Age-Critical Frameless ALOHA Protocol for Grant-Free Massive Access

In this paper, we analyze the freshness of information in grant-free massive access via a new metrics named age of information (AoI), and propose an age-critical frameless ALOHA (ACFA) random access protocol, where the average AoI (AAoI) is implicitly reduced by banning the transmission of activated user equipments (UEs) recovery successful in the last frame. In particular, in order to analyze the AAoI performance of the ACFA random access protocol, we define two metrics named the average channel load and packets recovery rate (PRR) of ACFA protocol, and tracking the evolution of the number of access-allowed UEs in each frame. Then we derive an analytical expression of AAoI as a function of the frame length and the PRR in the ACFA random access protocol. Simulation results validate the accuracy of our theoretical analysis and show the great potential of ACFA random access protocol in minimizing AAoI.