Modern wireless communication systems transmit complex modulated signals with high peak to average ratio in order to deliver high data rates. It demands wide bandwidth and rigorous efficiency performance for power amplifiers. Today’s conventional RF power amplifiers have relatively poor operating efficiency and require more power and area for operation. Therefore, more research on high efficiency power amplifier is crucial to the growth of the wireless industry. Until recent days, WiMAX systems are using technology processes such as Gallium Arsenide (GaAs) and Si LDMOSFET to obtain the performance. Although they are providing the required functional performance, they do not optimize cost and/or size. The primary focus of this thesis is to enhance the efficiency and output power of a compact microwave Power Amplifier suitable for a WiMAX base station. To achieve this goal, this thesis explores the highly efficient switched mode Class E microwave power amplifier using the Gallium Nitride on Silicon Carbide HFET (GaN-on-SiC) technology. The smallest gate length (0.15 µm) device recently released by NRC is used in this design. It provides higher performance at lower cost and area than the alternative Gallium Arsenide (GaAs) technology. Importance is given in designing the bias network of the device. The biasing network has a great impact on efficiency of power amplifiers. Many new techniques of Class E design have been presented to date, but there is not significant improvement related to the biasing network. A highly efficient Class E power amplifier for WiMAX base station transmitter was developed in this thesis for 2.5 GHz application. An improved bias network was introduced for biasing the active device. This successful design shows acceptable simulated performance with a gain of 10.12 dB, an output power of 34.12 dB, and a power added efficiency of 41.7 % at the peak output power.

A common issue with the power grid during natural disasters is low availability. Many critical applications that are required during and after natural disasters, for rescue and logistical operations require highly available power supplies. Microgrids with distributed generation resources along with the grid provide promising solutions in order to improve the availability of power supply during natural disasters. However, distributed generators (DGs) such as diesel gensets depend on lifelines such as transportation networks whose behavior during disasters affects the genset fuel delivery systems and as a result affect the availability. Renewable sources depend on natural phenomena that have both deterministic as well as stochastic aspects to their behavior, which usually results in high variability in the output. Therefore DGs require energy storage in order to make them dispatchable sources. The microgrids availability depends on the availability characteristics of its distributed generators and energy storage and their dependent infrastructure, the distribution architecture and the power electronic interfaces. This dissertation presents models to evaluate the availability of power supply from the various distributed energy resources of a microgrid during natural disasters. The stochastic behavior of the distributed generators, storage and interfaces are modeled using Markov processes and the effect of the distribution network on availability is also considered. The presented models supported by empirical data can be hence used for microgrid planning. / text

The placement of base stations is an important issue in planning wireless systems because it has a significant influence on overall system performance. In order to achieve good performance in an interference limited CDMA system, a large number of variables must be considered simultaneously during the planning stage. A traditional manual planning approach that involves an iterative application of analysis may not produce satisfactory results since it can only consider a small number of variables simultaneously. This thesis proposes the use of automatic optimisation that allows more variables to be considered and more solutions to be examined within the same time period. This thesis aims to produce a unique framework for creating an automatic optimisation tool for solving the CDMA base station placement problem. This framework contains a number of mathematical models that describe various deployment scenarios and a number of customised optimisation algorithms that solve these models. Although the work presented in this thesis does not result in a complete design tool, the findings are expected to provide a solid foundation for the development of such a tool. During the course of study, a number of issues associated with the proposed planning approach have been discussed and some future research directions have been identified. The results from the example problems have shown that automatic optimisation has the potential to reduce the planning time significantly, assess system performance accurately and utilise limited resources efficiently. These benefits certainly confirm the need for such a tool and reinforce the importance of the work documented in this thesis. / Industrial Research Limited and Telecom NZ Limited

The placement of base stations is an important issue in planning wireless systems because it has a significant influence on overall system performance. In order to achieve good performance in an interference limited CDMA system, a large number of variables must be considered simultaneously during the planning stage. A traditional manual planning approach that involves an iterative application of analysis may not produce satisfactory results since it can only consider a small number of variables simultaneously. This thesis proposes the use of automatic optimisation that allows more variables to be considered and more solutions to be examined within the same time period. This thesis aims to produce a unique framework for creating an automatic optimisation tool for solving the CDMA base station placement problem. This framework contains a number of mathematical models that describe various deployment scenarios and a number of customised optimisation algorithms that solve these models. Although the work presented in this thesis does not result in a complete design tool, the findings are expected to provide a solid foundation for the development of such a tool. During the course of study, a number of issues associated with the proposed planning approach have been discussed and some future research directions have been identified. The results from the example problems have shown that automatic optimisation has the potential to reduce the planning time significantly, assess system performance accurately and utilise limited resources efficiently. These benefits certainly confirm the need for such a tool and reinforce the importance of the work documented in this thesis. / Industrial Research Limited and Telecom NZ Limited

