  The uplink (UL)/downlink (DL) decoupled access has been emerging as a novel
access architecture to improve the performance gains in cellular networks. In
this paper, we investigate the UL/DL decoupled access performance in cellular
vehicle-to-everything (C-V2X). We propose a unified analytical framework for
the UL/DL decoupled access in C-V2X from the perspective of spectral efficiency
(SE). By modeling the UL/DL decoupled access C-V2X as a Cox process and
leveraging the stochastic geometry, we obtain the joint association
probability, the UL/DL distance distributions to serving base stations and the
SE for the UL/DL decoupled access in C-V2X networks with different association
cases. We conduct extensive Monte Carlo simulations to verify the accuracy of
the proposed unified analytical framework, and the results show a better system
average SE of UL/DL decoupled access in C-V2X.
