Cognitive radios have applied various forms of artificial intelligence (AI) to wireless systems in order to solve the complex problems presented by proper link management, network traffic balance, and system efficiency. Casebased reasoning (CBR) has seen attention as a prospective avenue for storing and organizing past information in order to allow the cognitive engine to learn from previous experience. CBR uses past information and observed outcomes to form empirical relationships that may be difficult to model apriori. As wireless systems become more complex and more tightly time constrained, scalability becomes an apparent concern to store large amounts of information over multiple dimensions. This thesis presents a renewed look at an abstract application of CBR to CR. By appropriately designing a case structure with useful information both to the cognitive entity as well as the underlying similarity relationships between cases, an accurate problem description can be developed and indexed. By separating the components of a case from the parameters that are meaningful to similarity, the situation can be quickly identified and queried given proper design. A data structure with this in mind is presented that orders cases in terms of general placement in Euclidean space, but does not require the discrete calculation of distance between the query case and all cases stored. By grouping possible similarity dimension values into distinct partitions called "similarity buckets", a data structure is developed with constant (O(1)) access time, which is an improvement of several orders of magnitude over traditional linear approaches (O(n)). / Master of Science

In recent years, cellular systems based on orthogonal frequency division multiple access – time division duplex (OFDMA-TDD) have gained considerable popularity. Two of the major reasons for this are, on the one hand, that OFDMA enables the receiver to effectively cope with multipath propagation while keeping the complexity low. On the other hand, TDD offers efficient support for cell-specific uplink (UL)/downlink (DL) asymmetry demands by allowing each cell to independently set its UL/DL switching point (SP). However, cell-independent SP gives rise to crossed slots. In particular, crossed slots arise when neighbouring cells use the same slot in opposing link directions, resulting in base station (BS)-to-BS interference and mobile station (MS)-to-MS interference. BS-to-BS interference, in particular, can be quite detrimental due to the exposed location of BSs, which leads to high probability of line-of-sight (LOS) conditions. The aim of this thesis is to address the BS-to-BS interference problem in OFDMA-TDDcellular networks. A simulation-based approach is used to demonstrate the severity of BS-to-BS interference and a signal-to-interference-plus-noise ratio (SINR) equation for OFDMA is formulated to aid system performance analysis. The detrimental effects of crossed slot interference in OFDMA-TDD cellular networks are highlighted by comparing methods specifically targeting the crossed slots interference problem. In particular, the interference avoidance method fixed slot allocation (FSA) is compared against state of the art interference mitigation approaches, viz: random time slot opposing (RTSO) and zone division (ZD). The comparison is done based on Monte Carlo simulations and the main comparison metric is spectral efficiency calculated using the SINR equation formulated in this thesis. The simulation results demonstrate that when LOS conditions among BSs are present, both RTSO and ZD perform worse than FSA for all considered performance metrics. It is concluded from the results that current interference mitigation techniques do not offer an effective solution to the BS-to-BS interference problem. Hence, new interference avoidance methods, which unlike FSA, do not sacrifice the advantages of TDD are open research issues addressed in this thesis. The major contribution of this thesis is a novel cooperative resource balancing technique that offers a solution to the crossed slot problem. The novel concept, termed asymmetry balancing, is targeted towards next-generation cellular systems, envisaged to have ad hoc and multi-hop capabilities. Asymmetry balancing completely avoids crossed slots by keeping the TDD SPs synchronised among BSs. At the same time, the advantages of TDD are retained, which is enabled by introducing cooperation among the entities in the network. If a cell faces resource shortage in one link direction, while having free resources in the opposite link direction, the free resources can be used to support the overloaded link direction. In particular, traffic can be offloaded to near-by mobile stations at neighbouring cells that have available resources. To model the gains attained with asymmetry balancing, a mathematical framework is developed which is verified by Monte Carlo simulations. In addition, asymmetry balancing is compared against both ZD and FSA based on simulations and the results demonstrate the superior performance of asymmetry balancing. It can be concluded that the novel interference avoidance approach is a very promising candidate to.

