Multivariate ARMA modeling by scalar algorithms

An algorithm for multichannel autoregressive moving average (ARMA) modeling which uses scalar computations only and is well suited for parallel implementation is proposed. The given ARMA process is converted to an equivalent scalar, periodic ARMA process. The scalar autoregressive (AR) parameters are estimated by first deriving a set of modified Yule-Walker-type equations and then solving them by a parallel, order recursive algorithm. The moving average (MA) parameters are estimated by a least squares method from the estimates of the input samples obtained via a high-order, periodic AR approximation of the scalar process     

A space-based microwave radar concept

A space-based microwave radar (SBR) concept is defined using a tether trans/receive antenna supported between two gravity gradient low Earth-orbiting satellites. A cluster of four tether antennas, each of 6 km maximum length and 1.5 km separation between tethers, constitutes a radar. A system of 8 to 11 such clusters constitutes the overall radar scheme, which will cover approximately one third of the Earth's surface for detecting sea-based targets. Issues identified are the array structure, the coherence of tethered arrays, grating lobe energy clamping, clutter effects, communications, system requirements, and the overall radar system concept, including stability considerations. The baseline definition of an alternate space-based radar scheme is presented. A significant amount of R&D efforts will be required to derive practical solutions of the proposed scheme     

A Distributed Routing Method for Dynamic Multicasting

Single point, sender based control does not scale well for multicast delivery. For applications, such as group video or teleconferencing a low total cost multicast tree is required. In this article we present a destination driven algorithm to minimize the total tree cost of multicast tree in a dynamic situation for the whole session duration. In this heuristic approach we considered the staying duration of participants are available at the time of joining. The performance of our algorithm is analyzed through extensive simulation and evaluated against several other existing dynamic multicast routing and also against one well known near optimum heuristic algorithm used for solving Steiner tree problem. We have further tested our algorithm using erroneous information given by the joining participants. Simulation results show that its performance does not degrade that much even when the range of error is considerably high, which proves the robustness of our algorithm.     

An efficient algorithm for solving general periodic Toeplitzsystems

An efficient algorithm is presented for inverting matrices which are periodically Toeplitz, i.e., whose diagonal and subdiagonal entries exhibit periodic repetitions. Such matrices are not per symmetric and thus cannot be inverted by Trench's (1964) method. An alternative approach based on appropriate matrix factorization and partitioning is suggested. The algorithm provides certain insight on the formation of the inverse matrix, is implementable on a set of circularly pipelined processors and, as a special case, can be used for inverting a set of block Toeplitz matrices without requiring any matrix operation     

4D Printing of Shape Memory Materials for Textiles: Mechanism,Mathematical Modeling,and Challenges

Shape memory materials (SMMs) in 3D printing (3DP) technology garnered much attention due to their ability to respond to external stimuli, which direct this technology toward an emerging area of research, “4D printing (4DP) technology.” In contrast to classical 3D printed objects, the fourth dimension, time, allows printed objects to undergo significant changes in shape, size, or color when subjected to external stimuli. Highly precise and calibrated 4D materials, which can perform together to achieve robust 4D objects, are in great demand in various fields such as military applications, space suits, robotic systems, apparel, healthcare, sports, etc. This review, for the first time, to the best of the authors’ knowledge, focuses on recent advances in SMMs (e.g., polymers, metals, etc.) based wearable smart textiles and fashion goods. This review integrates the basic overview of 3DP technology, fabrication methods, the transition of 3DP to 4DP, the chemistry behind the fundamental working principles of 4D printed objects, materials selection for smart textiles and fashion goods. The central part summarizes the effect of major external stimuli on 4D textile materials followed by the major applications. Lastly, prospects and challenges are discussed, so that future researchers can continue the progress of this technology.     

Aperture Field Estimation in E Plane and H-Plane T-Junctions Using Field Theoretic Analysis

Wireless Personal Communications - This paper presents method of moment based analysis of E Plane and H-Plane T-junctions to find the field distributions on different transverse and longitudinal...     

Analysis and Optimization of an Adaptive Selective-Repeat Scheme for Time-Varying Channels with Feedback Errors

In this article, an adaptive SR ARQ scheme is analyzed and optimized in a time-varying channel environment with unreliable feedback. Two-state Markov models are assumed for both the forward and the returnchannel.This enables the time behaviour of the entire system to be modelledby a Markov chain. To have an easy-to-implement scheme, we choose the smaller packet size to be half of the bigger one. Thus, there is only oneindependent design parameter related to packet size. The other two parametersare associated with channel sensing. The performance of the adaptive schemeis measured by its average throughput, which is upper-bounded by the throughput of the so-called ideal adaptive scheme. This upper bound is very useful in the optimization of the packet size and other design parameters. From the results, it can be concluded that the selection of the packet size is at least as critical as the optimization of the other parameters. The feedback errors degrade the throughput of the scheme, but their effect on the parameter optimization turns out to be almost negligible.     

Reliability bounds and other inequalities for discrete life distributions

In this paper we give sharp bounds on the reliability of discrete IFR, IFRA, NBU, DFR, DFRA and NWU classes, based on one known moment. Subsequently the discrete analogues of several continuous-time results related to maintained systems are also presented.     

Scanning and Address Allocation Delays in Vehicular Communications

WLAN-based roadside-to-vehicle communications is an increasingly popular research trend. This paper examines the applicability of WLANs in the Intelligent Transportation Systems with focus on reducing the scanning phase delay and the address allocation delay. The handover delays become intolerable when the indoor WLAN Access Poins are accessed from by the outdoor mobile nodes at vehicular speeds. In this work, we propose a baseline scheme which calls for passively scanning only the orthogonal channels to reduce the scanning phase delay in the overall handover latency. We argue that the interference free orthogonal channels are ideal for conveying time critical information in vehicular environments. Secondly, this paper evaluates the delays incurred by the Dynamic Host Configuration Protocol (DHCP) in the handover process. The focus on establishing the amount of delay contributed by each DHCP phase and make some meaningful comments at the end. The conclusions made in this paper are based on real-world experiments and tests.