Simultaneous quantum and classical communication using pulse position modulation for inter-satellite links

We propose a terahertz continuous-variable quantum key distribution protocol using pulse position modulation, which enables simultaneous quantum and classical communication for inter-satellite links. In this scheme, classical information is conveyed through the relative positioning of encoded pulses while quantum information is encoded using Gaussian modulation to generate thermal terahertz (THz) signals. Coherent detection is employed to measure all the relevant parameters. Extensive multi-parameter simulations were conducted to validate the protocol, examining the bit error rate, secret key rate, and transmission distance under varying pulse position modulation (PPM) settings and other parameters. The results demonstrate that the protocol is feasible and represents an effective method for quantum key distribution. The proposed approach offers a promising pathway for the deployment of inter-satellite quantum communication networks.