Constructions of rate (n-1)/n puncturedconvolutional codes with minimum required SNR criterion

Rate (n-1)/n punctured convolutional codes (n up to 10 and memory length up to 8) are constructed which minimize the required signal-to-noise ratio (SNR) for a bit-error rate (BER) of 10^-9 with and without the restriction of using only four different code generators. Many of these codes improve the free distance and reduce the required SNR more than half a decibel over previously reported codes with the same parameters. This is equivalent to reducing the decoder complexity by one half for the same performance. These codes have many potential applications in systems that require performance improvements with little room for coding overhead     

An O(kn) algorithm for a circularconsecutive-k-out-of-n:F system

An O(k×n) algorithm is described for evaluating the reliability of a circular consecutive-k-out- n:F system     

An efficient non-recursive algorithm for computing the reliabilityof k-out-of-n systems

An algorithm for computing the reliability of k-out-of- n systems is proposed. It is simple, easy to implement on a computer, time and memory efficient, and good for numerical computation. The memory complexity is O(n-k), and for a given value of n-k the computation time is proportional to n . Its FORTRAN implementation is presented     

An O(kn)-time algorithm for computing thereliability of a circular consecutive-k-out-of-n:Fsystem

I. Antonopoulou and S. Papastavridis (1987) published an algorithm for computing the reliability of a circular consecutive-k-out-of-n:F system which claimed O (kn) time. J.S. Wu and R.J. Chen (1993) correctly pointed out that the algorithm achieved only O(kn²) time. The present study shows that the algorithm can be implemented for O(kn) time     

L- and S-band low-noise cryogenic GaAs FETamplifiers

The authors present the results of the construction and testing of three cryogenic low-noise GaAs FET amplifiers, based on a National Radio Astronomy Observatory design, to be used in a detector for the axion, a hypothetical particle. The amplifiers are centered on 1.1 GHz, and 2.4 GHz, have a gain of approximately 30 dB in bandwidths of 300 MHz, 225 MHz, and 310 MHz, and have minimum noise temperatures of 7.8 K, 8 K, and 15 K, respectively     

Optimal replacement policies for k-out-of-nsystems

The authors study a discrete-time, infinite-horizon, dynamic programming model for the replacement of components in a binary k -out-of-n:F system. The goal is to trade off the component replacement and system failure costs. Under the criterion of minimizing the long-run average cost per period, it is optimal to follow a critical component policy (CCP), viz., a policy specified by a critical component set and the rule: replace a component if and only if it is failed and is in the critical component set. Computing an optimal CCP is a binary nonlinear programming problem, which can be solved by searching through a set with O(n^k-1) points. This approach to finding an optimal CCP is practical when k is small. In particular, assuming s-independent components, it requires O(n^2k-1) calculations. The authors analyze in detail the two most important cases with small k: the series (1-out-of-n:F) system and the 2-out-of-n:F system     

Invariant permutations for consecutive k-out-of-ncycles

Consecutive-k-out-of-n cycles are proposed as topologies for k-loop computer networks and describe a circular system of n components where the system fails if and only if any k consecutive components all fail. Suppose that the components are interchangeable. The the question arises as to which permutation maximizes the system reliability, assuming that the components have unequal reliabilities. If there exists on optimal permutation which depends on the ordering, but not the values, of the component reliabilities, then the system (and the permutation) is called invariant. The circular system is found to be not invariant except for k=1, 2, n-2, n-1, and n     

A limit theorem for n-phase Barker sequences

It is proved that for 3⩽L⩽19, except for L =6, the total number of normalized n-phase Barker sequences of length L increases without limit as n goes to infinity     

Reliability of a k-out-of-n warm-standby system

A general closed-form equation is developed for system reliability of a k-out-of-n warm-standby system (dormant failures). The equation reduces to the hot and cold standby cases under the appropriate restrictions     

A coding scheme for m-out-of-n codes

A scheme for the construction of m-out-of-n codes based on the arithmetic coding technique is described. For appropriate values of n, k, and m, the scheme can be used to construct an (n,k) block code in which all the codewords are of weight m. Such codes are useful, for example, in providing perfect error detection capability in asymmetric channels such as optical communication links and laser disks. The encoding and decoding algorithms of the scheme perform simple arithmetic operations recursively, thereby facilitating the construction of codes with relatively long block sizes. The scheme also allows the construction of optimal or nearly optimal m-out-of-n codes for a wide range of block sizes limited only by the arithmetic precision used     

An AlGaAs/InGaAs pseudomorphic high electron mobility transistorwith improved breakdown voltage for X- and Ku-bandpower applications

The authors determined that RF drain current degradation is responsible for the poor power performance of wide-recessed pseudomorphic high-electron-mobility transistors (PHEMTs). A model based on surface states was proposed to explain this phenomenon, which then led to the use of charge-screen layers and a double-recessed gate process to suppress surface effects. Combined, these two modifications increased the device's gate-drain reverse breakdown voltage without causing a degradation in the transistor's RF drain current. This allowed the simultaneous achievement of high power-added efficiency and high power density which established a new performance record for power PHEMTs at X- and Ku-bands. Delay time analysis of single- and double-recessed PHEMTs revealed that the benefit of a larger breakdown voltage in the latter device design came at the cost of a larger drain delay time. Drain delay accounted for 45% of the total delay when the 0.35-μm double-recessed PHEMT was biased at V_ds=6 V     

