  When considering the future generation wireless networks, non-orthogonal
multiple access (NOMA) represents a viable multiple access technique for
improving the spectral efficiency. The basic performance of NOMA is often
enhanced using downlink beamforming and power allocation techniques. Although
downlink beamforming has been previously studied with different performance
criteria, such as sum-rate and max-min rate, it has not been studied in the
multiuser, multiple-input single-output (MISO) case, particularly with the
energy efficiency criteria. In this paper, we investigate the design of an
energy efficient beamforming technique for downlink transmission in the context
of a multiuser MISO-NOMA system. In particular, this beamforming design is
formulated as a global energy efficiency (GEE) maximization problem with
minimum user rate requirements and transmit power constraints. By using the
sequential convex approximation (SCA) technique and the Dinkelbach's algorithm
to handle the non-convex nature of the GEE-Max problem, we propose two novel
algorithms for solving the downlink beamforming problem for the MISO-NOMA
system. Our evaluation of the proposed algorithms shows that they offer similar
optimal designs and are effective in offering substantial energy efficiencies
compared to the designs based on conventional methods.
