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標題: | 修改MAC層之適當Backoff Unit以提升Zigbee在異質網路中與Wi-Fi共存之能力 Modifying the Backoff Unit in MAC Layer to Enhance the Capability of Zigbee to Coexist with Wi-Fi in Heterogeneous Network |
作者: | Jia-Pei Lu 呂佳沛 |
指導教授: | 鄭士康(Shyh-Kang Jeng) |
關鍵字: | 物聯網,異質網路,共存, IoT,Zigbee,Wi-Fi,heterogeneous network,coexistence,ISM band,backoff unit, |
出版年 : | 2015 |
學位: | 碩士 |
摘要: | 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. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/54034 |
全文授權: | 有償授權 |
顯示於系所單位: | 電信工程學研究所 |
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