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In this paper, a round-robin-based relay protocol dubbed round-robin relaying with source selection protocol (R3SSP) is proposed to achieve full cooperative diversity in multisource cooperative communication networks. In R3SSP, all the sources transmit their individual information in turn. The relays then forward the messages of some specific sources in a fixed order according to the limited feedback information. Compared with traditional relay selection-based protocols, R3SSP is based on round-robin relaying, thus avoiding relay selection and requiring no specific channel state information feedback. R3SSP can therefore be implemented with lower complexity. Furthermore, the exact and asymptotic expressions of the outage probability are derived. The diversity-multiplexing tradeoff (DMT) performance is also analyzed. Theoretical analysis shows that R3SSP achieves full cooperative diversity and provides better DMT performance than relay selection-based protocols in a system where the number of sources is higher than that of the relays. Based on the DMT analysis, we further propose an adaptive relay activation scheme that is capable of achieving higher DMT by dynamically selecting the number of relays to be activated in the entire network. Simulation results also verify the validity and superiority of R3SSP.