## 5 Simulation Results
### Throughput and PLR
For the lower EH rates \(\bar{\beta}=1\) and \(\bar{\beta}=2\) cases, the normalized throughput of the proposed policy, EBP and NBP all increase linearly with the increase of network size. The performance of EBP is nearly the same as that of the proposed policy, because in these scenarios, the transmission probability of each EH-ST is limited by the EH rate. The performance of NBP is a little worse than that of the proposed policy and EBP, because in these scenarios, \(\eta_{PLR_{th}}>\beta(B\geq l)\), which means the transmission probability of each EH-ST is larger than the energy arrival rate. Therefore, more EH-STs are in the state of energy exhausted. From the perspective of \(PLR\), all these three policies are able to control the \(PLR\) under the \(PLR\) threshold in the lower EH rate cases. Interestingly, the performance of GP seems better than the other three policies. In fact, under GP, EH-STs will always transmit packets as long as they have energy, which increases the traffic load; thus, GP can achieve a higher throughput. However, due to the low EH rate, most EH-STs have no energy to transmit packet replicas, which makes the collided packets unable to be recovered and increases the \(PLR\). Actually, Figure 6 shows the \(PLR\) of GP is beyond the threshold even though the traffic load is light. A large \(PLR\) leads to packets retransmission frequent, which will cause unacceptable large communication latencies in the satellite networks and expand more energy units for the EH-STs. On the other hand, when \(\bar{\beta}=3\), the performance of NBP and EBP is close to the proposed policy for the light and moderate traffic load. When the traffic load becomes heavier, the normalized throughput of NBP and the proposed policy tends to be flat at 0.6 packets/slot, while the performance of EBP drops dramatically. This is because for the lighter traffic load, \(\beta(B\geq l)<\eta_{PLR_{th}}\)  
Figure 5: Normalized throughput of different policies comparison for different network sizes, under different EH rates \(\beta\in\{1,2,3\}\), \(e_{max}=10\). For RA schemes, number of time slots in each frame \(N=200\), QPSK modulation, \(E_{s}/N_{0}=10\) dB. the performance of these three policies is still constrained by the EH rate. As the network size grows larger, packet collisions become severe. EH-STs employ NBP and the proposed policy transmitting the packets with probability of \(\eta_{PLR_{\text{H}}}\), but those who employ EBP transmit the packets with a probability of \(\beta(B\geq l)\). At this time, \(\beta(B\geq l)>\eta_{PLR_{\text{H}}}\), which results in the \(PLR\) of EBP, exceeds the threshold. Thus, the performance of EBP becomes worse for the larger network size. GP seems to behave better than the other three policies in the small and medium network size scenario. However, as mentioned above, the \(PLR\) of GP exceeds the threshold even for the light traffic load. Moreover, the maximum normalized throughput of EBP and GP is similar with that of CRDSA with 3 replicas, which almost reaches 0.64 packets/slot. However, when the performance achieves the peak, the \(PLR\) is beyond the threshold. Notice that all the policies cannot perform as well as the CRDSA protocols for the small and medium network size, because conventional CRDSA does not consider the limitation of energy and the EH process. Therefore, terminals employing conventional CRDSA protocols are assumed to always have enough energy to transmit their packet replicas. In other words, if the EH rate is high enough, the proposed RA scheme can perform as well as CRDSA protocols.