# A Multiarmed Bandit Approach for LTE-U/Wi-Fi Coexistence in a Multicell Scenario
## 2 Related Works  
The coexistence of 3 GPP systems and Wi-Fi in the unlicensed 5 GHz band began a few years ago when companies and standardization bodies began to outline the corresponding specifications. The goal was to improve user experience by allowing the usage of the unlicensed spectrum while coexisting with Wi-Fi and other technologies. For example, the LTE-U, originally proposed and led by Qualcomm, is specifically designed for deployments and regions that do not require Listen Before Talk (LBT) and has led to the creation of the LTE-U Forum, which is responsible for defining tests for coexistence scenarios [4; 11; 12]. 3 GPP also defined two other solutions in Release 13 [13]: the LTE-LAA and LTE-WLAN Link Aggregation (LWA). LTE-LAA is designed for deployments in Europe and Japan [3; 14], while LWA targets deployments where operators already have carrier Wi-Fi networks [15]. However, before specification efforts, 3 GPP conducted studies on the feasibility of LTE operating on unlicensed bands. The focus was on fairness, and the criterion was that an LTE network could not impact neighboring Wi-Fi more than another Wi-Fi network. Qualcomm also developed a proprietary and patented solution, called MuLTEFire, based on 3 GPP Releases 13 and 14 for Licensed Assisted Access (LAA/e-LAA) [16; 17]. This technology can be deployed without a primary LTE anchor and can coexist or overlap alongside other wireless networks, such as Wi-Fi and MuLTEFire itself. Release 16 of 3 GPP systems has standardized 5G NR-U radio access technology as an evolution of the 4 GLTE-LAA standards. Similar to MuLTEFire, NR-U could operate in the unlicensed 6 GHz band without any dependency on licensed network operators. In addition to these, several academic studies have investigated the coexistence between LTE, a technology primarily built for the licensed spectrum, and Wi-Fi, which operates in an unlicensed spectrum. For example, the authors of [18] overview and compare some of the access mechanisms mentioned above, while the authors of [19] show through an experimental analysis that a single LTE parameter can greatly impact WiFi's performance. Moreover, we want to highlight the studies [6; 20; 21; 22; 23], which have made important contributions to the field. We highlight below their most promising remarks:  
* An LTE operator is the best neighbor for a Wi-Fi operator in terms of interference and capacity, even if compared with the coexistence of two Wi-Fi networks. * The mechanism for accessing the LTE environment in the unlicensed spectrum must be dynamically adjusted to ensure that no additional configuration is required from the user. The first conclusion is only true if this condition is satisfied. * Due to the dynamic aspect of traffic load demand, interference, and usage of different technologies, machine learning techniques are strong candidates for the coexistence problem. Therefore, numerous papers focus on the features of access mechanisms, and since they define how the technologies can access the spectrum, their parameters must be configured correctly. This helps to ensure that all technologies fairly share the unlicensed spectrum. For example, in [24], the authors present a comparison between the Duty Cycle (DC) and LBT mechanisms in terms of fairness and optimal throughput performance. They show that if one parameter is properly tuned, the LBT mechanism can achieve a performance limit comparable to the DC. The authors of [11] investigate how the DC adjustment impacts the system throughput on LTE-U, and the authors of [25] present a summary of the problems and solutions involved in achieving fair coexistence between LTE and Wi-Fi. They discuss mechanisms that prevent one technology from harming the other. A notable conclusion is that a Wi-Fi network performs better when coexisting with LTE-LAA than when coexisting with another Wi-Fi. The coexistence problem is frequently approached as a classic optimization problem, as demonstrated in the papers mapped by the authors of [10].