## 1 Introduction
### Related Work
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Reference** & **Objective** & **Proposed Algorithm** \\ \hline \multirow{3}{*}{[4]} & Fairness criteria in downlink NOMA & \multirow{3}{*}{Bisection iterative algorithms (BIAs) for} \\  & systems with instantaneous channel state & \\  & information (CSI) and average CSI & \\ \hline \multirow{3}{*}{[8]} & Maximum–minimum fairness scheme to \\  & maximise the minimum achievable user & \multirow{3}{*}{Beamforming and power allocation as a} \\  & fairness on the basis of a mm-wave & joint problem \\  & NOMA system & \\ \hline \multirow{3}{*}{[9]} & To determine the minimum time window & \multirow{3}{*}{Simple alternate optimisation (AO)} \\  & to guarantee and evaluate the specified \\  & fairness using [PERSON]’s fairness index (_IFI_) & \\  & for a short-term fairness NOMA system & \\ \hline \multirow{3}{*}{[10]} & Achieve equal data rate and maximum & \multirow{3}{*}{\begin{tabular}{c} \\ energy efficiency for a downlink \\ multiple-input and multiple-output \\ (MIMO) NOMA system \\ \end{tabular} } & \multirow{3}{*}{\begin{tabular}{c} \\ \end{tabular} } \\  & & \\ \cline{1-1}  & \begin{tabular}{c} To achieve a better trade-off between \\ throughput and fairness for a downlink \\ NOMA system in 5G networks \\ \end{tabular} & \begin{tabular}{c} Two-stage algorithm that uses \\ proportional fairness with zero-forcing \\ beamforming \\ \end{tabular} \\ \hline \multirow{3}{*}{[12]} & To achieve maximum–minimum fairness & \multirow{3}{*}{\begin{tabular}{c} Finite blocklength (FBL) to attain an \\ optimal power allocation \\ \end{tabular} } \\  & and throughput for a downlink NOMA & & \\ \cline{1-1}  & system with two users & \\ \hline \multirow{3}{*}{[13]} & Maximise energy efficiency and & Power and time resource allocation \\  & throughput fairness for downlink & \multirow{3}{*}{\
\begin{tabular}{c} Optimisation based on time-sharing using \\ an unmanned aerial vehicle (UAV) \\ \end{tabular} } \\  & time-NOMA (T-NOMA) systems & & \\ \hline \multirow{3}{*}{[14]} & Achieve the minimum required data rate & \multirow{3}{*}{
\begin{tabular}{c} Power discretisation method \\ Global optimal search (GOS) \\ \end{tabular} } \\  & for each user and throughput & & Adaptive proportional fair (APF) and \\ \cline{1-1}  & maximisation & & classical waterfalling based on matching \\ \cline{1-1}  & & & theory (MWF) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of the literature review. The authors of [17] developed a scheme for a fairness system based on a nonuniform power distribution to measure the rate difference between users to achieve data fairness. A user's data rate is measured with a fraction of the total power allocated to the user whilst continuously checking the fairness index, where a value of '1' is attained at fair rates. In ref. [14], [PERSON], [PERSON], [PERSON], and [PERSON] investigated spectrum resource and power allocation to achieve the minimum required data rate for each user and throughput maximisation as a trade-off scheme for a NOMA system. Their work formulated the problem as a double-objective optimisation problem; the power discretisation method was then used to convert the problem into a single-objective optimisation problem. Moreover, matching the user-subchannel problem and power allocation is achieved by conducting GOS to determine the upper bound of user throughput due to high complexity. The power allocation scheme considers APF for throughput fairness and applied power allocation using MWF. Alternatively, the authors of [13] proposed power and time resource allocation optimisation based on time-sharing to maximise energy efficiency and throughput fairness for downlink T-NOMA systems using UAV. The joint optimisation scheme was proposed to utilise the advantages of UAVs in communication systems for the maximisation of throughput fairness and energy efficiency. In ref. [6], a standalone simulated annealing algorithm was proposed for resource allocation to maximise throughput for a NOMA system.