Abstract
Reliable spectrum sensing (SS) is fundamental to cognitive radio (CR) and integrated sensing-and-communications (ISAC) systems. We propose a fluid antenna system (FAS)-aided improved energy detector (IED) that harnesses FAS port-selection diversity with a single RF chain. For an L-port FAS operating over correlated channels, we derive closed-form expressions for the average detection probability and the area under the receiver operating characteristic (ROC) curve (AUC) over fading and non-fading channels, along with their Gauss-Laguerre quadrature approximated expressions. Monte Carlo simulations validate the derivations and show consistent gains over classical energy detector (ED), highlighting the diversity benefits of FAS and the robustness advantages of p-norm detection. The results show that the IED with p=5 achieves a 7.8-times improvement over the classical ED. Moreover, the results quantify design trade-offs involving antenna size/spacing, number of ports, sensing time, threshold, and p, establishing FAS-aided IED as a low-hardware-complexity solution for robust SS in CR/ISAC.