Abstract
This paper considers applying bit loading to multicarrier non-othogonal
multiple access (NOMA) systems. The objective is to maximize the system
total throughput while satisfying the users’ individual quality of
service (QoS) constraints. Although bit loading is generally an NP-hard
problem, even for orthogonal multiple access (OMA), the mutual
interference between the users and the dependence of power coefficients
and modulation orders are additional challenges that add substantial
complexity to the optimization problem. Therefore, we propose in this
paper an efficient bit loading algorithm for multicarrier NOMA systems
and compares the complexity and throughput with OMA. The obtained
results show that NOMA has virtual cognition and hybrid modes of
operation, NOMA/OMA, that enables NOMA to outperform OMA by 100% for
the two-user scenario. The complexity of the loading process for NOMA is
noticeably higher than OMA, which is due to the high computational
complexity of bit error rate (BER) computation for NOMA. The obtained
results show that the NOMA throughput depends on which user is loaded
first, and on the initially loaded bits.