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no / In cognitive radio cooperative communication (CR-CC) systems, the achievable data rate can be improved by increasing the transmission power. However, the increase in power consumption may cause the interference with primary users and reduce the network lifetime. Most previous work on CR-CC did not take into account the tradeoff between the achievable data rate and network lifetime. To fill this gap, this paper proposes an energy-efficient joint relay selection and power allocation scheme in which the state of a relay is characterized by the channel condition of all related links and its residual energy. The CR-CC system is formulated as a multi-armed restless bandit problem where the optimal policy is decided in a distributed way. The solution to the restless bandit formulation is obtained through a first-order relaxation method and a primal-dual priority-index heuristic, which can reduce dramatically the on-line computation and implementation complexity. According to the obtained index, each relay can determine whether to provide relaying or not and also can control the corresponding transmission power. Extensive simulation experiments are conducted to investigate the effectiveness of the proposed scheme. The results demonstrate that the power consumption is reduced significantly and the network lifetime is increased more than 40%.

Yes / This paper presents a robust framework for active and reactive power management in distribution networks using electric vehicles (EVs). The method simultaneously minimizes the energy cost and the voltage deviation subject to network and EVs constraints. The uncertainties related to active and reactive loads, required energy to charge EV batteries, charge rate of batteries and charger capacity of EVs are modeled using deterministic uncertainty sets. Firstly, based on duality theory, the max min form of the model is converted to a max form. Secondly, Benders decomposition is employed to solve the problem. The effectiveness of the proposed method is demonstrated with a 33-bus distribution network.

This study proposes various methods to harvest the mechanical energy present in railcar suspensions and railroad tracks to generate electricity that is suitable for onboard or trackside electronics, using electromagnetic generators. Compact electromagnetic energy harvesters that can be installed onboard railcars or wayside on railroad tracks are designed, fabricated, and tested. The designs integrate a mechanical motion rectifier (MMR) with embedded one-way clutches in the bevel gears in order to convert the bi-directional mechanical energy that commonly exists in the form of vibrations into a unidirectional rotation of the generator. The ball screw mechanism is configured such that it has reduced backlash and thus can more efficiently harvest energy from low-amplitude vibrations. Two prototype harvesters are fabricated and tested extensively in the laboratory using a suspension dynamometer and in the field onboard a railcar and on a test track. A power management system with an energy storage circuit has also been developed for this onboard harvester. The laboratory evaluation indicate that the harvesters are capable of harvesting power with sufficient current and voltage for successfully powering light electronics or charging a low demand battery pack. The harvested power varies widely from a few to tens of Watts, depending on the resistive load across the harvester and the amplitude and frequency of the mechanical motion. The laboratory test results are verified through field testing. One harvester is tested onboard a freight railcar, placing it across the wedge suspension, to use the small amount of relative displacement at the wedge suspension to harvest energy. A second harvester is placed on a test track to use the vertical motion that occurs due to passing wheels for wayside energy harvesting. Both onboard and wayside tests confirm the laboratory test results in terms of the success of the design concept in providing low-power electrical power. The harvester design is further integrated into a conventional railroad tie for ease of field installation and for improving the efficiency of harvesting the mechanical energy at the rail. The integrated design, referred to as the "smart tie," not only protects the energy harvester, the wiring harness, and supporting electronics from the maintenance-of-the-way equipment, but also positions the harvester in a mechanically advantageous position that can maximize the track-induced motion, and hence the harvested power. Although for testing purposes, the smart tie uses a modified composite tie, it can be integrated into other track tie arrangements that are used for revenue service track, including concrete and wooden ties. A prototype smart tie is fabricated for laboratory testing, and the results nearly surpass the results obtained earlier from the wayside harvester. The smart tie is currently being considered for revenue service field testing over an extended length of time, potentially at a railroad mega site or similarly suitable location. / Doctor of Philosophy / This dissertation proposes three different electromagnetic energy harvesters for harvesting railroad track and railcar suspension vibration energy. The concept is similar to what you may have seen in self-powering flashlights that are often advertised in late-night TV commercials. You shake the flashlight vigorously, which moves an energy harvester devoice and, Voila, the light bulb comes on. The device design in this study uses the mechanical energy that is present in a vehicle or at a railroad track to harvest the mechanical energy that is naturally present in the form of electrical energy, which can then be used for powering electronic devices and sensors of various kinds. Such sensors and electronics would help with improving the operational efficiency of railroads. The energy harvesters can be installed onboard a railcar or at the track. In either case, the movement of the train creates a small amount of vibration energy that is turned into electrical power. When onboard a train the power can be used for sensors, GPS, and similar devices to allow the operator to better monitor the condition and location of the train. Note that most railcars, especially the freight railcars, do not have any onboard electrical power. Similarly, the energy harvester can be installed at the track to convert the small amount of up and down motion that happens with the passing of each wheel into energy that could be used for integration of sensors that make the track "smarter." This means that the sensors can potentially alert the engineers who are responsible for monitoring the track of an existing or impending problem with the track. Both the railcar and track integration of the energy harvester that is designed, fabricated, and tested during this study are exciting concepts that can improve the rail industry in the U.S. This document includes the details of designing efficient energy harvesters, specifically for rail applications. A prototype of the energy harvester is fabricated and tested extensively in the lab and in the field, albeit to a more limited extent. The test results were quite successful, which is why I am telling you about them! Both the laboratory and field test results show that the device holds significant promise for rail applications.

