intra-cluster beamforming and PBPA/IBPA as user pairing
algorithms.
The difference between H-NOMA/SUPA [15] and the
proposed beamforming algorithms can be concluded as
follows.
1) Note that the H-NOMA precoding is originally
proposed for two-user scenario, thus, it does not take
inter-cluster interference into consideration. Moreover,
the H-NOMA precoding for K-user (K > 2) counterpart
is not specified in [15]. Mathematically, if users
m and n are paired into one cluster (khmk ≥ khnk),
the H-NOMA precoding vectors wi (i = m, n) should
be obtained by solving the following optimization
problem.