On trading wavelengths with fibers: a cost-performance based study

We consider the effect of multiple fibers on wavelength division multiplexing networks without wavelength conversion. We study networks with dynamic wavelength routing and develop accurate analytical models to compare various possible options using single- and multiple-fiber networks. We use results of an analytical model and simulation-based studies to evaluate the blocking performance and cost of multifiber networks. The number of fibers required providing high performance in multifiber networks and their costs are compared. A case is made for using multiple fibers in each link with fewer wavelengths instead of using a single fiber with many wavelengths. In particular, we show that a network with four fibers per link and with four wavelengths on each fiber without any wavelength conversion on any node yields similar same performance as the networks with one fiber per link and 16 wavelengths per fiber on each link and with full wavelength conversion capability on all nodes. In addition, the multifiber network may also offer the cost advantage depending on the relative cost of components. We develop a parametric cost model to show that multiple fibers in each link are an attractive option. Finally, such multifiber networks also has fault tolerance, with respect to a single fiber failure, already built into the system.     

Development of system specification for laser-optimized 50-/spl mu/m multimode fiber for multigigabit short-wavelength LANs

This paper presents the scientific arguments used in the specification development process by the Telecommunications Industry Association (TIA) Working Group FO-2.2.1 to develop the new multimode fiber and vertical-cavity surface-emitting laser specifications for high-speed application in data communications. Numerous engineering and commercial tradeoffs are described. The specification minimizes the link failure rate and overall link cost through utilization of communication-theory-based modeling and experimental verification. This was balanced against the reality of manufacturing costs attempting to maximize the yield of individual link components. The specific application used as an example has 50-/spl mu/m graded-index multimode fiber operating at 10 Gb/s (e.g., 10 Gb/s Ethernet and fiber channel). The link performance is determined by the interaction of the fiber intermodal dispersion measured by the differential modal delay, and the transceiver launch distribution into the multimode fiber measured by encircled flux. A theoretically based model and the simulation approach that were used to simulate 40 000 links are described. The information from these simulations was used to determine the specification limits. In addition, sensitivity to the specification limits was evaluated. The experimental results of a round robin conducted by the TIA are presented, which confirm that the modeled performance would yield the expected results in actual practice.     

Optical fiber interconnection for the scalable parallel computingsystem

In this paper, we discuss the optical fiber interconnection technologies applied in the two types of parallel processing systems: 1) a backplane interconnection in a parallel processor array system and 2) a computing cluster network. We have set up a parallel processor array system using optical fiber to make point-to-point interconnection between processor elements and are developing a low-cost virtual parallel optical fiber interconnection link (VPOFLink) complying with peripheral component interconnect (PCI) local bus specifications for the computing cluster. VPOFLink is integrated with the popular PCI bus interface in order to make the link hold the same bandwidth as that of the PCI bus. It was fabricated as an available peripheral device that can been inserted into the bus slots of commercial computers directly and can operate under the control of PCI bus. Also in this paper, we demonstrate the optical fiber link for a ring network and the architecture of the ring network     

Prediction of myelinated nerve fiber stimulation thresholds: limitations of linear models

Computer models of neurons are used to simulate neural behavior, and are important tools for designing neural prostheses. Computation time remains an issue when simulating large numbers of neurons or applying models to real time applications. Warman et al. developed a method to predict excitation thresholds for axons using linear models and a predetermined critical voltage. We calculated threshold prediction error as a function of the location of an extracellular electrode using two different axon models to examine further threshold prediction using linear models. Threshold prediction error was low (<3% error) under the conditions examined by Warman et al., but under more general conditions, threshold prediction error was as high as 23.6%. Linear models were limited as effective tools for single fiber threshold prediction because accuracy was dependent on the nonlinear and linear models used, and any parameter that affected the extracellular potential distribution. Threshold prediction could be improved by appropriately choosing the membrane conductance of the linear model, but determination of an optimal conductance was computationally expensive. Finally, although single fiber threshold prediction error was partially masked when considering the input-output (I/O) properties of populations of axons, relatively large errors still occurred in population I/O curves generated with linear models.     

