## 6 Numerical Results and Discussions
In this case, although the error performance of the SECps is improved, the complexity of branch estimations increases. In addition, based on (74), (75) and (82), Figure 9 illustrates the ASEP values of BPSK and MQAM for dual-branch SSC as a function of the average SNR per symbol for i.i.d. (\(m=2\), \(n=5\), \(\gamma_{\tau}=5\) dB) and n.i.d. (\(\rho_{G}=\rho_{N}=0.5\)). At the same time, the optimum ASEP analysis (i.i.d.-opt) is also presented by using (76) and (83). It is clear that the ASEP performance of SSC improves as the average SNR grows and decreases with the increase of modulation order \(M\). Figure 8: ABEP values of DPSK for the switched diversity systems as a function of the switching threshold (\(\gamma_{\tau}\)) over Fisher–Snedecor \(\mathcal{F}\) fading channels with \(m=2\), \(n=5\), and \(\overline{\gamma}_{1}=10\) dB. Figure 7: ABEP values of DPSK for the SEC and the SECps as a function of the average SNR of the first branch (\(\overline{\gamma}_{1}\)) over i.i.d. Fisher–Snedecor \(\mathcal{F}\) fading channels with \(m=2\), \(n=5\), and \(\gamma_{\tau}=6\) dB. Based on (90), (92), (93) and (94), the average capacity per unit bandwidth of the switched diversity systems as a function of the average SNR of the first branch (\(\overline{\gamma}_{1}\)) over Fisher-Snedecor \(\mathcal{F}\) fading channels with \(m=2\), \(n=5\), and \(\gamma_{\tau}=6\) dB is depicted in Figure 10. As a comparison, the average capacities of the PSC (i.i.d.) and single-branch system (no diversity) are also shown. From Figure 10, it is evident that the average capacity for all of the cases improves with the increase of the average SNR. It is interesting that the average capacity of the dual-branch SSC receiver falls between the PSC and the single-branch system, while the SEC and the SECps show better performance only in the low and middle SNR regions and tend toward that of the single-branch system in the high SNR region. These results are similar to those shown in Figure 7. In Figure 11, we compare the average capacity per unit bandwidth of the switched diversity systems as a function of the switching threshold (\(\gamma_{\tau}\)), where \(m=2\), \(n=5\), and \(\overline{\gamma}_{1}=10\) dB. It is observed that the optimum threshold for the maximum average capacity can be easily obtained by numerical analysis. These results in Figure 11 suggest the same conclusions as those in Figure 2:0 Therefore, it is necessary for the switched diversity systems to choose an appropriate switching threshold to balance the system performance and the branch estimations. Additionally, the switched diversity systems can provide the diversity gain in the low and middle SNR regions and have no distinct gain in the high SNR region compared with the single-branch system, which is helpful for enhancing the system reliability for wearable devices and IoT sensor nodes in low-power receiving scenarios. Figure 2:1 ASEP values of BPSK and MQAM for the SSC system as a function of the average SNR of the first branch (\(\overline{\gamma}_{1}\)) over Fisher–Snedecor \(\mathcal{F}\) fading channels with \(m=2\), \(n=5\), and \(\gamma_{\tau}=6\) dB.