Traffic classification and scheduling in ATM networks

Virtual paths (VPs) are an integral part of the resource management and control hierarchy of ATM (asynchronous transfer mode) networks. To improve the utilization of network resources and facilitate management and control, source types are organized into traffic classes. Each traffic class is transported by its own virtual path subnetwork. In this paper, we consider issues related to the design of traffic classes. We consider an ATM switch node to which cells arrive from a diverse set of source types. Traffic classes are assumed to be served according to a weighted round robin policy, while cells belonging to a given traffic class are served in first-come-first-served order. We consider the problem of determining the optimal set of traffic classes. Under suitable simplifying assumptions, it is shown that the above problem can be modeled as a set-partitioning problem. The structure of the problem at hand is then exploited to develop an efficient heuristic. Several examples are given to illustrate the developed methodology.Supported partially through NSF Grant NCR-891447 and AT&T Grant 5-23690.     

The error performance of Gray encoded QPSK and 8-PSK schemes in afading channel with cochannel interference

Closed-form BER (bit error rate) expressions are derived for Gray-encoded QPSK (quadrature phase shift keying) and 8-PSK schemes using coherent detection in a slow Rayleigh fading narrowband channel with fading cochannel interference. Earlier work has been limited to deriving the approximate BER using the canonical Stein (1961) receiver concept. The symbol error rate (SER) for the QPSK scheme is also derived. The desired signal and the cochannel interferer are both PSK signals, modulated by different baseband pulses with identical signaling rate     

Polynomial modeling and reduction of RF body coil spatial inhomogeneity in MRI

The usefulness of statistical clustering algorithms developed for automatic segmentation of lesions and organs in magnetic resonance imaging (MRI) intensity data sets suffers from spatial nonstationarities introduced into the data sets by the acquisition instrumentation. The major intensity inhomogeneity in MRI is caused by variations in the B1-field of the radio frequency (RF) coil. A three-step method was developed to model and then reduce the effect. Using a least squares formulation, the inhomogeneity is modeled as a maximum variation order two polynomial. In the log domain the polynomial model is subtracted from the actual patient data set resulting in a compensated data set. The compensated data set is exponentiated and rescaled. Statistical comparisons indicate volumes of significant corruption undergo a large reduction in the inhomogeneity, whereas volumes of minimal corruption are not significantly changed. Acting as a preprocessor, the proposed technique can enhance the role of statistical segmentation algorithms in body MRI data sets.     

A finite range failure model

In the present article the characterstics of a finite range failure time distribution, that includes the rectangular distribution as a particular case, are studied. When shape parameter surpass unity then the distribution is IFR otherwise it always remains IFRA. A graphic shape of the distribution is also formed for certain admissible values of the constants.     

A two-unit priority standby system subject to random shocks and Releigh failure-time distribution

This paper deals with the cost-benifit analysis of a two-unit priority standby system subject to random shocks. The priority unit gets preference both for repair and operation over the ordinary unit and has three modes- Normal, Quasi-normal and Total-failure. The ordinary unit has only two-modes- Normal and Total-failure. The distributions of shock-time, repair-time of the ordinary unit and failure time of the priority unit are negative exponential. The distribution of the repair-time of the priority unit is taken to be general while the time to failure of ordinary unit follows Releigh distribution. Various characteristics related to system effectiveness have been obtained by using the regenerative point technique.     

Tracking antenna architectures based on a planar two-portmicrostrip patch mixer antenna

This paper describes the behavior of a compact two-port integrated mixer active antenna element with low cross polarization, high two-port circuit isolation, and good mixer detection sensitivity. Using this element as an elemental building block, a self-tracking antenna array has been realized which uses an in-band carrier signal for self calibration. The array is relatively insensitive to absolute carrier power level and is capable of tracking incoming signals over ±80°. By minor alteration of the antenna topology, a minimum complexity variant of a heterodyne retrodirective array has been demonstrated over a ±40° retransmission angle. Finally, the use of the antenna in conjunction with an injection-locked voltage-controlled oscillator (VCO) is included in order to demonstrate ±35° phase-shifterless beam steering     

Miniaturized Microstrip Patch Antenna Array for ISM Band Using Complementary Split Ring Resonator

Wireless Personal Communications - These days patch antenna arrays are widely used in various communication systems. In this research design of miniaturized microstrip patch antenna array is...     

Multiport network model for CAD of electromagnetically coupledmicrostrip patch antennas

In this paper, electromagnetically coupled (EMC) patch-antenna configurations on two-layered dielectric substrates are investigated. The radiating patch is located on the top of the upper substrate and is excited by feed circuitry underneath it on the lower substrate. The electromagnetic field problem is transformed into a network problem and a multiport network model (MNM) is developed to characterize the three-dimensional (3-D) fields associated with the radiating structure. Antenna characteristics such as input impedance and radiation pattern are computed using the MNM model and the approach is validated by comparison with experimental results     

Cut off frequency and transit time analysis of lightly doped drain (LDD) MOSFETs

Analytical model for the transconductance, cut off frequency, transit time and fringing capacitance of LDD MOSFETs is presented with a simple approach. The analysis is carried out considering the LDD device as a conventional MOSFET with a series resistance [Z.-H. Liu et al., Threshold voltage model for submicrometer MOSFETs. IEEE Trans Electron Devices 1993; ED-40: 86–94] and a simple closed form expressions for cut off frequency and transit time is obtained. The total gate capacitance, i.e. the geometric and fringing capacitance, is calculated for both LDD and non-LDD devices and lower fringing capacitance is reported in LDD devices. Lower cut-off frequencies and higher transit time are reported in LDD devices for the same channel length.     

Design, development and testing of a large-size solar cooker for animal feed

A large-size solar cooker for animal feed has been designed, developed and tested. The cooker employs locally available materials of low cost, e.g. pearl-millet husk and horse excreata. The commercial materials required for its fabrication are plain glass, mild steel angle and sheet, wood and aluminium sheet cooking utensils. The solar cooker is capable of boiling 10 kg of animal feed, sufficient for five cattle per day. The efficiency of the solar cooker is 21·8%. The cost of the cooker is only Rs 1200, which can be recovered in 0·45-1·36 years depending upon the fuel it replaces. The short payback periods suggest that the use of the solar cooker is economic. The use of the cooker will save a lot of firewood, cowdung cake and agricultural waste which are presently used for the boiling of animal feed.