Blank Slot: Hidden Node Problem Mitigation in IEEE 802.11 WLANs = Blank Slot: IEEE 802.11 무선랜의 은닉 노드 문제 완화

다국어 초록 (Multilingual Abstract)

WLANs based on IEEE 802.11 are widely deployed to satisfy the increasing demands of wireless communication, however, they are facing number of challenges including interference and packet collisions due to the hidden nodes.
Although the RTS/CTS mechanism has been proposed to mitigate the hidden node problem, it still has several drawbacks; the control packets can collide among themselves and they increase overheads which lead to the performance degradation.
Moreover, the RTS/CTS mechanism can result in the false blocking and deadlock where nodes have to defer the channel access unnecessarily. In this paper, we propose a solution called Blank slot mechanism.
In the proposed mechanism, node will not transmit or reserve some slot time after certain number of successful transmissions which allows other nodes to transmit and, thus, mitigates packet collisions and interference due to hidden nodes.
This mechanism does not require any change on either PHY or MAC layer or packet format based on current standard. Also, the solution does not cause overheads and blocking or deadlock. It works in a distributed way without any additional signaling mechanism. As well as decreasing the transmission failure due to collision or interference, this mechanism improves time fairness among nodes since the node with high rate will serve less time for blank slot than one with low rate and all the nodes release and serve the blank slot.

목차 (Table of Contents)

• Abstract = i
• Contents = iii
• List of Figures = v
• Chapter 1 = 1
• Introduction = 1
• 1.1 How is the hidden Node effect happen? = 2
• 1.2 Hidden nodes = 3
• Chapter 2 = 7
• Related work = 7
• 2.1 Virtual Carrier Sensing (The RTS/CTS mechanism) = 7
• 2.1.1 How is RTS/CTS exchange increase sensing range? = 8
• 2.1.2 How is the RTS/CTS exchange mitigate hidden node problem? = 9
• 2.1.3 Overhead issues of RTS/CTS exchange = 10
• 2.2 Other related works = 16
• Chapter 3 = 25
• Blank slot mechanism = 25
• 3.1 How it works = 25
• 3.2 T_blank Calculation = 26
• 3.3 Conditions and advantages under blank-slot = 30
• Chapter 4 = 33
• Simulation models and results = 33
• 4.1 Line topology = 35
• 4.2 Grid topology = 39
• 4.3 Random topology = 42
• 4.4 Variations of Number of successful transmission (Ntx) to serve Black-Slot time = 44
• 4.5 Dependence of Blank slot time (Tblank) with Transmission rate and packet size = 46
• 4.6 Effect of Larger Contention Window in comparison with Blank-slot mechanism = 50
• Chapter 5 = 53
• Conclusion = 53
• Bibliography = 54