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Performance Limits in CDMA PN Code Acquisition
No full textThis paper addresses timing acquisition aspects in direct-sequence code division multiple access (DS-CDMA) systems. Various chip waveform shaping schemes are considered,including both one-chip long full-response pulses, and partial response ones occupying several chip periods. Different figures of merits are considered in a comparative analysis that seeks to establish performance limits in terms of correct timing detection capability, false alarm rate, bandwidth occupancy, multiple access interference (MAI), and inter-chip interference (ICI). A waveform design algorithm is formulated to optimize system performance in terms of signal-to-interference-ratio (SIR) subject to other signalling constraints, and a solution based on the use of prolate spheroidal wave functions (PSWF) is derived. Numerous waveform design examples are then constructed to illustrate acquisition detection capability versus system load for both faded and unfaded cases. A comparative assessment of the performance of conventional signalling waveforms against the optimized ones is also presented. In particular, the numerical results show that the half-sine pulse used in Minimum Shift Keying (MSK) is quasi-optimal within the full-response category, while Root-Raised Cosine (RRC) Nyquist filtering with 22% rolloff (used in third generation CDMA standards) is also close to optimal when considering many-chip-long pulses
An Analytical Simulator for Deploying IP Telephony
Get PDFDeploying IP telephony or voice over IP (VoIP) is a major and challenging task. This paper describes an analytical design and planning simulator to assess the readiness of existing IP networks for the deployment of VoIP. The analytical simulator utilizes techniques used for network flows and queueing network analysis to compute two key performance bounds for VoIP: delay and bandwidth. The simulator is GUI-based and has an interface with drag-and-drop features to easily construct any generic network topology. The simulator has an engine that automates and implements the analytical techniques. The engine determines the number of VoIP calls that can be sustained by the constructed network while satisfying VoIP QoS requirements and leaving adequate capacity for future growth. As a case study, the paper illustrates how the simulator can be utilized to assess the readiness to deploy VoIP for a typical network of a small enterprise. We have made the analytical simulator publicly available in order to improve and ease the process of VoIP deployment
A Modular Reconfigurable Architecture for Asymmetric and Symmetric-key Cryptographic Algorithms
Get PDFIt is widely recognized that security issues will play a crucial role in the majority of future computer and communication systems. Cryptographic algorithms are the central tools for achieving system security. Numerous such algorithms have been devised, and many have found popularity in different domains. High throughput and low-cost implementation of these algorithms is critical for achieving both high security and high-speed processing in an increasingly digital global economy. Conventional methods for implementing ciphers are unable to provide all three crucial characteristics in a single solution: high throughput, low-cost, and cipher-agility. This thesis develops a reconfigurable architecture capable of implementing most symmetric-key as well as asymmetric-key ciphers. The reconfigurable nature of the architecture provides flexibility equivalent to software implementations, with the low-cost and throughput figures approaching ASIC implementations of these ciphers. Detailed discussions of the development of this architecture, along with the top-level design and interconnection scheme, have been provided. The individual components developed have been synthesized on a standard-cell library to provide an estimate of the area/performance characteristics of the design. Preliminary results show throughput values equivalent to FPGA based implementations for most of the tested ciphers, and approaching ASIC based implementations. Keywords: Reconfigurable Computing, Cryptography, Symmetric-Key, Asymmetric-Key, Domain-specific Reconfigurable Architecture
"Large signal performance of micromachined silicon condenser microphones"
