Parallel PAM for Secure Transmission

Physical layer security is a promising approach to enhancing the security of multi-user networks. However, user interference causes constellation points from different users to overlap, limiting both network reliability and security. To address this, we propose a parallel pulse amplitude modulation (PAM) scheme that ensures constellations are regularly superimposed at the legitimate receiver while appearing chaotic to the eavesdropper. Consequently, the eavesdropper experiences a consistently high bit/symbol error rate, whereas the legitimate receiver maintains a very low error rate. Furthermore, we extend the parallel PAM scheme to both the in-phase and quadrature components of the signal, forming a heterogeneous quadrature amplitude modulation (QAM) scheme. This enhances transmission efficiency while preserving security. We analyze the bit/symbol error rates at both the legitimate receiver and the eavesdropper, deriving a lower bound for the eavesdropper’s error rate. Finally, simulation results validate our theoretical analysis.