arXiv subjects

David Smith

Publications and source records attributed to David Smith.

At least 73 records · Page 4Linked to original sources

arXiv2018

Robust Wireless Body Area Networks Coexistence: A Game Theoretic Approach to Time-Division MAC

The enabling of wireless body area networks (WBANs) coexistence by radio interference mitigation is very important due to a rapid growth in potential users, and a lack of a central coordinator among WBANs that are closely located. In this paper, we propose a TDMA based MAC layer Scheme, with a back-off mechanism that reduces packet collision probability; and estimate performance using a Markov chain model. Based on the MAC layer scheme, a novel non-cooperative game is proposed to jointly adjust sensor node's transmit power and rate. In comparison with the state-of-art, simulation that includes empirical data shows that the proposed approach leads to higher throughput and longer node lifespan as WBAN wearers dynamically move into each other's vicinity. Moreover, by adaptively tuning contention windows size an alternative game is developed, which significantly reduces the latency. Both proposed games provide robust transmission under strong inter-WBAN interferences, but are demonstrated to be applicable to different scenarios. The uniqueness and existence of Nash Equilibrium (NE), as well as close-to-optimum social efficiency, is also proven for both games.

eess.SP↗

arXiv2018

Fairness in Multiterminal Data Compression: A Splitting Method for The Egalitarian Solution

This paper proposes a novel splitting (SPLIT) algorithm to achieve fairness in the multiterminal lossless data compression problem. It finds the egalitarian solution in the Slepian-Wolf region and completes in strongly polynomial time. We show that the SPLIT algorithm adaptively updates the source coding rates to the optimal solution, while recursively splitting the terminal set, enabling parallel and distributed computation. The result of an experiment demonstrates a significant reduction in computation time by the parallel implementation when the number of terminals becomes large. The achieved egalitarian solution is also shown to be superior to the Shapley value in distributed networks, e.g., wireless sensor networks, in that it best balances the nodes' energy consumption and is far less computationally complex to obtain.

cs.IT↗

arXiv2018

Distributed Data Compression in Sensor Clusters: A Maximum Independent Flow Approach

Let a cluster (network) of sensors be connected by the communication links, each link having a capacity upper bound. Each sensor observes a discrete random variable in private and one sensor serves as a cluster header or sink. Here, we formulate the problem of how to let the sensors encode their observations such that the direction of compressed data is a feasible flow towards the sink. We demonstrate that this problem can be solved by an existing maximum independent flow (MIF) algorithm in polynomial time. Further, we reveal that this algorithm in fact determines an optimal solution by recursively pushing the remaining randomness in the sources via unsaturated communication links towards the sink. We then show that the MIF algorithm can be implemented in a distributed manner. For those networks with integral communication capacities, we propose an integral MIF algorithm which completes much faster than MIF. Finally, we point out that the nature of the data compression problem in a sensor cluster is to seek the maximum independent information flow in the intersection of two submodular polyhedra, which can be further utilized to improve the MIF algorithm in the future.

cs.IT↗

arXiv2018

Fairness in Multiterminal Data Compression: Decomposition of Shapley Value

We consider the problem of how to determine a fair source coding rate allocation method for the lossless data compression problem in multiterminal networks, e.g, the wireless sensor network where there are a large number of sources to be encoded. We model this problem by a game-theoretic approach and present a decomposition method for obtaining the Shapley value, a fair source coding rate vector in the Slepian-Wolf achievable region. We formulate a coalitional game model where the entropy function quantifies the cost incurred due to the source coding rates in each coalition. In the typical case for which the game is decomposable, we show that the Shapley value can be obtained separately for each subgame. The complexity of this decomposition method is determined by the maximum size of subgames, which is strictly smaller than the total number of sources and contributes to a considerable reduction in computational complexity. Experiments demonstrate large complexity reduction when the number of sources becomes large.

