## 5 Implementation and Performance Analysis
### Number of CCs Is Not Fixed  
The number of CCs is not fixed, which means that SUs can configure the different number of CCs for SA and the SUs' data transmission can be switched between CCs, depending on the SUs' delay requirement. Assume there are 10 CCs and each CC has same condition as shown in Table 1. \(F\) is fixed and equal to 1 Mbits.  
The simulation results presented in Figure 5 show the average delay time of the proposed RT-CCCS scheme and the Ceq-CCCS scheme with different SU and PU arrival rates. From Figure 5, it can be observed that the average delay time of Ceq-CCCS is considerably higher than that of RT-CCCS when the SUs' arrival rate is higher than 5 users per second. As the SUs' arrival rate increases, the average delay time of RT-CCCS is roughly stable overall and almost less than 200 ms, but the average delay time of Ceq-CCCS is almost up to 40,000 ms when the SUs' arrival rate changes from 5 users per second to 50 users per second. This means that RT-CCCS has the better delay performance than Ceq-CCCS in the CR-based SA, and RT-CCCS can satisfy the request of the delay and is more suitable for CC configuration and switching in the CR-based SA system. These are the results that are expected in this paper.  
\begin{table}
\begin{tabular}{c c} \hline
**Parameter** & **Setting/Description** \\ \hline Carrier aggregation pattern & 3 MHz per CC \\ Number of RBs per CC & 50 (12 subcarriers per RB) \\ Sub-frame duration & 1 ms (11 OFDM data symbols plus 3 control symbols) \\ Modulation and coding schemes & 64 QAM (5/6) \\ Traffic model & M/M/1 for PUs \\ Delay requirement & 200 ms \\ Admission control constraint & Maximum 50 SUs for the CCs \\ \hline \end{tabular}
\end{table}
Table 1: Simulation settings.  
The numbers of CCs used for RT-CCCS and Ceq-CCCS under different SU and PU arrival rates are shown in Figure 6. From Figure 6, we can see that the number of CCs used for RT-CCCS varies with the SUs arrival rate and PUs arrival rate, but that of Ceq-CCCS does not. The number of CCs used for Ceq-CCCS may vary with the PU arrival rate, but the PU arrival rate or payload size \(F\) is not large enough and the number of CCs used for Ceq-CCCS does not vary with the PUs' arrival rate. This means that RT-CCCS can configure the different CCs and switch the SUs' data transmission between the CCs based on the PUs' arrival rate of each CC and SU arrival rate. The delay performance of RT-CCCS is better than that of Ceq-CCCS at the cost of more resources.  
Figure 5: Average delay time of RT-CCCS and Ceq-CCCS under different SU and PU arrival rates (_F_ is fixed and equal to 1 Mbits).  
Figure 6: Number of CCs used for RT-CCCS and Ceq-CCCS under different SU and PU arrival rates (_F_ is fixed and equal to 1 Mbits).  
Figure 7 presents the resource efficiency of the RT-CCCS scheme and the Ceq-CCCS scheme under different SU and PU arrival rates. The simulation results show that the resource efficiency of RT-CCCS is significantly lower than that of Ceq-CCCS. The resource efficiency of Ceq-CCCS is increased with increasing SU arrival rate, and it is up to 100% when the SU arrival rate is larger than 10 users per second. The resource efficiency of RT-CCCS is also increased with increasing SU arrival rate, and it is about 90% when the SU arrival rate is larger than 25 users per second. The delay performance of RT-CCCS is better than that of Ceq-CCCS at the cost of low resource efficiency.  
Therefore, we can draw the conclusion that the RT-CCCS scheme can satisfy the request of the delay and is suitable for CC configuration and switching in the CR-based SA system. The delay performance of RT-CCCS is better than that of Ceq-CCCS at the cost of more resources and low resource efficiency.