  Discrete-modulated continuous-variable quantum key distribution with homodyne
detection is widely recognized for its ease of implementation, efficiency with
respect to error correction, and its compatibility with modern optical
communication devices. However, recent studies report that the application of
homodyne detection obtains poor tolerance to excess noise and insufficient
transmission distance, hence seriously restricting the large-scale deployment
of quantum secure communication networks. In this paper, we propose a homodyne
detection protocol using the quadrature phase shift keying technique. By
limiting information leakage, our proposed protocol enhances excess noise
tolerance to a high level. Furthermore, we demonstrate that homodyne detection
performs better than heterodyne detection in quaternary-modulated
continuous-variable quantum key distribution under the untrusted detector noise
scenario. The security is analyzed using the tight numerical method against
collective attacks in the asymptotic regime. Our results imply that the current
protocol is able to distribute keys in nearly intercity area and thus paves the
way for constructing low-cost quantum secure communication networks.