The placement of base stations is an important issue in planning wireless systems because it has a significant influence on overall system performance. In order to achieve good performance in an interference limited CDMA system, a large number of variables must be considered simultaneously during the planning stage. A traditional manual planning approach that involves an iterative application of analysis may not produce satisfactory results since it can only consider a small number of variables simultaneously. This thesis proposes the use of automatic optimisation that allows more variables to be considered and more solutions to be examined within the same time period. This thesis aims to produce a unique framework for creating an automatic optimisation tool for solving the CDMA base station placement problem. This framework contains a number of mathematical models that describe various deployment scenarios and a number of customised optimisation algorithms that solve these models. Although the work presented in this thesis does not result in a complete design tool, the findings are expected to provide a solid foundation for the development of such a tool. During the course of study, a number of issues associated with the proposed planning approach have been discussed and some future research directions have been identified. The results from the example problems have shown that automatic optimisation has the potential to reduce the planning time significantly, assess system performance accurately and utilise limited resources efficiently. These benefits certainly confirm the need for such a tool and reinforce the importance of the work documented in this thesis. / Industrial Research Limited and Telecom NZ Limited

The placement of base stations is an important issue in planning wireless systems because it has a significant influence on overall system performance. In order to achieve good performance in an interference limited CDMA system, a large number of variables must be considered simultaneously during the planning stage. A traditional manual planning approach that involves an iterative application of analysis may not produce satisfactory results since it can only consider a small number of variables simultaneously. This thesis proposes the use of automatic optimisation that allows more variables to be considered and more solutions to be examined within the same time period. This thesis aims to produce a unique framework for creating an automatic optimisation tool for solving the CDMA base station placement problem. This framework contains a number of mathematical models that describe various deployment scenarios and a number of customised optimisation algorithms that solve these models. Although the work presented in this thesis does not result in a complete design tool, the findings are expected to provide a solid foundation for the development of such a tool. During the course of study, a number of issues associated with the proposed planning approach have been discussed and some future research directions have been identified. The results from the example problems have shown that automatic optimisation has the potential to reduce the planning time significantly, assess system performance accurately and utilise limited resources efficiently. These benefits certainly confirm the need for such a tool and reinforce the importance of the work documented in this thesis. / Industrial Research Limited and Telecom NZ Limited

Mobile edge computing (MEC) has been considered as a promising technology to handle computation-intensive and latency-sensitive tasks for mobile user equipments (UEs) in next-generation mobile networks. Mobile UEs can offload these tasks to nearby edge servers, which are typically deployed on base stations (BSs) that are equipped with computation resources. Thus, the task execution latency as well as the energy consumption of mobile devices can be reduced. Mobility management has played a fundamental role in MEC, which associates UEs with the appropriate BSs. In the existing handover decision-making process, the communication costs dominate. However, in edge scenario, the computation capacity constraints should also be considered. Due to user mobility, mobile UEs are nonuniformly distributed over time and space. Edge servers in hot-spot areas can be overloaded while others are underloaded. When edge servers are densely deployed, each UE may have multiple choices to offload its tasks. Instead, if edge servers are sparsely deployed, UEs may only have one option for task offloading. This aggravates the unbalanced workload of the deployed edge servers. Therefore, how to serve the dynamic hot-spot areas needs to be addressed in different edge server deployment scenarios. Considering these two scenarios discussed above, two problems are addressed in this thesis: 1) with densely deployed edge servers, for each mobile UE, how to choose the appropriate edge servers independently without full system information is inves- tigated, and 2) with sparsely deployed edge servers, how to serve dynamic hot-spot areas in an efficient and flexible way is emphasized. First, with BSs densely de- ployed in hot-spot areas, mobile UEs can offload their tasks to one of the available edge servers nearby. However, precise full system information such as the server workload can be hard to be synchronized in real time, which also introduces extra signaling overhead for mobility management decision-making. Thus, a user-centric reinforcement-learning-based mobility management scheme is proposed to handle sys- tem uncertainties. Each UE observes the task latency and automatically learns the optimal mobility management strategy through trial and feedback. Simulation results show that the proposed scheme manifests superiority in dealing with system uncer- tainties. When compared with the traditional received signal strength (RSS)-based handover scheme, the proposed scheme reduces the task execution latency by about 30%. Second, fixed edge servers that are sparsely deployed around mobile UEs are not flexible enough to deal with time-varying task offloading. Dispatching mobile servers is formulated as a variable-sized bin-packing problem with geographic constraints. A novel online unmanned aerial vehicle (UAV)-mounted edge server dispatching scheme is proposed to provide flexible mobile-to-mobile edge computing services. UAVs are dispatched to the appropriate hover locations by identifying the hot-spot areas sequen- tially. Theoretical analysis is provided with the worst-case performance guarantee. Extensive evaluations driven by real-world mobile requests show that, with a given task finish time, the mobile dispatching scheme can serve 59% more users on aver- age when compared with the fixed deployment. In addition, the server utilization reaches 98% during the daytime with intensive task requests. Utilizing both the fixed and mobile edge servers can satisfy even more UE demands with fewer UAVs to be dispatched and a better server utilization. To sum up, not only the communication condition but also the computation lim- itation have an impact on the edge server selection and mobility management in MEC. Moreover, dispatching mobile edge servers can be an effective and flexible way to supplement the fixed servers and deal with dynamic offloading requests. / Graduate

