On the Energy Efficiency of RSMA-Based VLC Systems with Confidential Private Messages

This paper investigates the energy efficiency (EE) of rate-splitting multiple access (RSMA)-based visible light communications (VLC) with confidential private messages. We first formulate an EE maximization problem that takes into account the achievable rate of the common message and the sum secrecy rate of private messages. Due to the fractional non-convex nature of the design problem, an algorithm that leverages the Dinkelbach algorithm and convex-concave procedure (CCP) is proposed to solve local optima. In this study, the channel similarity
$S_{C}$
and the rate-splitting power allocation ratio
$\rho$
are jointly considered to evaluate EE performance and trade-offs between the achievable common rate and the sum secrecy rate. Numerical results reveal that when
$S_{C}$
is below 0.7, the EE saturates at its optimum as
$\rho$
increases, while when
$S_{C}$
exceeds 0.7, an optimal
$\rho$
exists beyond which the EE starts declining. Moreover, it is observed that while the relationship between the sum secrecy rate and
$S_{C}$
is inversely proportional, it is directly proportional in the case of the common rate.