Experimental Study of Transport Layer Protocols for Wireless Networked Control Systems

TL;DR

This work tackles the challenge of preserving control performance in Wireless Networked Control Systems (WNCSs) when multiple control loops share a wireless medium, where conventional transport-layer policies fall short under congestion. It introduces a relevance- and congestion-aware transport-layer framework featuring controller-state augmentation, a distributed Threshold Adaptation (TA) mechanism, and two Zero-Wait ET schemes (ZW_ET, AUGM_ZW_ET), all validated on a hardware testbed with up to five loops using Zolertia Re-Motes over IEEE $802.15.4$. The hardware experiments demonstrate that relevance- and congestion-aware TL policies outperform UDP/TCP and AoI-centric approaches, achieving up to 40% gains from TA and an additional ~30% improvement when augmentation is combined with ET, while remaining robust to varying network conditions. Overall, the paper provides a practical, hardware-validated pathway for integrating control-relevance into transport-layer design to sustain control performance in industrial IoT deployments.

Abstract

In Wireless Networked Control Systems (WNCSs), the feedback control loops are closed over a wireless communication network. The proliferation of WNCSs requires efficient network resource management mechanisms since the control performance is significantly affected by the impairments caused by network limitations. In conventional communication networks, the amount of transmitted data is one of the key performance indicators. In contrast, in WNCSs, the efficiency of the network is measured by its ability to facilitate control applications, and the data transmission rate should be limited to avoid network congestion. In this work, we consider an experimental setup where multiple control loops share a wireless communication network. Our testbed comprises up to five control loops that include Zolertia Re-Mote devices implementing IEEE 802.15.4 standard. We propose a novel relevance- and network-aware transport layer (TL) scheme for WNCSs. The proposed scheme admits the most important measurements for the control process into the network while taking current network conditions into account. Moreover, we propose a mechanism for the scheme parameters adaptation in dynamic scenarios with unknown network statistics. Unlike the conventional TL mechanisms failing to provide adequate control performance due to either congestion in the network or inefficient utilization of available resources, our method prevents network congestion while keeping the control performance high. We argue that relevance- and network-awareness are critical components of network protocol design to avoid control performance degradation in practice.

Figures (6)

• Figure 1: Considered scenario with $N$ control loops, where sensors' measurements are sent to corresponding controllers via a shared wireless communication network.
• Figure 2: Experimental round trip time statistics.
• Figure 3: The experimental testbed. Plant and controller processes of all loops run in parallel on one PC. Each process is connected to one Zolertia Re-Mote sensor. Sensors communicate over a wireless network.
• Figure 4: Control performance of conventional, SotA and ZW ET schemes. Markers denote the medians of corresponding distributions.
• Figure 5: Control performance of proposed ZW ET and AUGM ZW ET schemes for different threshold values and for adaptive threshold. Markers denote the medians of corresponding distributions.