Modifying the Backoff Unit in MAC Layer to Enhance the Capability of Zigbee to Coexist with Wi-Fi in Heterogeneous Network

• Main Authors: Jia-Pei Lu, 呂佳沛
• Other Authors: Shyh-Kang Jeng
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/35757937058745389365

碩士 === 國立臺灣大學 === 電信工程學研究所 === 103 === 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.