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991.
R. Jayaparvathy S. Anand S. Dharmaraja S. Srikanth 《International Journal of Communication Systems》2007,20(3):273-296
In this paper, we present a performance study to evaluate the mean delay and the average system throughput of IEEE 802.11‐based wireless local area networks (WLANs). We consider the distributed co‐ordination function (DCF) mode of medium access control (MAC). Stochastic reward nets (SRNs) are used as a modelling formalism as it readily captures the synchronization between events in the DCF mode of access. We present a SRN‐based analytical model to evaluate the mean delay and the average system throughput of the IEEE 802.11 DCF by considering an on–off traffic model and taking into account the freezing of the back‐off counter due to channel capture by other stations. We also compute the mean delay suffered by a packet in the system using the SRN formulation and by modelling each station as an M/G/1 queue. We validate our analytical model by comparison with simulations. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
992.
Performance benchmarking of wireless Web servers 总被引:1,自引:0,他引:1
The advent of mobile computers and wireless networks enables the deployment of wireless Web servers and clients in short-lived ad hoc network environments, such as classroom area networks. The purpose of this paper is to benchmark the performance capabilities of wireless Web servers in such an environment. Network traffic measurements are conducted on an in-building IEEE 802.11b wireless ad hoc network, using a wireless-enabled Apache Web server, several wireless clients, and a wireless network traffic analyzer. The experiments focus on the HTTP transaction rate and end-to-end throughput achievable in such an ad hoc network environment, and the impacts of factors such as Web object size, number of clients, and persistent HTTP connections. The results show that the wireless network bottleneck manifests itself in several ways: inefficient HTTP performance, client-side packet losses, server-side packet losses, network thrashing, and unfairness among Web clients. Persistent HTTP connections offer up to 350% improvement in HTTP transaction rate and user-level throughput, while also improving fairness for mobile clients accessing content from a wireless Web server. 相似文献
993.
In this paper, we present a study of the dedicated short range communications (DSRC) receiver performance under varying signal to noise ratio, velocity, symbol durations and packet lengths. Conventional channel estimation, which is used in IEEE 802.11a, assumes static channel characteristics for the entire packet duration. That is found to be infeasible for high velocity DSRC applications. Simulation results show that the packet-error-rate increases with the increase in relative velocity. Viterbi decoding substantially improves the performance, but the sensitivity to Doppler shift still exists. Analysis and simulation results show that extending the symbol duration or increasing packet length results in an increase of the packet-error-rate. These results may serve as benchmarks for future DSRC channel estimation methods. 相似文献
994.
Frank Nielsen 《Entropy (Basel, Switzerland)》2021,23(11)
The Jeffreys divergence is a renown arithmetic symmetrization of the oriented Kullback–Leibler divergence broadly used in information sciences. Since the Jeffreys divergence between Gaussian mixture models is not available in closed-form, various techniques with advantages and disadvantages have been proposed in the literature to either estimate, approximate, or lower and upper bound this divergence. In this paper, we propose a simple yet fast heuristic to approximate the Jeffreys divergence between two univariate Gaussian mixtures with arbitrary number of components. Our heuristic relies on converting the mixtures into pairs of dually parameterized probability densities belonging to an exponential-polynomial family. To measure with a closed-form formula the goodness of fit between a Gaussian mixture and an exponential-polynomial density approximating it, we generalize the Hyvärinen divergence to -Hyvärinen divergences. In particular, the 2-Hyvärinen divergence allows us to perform model selection by choosing the order of the exponential-polynomial densities used to approximate the mixtures. We experimentally demonstrate that our heuristic to approximate the Jeffreys divergence between mixtures improves over the computational time of stochastic Monte Carlo estimations by several orders of magnitude while approximating the Jeffreys divergence reasonably well, especially when the mixtures have a very small number of modes. 相似文献
995.