Stable propagation of solitons in strongly dispersion-managedunequal-length optical fiber link with loss

Using average approximation, we obtained a phase plane evolution picture of soliton propagated in strongly dispersion-managed optical fiber link with loss. After analyzed this picture, we proposed a new picture to keep soliton propagation stably in this system. Stable propagation parameters are given and twenty points we are interested in are selected. Using these parameters, we can construct any type of optical fiber link. Considering the length of article, we give two types of link with peak power 2 and 8 mW. With an input pulse train consisting of 32 bits in return-to-zero (RZ) format, numerical simulation has been done. We find that soliton can stably propagate through these optical fiber link constructed by ten unequal-length unit with a data rate of 13.33 Gb/s     

Model-Based Design Analysis and Yield Optimization

Fluctuations are inherent to any fabrication process. Integrated circuits and microelectromechanical systems are particularly affected by these variations, and due to high-quality requirements the effect on the devices' performance has to be understood quantitatively. In recent years, it has become possible to model the performance of such complex systems on the basis of design specifications, and model-based sensitivity analysis has made its way into industrial engineering. We show how an efficient Bayesian approach, using a Gaussian process prior, can replace the commonly used brute-force Monte Carlo scheme, making it possible to apply the analysis to computationally costly models. We introduce a number of global, statistically justified sensitivity measures for design analysis and optimization. Two models of integrated systems serve us as case studies to introduce the analysis and to assess its convergence properties. We show that the Bayesian Monte Carlo scheme can save costly simulation runs and can ensure a reliable accuracy of the analysis     

Analyzing carbon-fiber composite materials with equivalent-Layer models

The purpose of this paper is to investigate the use of equivalent-layer models for the analysis of carbon-fiber composite materials. In this paper, we present three different models for the electromagnetic characterization (effective material properties) of fiber composites that are commonly used in aircraft and EMC/EMI shielding materials. These three models represent various orders (or levels) of detail in the fiber composite structure and, hence, capture various physical aspects of the composite. These models can be used to efficiently calculate the reflection and transmission coefficients, as well as the shielding effectiveness, of these fiber composites. We compare results of the reflection coefficient and shielding effectiveness obtained from these effective-property models to results obtained from a full numerical solution based on the finite-element (FE) method of the actual periodic fiber composite. We show that, as expected, as more of the geometric detail of the fiber composite is captured with the different models, the upper frequency limit of validity increases.     

Is 25 Gb/s On-Board Signaling Viable?

What package improvements are required for dense, high-aggregate bandwidth buses running at data rates beyond 10 Gb/s per channel, and when might optical interconnects on the board be required? We present a study of distance and speed limits for electrical on-board module-to-module links with an eye to answering these questions. Hardware-validated models of advanced organic modules and printed circuit boards were used to explore these limits. Simulations of link performance performed with an internal link modeling tool allowed us to explore the effect of equalization and modulation formats at different data rates on link bit error rate and eye opening. Our link models have been validated with active, high-speed differential bus measurements utilizing a 16-channel link chip with programmable equalization and a per-channel data rate of up to 11 Gb/s. Electrical signaling limits were then determined by extrapolating these hardware-correlated models to higher speeds, and these limits were compared to the results of recent work on on-board optical interconnects.      

Modeling Interference Effects for Land-Mobile and Air-Mobile Communications

Analytic and computer models are presented that can provide an assessment of land-mobile and air-mobile communications performance in interference environments. The results obtained with these models, based on a communications region of operability criterion, include the effects of greater-than-free-space propagation path losses associated with low-elevation signal paths. The analytic models are used to examine the effects of higher order path loss on signal-to-interference contours for single and linearly distributed interference scenarios. The computer model can be used to investigate link performance for interference environments in which the link assets and each source of interference are arbitrarily located in three dimensions. A propagation submodel permits independent calculation of the loss over each link or interference signal path. Computer-generated plots are presented that illustrate the effect of antenna heights and frequency on the shape of the signal-to-interference (S/I) contours. Of particular interest is the effect on link region of operability when either the link transmitter or the sources of interference are at a higher altitude than the other.     

