Electrical and Electronic Engineering - Theses
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ItemEnergy efficiency of wireless network using coordinated gated narrow beams( 2019)With the ever-increasing demand for wireless service and higher data rate, the wireless network has experienced an unprecedented growth worldwide in the past decade and it is expected to grow continuously. Energy efficiency of the wireless network has become a growing concern for network operators and standardization authorities, not only to reduce the overall electric energy usage but also to reduce its environmental footprint. This has triggered research work to explore future, green wireless technologies and strategies in order to bring energy efficiency improvements in the entire network. In this thesis, we investigate the opportunity of improving energy efficiency through the use of coordinated gated narrow beams for downlink transmission of data. This is a class of Coordinated Multipoint (CoMP) transmission technique which is originally proposed in LTE standards for enhancing cell-edge throughput. The principle is that multiple base stations are coordinated with each other so that potential interfering source from the adjacent base station can be steered away by appropriate beamforming and scheduling. The thesis is divided into three parts. In the first part, we develop a realistic coordinated beamforming strategy using gated narrow beams and estimate the network throughput and base station power consumption based on network level simulation. In the simulator, we apply a practical traffic model in which users entering at a rate consistent with time of day dependent traffic level, and a proportional fair resource scheduling scheme to ensure fairness between users. Then, we analyse the required channel state information to support the beam coordination and resource scheduling, and develop a low-overhead signalling and control framework that provides sufficient signalling information. The signalling design and its implementation leverage signalling functionality and protocol in current standards. We develop methodologies for quantifying the signalling overheads introduced in terms of the percentage of downlink resource occupied by additional coordination reference signals. Finally, we develop energy consumption models of the functional components and processes in the coordinated network architecture, including backhaul switches and interfaces, and a central coordination unit. We quantify the additional energy costs associated with the coordination and signalling functions, and perform a comprehensive evaluation on the energy efficiency of an LTE network employing the proposed coordinated gated narrow beams. Our results show that significant energy savings can be achieved compared with a conventional network with no coordination.
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ItemEnergy consumption of Internet of Things applications and services( 2018)The Internet of Things (IoT) is a new paradigm of interconnectivity that has recently garnered attention in the field of ICT, with an estimated proliferation of 50-200 billion connected devices (i.e. IoT/smart devices) by the end of the decade. This exponential device growth raises concerns as it elicits potential risks including an increase in global energy consumption arising from the deployment of such numbers of devices, the additional network energy cost for handling potential IP traffic increment and the potential impact on the global energy consumption and carbon footprint of the ICT industry. However, due to the development/deployment of many IoT services being in their embryonic stage, there is little research on the characterisation of energy consumption of these services in the literature. In this thesis, we aim to investigate and gain a better understanding of the energy consumption of IoT network applications and services. We do so by developing energy consumption models and in turn, energy-efficient network architectures for the delivery of IoT services. To achieve this goal, we employ and model a few case studies including two of the most well-known and widely deployed IoT services, home automation and security (HAS) and video surveillance services. For the assessment of energy consumption of an IoT service, we obtained a range of IoT products including a consumer-off-the-shelf (COTS) HAS system, as a representative example. We analyse and model (through direct measurements) the energy consumption of each component and the complete system including an IoT attributable share of the home gateway energy consumption. Our results reveal that the energy consumption of a simple COTS IoT service is non-trivial (more than one-third) when compared to the annual energy usage of a mid-size suburban home. HAS energy consumption globally becomes substantial, in comparison with the ICT industry’s energy consumption projections, when IoT service numbers are scaled using published deployment estimates. The IoT leverages a number of existing and emerging technologies to provide a complete end-to-end service, one of which is short-range wireless network protocols. We obtained, measured and analysed the energy-efficiency of five of the most popular COTS wireless protocol modules, Bluetooth Classic & Low Energy, ZigBee, Wi-Fi and RF 433 MHz. We compare these technologies through their application in a simple domestic stock-control IoT service with three communication paradigm options. The results demonstrate that careful consideration should be given to the choice of a communication mode and wireless interface in IoT application development. Such a decision should be driven by the volume of traffic exchange and the frequency of transmission of the application/service. The emergence of edge/fog computing as an alternative to cloud computing promises to tackle some critical pitfalls of cloud including energy consumption. To investigate the energy efficiency of IoT network architectures, the data-intensive video surveillance IoT service is employed as a case study. Using the end-to-end energy models developed, we investigate four (Local, Edge and Cloud) dissimilar network architectures for the delivery of IoT services. We show that it is more energy-wise to adopt an edge-based architecture for on-demand streaming applications but both live streaming and computationally-intensive applications are more energy-efficient when designed with a local access architecture. We further study a number of access network technologies for the IoT. They include very-high-bit-rate digital subscriber line (VDSL2), passive optical network (PON), point-to-point optical network (PtP), fourth generation long term evolution (4G LTE), low-power wide area networks (LPWA) and Wi-Fi access (Shared and Unshared). We show that for low data access rates, LPWA is more energy-efficient while Shared Wi-Fi access with PON backhaul is most energy-efficient for medium to higher data access rates. The findings in this thesis reinforce the need for careful design consideration when developing future IoT solutions.
