臺灣博碩士論文加值系統

Wi-Fi與Zigbee兩者被視為物聯網 (IoT) 的關鍵技術。Wi-Fi與Zigbee兩者皆運行在相同的2.4 GHz的工業、科學及醫學 (ISM) 頻帶。這些不同的無線網路技術有極高機率設置在彼此周圍並且必須彼此共存。然而Wi-Fi設備相比於ZigBee設備擁有更高的傳送功率。在本研究中，我們深度研究這兩種技術的媒體存取控制協定 (medium access control)。我們發現雖然在每次進行傳輸之前兩者都需要運行載波偵聽多路存取/碰撞避免 (CSMA/CA) 此項機制，但是基於IEEE 802.15.4的協定，Zigbee的感測時槽 (slot time) 是320微秒 ( extmu s)，而基於IEEE 802.11 的協定，相比之下Wi-Fi的感測時槽為較短的20微秒。此項差異將導致當兩者同時欲存取頻帶資源，為了獲得空閒的頻帶進行傳輸，Zigbee將等待更長的時間，並且重新傳送是可預期的，而該裝置的電池更快地消耗亦同樣在預期之中。本研究中首先計算Zigbee合理的感測時槽長度基於令Zigbee與Wi-Fi存取頻帶資源的機率相等的目標。接著本研究修改MAC層之適當Backoff Unit以提升Zigbee與Wi-Fi共存之能力。根據分析結果並應用本研究中研擬的競爭策略，實驗結果表明相較於原始的協定規範，此競爭策略能夠在不影響Wi-Fi的表現下提高頻帶使用效率和網路吞吐量。本研究不僅能提升網路吞吐量，而且能夠節省Zigbee設備的功率消耗。這是由於此競爭策略能夠降低Zigbee競爭失敗的機率，因此也降低了會導致裝置電池更快地消耗的重新傳送機率。因此，此競爭策略能夠使Zigbee和Wi-Fi和諧且公平的共存於此異質網路中。

Wi-Fi and Zigbee are regarded as the key technologies of internet of things. Both of Wi-Fi and Zigbee are operating over the same 2.4 GHz industrial, scientific and medical (ISM) band. Such technologies possibly place nearby and have to coexist with each other. However, Wi-Fi device transmits with a higher power level compared to Zigbee device. And when we investigate medium access control specification of the two techniques in depth. We find out although both require to apply the CSMA/CA mechanism before every transmission, the slot time for Zigbee based on IEEE 802.15.4 is 320 extmu s while the slot time for Wi-Fi based on IEEE 802.11 is much shorter at 20 extmu s. This lead to when they access the medium at the same time, Zigbee will wait longer to get free medium for transmission, and with the expected retransmission, faster draining of the device battery is prospective. In this work, we first calculate the proper slot time for Zigbee, based on the object that let the probability of accessing medium be equal for both of them. Thence, we modify the backoff unit in MAC layer to enhance the capability of Zigbee to coexist with Wi-Fi. Based on the analysis result and applying the strategic planning, the experimental result shows improved spectrum efficiency and network throughput over the original setting without affecting the performance of Wi-Fi. This approach not only can improve the network throughput but also can save the power of Zigbee. Due to reduce the chance of retransmissions where retransmissions will lead to faster drain of the device battery. Hence, our approach can make Zigbee peacefully and fairly coexist with Wi-Fi.

口試委員會審定書 i
致謝 ii
中文摘要 iv
Abstract v
Contents vi
List of Figures viii
List of Tables x
1 Introduction 1
1.1 Coexistence Problem on the 2.4 GHz ISM Band 1
1.2 Motivation and Objectives 4
1.3 Contributions 5
1.4 Literature Survey on the Research for Coexistence Problem of Zigbee and Wi-Fi 6
1.5 Thesis Outline 9
2 Fundamentals 11
2.1 Overview of IEEE 802.15.4 (Zigbee) Channel Access Mechanism 11
2.2 Overview of IEEE 802.11 (Wi-Fi) Channel Access Mechanism 14
2.3 The Fundamental MAC Specification of The IEEE WLAN and WPAN Standard 16
3 Proposed Approach 18
3.1 Coexistent Problem of Zigbee and Wi-Fi 18
3.2 Proposed Method 19
4 Numerical Simulations 22
4.1 Introduction to the OMNeT++ Simulator 22
4.1.1 Editing NED (.ned) files 25
4.1.2 Editing INI (.ini) Files 26
4.2 Simulation Scenarios 27
4.2.1 Scenario 1: One Pair Zigbee and One Pair Wi-Fi 27
4.2.2 Scenario 2: Multiple Transmission Environment 27
4.2.3 Scenario 3: Symmetrical Placement, Comparison of Before and After 28
4.2.4 Scenario 4: Crowded Environment 28
5 Results and Discussions 30
5.1 Results of Scenario 1 30
5.2 Results of Scenario 2 32
5.3 Results of Scenario 3 34
5.4 Discussions 36
6 Conclusions 40
Bibliography 42

