Wonsuck Lee

Electronic predistortion and fiber nonlinearity

We compare the impact of fiber nonlinearities in systems using electronic predistortion (EPD) to systems using in-line optical dispersion compensation. We show that EPD is significantly more susceptible to fiber nonlinearities

Design tools for transparent optical networks

Optical technology promises to revolutionize data networking by providing enormous bandwidth for data transport at minimal cost. A key to cost reduction is to increase transparency, that is, to keep a data stream encoded as an optical signal for as long as possible. Wavelength switching increases transparency by allowing different data streams, each encoded in a different wavelength of light, to be independently routed through an optical network. We discuss Bell Labs-developed software tools that help design wavelength-switched optical networks. The software tools simultaneously minimize the cost of the designed network, reduce the time and cost to perform the design, and ensure compliance with engineering constraints. The tools span three levels of abstraction, from routing and reconfigurable add/drop multiplexer (ROADM) choice, to span engineering, to power dynamics simulation. Each level represents a different tradeoff between design scope and level of detail. For each class of tool, we briefly describe design philosophy, algorithms, performance, and resulting value for Lucents customers.

GERI - Bell Labs Smart Grid Research Focus: Economic Modeling, Networking, and Security & Privacy

In this paper, we outline the Grid 2.0 Research, a collaborative Smart Grid research program between Gachon Energy Research Institute (GERI) of Kyungwon University and Bell Labs of Alcatel-Lucent. Salient features of the Grid 2.0 Research are the active role of distributed fixed and mobile energy storage, distributed renewable energy sources, and active load-side participation. Our focus is not on the energy storage itself but rather on the supporting infrastructure including communication network, security, and economics of the Smart Grid. Grid 2.0 Research views the Smart Grid as an ecosystem. In this regard, we pay close attention to the components and systems which require significant fundamental advancement or systems which do not exist today, thus requiring innovative solutions or greater sophistication. In order to realize a functioning ecosystem, critical components and tools of the envisioned Smart Grid are identified. This research work has been motivated by the Smart Grid roadmap of KEPCO and the Jeju Island Smart Grid Test-bed of Korea which will be discussed following the introduction section. Areas of research focus will be explained in a concise manner in the subsequent sections.

Enabling interactive and collaborative oil reservoir simulations on the Grid

Grid‐enabled infrastructures and problem‐solving environments can significantly increase the scale, cost‐effectiveness and utility of scientific simulations, enabling highly accurate simulations that provide in‐depth insight into complex phenomena. This paper presents a prototype of such an environment, i.e. an interactive and collaborative problem‐solving environment for the formulation, development, deployment and management of oil reservoir and environmental flow simulations in computational Grid environments. The project builds on three independent research efforts: (1) the IPARS oil reservoir and environmental flow simulation framework; (2) the NetSolve Grid engine; and (3) the Discover Grid‐based computational collaboratory. Its primary objective is to demonstrate the advantages of an integrated simulation infrastructure towards effectively supporting scientific investigation on the Grid, and to investigate the components and capabilities of such an infrastructure. Copyright

MAC aggregation resilient to DoS attacks

In todays and future building management systems, scores of cheap low-power sensors report measurements, such as temperature, electricity consumption and other parameters, to a control node. To save power and reduce deployment costs, it is often the case that data is sent wirelessly, and sensors serve as relay nodes that retransmit messages from other, more remote sensors. To prevent en route accidental and malicious data corruption, each message is authenticated with a MAC (Message Authentication Code), keyed with a key known to the generating sensor and the control node.

Numerical Simulation of Fluid Flow in Microchannels With Superhydrophobic Walls

The three-dimensional flow of a Newtonian fluid in a microchannel with superhydrophobic walls is computed using a finite element analysis. Calculations of the fully-developed laminar flow of water under a pressure gradient of 1 psi/cm in an 80 μm high channel with superhydrophobic upper and lower surfaces containing a 2 μm pitch array of 0.2 μm square posts shows a 40 percent flow enhancement relative to the smooth, non-patterned surface case, and an apparent slip length of 5.4 μm. A sharp gradient is observed in the axial velocity field within 0.5 μm of the post surface and normal to the post center. The calculated axial velocity field away from the superhydrophobic surface agrees well with the analytical solution for two-dimensional channel flow with Navier’s slip condition applying at the channel wall. Mesh refinement studies indicate the important role that adequate resolution of the sharp gradient in the velocity field adjacent to the post surface plays in obtaining accurate flow enhancement predictions. Decreasing the relative contact area of the fluid with the solid portion of the channel surface, either by increasing the post-to-post spacing or decreasing the post size, results in a monotonic increase in the flow enhancement. Wetting of the fluid into the post structure is shown to dramatically decrease the calculated flow enhancement. Calculations of the flow enhancement for fixed surface properties and varying channel heights result in apparent slip lengths that agree to within 1 percent, suggesting that the macroscopic flow behavior is adequately characterized in terms of an apparent slip model, with the magnitude of the slip length a function of the post size, post spacing and wetting behavior that characterize the local flow field.© 2005 ASME

