IRSA-based Unsourced Random Access over Gaussian Channel

Grant-free massive access schemes based on irregular repetition slotted ALOHA (IRSA) are investigated as an option for unsourced random access over the Gaussian multiple access channel. The goal is to carry out a performance analysis over a noisy channel, seeking for achievable limits on packet loss probability and energy efficiency. A novel performance analysis framework is developed for IRSA-based random access in asymptotic conditions in presence of both collisions and slot decoding errors. It includes density-evolution equations, asymptotic limits for minimum packet loss probability and average load threshold, and a converse bound for threshold values. The analysis is exploited as a tool to evaluate performance limits in terms of achievable $E_{b}/N_{0}$ and tradeoff between energy and spectrum efficiency. Numerical results show that IRSA-based schemes have a convergence boundary limit within few dB from the random coding bound for a large enough number of active transmitters.