Age of Information in Random Access Channels

In applications of remote sensing, estimation, and control, timely communication is not always ensured by high-rate communication. Oftentimes, it is observed that as the capacity of a system is approached, delay increases significantly and so does age of information – a metric recently proposed to capture freshness and timeliness of information. This work proposes decentralized age-efficient transmission policies for random access channels with M transmitters and provides asymptotic results for the age of information as M → ∞. Slotted ALOHA-type algorithms are shown to be asymptotically age-optimal for arrival rates below $\frac{1}{{eM}}$ and far from optimal for larger arrival rates. For larger arrival rates, novel decentralized age-based policies are proposed that benefit from the availability of fresh packets to reduce age of information. For arrival rates θ, $\theta = \frac{1}{{o(M)}}$,1 the proposed algorithms provide a multiplicative gain factor of at least two compared to the state-of-the-art schemes. We conclude that it is beneficial to increase the sampling rate (and hence the arrival rate) and transmit packets selectively based on their "age-gains", a notion defined in the paper. This is surprising and contrary to common practice where the arrival rate is optimized to attain the minimum AoI.