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Subject: search.filters.subject.400608 Wireless communication systems and technologies (incl. microwave and millimetrewave)

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    Novel visible light positioning techniques : a thesis presented in partial fulfilment of the requirements of the degree of Doctor of Philosophy in Department of Mechanical and Electrical Engineering at Massey University, Albany, New Zealand
    (Massey University, 2024-01-31) Chew, Moi Tin
    Localization is the process of finding an object’s position within the space that it is situated in. Localization can be categorised into two types, indoors and outdoors. Outdoor localization is already a matured technology which mainly relies on well-known positioning satellite systems such as Global Positioning System (GPS) and GLObal NAvigation Satellite System (GLONASS). However, the indoor localization is still a growing area of research. Visible Light Positioning (VLP) has been getting the attention of researchers due to several advantageous factors. VLP is more accurate than many of the competing techniques. As Light Emitting Diode (LED) based luminaires have become an integral part of the indoor lighting systems in modern buildings and residences, such lighting infrastructure can be leveraged for localizing objects. The VLP systems are also suitable in places like hospitals and airports due to the fact that LED does not generate electromagnetic interference which can potentially affect the operation of many equipment used in those places. This doctoral research develops novel techniques and applications for VLP, and these are fully supported by experimental results and data analysis. Fingerprinting is a common positioning method used in VLP systems that employs Received Signal Strength (RSS) as the signal characteristics. Weighted K-Nearest Neighbour (WKNN) is one of the most popular algorithms for such localization systems. This thesis investigates the impact of distance metrics used to compute the weights of the WKNN algorithm on the localization accuracy of the VLP. Experimental results show that Squared Chord distance is the most robust and accurate metric and significantly outperforms the commonly used Euclidean distance metric. Robot navigation is one of the many potential applications of VLP. Recent literature shows a small number of works on robots being controlled by fusing location information acquired by VLP that uses rolling shutter effect camera as a receiver with other sensor data. In contrast, this thesis reports the experimental performance of a cartesian robot that was controlled solely by a VLP system using a cheap photodiode-based receiver. Two different methods (Direct Method and Spring Relaxation Method) were developed to leverage the VLP as an online navigation system to control the robot. The experiments consisted of the robot autonomously repeating various paths multiple times. The results show that both methods offer promising accuracy, with Direct Method and Spring Relaxation Method reaching the target positions of median / 90-percentile error of 27.16mm / 37.04mm, and 26.05mm / 47.48mm respectively. The operation of VLP is very much dependent on the line of sight (LOS) link between the luminaires and the receiver. Unfortunately, in a practical environment, luminaires are positioned to serve illumination needs. Therefore, enough luminaires may not be visible for the purpose of positioning the target. One way to compensate this would be to utilise an ultrasound system to eliminate the “blind spots” of the VLP system. The final part of this work consists of a study of the ultrasound based indoor localization. A bespoke system employing an ultrasonic array to transmit chirp signals and time of flight measurement for ranging was developed. The position of the receiver is estimated iteratively using the spring relaxation technique. The spring relaxation technique, which has not been used for ultrasonic localization in the literature, outperforms the widely adopted linear least square-based lateration technique. The experimental results show that the ultrasonic system can be a viable option for fusing with a VLP system.
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    Effective relaying mechanisms in future device to device communication : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in School of Food and Advanced Technology at Massey University, Palmerston North, New Zealand
    (Massey University, 2020) Zaidi, Syeda Kanwal
    Future wireless networks embrace a large number of assorted network-enabled devices such as mobile phones, sensor nodes, drones, smart gears, etc., with different applications and purpose, but they all share one common characteristic which is the dependence on strong network connectivity. Growing demand of internet-connected devices and data applications is burdensome for the currently deployed cellular wireless networks. For this reason, future networks are likely to embrace cutting-edge technological advancements in network infrastructure such as, small cells, device-to-device communication, non-orthogonal multiple access scheme (NOMA), multiple-input-multiple out, etc., to increase spectral efficiency, improve network coverage, and reduce network latency. Individual devices acquire network connectivity by accessing radio resources in orthogonal manner which limits spectrum utilisation resulting in data congestion and latency in dense cellular networks. NOMA is a prominent scheme in which multiple users are paired together and access radio resources by slicing the power domain. While several research works study power control mechanisms by base station to communicate with NOMA users, it is equally important to maintain distinction between the users in uplink communication. Furthermore, these users in a NOMA pair are able to perform cooperative relaying where one device assists another device in a NOMA pair to increase signal diversity. However, the benefits of using a NOMA pair in improving network coverage is still overlooked. With a varierty of cellular connected devices, use of NOMA is studied on devices with similar channel characteristics and the need of adopting NOMA for aerial devices has not been investigated. Therefore, this research establishes a novel mechanism to offer distinction in uplink communication for NOMA pair, a relaying scheme to extend the coverage of a base station by utilising NOMA pair and a ranking scheme for ground and aerial devices to access radio resources by NOMA.
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    The investigation of non-contact vital signs detection microwave theoretical models and smart sensing systems : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Department of Mechanical and Electrical Engineering, SF&AT at Massey University, Palmerston North, New Zealand
    (Massey University, 2020) Nguyen, Thi Phuoc Van
    Natural disasters, such as floods, landslides and earthquakes, occur frequently around the world. The consequences of such disasters in developing countries tend to be more severe due to the lack of effective life detector systems. Life signs detecting has been an active and challenging research field that has great potential in the applications such as finding human lives under debris and non-invasive diagnosis and health monitoring. There are obvious limitations of conventional devices such as optical or acoustic detectors. The optical equipment requires operation from experts, while the acoustics need a quiet environment. The detectors with the thermal sensors and wireless tracking systems are also insufficient when the "non-line of sight" problem appears. In addition, vital signs information (such as heartbeat and breathing rate) from non-invasive microwave sensors are very important to locate people or predict health conditions in the cases of defense, smart home applications, and baby monitoring. Since NASA proposed the use of microwave radar sensing system for life detecting, research and implementation on sensitive, effective, and economic vital signs sensing systems based on microwave signals have become very active. Until now, most research on life detectors has concentrated on hardware development, signal processing, and development of new algorithms to improve accuracy of vital signs detection. The present study has focused on microwave sensors, studying microwave theoretical models and searching for life detecting, health care and smart home applications. In this research, the antennae systems for vital signs detection, such as breathing rate, were first investigated to validate their performance in a system at different frequencies. The antennae system had an extremely large band width, operating from L band to the X band. Based on the proposed antennae system, models to evaluate the false alarm/detection probabilities of a microwave sensing system were then developed and validated to examine the accuracy of the system in advance. These models are very useful for hardware development of microwave radar sensors. Further investigation into the theoretical models, proposed a novel system that was inspired by the micro bat animal's physical structure. This system showed an enhancement in the accuracy and directional signals of the microwave sensing system. Artificial intelligence was then integrated with the radar sensing system to develop the smart microwave radar sensing system. The machine learning/ deep learning models based on the collected data were developed. The study indicated high accuracy in classifying different types of breathing disorders.