This dissertation studies the problem of increasing battery life-time and reducing CPU heat dissipation without degrading system performance in commodity-OS-based general-purpose (GP) mobile computers using the dynamic voltage scaling (DVS) function of modern CPUs. The dissertation especially focuses on the impact of task scheduling on the effectiveness of DVS in achieving this goal. The task scheduling mechanism used in most contemporary general-purpose operating systems (GPOS) prioritizes tasks based only on their CPU occupancies irrespective of their deadlines. In currently available autonomous DVS schemes for GP mobile systems, the impact of this GPOS task scheduling is ignored and a DVS scheme merely predicts and enforces the lowest CPU speed that can meet tasks' deadlines without meddling with task scheduling. This research, however, shows that it is impossible to take full advantage of DVS in balancing energy/power and performance in the current DVS paradigm due to the mismatch between the urgency (i.e., having a nearer deadline) and priority of tasks under the GPOS task scheduling. This research also shows that, consequently, a new DVS paradigm is necessary, where a "DVS-friendly" task scheduling assigns higher priorities to more urgent tasks. The dissertation begins by showing how the mismatch between the urgency and priority of tasks limits the effectiveness of DVS and why conventional real-time (RT) task scheduling, which is intrinsically DVS-friendly cannot be used in GP systems. Then, the dissertation describes the requirements for "DVS-friendly GP" task scheduling as follows. Unlike the existing GPOS task scheduling, it should prioritize tasks by their deadline. But, at the same time, it must be able to do so without a priori knowledge of the deadlines and be able to handle the various tasks running in today's GP systems, unlike conventional RT task scheduling. The various tasks include sporadic tasks such as user-interactive tasks and tasks having dependencies on each other such as a family of threads and user-interface server/clients tasks. Therefore, the first major result of this research is to propose a new DVS paradigm for commodity-OS-based GP mobile systems in which DVS is performed under a DVS-friendly GP task scheduling that meets these requirements. The dissertation then proposes GPSched, a DVS-friendly GP task scheduling mechanism for commodity-Linux-based GP mobile systems, as the second major result. GPSched autonomously prioritizes tasks by their deadlines using the type of services that each task is involved with as the indicator of the deadline. At the same time, GPSched properly handles a family of threads and user-interface server/clients tasks by distinguishing and scheduling them as a group, and user-interactive tasks by incorporating a feature of current GPOS task scheduling — raising the priority of a task that is idle most of the time — which is desirable to quickly respond to user input events in its prioritization mechanism. The final major result is GPScheDVS, the integration of GPSched and a task-based DVS scheme customized for GPSched called GPSDVS. GPScheDVS provides two alternative modes: (1) the system-energy-centric (SE) mode aiming at a longer battery life-time by reducing system energy consumption and (2) the CPU-power-centric (CP) mode focusing on limiting CPU heat dissipation by reducing CPU power consumption. Experiments conducted under a set of real-life usage scenarios on a laptop show that the best, worst, and average reductions of system energy consumption by the SE mode GPScheDVS were 24%, -1%, and 17%, respectively, over the no-DVS case and 11%, -1%, and 5%, respectively, over the state-of-the-art task-based DVS scheme in the current DVS paradigm. The experiments also show that the best, worst, and average reductions of CPU energy consumption by the SE mode GPScheDVS were 69%, 0%, and 43% over the no-DVS case and 26%, -1%, and 13% over the state-of-the-art task-based DVS scheme in the current DVS paradigm. Considering that no power management was performed on non-CPU components for the experiments, these results imply that the system energy savings achievable by GPScheDVS will be increased if the non-CPU components' power is properly managed. On the other hand, the best, worst, and average reductions of average CPU power by the CP mode GPScheDVS were 69%, 49%, and 60% over the no-DVS case and 63%, 0%, and 30% over the existing task-based DVS scheme. Furthermore, oscilloscope measurements show that the best, worst, and average reduction of peak system power by the CP mode GPScheDVS were 29%, 10%, and 23% over the no-DVS case and 28%, 6%, and 22% over the existing task-based DVS scheme signifying that GPScheDVS is effective also in restraining the peak CPU power. On the top of these advantages in energy and power, the experimental results show that GPScheDVS even improves system performance in either mode due to its deadline-based task scheduling property. For example, the deadline meet ratio on continuous videos by GPScheDVS was at least 91.2%, whereas the ratios by the no-DVS case and the existing task-based DVS scheme were down to 71.3% and 71.0%, respectively. / Ph. D.

