We propose a multiuser two-hop cooperative network protocol, where several source/destination pairs communicate concurrently over the same physical channel without interfering to each other. A set of half-duplex amplify-andforward relays assisting them are partitioned into two clusters which have different needs for channel state information (CSI) for calculating the relay gain factors. The cluster composed of relays requiring only local CSI contributes to the received signal power at the

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... ations, i.e., array gain, but causes multiuser interference. The second cluster needing global CSI within the cluster, cancels the multiuser interference at the destinations in a zero-forcing manner, and can achieve distributed diversity gain through relay selection. It is shown that with drastically reduced CSI exchange overhead, the proposed protocol approaches the rate performances of conventional multiuser relaying systems requiring global network CSI.