Using combinatorial designs to construct partial concentrators

Partial concentrators have been shown to be useful in the construction of various types of interconnecting networks. It is shown how a large class of combinatorial designs, which are well studied in the literature, can be used to construct partial concentrators and thus provide a direct link between the fields of combinatorial designs and switching networks. A construction efficiency factor called the cost ratio is introduced, and some lower bounds on the capacity of partial concentrators having certain characteristics are established. It is shown how to use various combinatorial designs to construct partial concentrators having these same characteristics and corresponding capacities     

Rondine® PV concentrators: Field results and developments

In this work the experimental results of a new PV concentrator (named Rondine®) are presented. This concentrating module has a medium concentration level (∼25×) and employs silicon solar cells. The tests have been carried out in Italy and the energy production of a prototype module is compared with that produced from a tracking flat plate crystalline PV panel. The non‐imaging optics of the concentrator allows for larger angular acceptance with respect to many solar concentrators, giving us the possibility to employ trackers for standard PV modules. The first results of complete systems of 3·9 and 4·8 kW of peak power installed in summer 2008 are presented here. Copyright © 2009 John Wiley & Sons, Ltd.     

Lightpath concentrators for all-optical networks

In some deployments of all-optical networks, it is necessary to concentrate the lightpaths from some fibers to fewer fibers. An N/spl times/M lightpath concentrator is an optical component for this purpose, and it concentrates the lightpaths from N incoming fibers to M outgoing fibers. In this paper, three designs of N/spl times/M lightpath concentrators are proposed. The first design is a generalization of optical crossconnects, and it requires M/spl times/M optical switches. The second design incorporates the concept of partial concentration so that it requires only m/spl times/m optical switches (where m相似文献   

Asymptotic results for maximum likelihood estimation with an arrayof sensors

In many cases, the maximum likelihood (ML) estimator is consistent and asymptotically normal with covariance equal to the inverse of the Fisher's information matrix. It does not follow, though, that the covariance of the ML estimator approaches the Cramer-Rao lower bound as the sample size increases. However, it is possible to draw such a conclusion for the adaptive array problem in which direction of arrival and signal magnitude are being estimated. Proofs of w-asymptotic efficiency, which comes with a convergence-of-moments condition, and strong consistency (almost-sure convergence) of the ML estimator are given. Strong consistency is also proved for a popular quasi-ML estimator     

Asymptotic results for decentralized detection in power constrained wireless sensor networks

In this paper, we study a binary decentralized detection problem in which a set of sensor nodes provides partial information about the state of nature to a fusion center. Sensor nodes have access to conditionally independent and identically distributed observations, given the state of nature, and transmit their data over a wireless channel. Upon reception of the information, the fusion center attempts to accurately reconstruct the state of nature. Specifically, we extend existing asymptotic results about large sensor networks to the case where the network is subject to a joint power constraint, and where the communication channel from each sensor node to the fusion center is corrupted by additive noise. Large deviation theory is used to show that having identical sensor nodes, i.e., each node using the same transmission scheme, is asymptotically optimal. Furthermore, a performance metric by which sensor node candidates can be compared is established. We supplement the theory with examples to illustrate how the results derived in this paper apply to the design of practical sensing systems.     

Operating regimes for second generation luminescent solar concentrators

In this paper, we introduce the concept of first and second generation luminescent solar concentrators. Traditional, first generation devices are characterised by their randomly oriented molecules that absorb sunlight and emit luminescence isotropically. By applying detailed balance to the absorbed and emitted photon fluxes we derive the Shockley–Queisser limit for these devices. It is found that they have inherently low efficiency due to optical losses (the well known reabsorption problem) and also that device performance is strongly affected by the areal ratio between the top and edge surfaces. This latter property makes it very difficult to achieve significant cost reductions because as the edge area is reduced (to lessen the amount of expensive photovoltaic material required for conversion), the efficiency of the system diminishes. First generation concentrators have now approached the fundamental limits which we predict here, thus to achieve a stand‐alone luminescent concentrator that enables significant cost reductions, second generation approaches are now needed. New, second generation devices are characterised by either directional emitters or photonic filters which enhance the waveguiding mechanism, allowing high efficiency and large sizes to be achieved simultaneously. Here we define the fundamental operating regime in which second generation technology must reach to surpass the limit of first generation devices. Copyright © 2011 John Wiley & Sons, Ltd.     

