Modeling age of information in a cooperative slotted Aloha network

In this paper, we study a slotted Aloha cooperative network where a source node and a relay node send status updates of two underlying stochastic processes to a common destination. Additionally, the relay node cooperates with the source by accepting its packets for further re-transmissions using probabilistic acceptance and relaying. We obtain the exact steady state distributions of Age of Information (AoI) and Peak AoI sequences of both nodes using Quasi-Birth-Death Markov chains. The analytical model is first validated by simulations and then used to obtain optimal cooperation policies when transmission probabilities are fixed. Subsequently, we study the more general problem of joint optimization of the transmission probabilities and cooperation level between the source and relay, with detailed numerical examples.