Energy-Efficient THz Sensing with Hybrid THz/VLC Communication Under Human Blockage Effects

Abstract: This paper presents an energy-efficient indoor system integrating \ac{THz} with \ac{VLC}. \ac{THz} communication offers ultra-high-capacity links but is limited by severe path loss, atmospheric absorption, and susceptibility to blockages. In contrast, \ac{VLC} provides robust, wide indoor coverage with illumination support, thereby enabling reliable, high-speed hybrid connectivity. To leverage their respective strengths, we propose a hybrid framework that integrates \ac{$THz_s-AP$} with hybrid \ac{$THz_c/VLC_c-AP$}, enabling reliable coverage and enhancing the \ac{EE} from an \ac{ISAC} perspective. We first perform optimal power allocation between the \ac{$THz_s-AP$} and \ac{$THz_c-AP$} to optimized the set of users served by the \ac{$THz_c-AP$} link, considering monostatic sensing performance metrics such as \ac{$P_d$}, \ac{$FA_p$} and \ac{$SC_p$} under the impact of human blockages are evaluated. Subsequently, the overall network power consumption is minimized via a mixed-integer linear programming (MILP) optimization that optimally selects the active \ac{$VLC_c-APs$} and assigns transmit powers. Furthermore, extensive performance evaluations are conducted to analyze key metrics, including average energy efficiency, average spectral efficiency, average sensing rate, and average communication rate. Simulation results demonstrate that, under \ac{THz} sensing, most users are connected to the \ac{$THz_c-AP$} in the absence of blockages, whereas in the presence of blockages, the majority are served by the \ac{$VLC_c-APs$}. Overall, all users maintain reliable coverage with high \ac{EE}.