## 1 Introduction  
IoT is one of the main research directions for future 5G wireless network applications and plays an important role in industrial asset monitoring, smart cities, logistics and environmental data sensing [1; 2; 3; 4]. As the number of IoT terminals increases, the number of terminals that can be served by a single terrestrial access point is limited, making it difficult to achieve massive information transmission. At present, information transmission between IoT terminals and base stations mainly relies on local area networks such as terrestrial wireless networks and Wi-Fi, which require the construction of a large number of terrestrial base stations to support. However, when IoT is applied in mountainous, marine and desert areas, there is a conflict between service capacity and network QoS requirements, as terrestrial base stations are not suitable for construction and maintenance in these remote areas [5]. Satellite communication systems have become an important complementary network to meet the global coverage requirements of 5G IoT applications due to their wide coverage range [6]. Therefore, IoT networks based on LEO satellites such as OneWeb, Starlink and Telesat LEO satellite constellation development plans have become a research hotspot in the field of IoT [7; 8]. In the current LEO satellite communication scenario, an LEO satellite can cover a large number of IoT terminals, which use RA to exchange information with the satellite. RA will make different terminals occupy the same channel resources during communication, resulting in a collision between signals. For packets without collision, the receiver can demodulate them directly. However, if a collision occurs, packets will be lost or retransmitted, which leads to a decrease in system communication capacity and an increase in delay. At the same time, due to the long propagation delay between satellites and terminals, it is difficult for cheap IoT terminals to achieve strict network time synchronization. Therefore, the RA protocol of the asynchronous system is more suitable for the LEO IoT scene. However, the throughput performance of traditional RA protocols such as Pure-ALOHA (P-ALOHA), S-ALOHA (S-ALOHA) and diversity slotted ALOHA (DSA) is poor and can only be used for scenarios with a small number of terminals [9; 10; 11]. In pure ALOHA protocol, as long as the user is ready to send the packet, it will be sent immediately without checking whether other terminals are active. This system is simple to implement and suitable for situations with light traffic loads. However, when the load increases, the possibility of devices accessing simultaneously greatly increases, which will cause a sharp deterioration in access performance. Therefore, P-ALOHA has a peak load of only 0.184. S-ALOHA improves on P-ALOHA by dividing time into slots equal to the length of packets to ensure that no other packets arrive during the slot in which a single packet begins sending. This mechanism is an effective measure to reduce collisions and avoid arbitrary sending of packets by terminals, increasing throughput performance to 0.368. DSA protocol is an improved version of the S-ALOHA protocol. Although terminal packet transmission randomness was limited by introducing time slots in S-ALOHA protocol and reducing collision probability between packets. However, in the actual system, packet collisions still occur frequently, especially when the number of terminals in the system is large. The packets with collisions need to be present, which seriously increases the access delay of satellite terminals. To alleviate this phenomenon, the DSA protocol uses the idea of time diversity, where each terminal makes a copy of the packet it wants to send and then randomly selects two different time slots within a data frame to send it. Some improved ALOHA solutions, such as collision resolution diversity slotted ALOHA (CRDSA), irregular repetition slotted ALOHA (IRSA) and coded slotted ALOHA (CSA), have all increased the throughput of the system.