Grant-X Random Access Protocol for Satellite IoT Systems

Satellite communication is an effective supplement of terrestrial communication to support IoT networks in remote areas. However, due to the shortages of satellite communications, such as large propagation delay, limited resources, and processing capability, it is difficult to support massive accesses of various IoT users. In this paper, to integrate the benefits of both grant-based and grant-free access protocols, we propose a grant-X access protocol. Both grant-based and grant-free access approaches can be supported and the resource allocation ratio of them is determined by the current traffic features. The proposed protocol can support more users with fewer retransmissions and shorter transmission delays, compared to the conventional grant-based and grant-free access approaches. The resource allocation ratio is an important parameter in the proposed protocol, which will greatly affect system performance. Theoretical analysis of the minimum collision probability is conducted to derive the optimal allocation strategy for the proposed protocol when considering the random spatial distributions of users, packet arrival, packet duration, etc. Then, numerical results are presented based on a practical satellite IoT system.