1,721,327 research outputs found
FIR filter synthesis algorithms for minimizing the delay and the number of adders
No full textAs the complexity of digital filters is dominated by the number of multiplications, many works have focused on minimizing the complexity of multiplier blocks that compute the constant coefficient multiplications required in filters. Although the complexity of multiplier blocks is significantly reduced by using efficient techniques such as decomposing multiplications into simple operations and sharing common subexpressions, previous works have not considered the delay of multiplier blocks which is a critical factor in the design of complex filters. In this paper, we present new algorithms to minimize the complexity of multiplier blocks under the given delay constraints. By analyzing multiplier blocks in view of delay, three delay reduction methods are proposed and combined into previous algorithms. Since the proposed algorithms can generate multiplier blocks that meet the specified delay, a trade-off between delay and hardware complexity is enabled by changing the delay constraints. Experimental results show that the proposed algorithms can reduce the delay of multiplier blocks at the cost of a little increase of complexity
Unstructured mesh Navier-Stokes calculations of the flow field of a helicopter rotor in hover
No full textThree-dimensional viscous flow field around a lifting helicopter rotor in hover is calculated by using an unstructured mesh methodology. The flow solver utilizes a cell-centered finite-volume scheme that is based on Roe's flux-difference splitting and an implicit Jacobi/Gauss-Seidel time integration. The effect of turbulence is estimated by the Spalart-Allmaras one-equation model coupled with a wall function boundary condition. A soIution-adaptive mesh refinement technique is used for efficient capturing of the tip vortex. Calculations are performed at two operating conditions with varying tip Mach number and collective pitch setting. Formation of the tip vortex is well captured through a series of adaptive mesh refinement procedure starting from a coarse initial mesh. Good agreements are obtained between the numerical result and the experiment for both the blade loading and the tip vortex behavior. It is demonstrated that the rotor performance and the flow field are significantly affected by viscosity. The process of tip vortex formation around the blade tip is also qualitatively investigated
Digital filter synthesis based on an algorithm to generate all minimal signed digit representations
No full textIn this paper, the authors propose an algorithm to find all the minimal signed digit (MSD) representations of a constant and present an algorithm to synthesize digital filters based on the MSD representation. The hardware complexity of a digital signal processing system is dependent on the number system used for the implementation. Although the canonical signed digit (CSD) representation is widely employed, as it is unique and guarantees the minimal number of nonzero digits for a constant, the MSD representation provides multiple representations that have the same number of nonzero digits as the CSD representation. The proposed filter synthesis algorithm utilizes this redundancy of the MSD representation to make common subexpressions, as many as possible, leading to smaller filters. By applying the proposed algorithm to the hardware synthesis of finite impulse response filters, the authors obtained multiplier blocks that are 7% smaller than those generated from the CSD representation
SAT-based unbounded symbolic model checking
No full textThis paper describes a Boolean satisfiability checking (SAT)-based unbounded symbolic model-checking algorithm. The conjunctive normal form is used to represent sets of states and transition relation. A logical operation on state sets is implemented as an operation on conjunctive normal form formulas. A satisfy-all procedure is proposed to compute the existential quantification required in obtaining the preimage and fix point. The proposed satisfy-all procedure is implemented by modifying a SAT procedure to generate all the satisfying assignments of the input formula, which is based on new efficient techniques such as line justification to make an assignment covering more search space, excluding clause management, and two-level logic minimization to compress the set of found assignments. In addition, a cache table is introduced into the satisfy-all procedure. It is a difficult problem for a satisfy-all procedure to detect the case that a previous result can be reused. This paper shows that the case can be detected by comparing sets of undetermined variables and clauses. Experimental results show that the proposed algorithm can check more circuits than binary decision diagram-based and previous SAT-based model-checking algorithms.This work was supported in part by the Korea
Science and Engineering Foundation through the MICROS Center, in part by the
Ministry of Science and Technology and the Ministry of Commerce, Industry
and Energy through the System IC 2010 project, and in part by the Ministry of
Information and Communication through the IT-SoC project. This paper was
recommended by Associate Editor J. H. Kukula
Effect of wake adaptation on rotor hover simulations using unstructured meshes
No full textA three-dimensional inviscid flow solver is developed for simulating the flowfield of hovering helicopter rotor using unstructured meshes. The flow solver utilizes a cell-centered finite volume scheme that is based on the Roe's flux-difference splitting with an implicit Jacobi/Gauss-Seidel time integration. Calculations are performed at two operating conditions of subsonic and transonic tip Mach numbers. A solution-adaptive mesh refinement technique is adopted to improve the resolution of flow features on the blade surface. It is demonstrated that the trajectory of the tip vortex can be captured through a series of adaptive mesh refinements starting from a very coarse initial grid. It was found that not only the strength of the tip vortex, but also its trajectory, is strongly dependent on the mesh resolution in the wake. Good agreement is obtained between the numerical result and the experiment for both the blade loading and the tip vortex behavior
Optimal approximation of discrete probability distribution with kth-order dependency and its application to combining multiple classifiers
No full textIn order to probabilistically combine multiple decisions of K classifiers obtained from samples, a (K + 1)st-order probability distribution is needed. It is well known that storing and estimating the distribution is exponentially complex and is unmanageable even for small K. Chow and Liu (1968) as well as Lewis (1959) proposed an approximation of nth-order probability distributions with a product of second-order distributions considering first-order tree dependency. However, often we face cases in which a decision is based on more than two other classifiers. In such cases, first-order dependency would not be suitable to estimate a high order distribution properly. In this paper, a new method is proposed to optimally approximate a high order distribution with a product of kth-order dependencies, or (k + 1)st-order distributions, where 1 less than or equal to k less than or equal to K. The authors also proposed the way to identify high order dependencies from training samples. The superior performance of the new method is demonstrated by experiments on the recognition of standardized CENPARMI handwritten numerals and KAIST on-line handwritten numerals. (C) 1997 Published by Elsevier Science B.V
Approximating optimally discrete probability distribution with kth-order dependency for combining multiple decisions
No full textA probabilistic combination of K classifiers' decisions obtained from samples needs a (K + 1)st-order probability distribution. Chow and Liu (1968) as well as Lewis (1959) proposed an approximation scheme of such a high-order distribution with a product of only first-order tree dependencies. However, if a classifier follows more than two classifiers, such first-order dependency does not estimate adequately a high-order distribution. Therefore, a new method is proposed to approximate optimally the (K + 1)st-order distribution with a product set of kth-order dependencies where 1 less than or equal to k less than or equal to K, which are identified by a systematic dependency-directed approach. And also, a new method is presented to combine probabilistically multiple decisions with the product set of the kth-order dependencies, using a Bayesian formalism
An efficient handover mechanism using the general switch management protocol on a multi-protocol label switching network
No full textUsing the general switch management protocol on a multi-protocol label switching network, we present an efficient method for handling handovers. The proposed method directly changes an established path into a new path for supporting a handover. Our investigation reveals the effects of the proposed scheme and demonstrates that this method significantly reduces signaling costs and delays
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