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在无线局域网中提供服务质量(QoS)保证的MAC 算法应该满足业务区分服务的要求和系统性能的整体最优.以往的此类自适应MAC 算法依赖于对不同级别的竞争业务数目进行估计,计算过于复杂.提出一种基于QoS区分的自适应p-persistent MAC 算法,QDA-MAC(QoS differentiation based adaptive MAC scheme).该算法引入了新的参数-坚持因子(persistent factor),其优化值能够实时反映网络负载的变化情况,结合近似优化的自适应方法,每次发送尝试后,该算法不需要估计每类竞争业务的数目,利用坚持因子的优化值实时更新各类优先级业务的发送概率,调整相应的协议参数,系统的性能也能接近最优.仿真结果验证了该算法不仅能够根据竞争业务数目的变化对系统的性能进行整体优化,而且能够提供业务区分服务,在QoS区分的基础上可以为实时业务提供严格的QoS保证,尤其在信道利用率和时延等方面明显优于标准的IEEE 802.11 DCF 和IEEE 802.11e EDCA 机制.  相似文献
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Gradient projection (GP) algorithm has been shown as an efficient algorithm for solving the traditional traffic equilibrium problem with additive route costs. Recently, GP has been extended to solve the nonadditive traffic equilibrium problem (NaTEP), in which the cost incurred on each route is not just a simple sum of the link costs on that route. However, choosing an appropriate stepsize, which is not known a priori, is a critical issue in GP for solving the NaTEP. Inappropriate selection of the stepsize can significantly increase the computational burden, or even deteriorate the convergence. In this paper, a self-adaptive gradient projection (SAGP) algorithm is proposed. The self-adaptive scheme has the ability to automatically adjust the stepsize according to the information derived from previous iterations. Furthermore, the SAGP algorithm still retains the efficient flow update strategy that only requires a simple projection onto the nonnegative orthant. Numerical results are also provided to illustrate the efficiency and robustness of the proposed algorithm.  相似文献
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柴天佑 《信息与控制》1992,21(4):193-200
本文将广义最小方差控制策略和前馈控制策略结合进来,提出了解耦控制器并讨论了如何采用修改最小二乘辨识算法和直接方案对具有任意延时结构的一般随机多变量系统实现自适应解耦控制,本文还证明了所提出的自适应算法即使用于开环不稳定或非最小相位系统也具有整体稳定性和收敛性。  相似文献
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We propose to use adaptive wavelet lifting for image retrieval systems that are based on shape detection and multiresolution structures of objects in a database against a background of texture. To measure the performance of our approach, feature vectors are computed based on moment invariants of detail coefficients produced by the adaptive lifting scheme and retrieval rates are obtained by measuring distances between these vectors. Retrieval rates are compared with the rates obtained when using non-adaptive wavelet filtering as a preprocessing step. A synthetic database is created for this simulation.  相似文献
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详细论述了基于块匹配的鲁棒运动估计算法。跟已有的基于块匹配的运动估计算法比较,首先,我们引入颜色信息来提高运动估计的准确性;其次,在更广泛的意义上运用自适应策略来减少计算量并同时保证算法的鲁棒性;最后,提出的基于预测修正的复合查找方法充分利用了物体运动的全局信息,克服了三步查找算法以及全查找算法的缺点并充分发挥它们二者的优点从而提高查找的效率和匹配精度。实验结果表明基于块匹配的鲁棒运动估计算法具有抗干扰能力强、运动估计准确、计算效率高等优点。  相似文献
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In this paper we discuss an adaptive method for the compulation of discontinuous solutions of hyperbolic conservation laws. In each time level we use very simple sensors for detecting discontinuities of the solution. The adaptive scheme use first order upwind flux computation in the immediate neighborhood of these irregularities. Since the differential equation holds in the smoothness domain, we follow the characteristics in the lime marching procedure at grid points in that domain.  相似文献
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