Atmospheric turbulence and pointing errors are major hindrances behind the proliferation of free-space-optics (FSO) technology in next-generation fronthaul networks. This paper investigates the effect of a decode-and-forward relay in overcoming these impairments and how an additional source-to-relay millimeter-wave (mmWave) radio-frequency (RF) backup link improves the performance of the relay-aided FSO system further; i.e., we study the performance of a hybrid FSO/(FSO-FSO)/(RF-FSO) system. Generalized Málaga distribution is adopted to model atmospheric turbulence in FSO links, whereas the fading statistics of the mmWave RF link is modeled by Nakagami-$m$ distribution. The performance of the hybrid system is studied on the basis of analytical expressions derived for metrics such as outage probability, bit error rate, and ergodic capacity, and the results show the supremacy of the proposed hybrid FSO system. The improvement is, however, dependent on factors such as turbulence location and signal-to-noise ratio per bit, and not all performance metrics exhibit equal improvement.
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