Design and Analysis of Octa-phase Shift Keying Based Quantum Key Distribution System

This letter proposes a novel modulation signaling-based quantum key distribution (QKD) protocol that employs eight phases of the optical carrier, therefore named octa-phase shift keying QKD (8PSK-QKD). The proposed QKD protocol shares two key bits simultaneously and consequently exhibits increased spectral efficiency compared to existing modulation signaling-based QKD protocols. Different performance metrics, viz., probability of sifted keys (
$P _{\text{sift}}$
), quantum bit error rate, probability of sifted keys of Eve, and Eve’s error probability (
$P _{\text{eve}}$
), are determined using a novel analytical framework for a free-space optical channel under the combined effect of atmospheric turbulence and pointing error. To inspect the potential of the system, the 8PSK-QKD system is compared with the quadrature phase shift keying-based QKD (QPSK-QKD) and subcarrier intensity modulation binary phase shift keying-based QKD (SIM/BPSK-QKD) systems. Numerical results reveal that the 8PSK-QKD system follows the criteria of an acceptable QKD system even with transmitting two key bits at a time. Additionally, the 8PSK-QKD system outperform the SIM/BPSK-QKD and QPSK-QKD by offering better
$P _{\text{sift}}$
and
$P _{\text{eve}}$
.