Quantum dot solar concentrators

The luminescent properties of core-shell quantum dots are being exploited in an unconventional solar concentrator, which promises to reduce the cost of photovoltaic electricity. Luminescent solar collectors have advantages over geometric concentrators in that tracking is unnecessary and both direct and diffuse radiation can be collected. However, development has been limited by the performance of luminescent dyes. We present experimental and theoretical results with a novel concentrator in which the dyes are replaced by quantum dots. We have developed a self-consistent thermodynamic model for planar concentrators and find that this three-dimensional flux model shows excellent agreement with experiment.     

Asymptotic S/N results for an adaptive polyspectral canceller usingsample matrix inversion

An adaptive polyspectral canceller configuration is defined, whereby auxiliary canceller channels are formed using distinct monomial expressions of the auxiliary sensor channels. If noises in the auxiliary canceller channels are correlated with the noise in a main channel, then improvement in output signal-to-noise (S/N) power ratio is possible by cancelling in linear fashion the correlated auxiliary canceller channels with the main channel. The convergence performance of the polyspectral canceller is analyzed. A simple expression is derived for the asymptotic S/N efficiency of the adaptive polyspectral canceller as a function of the number of independent input sample vectors used to calculate the adaptive canceller weights and other canceller/noise model parameters. It is shown by simulation for low-order polyspectral cancellers of a specific form with Gaussian inputs that this asymptotic expression is a good approximation of the actual S/N efficiency for a moderate number of input sample vectors. However, for moderate-to-high order polyspectral cancellers, the asymptotic expression is a poor indicator of performance     

无线光通信中的非成像集中器

在无线光通信领域,利用非成像光学设计的集中器能够聚集光辐射能量,而且相对于成像性集中器具有更紧凑的结构和更高的增益.利用光线追迹法对半球形集中器的性质进行了分析与研究.对好几种非成像集中器:半球形集中器,复合抛物线形集中器,介质内部全反射集中器,多表面集中器,多相介质集中器,从设计原理、增益和视场进行比较,并分析其应用场合.     

Crosspoint complexity of sparse crossbar concentrators

A sparse crossbar (n,m,c)-concentrator is a bipartite graph with n inputs and m outputs in which any c or fewer inputs can be matched with an equal number of outputs, where c is called its capacity. We present a number of new results on the crosspoint complexity of such concentrators. First, we describe a sparse crossbar (n, m, m)-concentrator whose crosspoint complexity matches Nakamura-Masson's (1982, 1977) lower bound for any given n and m. Second, we present a sparse crossbar (2m, m, m)-concentrator with crosspoint complexity also matching Nakamura-Masson's lower bound, and with fixed fan-in and nearly fixed fan-out. Third, we derive an easily computable lower bound on the crosspoint complexity of sparse crossbar (n, m, c)-concentrators. Finally, we show that this bound is attainable within a factor of two when n-m⩽c⩽[m/c]     

Locating concentrators for primary and secondary coverage in acomputer communications network

A model is developed that assigns primary and secondary (backup) concentrator coverage to each terminal site. The objective is to minimize communications costs as well as costs for setting up and operating the concentrators subject to capacity constraints. A relaxation of the problem is studied, and an effective solution procedure that makes the use of this relaxation is developed. Experimental results over a wide range of problem structures show that this solution procedure is very effective. It is also found to be significantly faster than a state-of-the-art commercial integer programming package     

High performance concentrators and superconcentrators usingmultiplexing schemes

Concentrators are used to interface and combine together low speed communication channels onto higher speed transmission links to alleviate transmission costs. They are also used to construct more powerful switching fabrics such as permutation and broadcast networks. Using an adaptive binary sorting network model, this paper constructs new concentrators and superconcentrators. Unlike the previously reported concentrators and superconcentrators, these new constructions are fast, and ran easily be implemented using simple switching devices. More specifically, for n inputs, they can be constructed with O(n lg lg n) constant fanin bit-level multiplexers and demultiplexers, and can be routed in O(lg² n) bit-level time     

