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A downlink multiuser amplify-and-forward (AF) relay system is considered in which the source is equipped with multiple antennas, whereas the relay and each of multiple destinations have a single antenna. Orthogonal space-time block coding (OSTBC) is employed to achieve spatial diversity, and normalized SNR-based scheduling is used to obtain multiuser diversity while maintaining fairness among users. New exact expressions for outage probability and average symbol error rate (SER) in independent but nonidentically 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 a 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 between the two relaying methods and that with multiuser point-to-point systems are made, and some insights are provided.