Performance and Buffering Requirements of Internet Protocols over ATM ABR and UBR Services

The Asynchronous Transfer Mode (ATM) networks are quickly being adopted as backbones over various parts of the Internet. This paper analyzes the performance of TCP/IP protocols over ATM network's Available Bit Rate (ABR) and Unspecified Bit Rate (UBR) services. It is shown that ABR pushes congestion to the edges of the ATM network while UBR leaves it inside the ATM portion.Comment: IEEE Communications Magazine, Vol 36, no 6, pp152-15

Optimal power flow based congestion management using enhanced genetic algorithms

Congestion management (CM) in the deregulated power systems is germane and of central importance to the power industry. In this paper, an optimal power flow (OPF) based CM approach is proposed whose objective is to minimize the absolute MW of rescheduling. The proposed optimization problem is solved with the objectives of total generation cost minimization and the total congestion cost minimization. In the centralized market clearing model, the sellers (i.e., the competitive generators) submit their incremental and decremental bid prices in a real-time balancing market. These can then be incorporated in the OPF problem to yield the incremental/ decremental change in the generator outputs. In the bilateral market model, every transaction contract will include a compensation price that the buyer-seller pair is willing to accept for its transaction to be curtailed. The modeling of bilateral transactions are equivalent to the modifying the power injections at seller and buyer buses. The proposed CM approach is solved by using the evolutionary based Enhanced Genetic Algorithms (EGA). IEEE 30 bus system is considered to show the effectiveness of proposed CM approach

Performance of Bursty World Wide Web (WWW) Sources over ABR

We model World Wide Web (WWW) servers and clients running over an ATM network using the ABR (available bit rate) service. The WWW servers are modeled using a variant of the SPECweb96 benchmark, while the WWW clients are based on a model by Mah. The traffic generated by this application is typically bursty, i.e., it has active and idle periods in transmission. A timeout occurs after given amount of idle period. During idle period the underlying TCP congestion windows remain open until a timeout expires. These open windows may be used to send data in a burst when the application becomes active again. This raises the possibility of large switch queues if the source rates are not controlled by ABR. We study this problem and show that ABR scales well with a large number of bursty TCP sources in the system.Comment: Submitted to WebNet `97, Toronto, November 9

Social welfare maximization based optimal energy and reactive power dispatch using ant lion optimization algorithm

In this paper an optimal energy and reactive power dispatch problem is solved by using the ant lion optimization (ALO) algorithm by considering the total cost minimization and social welfare maximization (SWM) objectives. Two different market models are proposed in this work, i.e., conventional/sequential market clearing and the proposed/simultaneous market clearing. In each market model, two objectives, i.e., total cost minimization and SWM are considered. The conventional social welfare (SW) consists the benefit function of consumers and the cost function of active power generation. In this paper, the conventional SW is modified by including the reactive power cost function. The reactive power cost calculation is exactly same as that in the conventional practice. The most important difference is that instead of doing cost calculation in post-facto manner as in conventional practice, simultaneous approach is proposed in this work. The scientificity and suitability of the proposed simultaneous active and reactive power methodology has been examined on standard IEEE 30 bus test system

Dynamic Channel Adaptation for AC Synchronized Powerline Channel

Broadband Power Line Communications (PLC) technology allows the usage of electrical power supply networks for communications purposes, such as audio/video streaming and broadband internet access. The powerline has an inherent characteristic that is the cyclic variation of channel and noise with the phase of the AC line cycle. To achieve either high throughput or high robustness, we apply dynamic channel adaptation scheme that exploits the cyclic variation of powerline characteristics. In this paper, we introduce an expedient, dynamic channel adaptation which is robust against the short-time variation of the AC synchronized powerline channel and noise. We analyze the performance enhancement for the measured powerline channel and noise when the proposed adaptation scheme is applied to the Korean standard on high speed powerline communications. Analysis of the simulation result has shown that an average of 30% improvement in the throughput can be achieved by using AC line based adaptation.This work is supported by UPLC Power IT project

Joint Channel Estimation with Phase Noise Suppression and Soft Decision Decoding Scheme for OFDM-based WLANs

In orthogonal frequency-division multiplexing (OFDM)-based wireless local area networks (WLANs), phase noise (PHN) and channel estimation errors can degrade the performance of the system. This letter provides a soft decision decoding scheme analysis for OFDM-based WLANs in the presence of PHN and channel estimation errors. Basing on this analysis, we propose a novel iterative scheme for joint channel estimation with PHN suppression and soft decision decoding. In addition, the soft decision decoding metric for QAM OFDM systems is modified to mitigate the effects of PHN and channel estimation errors. The simulation results show that the proposed scheme mitigates the performance degradation due to PHN and channel estimation errors effectively

Performance Analysis of LDPC Coded DMT Systems with Bit-loading Algorithms for Powerline Channel

This paper deals with two different approaches to overcome unfavorable channel characteristics and to obtain higher performance of PLC systems: Low Density Parity Check (LDPC) coding and bit-loading algorithms for Discrete Multitone (DMT) modulation. We analyze the performance of LDPC coded DMT systems with bit-loading algorithms in terms of bit-error rate and data rate. Simulations are performed with statistically modeled in-home PLC channel and noise. Several bit-loading scenarios and LDPC coding schemes are also considered. The performances of the proposed DMT systems with and without LDPC codes are analyzed for the broadband PLC system design

Nanostructured ZnO Arrays with Self-ZnO Layer Created Using Simple Electrostatic Layer-by-Layer Assembly

Formation of unique ZnO nanoarrays utilizing photodynamic polymer, surface-relief grating structures, and unique electrostatic layer-by-layer assembly as a simple and economical methodology was demonstrated. Atomic force microscope (AFM), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDAX) analysis were employed to characterize elemental composition and morphology of the resulting ZnO nanostructures with self-ZnO layer. Optical behavior of the final product was studied by UV-vis-NIR absorption and photoluminescence (PL) spectra