Modeling a shared-load k-out-of-n:G system

A Markov model for analyzing the reliability and availability of an n-unit shared-load repairable k-out-of-n:G system with imperfect switching is presented. The equations for both time-dependent and steady-state system availability are given. An inverse Laplace transform is used to solve the simultaneous differential equations for the nonrepairable case. A generalized analytic function for system reliability is obtained. Examples are provided to demonstrate the model and the impact of a load-sharing strategy on the reliability. The load-sharing strategy can improve system reliability and availability, if the controller and switching parameters are adequate. The proposed approach and solution are helpful to system engineers and reliability analysts     

On computing MTBF for a k-out-of-n:G repairablesystem

It is often necessary to calculate the MTBF (mean time between failures) quickly in order to make timely design decisions. An important system for which such calculations must be made is a k-out-of- n:G parallel system with unlimited repair and exponential interfailure and repair times at the unit level. Although a general formula is known, it is not easily remembered or derived. A method for deriving a formula for MTBF in this situation that is easily reproduced quickly by remembering a few simple concepts is presented     

An enhanced integer simplicial optimization method for minimum costspares for k-out-of-n systems

The authors report two enhancements to an integer simplicial optimization method developed for a spares allocation problem where it is necessary to minimize the spares cost of a k-out-of-n system configuration subject to an availability constraint. The first is an automated, simple, general method for generating an initial feasible good starting vector for optimization. This vector increases the likelihood of convergence to a global optimal solution and does not require homogenization of a suboptimum solution vector prior to restarting the optimization process of the penalty function for the lower values of the multipliers. The second is treatment of cases where the simplex strays into the feasible region. Results of testing the integer simplicial optimization procedure with the enhancements are compared to those obtained from methods developed specifically for dealing with this type of nonlinear integer problem. The tests were conducted for systems with various numbers of subsystems     

The efficiency of computing the reliability of k-out-of n systems

It is shown that the algorithm of R.S. Barlow and K.D. Heidtmann (ibid., vol.R-33, p.322-3, Oct. 1984) is more computationally efficient than those reported by S.P. Jain and K. Gopal (ibid., vol.R-34, p.144-6, June 1985) and S. Rai et al. (ibid., vol.R-36, p.261-5, June 1987). Efficiency is measured here by the number of multiplications     

Automatic VT extractors based on ann×n2 MOS transistor array and theirapplication

The development of incremental and decremental V_T extractors based on the square-law characteristic and an n ×n² transistor array is described. Different implementations have been discussed and the effect of nonidealities such as mobility reduction, channel-length modulation, mismatch, and body effect has been analyzed. Besides automatic V_T extraction, parameter K of an MOS transistor can also be extracted automatically using the V_T extractor, without any need of calculation and delay, and the extracted V_T and K are, respectively, in voltage and current. Experimental results are presented and indicate that the differences between extracted values using the V_T extractor and the most popular numerical method are as small as 0.15% and 0.064%. Additional applications, such as in level shifting, temperature compensation, and temperature measurement, where the V_T extractor can be used either as a PTAT sensor or as a centigrade sensor, are presented     

Comment on `Modeling a shared-load k-out-of-n*Gsystem'

The commenter states that there is no reason to perform the steady-state analysis as attempted by J. Shao and L.R. Lamberson (see ibid., vol.40, no.2, p.205-9, June 1991) for a Markov chain that has an absorbing failure state. Corrected expressions are provided     

Optimal designs of{k,n-k+1}-out-of-n:F systems(subject to 2 failure modes)

The problem of achieving optimal system size (n) for {k,n-k+1}-out-of-n systems, assuming that failure may take either of two forms, is studied. It is assumed that components are independently identically distributed (i.i.d.) and that the two kinds of system failures can have different costs. The optimal k or n that maximizes mean system-profit is determined, and the effect of system parameters on the optimal k or n is studied. It is shown that there does not exist a pair (k,n) maximizing the mean system-profit     

Frequency-diversity improvement in n/1 high-capacitydigital microwave radio

Frequency diversity performance of digital microwave radio is investigated. Improvement ratio in n/1 systems is computed, based on the improvement ratio in 1/1 systems and the frequency dependence of the latter. Computed curves showing the dependence of IR on the channel position and of the position of the standby channel are given     

m-consecutive-k-out-of-n:F systems

An m-consecutive-k-out-of-n:F system, consists of n components ordered on a line; the system fails if and only if there are at least m nonoverlapping runs of k consecutive failed components. Three theorems concerning such systems are stated and proved. Theorem one is a recursive formula to compute the failure probability of such a system. Theorem two is an exact formula for the failure probability. Theorem three is a limit theorem for the failure probability