Minimizing Age of Collection for Multiple Access in Wireless Industrial Internet of Things

TL;DR

The paper addresses how to minimize the Age of Collection (AoC) in IIoT systems where multiple devices cooperatively update a shared target. It develops three orthogonal access schemes—TDMA without retransmission (TDMA-NR), TDMA with retransmission (TDMA-R), and FDMA—and analyzes AoC using Markov-chain models, deriving closed-form expressions for average AoC under each scheme. Through USRP SDR experiments, the authors reveal that TDMA-R theoretically offers the best AoC, but FDMA can outperform in high-SNR regimes when MAC overhead is significant, with TDMA-R providing the most stable AoC across SNRs. The work contributes a theoretical-plus-experimental AoC framework for cooperative IIoT status updates and offers guidance on resource allocation under practical constraints.

Abstract

This paper investigates the information freshness of Industrial Internet of Things (IIoT) systems, where each IoT device makes a partial observation of a common target and transmits the information update to a central receiver to recover the complete observation. We consider the age of collection (AoC) performance as a measure of information freshness. Unlike the conventional age of information (AoI) metric, the instantaneous AoC decreases only when all cooperative packets for a common observation are successfully received. Hence, effectively allocating wireless time-frequency resources among IoT devices to achieve a low average AoC at the central receiver is paramount. Three multiple access schemes are considered in this paper: time-division multiple access (TDMA) without retransmission, TDMA with retransmission, and frequency-division multiple access (FDMA). First, our theoretical analysis indicates that TDMA with retransmission outperforms the other two schemes in terms of average AoC. Subsequently, we implement information update systems based on the three schemes on software-defined radios. Experimental results demonstrate that considering the medium access control (MAC) overhead in practice, FDMA achieves a lower average AoC than TDMA with or without retransmission in the high signal-to-noise ratio (SNR) regime. In contrast, TDMA with retransmission provides a stable and relatively low average AoC over a wide SNR range, which is favorable for IIoT applications. Overall, we present a theoretical-plus-experimental investigation of AoC in IIoT information update systems.

Figures (15)

• Figure 1: A wireless IIoT network with $N$ devices (e.g., sensors) observes common phenomena and reports them to an AP.
• Figure 2: The TDMA scheme where devices take turns to access the channel.
• Figure 3: An example of the instantaneous AoC, $\Delta_{TD-NR} (t)$, of an $N$-device system using the TDMA-NR scheme.
• Figure 4: The state transition diagram of TDMA-NR.
• Figure 5: An example of the instantaneous AoC, $\Delta_{TD-R} (t)$, of an $N$-device TDMA-R system.