In this paper, we prove the asymptotic sum-rate growth like 2 log log N can be achieved in 2脳N脳2 dual-hop relaying systems with 2 transmit antennas at a base station (or a source), N 驴 2 single receive/transmit antenna relays and 2 destination users with a single antenna. The capacity is achieved when the base station transmits with zero-forcing beamforming and the relays that actively transmit are selected with semi-orthogonal relay selection principle. Since the base station should know the channel information to the relays, the feedback load grows prohibitively large if N 驴 驴. To reduce the feedback load from the relays to the base station, we use quality-based channel state reporting (QBR). Numerical results show that the sum-rate achieved by N relays gets close to its multiuser counterpart if the amplifying gain at the relay is large. We also show how QBR is effective in reducing the feedback load when N is large.
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