  Compared to fiber continuous-variable quantum key distribution (CVQKD),
atmospheric link offers the possibility of a broader geographical coverage and
more flexible transmission.However, there are many negative features of the
atmospheric channel that will reduce the achievable secret key rate, such as
beam extinction and a variety of turbulence effects. Here we show how these
factors affect performance of CVQKD, by considering our newly derived key rate
formulas for fading channels,which involves detection imperfections, thus form
a transmission model for CVQKD. This model can help evaluate the feasibility of
experiment scheme in practical applications.We found that performance
deterioration of horizontal link within the boundary layer is primarily caused
by transmittance fluctuations (including beam wandering, broadening,
deformation, and scintillation),while transmittance change due to pulse
broadening under weak turbulence is negligible. Besides,we also found that
communication interruptions can also cause a perceptible key rate reduction
when the transmission distance is longer, while phase excess noise due to
arrival time fluctuations requires new compensation techniques to reduce it to
a negligible level. Furthermore, it is found that performing homodyne detection
enables longer transmission distances, whereas heterodyne allows higher
achievable key rate over short distances.