Modeling photon transport in fluorescent solar concentrators

Fluorescent solar concentrators (FSC) can concentrate light onto solar cells by trapping fluorescence through total internal reflection. In an ideal FSC, the major obstacle to efficient photon transport is the re‐absorption of the fluorescence emitted. In order to decompose the contribution of different photon flux streams within a FSC, the angular dependent re‐absorption probability is introduced and modeled in this paper. This is used to analyze the performance of different FSC configurations and is also compared with experimental results. To illustrate the application of the modeling, the collection efficiency of ideal devices has also been calculated from the re‐absorption probability and is shown to be useful for estimating non‐ideal losses such as those due to scattering or reflection from mirrors. The results also indicate that among the FSCs studied, the performance of those surrounded by four edge solar cells is close to ideal. The rapid optimization of FSCs has also been presented as another practical application of the models presented in this paper. © 2014 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons, Ltd.     

Optimal use of partial redundancy and the system reliability which results

Partial system triplication with a single majority vote is analysed to find (a) the region of superiority of partial triplication over total triplication and (b) over no redundancy, (c) the degree of partial triplication which maximises reliability, (d) the maximum system reliability produced by partial redundancy. Only approximate or numerical solutions to (a) and (c) have appeared previously. (b) and (d) are entirely new.     

Asymptotic multiuser efficiencies for decision-directed multiuserdetectors

The asymptotic multiuser efficiencies (AMEs) are derived for various classes of decision-directed multiuser detectors, including multistage detectors, and decision-feedback detectors. Novel classes of soft-decision multistage detectors are proposed and analyzed. Each class is specified in part by a soft-decision nonlinearity, such as a symmetric quantizer or a linear clipper. Closed-form expressions for two-user AMEs are derived for soft-decision two-stage detectors and can be used as a design criterion to optimize the soft-decision nonlinearities. For a special case of two synchronous users, the soft-decision two-stage detector using an optimized linear clipper with either conventional or decorrelated tentative decisions is shown to achieve optimum AME. Upper and lower bounds on the AME are obtained for decision-feedback detectors using either conventional or decorrelated tentative decisions. It is demonstrated that decision-directed multiuser detectors with conventional tentative decisions have low near-far resistance compared to those with decorrelated tentative decisions     

Asymptotic Throughput Analysis for Channel-Aware Scheduling

In this paper, we provide an asymptotic performance analysis of channel-aware packet scheduling based on extreme value theory. We first address the average throughput of systems with a homogeneous average signal-to-noise ratio (SNR) and obtain its asymptotic expression. Compared with the exact throughput expression, the asymptotic one, which is applicable to a broader range of fading channels, is more concise and easier to get insights. Furthermore, we confirm the accuracy of the asymptotic results by theoretical analysis and numerical simulation. For a system with heterogeneous SNRs, normalized-SNR-based scheduling needs to be used for fairness. We also investigate the asymptotic average throughput of the normalized-SNR-based scheduling, and prove that the average throughput in this case is less than that in the homogeneous case with a power constraint.     

Asymptotic formula for elliptic function modulus

Elliptic functions have applications in microwaves and nonlinear optics. Numerical calculations of elliptic functions require the knowledge of both the modulus k and quarter period K. In the letter the procedure to calculate accurately the value of K from k is discussed. An asymptotic formula for calculating k from K is also presented.     

Asymptotic redundancies for universal quantum coding

Clarke and Barren (1990, 1994, 1995) have shown that the Jeffreys' invariant prior of Bayesian theory yields the common asymptotic (minimax and maximin) redundancy of universal data compression in a parametric setting. We seek a possible analog of this result for the two-level quantum systems. We restrict our considerations to prior probability distributions belonging to a certain one-parameter family, q_u,-∞n×2ⁿ (Bayesian density) matrices, ζ _n(u). These matrices are the weighted averages (with respect to q_u) of all possible tensor products of n identical 2×2 density matrices, representing the two-level quantum systems. We propose a form of universal coding for the situation in which the density matrix describing an ensemble of quantum signal states is unknown. A sequence of n signals would be projected onto the dominant eigenspaces of ζ_n(u)