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ItemEnergy and carbon footprint of ubiquitous broadband( 2017)This thesis concerns ubiquitous broadband in Australia. We use a comparative-static computable general equilibrium model to analyse the economic effects, and to derive the environmental effects of the National Broadband Network (NBN) in the short term and long term. While investment is significantly increased due to NBN deployment in the short term, overall economic activity increases marginally. We find that national greenhouse gas (GHG) emissions are effectively unchanged by the construction of the NBN. We run model long-run simulations to analyse the impact of new services and new ways of working that are enabled by the NBN. The simulation results are dependent on our estimates of the incremental impact of the NBN on service delivery. For this purpose, we map the coverage of broadband in Australian regions using an open-source geographical information system (GIS). We then define two sets of service requirements and determine service availability across regions with and without the NBN. The results show that the NBN produces substantial benefit when services require higher bandwidths than today’s offerings to the majority of end users. In this scenario, the economic effects of productivity improvements facilitated by electronic commerce, telework or telehealth practice made widely available through the NBN will be sufficient to achieve a net improvement to the Australian economy over and above the economic cost of deploying the NBN itself. If, on the other hand, the NBN has a significant effect only on the availability of entertainment services, then the net effect will not be sufficient to outweigh the cost of deployment. We find that national GHG emissions increase with service availability and are higher with the NBN. We construct an NBN power consumption model to estimate the purchased electricity and GHG emissions of the NBN network in the long term post NBN deployment. We find that the NBN network increases energy demand and GHG emissions marginally. The main contributions resulting from this thesis relate to the model simulations. Detailed analysis of the economic and environmental effects of the NBN on the Australian economy provides policymakers and researchers new insights based on a state-of-the-art methodology. Beyond the regional scope of this thesis, the results provide fresh evidence of the rebound effect and GHG emissions abatement potential of ubiquitous technologies such as broadband. While this thesis points at the possible trade-offs when evaluating economic policy faced by various individuals or groups, an efficient way to achieve a more sustainable outcome is to address externalities related to GHG emissions directly by way of implementing appropriate environmental policies.
