Techniques for automated parameter estimation in computational models of probabilistic systems

The main contribution of this dissertation is the design of two new algorithms for automatically synthesizing values of numerical parameters of computational models of complex stochastic systems such that the resultant model meets user-specified behavioral specifications. These algorithms are designed to operate on probabilistic systems – systems that, in general, behave differently under identical conditions. The algorithms work using an approach that combines formal verification and mathematical optimization to explore a model\u27s parameter space. The problem of determining whether a model instantiated with a given set of parameter values satisfies the desired specification is first defined using formal verification terminology, and then reformulated in terms of statistical hypothesis testing. Parameter space exploration involves determining the outcome of the hypothesis testing query for each parameter point and is guided using simulated annealing. The first algorithm uses the sequential probability ratio test (SPRT) to solve the hypothesis testing problems, whereas the second algorithm uses an approach based on Bayesian statistical model checking (BSMC). The SPRT-based parameter synthesis algorithm was used to validate that a given model of glucose-insulin metabolism has the capability of representing diabetic behavior by synthesizing values of three parameters that ensure that the glucose-insulin subsystem spends at least 20 minutes in a diabetic scenario. The BSMC-based algorithm was used to discover the values of parameters in a physiological model of the acute inflammatory response that guarantee a set of desired clinical outcomes. These two applications demonstrate how our algorithms use formal verification, statistical hypothesis testing and mathematical optimization to automatically synthesize parameters of complex probabilistic models in order to meet user-specified behavioral propertie

Impact of LFSR Seeding on the Test Pattern Generator in BIST

This paper considers the problem of minimizing the power required to test a BIST based combinational circuit without modifying the test pattern generator and with no extra area or delay overhead. The objective of this paper is to analyze the impact of the polynomial and seed selection of the LFSR on the power consumed by the circuit. It is shown that proper selection of the seed of the LFSR can lead to significant decrease in the power consumption of the BIST sessions. For this purpose, a Bit Flipping LFSR is used as a test pattern generator in the BIST design. Experimental results using the ISCAS benchmark circuits are reported, showing variations of the seed selected for the LFSR, the power consumed is ranging from 5.5% to 13.5%

Multimedia Traffic Engineering in Next Generation Networks

Due to high speed Internet and Multimedia applications, future wireless communication are expected to support multimedia traffic such as voice, video and text with a variety of Quality of Service (QoS) requirements and make efficient use of radio resources. Such kind of traffic requires high level of QoS guarantees. Traffic management is a process of regulating the traffic over network. Since, multimedia traffic is more sensitive, therefore it requires special measures while transmission, especially in wireless networks. There are different queuing disciplines which are used to police the traffic, the Priority Queue and RIO (RED with In/Out) are queuing disciplines, PQ is used to prioritize the traffic, and the later is used to drop the lower priority packets at the time of congestion. Proposed solution is the integration of Priority Queue with RIO, which will serve as a classifier to prioritize the traffic and then it will also serve as a scheduler by dropping lower priority traffic when the congestion state occur. Simulation results show that by applying proposed Traffic Management Strategy (PriRIO), it assigns stable bandwidth to the Multimedia Traffic Flow and enhances its throughput. It also shows that Packet Losses for Multimedia Traffic are very minor, that is, equivalent to none. Further, delay values for Multimedia traffic also remain below the Best Effort traffic flows. Thus, on the basis of these simulation results and analysis, PriRIO outperforms significantly, as compare to other Traffic Management Strategies

A Comprehensive Survey on Moving Networks

The unprecedented increase in the demand for mobile data, fuelled by new emerging applications such as HD video streaming and heightened online activities has caused massive strain on the existing cellular networks. As a solution, the 5G technology has been introduced to improve network performance through various innovative features such as mmWave spectrum and HetNets. In essence, HetNets include several small cells underlaid within macro-cell to serve densely populated regions. Recently, a mobile layer of HetNet has been under consideration by the researchers and is often referred to as moving networks. Moving networks comprise of mobile cells that are primarily introduced to improve QoS for commuting users inside public transport because the QoS is deteriorated due to vehicular penetration losses. Furthermore, the users inside fast moving public transport also exert excessive load on the core network due to large group handovers. To this end, mobile cells will play a crucial role in reducing overall handover count and will help in alleviating these problems by decoupling in-vehicle users from the core network. To date, remarkable research results have been achieved by the research community in addressing challenges linked to moving networks. However, to the best of our knowledge, a discussion on moving networks in a holistic way is missing in the current literature. To fill the gap, in this paper, we comprehensively survey moving networks. We cover the technological aspects and their applications in the futuristic applications. We also discuss the use-cases and value additions that moving networks may bring to future cellular architecture and identify the challenges associated with them. Based on the identified challenges we discuss the future research directions.Comment: This survey has been submitted to IEEE Communications Surveys & Tutorial

Vibrational analysis of PDC bits in a laboratory compliant drillstring

Excessive vibrations during drilling operations can shorten the life of downhole equipment and instruments. One of the major contributors to drilling vibrations is bit-rock interaction. Therefore, controlling drillstring vibrations increases the range of drilling operating parameters to maintain a safe drilling operation. The goal of the research is to study the effect of drillstring vibration on drill bit dynamics and to estimate the frictional parameters of various bit-rock interaction models using laboratory testing data. In collaboration with Sandia National Laboratory (SNL), drilling tests in a controlled laboratory environment with multiple drillstring configurations mimicking field drillstring vibrations were performed at the Hard Rock Drilling Facility (HRDF). The rigid configuration was used as a base case to compare the effect of drillstring vibration on drill bit dynamics. The various drillstring configurations were investigated using two 3¾ inches of Polycrystalline Diamond Compact (PDC) bits with 4 and 5-blade designs. Drilling tests were conducted at 500 lb axial load increments up to 5500 lb at three constant rotating speeds of 80, 120, and 160 RPM. The results showed that the flywheel configuration provides a stable torque to the bit, while the torsional compliance configuration produced less torque at the same weight on bit (WOB) compared to the rigid configuration for the 4-bladed bit. The axial compliance configuration increases the WOB variation. The combined axial torsional compliance configuration showed increased fluctuation in WOB, rotational speed, and applied torque. Overall, traditional rigid drillstring experiments overestimate drilling vibrations frequencies by an average of 26.3% in the axial direction and 35% in the torsional direction when compared to the combined axial and torsional compliance for both bit designs. The use of the 5-bladed PDC bit in hard rock reduces axial vibrations by 53.7% in the axial direction and 14.2% in the torsional direction. The drilling test data were compared with one coupled axial and torsional bit-rock interaction model, and three uncoupled torsional bit-rock interaction models to perform a sensitivity analysis and determine the frictional constants for the testing data. The sensitivity of models showed difficulties in predicting actual laboratory conditions where such models are highly dependent on the frictional constants which are difficult to obtain for a certain drilling condition