Outage Performance of Cooperative Relaying Systems with Randomly Available Relays

In this paper we investigate the outage performance of a decode-and-forward cooperative relaying system in which the relays are randomly available. The upper and lower bounds on the outage probability are derived for Rayleigh fading channels. Our analytical derivation reveals that the unreliable cooperative relaying contributes no diversity gain to the system and the outage probability of relaying approaches a constant at high signal-to-noise ratio (SNR). We also demonstrate that, if the average number of available relays is fixed, the outage probability of relaying grows asymptotically with increasing the total number of relays. Simulation results agree well with our theoretical analysis.