Age of Information Analysis for NOMA-Aided Grant-Free Transmissions

This paper aims to study the impact of non-orthogonal multiple access (NOMA) assisted grant-free transmissions on reducing age of information (AoI) in status updating systems. Particularly, an uplink communication scenario is considered, where multiple users upload their status updates to a destination competitively. To mitigate collisions among users, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$K$</tex> reception signal-to-noise ratio (SNR) levels are pre-configured, which can be chosen randomly by the users. By applying NOMA, successive interference cancellation (SIC) is carried out at the receiver to decode the signals from different users sequentially. Different from most existing works which adopt generate-at-will (GAW) model for modeling the generating process of status updates' arrivals, this paper considers a more general model to characterize the randomness of the status updates' arrivals. Closed-form expressions for AoI achieved by the proposed NOMA assisted grant-free scheme is obtained. Numerical results are provided to validate the accuracy of the analytical results and also demonstrate the superior performance of the proposed scheme in reducing AoI compared to conventional OMA based methods.