Age of Information in Grant-Free Random Access with Massive MIMO

This letter aims to analyze and optimize the status update performance in a grant-free random access system with massive multiple-input multiple-output. We analyze the status update process, and derive a closed-form approximate expression of the average age of information (AoI). Then, in the asymptotic case where the large number of antennas at the base station causes the packet error rate to approach zero, we jointly optimize access control and pilot length to reduce the average AoI. Simulation and numerical results verify the correctness of the theoretical analysis, and show that the proposed scheme can achieve the same performance as the exhaustive search scheme and outperforms the benchmark ones.