Network simulation via hybrid system modeling: a time-stepped approach

The ever increasing complexity of networks dramatically increases the challenges faced by service providers to analyze network behavior and (re)provision resources to support multiple complex distributed applications. Accurate and scalable simulation tools are pivotal to this cause. The recently proposed hybrid systems model for data communication networks shows promise in achieving performance characteristics comparable to fluid models while retaining the accuracy of discrete models. Using the hybrid systems paradigm, this paper provides contributions to the modeling of TCP behavior and the analysis/simulation of data communication networks based on these models. An important distinguishing feature of our simulation framework is a faithful accounting of link propagation delays which has been ignored in previous work for the sake of simplicity. Other salient aspects of the work include a new finite state machine model for a drop-tail queue, a new model for fast recovery/fast retransmit mode, a revised sending rate model, and an embedded time-out mode transition mechanism all of which employ a time-stepped solution method to solve the hybrid system network models. Our simulation results are consistent with well-known packet based simulators such as ns-2, thus demonstrating the accuracy of our hybrid model. Our future efforts will be directed towards studying and improving the computational performance of hybrid model based simulations.

MAC aggregation protocols resilient to DoS attacks

In smart grid, sensor measurements are often sent to a control node over a hop–by–hop network of sensors themselves. To prevent en route accidental and malicious data corruption, each message is authenticated with a MAC, keyed with a symmetric key known to the generating sensor and the control node. MACs represent a significant overhead: a typical 128–bit MAC may often authenticate a 10–bit temperature reading. To mitigate these overheads, MAC aggregation methods were proposed. However, previously proposed MAC aggregation schemes are not resilient to Denial–of–Service (DoS) attacks, where a rogue node or a man–in–the–middle attacker can easily disrupt the entire set of MACs, and hence prevent using any of the transmitted data. In this work we propose a new way of MAC aggregation, which will allow the relay sensors to greatly reduce transmission overhead due to MACs, while achieving full unforgeability, and, simultaneously, much stronger resilience to DoS attacks.

A Computational Agent-Based Modeling Approach for Competitive Wireless Service Market

Using an agent-based modeling method, we study market dynamism with regard to wireless cellular services that are in competition for a greater market share and profit. In the proposed model, service providers and consumers are described as agents who interact with each other and actively participate in an economically well-defined marketplace. Parameters of the model are optimized using the Levenberg-Marquardt method. The quantitative prediction capabilities of the proposed model are examined through data reproducibility using past data from the U.S. and Korean wireless service markets. Finally, we investigate a disruptive market event, namely the introduction of the iPhone into the U.S. in 2007 and the resulting changes in the modeling parameters. We predict and analyze the impacts of the introduction of the iPhone into the Korean wireless service market assuming a release date of 2Q09 based on earlier data.

Enhancing objective evaluation of speech quality algorithm: current efforts, limitations and future directions

We discuss a performance improvement over the current state-of-the-art objective speech quality assessment algorithm by means of a parameter study. The state-of-the-art algorithm computes a certain measure of disturbances surface, and applies a cognitive model to map the computed value to the scale used mean opinion score (MOS). We note that many parameters, including the used metric of L P space, do not appear to be robust enough in terms of the performance of the algorithm. First, we search for optimum L p -norms over the frequency-time domain disturbance surface. The optimum L p -norms yield the most desirable correspondence between symmetric/asymmetric disturbance terms and subjective scores. New features are added to the cognitive processing algorithm. Improvements are substantial, but still only incrementally improve the performance. Limitations and bottlenecks of the current standardised approaches, as well as emerging new ideas, are reviewed. Finally, we call for more innovative, rather than renovative, research efforts in objective speech quality measurement for fundamental enhancement of the algorithm. Copyright