Practical System Configuration Research Articles

Queuing Network Models of Multiservice RANs

In this paper, we present a new queuing network model for the analysis of a portion of a radio access network (RAN) comprising macro cell base stations (BSs) and small cell BSs offering ”streaming” and ”elastic” services. Streaming services require a certain data rate for a random time. The required data rates depend on the type of service, e.g., audio and video. Elastic services require the transfer of random data volumes, and their data rate adjusts dynamically based on the capacity not utilized by the streaming services. To derive performance measures for the proposed model we develop a computationally efficient framework that exploits a new product form result for streaming services, relying on a well-known blocking policy, and an approximate product form for elastic services. Insensitivity to the distribution of service requirements holds in the case of negligible end user mobility. We show the high accuracy of our model in predicting the performance of practical system configurations by conducting a thorough comparison between the model’s results and those obtained from a detailed discrete-event simulator. Through this analysis, we uncover significant counter-intuitive behaviors that arise from the competition between streaming services with diverse demands, and that are effectively captured and predicted by our modeling approach. Our computationally efficient queuing model is a useful new tool to support design and planning of multiservice RANs whose complex structures result from the coexistence of BSs of different generations in dense areas.

Adaptive Distance Protection Scheme for Mutually Coupled Line

The availability of zero-sequence current, under normal circumstances, determines the accuracy of the operation of a distance relay which is connected to a mutually coupled parallel line. When this is not available, the system adopts a different compensation factor which if, not properly calculated introduces errors in the relay operation. The proposed adaptive protection scheme, described in this paper, consists of three modular artificial neural networks model (ANN). This is developed using the feed-forward nonlinear backpropagation Levenberg–Marquardt algorithm that determines the actual status of the mutually coupled lines. The remote terminal units connected to the current and voltage transformers are used to acquire the appropriate data. The proposed scheme also carefully determines the ground distance element reach settings by calculating the apparent impedance while considering mutual coupling for all practical system configurations from the ANN; this eliminates the need for a compensation factor. The results of the apparent impedance (R + jX) calculated by the proposed adaptive and the conventional schemes, showed an average percentage error of (0.06% and 0.02%) and (15% and 41.5%) respectively. Having obtained this result, the performance of the proposed adaptive scheme showed the exact fault location with a higher accuracy when compared with a compensated conventional scheme.

Characterization of Core-Shell Spherical Lens for Microtracking Concentrator Photovoltaic System

The optical characteristics of a radially symmetrical core-shell spherical (CSSP) lens is analyzed for its suitability to application in microtracking concentrator photovoltaic systems (MTCPVs). The CSSP lens is compared to a conventional homogenous spherical lens through both ray-tracing simulations and outdoor experiments. Simulation results show that the CSSP lens is superior to the conventional homogenous spherical lens in terms of its optical efficiency for long focal lengths, for which the CSSP lens exhibits less spherical and chromatic aberrations. Outdoor experiments are conducted using test concentrator photovoltaic (CPV) modules with prototype CSSP and homogenous spherical lenses; the trend of the measured short circuit current agrees with the that of the simulated optical efficiency for both lenses. Furthermore, compared to the homogenous lens, the CSSP lens significantly increases module efficiency because of its better illumination uniformity at the solar cell surface. The optical characteristics of the CSSP lens are preferable for MTCPVs with a spherical lens array to achieve a higher module efficiency for a wider incidence angle although further studies on more practical system configurations are needed.

Power Efficient Deployment Planning for Wireless Oceanographic Systems

A wireless oceanographic system is an underwater wireless-networked sensing system for oceanographic data collection, remote monitoring, and control. It represents a cutting-edge technology that could eliminate the need of long and expensive subsea cables while featuring real-time acquisition, flexible, and convenient deployment. Mainly powered by batteries, the wireless oceanographic system calls for power efficient deployment plans to extend the system lifetime. In this work, we first propose an architecture of wireless oceanographic system and then introduce a framework for the deployment planning. Specifically, we investigate the power consumption profile of the sensor nodes in the system. We employ a battery model for more accurate power estimation. Further, we analyzed the system lifetime with the consideration of the sensor node interactions. As a case study, the framework is applied to the Ocean-TUNE Long Island Sound (LIS) testbed, a real wireless oceanographic system with practical system configurations, and real data.

