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The design of modulation schemes for the physical layer network-coded two-way relaying scenario is considered with a protocol which employs two phases: multiple access (MA) phase and broadcast (BC) phase. It was observed by Koike-...
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The design of modulation schemes for the physical layer network-coded two-way relaying scenario is considered with a protocol which employs two phases: multiple access (MA) phase and broadcast (BC) phase. It was observed by Koike-Akino et al. that adaptively changing the network coding map used at the relay according to the channel conditions greatly reduces the impact of MA interference which occurs at the relay during the MA phase and all these network coding maps should satisfy a requirement called the exclusive law. We show that every network coding map that satisfies the exclusive law is representable by a Latin Square and conversely, that this relationship can be used to get the network coding maps satisfying the exclusive law. The channel fade states for which the minimum distance of the effective constellation at the relay become zero are referred to as the singular fade states. For $M-$ PSK modulation ($M$ any power of 2), it is shown that there are $left ({{M^{2}}/{4}}- {{M}/{2}}+1 right)M$ singular fade states. Also, it is shown that the constraints which the network coding maps should satisfy so that the harmful effects of the singular fade states are removed, can be viewed equivalently as partially filled Latin Squares (PFLS). The problem of finding all the required maps is reduced to finding a small set of maps for $M-$ PSK constellations ($M$ any power of 2), obtained by the completion of PFLS. Even though the completability of $M times M$ PFLS using $M$ symbols is an open problem, specific c- ses where such a completion is always possible are identified and explicit construction procedures are provided. Having obtained the network coding maps, the set of all possible channel realizations (the complex plane) is quantized into a finite number of regions, with a specific network coding map chosen in a particular region. It is shown that the complex plane can be partitioned into two regions: a region in which any network coding map which satisfies the exclusive law gives the same best performance and a region in which the choice of the network coding map affects the performance. The quantization thus obtained analytically, leads to the same as the one obtained using computer search for 4-PSK signal set by Koike-Akino et al., when specialized for $M=4.$ Simulation results show that the proposed scheme performs better than the conventional exclusive-OR (XOR) network coding and in some cases outperforms the scheme proposed by Koike-Akino 收起
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A Rayleigh fading spatially correlated broadcast setting with $M = 2$ antennas at the transmitter and two users (each with a single antenna) is considered. It is assumed that the users have perfect channel information about their ...
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A Rayleigh fading spatially correlated broadcast setting with $M = 2$ antennas at the transmitter and two users (each with a single antenna) is considered. It is assumed that the users have perfect channel information about their links, whereas the transmitter has only statistical information of each user's link (covariance matrix of the vector channel). A low-complexity linear beamforming strategy that allocates equal power and one spatial eigenmode to each user is employed at the transmitter. Beamforming vectors on the Grassmann manifold that depend only on statistical information are to be designed at the transmitter to maximize the ergodic sum-rate delivered to the two users. Toward this goal, the beamforming vectors are first fixed and a closed-form expression is obtained for the ergodic sum-rate in terms of the covariance matrices of the links. This expression is nonconvex in the beamforming vectors ensuring that the classical Lagrange multiplier technique is not applicable. Despite this difficulty, the optimal solution to this problem is shown to be the same as the solution to the maximization of an appropriately defined average signal-to-interference and noise ratio metric for each user. This solution is the dominant generalized eigenvector of a pair of positive-definite matrices where the first matrix is the covariance matrix of the forward link and the second is an appropriately designed “effective” interference covariance matrix. In this sense, our work is a generalization of optimal signalling along the dominant eigenmode of the transmit covariance matrix in the single-user case. Finally, the ergodic sum-rate for the general broadcast setting with $M$ antennas at the transmitter and $M$-users (each with a single antenna) is obtained in term- of the covariance matrices of the links and the beamforming vectors.
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Although the North American power grid has been recognized as the most important engineering achievement of the 20th century, the modern power grid faces major challenges [87]. Increasingly complex interconnections even at the con...
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Although the North American power grid has been recognized as the most important engineering achievement of the 20th century, the modern power grid faces major challenges [87]. Increasingly complex interconnections even at the continent size render prevention of the rare yet catastrophic cascade failures a strenuous concern. Environmental incentives require carefully revisiting how electrical power is generated, transmitted, and consumed, with particular emphasis on the integration of renewable energy resources. Pervasive use of digital technology in grid operation demands resiliency against physical and cyberattacks on the power infrastructure. Enhancing grid efficiency without compromising stability and quality in the face of deregulation is imperative. Soliciting consumer participation and exploring new business opportunities facilitated by the intelligent grid infrastructure hold a great economic potential.