Today more devices are being connected to the Internet via mobile networks. With more devices in mobile networks, the workload on radio base stations increases. Radio base stations must be energy efficient and cheap which makes high-performance central processing units (CPUs) a bad alternative to meet the increasing workload. An alternative could be a graphics processing unit (GPU) which have a different hardware architecture more suitable for data parallel problems. This thesis has investigated the parallelisation possibilities in the user-equipment handling part of radio base stations, and the aim was to use a GPU to take advantage of the parallelism. The investigation found a mixed pipeline and data parallelism in user-equipment handling. A parallelism suitable for a graphics processing unit (GPU) execution. The tasks which handle user-equipment were divided into smaller communication-free sub-tasks. Sub-task batches of user-equipment were collected and offloaded to a GPU. A peak throughput gain of 62.2 times over the single-threaded CPU was achieved, but with an impact on latency with more than a magnitude. The latency was for all workloads at least 1.24 higher for the GPU implementations compared to the CPU implementations. A radio base station with many more user-equipment than the once existing today was simulated. For this radio base station, a gain of 14.0 times the single-threaded CPU was achieved, while the latency increased by 2.4 times. To really make use of a GPU implementation the number of user-equipment, the load, must be higher than in existing radio base stations today.

Η αυξανόμενη ζήτηση κινητών τηλεφώνων οδήγησε στην εισαγωγή του κυτταρικού ή κυψελοειδούς συστήματος κινητής ραδιοτηλεφωνίας (Cellular mobile radio). Σύμφωνα με το σύστημα αυτό διαιρείται η προς εξυπηρέτηση περιοχή σε εξάγωνα - Kυψέλες ή Κύτταρα - καθένα από τα οποία περιλαμβάνει ένα πομπό χαμηλής ισχύος τοποθετημένο στο σταθερό σταθμό (σταθμός κυττάρου Σ.Κ.). Κάθε σταθμός κυττάρου είναι συνδεμένος σε ένα τηλεφωνικό κέντρο κινητής ραδιοτηλεφωνίας (ΤΚΚΡ), που έχει πρόσβαση στο αστικό και υπεραστικό τηλεφωνικό δίκτυο. Το κέντρο αυτό διαθέτει κατάλληλο ηλεκτρονικό εξοπλισμό και ελέγχει όλη την περιοχή. Στο πλαίσιο αυτής της εργασίας μελετάμε την διαδικασία κυψελοειδούς σχεδιασμού και εξετάζουμε τις παραμέτρους που την επηρεάζουν. Επιπλέον διεξάγουμε πειραματικές μετρήσεις στην περιοχή της Πάτρας, οι οποίες μας οδηγούν σε σημαντικά συμπεράσματα σχετικά με τον σχεδιασμό ενός κυτταρικού συστήματος κινητης τηλεφωνίας. Στο 1ο κεφάλαιο παραθέτουμε απαραίτητα στοιχεία και έννοιες, όπως για παράδειγμα η ¨κάλυψη¨(coverage), που αφορούν στον κυψελοειδή σχεδιασμό, ενώ στο 2ο κεφάλαιο παρουσιάζουμε θεμελιώδεις αρχές λειτουργίας των συστημάτων ασύρματων επικοινωνιών GSM και TETRA. Στο 3ο κεφάλαιο αυτό επιχειρούμε να εμβαθύνουμε στην έννοια του σχεδιασμού κυψελοειδών κυτταρικών συστημάτων. Υπάρχουν κάποιοι γενικοί στόχοι που πρέπει ένα κυτταρικό σύστημα να ικανοποιεί, όπως η κατάλληλη ράδιο κάλυψη, η ελαχιστοποίηση του κόστους και η υψηλή ποιότητα υπηρεσιών, όμως οι μέθοδοι σχεδιασμού που οδηγούν στην υλοποίηση του κατάλληλου συστήματος που θα ικανοποιεί τους παραπάνω στόχους ποικίλουν. Κάθε μέθοδος αποτελεί μια ξεχωριστή προσέγγιση σχεδιασμού με τις δικές τις συνθήκες, το δικό της κυτταρικό και μαθηματικό μοντέλο. Στο 4ο κεφάλαιο μελετάμε ορισμένα