  A theoretical research and numerical simulation of the noise influence caused
by spontaneous Raman scattering, four-wave mixing, and linear channel crosstalk
on the performance of QKD systems was conducted. Three types of QKD systems
were considered: coherent one-way (COW) QKD protocol, subcarrier-wave (SCW) QKD
system, and continuous-variable (CV) QKD integrated with classical DWDM
channels. We calculate the secure key generation rate for the systems mentioned
addressing different channel allocation schemes (i.e., configurations). A
uniform DWDM grid is considered with quantum channel located in C-band and
O-band (at 1310 nm) of a telecommunication window. The systems' performance is
analyzed in terms of the maximal achievable distance values. Configurations for
the further analysis and investigation are chosen optimally, i.e., their
maximal achievable distances are the best.