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This paper presents a game-theoretic approach to node activation control in parameter estimation via diffusion least mean squares (LMS). Nodes cooperate by exchanging estimates over links characterized by the connectivity graph of...
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This paper presents a game-theoretic approach to node activation control in parameter estimation via diffusion least mean squares (LMS). Nodes cooperate by exchanging estimates over links characterized by the connectivity graph of the network. The energy-aware activation control is formulated as a noncooperative repeated game where nodes autonomously decide when to activate based on a utility function that captures the trade-off between individual node's contribution and energy expenditure. The diffusion LMS stochastic approximation is combined with a game-theoretic learning algorithm such that the overall energy-aware diffusion LMS has two timescales: the fast timescale corresponds to the game-theoretic activation mechanism, whereby nodes distributively learn their optimal activation strategies, whereas the slow timescale corresponds to the diffusion LMS. The convergence analysis shows that the parameter estimates weakly converge to the true parameter across the network, yet the global activation behavior along the way tracks the set of correlated equilibria of the underlying activation control game.
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This paper presents one perspective on recent developments related to software engineering in the industrial automation sector that spans from manufacturing factory automation to process control systems and energy automation syste...
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This paper presents one perspective on recent developments related to software engineering in the industrial automation sector that spans from manufacturing factory automation to process control systems and energy automation systems. The survey's methodology is based on the classic SWEBOK reference document that comprehensively defines the taxonomy of software engineering domain. This is mixed with classic automation artefacts, such as the set of the most influential international standards and dominating industrial practices. The survey focuses mainly on research publications which are believed to be representative of advanced industrial practices as well.
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Convexity properties of error rates of a class of decoders, including the maximum-likelihood/min-distance one as a special case, are studied for arbitrary constellations, bit mapping, and coding. Earlier results obtained for the a...
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Convexity properties of error rates of a class of decoders, including the maximum-likelihood/min-distance one as a special case, are studied for arbitrary constellations, bit mapping, and coding. Earlier results obtained for the additive white Gaussian noise channel are extended to a wide class of noise densities, including unimodal and spherically invariant noise. Under these broad conditions, symbol and bit error rates are shown to be convex functions of the signal-to-noise ratio (SNR) in the high-SNR regime with an explicitly determined threshold, which depends only on the constellation dimensionality and minimum distance, thus enabling an application of the powerful tools of convex optimization to such digital communication systems in a rigorous way. It is the decreasing nature of the noise power density around the decision region boundaries that ensures the convexity of symbol error rates in the general case. The known high/low-SNR bounds of the convexity/concavity regions are tightened and no further improvement is shown to be possible in general. The high-SNR bound fits closely into the channel coding theorem: all codes, including capacity-achieving ones, whose decision regions include the hardened noise spheres (from the noise sphere hardening argument in the channel coding theorem), satisfy this high-SNR requirement and thus has convex error rates in both SNR and noise power. We conjecture that all capacity-achieving codes have convex error rates. Convexity properties in signal amplitude and noise power are also investigated. Some applications of the results are discussed. In particular, it is shown that fading is convexity-preserving and is never good in low dimensions under spherically invariant noise, which may also include any linear diversity combining.
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Although the behavior of dielectric materials has been known since 1939 when R.D. Richtmyer showed that unmetalized dielectrics can operate as microwave resonators [1], it was only in the 1970s when real breakthroughs occurred in ...
