Adaptive Frequency-Domain CFAR for Robust Spectrum Sensing Under Jamming and Administrator-Controlled Counter-Access

Cognitive radio networks (CRN) enable secondary users (SUs) to opportunistically access under utilized licensed spectrum while protecting primary users (PUs) from interference. However, robust spectrum sensing under heterogeneous interference and noise uncertainty remains challenging. Con ventional energy detection, matched filtering, and cyclostationary approaches either require extensive prior knowledge or suffer performance degradation under interference, leading to excessive false alarms and service denial. We propose an adaptive frequency-domain constant false alarm rate (CFAR) spectrum sensing approach that dynamically sets frequency-specific thresholds based on neighboring spectral samples. This independent enhancement in SU devices requires minimal prior knowledge. To address potential security risks from untrusted SUs exploiting the proposed resilient CFAR scheme, we introduce a centralized counter-access mechanism: an administrator-controlled jammer that defeats CFAR-equipped adversaries, preventing unauthorized access during emergencies. It safeguards pri mary communications by creating strategic frequency gaps that avoid known jammed PU channels. Using APCO Project 25 waveforms for PUs and OFDMA for SUs, Monte Carlo simulations evaluate cell-averaging (CA), greatest-of (GO), smallest-of (SO), order-statistics (OS), and censored CFAR variants across different channel models combined with multiple jamming scenarios. Results show OS and censored CFAR variants best stabilize false alarm rates and enhance detection in heterogeneous conditions, outperforming CA and GO/SO schemes. The comb-sweep jammer effectively denies ser vice to CFAR-equipped SUs without impacting PUs, though at the expense of reduced spectrum availability. This work frames spectrum sensing and jamming in CRNs as a two-sided interaction between electronic protection for secondary users and administrative electronic attack for controlled denial.