Effects of semiconductor-optical-amplifier nonlinearity on theperformance of high-speed intensity-modulation lightwave systems

It is shown that when the amplifier is driven near saturation, its inherent nonlinearity causes significant bit-pattern-dependent pulse distortion, particularly in the bit-rate range between about 2 and 32 GB/s. Without proper countermeasures, this distortion can degrade system performance appreciably due to two basic mechanisms. The first, which can result in a system power penalty of as much as 10 dB, occurs in a standard decision circuit that automatically sets the threshold voltage to the average signal level, rather than in the middle of the eye opening. The second mechanism, which occurs even with the threshold set properly, is due to the nonlinear enhancement of the simple linear intersymbol interference (ISI) within the receiver filter. For example, computations of system performance at 8 Gb/s using an RC filter that gives a quite acceptable 10% of eye closure under linear conditions show that when the amplifier is driven to its saturation output power level, this mechanism causes a system power penalty of about 1 dB, which increases to about 4.5 dB when the power is doubled. Interestingly, with the proper threshold setting, an ideal integrate-and-dump receiver, which introduces no ISI, is shown to suffer no power penalty due to amplifier nonlinearity     

Combined effects of sub-cooling and operating pressure on theperformance of a two-chamber thermosyphon

The heat dissipation rates at the chip level are projected to reach the 50-100 W/cm² mark for some future high performance electronic systems. Liquid cooling with phase change has been demonstrated to be a very efficient technique for thermal management of such high heat dissipation rates. Past work on liquid immersion cooling using fluorocarbons has shown the advantage of using enhanced structures to reduce boiling incipience excursion and raise the critical heat flux (CHF). Thermosyphons, employing these enhanced structures are an alternative to liquid immersion and are suitable for point cooling applications, where very compact evaporators are needed. This study investigates the combined effect of sub-cooling and pressure on the performance of an enhanced microstructure based thermosyphon, which has shown very high heat transfer rates (up to 100 W/cm² with a wall superheat of 27.8°C). The pressure levels tested were partial vacuum (40-101.3 kPa), atmospheric pressure (101.3 kPa) and high pressure (101.3-370 kPa). The experiments were initiated at room temperature, and hence the sub-cooling corresponded to the difference in the liquid saturation temperature at the starting system pressure and room temperature. The results show a reduction in wall superheat values at higher pressures, at a given heat flux. The performance of the system was evaluated by defining a surface-to-ambient resistance. Results show that a partial vacuum at all heat fluxes results in better performance compared to higher pressures. The combined effect of pressure and sub-cooling was also tested for a compact evaporator and the results obtained were similar to the baseline case (larger evaporator)     

Effect of the nonlinear gain in semiconductor lasers on theperformance of multigigabit-per-second lightwave systems

The implications on performance of the functional form of the nonlinear gain in single-mode semiconductor lasers are studied for multigigabit-per-second, intensity-modulation, direct-detection lightwave systems. Compared to a previously used functional dependence on the photon and carrier densities, a new result due to G. Agrawal (1988) can, depending on the fiber dispersion and gain compression factor, yield quite different receiver sensitivities     

Characterization of the MIC/MILC interface and its effects on theperformance of MILC thin-film transistors

Process and material characterization of the crystallization of amorphous silicon by metal-induced crystallization (MIC) and metal-induced lateral crystallization (MILC) using evaporated Ni has been performed. An activation energy of about 2 eV has been obtained for the MILC rate. The Ni content in the MILC area is about 0.02 atomic %, significantly higher than the solid solubility limit of Ni in crystalline Si at the crystallization temperature of 500°C. A prominent Ni peak has been detected at the MILC front using scanning secondary ion mass spectrometry. The MIC/MILC interface has been determined to be highly defective, comprising a continuous grain boundary with high Ni concentration. The effects of the relative locations of this interface and the metallurgical junctions on TFT performance have been studied     

Modeling and analyzing vertical interconnections

Continual interest in miniaturization is driving electronic packaging toward three-dimensional (3-D) structures and system integration. Utilization of a third dimension allows designers much more freedom, but at the same time it leads to an increase in the complexity of signal routing. High-density of components and interconnection increases the need for electromagnetic (EM) modeling. This paper focuses on EM modeling and the analysis of vertical interconnection in a stacked 3-D package. Solder-plated polymer balls are used in vertical interconnection between interposers and laser-drilled vias through the interposers. High-frequency responses of the vertical interconnections were studied with 3-D full-wave software. Based on the EM analysis, we propose equivalent circuit models for vertical connections, which were verified with measurements. In addition, an impedance-matching technique in vertical interconnection is discussed.     