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Although the behavior of dielectric materials has been known since 1939 when R.D. Richtmyer showed that unmetalized dielectrics can operate as microwave resonators [1], it was only in the 1970s when real breakthroughs occurred in ceramic technology, and low loss and temperature stable ceramics were developed. In 1975 the first practical dielectric resonator (DR) loaded microwave filter was reported at the IEEE MTT-S International Microwave Symposium [2]. Significant advancements in ceramic technology and the progress in satellite and mobile communications in the 1990s revived interest in DR applications for a wide variety of microwave components. A number of new materials such as zirconium-tin titanate, ZST ((Zr ? Sn)TiO4), barium zinc tantalate, BZT (Ba(Zn,Ta)O3), and barium magnesium tantalate, BMT (Ba(Mg,Ta)O3), with high-dielectric constant, high-quality factor and low-temperature coefficient were developed [3]. These new materials, along with the application of rigorous full-wave modeling and analysis methods, fueled the development of new DR filter configurations such as single and dual mode filters with elliptic transfer function. Today, DR filters and output multiplexers (OMUXs) are widely used in satellite communications because of their superior characteristics, such as smaller size, better temperature stability, and higher unloaded Q compared to conventional cavity-based OMUXs. A number of papers have been published on DR filters and OMUXs [4]?[6], [8], [9], but no comprehensive paper on the design of a DR-based OMUX has been reported. The large interchannel interaction (due to contiguity of channel filter frequencies, performance of one channel filter is effected by the presence of other channel filters), wide spurious free frequency band, and stringent in-band and out-of-band (OOB) specifications (such as large near band and far band rejections, small passband group delay and flatness), along with the requirement of high Q, low frequency drift with tem- erature, and high power handling capability, make the design of DR OMUXs extremely challenging. This article presents a practical approach to the design of C-band high power OMUXs based on single mode DR filters for space application (Figures 1 and 2), making extensive use of present day simulation capabilities. All the major steps involved in the design of a DR OMUX such as the concept of a singly terminated filter, conversion of doubly terminated filters to singly terminated filters using a series L-C circuit, modeling of the DR OMUX in a circuit simulator incorporating full wave effects, and the OMUX optimization sequence are explained in detail. A successful design of the DR filter is crucial to the eventual design of the DR OMUX.
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Real-time heuristic search algorithms satisfy a constant bound on the amount of planning per action, independent of the problem size. These algorithms are useful when the amount of time or memory resources are limited, or a rapid ...
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Real-time heuristic search algorithms satisfy a constant bound on the amount of planning per action, independent of the problem size. These algorithms are useful when the amount of time or memory resources are limited, or a rapid response time is required. An example of such a problem is pathfinding in video games where numerous units may be simultaneously required to react promptly to a player's commands. Classic real-time heuristic search algorithms cannot be deployed due to their obvious state revisitation (“scrubbing”). Recent algorithms have improved performance by using a database of precomputed subgoals. However, a common issue is that the precomputation time can be large, and there is no guarantee that the precomputed data adequately cover the search space. In this paper, we present a new approach that guarantees coverage by abstracting the search space, using the same algorithm that performs the real-time search. It reduces the precomputation time via the use of dynamic programming. The new approach eliminates the learning component and the resultant “scrubbing.” Experimental results on maps of tens of millions of grid cells from Counter-Strike: Source and benchmark maps from Dragon Age: Origins show significantly faster execution times and improved optimality results compared to previous real-time algorithms.
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This work provides an overview of a parallel, high-order, error-controllable framework for solving large-scale scattering problems in electromagnetics, as well as open problems pertinent to such solutions. The method is based on t...
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This work provides an overview of a parallel, high-order, error-controllable framework for solving large-scale scattering problems in electromagnetics, as well as open problems pertinent to such solutions. The method is based on the higher-order locally corrected Nyström (LCN) discretization of the combined-field integral equation (CFIE), accelerated with the error-controlled Multi-Level Fast Multipole Algorithm (MLFMA). Mechanisms for controlling the accuracy of calculations are discussed, including geometric representation, stages of the locally corrected Nyström method, and the MLFMA. Also presented are the key attributes of parallelization for the developed numerical framework. Numerical results validate the proposed numerical scheme by demonstrating higher-order error convergence for smooth scatterers. For the problem of scattering from a sphere, the developed numerical solution is shown to have the ability to produce a solution with a maximum relative error of the order 10−9. Open-ended problems, such as treatment of general scatterers with geometric singularities, construction of well-conditioned operators, and current challenges in development of fast iterative and direct algorithms, are also discussed.
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Switched reluctance machines (SRMs) suffer from ultra-low-frequency torque ripple in single pulse mode. This ripple is the result of an imbalance in phase currents, when multiphase excitation occurs. This paper investigates the or...
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Switched reluctance machines (SRMs) suffer from ultra-low-frequency torque ripple in single pulse mode. This ripple is the result of an imbalance in phase currents, when multiphase excitation occurs. This paper investigates the origin of this imbalance and identifies the imbalanced phase. Excitation shifting strategy, which delays excitation of the imbalanced phase, is then proposed. The delay angle adjusts current amplitude in the imbalanced phase to attain a perfect balance between all phases. The excitation shifting strategy is a general solution, which is applicable to both three-phase and four-phase machines. In addition, the proposed method can be implemented by a much simpler drive structure, when compared to the existing balancing methods. Hardware measurements are provided to verify superior performance of the proposed current balancing technique.
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