  In this paper, we propose to use the decoy-state technique to improve the
security of the quantum key distribution (QKD) systems based on homodyne
detection against the photon number splitting (PNS) attack. The decoy-state
technique is a powerful tool that can significantly boost the secure
transmission range of the QKD systems. However it has not yet been applied to
the systems that use coherent detection. After adapting this theory to the
systems based on homodyne detection, we quantify the secure performance and
transmission range of the resulting system.
