7294 research outputs found
Sort by
A Higher-order Accurate FDTD Solution to Scalar SHG Problems
No full textA higher-order accurate FDTD simulation algorithm for the solution of the phase-dependent SHG problem is presented. This algorithm approximates the spatial derivatives in the propagation direction using 4th order FD schemes. It has been shown that this scheme guarantees the convergence of the solution using significantly less computation time and less memory requirement as compared to 2nd order scheme
Decentralized, Self-organizing, Potential field-based Control for Individually-motivated, Mobile Agents in a Cluttered Environment: A Vector-Harmonic Potential Field Approach
No full textAbstract—Spatial multiagency has been receiving growing attention from researchers exploring many of the aspects and modalities of this phenomenon. The aim is to develop the theoretical background needed for a multitude of applications involving the sharing of resources by more than one agent. A traffic management system is one of these applications. Here, a large group of mobile robots that are operating in communication-limited, and sensory-limited modes are required to cope with each others presence as well as the contents of their environment while preserving their ability to reach their preset independent goals. This paper explores the construction of a decentralized traffic controller for a large group of agents sharing a workspace with stationary forbidden regions. The suggested multiagent motion controller is complete provided that a lenient condition on the geometry of the workspace is upheld. It has a low computational effort that linearly increases with the number of agents. The controller is also self-organizing; therefore, it is able to deal, on its own, with incomplete information and unexpected situations. In addition to the above, the controller has an open structure to enable any agent to join or leave the group without the remaining agents having to adjust the manner in which they function. To meet these requirements, a definition of decentralization is suggested. This definition equates decentralization to self-organization in a group of agents operating in an artificial-life mode. The definition is used to provide guidelines for the construction of the multiagent controller. The controller is realized using the potential field approach. Theoretical developments, as well as simulation results are provided
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 Improved MAC Algorithm for Enhanced Performance for Saturation and Non-Saturation Conditions in IEEE 802.11 WLANs
Get PDF"Blind Adaptive Modulation Systems for Wireless Channels with Binary Feedback"
No full textIn this paper, we investigate the performance of a blind adaptive modulation scheme that does not require any channel knowledge and just uses binary feedback, thereby decreasing feedback load. Retransmission of erroneous packet is not considered. In particular, we present an analytical framework for the performance evaluation of a simple wireless system in terms of receiver and transmitter structure. The system requires no knowledge of the channel and relies on a binary feedback. Slow and fast Rayleigh fading channel conditions are considered. The paper includes the derivation of the closed-form expressions of the spectral efficiency. In some cases, closed-form expression for packet error rate (PER) are derived. Our results show relatively high PER but some applications can still operate in a satisfactory fashion in these conditions, such as voice communication. Using coded modulation with high coding gain and increasing the number of blocks per time slot decrease the PER even more. An advantage of this system is that it uses a low complexity receiver, which sends binary feedback
Parallel Inverse Halftoning by Look-Up Table (LUT) Partitioning
Get PDFLook-Up Table (LUT) method for inverse halftoning is computation less, fast, and also yields goods results. It employs a single LUT that is stored in a ROM and contains pre-computed contone (gray level) values for inverse halftone operation. This paper proposes an algorithm that can perform parallel inverse halftone operation by partitioning the single LUT into N smaller Look-Up Tables (s-LUTs). Thereby, upto k (k≤N) pixels can be concurrently fetched from the halftone image, and their contone values can also be fetched concurrently from separate smaller Look-Up Tables (s-LUT). The parallelization increases the speed of inverse halftoning by upto k times while the total entries in all s-LUTs remains equal to the entries in the single LUT of the serial LUT method. Some degradation in image quality is possible due to pixel loss during parallel fetching. This is due to some contone values cannot be fetched in the same cycle because some other contone value is being fetched from the s-LUT. The complete implementation of the algorithm requires two CPLD devices for computational portion, external content addressable memories (CAM) and static RAMs to store s-LUTs
Efficient utilization of scalable multipliers in parallel to compute GF(p) elliptic curve cryptographic operations
Get PDFThis paper presents the design and implementation of an elliptic curve cryptographic core to realize point scalar multiplication operations used for the GF(p) elliptic curve encryption/decryption and the elliptic curve digital signature algorithm (ECDSA). The design makes use of projective coordinates together with scalable Montgomery multipliers for data size of up to 256-bits. We propose using four multiplier cores together with the ordinary projective coordinates which outperform implementations with Jacobean coordinates typically believed to perform better. The proposed architecture is particularly attractive for elliptic curve cryptosystems when hardware area optimization is the key concern
Analysis of Spatially Distributed FU-FB S-ALOHA in Fading Channels Using TUA
Get PDFThe Tagged user analysis (TUA) is a generic approximate method developed to analyze random access protocols for finite-user finite-buffer systems that avoids complexities of Markovian analysis by using available queuing results. In this paper, TUA method is extended to the analysis of finite buffer S-ALOHA operating over flat fading radio channels when the user population is spatially distributed. The expressions for systemperformance indices are derived. It is shown that formoderate number of active users, the simulation and analytical results have a close fit
A Novel Current-Mode OTA-C Universal Filter
Get PDFA novel current-mode biquad circuit is presented. The circuit uses two single-output-, one multiple-output-operational transconductance amplifiers (OTAs), two grounded capacitors and can realize lowpass, highpass, bandpass, notch, lowpass notch, highpass notch and allpass responses from the same topology. The parameters ωo and ωo/Qo enjoy independent electronic tunability. Simulation results are included