  We study a cooperative network with a buffer-aided multi-antenna source,
multiple half-duplex (HD) buffer-aided relays and a single destination. Such a
setup could represent a cellular downlink scenario, in which the source can be
a more powerful wireless device with a buffer and multiple antennas, while a
set of intermediate less powerful devices are used as relays to reach the
destination. The main target is to recover the multiplexing loss of the network
by having the source and a relay to simultaneously transmit their information
to another relay and the destination, respectively. Successive transmissions in
such a cooperative network, however, cause inter-relay interference (IRI).
First, by assuming global channel state information (CSI), we show that the
detrimental effect of IRI can be alleviated by precoding at the source,
mitigating or even fully cancelling the interference. A cooperative relaying
policy is proposed that employs a joint precoding design and relay-pair
selection. Note that both fixed rate and adaptive rate transmissions can be
considered. For the case when channel state information is only available at
the receiver side (CSIR), we propose a relay selection policy that employs a
phase alignment technique to reduce the IRI. The performance of the two
proposed relay pair selection policies are evaluated and compared with other
state-of-the-art relaying schemes in terms of outage and throughput. The
results show that the use of a powerful source can provide considerable
performance improvements.