A new estimation approach based on periodic inspection

The authors present a novel approach for estimating the failure-time distribution using count data, the number of failures per interval, from periodic inspection of a standby redundant system. The procedure is based on a result for stationary renewal processes that related the forward recurrence time to the interevent time distribution. The procedure performed well in a simulation study for five Weibull distributions and is general enough to work for any failure-time distribution     

编码TCP的建模与性能分析

研究了无线网络端到端分组丢失和编码纠错对TCP协议工作过程的影响机制,基于三维Markov链建模描述TCP拥塞窗口和可用窗口的变迁过程,在忽略慢启动阶段的条件下,以最大窗口尺寸、端到端分组丢失率和编码冗余系数为输入参数,通过数值计算求解编码TCP的吞吐率,据此定量分析影响编码TCP性能的因素。基于NS2的模拟实验结果表明基于Markov链的数值计算结果具有较高的准确度。     

Modeling and analyzing the correctness of geographic face routing under realistic conditions

Geographic protocols are very promising for wireless ad hoc and sensor networks due to the low state storage and low message overhead. Under certain idealized conditions, geographic routing – using a combination of greedy forwarding and face routing – has been shown to work correctly and efficiently. In this work we model and analyze the correctness of geographic routing under non-ideal realistic conditions. We present a systematic methodology for micro-level behavioral analysis that shows that conditions that violate the unit-graph assumption of network connectivity, such as location errors, obstacles and radio irregularity, cause failure in planarization and consequently face routing. We then discuss the limitations of fixing these failures and prove that local algorithms that use only information up to a limited number of hops are not sufficient to guarantee face routing delivery under arbitrary connectivity. In addition, we analyze the effect of location errors in more detail to identify the possible protocol error scenarios and their conditions. We present results from an extensive simulation study about the effects of location errors on GPSR and GHT to quantify their performance degradation at different error ranges, distributions and error models. Based on our analysis we present a potential fix based on local information sharing that improves the performance significantly but does not remove all failures. Finally, we conclude that in order to avoid all failures under arbitrary connectivity, we need a non-local algorithm that can search or propagate information for an unlimited number of hops.     

Impact of super-steep-retrograde channel doping profiles on theperformance of scaled devices

Super-steep retrograded (SSR) channels were compared to uniformly doped (UD) channels as devices are scaled down from 250 nm to the 50 nm technology node, according to the scheme targeted by the National Technology Roadmap for Semiconductors (1997). The comparison was done at the same gate length L_gate and the same off-state leakage current I_off, where it was found that SSR profiles always have higher threshold voltages, poorer subthreshold swings, higher linear currents, and lower saturation currents than UD profiles. Using a simulation strategy that takes into account the impact of short-channel effects on drive current, it was found that the improved short-channel effect of retrograde profiles is not enough to translate into a higher performance over the UD channels for all technologies. Hence, if the effective gate-dielectric thickness scales linearly with technology, retrograde doping will not be useful from a performance point of view. However, if the scaling of the gate-dielectric is limited to about 2 nm, SSR profiles can give higher drive current than UD channels for the end of the roadmap devices. Thus, the suitability of SSR channels over UD channels depends on the gate-dielectric scaling strategy. Simulations using a self-consistent Schrodinger-Poisson solver were also used to show that the impact of quantum mechanical (QM) effects on the long-channel characteristics of SSR and UD MOSFET's will be similar     

Modeling and minimization of FWM effects in DWDM-based long-haul optical communication systems

Photonic Network Communications - Optical communication systems (OCSs) mainly represent the backbone of modern long-haul communication networks because of low loss transmission over long distances...     

Effects of longitudinal and latitudinal grain boundaries on theperformance of large-grain polysilicon MOSFET

The effects of longitudinal and latitudinal polysilicon grain boundaries on the performance metal oxide semiconductor field effect transistors (MOSFETs) fabricated on large-grain polysilicon-on-insulator (LPSOI) have been investigated. Unlike conventional thin-film-transistors (TFTs) with random grain distribution, MOSFETs fabricated on the LPSOI film contains the combination of only longitudinal or latitudinal grain boundaries. Longitudinal GBs parallel to the direction of current flow has smaller impact to the current flow, but provided extra leakage current that caused early device shortage, especially in wide devices. The latitudinal GBs perpendicular to the direction of current flow offered higher resistance to the inversion carriers thus causing lower current drive, higher threshold voltage, and gentler subthreshold slope. The result of the study can be used to optimize device design for high performance on MOSFETs on the LPSOI substrate     

Efficiently analyzing the impact of aging effects on large integrated circuits

Time-dependent variations have not received a lot of attention in the past. However, they gain in importance with each now process generation. Our goal is an accurate analysis of the timing degradation of large integrated circuits caused by aging effects. We present an aging-analysis flow on gate level that considers the two dominant aging-effects, NBTI and HCI. Furthermore, an aging model on module-level is proposed to handle even larger circuits. This aging model is on average 30× faster than an analysis on gate level while providing the same accuracy.     

