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1.
Next generation wireless technologies will need to incorporate new sets of traffic control procedures in order to cope with the challenges related to supporting both the existing and the ever-increasing new multimedia services. The work presented in this paper focuses on traffic control for MPEG-4 videoconference over cellular networks, and is twofold. We first introduce a traffic model for medium quality MPEG-4 videoconference traffic. We then proceed to use this model, as well as a previously developed model for high quality MPEG-4 traffic, in the implementation of a new Call Admission Control (CAC) mechanism. Providers need to use efficient resource management mechanisms in order to keep existing clients satisfied and attract new customers, so that they can increase their revenue. Towards this goal, our CAC mechanism makes decisions on the acceptance/rejection of a new video call not only based on the predicted capacity that users will consume, but also on the possible revenue gained for the provider when degrading current users in order to accommodate new ones. Our mechanism is implemented with both a static and a dynamic pricing policy and is shown, via an extensive simulation study, to provide excellent Quality of Service (QoS) to wireless videoconference users. 相似文献
2.
Antonio Lpez Rafael Molina Aggelos K. Katsaggelos Antonio Rodriguez Jos M. Lpez Jos M. Llamas 《International journal of imaging systems and technology》2004,14(1):21-27
Despite the adequacy of Bayesian methods to reconstruct nuclear medicine SPECT (single‐photon emission computed tomography) images, they are rarely used in everyday medical practice. This is primarily because of their computational cost and the need to appropriately select the prior model hyperparameters. We propose a simple procedure for the estimation of these hyperparameters and the reconstruction of the original image and test the procedure on both synthetic and real SPECT images. The experimental results demonstrate that the proposed hyperparameter estimation method produces satisfactory reconstructions. Although we have used generalized Gaussian Markov random fields (GGMRF) as prior models, the proposed estimation method can be applied to any priors with convex potential and tractable partition function with respect to the scale hyperparameter. © 2004 Wiley Periodicals, Inc. Int J Imaging Syst Technol 14, 21–27, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.20003 相似文献
3.
Emmanouil K. Oikonomou Vassilios Kilias Aggelos Goumas Alexandrous Rigopoulos Eirini Karakatsani Markos Damasiotis Dimitrios Papastefanakis Natassa Marini 《Energy Policy》2009,37(11):4874-4883
The increasing energy challenges faced, in particular, by isolated communities, such as insular communities, call for an integrated, flexible and easy-to-apply methodology aiming at providing a list of renewable energy sources) (RES) projects capable to reduce green house gas (GHG) emissions, satisfy future energy forecasts and reach the objectives of international/national energy directives and obligations, as, for example, the ones set by the Kyoto Protocol by 2010. The EU project EMERGENCE 2010 developed such a methodology that is implemented here in the case study of wind parks in the Dodecanese islands in Greece. The results obtained consist of a final list of financially viable RES wind projects, for which various barriers have been previously identified and assessed. The additional advantages of the proposed methodology is that besides providing as an end result a comprehensive list of RES projects adopted to specific criteria and regional priorities, it also allows space for involving – from early stages – the local community and stakeholders in the decision-making process (participatory planning); in this way, the EMERGENCE 2010 methodology may assist towards the RES promotion and public acceptance, the profitability of RES investments and the regional sustainable development. 相似文献
4.
In this paper we design and study the performance of a Medium Access Control (MAC) scheme for the multiplexing and the integrated
delivery of voice, mobile messaging, IP, gaming and H.264 videoconference traffic over a high-speed cellular TDMA channel
with errors and capture. To the best of our knowledge, this is one of the first papers in the literature investigating the
integration of actual H.264 video traces and gaming traffic with other types of traffic over wireless networks. Our results
show that the proposed scheme achieves high throughput results while preserving the strict Quality of Service (QoS) requirements
of each traffic type, and outperforms two efficient schemes previously proposed in the literature. 相似文献
5.
Miguel Vega Javier Mateos Rafael Molina Aggelos K. Katsaggelos 《Journal of Signal Processing Systems》2011,65(3):509-523
In this paper we propose a novel super-resolution based algorithm for the pansharpening of multispectral images. Within the
Bayesian formulation, the proposed methodology incorporates prior knowledge on the expected characteristics of multispectral
images; that is, it imposes smoothness within each band by means of the energy associated with the ℓ1 norm of vertical and
horizontal first order differences of image pixel values and also takes into account the correlation among the bands of the
multispectral image. The observation process is modeled using the sensor characteristics of both panchromatic and multispectral
images. The method is tested on real and synthetic images, compared with other pansharpening methods, and the quality of the
results assessed both qualitatively and quantitatively. 相似文献
6.
