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Real-time systems are those whose correctness depends not only on logical results of computations, but also on the time at which the results are produced. This thesis provides a formal definition for real-time systems and includes the following original contributions on real-time scheduling algorithms. The first topic studied in the thesis is minimizing the total penalty to be paid in scheduling a set of soft real-time tasks. The problem is NP-hard. We prove the properties of any optimal scheduling algorithm. We also derive a number of heuristic algorithms which satisfy the properties obtained. Moreover, we obtain a tight upper bound for the optimal solution to the problem. Numerical results that compare the upper bound with the optimal solution and the heuristic algorithms are provided. In the second part of this thesis, we study the problem of minimizing the number of processors required for scheduling a set of periodic preemptive independent hard real-time tasks. We use a partitioning strategy with an EDF scheduling algorithm on each processor. The problem is NP-hard. We derive lower and upper bounds for the number of processors required to satisfy the constraints of the problem. We also compare a number of heuristic algorithms with each other and with the bounds derived in this research. Numerical results demonstrate that our lower bound is very tight. In the third part of the thesis, we study the problem of uplink scheduling in telecommunication systems with two dimensional resources. Our goal is to maximize the total value of the packets sent in uplink subframe such that system constraints and requirements are satisfied. The packets have various QoS requirements and have either soft or hard deadlines. We take two approaches, namely 0-1 and fractional approaches, to model the problem. Considering the properties of the application, we derive globally optimal solutions in polynomial time for the models. We also present a method to fine-tune the models. Numerical results are provided to compare the performance of the various optimal algorithms each corresponding to a model. / Thesis (Ph.D, Computing) -- Queen's University, 2009-04-24 08:22:04.238

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A cognitive process model is developed that predicts the 3 major symbolic comparison response time effects (distance, end, and semantic congruity) found in the results of the linear syllogistic reasoning task. The model assumes that people generate an ordering of a finite set of symbolic stimuli on the basis of information contained in the pairwise relations between adjacent stimulus items. The learning of this ordering is simulated within a simple connectionist framework. The decision-making component of the model utilizes 2 separate evidence accrual processes operating in parallel. One process accumulates information about the positional difference between the stimulus items being compared, and the other accumulates information about the endpoint status of each of those items. A response occurs whenever enough evidence favouring it has been accumulated within either of these processes. The model also assumes that the congruencies between the positions of the stimulus items within the ordering and the form of the comparative instruction can lead to either interfering or facilitating effects on the rate of evidence accumulation within each of these accrual processes. To test the model, data are obtained from the single-session performances of a group of 16 subjects and the multiple-session performances of an additional 2 subjects. The task is a variant of the one used by Trabasso, Riley, and Wilson (1975) and involves paired comparisons of ordered symbolic stimuli (three-letter names). Simulations of the model provide an excellent account of the group mean correct response times, as well as a very good account of the full set of data obtained from the 2 additional subjects (including percentage correct and response time distributional data).

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This thesis investigates the relationship between communication and place, and the informational environment it forms. The thesis takes as its object of analysis signage, and examines signage as an implaced medium of communication. / In this work communication, including its practices and technologies, is treated as a dynamic ritual formed by the marking, naming, connecting, and interpreting the environment in the process of wayfinding. Such an approach underscores the inherent duality of communication: its manifestations framed by transmission and ritual; its boundedness by both space and time; and its expression in both mobile and fixed (implaced) media. The thesis thus shifts the disciplinary discourse from the usual text- and language-based focus to a more comprehensive focus that encompasses architectural and infrastructural environments and the grounding action of physical presences. Through its focus on the navigational aspects of communication, and framing by such concepts as wayfinding and signposting, the thesis shows how we can reconfigure the notion of the visual to include the embodied, experiential, and implaced. This in turn can help us gain a new perspective on the changing nature of text, image, representation, information and reality. / The thesis argues that as the themes of orientation, navigation, and interface grow alongside the new communication technologies, they make it important to attend to the original mediating role of the built environment and the navigational dimensions of place. It is here, within our foundational spatial orientation and wayfinding, that we turn for the metaphors, conceptual structures, and grounding as we chart our ways through the emerging informational environments. / In examining signage as a system of interfaces used in negotiating informational environments, as way-markers in a process of wayfinding, the thesis demonstrates the ways in which the concepts of wayfinding and navigation have become consequential to communication scholarship. It proposes that fruitful cues for the theorising and understanding of emerging informational realms can be drawn from the communicative dimensions of the most familiar immersive environments and their related practices: the physical spaces and built environments that we inhabit and negotiate daily.