The batteries used to power wireless sensor nodes have become a major roadblock for the wide deployment. Harvesting energy from mechanical vibrations using piezoelectric cantilevers provides possible means to recharge the batteries or eliminate them. Raw power harvested from ambient sources should be conditioned and regulated to a desired voltage level before its application to electronic devices. The efficiency and self-powered operation of a power conditioning and management circuit is a key design issue. In this research, we investigate the characteristics of piezoelectric cantilevers and requirements of power conditioning and management circuits. A two-stage conditioning circuit with a rectifier and a DC-DC converter is proposed to match the source impedance dynamically. Several low-power design methods are proposed to reduce power consumption of the circuit including: (i) use of a discontinuous conduction mode (DCM) flyback converter, (ii) constant on-time modulation, and (iii) control of the clock frequency of a microcontroller unit (MCU). The DCM flyback converter behaves as a lossless resistor to match the source impedance for maximum power point tracking (MPPT). The constant on-time modulation lowers the clock frequency of the MCU by more than an order of magnitude, which reduces dynamic power dissipation of the MCU. MPPT is executed by the MCU at intermittent time interval to save power. Experimental results indicate that the proposed system harvests up to 8.4 mW of power under 0.5-g base acceleration using four parallel piezoelectric cantilevers and achieves 72 percent power efficiency. Sources of power losses in the system are analyzed. The diode and the controller (specifically the MCU) are the two major sources for the power loss. In order to further improve the power efficiency, the power conditioning circuit is implemented in a monolithic IC using 0.18-μ­m CMOS process. Synchronous rectifiers instead of diodes are used to reduce the conduction loss. A mixed-signal control circuit is adopted to replace the MCU to realize the MPPT function. Simulation and experimental results verify the DCM operation of the power stage and function of the MPPT circuit. The power consumption of the mixed-signal control circuit is reduced to 16 percent of that of the MCU. / Ph. D.

