Analysis and simulation of interrupt overhead impact on OS throughput in high‐speed networks

The paper presents analytical and simulation models to study the impact of interrupt overhead on operating system throughput of network elements such as PC‐based routers, servers, and hosts when subjected to high‐speed network traffic. Under such high network traffic, the system throughput will be negatively affected due to interrupt overhead caused by the incoming traffic. We first present an analytical model for the ideal system when interrupt overhead is ignored. We then present two models which describe the impact of high interrupt rate on system throughput. One model is for employing PIO in which network adapters are not equipped with DMA engines, and the other model is for employing DMA in which network adapters are equipped with DMA engines. The paper also describes detailed discrete‐event simulation models for the ideal system and for systems with DMA and PIO. Simulations results as well as reported experimental measurements show that our analytical models are valid and give a good approximation. Our analysis and simulation work can be valuable in providing insight to understand and predict system behaviour, as well as improving and maintaining good host performance. The paper identifies analytically critical design operation points such as that of overload condition. The paper also proposes solutions and recommendations for improving performance. Copyright © 2005 John Wiley & Sons, Ltd.     

Iterative interference cancellation for high spectral efficiencysatellite communications

The problem of efficient utilization of the frequency spectrum for satellite systems is investigated; one which results as a consequence of highly crowding adjacent channels. An analytical characterization of the resulting interference channel is introduced and then exploited for interference cancellation. Two classes of cancelers are investigated. The first approach does not benefit from the forward error control (FEC) coding information which limits the performance gain. This motivates the second approach where a joint implementation of interference cancellation and decoding is developed using soft-input-soft-output (SISO) modules along with the iterative structure. It is shown that iterative interference cancellation techniques can achieve significant gains compared with the single-user matched filter receiver     

NAR estimators of spatial covariance matrices for adaptive arraydetection

The theory of noise-alone-reference (NAR) power estimation is extended to the estimation of spatial covariance matrices. A NAR covariance estimator insensitive to signal presence is derived. The SNR (signal-to-noise ratio) loss incurred by using this estimator is independent of the input SNR and is less than that encountered with the maximum likelihood covariance estimator given that the same number of uncorrelated snapshots is available to both estimators. The analysis assumes first a deterministic signal. The results are extended and generalized to signals with unknown parameters or random signals. For the random signal case, generalized and quasi-NAR covariance estimators are presented     

ECRP: an energy-aware cluster-based routing protocol for wireless sensor networks

Energy conservation is the main issue in wireless sensor networks. Many existing clustering protocols have been proposed to balance the energy consumption and maximize the battery lifetime of sensor nodes. However, these protocols suffer from the excessive overhead due to repetitive clustering resulting in high-energy consumption. In this paper, we propose energy-aware cluster-based routing protocol (ECRP) in which not only the cluster head (CH) role rotates based on energy around all cluster members until the end of network functioning to avoid frequent re-clustering, but also it can adapt the network topology change. Further, ECRP introduces a multi-hop routing algorithm so that the energy consumption is minimized and balanced. As well, a fault-tolerant mechanism is proposed to cope up with the failure of CHs and relay nodes. We perform extensive simulations on the proposed protocol using different network scenarios. The simulation results demonstrate the superiority of ECRP compared with recent and relevant existing protocols in terms of main performance metrics.

     

A hydrodynamic transport model and its applications in semiconductor device simulation

In this paper, a generalized hydrodynamic model that includes four conservation equations for a general, position-dependent energy band structure and effective mass is presented. An analytical mobility model is extended to simulate two-valley semiconductor devices. A semiconductor device simulation package, DYNA, is introduced. Simulation results for both bulk materials and submicron-gate GaAs MESFETs show good agreement with experimental data and Monte Carlo device simulation results.     

Holographic SAR image formation by coherent summation of impulseresponse derivatives

Using the physical optics approximation, the radar image of a target can be constructed from a knowledge of the monostatic backscattered field or hologram for all frequencies and all aspects angles. The target image is the two-dimensional Fourier transform of the hologram. This is based on the same principle as conventional holography. In the near-field the image is computed by the coherent summation of back-projected range responses which are derived from complex impulse responses. Consequently, the image can be interpreted as a tomographic reconstruction. If the target is within the antenna beam at each radar position in the linear synthetic-aperture radar (SAR) geometry, then the algorithm for the coherent summation of impulse response derivatives (IRDs) can be applied. Experimental results for the near-field of a wheat field and a Peugeot 504 automobile are presented to verify the effectiveness of the method     

Capacitance and conductance of ZnxCd1-xS/ZnTeheterojunctions

Capacitance-voltage and conductance-voltage characteristics of RF-sputtered ZnCdS films on ZnTe single crystals are studied as a function of frequency up to 1 MHz. It is found that the measured capacitance decreases with frequency while the conductance increases. A physical circuit model of the junction is proposed to explain this dependence. A relationship relating the junction capacitance to the polycrystalline film properties and the built-in voltage of the junction is derived. It shows that the junction capacitance is related to the average carrier concentration rather than the doping concentration of the polycrystalline material. From a C^-2 versus V plot an average carrier concentration in the films which is in good agreement with that obtained by Hall measurement is obtained. The lower average electron concentration in the ZnCdS film near the substrate is due to either interdiffusion of Cd from the film into substrate or due to higher density of grain boundary states in the starting deposition portion of the film     

Congestion‐aware multiaccess edge computing collaboration model for 5G

In 5G cloud computing, the most notable and considered design issues are the energy efficiency and delay. The majority of the recent studies were dedicated to optimizing the delay issue by leveraging the edge computing concept, while other studies directed its efforts towards realizing a green cloud by minimizing the energy consumption in the cloud. Active queue management‐based green cloud model (AGCM) as one of the recent green cloud models reduced the delay and energy consumption while maintaining a reliable throughput. Multiaccess edge computing (MEC) was established as a model for the edge computing concept and achieved remarkable enhancement to the delay issue. In this paper, we present a handoff scenario between the two cloud models, AGCM and MEC, to acquire the potential gain of such collaboration and investigate its impact on the cloud fundamental constraints; energy consumption, delay, and throughput. We examined our proposed model with simulation showing great enhancement for the delay, energy consumption, and throughput over either model when employed separately.     

Noncoherent space-time coding: An algebraic perspective

The design of space-time signals for noncoherent block-fading channels where the channel state information is not known a priori at the transmitter and the receiver is considered. In particular, a new algebraic formulation for the diversity advantage design criterion is developed. The new criterion encompasses, as a special case, the well-known diversity advantage for unitary space-time signals and, more importantly, applies to arbitrary signaling schemes and arbitrary channel distributions. This criterion is used to establish the optimal diversity-versus-rate tradeoff for training based schemes in block-fading channels. Our results are then specialized to the class of affine space-time signals which allows for a low complexity decoder. Within this class, space-time constellations based on the threaded algebraic space-time (TAST) architecture are considered. These constellations achieve the optimal diversity-versus-rate tradeoff over noncoherent block-fading channels and outperform previously proposed codes in the considered scenarios as demonstrated by the numerical results. Using the analytical and numerical results developed in this paper, nonunitary space-time codes are argued to offer certain advantages in block-fading channels where the appropriate use of coherent space-time codes is shown to offer a very efficient solution to the noncoherent space-time communication paradigm.