  In this letter, we consider the scenario of decode-and-forward relay network
with reconfigurable intelligent surface (RIS)-assisted source and relays in the
presence of interference. We derive approximate closed-form expression for the
system outage probability assuming Rayleigh fading channels and opportunistic
relaying scheme. In addition, we study the system behavior at the high
signal-to-noise ratio (SNR) regime, where the diversity order and coding gain
are obtained and analyzed. The results show that the system can achieve a
diversity order of Gd = min(N1,N2)K, where N1 and N2 are the numbers of
reflecting elements at the source and relays, respectively, and K is the number
of relays. In addition, findings illustrate that for the same diversity order,
utilizing one relay with multiple reflecting elements gives better performance
than utilizing multiple relays with a single reflecting element. Furthermore,
findings illustrate that the interference at the destination is more severe on
the system performance than the interference at the relays. Therefore, under
the same interference powers and for a fixed number of relays K, results show
that the case where the first hop is dominating the performance N1 < N2 gives
better results in terms of coding gain than the case where N2 < N1.
