In Mixed-Line-Rate (MLR) networks, different line rates on different wavelengths can coexist on the same fiber. MLR brings flexibility to handle diverse demands by allowing each lightpath to be established end-to-end with different line rates, if necessary. High line rates require advanced modulation techniques, such as DQPSK and DP-QPSK. On the other hand, signals being propagated over transparent paths are exposed to detrimental effects of physical-layer impairments (PLIs). Advanced modulation techniques are highly susceptible to PLI, especially to the cross-phase modulation (XPM) induced by intensity-modulated channels.