Electrical and Electronic Engineering - Theses
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ItemFinite-time algorithms and performance bounds for real-time Internet of Things( 2019)Rapid developments in technology have enabled a large scale deployment of interconnected sensors and actuators, captured under the umbrella term Internet of Things (IoT). Real-time IoT applications in smart grid, smart traffic control etc. are made possible by the real-time processing of high volume data, generated from dedicated and multi-purpose sensors, and exchanged over heterogeneous wired or wireless communication networks. Our work focuses explicitly on smart intersection management applications and develops and analyses algorithms to cater to its stringent latency, mobility and geo-distribution requirements. Considering the communication delays, distributed IoT implementations like these prefer fog/hybrid architecture-based data processing to the conventional centralised and cloud-based approach. Further, for relevant distributed real-time IoT algorithms, finite-time performance matters more than the asymptotic results in the literature . Thus, precise estimates have to be obtained on the delay needed for an optimisation algorithm to compute a solution within the desired proximity of the optimal solution. Such trade-offs are inevitable for the design of real-time algorithms over an IoT network. This thesis develops distributed optimisation algorithms, which involve explicit delay-accuracy trade-offs possible and studies the effects of channel impairments and communication network structure on them. We introduce a finite-time distributed optimisation algorithm and derives universal performance bounds for an asymptotic algorithm solving a quadratic Network Utility Maximisation (NUM) problem using quantised inter-agent communication. The finite-time algorithm is then used to solve a Model Predictive Control (MPC) problem and applied to a smart traffic intersection management scenario.
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ItemOptimization and deep learning techniques for next-generation wireless communication networks( 2019)Due to the explosive growth of consumer electronic devices, such as smartphones, tablets, and the Internet of Things, the global mobile data traffic is estimated to increase seven fold by 2022 in the fifth generation (5G) of wireless communication networks. At the same time, the mobile network connection speed is envisioned to increase more than three-fold by 2022. Many technologies have been proposed to fulfill such unprecedented user demands. On the macroscopic level, the network architecture largely determines the performance of the network. Novel network architectures, such as heterogeneous networks (HetNets) and centralized radio access networks (C-RANs), have been proposed to accommodate massive numbers of wireless devices. On the microscopic level, the control of all devices is vital for network operations on a daily basis. Intelligent control agents are hence required to operate networks without human intervention. In this thesis, we start off by focusing on the architecture side of network and investigate a MINLP problem of a joint backhual-access HetNet by using a classical optimization approach. Then, we move on to the operational side of networks and focus on spectrum sharing in cognitive radio networks and topology control in wireless sensor networks. In these problems, we employ deep learning approaches that can learn from collected data and adapt to the changing radio environment without a priori knowledge about the network. We show the applicability and superiority of our deep learning-based algorithms compared with classical analytic approaches. More importantly, we show the novel applicability of deep learning in solving MINLP problems that are commonly encountered engineering problems in wireless communication networks.
