11 Family of Protocols 1
1.1.1 IEEE 802.11 1
1.1.2 IEEE 802.11b/a/g 2
1.1.3 IEEE 802.11e 2
1.1.4 IEEE 802.11ah 3
1.2 Challenges 3
1.3 Research Contribution 4
1.3.1 Adaptive Backoff Algorithm for IEEE 802.11 WLANs 4
1.3.2 Performance Enhancement in IEEE 802.11e WLANs 4
1.3.3 Performance Evaluation for IEEE 802.11ah 5
1.4 Organization of the Dissertation 5
Chapter 2 BACKGROUND 7
2.1 Wireless Local Area Networks 7
2.1.1 WLAN System Architecture 8
2.1.2 Types of Wireless LANs 9
2.1.3 Physical Layer 10
2.1.4 Medium Access Layer 12
Chapter 3 A NEW MAC FOR DENSE WLANS 19
3.1 Introduction 19
3.2 Problem Statement and Contributions 22
3.3 A New MAC Protocol for IEEE 802.11 23
3.3.1 Channel-State Estimation 25
3.3.2 Contention Window Optimization 26
3.3.3 Number of Active Stations Estimation 27
3.3.4 Adaptive Backoff Algorithm for Contention Window 29
3.4 Performance Analysis of ABA-CW Algorithm 30
3.4.1 Channel-State Probabilities 30
3.4.2 Throughput Analysis 32
3.4.3 Fairness Calculation 33
3.4.4 Channel Utilization 33
3.4.5 Delay Analysis 34
3.5 Performance Evaluation 34
3.5.1 Performance Validation 34
3.6 Summary 44
Chapter 4 QoS ENHANCEMENT IN IEEE 802.11e 45
4.1 Introduction 45
4.2 Problem Statement and Contributions 48
4.3 Adaptive Contention Window-Based Backoff Algorithm for QoS 50
4.3.1 Optimal Contention Window Calculation 51
4.3.2 Estimation of Number of Active Stations 53
4.4 Analytical Model 55
4.4.1 Markov Chain Model 56
4.4.2 Mean Frame Delay Analysis 60
4.4.3 Frame Dropping Probability 61
4.4.4 Throughput Analysis 62
4.5 Performance Evaluation 62
4.5.1 Analysis Validation 64
4.5.2 Performance Comparison 67
4.6 Summary 71
Chapter 5 PERFORMANCE ANALYSIS OF IEEE 802.11ah 72
5.1 Introduction 72
5.2 IEEE 802.11 ah 74
5.2.1 PHY Layer 74
5.2.2 MAC Layer 77
5.2.3 Support of Large Number of Associated Stations 79
5.2.4 Power Saving Mechanisms in IEEE 802.11ah 80
5.2.5 Channel Access Mechanism 82
5.3 Analysis Model 84
5.4 Performance Evaluation and Analysis 86
5.4.1 Performance Evaluation of RAW mechanism 87
5.4.2 RAW and ABACW performance Comparison 91
5.5 Summary 93
Chapter 6 Conclusion 94
Chapter 7 References 96

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