  In this paper, we consider a mixed RF and hybrid RF/FSO system where several
mobile users transmit their data over an RF link to a relay node (e.g. a small
cell base station) and the relay forwards the information to a destination
(e.g. a macro cell base station) over a hybrid RF/FSO backhaul link. The relay
and the destination employ multiple antennas for transmission and reception
over the RF links while each mobile user has a single antenna. The RF links are
full-duplex with respect to the FSO link and half-duplex with respect to each
other, i.e., either the user-relay RF link or the relay-destination RF link is
active. For this communication setup, we derive the optimal resource allocation
policy for sharing the RF bandwidth resource between the RF links. Our
numerical results show the effectiveness of the proposed communication
architecture and resource allocation policy, and their superiority compared to
existing schemes which employ only one type of backhaul link.
