  The performance of an underlay cognitive (secondary) dual-hop relaying system
with multiple antennas and hardware impairments at each transceiver is
investigated. In particular, the outage probability of the end-to-end (e2e)
communication is derived in closed-form, when either transmit antenna selection
with maximum ratio combining (TAS/MRC), or TAS with selection combining
(TAS/SC) are established in each hop. Simplified asymptotic outage expressions
are also obtained, which manifest the diversity and array order of the system,
the effectiveness of the balance on the number of transmit/receive antennas,
and the impact of hardware impairments to the e2e communication.