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ItemPrivacy-preserving machine learning and data aggregation for Internet of Things( 2018)The proliferation of Internet of Things (IoT) devices has contributed to the emergence of participatory sensing (PS) and collaborative learning (CL), where multiple participants collect and report their data to a cloud service to analyse the union of the collected data in the server-based framework. While in the decentralized framework, multiple participants collaboratively train a more accurate global model or multiple local models. However, the possibility of the cloud service or any participant being semi-honest or malicious pose a serious challenge of preserving the participants' privacy. Privacy-preserving machine learning and data aggregation aim to discover or derive useful statistics without compromising privacy. This thesis systematically investigates state-of-the-art techniques for privacy-preserving machine learning and data aggregation in a range of IoT applications. Extensive theoretical and experimental results are provided to support the following primary contributions. First, we explore three privacy-preserving machine learning applications. Examples include collaborative anomaly detection, human activity recognition and decentralized collaboration in a biomedical domain. We tackle security challenges in collaborative anomaly detection with a two-stage scheme called RG+RT: in the first stage, participants individually perturb their data by passing through a nonlinear function called repeated Gompertz (RG); in the second stage, the perturbed data are projected to a lower dimension using a participant-specific uniform random transformation (RT) matrix. The nonlinear RG function is designed to mitigate maximum a posteriori (MAP) estimation attacks, while random transformation resists independent component analysis (ICA) attacks. For human activity recognition, a similar two-stage scheme called RG+RP is proposed, the difference lies in the second stage, where participants project their perturbed data to a lower dimension in an (almost) distance-preserving manner, using a random projection (RP) matrix. The random projection can both resist ICA attacks and maintain model accuracy. These proposed two-stage randomisation schemes are assessed in terms of their recovery resistance to MAP estimation attacks. Preliminary theoretical analysis as well as experimental results on synthetic and real-world datasets indicate that both RG+RT and RG+RP exhibit better recovery resistance to MAP estimation attacks than most state-of-the-art techniques, meanwhile high utility is guaranteed. To mitigate the inherent limitations in the centralized framework, and investigate the applicability of the decentralized framework, we study the decentralized collaboration in a biomedical domain. In particular, we develop an efficient Decentralized Privacy-Preserving Centroid Classifier (DPPCC) considering three practical scenarios, where distributed differential privacy (DDP) is combined with distributed exponential ElGamal cryptosystem to preserve privacy and maintain utility. We realize DDP using discrete Gaussian mechanism without any restriction on ε as in the traditional Gaussian mechanism, and only the encrypted noisy model parameters or test results are shared among all parties. It ensures each party learns nothing but the noisy sum of local statistics. Second, we examine privacy-preserving data aggregation in smart grid application. To this end, we propose a multi-level aggregation framework based on fog architecture, which
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ItemBig data clustering for smart city applications( 2016)The Internet of Things (IoT) infrastructure for the creation of smart cities consists of internet connected sensors, devices and citizens. This IoT infrastructure generates an enormous amount of data in the form of city-scale physical measurements and public opinions, constituting big data. Smart cities aim to efficiently use this wealth of data to manage and solve the problems faced by modern cities for better decision making. However, interpretation of the massive amount of smart city generated big data to create actionable knowledge is a challenging task. Aggregation and Summarization (data clustering) is a useful tool to create knowledge from raw data from different sources. However, traditional data clustering algorithms are not suitable for unlabelled smart city data owing to its high volume and generation velocity and limited experience about generating phenomenon. This thesis presents a novel framework for clustering tendency assessment for big data: clusiVAT, which provides an aggregated view of the big data to create actionable knowledge. clusiVAT intelligently selects a small number of samples from the data such that the samples retain the approximate geometry of the big dataset. The reordered dissimilarity image of the samples generated using single linkage minimum spanning tree (MST) suggests the number of clusters in the data, which is required as an input for most popular clustering algorithms. The cluster labels are then extended to the non-sampled points using the nearest prototype rule. The clusiVAT framework was applied to two real life smart city applications to understand the underlying patterns hidden in the huge volumes of data to generate knowledge. The first application used clusiVAT for clustering and anomaly detection from the pedestrian and vehicle trajectories obtained from a video surveillance system. Experiments were performed on a real-life MIT trajectories dataset of vehicles and pedestrians from a parking lot scene. The trajectory clusters and anomalies thus obtained were helpful in the high-level interpretation of a scene (crowd behavior modeling), as feedback for a low-level (individual) tracking and activity prediction system and as an alarm for human supervisor. For the second application, clusiVAT was used to cluster large scale (of the order of millions) vehicular trajectories obtained from the GPS traces of taxis in the city of Beijing and Singapore using a novel Dijkstra-based dynamic time warping distance measure. The results facilitated the understanding of spatial and temporal patterns in trajectories and were of great significance for decision-makers to understand road traffic conditions and to propose metro bus corridors and light rail systems for better public transport. Another prominent data generated by smart city IoT infrastructure are high-velocity data streams. Automatic interpretation of these evolving big data is required for timely detection of unusual events. This thesis presents a computationally efficient 'hot' update approach for incremental visualization of evolving cluster structure in streaming data. The new algorithms were demonstrated for two applications: online anomaly detection and sliding window based clustering of time series data. Numerical experiments on weather monitoring data from great barrier reef and the city of Melbourne provided visual clues to the onset of the new structure in streaming data.