Aggelos Kiayias Yona Raekow Alexander Russell Narasimha Shashidhar 《Journal of Cryptology》2014,27(1):23-44
We present the first information-theoretic steganographic protocol with an asymptotically optimal ratio of key length to message length that operates on arbitrary covertext distributions with constant min-entropy. Our results are also applicable to the computational setting: our stegosystem can be composed over a pseudorandom generator to send longer messages in a computationally secure fashion. In this respect our scheme offers a significant improvement in terms of the number of pseudorandom bits generated by the two parties in comparison to previous results known in the computational setting. Central to our approach for improving the overhead for general distributions is the use of combinatorial constructions that have been found to be useful in other contexts for derandomization: almost t-wise independent function families. 相似文献
7.
Jay J. Williams Janet C. Rutledge Aggelos K. Katsaggelos Dean C. Garstecki 《The Journal of VLSI Signal Processing》1998,20(1-2):7-23
Current video conference and phone systems do not provide the necessary temporal resolution and motion for speechreading. In this paper the perceptual boundaries which effect speechreading performance are investigated. Analysis of the relationships between viseme groupings, accuracy of viseme recognition and presentation frame rate is presented based on the results of subject testing. Results reveal a minimum frame rate of 10 frames per second (fps) for distinguishing viseme groupings. Confusion analysis results demonstrate the importance of the tongue and teeth oral features for speechreading. These results are critical to the design of speech-assisted video systems to enhance speechreading for individuals with impaired hearing. 相似文献
8.
Rate-distortion optimal video summary generation. 总被引:1,自引:0,他引:1
Zhu Li Guido M Schuster Aggelos K Katsaggelos Bhavan Gandhi 《IEEE transactions on image processing》2005,14(10):1550-1560
The need for video summarization originates primarily from a viewing time constraint. A shorter version of the original video sequence is desirable in a number of applications. Clearly, a shorter version is also necessary in applications where storage, communication bandwidth, and/or power are limited. The summarization process inevitably introduces distortion. The amount of summarization distortion is related to its "conciseness," or the number of frames available in the summary. If there are m frames in the original sequence and n frames in the summary, we define the summarization rate as m/n, to characterize this "conciseness". We also develop a new summarization distortion metric and formulate the summarization problem as a rate-distortion optimization problem. Optimal algorithms based on dynamic programming are presented and compared experimentally with heuristic algorithms. Practical constraints, like the maximum number of frames that can be skipped, are also considered in the formulation and solution of the problem. 相似文献
9.
Evaluation of Kalman filtering for network time keeping 总被引:6,自引:0,他引:6
Bletsas A 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2005,52(9):1452-1460
Time information is critical for a variety of applications in distributed environments that facilitate pervasive computing and communication. This work describes and evaluates a novel Kalman filtering algorithm for end-to-end time synchronization between a client computer and a server of "true" time [e.g., a Global Positioning System (GPS) source] using messages transmitted over packet-switched networks, such as the internet. The messages exchanged have the network time protocol (NTP) format, and the algorithm evaluated, is performed only at the client side. The Kalman filtering algorithm is compared to two other techniques widely used, based on linear programming and statistical averaging, and the experiments involve independent consecutive measurements (Gaussian case) or measurements exhibiting long-range dependence (self-similar case). Performance is evaluated according to the estimation error of frequency offset and time offset between client and server clock, the standard deviation of the estimates and the number of packets used for a specific estimation. The algorithms could exploit existing NTP infrastructure, and a specific example is presented. 相似文献
10.
We report application of a near-real-time method to determine layer thickness on electroplated coin blanks. The method was developed on a simple laser-induced-breakdown spectroscopy (LIBS) arrangement by monitoring relative emission-line intensities from key probe elements via successive laser ablation shots. This is a unique LIBS application where no other current spectroscopic method (inductively coupled plasma or x-ray fluorescence) can be applied effectively. Method development is discussed, and results with precalibrated coins are presented. 相似文献