Secrecy energy efficiency of hybrid wireless body area networks

Hybrid Wireless Body Area Networks (HyWBANs) are revolutionizing healthcare by integrating joint sensing and communication capabilities. However, this advancement introduces critical security challenges, as attackers can exploit sensing channels to intercept sensitive medical data. This paper introduces Secrecy Energy Efficiency (SEE) as a new performance metric for hybrid radio-optical wireless networks, enabling a quantitative assessment of secure communication under power-constrained conditions. We formulate and solve optimization problems to maximize the optical secrecy rate and SEE. We extend this analysis to a joint allocation framework for Ultra Wideband (UWB) and Near-Infrared (NIR) channels. Our approach leverages Sequential Fractional Programming (SFP), which enables to tackle the non-convex SEE maximization problem by a sequence of convex problems, addressing secure transmissions' inherent non-convexity and fractional nature with intentional jamming. Based on lab-based in-body measurements through porcine tissue and on radio and optical average synthetic phantoms, numerical evaluations demonstrate that the NIR link can achieve approximately 3 bit/Hz/Joule in SEE. Further, we show that optimal power allocation significantly outperforms random allocation methods, highlighting the potential of this approach for mission-critical healthcare applications. These findings provide a robust foundation for designing next-generation, low-power medical communication systems that balance security requirements with stringent energy constraints.