## 5 Simulation Results
Figure 8 compares SU spectral efficiency \(\hat{\mathcal{C}}\) of the proposed ST-CSS scheme versus sensing SNR with CSS based on general frame structure, when the algorithm of optimal sensing settings is employed to decision fusion rules of OFR, MFR, and AFR, respectively. It is assumed that \(M=5\) and \(\hat{\mathcal{C}}_{d}^{th}=0.9\). In Figure 8, it is obviously seen that the spectral efficiency enhances as SNR increases. Moreover, MFR exhibits the best performance of spectral efficiency than other two combining fusion rules for all SNR values. In lower SNR region of \(-6\) dB-12 dB, OFR is sub-optimal, while AFR becomes sub-optimal when the value of SNR in higher region ranged from 10 dB-16 dB. In the SNR region of more than 16 dB, there is little difference in respect of SU spectrum usage for those three decision combing schemes. It is further concluded that MFR is the optimal rule which aims at maximizing the spectral efficiency with sufficient protection to PU. Figure 8: SU spectral efficiency \(\hat{\mathcal{C}}\) versus SNR \(\gamma\) for the Novel ST-CSS scheme under hard decision fusion rules of OFR, MFR and AFR, respectively. Figure 7: Spectral efficiency \(\hat{\mathcal{C}}\) versus scheduling strategy for the novel CSS scheme under fusion rules of AFR (and fusion rule), OFR (or fusion rule) and MFR (majority fusion rule), respectively. Figure 9 presents SU spectral efficiency versus the targeted cooperative detection probability \(\hat{Q}_{d}^{th}\) for novel ST-CSS and general CSS with counting fusion schemes, in which the average SNR \(\overline{\gamma}\) is \(-6\) dB and the optimal sensing time is employed. As the dashed curves shown in Figure 9, the novel ST-CSS improves SU spectral efficiency compared with the general CSS. This is because in the framework of the novel ST-CSS scheme, individual SU reporting time can be used for other SU sensing. In this way, each SU gets a longer sensing duration without additional time overhead and the probability of false alarm can be reduced, which results in higher SU spectral efficiency. Additionally, aggregating the sensing results at different time mini-slots is expected to actualize a time diversity gain in spectrum utilization, which contributes to SU spectral efficiency. It is also can be seen from Figure 9 that SU spectral efficiency increases with the decreasing protection to PU. A relaxing constrained on \(\hat{Q}_{d}^{th}\) can identify more spectrum opportunities, especially when \(\hat{Q}_{d}^{th}\) becomes larger. For example, the SU spectral efficiency for novel ST-CSS with MFR improves approximately 14% when \(\hat{Q}_{d}^{th}\) decreases from 0.75 to 0.5. However, it enhances 63% when \(\hat{Q}_{d}^{th}\) decreases from 0.95 to 0.9. Therefore, the novel ST-CSS with MFR achieves best spectrum reuse with the same protection constraint. Figure 10 shows SU spectral efficiency versus the number of cooperating SU for the proposed ST-CSS scheme and the general CSS scheme under different values of reporting time. The optimal compressed sensing time and the optimal fusion rule are adopted in this simulation. The spectral efficiency relies on both reporting time \(t_{r}\) and number of secondary user \(K\). For \(K=9\), the spectral efficiency of the novel ST-CSS scheme and the general CSS scheme are approximately 1.180 and 1.088 when \(t_{r}=1\) ms, and approximately 1.178 and 1.032 when \(t_{r}=2\) ms. In the case of \(K=4\), the spectral efficiency of the two schemes are approximately 0.940 and 0.915 when \(t_{r}=1\) ms, and approximately 0.934 and 0.896 when \(t_{r}=2\) ms, respectively. Thus, the novel ST-CSS scheme can achieve a significant improvement on spectral efficiency than that of the general CSS scheme. Additionally, it is clear that more time spending for reporting sensing results to FC predicts lower spectral efficiency, especially for the general CSS. This is because in the conventional CSS structure, there is less time for transmission when allocates more time for reporting for the fixed frame length.