RELAY-AIDED RANDOM ACCESS IN SPACE-AIR-GROUND INTEGRATED NETWORKS

The Internet of Things (IoT) has been extensively investigated as an enabling technology for improving our daily life. With increasing demands for seamless connectivity, the space-air-ground integrated network (SAGIN) is expected to provide reliable communications for IoT devices anywhere and anytime. Since IoT devices have sparse activity and low signaling overhead, random access can be an efficient means to relieve the burden of machine-type communication, which provides connections among massive IoT devices. However, there are a few drawbacks. For example, random access suffers from signal collisions, and low-energy IoT devices may have limited transmission coverage. To overcome these drawbacks, in this article, relay-aided random access (RRA) is proposed as a promising strategy to support massive IoT devices in the SAGIN. We first introduce the RRA structure and scheme as well as several advantages over conventional random access. Then we present some of the key technologies of RRA, including energy harvesting, arrival time detection, and signal number detection. Finally, different scenarios or use cases for practical applications of RRA schemes in the SAGIN are discussed.