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NOMA-2000 Versus PD-NOMA: An Outage Probability Comparison

2021    Cosandal, Ismail; Koca, Mutlu; Biglieri, Ezio; Sari, Hikmet

Non-orthogonal multiple access (NOMA) is an emerging technique promising to accommodate the increasing data rate requirements of next generation networks. In power-domain (PD) NOMA, this challenge is addressed by allocating two or more users on each orthogonal resource block while assigning significantly different power levels to all users. Recently, an interesting alternative to conventional PD-NOMA has been NOMA-2000 where multiple access is done using two sets of orthogonal waveforms. In this letter we make a comparison of these two NOMA schemes based on their outage probabilities where the analytical expressions are derived without any simplifying assumption about the statistical dependencies caused by the presence of more than one user signal in each resource block. These derivations are validated by computer simulation results, which appear in tight agreement with the analysis and corroborate the claim that NOMA-2000 may significantly outperform PD-NOMA under realistic channel conditions and with different overload factors.