Quality Determination for Gate Delay Fault Tests Considering Three-State Elements

Most industrial digital circuits contain three-state elements besides pure logic gates. This paper presents a gate delay fault simulator for combinational circuits that can handle three-state elements like bus drivers, transmission gates and pulled busses. The well known delay faults--slow-to-rise and slow-to-fall--are considered as well as delayed transitions from isolating signal state high impedance to binary states 0 and 1 and vice versa. The presented parallel delay fault simulator distinguishes between non-robust, robust and hazard free tests and determines the quality of a test. Experimental results for ISCAS85/89 benchmark circuits are presented as well as results for industrial circuits containing three-state elements.     

Novel Ion-Lens Configurations: A Further Step to 2-nm Ion-Beam Lithography

Composite axially symmetric immersion ion lenses are considered that consist of an electrostatic and a magnetic lens. For the first time, their performance is evaluated over the entire range of operating conditions: from the case of a zero magnetic field to the case of a zero ion energy on the target. Operating conditions are characterized in terms of = W _t/W ₀, where W ₀ is the energy of an ion at the boundary of the region in which the trajectories are parallel to the axis and W _t is that on the target. For the first time, simple analytical approximations are derived for C _c/r, C _s/r, f/r, and NI, where C _c is the chromatic-aberration coefficient, C _s is the third-order spherical-aberration coefficient, f is the focal distance, NI is the magnetomotive force of the coil, and r is the outer radius of the coil. The behavior of the four quantities is explored as a function of . The following conclusions are drawn: (i) The aberrations are maximum for a zero magnetic field. (ii) The aberration coefficients decrease monotonically with increasing NIand decreasing , the lens changing from an accelerating to a decelerating one. (iii) If , then C _s/r – ^1/4, C _c/r – ^1/6, f/r– ^1/3, and NI – ^–1/2. (iv) The lenses are suitable for resistless heavy-ion projection lithography and can provide 20 × 10¹¹ pixels of area 2 × 2 nm² for an exposed area of 3 × 3 mm². (v) Used in heavy-ion microprobe systems, the lenses could enable resistless lithography over much larger areas than existing equipment.     

Surface-Photovoltage Measurement of Volume Electron Lifetime in p-Si Wafers

The problem of estimating the volume lifetime _v of minority carriers in p-type Si wafers by surface-photovoltage measurements is addressed. An experiment is conducted in order to ascertain the relationship between measured and actual values of _v. The measurements are carried out on circular specimens whose thickness is reduced from about 2000 to 450 m by stepwise etching. The specimens are cut from a Czochralski-grown rod, their actual values of _v ranging from 10 to 300 s. The surface recombination rate of minority carriers is determined on both sides of the specimens covered with native oxide, the sides differing in surface finish. The results of the experiment allow one to determine _v up to about 400 s.     

On the distribution of characteristics in bijective mappings

Differential cryptanalysis is a method of attacking iterated mappings based on differences known as characteristics. The probability of a given characteristic is derived from the XOR tables associated with the iterated mapping. If is a mapping : Z ₂ ^m , then for each , X, Y Z ₂ ^m the XOR table for gives the number of input pairs of difference X=X+X for which gp(X)+(X)=Y.The complexity of a differential attack depends upon two properties of the XOR tables: the density of zero entries in the table, and the size of the largest entry in the table. In this paper we present the first results on the expected values of these properties for a general class of mappings . We prove that if : Z ₂ ^m Z ₂ ^m is a bijective mapping, then the expected size of the largest entry in the XOR table for is bounded by 2m, while the fraction of the XOR table that is zero approaches e ^–1/2=0.60653. We are then able to demonstrate that there are easily constructed classes of iterated mappings for which the probability of a differential-like attack succeeding is very small.The author is presently employed by the Distributed System Technology Center, Brisbane, Australia.     

Gaussian radial basis functions and inner product spaces

An approximation result is given concerning Gaussian radial basis functions in a general inner product space. Applications are described concerning the classification of the elements of disjoint sets of signals, and also the approximation of continuous real functions defined on all of ⁿ using radial basis function (RBF) networks. More specifically, it is shown that an important large class of classification problems involving signals can be solved using a structure consisting of only a generalized RBF network followed by a quantizer. It is also shown that Gaussian radial basis functions defined on ⁿ can uniformly approximate arbitrarily well over all of ⁿ any continuous real functionalf on ⁿ that meets the condition that |f(x)|0 as x.     

