In this paper, we investigate the performance of the non-orthogonal multiple access (NOMA) system with incremental relaying,\nwhere the relay is employed with amplify-and-forward (AF) or decode-and-forward (DF) protocols. To characterize the outage\nbehaviors of the incremental cooperative NOMA (ICN) system, new closed-form expressions of both exact and asymptotic\noutage probability for two users are derived. In addition, the performance of the conventional cooperative NOMA (CCN)\nsystem is analyzed as a benchmark for the the purpose of comparison. We confirm that the outage performance of the distant\nuser is enhanced when ICN system is employed. Numerical results are presented to demonstrate that (1) the near user of the\nICN system achieves better outage behavior than that of the CCN system in the low signal-to-noise ratio (SNR) region; (2) the\noutage performance of distant user for the DF-based ICN system is superior to that of the AF-based ICN system when the\nsystem works in cooperative NOMA transmission mode; and (3) in the low SNR, the throughput of the ICN system is higher\nthan that of the CCN system.
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