Age-Threshold Slotted ALOHA for Optimizing Information Freshness in Mobile Networks

TL;DR

This work analyzes AoI in large, mobile random-access networks using age-threshold slotted ALOHA (TSA) under an SINR model. It derives a fixed-point characterization for transmission success probability and closed-form AoI expressions, then jointly optimizes update rate and age threshold to minimize mean peak AoI and time-average AoI, revealing that update rate set to unity is optimal at the time-average optimum and that TSA can halve the growth of time-average AoI with deployment density compared to conventional slotted ALOHA. The paper also develops a robust optimization approach to handle bistable regions and proves convergence and complexity properties, supported by simulations. Overall, TSA offers notable improvements in higher-order AoI metrics and scalability, particularly in dense, mobile networks, with practical design insights for parameter tuning and robustness.

Abstract

We optimize the Age of Information (AoI) in mobile networks using the age-threshold slotted ALOHA (TSA) protocol. The network comprises multiple source-destination pairs, where each source sends a sequence of status update packets to its destination over a shared spectrum. The TSA protocol stipulates that a source node must remain silent until its AoI reaches a predefined threshold, after which the node accesses the radio channel with a certain probability. Using stochastic geometry tools, we derive analytical expressions for the transmission success probability, mean peak AoI, and time-average AoI. Subsequently, we obtain closed-form expressions for the optimal update rate and age threshold that minimize the mean peak and time-average AoI, respectively. In addition, we establish a scaling law for the mean peak AoI and time-average AoI in mobile networks, revealing that the optimal mean peak AoI and time-average AoI increase linearly with the deployment density. Notably, the growth rate of time-average AoI under TSA is half of that under conventional slotted ALOHA. When considering the optimal mean peak AoI, the TSA protocol exhibits comparable performance to the traditional slotted ALOHA protocol. These findings conclusively affirm the advantage of TSA in reducing higher-order AoI, particularly in densely deployed networks.

Figures (9)

• Figure 1: An illustration of the evolution of the age of information over the link under consideration in the discrete-time model.
• Figure 2: Approximate trajectory of $p_{\mathrm{s},n}$. Spatial deployment density $\lambda =0.15$, update rate $\eta=1$, decoding threshold $\theta=0~\text{dB}$, SNR $\rho=20~\text{dB}$, path-loss exponent $\alpha= 3.8$, and transceiver distance $r = 3$.
• Figure 3: Bistable region $\mathcal{B}$ and monostable region $\mathcal{M}$.
• Figure 4: Transmission success probability versus age threshold. Network parameters are set as: $\eta=1$, $\lambda\in\{0.001,0.003,0.005,0.01\}$, $\theta=0~\text{dB}$, $\rho=20~\text{dB}$, $\alpha= 3.8$, and $r = 3$.
• Figure 5: AoI performance versus update rate under different age thresholds. Network parameters are set as: $\lambda = 0.02$, $\theta=0$ dB, $\rho=20~\text{dB}$, $\alpha= 3.8$, and $r=4$.

Theorems & Definitions (15)

• Remark 1
• Corollary 1
• Corollary 2
• Corollary 3
• lemma 1
• lemma 2
• Remark 2
• lemma 3
• lemma 4
• Remark 3