Symmetry relations in multidimensional Fourier transform pairs

A relation between the types of symmetries that exist in signal and Fourier transform domain representations is derived for continuous as well as discrete domain signals. The symmetry is expressed by a set of parameters, and the relations derived in this paper will help to find the parameters of a symmetry in the signal or transform domain resulting from a given symmetry in the transform or signal domain respectively. A duality among the relations governing the conversion of the parameters of symmetry in the two domains is also brought to light. The application of the relations is illustrated by a number of two-dimensional examples.Notation R the set of real numbers - R ^m R × R × ... × R m-dimensional real vector space - continuous domain real vector - L {¦ – _i , i = 1,2,..., m} - m-dimensional frequency vector - W { – _i ,i=1,2,..., m} - m-dimensional normalized frequency vector - _P {¦ – _i , i=1,2,...,m} - g(ol) g (₁,₂,..., _m ) continuous domain signal - () ( _{1 2},..., _m )=G (j ₁,j ₂,..., j _m ) Fourier transform ofg (ol) - (A,b,,,) parameters ofT- symmetry - N the set of integers - N ^m N × N × ... × N m-dimensional integer vector spacem-dimensional lattice - h(n) h (n ₁,.,n _m ) discrete domain signal - H() Fourier transform ofh (n) - v ₁,v ₂,..., v_m m sample-direction and interval vectors - V (v ₁ v ₂ ...v _m ) sampling basis matrix - [x]^* complex conjugate ofx - detA determinant ofA - X {x¦ – x _i , i=1,2,..., m} - A ^–t [A ^–1] ^t ,t stands for transpose This work was supported in part by the Natural Sciences and Engineering Research Council of Canada under Grant A-7739 to M. N. S. Swamy and in part by Tennessee Technological University under its Faculty Research support program to P. K. Rajan.     

Linear phase FIR approximation of magnitude response |1/ω| for maximal flatness at an arbitrary frequency ω0, 0<ω0<π*

In many signal processing situations, the desired (ideal) magnitude response of the filter is a rational function: (a digital integrator). The requirements of a linear phase response and guaranteed stable performance limit the design to a finite impulse response (FIR) structure. In many applications we require the FIR filter to yield a highly accurate magnitude response for a narrow band of frequencies with maximal flatness at an arbitrary frequency ₀ in the spectrum (0, ). No techniques for meeting such requirements with respect to approximation of are known in the literature. This paper suggests a design by which the linear phase magnitude response can be approximated by an FIR configuration giving a maximally flat (in the Butterworth sense) response at an arbitrary frequency ₀, 0<₀<^*. A technique to compute exact weights for the design has also been given.     

Synthesis of arbitrary digital transfer functions using allpass-based structures derived via LBR two-pair extraction procedure

The implementation of a digital filter transfer function with all transmission zeros on the unit circle is developed via the synthesis of an appropriate allpass function. The synthesis procedure is based on the LBR-extraction approach. The resulting structure is in the form of a doubly terminated cascade of lossless (LBR) two-pairs, with each two-pair realizing a single real or a pair of complex transmission zeros. The Concepts of complete and partial 1 removals, and 1 shifting are introduced and utilized during the synthesis process. The resulting structures have several properties in common with the Gray and Markel lattice filters, but do not require tap coefficients for numerator realization. The building blocks used in this paper are similar to those in certain wave-digital filters and orthogonal filters.Work supported in part by NSF Grant Number ECS 82-18310 and in part by NSF Grant Number ECS-8508017.     

Predictive Caching Strategy for On-Demand Routing Protocols in Wireless Ad Hoc Networks

Route caching strategy is important in on-demand routing protocols in wireless ad hoc networks. While high routing overhead usually has a significant performance impact in low bandwidth wireless networks, a good route caching strategy can reduce routing overheads by making use of the available route information more efficiently. In this paper, we first study the effects of two cache schemes, link cache and path cache, on the performance of on-demand routing protocols through simulations based on the Dynamic Source Routing (DSR) protocol. Since the path cache DSR has been extensively studied, we focus in this paper on the link cache DSR in combination with timer-based stale link expiry mechanisms. The effects of different link lifetime values on the performance of routing protocol in terms of routing overhead, packet delivery ratio and packet latency are investigated. A caching strategy incorporating adaptive link timeout is then proposed, which aims at tracking the optimal link lifetime under various node mobility levels by adaptively adjusting the link lifetime based on the real link lifetime statistics. The performance of the proposed strategy is then compared with the conventional path cache DSR. The results show that without a timeout mechanism, a link cache scheme may suffer severe performance degradation due to the use of broken routes, while the proposed adaptive link cache strategy achieves significantly improved performance by reducing the routing overhead when the network traffic load is high.     