cs.IT↗

arXiv2017

U-BeAS: A Stackelberg Game for Device-to-Device Communications

User-behavior-aware communications will be a key feature of future generation cellular networks, so user experience is enhanced with greater benefit to users. In this paper, a user-behavior-aware Stackelberg (U-BeAS) game for device-to-device (D2D) communications overlaying cellular communications is proposed. Our proposed game provides an optimal trade-off between minimizing transmit power and maximizing packet delivery ratio (PDR), with respect to D2D user-behavior for all D2D pairs. The Stackelberg leader, base station (BS), selects its satisfaction with the social welfare of the D2D followers by considering the reaction of the followers to the price it charges. All followers (D2D pairs) select transmit power so as to guarantee a desired quality-of-experience (QoE), where each follower enacts one of three possible behaviors: (i) casual; (ii) intermediate; or (iii) serious. Analysis shows that there exists a sub-game perfect Stackelberg Equilibrium across all players. Analysis and simulation demonstrates that the BS leader rapidly converges to an optimal satisfaction while guaranteeing social welfare across D2D users, and all D2D followers then rapidly converge to a Pareto-efficient outcome with respect to transmit power and PDR.

cs.NI↗

arXiv2017

Polarizability Extraction for Waveguide-Fed Metasurfaces

We consider the design and modeling of metasurfaces that couple energy from guided waves to propagating wavefronts. This is a first step towards a comprehensive, multiscale modeling platform for metasurface antennas-large arrays of metamaterial elements embedded in a waveguide structure that radiates into free-space--in which the detailed electromagnetic responses of metamaterial elements are replaced by polarizable dipoles. We present two methods to extract the effective polarizability of a metamaterial element embedded in a one- or two-dimensional waveguide. The first method invokes surface equivalence principles, averaging over the effective surface currents and charges within an element to obtain the effective dipole moments; the second method is based on computing the coefficients of the scattered waves within the waveguide, from which the effective polarizability can be inferred. We demonstrate these methods on several variants of waveguide-fed metasurface elements, finding excellent agreement between the two, as well as with analytical expressions derived for irises with simpler geometries. Extending the polarizability extraction technique to higher order multipoles, we confirm the validity of the dipole approximation for common metamaterial elements. With the effective polarizabilities of the metamaterial elements accurately determined, the radiated fields generated by a metasurface antenna (inside and outside the antenna) can be found self-consistently by including the interactions between polarizable dipoles. The dipole description provides an alternative language and computational framework for engineering metasurface antennas, holograms, lenses, beam-forming arrays, and other electrically large, waveguide-fed metasurface structures.

physics.app-ph↗

arXiv2017

Stability conditions, $τ$-tilting Theory and Maximal Green Sequences

Extending the notion of maximal green sequences to an abelian category, we characterize the stability functions, as defined by Rudakov, that induce a maximal green sequence in an abelian length category. Furthermore, we use $τ$-tilting theory to give a description of the wall and chamber structure of any finite dimensional algebra. Finally we introduce the notion of green paths in the wall and chamber structure of an algebra and show that green paths serve as geometrical generalization of maximal green sequences in this context.

math.RT↗

arXiv2017

Computational Microwave Imaging Using 3D Printed Conductive Polymer Frequency-Diverse Metasurface Antennas

A frequency-diverse computational imaging system synthesized using three-dimensional (3D) printed frequency-diverse metasurface antennas is demonstrated. The 3D fabrication of the antennas is achieved using a combination of PolyLactic Acid (PLA) polymer material and conductive polymer material (Electrifi), circumventing the requirement for expensive and time-consuming conventional fabrication techniques, such as machine milling, photolithography and laser-etching. Using the 3D printed frequency- diverse metasurface antennas, a composite aperture is designed and simulated for imaging in the K-band frequency regime (17.5-26.5 GHz). The frequency-diverse system is capable of imaging by means of a simple frequency-sweep in an-all electronic manner, avoiding mechanical scanning and active circuit components. Using the synthesized system, microwave imaging of objects is achieved at the diffraction limit. It is also demonstrated that the conductivity of the Electrifi polymer material significantly affects the performance of the 3D printed antennas and therefore is a critical factor governing the fidelity of the reconstructed images.

physics.ins-det↗

arXiv2016

A numerical implementation of the unified Fokas transform for evolution problems on a finite interval

We present the numerical solution of two-point boundary value problems for a third order linear PDE, representing a linear evolution in one space dimension. The difficulty of this problem is in the numerical imposition of the boundary conditions, and to our knowledge, no such computations exist. Instead of computing the evolution numerically, we evaluate the solution representation formula obtained by the unified transform of Fokas. This representation involves complex line integrals, but in order to evaluate these integrals numerically, it is necessary to deform the integration contours using appropriate deformation mappings. We formulate a strategy to implement effectively this deformation, which allows us to obtain accurate numerical results.

