  In this paper, we investigate the scheduling scheme to combine cooperative
diversity (CD) and multiuser diversity (MUD) in multiuser cooperative networks
under the time resource allocation (TRA) framework in which the whole
transmission is divided into two phases: the broadcast phase and the relay
phase. The broadcast phase is for direct transmission whereas the relay phase
is for relay transmission. Based on this TRA framework, a user selection based
low complexity relay protocol (US-LCRP) is proposed to combine CD and MUD. In
each time slot (TS) of the broadcast phase, a "best" user is selected for
transmission in order to obtain MUD. In the relay phase, the relays forward the
messages of some specific users in a fixed order and then invoke the limited
feedback information to achieve CD. We demonstrate that the
diversity-multiplexing tradeoff (DMT) of the US-LCRP is superior to that of the
existing schemes, where more TSs are allocated for direct transmission in order
to jointly exploit CD and MUD. Our analytical and numerical results show that
the US-LCRP constitutes a more efficient resource utilization approach than the
existing schemes. Additionally, the US-LCRP can be implemented with low
complexity because only the direct links' channel state information (CSI) is
estimated during the whole transmission.