On the zeros of discrete-time linear periodic systems

Discrete-time linear periodic single-input/single-output (SISO) systems having uniform relative degree are considered. A closed-form expression of the blocking input is derived and exploited to obtain a computationally advantageous characterization of the structural zeros. Indeed, it suffices to compute the eigenvalues of a suitably defined (n × n) matrix, wheren is the system order. It is shown that, in contrast to the general case studied in previous papers, the number of zeros of linear periodic SISO systems with uniform relative degree is always time invariant and equal to the difference between the system order and the relative degree. The new characterization is also used to provide a simple expression for the zeros of linear periodic systems described by input-output difference equations.This paper has been partially supported by MURST Project Model Identification, System Control, Signal Processing.     

Linear periodic systems and multirate filter design

We present a systematic procedure for the design of filters intended for multirate systems. This procedure Is motivated by viewing the equiripple design of filters in linear time-invariant systems as a process of obtaining optimum minimax filters for a class of bounded energy input signals. The philosophy of designing optimum minimax filters for classes of input signals is extended to multirate systems, which are not time-invariant. We develop a generalized Fourier analysis appropriate for linear periodic systems and use it to derive new error criteria for multirate filter design. Using such criteria yields optimum minimax multirate filters for the input signal class. The utility of our method is demonstrated by using it to analyze several multirate systems. We give numerical results on the design of a multirate implementation of a narrowband filter and compare our work to previous work on multirate filter design. Our numerical analysis is based upon a new formulation of the design as a semi-infinite linear programming problem     

On the relationship between measures of discrimination and theperformance of suboptimal detectors

The problem of designing and analyzing suboptimal detectors via statistical distance measures is considered. As a preliminary result, we show that only the minimum and maximum probability of error are valid measures of discrimination between the input statistics. This result would seem then to imply that the use of distance measures in this context can be inappropriate. However, to overcome this apparent obstacle, we demonstrate explicit relationships between various f-divergences and the loss in performance of an arbitrary detector relative to the optimal detector. In particular, we establish both upper and lower bounds on the performance loss of a suboptimal detector in terms of the “distance” between the pertinent statistics of both the optimal and suboptimal detectors. While designing detectors by minimizing these upper bounds can be an elusive task, in many practical cases, the lower bound presented herein holds with equality. In this case, minimizing the separation of the output statistics of the detector with respect to a particular f-divergence equivalently minimizes the resulting probability of error of the detector. To facilitate design, other researchers have established conditions under which one may design arbitrary detection strategies with respect to a specific f-divergence (Kullback-Leibler distance being a principal example). We extend this approach by deriving necessary and sufficient conditions under which one may design detection strategies with respect to an arbitrarily chosen f-divergence. Thus when these conditions are met, one may optimize a detector with respect to the most analytically tractable distance measure to obtain the minimum probability of error detector over a selected class of detection strategies. Examples demonstrating the utility of this theory for the problem of designing optimal linear detectors and optimal signal sets are presented     

Influence of spherical aberration of the active medium on theperformance of Nd:YAG lasers

In general, the temperature distribution in Nd:YAG laser rods deviates from a parabolic functional form due to the temperature dependence of thermal conductivity and the inhomogeneity of pumping light distributions. An analytical expression is derived which relates the resulting radially dependent refractive power to the shape of the pumping light distribution. To first order, the refractive power has a parabolic radial dependence and this spherical aberration considerably affects the laser's output characteristics. The performance of both stable and unstable resonators is investigated theoretically by numerically solving the Fresnel-integrals, including the amplification, the refractive power and the aberration of the rod. High output power and good beam quality cannot be achieved simultaneously when aberration is present. Experiments for both resonator types were performed with a pulsed Nd:YAG laser capable of a maximum output of 320 watts of average power     

Towards generation of efficient test cases from UML/OCL models for complex safety-critical systems

This paper describes a new approach for model-based test case generation (MBTCG) for large systems, which not only supports the expression of complex requirements (constraints) using OCL, but also lays ground for improving the efficiency (i.e. maximum coverage with minimal number of test cases) of the generated test case set. For that purpose, UML/OCL models are transformed to (object-oriented) action systems, where test cases are generated by means of mutation. The resulting "abstract" test cases represent input/output sequences with possible branches according to valid alternatives in system responses. They have finally to be transformed to "concrete" test cases which can be applied to the target application. The described work is part of the European project MOGENTES.     

Influence of the dynamic response of the Fabry-Perot filter on theperformance of an OFDM-DD network

An analysis of the transient response of a Fabry-Perot filter (FPF) is presented. The impact of this phenomenon on the performance of optical frequency division multiplexing (OFDM) networks with direct detection is then analyzed. Results show that the transient effect of the filter can induce a considerable power penalty in OFDM networks when high bit rates are transmitted     

A note on periodic solutions in weakly nonlinear systems

A counterexample to a weakly nonlinear approach [1] to the existence of oscillations is presented.