Alexander P. Goncharov 《Mathematische Nachrichten》2000,220(1):45-57
We construct a basis in the spaces ofWhitney functions ℰ(K) for two model cases, where K ⊂ ℝ is a sequence of closed intervals tending to a point. In the proofwe use a convolution property for the coefficients of scaling Chebyshev polynomials. 相似文献
996.
Let {T(t)}t≥0 be a C0–semigroup on a Banach space X with generator A, and let H∞T be the space of all x ∈ X such that the local resolvent λ ↦ R(λ, A)x has a bounded holomorphic extension to the right half–plane. For the class of integrable functions ϕ on [0, ∞) whose Fourier transforms are integrable, we construct a functional calculus ϕ ↦ Tϕ, as operators on H∞T. Weshow that each orbit T(·)Tϕx is bounded and uniformly continuous, and T(t)Tϕx → 0 weakly as t → ∞, and we give a new proof that ∥T(t)R(μ, A)x∥ = O(t). We also show that ∥T(t)Tϕx∥ → 0 when T is sun –reflexive, and that ∥T(t)R(μ, A)x∥ = O(ln t) when T is a positive semigroup on a normal ordered space X and x is a positive vector in H∞T. 相似文献
997.
Shixun Dai Longjun Lu Tiefeng Xu Qiuhua Nie Xiang Shen Xunsi Wang 《Journal of Non》2007,353(28):2744-2749
Er2O3-doped Bi2O3-B2O3-Ga2O3 glasses were prepared by the conventional melt-quenching method, and the Er3+:4I13/2 → 4I15/2 fluorescence properties are studied for different Er3+ concentrations. when the Er2O3 concentration increases from 0.03 to 3.0 mol%, the measured lifetime of Er3+:4I13/2 level decrease from 2.24 to 0.9 m s, and from 0.25 to 0.20 m s for the Er3+:4I11/2 level. The fast energy migration among Er3+ ions cause the reduction of lifetime of the 4I13/2 level, whereas the change in the 4I11/2 level is mainly due to a cooperative upconversion process (4I11/2, 4I11/2) → (4F7/2, 4I15/2). Based on the dipole-dipole interaction theory, the interaction parameter, CEr,Er, for the migration rate of Er3+:4I13/2 ↔ 4I13/2 was calculated to be 32 × 10−40 cm6 s−1. 相似文献
998.
WiMAX技术标准的发展进程 总被引:1,自引:0,他引:1
IEEE 802.16 is very attractive since its publication,.The growth of WiMAX organization accxelerates the development of 802.16 standard,The mobile WiMAX——802.16e standard is especially attractive,This article presents the status quo and the development of WiMAX technical standard along with the work plan of the standard organization in the next stage.The article also introduces the conditions that the development of mobile WiMAX technical standard is attracting people's attention. 相似文献
999.
Wei Liu Xingqun Ma Yingying Jin Jie Zhang Yang Li Yuxia Tang Yong Song Shouju Wang 《Molecules (Basel, Switzerland)》2021,26(23)
To improve the tumor-targeting efficacy of photodynamic therapy, biotin was conjugated with chlorin e6 to develop a new tumor-targeting photosensitizer, Ce6-biotin. The Ce6-biotin had good water solubility and low aggregation. The singlet-oxygen generation rate of Ce6-biotin was slightly increased compared to Ce6. Flow cytometry and confocal laser scanning microscopy results confirmed Ce6-biotin had higher binding affinity toward biotin-receptor-positive HeLa human cervical carcinoma cells than its precursor, Ce6. Due to the BR-targeting ability of Ce6-biotin, it exhibited stronger cytotoxicity to HeLa cells upon laser irradiation. The IC50 against HeLa cells of Ce6-biotin and Ce6 were 1.28 µM and 2.31 µM, respectively. Furthermore, both Ce6-biotin and Ce6 showed minimal dark toxicity. The selectively enhanced therapeutic efficacy and low dark toxicity suggest that Ce6-biotin is a promising PS for BR-positive-tumor-targeting photodynamic therapy. 相似文献
1000.