| Author: | Tsoi, Man Ho |
| Title: | Internet of Things devices stability enhancement by noise filtering and collision avoidance |
| Advisors: | Choy, Yat Sze (ME) |
| Degree: | M.Phil. |
| Year: | 2026 |
| Subject: | Internet of things Acoustic surface wave devices Wireless communication systems Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Mechanical Engineering |
| Pages: | 90 pages : color illustrations |
| Language: | English |
| Abstract: | The concept of Internet of Things (IoT) applications has been proposed for decades but has not yet been implemented on a large scale. The reasons may include the high cost of individual wireless devices and the lack of a wireless solution that supports numerous devices with wide coverage while remaining robust against environmental noise. In this thesis, noise-rejection filters and collision-avoidance medium access control (MAC) protocols for IoT applications are investigated, so that the stability of large-scale IoT wireless networks can be improved by applying appropriate filters and MAC schemes. First, the low-cost wireless component, the surface acoustic wave (SAW) filter, is evaluated. The design and in-house fabrication process of the SAW filter are presented in this report. The detailed effects of interdigital transducer (IDT) variations are investigated by fabricating SAW filters with parametric variations, including the presence of reflectors, IDT length, port separation, and the number of reflectors and IDTs per port. The fabricated SAW filter achieves an insertion loss of less than 3 dB and a return loss of more than 10 dB at 480 MHz without any external lumped elements at the ports for impedance matching. Second, from a system perspective, among the available low-power wide-area network (LPWAN) IoT solutions, LoRa is one of the most promising options due to its attractive properties of low cost, high energy efficiency, wide coverage, and robustness to interference. However, the existing LoRaWAN MAC only offers a pure ALOHA mechanism designed for low-duty-cycle applications. Severe collisions are therefore expected if a large-scale system is deployed. To address this issue, multiple MAC schemes incorporating pure ALOHA, slotted ALOHA, and channel activity detection (CAD) are proposed and tested experimentally. The performance of these MAC schemes is evaluated by comparing the packet delivery ratio (PDR). A PDR of almost 100% is achieved by one of the proposed MAC schemes. Finally, the use cases of the tested MAC schemes are discussed. Third, Chapter 4 synthesizes insights from the previous discussions on filters and MAC protocols to explore their applicability in enhancing the stability of end devices within a commercial context. A long-term deployment project has been initiated in collaboration with a property management company, encompassing 205 end devices and a single gateway across 23 floors of an operational commercial building. The installation of water flood detection sensors aims to provide prompt notifications to the management team, thereby mitigating potential damage to critical infrastructure such as elevators and escalators. This deployment establishes a centralized IoT water flood detection system for commercial use and demonstrates the capability of a stable IoT system employing filters and collision-avoidance MAC schemes. |
| Rights: | All rights reserved |
| Access: | open access |
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