A Hidden Block in a Grid Connected Active Front End System: Modelling, Control and Stability Analysis

An LCL filter utilized in an active front end (AFE) converter can generate significant resonance, which can affect quality and stability of the system. Thus, a proper active or passive damping technique and/or a suitable controller is required to be designed for the converter. The duty cycle constraint—though inevitable in practical inverter systems—is often ignored in most of the existing literature. The effects of measurement noise on filter control system performance must be considered and evaluated under different conditions. Finally, almost all inverter control systems are implemented digitally using microcontrollers. Consequently, the effects of sampling on control system stability and performance should be evaluated as well. Thus, this paper presents stability analysis of an AFE converter-based filter design with a complete practical system configuration, including saturation and sampling blocks and measurement noises. Mathematical analysis and simulations have been carried out to validate the proposed method.

On the Use of Magnetically Coupled Resonators for Chirp-Based Timestamping

The knowledge of the time value at which an event of interest occurred is the typical feature needed to perform many kinds of postprocessing in distributed sensor networks. Consequently, network-based distributed systems must support time dissemination in order to ensure that relative clock errors among nodes remain below a certain threshold. Despite many protocols being well established for wired connections, the wireless sensor network paradigm required a new approach to address adverse characteristics of the wireless medium. In this paper, the adoption of low-frequency signaling is proposed for overcoming some issues of radio frequency transmissions when used for timestamping events. The proposed approach is characterized using numerical simulations and an experimental prototype, based on inductive coupling of tuned resonators. Experimental tests confirm the effectiveness and feasibility of this approach that achieves microsecond-order time recovery performance in practical system configurations.

Optimization of a dual‐energy contrast‐enhanced technique for a photon‐counting digital breast tomosynthesis system: I. A theoretical model

Dual-energy (DE) iodine contrast-enhanced x-ray imaging of the breast has been shown to identify cancers that would otherwise be mammographically occult. In this article, theoretical modeling was performed to obtain optimally enhanced iodine images for a photon-counting digital breast tomosynthesis (DBT) system using a DE acquisition technique. In the system examined, the breast is scanned with a multislit prepatient collimator aligned with a multidetector camera. Each detector collects a projection image at a unique angle during the scan. Low-energy (LE) and high-energy (HE) projection images are acquired simultaneously in a single scan by covering alternate collimator slits with Sn and Cu filters, respectively. Sn filters ranging from 0.08 to 0.22 mm thickness and Cu filters from 0.11 to 0.27 mm thickness were investigated. A tube voltage of 49 kV was selected. Tomographic images, hereafter referred to as DBT images, were reconstructed using a shift-and-add algorithm. Iodine-enhanced DBT images were acquired by performing a weighted logarithmic subtraction of the HE and LE DBT images, The DE technique was evaluated for 20-80 mm thick breasts. Weighting factors, w(t) that optimally cancel breast tissue were computed. Signal-difference-to-noise ratios (SDNRs) between iodine-enhanced and nonenhanced breast tissue normalized to the square root of the mean glandular dose (MGD) were computed as a function of the fraction of the MGD allocated to the HE images. Peak SDNR/ mean square root of MGD and optimal dose allocations were identified. SDNR/ mean square root of MGD and dose allocations were computed for several practical feasible system configurations (i.e., determined by the number of collimator slits covered by Sn and Cu). A practicalsystem configuration an d Sn-Cu filterpair that accounts for the trade-off between SDNR, tube-output, and MGD were selected. w(t) depends on the Sn-Cu filter combination used, as well as on the breast thickness; to optimally cancel 0% with 50% glandular breast tissue, w(t) values were found to range from 0.46 to 0.72 for all breast thicknesses and Sn-Cu filter pairs studied. The optimal w(t) values needed to cancel all possible breast tissue glandularites vary by less than 1% for 20 mm thick breasts and 18% for 80 mm breasts. The system configuration where one collimator slit covered by Sn is alternated with two collimator slits covered by Cu delivers SDNR/ mean square root of MGD nearest to the peak value. A reasonable compromise is a 0.16 mm Sn-0.23 mm Cu filter pair, resulting in SDNR values between 1.64 and 0.61 and MGD between 0.70 and 0.53 mGy for 20-80 mm thick breasts at the maximum tube current. A DE acquisition technique for a photon-counting DBT imaging system has been developed and optimized.

