Although relaying can be very beneficial for wireless systems, understanding which relaying schemes can achieve specific\r\nperformance objectives under realistic fading is crucial. In this paper we present a general framework for modeling and evaluating\r\nthe performance of dual-hop decode-and-forward (DF) relaying schemes over independent and not necessarily identically\r\ndistributed (INID) Nakagami-m fading channels.We obtain closed-form expressions for the statistics of the instantaneous output\r\nsignal-to-noise ratio of repetitive transmission with selection diversity. Furthermore, we present a unified statistical overview of\r\nother three significant relaying schemes with DF, one based on repetitive transmission with maximal-ratio diversity and the other\r\ntwo based on relay selection (RS). To compare the considered schemes, we present closed-form and analytical expressions for\r\nthe outage probability and the average symbol error probability under various modulation methods, respectively. Importantly,\r\nit is shown that when the channel state information for RS is perfect, RS-based schemes always outperform repetitive ones.\r\nFurthermore, when the direct link between the source and the destination nodes is sufficiently strong, relaying may not result\r\nin any gains, and it should be switched off.
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