Interactive Joint Transfer of Energy and Information

In some communication networks, such as passive RFID systems, the energy used to transfer information between a sender and a recipient can be reused for successive communication tasks. In fact, from known results in physics, any system that exchanges information via the transfer of given physical resources, such as radio waves, particles and qubits, can conceivably reuse, at least part, of the received resources. This paper aims at illustrating some of the new challenges that arise in the design of communication networks in which the signals exchanged by the nodes carry both information and energy. To this end, a baseline two-way communication system is considered in which two nodes communicate in an interactive fashion. In the system, a node can either send an "on" symbol (or "1"), which costs one unit of energy, or an "off" signal (or "0"), which does not require any energy expenditure. Upon reception of a "1" signal, the recipient node "harvests", with some probability, the energy contained in the signal and stores it for future communication tasks. Inner and outer bounds on the achievable rates are derived. Numerical results demonstrate the effectiveness of the proposed strategies and illustrate some key design insights.Comment: 29 pages, 11 figures, Submitted in IEEE Transactions on Communications. arXiv admin note: substantial text overlap with arXiv:1204.192

Modulation Classification for MIMO-OFDM Signals via Approximate Bayesian Inference

The problem of modulation classification for a multiple-antenna (MIMO) system employing orthogonal frequency division multiplexing (OFDM) is investigated under the assumption of unknown frequency-selective fading channels and signal-to-noise ratio (SNR). The classification problem is formulated as a Bayesian inference task, and solutions are proposed based on Gibbs sampling and mean field variational inference. The proposed methods rely on a selection of the prior distributions that adopts a latent Dirichlet model for the modulation type and on the Bayesian network formalism. The Gibbs sampling method converges to the optimal Bayesian solution and, using numerical results, its accuracy is seen to improve for small sample sizes when switching to the mean field variational inference technique after a number of iterations. The speed of convergence is shown to improve via annealing and random restarts. While most of the literature on modulation classification assume that the channels are flat fading, that the number of receive antennas is no less than that of transmit antennas, and that a large number of observed data symbols are available, the proposed methods perform well under more general conditions. Finally, the proposed Bayesian methods are demonstrated to improve over existing non-Bayesian approaches based on independent component analysis and on prior Bayesian methods based on the `superconstellation' method.Comment: To be appear in IEEE Trans. Veh. Technolog

Hypergraph-Based Analysis of Clustered Cooperative Beamforming with Application to Edge Caching

The evaluation of the performance of clustered cooperative beamforming in cellular networks generally requires the solution of complex non-convex optimization problems. In this letter, a framework based on a hypergraph formalism is proposed that enables the derivation of a performance characterization of clustered cooperative beamforming in terms of per-user degrees of freedom (DoF) via the efficient solution of a coloring problem. An emerging scenario in which clusters of cooperative base stations (BSs) arise is given by cellular networks with edge caching. In fact, clusters of BSs that share the same requested files can jointly beamform the corresponding encoded signals. Based on this observation, the proposed framework is applied to obtain quantitative insights into the optimal use of cache and backhaul resources in cellular systems with edge caching. Numerical examples are provided to illustrate the merits of the proposed framework.Comment: 10 pages, 5 figures, Submitte

Cylindrical thin-shell wormholes and energy conditions

We prove the impossibility of cylindrical thin-shell wormholes supported by matter satisfying the energy conditions everywhere, under reasonable assumptions about the asymptotic behaviour of the - in general different - metrics at each side of the throat. In particular, we reproduce for singular sources previous results corresponding to flat and conical asymptotics, and extend them to a more general asymptotic behaviour. Besides, we establish necessary conditions for the possibility of non exotic cylindrical thin-shell wormholes.Comment: 9 pages; slightly improved version of the article accepted in Int. J. Mod. Phys.

Evidence of a rudimentary colon in Leucoraja erinacea

During the transition of animals from water onto land, the colon is believed to have evolved as an essential water-absorbing organ in terrestrial vertebrates to prevent desiccation. The class Chondrichthyes, comprised of sharks, rays, and skates, are isotonic to their marine environment, and thus do not require a functional colon. The Chondrichthyes are an excellent organism for developmental and physiological studies in evolutionary context because they have undergone little evolutionary change since their appearance 450 million years ago. Previous histochemical studies demonstrate potential water absorbing properties in the digestive tract of the little skate, Leucoraja erinacea (Theodosiou et al., 2007). To further examine the ability of the skate spiral intestine to absorb water, I examined the expression of the water-specific channel protein, aquaporin 4. Aquaporin 4 is expressed in the skate digestive tract with high levels in the epithelium of the distal spiral intestine. In addition, I measured water uptake across the membrane of the spiral intestine directly using physiology experiments. The distal spiral intestine absorbs water at a greater rate than the stomach and proximal intestine, and water uptake was not pressure dependent. Currently, we are examining the conservation of embryonic colon patterning genes by studying the role of Hoxd13 in developing chick and skate embryos. With this study, we hope to understand the origin of the colon in terrestrial vertebrates

One for All: Employing People with Disabilities

One for All: Employing People with Disabilities Krista Simeone Faculty Sponsor: Susan Roush, Physical Therapy The creators of our constitution believed that all men are endowed with certain unalienable rights, one of which being the Pursuit of Happiness. We all measure happiness in our own lives differently, and many of us find happiness in what we do each day. President Theodore Roosevelt once said “Far and away the best prize that life offers is the chance to work hard at work worth doing.” Everyone should have the privilege of serving a purpose within their society, however, people with disabilities often find themselves overlooked and under-represented within the workforce due to misconceptions, stereotypes, and stigmas we have attached to what it means to be “disabled.” After graduation, I plan to become involved in public policy relating to disability issues by moving to Washington, DC and enrolling in a vocational rehabilitation counseling graduate program. In order to accomplish these goals, I need to have a deep understanding of what the employment situation looks like for people with disabilities, the programs in place to facilitate employment, and what still needs to be addressed. In light of this, my Senior Honors Project was an in-depth look at what disabled Americans face when attempting to enter the workforce, and what is being done to help them. Furthermore, I explored disability employment policy in two non-U.S. countries: China and the United Kingdom. While these countries are different from the United States (and in China’s case, vastly different), they offer something unique in the realm of employment efforts for people with disabilities. Furthermore, my presentation includes several interviews with disabled individuals from all walks of life describing their personal employment experiences, a summary of the events that took place at an informational disability employment workshop I coordinated at the University of Rhode Island on April 14, 2011, and my own public policy proposal regarding disability awareness targeting American employers. America works better when everyone is working, and my project invites the URI community to learn more about what is being done to ensure that people with disabilities are given every opportunity to gain employment and succeed as a worker. Keywords: disabled, employment, policy, America, UK, Chin

Joint Interference Alignment and Bi-Directional Scheduling for MIMO Two-Way Multi-Link Networks

By means of the emerging technique of dynamic Time Division Duplex (TDD), the switching point between uplink and downlink transmissions can be optimized across a multi-cell system in order to reduce the impact of inter-cell interference. It has been recently recognized that optimizing also the order in which uplink and downlink transmissions, or more generally the two directions of a two-way link, are scheduled can lead to significant benefits in terms of interference reduction. In this work, the optimization of bi-directional scheduling is investigated in conjunction with the design of linear precoding and equalization for a general multi-link MIMO two-way system. A simple algorithm is proposed that performs the joint optimization of the ordering of the transmissions in the two directions of the two-way links and of the linear transceivers, with the aim of minimizing the interference leakage power. Numerical results demonstrate the effectiveness of the proposed strategy.Comment: To be presented at ICC 2015, 6 pages, 7 figure