math.NA↗

arXiv2016

Management of Renewable Energy for A Shared Facility Controller in Smart Grid

This paper proposes an energy management scheme to maximize the use of solar energy in the smart grid. In this context, a shared facility controller (SFC) with a number of solar photovoltaic (PV) panels in a smart community is considered that has the capability to schedule the generated energy for consumption and trade to other entities. Particularly, a mechanism is designed for the SFC to decide on the energy surplus, if there is any, that it can use to charge its battery and sell to the households and the grid based on the offered prices. In this regard, a hierarchical energy management scheme is proposed with a view to reduce the total operational cost to the SFC. The concept of a virtual cost (VC) is introduced that aids the SFC to estimate its future operational cost based on some available current information. The energy management is conducted for three different cases and the optimal cost to the SFC is determined for each case via the theory of maxima and minima. A real-time algorithm is proposed to reach the optimal cost for all cases and some numerical examples are provided to demonstrate the beneficial properties of the proposed scheme.

eess.SY↗

arXiv2016

Radio emissions from double RHESSI TGFs

A detailed analysis of Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) terrestrial gamma ray flashes (TGFs) is performed in association with World Wide Lightning Location Network (WWLLN) sources and very low frequency (VLF) sferics recorded at Duke University. RHESSI clock offset is evaluated and found to experience changes on the 5 August 2005 and 21 October 2013, based on the analysis of TGF-WWLLN matches. The clock offsets were found for all three periods of observations with standard deviations less than 100 μs. This result opens the possibility for the precise comparative analyses of RHESSI TGFs with the other types of data (WWLLN, radio measurements, etc.) In case of multiple-peak TGFs, WWLLN detections are observed to be simultaneous with the last TGF peak for all 16 cases of multipeak RHESSI TGFs simultaneous with WWLLN sources. VLF magnetic field sferics were recorded for two of these 16 events at Duke University. These radio measurements also attribute VLF sferics to the second peak of the double TGFs, exhibiting no detectable radio emission during the first TGF peak. Possible scenarios explaining these observations are proposed. Double (multipeak) TGFs could help to distinguish between the VLF radio emission radiated by the recoil currents in the +IC leader channel and the VLF emission from the TGF producing electrons.

physics.space-ph↗

arXiv2016

Lifted Region-Based Belief Propagation

Due to the intractable nature of exact lifted inference, research has recently focused on the discovery of accurate and efficient approximate inference algorithms in Statistical Relational Models (SRMs), such as Lifted First-Order Belief Propagation. FOBP simulates propositional factor graph belief propagation without constructing the ground factor graph by identifying and lifting over redundant message computations. In this work, we propose a generalization of FOBP called Lifted Generalized Belief Propagation, in which both the region structure and the message structure can be lifted. This approach allows more of the inference to be performed intra-region (in the exact inference step of BP), thereby allowing simulation of propagation on a graph structure with larger region scopes and fewer edges, while still maintaining tractability. We demonstrate that the resulting algorithm converges in fewer iterations to more accurate results on a variety of SRMs.

cs.AI↗

arXiv2016

Cooperative communications for sleep monitoring in wireless body area networks

This paper investigates the performance of cooperative receive diversity, for the wireless body area network (WBAN) radio channel, compliant with the IEEE 802.15.6 Standard, in the case of monitoring a sleeping person. Extensive WBAN measurements near the 2.4 GHz ISM band were used. Up to 7 dB and 20% improvement for two-hop communications with the use of relays are empirically demonstrated with respect to outage probability and outage duration, with 3-branch cooperative selection combining and 3-branch cooperative switch-and-examine combining.