Get PDFA mathematical model for the open-circuit output voltage of a micromachined silicon condenser microphone with a single deeply corrugated diaphragm as a function of the applied acoustic pressure is presented. The model, basically a sine-series function, can easily yield closed-form expressions for the amplitudes of the output components resulting from a multisinusoidal input acoustic pressure. The special case of an equal-amplitude two-tone acoustic pressure input is considered in detail. The results show that the microphone generates only odd-order harmonic and intermodulation products. The results also show that the amplitudes of these components are strongly dependent on the microphone parameters, the corrugation depth and the ratio between the half-length of the diaphragm and its thickness. Moreover, the results show that the acoustic pressure required to produce a pre-specified output open-circuit voltage is strongly dependent on these parameters
Bias and Geometrical Effects on Optically Controlled MESFETs
Get PDFA detailed characterization of the optical response of illuminated MESFETs due to several operating and geometrical conditions is presented. The characterization targets important optical performance factors including terminal photocurrent peak value and discharge time. A figure-of-merit is defined to quantify the overall response to these effects. The simulation results should be very useful in device operation and optimization
Content-based Image Retrieval using Multiple Shape Descriptors
Get PDFIn this paper we investigate content-based image retrieval using various shape descriptors. The descriptors include 11 moment invariants, area ratios (3-concentric ring based and 8-sector based) and simple shape descriptors (eccentricity, compactness, convexity, rectangularity, and solidity). The similarity measures used are Euclidean distance and Cosine correlation coefficient. For testing, 220 binary images from SQUID categorized into 12 image groups are used. Simple Shape Descriptors with Euclidean distance achieve the best average precision (0.593). Combining simple shape descriptors and area ratios, also using Euclidean distance as similarity measure, results in 3.29% improvement
Statistical Analysis of Arabic Text to Support Optical Arabic Text Recognition
Get PDFملخص: تقدم هذه الدراسة ملخصا لنتائج دراسة إحصائية لأعداد ظهور حروف ومقاطع الكلمات في اللغة العربية. وتشمل النتائج المعروضة تكرار كل حرف من الحروف العربية في كل مقطع من المقاطع، وتكرار الحرف والحرف الذي يليه في المقاطع المختلفة لكل الحروف. كما تشمل الدراسة على إحصائيات استخدام الحروف والمقاطع ونسبة استخدام كل منها في حالات الاستخدام المختلفة في اللغة العربية. وقد تم تطبيق الدراسة عل كتابي صحيح البخاري ومسلم. وتفيد الدراسة في المساعدة في عملية التعرف الآلي على الكتابة العربية، كما تفيد في عملية تصحيح الأخطاء بعد عملية التعرف
Evaluating Parallel Simulated Evolution Strategies for VLSI Cell Placement
Get PDFSimulated Evolution (SimE) is an evolutionary metaheuristic that has produced results comparable to well established stochastic heuristics such as SA, TS and GA, with shorter runtimes. However, for optimization problems with a very large set of elements, such as in VLSI cell placement and routing, runtimes can still be very large and parallelization is an attractive option for reducing runtimes. Compared to other metaheuristics, parallelization of SimE has not been extensively explored. This paper presents a comprehensive set of parallelization approaches for SimE when applied to multiobjective VLSI cell placement problem. Each of these approaches are evaluated with respect to SimE characteristics and the constraints imposed by the problem instance. Conclusions drawn can be extended to parallelization of SimE when applied to other optimization problems
Failure Forecasting of Aircraft Air-Conditioning/Cooling Pack with Field Data
Get PDFThis paper presents methods for modeling the failure of air-conditioning/cooling packs for a particular type of aircraft with field data. In many regards, field data are highly desirable for more accurate failure prediction by aircraft operators, because the data implicitly account for all actual usage and environmental stresses. It is not always possible to accurately anticipate or simulate these stresses in a laboratory or even in a field test. Field data, in a larger extent, are also important to the manufacturer, because the data identify product deficiencies and areas of improvement. In this study, the failure of the aircraft air-conditioning/cooling pack under a customer-use environment is first modeled at the component level by using the Weibull distribution and its extensions. These include the two-parameter Weibull model, three-parameter Weibull model, mixture model, and phased bi-Weibull model. The number of failures over time is estimated by a renewal process. The failure of the air-conditioning/cooling pack at the system level is then modeled by using the power law process model. The failure trend is tested by the Laplace test. The results give an insight into the reliability and quality of the air-conditioning/cooling pack under actual operating conditions. The models presented here can be used by aircraft operators for assessing system and component failures and customizing the maintenance programs recommended by the manufacturer