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Tian Xia, "Strategies for Coexistence of 802.11 Wi-Fi and LTE in Context of Low Latency Communications," Master's Thesis, School of Electrical Engineering and Computer Science (EECS), TU Berlin (TUB), September 2022. (Advisor: Anatolij Zubow; Referees: Falko Dressler and Thomas Sikora)


With the rapid development of wireless communication technologies, there has been an increasing demand for high throughput and low latency communication. Regrettably, the spectrum resources of the licensed band are struggling to meet the demands of consumers across various industries [1]. In order to overcome this critical severity, researchers began to consider the possibility of offloading part of the LTE traffic to the 5 GHz unlicensed frequency band. Under the guidelines of the 3GPP consortium, several variants of LTE have been introduced ever since, including LTE-U and LAA (Licensed Assisted Access) that can extend the LTE operating spectrum to unlicensed frequency bands through Carrier Aggregation (CA). However, as Wi-Fi transmissions are currently using the 5 GHz unlicensed spectrum, LTE in the same frequency band can degrade the performance of Wi-Fi. One of the reasons is that LTE transmission frames are typically longer than Wi-Fi; this may lead to LTE occupying the channel and unfairly punishing Wi-Fi [2]. Therefore, achieving fair coexistence between LTE and Wi-Fi has become one of the most crucial issues. In this paper, we first introduced the evolution and frame structures of LAA and Wi-Fi with regard to their fundamental differences. Secondly, we explored several imperative prerequisites in the PHY and MAC layer, like Wi-Fi CSMA/CA, LTE-U duty cycle, and LAA Listen Before Talk (LBT). Then LBT Category4, defined in TR36.889 [3], is implemented with Network Simulator 3 (NS-3) to simulate the coexistence scenario of LAA and Wi-Fi. The scenario is simulated under different parameters like Clear Channel Assessment (CCA) thresholds, Transmission Opportunities (TXOP), as well as transport protocols. By analyzing the throughput and latency, parameters are optimized to achieve fair coexistence between LAA and Wi-Fi. Lastly, we addressed a new aspect of the coexistence performance that’s often overlooked. As LAA sends a reservation signal from the end of the LBT to the next unlicensed subframe boundary to secure the channel for LAA transmission, it could be unfair to Wi-Fi since it effectively prevents others from accessing the channel. By applying a reservation signal threshold, we study its impact on throughput, latency, and jitters in simple and complex scenarios. The results show that we can leverage the threshold to make coexistence fairer.

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Tian Xia

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    author = {Xia, Tian},
    title = {{Strategies for Coexistence of 802.11 Wi-Fi and LTE in Context of Low Latency Communications}},
    advisor = {Zubow, Anatolij},
    institution = {School of Electrical Engineering and Computer Science (EECS)},
    location = {Berlin, Germany},
    month = {9},
    referee = {Dressler, Falko and Sikora, Thomas},
    school = {TU Berlin (TUB)},
    type = {Master's Thesis},
    year = {2022},

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