Year 2000 — a Sytems Integration challenge

BT, along with virtually every other IT-dependent business worldwide, is tackling a problem which is quite unique and if not corrected could be disastrous. The problem, sometimes known as the Year 2000 bug or millennium time bomb, has been caused by the use of two digits to represent the year in the majority of our systems and applications. The problem is technically not difficult to fix but the volume of changes occurring, and the need to potentially test every system to ensure that it is year 2000 proof, presents unique and challenging difficulties for integration and testing. Why this is the case, what problems need to be addressed, and an overview of some of the proposed integration and test strategies to tackle these problems, is the subject of this paper.     

A VLSI decoder for a new type of constellations adapted to the Rayleigh Fading Channel

Diversity is the key solution to obtain efficient channel coding in wireless communications, where the signal is subject to fading (Rayleigh Fading Channel). For high spectral efficiency, the best solutions used nowadays are based on QAM constellations of 1-order diversity, associated with a binary code or a trellis coded modulation to increase the overall diversity. It has been shown that a new class of d-dimensional non-QAM constellations, named -constellations, can bring a d-order diversity without the addition of redundancy. Combined with classical coding techniques, -constellations are very efficient. However, the decoding algorithm is far more complicated for -constellations than for QAM-constellations. A sub-optimal algorithm that allows the decoding of -constellations is proposed. An example of an application for a 4 bits/Hz/s spectral efficiency with a 4-D -constellation is given. The VLSI architecture of the decoder is described. The implementation leads to 72 K gates, a binary rate of 32 Mbits/s and a BER of 10^-3 for a SNR of 14 dB.     

Stabilization of third-order, single-stage Sigma-Delta modulators

The issue of stability of higher-order, single-stage Sigma-Delta () modulators is addressed using a method from nonlinear system theory. As a result, theoretical bounds for the quantizer input of the modulators are derived. A new method for stabilizing the modulators is then presented. It uses the quantizer input bound for possible instability detection. Upon detection of such a state, the highest-order integrator is cut off, effectively reducing the order of the modulator, and thus resulting in a stable system. The method is easily implemented and results in a very good signal-to-noise ratio (SNR) and fast return to normal operation compared to other stabilization methods.Financial support from General Secretariat for Research and Technology of Greece under contract PENED 95/1729.     

A Novel EKF-Based Recovery in DS Scheme for DS/CDMA Systems Tracking Code Delay

Classical delay-lock loops (DLL) have beenwidely considered for code synchronization purposes inDS/CDMA systems, although they have not been devised foroperation when channel fading is present. This paper describes a new code synchronizationscheme based on a previously proposed extended Kalmanfilter (EKF) approach. The scheme proposed in this paperis able to operate under low signal-to-interference ratios (SIR), usual at the receiver input incellular CDMA mobile environments, and it outperformsthe behavior of previously proposed EKF-based schemes,which failed in such environments. Performance results under realistic mobile environment conditionsare shown in terms of the mean time to lose lock (MTLL)and the tracking error variance ² for a wide range ofSIR values and under Rayleigh fading. Moreover, the Cramer-Rao lower boundon ² is also computed inorder to validate the results obtained viasimulations.     

Fault diagnosis in reconfigurable VLSI and WSI processor arrays

A systematic efficient fault diagnosis method for reconfigurable VLSI/WSI array architectures is presented. The basic idea is to utilize the output data path independence among a subset of processing elements (PEs) based on the topology of the array under test. The divide and conquer technique is applied to reduce the complexity of test application and enhance the controllability and observability of a processor array. The array under test is divided into nonoverlapping diagnosis blocks. Those PEs in the same diagnosis block can be diagnosed concurrently. The problem of finding diagnosis blocks is shown equivalent to a generalizedEight Queens problem. Three types of PEs and one type of switches, which are designed to be easily testable and reconfigurable, are used to show how to apply this approach. The main contribution of this paper is an efficient switch and link testing procedure, and a novel PE fault diagnosis approach which can speed up the testing by at leastO(V^1/2) for the processor arrays considered in this paper, where V is the number of PEs. The significance of our approach is the ability to detect as well as to locate multiple PE, switch, and link faults with little or no hardware overhead.     

