# Polling Mechanisms for Industrial IoT Applications in Long-Range Wide-Area Networks
## 2 Related Work
The results show that the proposed scheme can significantly improve the uniformity of network traffic. This led to improved performance and energy efficiency. Nevertheless, authors conclude that future work should focus on the integration of the proposed scheme with other network protocols and the evaluation of the proposed scheme in real-world industrial IoT networks. These works describe new polling schemes that adapt wireless communications for industrial applications but are based on technologies that have been around for longer or ones requiring high bandwidth, such as Wi-Fi or 5G. Focusing on adapting IoT constrained devices, and especially on LoRaWAN as the candidate standard to use, authors in [9] discuss the challenges of implementing LoRaWAN scheduling and present a low-overhead synchronization and scheduling concept that is fully compliant with the LoRaWAN standard. The paper begins by discussing the scalability challenges of LoRaWAN, which is due to its Aloha-based MAC layer. Aloha is a random-access protocol that can lead to collisions, which can reduce the overall network performance. The paper then presents a low-overhead synchronization and scheduling concept that is designed to address the scalability challenges of LoRaWAN. The concept is based on the use of time synchronization and scheduling slots. Time synchronization is used to ensure that all devices in the network are synchronized to the same time reference. This is necessary for scheduling slots, as devices need to know when they are allowed to transmit data. The evaluation was conducted using a testbed of LoRaWAN nodes. The results of the evaluation showed that the proposed concept can significantly improve the PDR, especially under high network loads. The paper concludes by discussing the future work on LoRaWAN scheduling. The authors suggest that future works should focus on the following areas: scalability, security, and efficiency. In [10], TRILO, or Traffic Indication-based Downlink Communication Protocol (for LoRaWAN), describes a downlink communication protocol that is designed to improve the energy efficiency of LoRaWANs, by using a beacon-based polling mechanism to inform end devices when they have downlink traffic. When an end device receives a beacon, it checks the number of downlink messages that are pending for it. If there are any downlink messages pending, the end device will open a ping slot to receive the messages. The TRILO protocol has been shown to improve the energy efficiency of LoRaWANs by up to 20%. This is because TRILO reduces the amount of time that end devices spend listening for downlink traffic. Nevertheless, the solution proposed only implements sequential polling on the premise that it helps avoiding collisions, disregarding the multi-channel capabilities of LoRaWAN gateways. Also, it does not consider Class B operations, which are already similar to the proposal the authors describe. While [11] proposes a lightweight scheduling solution for LoRaWAN, it focuses on overall network traffic management and necessitates the deployment of a custom MAC layer named RS-LoRA. This proprietary approach introduces backward compatibility issues with existing LoRaWAN devices adhering to the standard MAC protocol. The article in [12] proposes a solution specifically for LoRaWAN-based AMR (Automatic Meter Reading) systems. It addresses this challenge by introducing a polling algorithm for the Outage Management System (OMS) that aims to critically reduce the number of queries needed to identify system conditions during outages, but it does so by analyzing outages and restorations to confirm without polling all the AMRs in the system, so it is not really applicable to other applications. In addition to the papers listed above, there are a number of other papers that have been published on the topic of polling systems in wireless industrial applications. A comprehensive review of all of the relevant literature is beyond the scope of this paper.