  In this paper, we investigate the performance of a dual-hop block fading
cognitive radio network with underlay spectrum sharing over independent but not
necessarily identically distributed (i.n.i.d.) Nakagami-$m$ fading channels.
The primary network consists of a source and a destination. Depending on
whether the secondary network which consists of two source nodes have a single
relay for cooperation or multiple relays thereby employs opportunistic relay
selection for cooperation and whether the two source nodes suffer from the
primary users' (PU) interference, two cases are considered in this paper, which
are referred to as Scenario (a) and Scenario (b), respectively. For the
considered underlay spectrum sharing, the transmit power constraint of the
proposed system is adjusted by interference limit on the primary network and
the interference imposed by primary user (PU). The developed new analysis
obtains new analytical results for the outage capacity (OC) and average symbol
error probability (ASEP). In particular, for Scenario (a), tight lower bounds
on the OC and ASEP of the secondary network are derived in closed-form. In
addition, a closed from expression for the end-to-end OC of Scenario (a) is
achieved. With regards to Scenario (b), a tight lower bound on the OC of the
secondary network is derived in closed-form. All analytical results are
corroborated using Monte Carlo simulation method.