Statistics of Electrical Dispersion Compensator Penalties of 10-Gb/s Multimode Fiber Links With Offset Connectors

In this letter, we investigate the penalty after a 10-Gb/s Ethernet signal is detected and processed. We study the statistics of ideal electrical dispersion-compensation (EDC) performance, measured by the penalty of an ideal decision feedback equalizer (PIE-D), of 300-m multimode fiber links to determine the theoretically best possible EDC performance. We calculate the channel responses using two methods: the individual-mode method and the average-mode method. We find a strong dependence of the PIE-D value on the channel model that is used, especially when there is a connector with a large offset in the link. In system design, one should choose a suitable channel model, taking into account the length of the fiber, the magnitude of offset, and the percentage of coverage     

A General Neural Network Model for Estimating Telecommunications Network Reliability

This paper puts forth a new encoding method for using neural network models to estimate the reliability of telecommunications networks with identical link reliabilities. Neural estimation is computationally speedy, and can be used during network design optimization by an iterative algorithm such as tabu search, or simulated annealing. Two significant drawbacks of previous approaches to using neural networks to model system reliability are the long vector length of the inputs required to represent the network link architecture, and the specificity of the neural network model to a certain system size. Our encoding method overcomes both of these drawbacks with a compact, general set of inputs that adequately describe the likely network reliability. We computationally demonstrate both the precision of the neural network estimate of reliability, and the ability of the neural network model to generalize to a variety of network sizes, including application to three actual large scale communications networks.      

Survivable WDM mesh networks

In a wavelength-division-multiplexing (WDM) optical network, the failure of network elements (e.g., fiber links and cross connects) may cause the failure of several optical channels, thereby leading to large data losses. This study examines different approaches to protect a mesh-based WDM optical network from such failures. These approaches are based on two survivability paradigms: 1) path protection/restoration and 2) link protection/restoration. The study examines the wavelength capacity requirements, and routing and wavelength assignment of primary and backup paths for path and link protection and proposes distributed protocols for path and link restoration. The study also examines the protection-switching time and the restoration time for each of these schemes, and the susceptibility of these schemes to multiple link failures. The numerical results obtained for a representative network topology with random traffic demands demonstrate that there is a tradeoff between the capacity utilization and the susceptibility to multiple link failures. We find that, on one hand, path protection provides significant capacity savings over link protection, and shared protection provides significant savings over dedicated protection; while on the other hand, path protection is more susceptible to multiple link failures than link protection, and shared protection is more susceptible to multiple link failures than dedicated protection. We formulate a model of protection-switching times for the different protection schemes based on a fully distributed control network. We propose distributed control protocols for path and link restoration. Numerical results obtained by simulating these protocols indicate that, for a representative network topology, path restoration has a better restoration efficiency than link restoration, and link restoration has a faster restoration time compared with path restoration.     

High-reliability topological architectures for networks under stress

In this paper, we consider the design of a physical network topology that meets a high level of reliability using unreliable network elements. We are motivated by the use of networks and, in particular, all-optical networks, for high-reliability applications which involve unusual and catastrophic stresses. Our network model is one in which nodes are invulnerable and links are subject to failure - a good approximation for optical networks with passive nodes and vulnerable fiber under stress of disconnection - and we focus on statistically independent link failures with initial steps taken toward generalization to dependent link failures. Our reliability metrics are the all-terminal connectedness measure and the less commonly considered two-terminal connectedness measure. We compare in the low and high stress regimes, via analytical approximations and simulations, common commercial architectures designed for all-terminal reliability when links are very reliable with alternative architectures which are mindful of both of our reliability metrics and regimes of stress. We derive new results especially for one of these alternative architectures, Harary graphs, which have been shown to possess attractive reliability properties. Furthermore, we show that for independent link failures network design should be optimized with respect to reliability under high stress, as reliability under low stress is less sensitive to graph structure; and that under high stress, very high node degrees and small network diameters are required to achieve moderate reliability performance. Finally, in our discussion of correlated failure models, we show the danger in relying on an independent failure model and the need for the network architect to minimize component failure dependencies.     