Thesis (M.Eng.). / Written for the Dept. of Electrical and Computer Engineering. Title from title page of PDF (viewed 2008/07/29). Includes bibliographical references.

Thesis (M. App. Sc.)--Carleton University, 2003. / Includes bibliographical references (p. 92-94). Also available in electronic format on the Internet.

This thesis presents the design, simulation and analysis of a new network based on the Automatic Packet Reporting System (APRS) concept to enhance communications of CubeSat. Created in the 1980s, APRS is arguably one of the world’s largest Radio Frequency (RF) networks maintained by a community of licensed amateur radio volunteers for a variety of terrestrial purposes. Using these established nodes we can create a virtualized ground station network for satellite downlinks. Based on literature reviews of CubeSat communications systems and their orbital elements, as well as direct surveys of the amateur radio community, comprehensive far-field antenna models were created in 4nec2 for both the ground and space sections of the CubeSat downlink. The ground station antenna models include: a directional AMSAT/OSCAR Yagi-Uda, an omnidirectional J-pole, ground plane, and a whip antenna. The CubeSat antenna models used include dipoles, monopoles, and turnstiles. These models were evaluated and then imported into the Analytical Graphics Inc (AGI) Systems Tool Kit (STK) to form a discrete event simulation based on nonhomogeneous WGS84 location data extracted from real world APRS Internet Gateway (I-Gate) packets. All objects within the simulation use realistic antenna models, node locations, propagation models and satellite orbital mechanics. This simulation can act as a suite of generally applicable example satellites models (ExampleSat) for analytical comparisons that include link budgets, access times, differing data rates, antenna designs, orbital altitudes and ground station locations. Furthermore, it represents a North American continental scale RF satellite communications downlink network model. Using the virtual ground station network alters the net probability distribution of the received signal from the spacecraft. Specifically, the thesis compares non-stationary time series analysis methods upon the net received signal. The virtualized ground station network enables the aggregated received signal to appear stationary. This in turn may allow for alternative signals analysis techniques to improve a CubeSat’s downlink performance. The simulation allows us to generate representative received signals from ExampleSat to the ground station nodes for exploratory analysis, utilizing less arbitrary assumptions. This simulation and the set of models enable a more rapid start to trade-off studies for link budget design. This set of ExampleSat downlink models can be used by new designers of small-satellite communications systems. / February 2017

Technology scaling has been the most obvious choice of designers and chip manufacturing companies to improve the performance of analog and digital circuits. With the ever shrinking technological node, process variations can no longer be ignored and play a significant role in determining the performance of nanoscaled devices. By choosing a worst case design methodology, circuit designers have been very munificent with the design parameters chosen, often manifesting in pessimistic designs with significant area overheads. Significant work has been done in estimating the impact of intra-die process variations on circuit performance, pertinently, noise margin and standby leakage power, for fixed transistor channel dimensions. However, for an optimal, high yield, SRAM cell design, it is absolutely imperative to analyze the impact of process variations at every design point, especially, since the distribution of process variations is a statistically varying parameter and has an inverse correlation with the area of the MOS transistor. Furthermore, the first order analytical models used for optimization of SRAM memories are not as accurate and the impact of voltage and its inclusion as an input, along with other design parameters, is often ignored. In this thesis, the performance parameters of a nano-scaled 6-T SRAM cell are modeled as an accurate, yield aware, empirical polynomial predictor, in the presence of intra-die process variations. The estimated empirical models are used in a constrained non-linear, robust optimization framework to design an SRAM cell, for a 45 nm CMOS technology, having optimal performance, according to bounds specified for the circuit performance parameters, with the objective of minimizing on-chip area. This statistically aware technique provides a more realistic design methodology to study the trade off between performance parameters of the SRAM. Furthermore, a dual optimization approach is followed by considering SRAM power supply and wordline voltages as additional input parameters, to simultaneously tune the design parameters, ensuring a high yield and considerable area reduction. In addition, the cell level optimization framework is extended to the system level optimization of caches, under both cell level and system level performance constraints.