Micromachining with a 50 W, 50 μJ, subpicosecond fiber laser system

A 50 W sub-picosecond fiber chirped pulse amplification system generating 50 muJ pulses at a repetition rate of 1 MHz is demonstrated. As required for precision high speed micro-machining, this system has a practical system configuration enabled by the fiber stretcher and 1780 l/mm dielectric diffraction grating compressor and is capable of ablation rates >0.17 mm3/s metal, ceramic, and glass.

Dispersion in multiwavelength optical code-division multiple-access systems: impact and remedies

Temporal skewing, a hitherto unexamined effect of chromatic dispersion on multiwavelength optical code-division multiple-access (MW-O-CDMA) systems, is explored through simulation of realistic networks. In addition, two novel methods for combating the deleterious effects of temporal skewing are proposed: optimum threshold detection and code-pattern preskewing. It is shown that for a practical system configuration with optimum threshold detection, MW-O-CDMA networks can maintain design bit error rate performance within an order of magnitude for link lengths of up to approximately 500 m. Our results show that the effect merits careful attention in the design and realization of any MW-O-CDMA system based on two-dimensional codes. Code pattern preskewing presents the possibility of completely eradicating the impact of temporal skewing.

A new approach to harmonic compensation in power systems. A combined system of series active and shunt passive filters.

A novel approach to compensate for harmonics in power systems is proposed. The approach differs from conventional passive and active filters in its compensation principle. A practical system configuration to implement the approach is presented. It consists of a small-VA-rating PWM (pulsewidth-modulated) converter and a passive filter. The compensation principle is described, and compensation characteristics are examined theoretically and experimentally. The practicability and validity of the approach are experimentally demonstrated. >

A Hierarchical General‐Purpose Pipeline System

AbstractThe intelligent links that orient realization of the computer system integrating data communication and processing have been proposed. However, the practical system configuration and control have not yet been discussed. Based on the general‐purpose pipeline concept to implement the intelligent link, this paper presents the hierarchical pipeline system configuration that is designed to obtain high efficiency of the total system by overlapped data communication and processing. The decision method of the processing time in the segment at a higher level which is a processing unit in the pipeline, is shown.The decision is made independently at each segment. Therefore, this hierarchical pipeline system enables parallel processing by distributed control. The routing algorithm in the general multitrack bus is proposed as a communication medium executing high‐speed data transmission among the lower‐level pipeline processing elements in the segment.

Performance Characteristics of a Thermosyphon Solar Domestic Hot Water System

Performance characteristics (i.e., system temperatures and mass flow rates) of a thermosyphon solar domestic hot water (SDHW) system that are representative of practical system configurations and sizes are presented. Experimental weather/radiation conditions, collector inlet/outlet temperatures, collector mass flow rates, and storage tank temperature profiles are presented for the same period. These form a consistent set of performance data to which numerical predictions are compared. An indirect method using the storage tank temperatures is used to experimentally determine the thermosyphon mass flow rate. The accuracy of this indirect method is verified by comparison to measurements taken with a turbine flow meter on a pumped SDHW system. System temperatures and mass flow rates are predicted using a general purpose transient SDHW computer program, SHOW (Solar Hot Water). This program contains models for the solar collector, storage tank, and the thermosyphon mass flow rate. The storage tank is modeled as a stratified liquid tank with internode convection and conduction, stored internal energy, heat losses from the tank exterior, and some mixing at the tank inlet/outlet boundaries. Comparisons of predicted collector inlet/outlet temperatures; storage tank temperature profiles, and mass flow rates show agreement with experiments.