Demonstration of timing skew compensation for bit-parallel WDM datatransmission with picosecond precision

We demonstrate transmission of seven wavelength-division-multiplexed (WDM) bit-parallel channels with a total of 15-nm spectral span over a 2.5-km standard single-mode fiber/dispersion-compensating fiber link with less than 3-ps timing skew. The synchronized WDM channels are generated by spectrally slicing pulses from a single femtosecond fiber laser using a femtosecond pulse shaper. The small residual timing skew arises from the residual dispersion slope of the link. We measure a dispersion slope of D'=0.017 ps/km/mn², which is roughly four times less than for an equivalent length of dispersion-shifted fiber. Our work shows that the dispersion-compensating fiber technique could significantly reduce the timing skew for WDM bit-parallel transmission over a several-kilometer fiber link     

Models for subthreshold and above-threshold currents in 0.1-μmpocket n-MOSFETs for low-voltage applications

We present a model for subthreshold current in deep-submicrometer pocket n-MOSFETs based on the diffusion current transport equation, the quasi-two-dimensional (2-D) Poisson equation and a doping-density-dependent mobility model, and a model for above-threshold current in deep-submicrometer pocket n-MOSFETs based on the drift-diffusion current transport equation for nonuniformly doped MOSFETs, the charge-sheet approximation, a solution of the one-dimensional (1-D) Poisson equation, a quasi-2-D model for the velocity saturation region, longitudinal- and transverse-field-dependent mobility models. The analytic models for subthreshold and above-threshold currents are used to efficiently construct viable design spaces locating well-designed 0.1-μm pocket n-MOSFETs that meet all the device design specifications of off-state (leakage) current, on-state (drive) current, and power-supply voltage. The model for subthreshold current correctly predicts an increase in off-state current in sub-100 nm pocket n-MOSFETs. The model for above-threshold current generates I_D-V_DS characteristics of a variety of deep-submicrometer pocket n-MOSFETs     

Long-distance parallel data link using WDM transmission withbit-skew compensation

This paper studies the advantages and disadvantages of using a parallel link based on wavelength division multiplexing (WDM) for long-distance data transmission through a single-mode fiber as an alternative to a high-speed serial link. A long-distance optical link operating near the 1.55 μm or 0.85 μm wavelength regions suffers the large group-delay dispersion of a standard fiber. On these wavelengths, the skew between bit-channels is the major problem for wordwide WDM transmission. We propose a method to compensate for bit skew greater than the bit time, and analyze its performance gain in terms of the increase in the maximum data throughput achievable. With bit-skew compensation, the wordwide parallel link achieves a maximum aggregate data rate that is greater than what a serial link can obtain for the same link length     

Proposal of Bow-Tie Antenna-Integrated Resonant Tunneling Diode Transmitter Utilizing Relaxation Oscillations and Its Application to Short-Distance Wireless Communications

We propose a resonant tunneling diode (RTD)-based relaxation oscillator and an oscillator-based terahertz (THz) wireless link that compensate for shortfalls in RF-oscillator emission power by adding several relaxation carrier wave harmonic modes. We believe that the proposed link can perform as well as or superior to large component-based wireless links that suppress power dissipation using collimating lenses and/or discrete antennas to add the power output of a relaxation oscillator. This hypothesis is investigated analytically using a physics-based equivalent circuit model of the proposed oscillator and a link budget analysis of the relaxation carrier wave. The model, which incorporates effects such as the non-linearity of the tunneling diode and the electromagnetic properties of the integrated bow-tie antenna on the oscillator, is used to quantitatively investigate the link characteristics in terms of the signal-to-noise ratio (SNR) and other parameters and to demonstrate that, by applying an appropriate device size and number of harmonic modes in the occupied bandwidth, link performance comparable to that of previously reported wireless links can be achieved. Based on these results, we discuss the potential for practical implementation of the proposed link configuration in mobile link applications for use in environments such as the Internet of Things (IoT).     

A method to analyze performance of digital connections

A comprehensive performance analysis method that models, at bit level, the error performance of individual links in an end-to-end connection is presented. The link model accounts for the burst-error behaviour of each individual link. A method to concatenate several individual links and extract a model for the end-to-end connection is given. This resulting end-to-end model can be used to calculate performance measures such as bit error rate and block error rate for any given block size. A procedure to compute the probability distribution of errors within a specific block is also developed. Finally, a method to compute the probability distribution of blocks having a certain error rate over a given period of time is presented. The utility and power of the model are illustrated with the help of an example connection