Thesis (M.App.Sc.) - Carleton University, 2002. / Includes bibliographical references (p. 124-127). Also available in electronic format on the Internet.

Thesis (Ph.D.) - Carleton University, 2006. / Includes bibliographical references (p. 156-164). Also available in electronic format on the Internet.

We present an on-disk sequence cache (ODSC), which improves disk drive performance. An ODSC uses a separate disk partition to store disk data in the order that the operating system requests it. Storing data in this order reduces the amount of seeking that the disk drive must do. As a result, the average disk access time is reduced. Reducing the disk access time improves the performance of the system, especially when booting the operating system, loading applications, and when main memory is limited. Experiments show that our ODSC speeds up application loads by as much as 413%. Our ODSC also reduces the disk access time of the Linux boot by 396%, and speeds up a Linux kernel make by 28%. We also show that an ODSC improves performance when main memory is limited.

Magnetic Resonance Imaging (MRI) can be used in many clinical situations, but they are limited by high costs and time-consuming properties. Most focus has been on improving the technical side of MRI, and not as much on process improvements. Long access times to MRI examinations can be the cause of inefficient workflows of the departments, which can cause adverse effects for the patients. A market research of the Swedish radiology departments that perform MRI examinations resulted in a wide range of median access times, ranging from approximately 21 days to 130 days. This indicates potential for improvement in their workflows. To improve workflows, they need to be analysed and measured. A model for process time efficiency analysis in MRI departments was created in this project which can assess 5 different metrics. These metrics are number of examinations, examination time, turnover time, scanner utility, and scheduling consistency. Potential improvement strategies to reduce the access times associated with the metrics in the model is discussed. Examination time is mostly affected by the technique and the examination protocol but making the change to an abbreviated version of the protocol has the potential to significantly reduce examination time. This is especially useful for screening purposes. Reduction in turnover time can be achieved by analysing the process in between examinations and making suitable changes in preparation of patients and examinations, and in architecture for a more streamlined throughput. The scheduling process has a large impact on efficiency and reduction in access times and increasing utility rate. It is important for the scheduling process to be flexible to increase efficiency. As a result of this report, the conclusion is that a benchmarking project could be conducted on Swedish radiology departments to determine best practices in workflows. / Magnetresonanstomografi (MRT) kan användas i många kliniska situationer, men de är begränsade av höga kostnader och tidskrävande egenskaper. Störst fokus har tidigare varit på de tekniska aspekterna av MRT och inte lika mycket på processförbättring. Långa väntetider till MRT-undersökningar kan vara orsaken av ineffektiva arbetssätt på avdelningarna, vilket skapar negativa effekter för patienter. En marknadsundersökning av de svenska radiologiavdelningarna som utför MRT-undersökningar resulterade i ett stort spann av väntetider, från ungefär 21 dagar till 130 dagar. Detta indikerar förbättringspotential i deras arbetssätt. För att förbättra arbetssätt måste de analyseras och mätas. En modell för att mäta effektivitet för processtder på MRT-avdelningar skapades i detta projekt med fem olika mätvärden. Dessa mätvärden är antal undersökningar, undersökningstid, tid mellan undersökningar, användningsgrad av maskiner och efterföljande av bokningstid. Potentiella förbättringsstrategier för att minska väntetider länkade till mätvärderna i modellen diskuteras. Undersökningstiden påverkas mest av tekniken och protokollet för undersökningen, men genom att byta till ett förkortat protokoll kan undersökningstiden minskas avsevärt. Detta kan vara särskilt användningsbart vid screeningundersökningar. Tiden mellan undersökningar kan minskas genom att analysera processen mellan undersökningarna och göra ändringar i förberedelser av patient och undersökning samt arkitektuella ändringar för en mer effektivserad genomströmning. Bokningsprocessen har en stor betydelse för effektiviteten, minskning av väntetider och ökad användningsgrad. Det är viktigt att bokningsprocessen är flexibel för att öka effektiviteten. Som resultat av denna rapport är slutsatsen att ett benchmarkning-projekt kan utföras på svenska radiologiavdelningar för att hitta bra arbetssätt.