To meet the high demand for mobile data, the Third Generation Partnership Project (3GPP) established a set of standards known as 5G New Radio (5G NR). The architecture of 5G NR includes a flexible radio access network and a core network. 3GPP has also been working on a new radio access technology, called 5G NR Unlicensed (5G NR-U), which aims at extending 5G NR to unlicensed bands. In this paper, we give an overview of the most recent 5G NR-U design elements and discuss potential concerns, including fair coexistence with other unlicensed technologies such as Wi-Fi. We use simulations to study coexistence between Wi-Fi and 5G NR-U systems. Our evaluation indicates that NR-U often achieves higher throughput and lower delay than Wi-Fi (802.11ac). The two systems experience different buffer occupancies and spectrum utilization statistics. We also discuss the improvements that NR-U offers over LTE Licensed Assisted Access (LTE-LAA). I. INTRODUCTION Next-generation wireless networks will support applications with widely diverse performance requirements. In its International Mobile Communications (IMT)-2020 recommendations, the International Telecommunications Union (ITU) specifies three use cases for next-generation wireless networks: Enhanced mobile broadband (eMBB), ultra-reliable and low latency communication (URLLC), and massive machine-type communication (mMTC). While these use cases embody different performance requirements, they all share the need for more spectrum. In its effort to extend 5G cellular operation to unlicensed spectrum, 3GPP is initially targeting the Unlicensed National Information Infrastructure (UNII) bands at 5 GHz and 6 GHz. Future specifications will address unlicensed millimeter wave (mmWave) bands at 60 GHz. Wireless systems can operate over unlicensed bands as long as they comply with spectrum regulations, which are intended to ensure harmonious coexistence of various incumbents that operate on the same band. The ubiquity of Wi-Fi networks makes achieving harmonious 5G NR-U and Wi-Fi coexistence a key objective for NR-U designers. To ensure fairness in channel access, NR-U should not impact an existing Wi-Fi system more than the impact of another Wi-Fi system [1]. Early works surveying 5G NR-U can be found in [2]-[5]. These works focused on pre-standard NR-U operation at sub-6 GHz and/or mmWave frequencies and discussed the feasibility of utilizing the channel access procedures of 'further enhanced' LTE LAA (feLAA) in 5G networks. The effectiveness of unlicensed bands for IoT applications was investigated in [6], where the authors studied challenges

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The heterogeneity of technologies that operate over the unlicensed 5 GHz spectrum, such as LTE-Licensed-Assisted-Access (LAA), 5G New Radio Unlicensed (NR-U), and Wi-Fi, calls for more intelligent and efficient techniques to coordinate channel access beyond what current standards offer. Wi-Fi standards require nodes to adopt a fixed value for the minimum contention window (CW min ), which prohibits a node from reacting to aggressive nodes that set their CW min to small values. To address this problem, we propose a framework called Intelligent-CW (ICW) that allows nodes to adapt their CW min values based on observed transmissions, ensuring they receive their fair share of the channel airtime. The CW min value at a node is set based on a random forest, a machine learning model that includes a large number of decision trees. We train the random forest in a supervised manner over a large number of WLAN scenarios, including different misbehaving and aggressive scenarios. Under aggressive scenarios, our simulation results reveal that ICW provides nodes with higher throughput (153.9% gain) and 64% lower frame latency than standard techniques. In order to measure the fairness contribution of individual nodes, we introduce a new fairness metric. Based on this metric, ICW is shown to provide 10.89× improvement in fairness in aggressive scenarios compared to standard techniques.

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