Age-Aware Frame Length Optimization for Frame Slotted ALOHA Toward Multichannel Random Access

Frame slotted ALOHA is one of the popular protocols for multiple access over massive sensor networks. However, how to design the frame length as well as access probability to release the ultimate performance in terms of information freshness is still not thoroughly studied. Age of information (AoI) is a novel concept to evaluate the information freshness, where the peak age outage probability can be used to assess the long-term AoI performance. Peak age outage probability, denoted by σ, is defined as the probability that the peak age exceeds a certain threshold. The threshold is called σ-AoI in this paper. To answer the afore-mentioned issue, we investigate the σ-AoI minimization problem for frame slotted ALOHA toward multichannel random access. On one hand, large frame length along with small access probability corresponds to the big success transmission probability. On the other hand, short frame length along with big access probability leads to the small access period. The success transmission probability and access period both have a remarkable influence on σ-AoI. To find out the optimal frame length as well as access probability, a two-fold method is proposed. Numerical results show that the optimal frame length is very sensitive to the number of sensors and surprisingly imply that the optimal access probability is one.