 over each sub- band S: QUAP) where(Umax,Psmax)=max Q(U,Ps) denotes the maximum argument of PF scheduling met- ric Q(U,Ps) for candidate user set U and allocated power set Ps over all users in the user set, n(k, U,Ps,t) is the instantaneous throughput of user k in subband S at time instance t (the time index of a subframe), whereas L(k,t) is the average throughput of user k. For power-domain NOMA, if we assume the possibility of dynamic switching between NOMA and orthogonal MA, then NOMA can be used only when it provides performance gains. Moreover, the number of users to be multiplexed over each subband is decided by searching all possible candidate user sets of different sizes up to m. The number of candidate user sets to be searched is given by [50-52]: In orthogonal MA schemes, the same MCS is selected over all subbands allocated to a sin- gle user. Therefore, the average signal-to-interference plus noise power ratio over all 366 Chapter 3 allocated subbands is used for MCS selection. However, when power-domain NOMA is uti- lized over each subband, user pairing and power allocation are performed over each sub- band. With such a mismatch between wideband MCS selection and subband power allocation granularities, the full-scale NOMA gains would not be realized. Furthermore, the higher the power allocation granularity, the more signaling overhead and thus performance degradation. Power control of uplink NOMA is different from that of downlink in two aspects. In the downlink direction, the transmission power is limited by the maximum transmission power of the base station; however, in the uplink, the transmission power optimization is con- strained by the maximum transmission power of individual UEs. In addition, there is a dif- ferent approach to transmit power control in the uplink. In the downlink, the superposed signal received at a UE experiences the same channel, that is, the signals of different UEs have the same channel gain at each UE receiver. Therefore, the design of downlink power control tries to crea