Integrating voice with the pi-persistentprotocol for unidirectional broadcast bus networks

A previously proposed protocol is extended to include voice for multiaccess communication over unidirectional broadcast bus networks. The authors use a framed approach for integrating these two traffic types where a frame, which is repeated, consists of a voice subframe followed by a data subframe. They use speech detectors for modeling speech sources in order to prevent the loss of about 60% of the bandwidth that would otherwise be required, and they use a moveable-boundary scheme in which the voice subframe size is estimated from the number of voice packets transmitted in the previous frame. The authors determine the fraction of speech loss and the fraction of wasted allocated bandwidth due to the estimator by formulating Markov chain for the number of ready voice stations at the frame boundaries. To analyze data performance, they use a nonhomogeneous Markov chain or a data station's buffer content just before the data slots visit that station. By proper control of the estimator function, they can guarantee an upper bound on the average speech loss at any voice station, and a combined voice-data throughput close to unity is achieved. Results from the analysis and from a simulation match closely     

A dynamic bandwidth-allocation-based priority mechanism for thepi-persistent protocol for MAN's

While a variety of medium access protocols have been proposed for metropolitan area networks (MANs), the problem of handling multipriority traffic effectively in these networks remains open. The authors present a simple and effective priority mechanism for an existing MAN protocol known as the p_i-persistent protocol, a probabilistic scheduling scheme that has been shown to be suitable for applications requiring large bandwidth over long, repeater-free distances. The mechanism works by clipping the low-priority stations in a controlled manner, thereby increasing the bandwidth available to the high-priority stations. This mechanism operates entirely within the framework of the basic p_i-persistent protocol and may be easily tailored to achieve specific performance goals by selection of a single operating parameter. A multipriority version of a distributed algorithm by which the stations can update their operating parameters and adapt to changing network conditions dynamically is also presented     

Dynamic control and accuracy of thepi-persistent protocol using channel feedback

The p_i-persistent protocol is based on a probabilistic scheduling mechanism (see Mukherjee and Meditch, 1988). The authors further develop the protocol to make it easily implementable, by allowing it to be sensitive to changing load conditions. They study various properties of a simple algorithm which stations execute independently by using channel feedback information. This results in a fully distributed control mechanism that continuously adjusts the station probabilities p_i at their proper levels as governed by the offered traffic. An extensive simulation model has been developed to study properties of this control mechanism such as p_i settling time and accuracy, behavior under step changes in traffic load, effect of injection of additional packets, and effect of various parameters associated with the underlying algorithm. These experiments indicate that this algorithm is suitable for implementing the protocol     

Two chi-square statistics for determining the orders p andq of an ARMA (p, q) process

The &thetas;, λ, and η functions have been previously proposed for use in choosing the autoregressive and moving-average orders of an ARMA (q, p) process visually. Two chi-square statistics associated with these three functions are presented and used here to determine the orders of an ARMA process statistically. It is shown that the two statistics are asymptotically equivalent to the Quenouille-Walker's goodness-of-fit test statistic, which is a Lagrange multiplier test statistic. Some numerical examples are presented to illustrate the usefulness of the two chi-square statistics as well as the three functions in ARMA modeling     

Thin-film, accumulation-mode p-channel SOI MOSFETs

Electrical characteristics of thin-film (100 nm), accumulation-mode SOI p-channel MOSFETs are reported and compared to simulation. In the OFF regime, the p-type channel is fully depleted. As a result, very low values of leakage current are obtained. Very good threshold voltage control is also obtained     

Delay analysis of a packet voice multiplexer by the ΣDi/D/1 queue

The performance of a statistical multiplexer whose inputs consist of a superposition of voice packet streams is studied. The delay for such a system is analyzed by solving the ΣD_i/ D/1 queue. The analytic method can be used to find the approximate mean delay for an arbitrarily large number of trunks and the approximate delay distribution when the number of trunks is less than 100. An efficient hybrid simulation of the packet voice multiplexer which can be used to find the delay distribution for a large number of trunks is presented. In addition, easily computable error bounds for the present approximation are provided, and the accuracy of the M/ D/1 approximation is investigated     

On the design of FIR digital differentiators which are maximallylinear at the frequency π/p, p ∈ {positiveintegers}

Digital differentiators (DDs) which are maximally linear at the spot frequency ω=π/p, p ∈ {positive integers} are proposed for operation over a narrow band of frequencies. The suggested DDs, besides giving zero phase error over the entire band of frequencies (-π⩽ω⩽π), can achieve very high accuracy in the magnitude response, over a given frequency range, with attractively low order of structure. For example, for p=3, magnitude accuracy better than 99.999% can be achieved over the passband 0.26π⩽ω⩽0.41π with an order of structure of 21. Mathematical formulas for the weighting coefficients required in the design have also been given     

Performance analysis of Ku-band VSAT networks

A critical parameter of a very small aperture terminal (VSAT) satellite network, namely the availability of its links, is defined as the percentage of time that information can be transmitted and received with acceptable quality. The information quality is quantified, and the factors that affect it are described. Link unavailability (outage) due to equipment problems and rainfall is discussed. The use of spread-spectrum techniques is considered. A performance analysis example is provided and some conclusions are drawn     

Gain measurements on the KrF(B→X), XeF(B→X), and XeF(C→A) lasertransitions in an XeF(C→A) laser gas mixture

