臺灣博碩士論文加值系統

Machine-to-Machine (M2M)通訊是一種對於機器之間可以進行獨立溝通的方式，能夠促使有線以及無線的通訊不須藉由人為的干涉，然而，當網路裝置的數量增加的時候，碰撞發生的情況也會增加，導致降低了媒體存取控制層(MAC layer protocol)的效能以及增加了能源消耗，為了要解決這個問題，本研究提出了強化的IEEE 802.11 CSMA/CA的媒體存取控制的方法，稱為CSMA/CA-RBTv，其中RBT代表Registered Backoff Time以及v代表的是vector。在本研究提出的CSMA/CA-RBTv中，當一個mobile node傳送data packet給AP時，會在data packet中附帶一個隨機的數值稱為RBT，用途為表明此mobile node接下來將要傳送其下一個data packet的時間，一旦AP收到packet，會從中取出RBT並將其存入Registered-Time-Slot-List (RTSL)作為排程的依據，在AP回傳ACK給mobile node之前，AP會進行(1)從RTSL中選擇擁有最小RBT的mobile node當作下一個將會存取網路的候選者，以及(2)使用RTSL製作bit vector來紀錄哪些time slots已經被註冊或預訂給data傳輸使用，最後AP將前面所提之兩種頻道存取資訊附加到ACK packet之中，因為ACK packet是用broadcast的方式傳送，所有在關注傳輸情形的mobile node皆會得知哪一個mobile node在接下來有存取權，以及會在哪一段time slots進行存取，總而言之，這樣可以減少碰撞發生的次數，進而減少一些能源消耗。模擬結果顯示本研究提出的CSMA/CA-RBTv在M2M網路環境中當mobile node的數量增加時，在傳輸效能以及能源效率擁有顯著的提升。

Machine-to-Machine (M2M) communication is a machine-independent communication paradigm that can facilitate wired and wireless communications without the need for human intervention. However, as the number of network devices increases, the occurrence of collisions rises, which results in the efficiency of the MAC layer protocol being degraded and the power consumption being increased. To resolve this problem, this thesis proposes an enhanced IEEE 802.11 CSMA/CA media access scheme designated as CSMA/CA-RBTv, in which RBT denotes the Registered Backoff Time and v denotes vector. In the proposed CSMA/CA-RBTv, when a mobile node transmits data to the AP, it attaches a random number called the RBT, which denotes the next time slot the mobile node would like to transmit its next data packet, to the packet. Once the AP receives the packet, it extracts the RBT and adds it to a Registered-Time-Slot-List (RTSL) used to conduct channel access scheduling. Before transmitting the ACK packet to the mobile node, the AP (1) selects the node with the smallest RBT from the RTSL list as the next one to access the wireless channel and (2) uses RTSL to make a bit vector marking which time slots have been registered/reserved for data transmission, i.e., channel access. Finally, the AP appends the aforementioned two pieces of channel access information to the ACK packet. Since the ACK packet is transmitted in a broadcast manner, all of the mobile nodes which overhear the transmission know which node has the next right to access the channel and which time slots are still available for channel access. Consequently, the occurrence of collisions can be reduced, which also results in decreasing power consuming. The simulation results show that the proposed CSMA/CA-RBTv scheme results in a significant improvement in both the transmission performance and the energy efficiency of the M2M network as the number of mobile nodes increases.

Contents
Contents IV
List of Figures V
List of Tables VII
Chapter 1 Introduction 1
Chapter 2 Related Works 5
Chapter 3 The Proposed CSMA/CA-RBTv scheme 7
Chapter 4 Contention Window Management 24
Chapter 5 Analysis of Power Consumption 30
Chapter 6 Performance Analysis 36
Chapter 7 Conclusion 57
Bibliography 58

List of Figures
Figure 1. The random backoff mechanism used in IEEE 802.11 protocols. 3
Figure 2. The structure of the bit vector in the ACK packet. 8
Figure 3. The execution flow of the CSMA/CA-RBTv scheme. 11
Figure 4. An illustrative example of the CSMA/CA execution procedure. 12
Figure 5. An Illustrated execution flow of the proposed CSMA/CA-RBT Scheme 14
Figure 6. An illustrative execution flow of the proposed CSMA/CA-RBTv scheme. 16
Figure 7. An illustrated execution flow when a collision occurs. 17
Figure 8. Case 1: Receive the bit vector and RBTs are different. 18
Figure 9. Case 2: Receive the bit vector and RBTs are the same. 19
Figure 10. Case 3: Transmit the 1st data packet before receiving any ACK packet and the RBT is not sure. 20
Figure 11. Case 4: Transmit the 1st data packet before receiving any ACK packet and the collision occurs. 21
Figure 12. Receiving the data from the other mobile node. 22
Figure 13. Receiving the data from the infrastructure. 23
Figure 14. An example of time slots in the visible area and blind area. 25
Figure 15. An illustrated example of the CW. 26
Figure 16. An illustrated example of the usage of CWV and CWB. 27
Figure 17. An illustrated example of the CWV and CWB after the collision occurs. 28
Figure 19. Variation of the average throughput with the number of mobile nodes. 39
Figure 20. Variation of delay time with the number of mobile nodes. 41
Figure 21. Variation of power consumption with the number of mobile nodes. 42
Figure 22. The collision rate vs. the number of mobile nodes. 43
Figure 23. Two-state Markov Gilbert-Elliott model. 44
Figure 24. The throughput vs. the number of mobile nodes using the CSMA/CA scheme with different error rates.. 45
Figure 25. The throughput vs. the number of mobile nodes using the CSMA/CA-RBT scheme with different error rates. 47
Figure 26. The throughput vs. the number of mobile nodes using the proposed CSMA/CA-RBTv scheme with different error rates. 49
Figure 27. The delay vs. the number of mobile nodes using the CSMA/CA scheme with different error rates. 51
Figure 28. The delay vs. the number of mobile nodes using the CSMA/CA-RBT scheme with different error rates. 52
Figure 29. The delay vs. the number of mobile nodes using the proposed CSMA/CA-RBTv scheme with different error rates. 54

List of Tables
Table 1. Power consumption rates of different 802.11 Wi-Fi cards. 31
Table 2. System parameters. 31
Table 3. Simulation parameters. 37
Table 4 Throughput for which the number of nodes is from 1 to 10. 37
Table 5 Delay for which the number of nodes is from 1 to 10. 39

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