# A Survey of Resource Allocation Techniques for Cellular Network's Operation in the Unlicensed Band
## 2 Related Work  
An in-depth survey of the coexistence of LTE-LAA and Wi-Fi on the 5 GHz unlicensed band has been presented in [11]. In [11], various coexistence related features of LTE-LAA and Wi-Fi have been discussed in detail. Furthermore, several deployment scenarios and scenario oriented decision-making along with possible research directions have been presented. However, fair coexistence of LTE-LAA (or LTE-U) and Wi-Fi is dependent on the resource allocation schemes used in LTE-LAA (or LTE-U) and Wi-Fi. Thus, in this work, we present a detailed survey of channel selection and channel access mechanisms for both LTE-LAA and LTE-U from the perspective of resource allocation.  
In [12], an overview of the challenges and requirements of the fronthaul technology in LTE-U based small cells (SCs) in 5G networks has been presented. Furthermore, the advantages and challenges for various candidate fronthaul technologies have been discussed. However, the important issues of fairness, coexistence, and handover have not been discussed in [12]. Similarly, in [13], the impact of several design parameters of the LAA-LBT evaluation framework on the channel access opportunities of LAA and its coexistence have been studied, for both single-channel as well as multi-channel operation. Key design specification with different channel access methods for coexistence framework of LAA and Wi-Fi based on release 13 have been presented in [13]. However, suitable resource allocation techniques to optimize the performance of LAA-LBT and Wi-Fi have not been discussed.  
In [14], an overview of the Rel-13 LAA technology including motivation, use cases, LTE enhancements for enabling the unlicensed band operation, and the coexistence evaluation results contributed by 3 GPP participants have been provided. Performance results for the LAA-LBT coexistence mechanism have been presented. However, coverage, capacity, or fairness with respect to number of users, access points (APs), and SC have not been discussed. In [15], an overview of various technical issues like coexistence among the different operators, different RAT, handover between RAT and LTE-U, traffic balancing, and traffic loading in Wi-Fi mechanism have been discussed. However, issues from real-time hardware implementation and analysis of the LTE-U and LAA-LBT from a resource allocation perspective have not been included.  
Unlike the existing surveys that are targeted only for coexistence of LTE and Wi-Fi, this paper focuses on the complete study of resource allocation techniques for LAA-LBT and LTE-U including game theory and machine learning for fair coexistence. We have also presented a summary on different traffic model, environments and performance evaluation of coverage, capacity and coordination for both uplink and downlink. Furthermore, we have discussed the real-time hardware implementation for LTE's operation in the unlicensed band. Additionally, we have explained some open issues and solutions for resource allocation in CSAT and LAA-LBT.  
Figure 1: A region wise classification of trials and deployments of various channel access mechanisms for LTE’s operation in the unlicensed band.