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Computation Complexity (computation + complexity)
Selected AbstractsHigh-Quality Adaptive Soft Shadow MappingCOMPUTER GRAPHICS FORUM, Issue 3 2007Gaël Guennebaud Abstract The recent soft shadow mapping technique [GBP06] allows the rendering in real-time of convincing soft shadows on complex and dynamic scenes using a single shadow map. While attractive, this method suffers from shadow overestimation and becomes both expensive and approximate when dealing with large penumbrae. This paper proposes new solutions removing these limitations and hence providing an efficient and practical technique for soft shadow generation. First, we propose a new visibility computation procedure based on the detection of occluder contours, that is more accurate and faster while reducing aliasing. Secondly, we present a shadow map multi-resolution strategy keeping the computation complexity almost independent on the light size while maintaining high-quality rendering. Finally, we propose a view-dependent adaptive strategy, that automatically reduces the screen resolution in the region of large penumbrae, thus allowing us to keep very high frame rates in any situation. [source] A new mutual authentication and key exchange protocol with balanced computational power for wireless settingsEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 2 2004Chou-Chen Yang Mutual authentication and key exchange protocols (MAKEP) provide two parties in communication with guarantee of true identity. And then the two parties end up sharing a common session key for privacy and data integrity during the session. In MAKEP, public-key-based schemes and symmetric-key-based schemes are often used. However, the former requires high computation complexity and hence, it is not suitable for applications in wireless settings. The latter has to maintain many distinct keys for different parties. Wong et al. proposed the Linear MAKEP to solve these problems. But in term of storage space, it is not optimal. In this paper, we propose a scheme that uses the geometric properties of line to achieve mutual authentication and key exchange. Compared with Wong et al.'s scheme, our scheme is efficient and requires less storage space. It can withstand the replay attack and the unknown key-share attack, and the server does not bear much more computation cost than the client in each session, hence we call it a protocal with balanced computational power. Copyright © 2004 AEI [source] A split,merge-based region-growing method for fMRI activation detectionHUMAN BRAIN MAPPING, Issue 4 2004Yingli Lu Abstract We introduce a hybrid method for functional magnetic resonance imaging (fMRI) activation detection based on the well-developed split,merge and region-growing techniques. The proposed method includes conjoining both of the spatio-temporal priors inherent in split,merge and the prior information afforded by the hypothesis-led component of region selection. Compared to the fuzzy c-means clustering analysis, this method avoids making assumptions about the number of clusters and the computation complexity is reduced markedly. We evaluated the effectiveness of the proposed method in comparison with the general linear model and the fuzzy c-means clustering method conducted on simulated and in vivo datasets. Experimental results show that our method successfully detected expected activated regions and has advantages over the other two methods. Hum. Brain Mapping 22:271,279, 2004. © 2004 Wiley-Liss, Inc. [source] A utility-based capacity optimization framework for achieving cooperative diversity in the hierarchical converged heterogeneous wireless networksINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 12 2008Mugen Peng Abstract A hierarchical convergence mechanism for the heterogeneous wireless communication system via the heterogeneous cooperative relay node is presented in this paper, in which the techniques of cooperative communication and wireless relay are utilized to improve performances of the individual user and the overall converged networks. In order to evaluate the benefits of the proposal, a utility-based capacity optimization framework for achieving the heterogeneous cooperative diversity gain is proposed. The heterogeneous cooperative capacity, relay selection and power allocation theoretical models are derived individually. The joint optimization model for relay selection and power allocation is presented as well. Owing to the computation complexity, the sub-optimal cooperative relay selection algorithm, the sub-optimal power allocation algorithm and the sub-optimal joint algorithm are determined to approach the maximum overall networks' spectrum efficiency. These proposed algorithms are designed in conformance to guarantee the equivalent transmission rates of the different wireless access networks. The simulation results demonstrate that the utility-based capacity model is available for the heterogeneous cooperative wireless communication system, and the proposed algorithms can improve performances by achieving the cooperative gain and taking full advantage of the cross-layer design. Copyright © 2008 John Wiley & Sons, Ltd. [source] On parameter estimation of a simple real-time flow aggregation modelINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 7 2006Huirong Fu Abstract There exists a clear need for a comprehensive framework for accurately analysing and realistically modelling the key traffic statistics that determine network performance. Recently, a novel traffic model, sinusoid with uniform noise (SUN), has been proposed, which outperforms other models in that it can simultaneously achieve tractability, parsimony, accuracy (in predicting network performance), and efficiency (in real-time capability). In this paper, we design, evaluate and compare several estimation approaches, including variance-based estimation (Var), minimum mean-square-error-based estimation (MMSE), MMSE with the constraint of variance (Var+MMSE), MMSE of autocorrelation function with the constraint of variance (Var+AutoCor+MMSE), and variance of secondary demand-based estimation (Secondary Variance), to determining the key parameters in the SUN model. Integrated with the SUN model, all the proposed methods are able to capture the basic behaviour of the aggregation reservation system and closely approximate the system performance. In addition, we find that: (1) the Var is very simple to operate and provides both upper and lower performance bounds. It can be integrated into other methods to provide very accurate approximation to the aggregation's performance and thus obtain an accurate solution; (2) Var+AutoCor+MMSE is superior to other proposed methods in the accuracy to determine system performance; and (3) Var+MMSE and Var+AutoCor+MMSE differ from the other three methods in that both adopt an experimental analysis method, which helps to improve the prediction accuracy while reducing computation complexity. Copyright © 2005 John Wiley & Sons, Ltd. [source] The computation of deterministic bounds to multiplexed MPEG video traffic using z -characterizationINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 8 2004Wai-Chung Poon Abstract In this paper, we propose a method called z -characterization for computing the deterministic bounds of an aggregated MPEG stream at frame level. Traditional deterministic characterization methods like empirical envelope generally suffer from the drawback of high computation complexity. In our approach, the I, P and B sub-traces of an MPEG trace will be characterized independently such that they possess their own empirical envelopes. By exploiting the periodic group-of-pictures (GOP) structure of MPEG video, the I, P and B sub-envelopes can act as building blocks for computing the characterization of the aggregate stream in real-time. Experimental results show that our proposed characterization closely bounds the empirical envelope in both homogenous and heterogeneous multiplexing scenarios. Copyright © 2004 John Wiley & Sons, Ltd. [source] | ||||||||||