One of the fundamental characteristics of the microprocessor application is its property of dynamic load change. Although idle most of the time, it wakes up in nanoseconds to support sudden workload demands, which are becoming increasingly severe in today's multi-core processors with large core count. From the standpoint of its voltage regulator (VR) design, it must have very good efficiency at light loads, while also supporting a very fast transient response. Thus, the variable-frequency constant on-time current-mode (COTCM) control scheme is widely used in the VRs, as it can automatically reduce its switching frequency during light-load conditions. But, from transient point of view, it has some limitations in response to heavy-load demands by microprocessors; this is resolved by adding different nonlinear controls in state-of-the-art control schemes. These nonlinear controls are difficult to optimize for the widely variable transient conditions in processors. Another major issue for this ripple-based COTCM control is that when the combined inductor-current ripple in multiphase operation becomes zero because of the ripple-cancellation effect, COTCM loses its controllability. Therefore, the goal of this research is to discover a new adaptive COT control scheme that is concurrently very efficient at light-load conditions and also provides a fast and optimized transient response without adding any nonlinear control; hence providing a complete solution for today's high-performance microprocessors. Firstly, the overview of state-of-the-art COTCM control is discussed in detail, and its limitations are analyzed. Analysis shows that one issue plaguing the COTCM control is its slow transient response in both single and multiphase operation. In this context, two methods have been proposed to improve the transient performance of conventional COTCM control in single and multiphase operations. These two methods can effectively reduce the output capacitor count in system, but the ripple-cancellation and phase overlapping issues in multiphase operation are yet to be improved. This provides motivation to search for a new COT control technique that can resolve all these problems together. Therefore, a new concept of inverse charge constant on-time (IQCOT) control is proposed to replace the conventional ripple-based COTCM; the goals are to improve noise immunity at the ripple-cancellation point without adding any external ramp into the system, and to improve the load step-up transient performance in multiphase operation by achieving natural and linear pulse overlapping without adding any nonlinear control. Additionally, the transient performance of the proposed IQCOT has been further improved by naturally increasing or decreasing the TON time during the load step-up or step-down transient period without adding any nonlinear control. As this transient property is inherent in proposed IQCOT control, it is adaptive to the widely variable transient requirements of processors, and always produces an optimized transient response. In order to design the proposed control with high bandwidth for supporting fast transient response, an accurate high-frequency small-signal model needs to be derived. Therefore, a high-frequency model for the proposed IQCOT control is derived using the describing function method. The model is also verified by simulation and hardware results in different operating conditions. From the derived model it is found that the quality factor (Q) of one double-pole set varies with changes in duty cycle. To overcome this challenge, an auto-tuning method for Q-value control is also proposed in this dissertation. / Ph. D.

This thesis presents a novel self-powered infrastructural traffic monitoring approach that estimates traffic information by combining three detection techniques. The traffic information can be obtained from the presented approach includes vehicle counts, speed estimation and vehicle classification based on size. Two categories of sensors are used including IR Lidar and IR camera. With the two sensors, three detection techniques are used: Time of Flight (ToF) based, vision based and Laser spot flow based. Each technique outputs observations about vehicle location at different time step. By fusing the three observations in the framework of Kalman filter, vehicle location is estimated, based on which other concerned traffic information including vehicle counts, speed and class is obtained. In this process, high reliability is achieved by combing the strength of each techniques. To achieve self-powering, a dynamic power management strategy is developed to reduce system total energy cost and optimize power supply in traffic monitoring based on traffic pattern recognition. The power manager attempts to adjust the power supply by reconfiguring system setup according to its estimation about current traffic condition. A system prototype has been built and multiple field experiments and simulations were conducted to demonstrate traffic monitoring accuracy and power reduction efficacy. / Master of Science

Dynamic Power Management (DPM) refers to the strategies employed at system level to reduce energy expenditure (i.e. to prolong battery life) in embedded systems. The trade-off involved in DPM techniques is between the reductions of energy consumption and latency incurred by the jobs to be executed by the system. Such trade-offs need to be decided at runtime making DPM an on-line problem. In this context, the contributions of this thesis are two-fold. Firstly, we formulate the DPM problem as a hybrid automaton control problem. We model a timed hybrid automaton to mathematically analyze various opportunities in optimizing energy in a given system model. Secondly, stochastic control is added to the automata model, whose control strategy is learnt dynamically using stochastic learning automata (SLA). Several linear and non-linear feedback algorithms are incorporated in the final Stochastic Learning Hybrid Automata (SLHA) model. Simulation-based experiments show the expediency of the feedback systems in stationary environments. Further experiments are conducted using real trace data to compare stochastic learning strategies to the outcomes of several former predictive algorithms. These reveal that SLHA attains better trade-offs than the other studied methods under certain trace data. Advanced characterization of trace sequences, which allows a better performance of SLHA, is a subject of further study. / Master of Science