Performance Analysis of NOMA-Based MEC Systems With Semi-Grant-Free Transmission

This letter investigates a non-orthogonal multiple access (NOMA) based mobile edge computing system with semi-grant-free (SGF) transmission, where a grant-based user (GBU) wants to securely offload its data to a computational access point (CAP) for processing with a time deadline in the presence of an eavesdropper, and a grant-free user (GFU) is scheduled from a group of GFUs to simultaneously offload its data to the CAP for processing based on SGF-NOMA and at the same time interfere with the eavesdropper to improve the GBU secrecy performance. Two GFU scheduling strategies, where one schedules the GFU with the maximum communication channel gain, and the other schedules the GFU with the maximum jamming channel gain, are proposed. The closed-form exact expressions of the system success probability are derived, from which the impacts of various system parameters are obtained. Simulation results confirm the theoretical results and show that the performance comparison between the two strategies depends on the system parameters such as the offloaded data size.