[1] Gil Reiter. Wireless connectivity for the internet of things. Technical report, Texas Instruments, 2014.
[2] Sofie Pollin, Ian Tan, Bill Hodge, Carl Chun, and Ahmad Bahai. Harmful coexistence between 802.15. 4 and 802.11: A measurement-based study. In Cognitive Radio Oriented Wireless Networks and Communications, 2008. CrownCom 2008. 3rd International Conference on, pages 1–6. IEEE, 2008.
[3] Jin-Shyan Lee, Yu-Wei Su, and Chung-Chou Shen. A comparative study of wireless protocols: Bluetooth, uwb, zigbee, and wi-fi. In Industrial Electronics Society, 2007. IECON 2007. 33rd Annual Conference of the IEEE, pages 46–51. IEEE, 2007.
[4] Federico Dominguez, Abdellah Touhafi, Jelmer Tiete, and Kris Steenhaut. Coexistence with wifi for a home automation zigbee product. In Communications and Vehicular Technology in the Benelux (SCVT), 2012 IEEE 19th Symposium on, pages 1–6. IEEE, 2012.
[5] Ting Han, Bingjun Han, Ling Zhang, Xin Zhang, Dacheng Yang, et al. Coexistence study for wifi and zigbee under smart home scenarios. 2012.
[6] Quan Liu, Xiaorui Li, Wenjun Xu, and Duzhong Zhang. Empirical analysis of Zigbee and wifi coexistence. In Innovative Design and Manufacturing (ICIDM), Proceedings of the 2014 International Conference on, pages 117–122. IEEE, 2014.
[7] Gianni Giorgetti, Alessandro Cidronali, Sandeep K.S. Gupta, and Gianfranco Manes. Exploiting low-cost directional antennas in 2.4 ghz ieee 802.15.4 wireless sensor networks. In Wireless Technologies, 2007 European Conference on, pages 217–220, Oct 2007.
[8] Hae-Moon Seo, Yong-Kuk Park, Woo-Chool Park, Dongsu Kim, Myung-Soo Lee, Hyeong-Seok Kim, and Pyung Choi. System design considerations for a zigbee rf receiver with regard to coexistence with wireless devices in the 2.4ghz ism-band. KSII Transactions on Internet and Information Systems (TIIS), 2(1):37–50, 2008.
[9] James Hou, Benjamin Chang, Dae-Ki Cho, and Mario Gerla. Minimizing 802.11 interference on zigbee medical sensors. In Proceedings of the Fourth International Conference on Body Area Networks, page 5. ICST (Institute for Computer Sciences, Social-Informatics and Telecommunications Engineering), 2009.
[10] Jun Huang, Guoliang Xing, Gang Zhou, and Ruogu Zhou. Beyond co-existence: Exploiting wifi white space for zigbee performance assurance. In Network Protocols (ICNP), 2010 18th IEEE International Conference on, pages 305–314, Oct 2010.
[11] Jie Yuan, T. Ward, S. Honarvar, Tingting Chen, and J. Thomas. Hmm-driven smart white-space-aware frame control protocol for coexistence of zigbee and wifi. In Pervasive Computing and Communications Workshops (PERCOM Workshops), 2013 IEEE International Conference on, pages 348–351, March 2013.
[12] Chieh-Jan Mike Liang, Nissanka Bodhi Priyantha, Jie Liu, and Andreas Terzis. Surviving wi-fi interference in low power zigbee networks. In Proceedings of the 8th ACM Conference on Embedded Networked Sensor Systems, pages 309–322. ACM, 2010.
[13] Axel Sikora and Voicu F. Groza. Coexistence of ieee802.15.4 with other systems in the 2.4 ghz-ism-band. In Instrumentation and Measurement Technology Conference, 2005. IMTC 2005. Proceedings of the IEEE, volume 3, pages 1786–1791, May 2005.
[14] Ieee standard for local and metropolitan area networks–part 15.4: Low-rate wireless personal area networks (lr-wpans). IEEE Std 802.15.4-2011 (Revision of IEEE Std 802.15.4-2006), pages 1–314, Sept 2011.
[15] András Varga et al. The omnet++ discrete event simulation system.
[16] Andras Varga. The omnet++ discrete event simulation system. version 4.3. user manual. URL: http://www. omnetpp. org, 2013.