Security and Reliability in D2D Communication Systems Utilizing Multiple Cooperative Jammers

Abstract

Battery-free device-to-device (D2D) links suit dense machine-type deployments, but removing the battery also removes the power margin that physical layer security (PLS) usually relies on. This paper quantifies that tension for a D2D pair whose transmitter is powered exclusively by a power beacon (PB) under a time-switching schedule, whose receiver applies M-branch selection combining, and whose confidentiality is protected by a cluster of N single-antenna cooperative jammers radiating mutually independent artificial noise. We derive closedform outage (OP) and intercept (IP) probabilities over Rayleigh fading. The OP expression is exact and reproduces Monte Carlo simulation to within 1.5%; the IP expression rests on an interference-limited approximation that we report as an upper bound, with its tightness characterised rather than assumed. Reliability and secrecy respond to different controls: raising the beacon power from 10 to 20 dB lowers the OP by about a decade but drives the IP from $3.5 \times 10^{-2}$ to $4.1 \times 10^{-1}$, whereas enlarging the cluster from $N=1$ to $N=10$ lowers the IP from $3.2 \times 10^{-1}$ to $5.5 \times 10^{-3}$ without appearing in the OP at all. We further show the IP depends on beacon and jammer power only through their ratio, so the cluster must be dimensioned relative to the beacon. Placement dominates: moving it from $d_{J E}=2 \mathbf{m}$ to 0.5 m is worth about three decades of IP.