Optimum energy extraction from an electron-beam-pumped XeF(C →A) laser is achieved with a five-component rare gas halide mixture. The characterization and modeling of laser action in such a gas mixture requires a knowledge of small-signal gain and absorption coefficients not only on the blue-green XeF(C→ A) transition, but also in the ultraviolet (UV) region for the competing XeF(B→X) and KrF(B→X ) transitions. The authors report gain measurements on the XeF(C→A) transition and small-signal gain and absorption coefficients at or near both the XeF(B→X ) (351 and 353 nm) and KrF(B→X) (248 nm) transitions. A study of the gain for the UV and visible transitions as a function of Kr and Xe partial pressure is reported, and its impact on the XeF(C→A) kinetics is discussed     

Robustness of mean E{X} and R charts

The effect of nonnormality on E{X} and R charts is reported. The effect of departure from normality can be examined by comparing the probabilities that E{X} and R lie outside their three-standard-deviation and two-standard-deviation control limits. Tukey's λ-family of symmetric distributions is used because it contains a wide spectrum of distributions with a variety of tail areas. The constants required to construct E{X} and R charts for the λ-family are computed. Control charts based on the assumption of normality give inaccurate results when the tails of the underlying distribution are thin or thick. The validity of the normality assumption is examined by using a numerical example     

Optimum control of N-input K-output matrixconverters

Significant developments of the general optimum control theory presented in a previous paper by the authors (1988) are discussed for the specific case of multiphase matrix converters. Results hold, regardless of system configuration, input and output voltage waveforms, and loads. Applications to the most practical converter structures are illustrated, and implementation criteria of the optimum control method are derived. Simulated results confirm the flexibility and effectiveness of the approach     

The performance of depressed-cladding single-mode fibers withdifferent b/a ratios

Depressed-cladding single-mode fibers with a first cladding-to-core ratio (b/a) ranging from seven to one and relative refractive-index differences of the core from 0.25 to 0.35% and of the cladding from 0 to -0.2% are investigated experimentally with respect to the LP₁₁ mode cutoff properties, the mode-field diameter, the dispersion, and the bending attenuation. Numerical calculations based on actual profile parameters of the bend loss and the mode-field diameter agree well with experiment. It is demonstrated that low attenuation and bend losses independent of b/a can be obtained if the cutoff wavelength is kept constant by adjusting the core radius, the core index or the index of the first cladding     

High-performance Ka-band and V-band HEMTlow-noise amplifiers

Quarter-micron-gate-length high-electron-mobility transistors (HEMTs) have exhibited state-of-the-art low-noise performance at millimeter-wave frequencies, with minimum noise figures of 1.2 dB and 32 GHz and 1.8 dB at 60 GHz. At Ka-band, two-stage and three-stage HEMT low-noise amplifiers have demonstrated noise figures of 1.7 and 1.9 dB, respectively, with associated gains of 17.0 and 24.0 dB at 32 GHz. At V-band, two stage and three-stage HEMT amplifiers yielded noise figures of 3.2 and 3.6 dB, respectively, with associated gains of 12.7 and 20.0 dB and 60 GHz. The 1-dB-gain compression point of all the amplifiers is greater than +6 dBm. The results clearly show the potential of short-gate-length HEMTs for high-performance millimeter-wave receiver application     

Closest coset decoding of |u|u+v| codes

The general concept of closest coset decoding (CCD) is presented, and a soft-decoding technique for block codes that is based on partitioning a code into a subcode and its cosets is described. The computational complexity of the CCD algorithm is significantly less than that required if a maximum-likelihood detector (MLD) is used. A set-partitioning procedure and details of the CCD algorithm for soft decoding of |u|u+v| codes are presented. Upper bounds on the bit-error-rate (BER) performance of the proposed algorithm are combined, and numerical results and computer simulation tests for the BER performance of second-order Reed-Muller codes of length 16 and 32 are presented. The algorithm is a suboptimum decoding scheme and, in the range of signal-to-noise-power-density ratios of interest, its BER performance is only a few tenths of a dB inferior to the performance of the MLD for the codes examined     

Relationships between m-sequences over GF(q) andGF(qm)

It is shown that m-sequences over GF(q^m ) of length q^nm-1 corresponding to primitive polynomials in GF[q^m,x] of degree n can be generated from known m-sequences over GF(q) of length q^nm-1 obtained from primitive polynomials in GF[q,x] of degree mn. A procedure for generating the m-sequences over GF(q²) from m-sequences over GF(q) was given which enables the generation of m-sequences over GF( p²ⁿ). In addition it was shown that all of the primitive polynomials in GF[q,^m,x] can be obtained from a complete set of the primitive polynomials in GF[q ,x]     

A k shortest path algorithm for adaptive routing incommunications networks

An efficient and flexible algorithm is presented for finding a k shortest loopless path with distinct initial links from one node to each other node. Low-order polynomial bounds are established for the worst-case time complexity of the algorithm, showing it to offer a substantial improvement over applying known algorithms to the problem. The algorithm can incorporate various extensions, including the ability to handle an algebraic objective, which enhance its applicability to diverse network models. In addition, the k shortest path formulation and algorithm are proposed as a basis for network survivability measures where path length bounds exist     

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     

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     

A technique for real-time measurement of Nth-orderderivativesdNV/dIN

A technique for the measurement of device derivatives d ^NV/dI^N of arbitrary order N described. Measurement is accomplished by injecting a test current composed of the sum of N square waves into the rest device, and then multiplying the corresponding voltage change by the product of those same square waves, followed by low-pass filtering. The algorithm is implemented in real time using a mixture of analog and digital circuitry, and its application to semiconductor laser control in high-speed optical communications is described