Higher-order terms in asymptotic expansion for information loss in quantized random processes

Uniform quantization of random vectors onto -grids ⁿ is considered. Higherorder terms in asymptotic expansions for the entropy of the -quantized random vector and for the loss of the mutual information between two random vectors under such quantization as 0+are obtained. The coefficients in these asymptotics are explicitly calculated for Gaussian distributed vectors. Taken for initial segments of stationary Gaussian sequences, these factors have limit average values per unit of time. For such sequences governed by state-space equations, computation of these average values is reduced to solutions of algebraic matrix Riccati and Lyapunov equations.Work supported by the Australian Research Council grant A 4970 2246.     

Minimizing the average cost of paging and registration: A timer-based method

Methods of balancing call registration and paging are developed in this paper. Given that the probability distribution on the user location as a function of time is either known or can be calculated, previous work shows the existence of lower bounds on the average cost of paging. Here these bounds are used in conjunction with a Poisson incoming-call arrival model to formulate the paging/registration optimization problem in terms oftimeout parameters, _m ; the maximum amount of time to wait before registering given the last known location wasm. Timer-based methods, as opposed to location-based methods, do not require the user to record and process location information during the time between location updates. This feature might be desirable for minimizing mobile transceiver use during idle periods. We then consider uniform motion processes where a spatial translation of starting location produces an identical spatial translation of the associated time-varying probability distribution. This leads to a universal timeout parameter which may be readily calculated. We study and the minimum cost of paging/registration for a simple model of user motion and compare our results to an earlier method of location-based paging/registration cost minimization.     

Scheduling and bandwidth allocation for the distribution of archived video in VOD systems

Providing costeffective videoondemand (VOD) services necessitates reducing the required bandwidth for transporting video over highspeed networks. In this paper, we investigate efficient schemes for transporting archived MPEGcoded video over a VOD distribution network. A video stream is characterized by a timevarying traffic envelope, which provides an upper bound on the bit rate. Using such envelopes, we show that video streams can be scheduled for transmission over the network such that the perstream allocated bandwidth is significantly less than the source peak rate. In a previous work [13], we investigated stream scheduling and bandwidth allocation using global traffic envelopes and homogeneous streams. In this paper, we generalize the scheduling scheme in [13] to include the heterogeneous case. We then investigate the allocation problem under windowbased traffic envelopes, which provide tight bounds on the bit rate. Using such envelopes, we introduce three streamscheduling schemes for multiplexing video connections at a server. The performance of these schemes is evaluated under static and dynamic scenarios. Our results indicate a significant reduction in the perstream allocated bandwidth when stream scheduling is used. While this reduction is obtained through statistical multiplexing, the transported streams are guaranteed stringent, deterministic quality of service (i.e., zero loss rate and small, bounded delay). In contrast to video smoothing, our approach requires virtually no buffer at the settop box since frames are delivered at their playback rate.     

Practical zero-knowledge proofs: Giving hints and using deficiencies

New zero-knowledge proofs are given for some number-theoretic problems. All of the problems are in NP, but the proofs given here are much more efficient than the previously known proofs. In addition, these proofs do not require the prover to be superpolynomial in power. A probabilistic polynomial-time prover with the appropriate trapdoor knowledge is sufficient. The proofs are perfect or statistical zero-knowledge in all cases except one.This research was supported in part by NSA Grant No. MDA904-88-H-2006.In this paper it will at times be convenient to think of the verifier as being named Vic, and the prover being named Peggy. Thus, he will refer to the verifier and she will refer to the prover.     

On the structure of the privacy hierarchy

An N argument function f(x ₁,...,x _N ) is called t-private if a protocol for computing f exists so that no coalition of at most t parties can infer any additional information from the execution, other than the value of the function. The motivation of this work is to understand what levels of privacy are attainable. So far, only two levels of privacy are known for N argument functions which are defined over finite domains: functions that are N-private and functions that are (N – 1)/2-private but not N/2-private.In this work we show that the privacy hierarchy for N-argument functions which are defined over finite domains, has exactly (N + 1)/2 levels. We prove this by constructing, for any N/2 t N – 2, an N-argument function which is t-private but not (t + 1)-private.This research was supported by US-Israel Binational Science Foundation Grant 88-00282.     

Some new results on stability robustness of two-dimensional discrete systems

In this paper, we study the problem of stability robustness of two-dimensional discrete systems in a local state-space setting. Two methods are proposed for efficient numerical evaluation of the exact complex perturbation bound . The first method combines Byers' bisection method with a three-point-pattern optimization technique to compute . The second method utilizes a direct optimization technique to find the bound. In addition, a 2-D Lyapunov approach is proposed to obtain two lower bounds of , and numerical techniques for solving the constant 2-D Lyapunov equation involved are presented. The paper is concluded with an example illustrating the main results obtained.