A multiuser Amplify-and-Forward (AF) relay system is considered in which the source is equipped with multiple antennas

while the relay and each of multiple destinations have a single antenna.Orthogonal Space-Time Block Coding (OSTBC) is employed to achieve spatial diversity and opportunistic scheduling is used to obtain multiuser diversity.Closed-form expressions for outage probability and average Symbol Error Rate (SER) in independent but not identically distributed (i.n.i.d.) Rayleigh fading multiuser environments are derived for adaptive-gain and fixed-gain relaying methods.Asymptotic expressions for outage probability and average SER at high SNR are presented and used to determine the diversity order of the two relaying systems.The combined effect of spatial and multiuser diversity is quantified for the proposed system.Monte Carlo simulations demonstrate the accuracy of the analyses presented.Comparisons among the relaying methods and multiuser point-to-point systems are provided along with insights.