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ItemEnergy efficient wireless system design( 2015)The demand for telecommunication networks is increasing rapidly. Wireless access is a major contributor to this trend. On the other hand, wireless is considered as a least energy efficient transmission medium mainly due to its unguided nature. The general focus of increasing wireless system energy efficiency is on reduction of the transmit power. However, this strategy may not save energy in short distance communication systems as the processing energy in hardware becomes more significant compared to the transmit radio energy. This thesis focuses on looking at the energy consumption of wireless systems by modeling the energy consumption as a function of several parameters such as receiver SNR, RF bandwidth, information rate, modulation scheme and code rate. We propose energy models for synchronization systems and other digital signal processing modules by considering the computational complexity of the algorithm and the required circuitry. Initially we focus on the synchronization aspects of wireless receivers. We study various algorithms on symbol timing recovery, carrier frequency recovery and carrier phase recovery and compare the performance in order to identify the suitable algorithms to operate at different SNR regions. We then develop energy models for those synchronization sub-systems by analyzing the computational complexity of circuitries based on a number of arithmetic, logic and memory operations. We define a new metric - energy consumption to achieve a given performance as a function of SNR - in order to compare the energy efficiency of different estimation algorithms. Next, we investigate the energy-efficiency trade-offs of a point-to-point wireless system by developing energy models of both the transmitter and receiver that include practical aspects such as error control coding, synchronization and channel equalization. In our system, a multipath Rayleigh-fading channel model and a low-density parity check (LDPC) coding scheme are chosen. We then develop a closed-form approximation for the total energy consumption as a function of receiver SNR and use it to find a minimum-energy transmission configuration. The results reveal that low SNR operation (i.e. low transmit power) is not always the most energy efficient strategy, especially in short distance communication. We present an optimal-SNR concept which can save a significant amount of energy mainly in short-range transmission systems. We then focus on cooperative relay systems. We investigate the energy efficiency trade-offs of single--relay networks by developing energy models for two relay strategies: amplify-and-forward (AF) and detect-and-forward (DF). We then optimize the location and power allocation of the relay to minimize the total energy consumption. The optimum location is found in two-dimensional space for constrained and unconstrained scenarios. We then optimize the total energy consumption over the spectral efficiency and derive expressions for the optimal spectral efficiency values. We use numerical simulations to verify our results. Finally, we focus on energy efficiency of multi-relay systems by considering a dual-relay cooperative system using DF protocol with full diversity. We propose a location-and-power-optimization approach for the relays to minimize the transmit radio energy. We then minimize the total system energy from spectral efficiency perspective for two scenarios: throughput-constrained and bandwidth-constrained configurations. Our proposed approach reduces the transmit energy consumption compared to an equal-power allocated and equidistant-located relay system. Finally, we present an optimal transmission scheme as a function of distance by considering single-hop and multi-hop schemes. The overall results imply that more relays are required as the transmission distance increases in order to maintain a higher energy efficiency.
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ItemFundamental energy requirements of information processing and transmission( 2015)This thesis investigates fundamental limits on the energy required to process and transmit information. By combining physical laws, such as the second law of thermodynamics, with information theory, we present novel limits on the efficiency of systems that track objects, perform stochastic control, switch communication systems and communicate information. This approach yields results that apply regardless of how the system is constructed. While the energy required to perform an ideal measurement of a static state has no known lower bound, this thesis demonstrates that this is not true for noisy measurements or if the state is evolving stochastically. We derive new lower bounds on the energy required to perform such tracking tasks, including Kalman filtering. The goal of stochastic control is usually to reduce the entropy of the controlled system. This is also the task of a Maxwell demon, a thought experiment in which a device or being reduces the thermodynamic entropy of a closed system, violating the second law of thermodynamics. We demonstrate that the same arguments that `exorcise' Maxwell's demon can be used to find lower bounds on the energy consumption of stochastic controllers. We show that the configuration of a switching system in communications, that directs input signals to the desired outputs, can be used to store information. Reconfiguring the switch therefore erases information, and must have an energy cost of at least $k_B T \ln(2)$ per bit due to Landauer's principle. We then calculate lower bounds on the energy required to perform finite-time switching in a one-input, two-output MEMS (microelectromechanical system) mirror switch subject to Brownian motion, demonstrating that the shape of the potential that the switch is subject to affects both the steady-state noise and the energy required to change the configuration. Finally, by modifying Feynman's ratchet and pawl heat engine in order to perform communication instead of doing work, we investigate the efficiency of communication systems that operate solely using the temperature difference between two thermal reservoirs. The lower bound for the energy consumption of any communication system operating between two thermal reservoirs, with no channel noise and using equiprobable partitions of heat energy taken from these reservoirs, is found to be $\frac{T_H T_C}{T_H-T_C} k_B \ln(2)$, where $T_H$ and $T_C$ are the temperatures of the hot and cold reservoir, and $k_B$ is Boltzmann's constant.