  This work analyzes the performance of an underlay cognitive radio based
decode-and-forward mixed multiple-input multiple-output (MIMO) radio
frequency/free space optical (RF/FSO) cooperative relay system with multiple
mobile secondary and primary user nodes. The effect of imperfect channel state
information (CSI) arising due to channel estimation error is also considered at
the secondary user transmitters (SU-TXs) and relay on the power control and
symbol detection processes respectively. A unique aspect of this work is that
both fixed and proportional interference power constraints are employed to
limit the interference at the primary user receivers (PU-RXs). Analytical
results are derived to characterize the exact and asymptotic outage and bit
error probabilities of the above system under practical conditions of node
mobility and imperfect CSI, together with impairments of the optical channel,
such as path loss, atmospheric turbulence, and pointing errors, for orthogonal
space-time block coded transmission between each SU-TX and relay. Finally,
simulation results are presented to yield various interesting insights into the
system performance such as the benefits of a midamble versus preamble for
channel estimation.
