Single-carrier uplink cooperative DF relay using instantaneous CSI-based adaptive modulation

An introduction of the adaptive modulation improves the throughput of a 2-time slot cooperative relay. The throughput depends on conditions of mobile terminal (MT)-base station (BS) link, MT-relay station (RS) link, and RS-BS link. However, the cooperative relay is effective when the MT-BS direct link quality is worse than the others. Therefore, the best modulation combination can be chosen using instantaneous CSIs of MT-RS link and RS-BS link In this paper, by neglecting the MT-BS direct link contribution, we introduce an adaptive modulation using instantaneous channel state information (CSI) of MT-RS link and RS-BS link. We evaluate, by computer simulation, the throughput performance of single-carrier (SC) 2-time slot cooperative decode-and-forward (DF) relay using adaptive modulation. It is shown that the introduction of adaptive modulation can reduce by about 1.8 dB the required transmit power for achieving a 1%-outage throughput of 1.4 bps/Hz compared to the conventional method.