cs.OH↗

arXiv2015

Energy Storage Sharing in Smart Grid: A Modified Auction Based Approach

This paper studies the solution of joint energy storage (ES) ownership sharing between multiple shared facility controllers (SFCs) and those dwelling in a residential community. The main objective is to enable the residential units (RUs) to decide on the fraction of their ES capacity that they want to share with the SFCs of the community in order to assist them storing electricity, e.g., for fulfilling the demand of various shared facilities. To this end, a modified auction-based mechanism is designed that captures the interaction between the SFCs and the RUs so as to determine the auction price and the allocation of ES shared by the RUs that governs the proposed joint ES ownership. The fraction of the capacity of the storage that each RU decides to put into the market to share with the SFCs and the auction price are determined by a noncooperative Stackelberg game formulated between the RUs and the auctioneer. It is shown that the proposed auction possesses the incentive compatibility and the individual rationality properties, which are leveraged via the unique Stackelberg equilibrium (SE) solution of the game. Numerical experiments are provided to confirm the effectiveness of the proposed scheme.

eess.SY↗

arXiv2015

Infinite friezes and triangulations of the strip

The infinite friezes of positive integers were introduced by Tschabold as a variation of the classical Conway-Coxeter frieze patterns. These infinite friezes were further shown be to realizable via triangulations of the infinite strip by Baur, Parsons and Tschabold. In this paper, we show that the construction of Baur, Parsons and Tschabold can be slightly adapted in order to obtain a bijection between the infinite friezes and the so-called admissible triangulations of the infinite strip with no special marked points on the upper boundary. As a consequence, we obtain that the infinite friezes with enough ones are in bijection with the admissible triangulations of the infinity-gon.

math.CO↗

arXiv2015

Price discrimination for energy trading in smart grid: A game theoretic approach

Pricing schemes are an important smart grid feature to affect typical energy usage behavior of energy users (EUs). However, most existing schemes use the assumption that a buyer pays the same price per unit of energy to all suppliers at any particular time when energy is bought. By contrast, here a discriminate pricing technique using game theory is studied. A cake cutting game is investigated, in which participating EUs in a smart community decide on the price per unit of energy to charge a shared facility controller (SFC) in order to sell surplus energy. The focus is to study fairness criteria to maximize sum benefits to EUs and ensure an envy-free energy trading market. A benefit function is designed that leverages generation of discriminate pricing by each EU, according to the amount of surplus energy that an EU trades with the SFC and the EU's sensitivity to price. It is shown that the game possesses a socially optimal, and hence also Pareto optimal, solution. Further, an algorithm that can be implemented by each EU in a distributed manner to reach the optimal solution is proposed. Numerical case studies are given that demonstrate beneficial properties of the scheme.

eess.SY↗

arXiv2015

Cost Minimization of Charging Stations with Photovoltaics: An Approach with EV Classification

This paper proposes a novel electric vehicle (EV) classification scheme for a photovoltaic (PV) powered EV charging station (CS) that reduces the effect of intermittency of electricity supply as well as reducing the cost of energy trading of the CS. Since not all EV drivers would like to be environmentally friendly, all vehicles in the CS are divided into three categories: 1) premium, 2) conservative, and 3) green, according to their charging behavior. Premium and conservative EVs are considered to be interested only in charging their batteries, with noticeably higher rate of charging for premium EVs. Green vehicles are more environmentally friendly, and thus assist the CS to reduce its cost of energy trading by allowing the CS to use their batteries as distributed storage. A different charging scheme is proposed for each type of EV, which is adopted by the CS to encourage more EVs to be green. A basic mixed integer programming (MIP) technique is used to facilitate the proposed classification scheme. It is shown that the uncertainty in PV generation can be effectively compensated, along with minimization of total cost of energy trading to the CS, by consolidating more green EVs. Real solar and pricing data are used for performance analysis of the system. It is demonstrated that the total cost to the CS reduces considerably as the percentage of green vehicles increases, and also that the contributions of green EVs in winter are greater than those in summer.

eess.SY↗

arXiv2015

Filtering subcategories of modules of an artinian algebra

Let $A$ be an artinian algebra, and let $\mathcal{C}$ be a subcategory of mod$A$ that is closed under extensions. When $\mathcal{C}$ is closed under kernels of epimorphisms (or closed under cokernels of monomorphisms), we describe the smallest class of modules that filters $\mathcal{C}$. As a consequence, we obtain sufficient conditions for the finitistic dimension of an algebra over a field to be finite. We also apply our results to the torsion pairs. In particular, when a torsion pair is induced by a tilting module, we show that the smallest classes of modules that filter the torsion and torsion-free classes are completely compatible with the quasi-equivalences of Brenner and Butler.

math.RT↗