Energy Efficiency of Uplink and Downlink Non-Orthogonal Multiple-Access Channels Under Gaussian-Mixture Interference

In this paper, we analyze the energy efficiency (EE) of uplink and downlink non-orthogonal multiple access (NOMA) channels with successive interference cancellation under Gaussian-mixture aggregate interference. The adopted nonGaussian model is a realistic noise plus interference model to capture the asynchronism in a heterogeneous cellular network. The considered EE is measured via the minimum energy per bit E
_b
/N
_0
min
for reliable communication and the wideband slope of the spectral efficiency as a function of energy per bit E
_b
/N
₀
. For completeness, both Gaussian signaling schemes and practical finite alphabet inputs are examined. To this end, our approach is to calculate E
_b
/N
_0
min
and the wideband slope region via the Kullback-Leibler divergence. Due to the presence of mixture of multiple Gaussian distributions, the Kullback-Leibler divergence cannot be expressed in closed-form. As an alternative, we exploit upper bounds on the divergence, and we show that the bounds are achievable at the limit points, i.e., when the signal-to-noiseratio (SNR) approaches zero. As a result, E
_b
/N
_0
min
of each user can be established in closed-form. Next, we apply Taylor series expressions and exploit the achievability in the previous step to evaluate the second derivative of the rates when SNR goes to zero. It is then shown that the wideband slope region can be found effectively. The proposed method can serve as an important tool for making more accurate throughput and EE evaluation of important wireless/cellular networks.