Two-Step Random Access Using Spatial Grouping and User Paring in Satellite Communication Systems

The two-step random access (2SR) is a promising scheme for satellite communication systems due to several ad-vantages over the conventional four-step random access (4SR) in terms of access delay and signaling overhead. In the 2SR procedure, MsgA consisting of the preamble and the payload is the first message transmitted from the user to the satellite base station in a contention-based manner. Without any prior scheduling information for MsgA, it becomes crucial to balance the collision probability and the resource utilization in the 2SR design. To this end, we propose an enhanced 2SR scheme for the MsgA transmission to improve the resource efficiency using the many-to-one mapping. In the proposed scheme, we use the elevation angle to divide one cell to several sub-cells, pair users in different sub-cells to multiplex the same payload resource, and adopt a successive interference cancellation (SIC) receiver to decode different users' payloads. Simulation results verify the effectiveness of our proposed scheme.