Power allocation with fairness for non-orthogonal multiple access systems

The non-orthogonal multiple access (NOMA) approach enables a number of users to share the same resource via superposition coding in the transmitter and successive detection in the receiver. In this study a power allocation (PA) approach based on the proportional fair division technique is proposed. In this regard, power is assigned to users such that it ensures the fairness of NOMA follows that of orthogonal multiple access. A straight forward approach that achieves this objective is stated and is followed by proposing three different algorithms. These algorithms loosen the strict proportionality criterion to fulfil the data rate of a specific user. Also, a new fairness index for NOMA based on data rate ratios is defined. Afterwards, a low-complexity strategy based on water filling (WF) for PA amongst resources is proposed. This second PA stage aims at improving the data rate of users. The proposed approaches are applied to NOMA systems with different pairing strategies and results are compared. Results show that the proposed approaches improve the fairness of NOMA and WF increases the total system rate.