A relay network approach is proposed that allows multiple source-destination pairs to communicate simultaneously. The communication is enabled by one multi-antenna relay, and is implemented in two slots; in the first slot, the sources transmit, and in the second slot, the relay forwards the received signals after processing them through a zeroforcing beamforming matrix. Imperfect relay channel state information (CSI) results in interference at the destinations. This effect can be controlled by increasing the number of relay antennas. To avoid high hardware cost, typically associated with transmitter RF-modules, an optimal antenna selection scheme is proposed, with optimization criterion being the minimization of the interference, or the outage probability.