# Intelligent Beam-Hopping-Based Grant-Free Random Access in Secure IoT-Oriented Satellite Networks
## 1 Introduction
Satellite communication involves a significant quantity of terminal equipment, several types of equipment, and a high likelihood of message collision. As the number of users increases, the likelihood of user collision also significantly increases, leading to a decline in all other evaluation metrics [17]. Hence, it is imperative to address the issue of user communication interference in satellite scenarios in order to establish effective communication and maximize efficiency for achieving low-latency and dependable access. This study assumes that the altitude of Low Earth Orbit (LEO) is 600 km, leading to a two-way propagation delay of four milliseconds and a transmission delay of one millisecond. This is attributable to the prevalence of short packet transmission in massive Machine-Type Communications (mMTC) [18; 19]. Considering the duration required for propagation, the processing time is relatively brief. An access slot is established to have a duration of six milliseconds [20]. The contention timer in the satellite connection can be configured to fifty milliseconds [21], allowing the transmission frame in this S-IoT system to accommodate eight access slots. In general, a large number of devices tend to transmit packets and signals to LEO satellites in a sporadic or periodic manner. In order to address the limitations of authorization-based random access, ref. [22] proposes an authorization-free random access protocol. In large-scale authorization-free random access, the base station is not required to perform dynamic scheduling authorization on an ongoing basis. Instead, a just-in-time transmission method is employed, whereby data are transmitted by a device as soon as it becomes avail able. It is possible that the traditional grant-based access scheme may prove inadequate for supporting the substantial number of connections anticipated in 5G networks. In light of the considerable projected increase in the number of UEs in future satellite IoT scenarios for mMTC applications [23], dedicated preamble allocations in traditional grant-based schemes are likely to be impractical. In the context of the GFRA protocol, two distinct types of resource management schemes have been identified: the random selection type and the pre-configuration type. In a GFRA-based random selection system, each activated user equipment (UE) randomly selects a preamble sequence from a predefined set and transmits it to the satellite along with the data payload. This can serve to mitigate the effects of system overload and preamble conflicts [24]. In the context of random-access GFRA, a more practical approach is proposed in [25], where the authors designed a novel random access scheme based on its fixed TA information. As the quantity of accommodated devices rises, the distribution of time-frequency resources may become limited. Thus, the satellite must utilize grant-free random access to markedly diminish access latency and signaling overhead, and this does not require higher computational requirements and complexity. Table 1 discusses and compares the advantages of grant based access and grant free access. Inspired by the above discussions and comparison, this paper puts forward a novel grant-free random access protocol, based on beam-hopping (BH-GFRA), which is designed to allocate radio resources in accordance with the beam-hopping pattern. The BH-GFRA