## 3 A Collaborative Multi-Satellite Selection Algorithm Based on Maximum SINR
### Proposed Satellite Selection Strategy
Thus, in theory, the SC-ACRDA2 scheme should be superior to the traditional RA scheme in both the peak throughput and high throughput load ranges (the throughput is greater than the load range of a specific value, which represents the packet processing capability of the scheme). Figure 7 shows that when the number of copies is 1, the peak throughput of SC-ACRDA2 reaches 0.806 when G = 1.05. ACA2 reaches a peak throughput of 0.505 when G = 0.6, ACRDA2 reaches a peak throughput of 0.614 when G = 0.75 and CRDSA2 reaches peak throughput of 0.552 when

Figure 6: Comparison of SINR performance in four collaboration scenarios. G = 0.6. When the number of copies is 2, SC-ACRDA3 reaches the peak throughput of 0.9939 when G = 1.40, ACA3 reaches the peak throughput of 0.886 when G = 1.0, ACRDA3 reaches the peak throughput of 0.7173 when G = 0.75 and CRDSA3 reaches the peak throughput of 0.700 when G = 0.7. Therefore, the peak throughput and high throughput load range of SC-ACRDA schemes are higher than those of traditional ACRDA schemes, regardless of one or two copies. The simulation curve is close to the theoretical curve, which verifies the correctness of the theoretical analysis. Figure 8 shows the comparison of the PLR of SC-ACRDA2, SC-ACRDA3 and other schemes. At low load G = 0.1, the PLR is at level \(10^{-3}\) (one copy) and \(10^{-5}\) (two copies) because the packet arrival rate is low, and the packets nearly do not collide. When the load increases, the total number of packets in the virtual frame increases, the average number of packets allocated to each virtual frame slot increases, and non-demodulated collided packets are generated. As a result, the PLR gradually increases. Because the node selection algorithm is adopted, some collided packets can be demodulated. Therefore, the PLR of the SC-ACRDA algorithm is generally lower than that of the ACRDA algorithm at the load range [0.0, 1.2]. However, when the load continues to rise, the PLR of various algorithms will gradually converge. This is because when the total amount of packets is large, almost every time slot will collide, so only a few un-collided packets or a simple collision of two packets can be demodulated, and the PLR of various schemes will eventually tend to 1. Since copies of packets can also be eliminated after demodulation, some collided packets may be demodulated when an iteration process is complete. Therefore, after the last packet is processed, the iteration will be repeated until no new packets are processed, so the throughput performance of the system is related to the number of iterations. Figure 9 shows the simulation diagram of the relationship between throughput and load under the condition that the number of copies of the SC-ACRDA scheme is \(N=2\) and the maximum number of iterations is \(N_{tier}=10\). It can be seen that when the load is less than 0.8, the throughput hardly improves with the increase in the number of iterations because of the small probability of packet collision. When the load is in the range [0.8, 1.4], two iterations bring a higher throughput benefit of about 0.10 bits/symbol, and the benefit of 6-10 iterations decreases gradually. When the load is greater than 1.6, iterative interference

Figure 7: Comparison of throughput of SC-ACRDA2 and SC-ACRDA3 with other schemes. cancellation cannot be carried out due to widespread packet collision, and the system performance cannot be improved anymore. ## 6 Conclusions

In this paper, we study the RA protocol packet collision problem in LEO IoT. In order to improve the throughput performance of the RA system, an asynchronous collision-tolerant ACRDA scheme based on satellite-selection collaboration-beamforming is proposed to solve the collision problem of packets in a multi-satellite co-view scenario. Compared with the traditional full-node collaboration scheme, the proposed scheme can improve the power

Figure 8: Comparison of PLR of SC-ACRDA2 and SC-ACRDA3 with other schemes. Figure 9: Throughput performance in relation to the number of iterations.