  In this paper, link selection for half-duplex buffer-aided relay systems is
revisited. A new fixed scheduling policy referred as alternate distributed
beamforming (ADB) is proposed, in which the relays are divided into two groups,
with one group receiving the same information broadcast from the source and the
other group transmitting the common messages to the destination via distributed
beamforming in each time slot. It is worth noting that the relays used for
reception and transmission are determined without the need of instantaneous
channel state information (CSI). Theoretical analysis of the achievable
throughput of the proposed scheme in Rayleigh fading is provided and the
approximate closed-form expressions are derived. Through numerical results, it
is shown that compared with existing link selection policies, the proposed
fixed scheduling ADB achieves a significant improvement in achievable
throughput.
