## 1 Introduction
To enable low-power, ultra-reliable, low-latency downlink communications to low-cost Internet of Things devices in [21], PSC and SSC schemes were involved as simple and promising solutions in Nakagami-m fading channels. In [22], the authors studied the impacts of inter-branch correlation on multichannel spectrum sensing by using PSC and SSC schemes in dual arbitrarily correlated Nakagami-m fading channels. For indoor millimeter-wave communications, the performance of SSC and SEC was analyzed in [23]. In [24], a SECps-based scheduling algorithm was designed for multiuser downlink wiretap networks. The authors in [25] applied PSC and SSC in mobile edge computing networks to choose computational access points over Nakagami-m fading channels. In [26], a distributed SSC receiver was designed for free space optical communications. The authors in [27] studied a SECps scheduling scheme for multirelay networks in shadowed Rician channels. However, in the above new wireless applications, only the impact of multipath fading on SSC, SEC, and SECps models is considered and the influence of the shadowing fading is still ignored, except in the method proposed in [27]. As a matter of fact, the composite fading effects combing multipath and shadowing effects are frequently encountered in emerging wireless communications scenarios, such as body area networks [2] and vehicle-to-vehicle applications [28]. In Table 1, we summarize the applications of the SDC schemes for new wireless communications systems. More recently, to achieve an appropriate balance between modeling accuracy and calculation complexity, a Fisher-Snedecor \(\mathcal{F}\) composite fading channel model was proposed in [29]. It accurately characterizes the composite effects of both small- and large-scale fading, in which the small-scale multipath fading follows the Nakagami-m distribution, whereas the large-scale shadowing fading follows an inverse Nakagami-m distribution. Compared to the well-known generalized K composite fading model, this model not only provides more tractable and simpler mathematical formulations of the statistical characteristics but also shows a better fit to experimental channel measurements in some emerging wireless communications applications, for example device-to-device communications and wireless body area networks. As a result, a good deal of research work has been done based on the Fisher-Snedecor \(\mathcal{F}\) composite fading channel model, such as [30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42] and references therein. By applying the diversity combining schemes, the authors in [34] analyzed the performance of the MRC system over independent and non-identically distributed (i.n.i.d.) Fisher-Snedecor \(\mathcal{F}\) channels, while the authors in [35] re-investigated the statistical characterization of the sum of i.n.i.d. Fisher-Snedecor \(\mathcal{F}\) random variables and presented a simple approximation by using another single \(\mathcal{F}\) random variable. The performance of the PSC scheme with i.n.i.d. branches was analyzed in [36]. The authors in [37] analyzed the channel capacity under different power adaption schemes for MRC diversity system over independent and identically distributed (i.i.d.) \(\mathcal{F}\) fading channels. The correlated performance of dual-branch MRC and PSC systems over identical Fisher-Snedecor \(\mathcal{F}\) fading channels was investigated in [38]. Furthermore, the performance of some emerging applications and techniques has also been involved in Fisher-Snedecor \(\mathcal{F}\) fading channels, such as cascaded fading scenarios [39], spectrum sensing networks [40], dual-hop relaying [41], and free-space optical systems [42]. Although the performance of MRC and PSC systems has been investigated over independent [34; 35; 36; 37] and correlated [38]\(\mathcal{F}\) fading channels, to the best of the authors' knowledge, the performance of the SDC systems over independent and correlated Fisher-Snedecor \(\mathcal{F}\) fading scenarios has yet to be considered in the open research literature.