Performance optimization of next generation low power Internet of Things (IoT) access networks
Creators: name: MANZOOR, Bisma
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400608
subject: Wireless communication systems and technologies (incl. microwave and millimetrewave)

description: Advancement in radio communication has been a vital part of technological evolution, where the recent emergence of the Internet-of-Things (IoT), an ecosystem of remotely connected devices, has revolutionized the ICT paradigm and changed the way machines and human interact with their surroundings. The accelerating growth of IoT applications is making the world a better-connected place, however it concurrently challenges the researchers and network operators to devise solutions that meet the demands of the expanding IoT networks. Most of the challenges are related to sustaining a massive number of devices while simultaneously ensuring deep coverage and prolonged battery life of the end IoT devices. Moreover, due to the ubiquity of IoT applications, it has become crucial to provide a global network coverage around the world. The low-complexity IoT devices which are supported by Low Power Wide Area Network (LPWAN), and require efficient energy consumption, low-throughput, and good coverage are classified as mMTC (massive Machine Type Communication), is a vital service category in 5G. While many of the popular IoT access technologies operate in the unlicensed frequency spectrum, 3GPP in 2015 standardized cellular IoT access technologies among which Narrow Band-IoT (NB-IoT) is popularly adopted by Telecom operators. However, the process of acquiring a new licensed spectrum poses financial and administrative challenges, especially for emerging small and medium-sized operators. This opens a door for the examination of deployment of NB-IoT in the unlicensed frequency bands, which will aid in the broader adoption of NB-IoT. Furthermore, one of the key characteristics of NB-IoT is to provide extended coverage. The coverage improvement is achieved by a repetition mechanism according to which the device repeats the same message multiple times. However, this technique comes at the cost of increased energy consumption of IoT devices. As a result, there is a trade-off between the coverage and energy expenditure of devices, thus calling for careful analysis and investigation.

Another challenge in the domain of IoT is to provide adequate connectivity to remote areas where terrestrial telecommunication infrastructure is hard to deploy, also during the times of natural disasters e.g., tsunami, earthquake when the terrestrial communication fails. One promising mean in enabling remote and global network coverage is the use of non-terrestrial infrastructure that includes satellite and UAV networks. Although communication via satellites was dominated by applications such as navigation, military, broadcasting, the recent advancement in technologies has paved the way for IoT communication over non-terrestrial networks (such as UAV and Satellite). However, coexistence of terrestrial IoT access technologies over the non-terrestrial networks requires proper investigation due to a distinct satellite-to-ground propagation channel between the satellite and IoT devices. This thesis aims at modeling and optimizing the characteristics of cellular IoT networks. To address the challenges mentioned above, we first develop a geometric model to analyze the coverage of a dense urban IoT network in 3D spatial dimensions. The model is built utilizing mathematical tools from stochastic geometry and is implemented and tested using simulations and Ray-Tracing methodologies. The model establishes the ground for further investigation and analysis of high capacity mMTC networks. After that, we examine the performance of NB-IoT operating in the unlicensed ISM frequency band under realistic interference scenarios while employing the packet-repetition feature to examine the extended coverage. The investigation is carried out by embedding the actual interference into the link level simulations for NB-IoT. The interference measurements are captured from the ISM band in a dense urban environment of Melbourne CBD, Australia, using a software-defined radio. The results pave the way for possible deployment of NB-IoT in the unlicensed spectrum. Furthermore, the developed framework is used to generate a coverage map of  IoT devices employing the repetition scheme, which aids in capturing the performance of IoT repetitions.

To further understand the impact of repetitions on energy expenditure of devices and the resource occupation, this research presents a new mathematical model for frame-repetition in LPWAN IoT networks. The model is developed for the IoT uplink and aims at obtaining the optimal repetition rate across an IoT cell. The work first captures the imbalance between the success, in terms of coverage probability, and the elevated interference, in a cell implementing a repetition scheme. The model then provides the flexibility of tuning the repetition profile of a cell to acquire an optimal performance zone.

In addition, the model is expanded to examine the energy cost of the devices employing repetitions. The analysis is carried out for two diversity combining techniques which are: (i) Selection Combining and (ii) Maximal Ratio Combining. Therefore, we shed light on the methodology that aids in improving service availability, radio resource efficiency, and energy consumption. The theoretical analysis and formulas are verified using Monte-Carlo simulations and proves the plausibility of the proposed optimization approach.

Finally, this work extends the application of the developed repetition model into the non-terrestrial network. The probability of coverage is analyzed by employing a non-terrestrial propagation channel in the uplink between the satellite and IoT devices located in the satellite's service area, accordingly an optimal repetition rate is formulated based on the satellite orbital and antenna parameters.