σημαντικά χαρακτηριστικά των καναλιών εξασθένισης και εξετάζουμε την επιρροή τους στην απόδοση ενός συστήματος διαμόρφωσης με κωδικοποίηση. Ακόμα, θεσπίζουμε όρια μέτρησης που μπορούν να χρησιμοποιηθούν για να βελτιώσουν την απόδοση των καναλιών εξασθένισης. Η εξασθένιση εμφανίζεται λόγω μείωσης του ραδιοσήματος μεταξύ πομπού και δέκτη όταν παρεμβάλλονται αντικείμενα και λόγω ανάκλασης και διασποράς του σήματος. Επίσης, η λαμβανόμενη ισχύς σήματος μειώνεται ανάλογα με την απόσταση μεταξύ πομπού και δέκτη. Στο 5ο κεφάλαιο παρουσιάζουμε και σχολιάζουμε τις μετρήσεις που πραγματοποιήσαμε στη περιοχή των Πατρών. Σκοπός των μετρήσεων είναι η αξιολόγηση της λαμβανόμενης στάθμης σήματος από τον κινητό χρήστη σε διαφορετικά περιβάλλοντα και περιοχές με ποικιλία χαρακτηριστικών, όσο αφορά στη γεωγραφία, τη δόμηση και άλλους παράγοντες. Τέτοιες πειραματικές μετρήσεις, στην περιοχή ενδιαφέροντος, αποτελούν βασική προϋπόθεση για να ¨στηθεί¨ ένα σύστημα κυψελοειδούς κυτταρικού σχεδιασμού. Εξ’ άλλου, η στάθμη σήματος αποτελεί το ιδανικό εργαλείο για να βγάλουμε συμπεράσματα ως προς την κάλυψη (coverage) και τα κανάλια εξασθένισης (fading channels), τα οποία εξετάσαμε σε προηγούμενα κεφάλαια. / -

It is often necessary to operate a number of radio communication channels from a single control room without time-sharing between the various channels. Here it is necessary to operate a number of transmitters and receivers simultaneously from the same base station or mobile unit without interference. The best method to achieve this has been found in the use of filters inserted in the transmission line between the antenna and the transmitter(s) on one hand and the receiver(s) on the other hand. The basic unit employed in the design of microwave filters is usually a cavity resonator of which the most important factors are the Q, insertion loss and resonant frequency. However, a problem which frequently arises with cavity resonators is the accurate determination of these resonant characteristics complicated by the presence of coupling port, materials and various design and geometrical deviations. Such cavities have been investigated in several cases and the results have been generalised, but this investigation has been conducted to examine thoroughly most of the problems being met in present practice. Design and development of some common resonant structures are considered. Emphasis is placed on solutions found to special problems especially regarding complicated boundary conditions. Furthermore, investigation includes methods for optimising resonant parameters such as insertion loss and Q, trading of insertion loss with coupled cavity selectivity, frequency tuning and compensation for frequency variations due to wide ranges of operating temperatures. By comparing Q values obtained in practice with theoretical values, it has been possible to establish an appropriate Q loss budget to as to facilitate accurate prediction of coupled cavity unloaded Q. A satisfactory agreement between theory and practice has been obtained. By application of the results of theoretical analysis and experiment, it is shown that microwave filters can be designed to have a desired insertion loss and off-band attenuation slope. Steps leading to designs of any number of cascaded cavities in a two-port network and, subsequently, multi-port networks are discussed in detail.