On--Off Digital Noise Modulation under Multi-User Co-Channel Interference

This letter analyzes the performance of on-off digital noise (OODN) modulation under multi-user scenarios. While prior works have addressed single-link operation, the impact of co-channel interference remains unexplored. We consider $K$ synchronous OODN interferers over AWGN and fading channels and derive a unified analytical framework for the bit error probability (BEP). The optimal likelihood-ratio detection threshold is obtained, along with a closed-form expression for the resulting irreducible error floor, which climbs geometrically with the number of co-channel interferers and yields a simple admission-control rule on network density. The analysis is extended to $\kappa$-$\mu$ fading, covering practical millimeter-wave channels with dominant line-of-sight components. Results, corroborated by Monte Carlo simulation, show that the floor is governed by the on-off interference and the non-coherent detector rather than by the noise waveform.