Maximizing the Spectral Efficiency of Amplify-and-Forward Relaying Systems over Nakagami-m Fading

In this paper, we propose and study a cooperative transmission scheme for amplify-and-forward (AF) relaying system with adaptive modulation. Unlike the conventional incremental relaying with adaptive modulation (IR-AM) scheme, which improves the spectral efficiency with the minimum usage of relaying, our proposed scheme adaptively utilizes cooperative relaying to maximize the system spectral efficiency. We quantify the average spectral efficiency performance of the proposed scheme through statistical analysis and obtain the closed-form solutions for some practical scenarios of interest. Selected numerical results demonstrate that the spectral efficiency gain of the proposed scheme over the IR-AM scheme occurs mainly over the median signal-to-noise ratio range.