IP forwarding alternatives in cell switched optical networks

Optical switching will enable core Internet packet switching to scale with future transmission rate increases. Currently proposed optical ATM switches do not allow packet reassembly, which is necessary for packet level forwarding. This results in the requirement to create end to end ATM virtual connections for flows even if they contain only one packet. In electronically switched networks MPOA and MPLS allow both cell and packet level forwarding to overcome this problem. This paper examines the feasibility of implementing such protocols over an optically switched network. Two different architectures are examined: use of an adjunct electrical router; and native optical packet reassembly. An examination of the optical reassembly buffer requirements show that the use of MPLS will require significantly more buffering than MPOA

An examination of IP/ATM cut-through forwarding in dynamically routed networks

Multiprotocol over ATM (MPOA), IP switching and multiprotocol label switching (MPLS) have distinctly different mechanisms for cut-through packet forwarding. MPOA and IP switching use flow-based cut-through (FBC) forwarding while MPLS uses routing table linked cut-through forwarding (TLC). This paper examines the sensitivity of each these cut-through forwarding mechanisms to changes in underlying routing tables. We examine a scenario where a congestion-sensitive dynamic routing protocol, such as OSPF optimised multipath, leads to frequently changing routing tables. We show that FBC forwarding reacts significantly worse than flow length distributions predict, taking up to 1200 seconds to react to route changes and forward at least 50% of packets on the new route. Flow characteristics are examined to determine ways to improve FBC sensitivity. We show that implementing a maximum flow length of 200 seconds improves the response to route changes significantly with a minimal decrease in the number of switched packets (1.5%)

Optical signal processing for fiber Bragg grating based wear sensors

In this study, we propose a simplified signal processing scheme for fiber Bragg grating (FBG) based wear sensing. Instead of using a chirped FBG and detecting the bandwidth, we use uniform gratings as sensors and measure the optical power reflected by the sensing grating to determine the length of the sensor grating, hence detect the wear. We demonstrate by the experiments that the proposed method is feasible and practical. The advantage of the proposed method lies in the fact that structure of the wear sensing system is simplified and therefore the cost can be significantly reduced. The principle of the proposed method, the design of the wear sensor, and the experiments are described

An improved channel model for ADSL and VDSL systems

This paper examines existing channel models used with xDSL systems and identifies a key shortcoming - namely, the implicit assumption that all impulse noise originates at the transmitter. Based on extensive data collected from the local loop, a new model is proposed which addresses this problem by combining a digital filter model of the transmission line with a distributed noise source. This better reflects the nature of a real telephone line, and thus provides a more solid basis for simulation and optimisation of xDSL systems

Fringe calibration using neural network signal mapping for structured light profilometers

We present a novel neural network signal calibration technique to improve the performance of triangulation based structured light profilometers. The performance of such profilometers is often hindered by the capture of noisy and aberrated pattern intensity distributions. We address this problem by employing neural networks and a spatial digital filter in a signal mapping approach. The performance of the calibration technique is gauged through both simulation and experimentation, with simulation results indicating that accuracy can be improved by more than 80%

Simulation of Capture Behaviour in IEEE 802.11 Radio Modems

In this paper we investigate the performance of common capture models in terms of the fairness properties they reflect across contenting hidden connections. We propose a new capture model, Message Retraining,as a means of providing an accurate description of experimental data. Using two fairness indices we undertake a quantitative study of the accuracy with which each capture model is able to reflect experimental data. Standard capture models are shown to be unable to accurately reflect the fairness properties of empirical data. The Message Retraining capture model is shown to provide a good estimate of actual system performance in varying signal strength conditions

Transition Analysis for Moderate Feedback Self-Mixing Interferometry

We present a theoretical analysis on the locations of transition points in moderate feedback self-mixing signal which is a fundamental issue to be addressed in preprocessing experimentally acquired data. Locations for the start and end points for upward and downward switchings are calculated based on the Lang-Kobayashi model and discussions are given, which provides guidance in achieving more accurate signal normalization

The fourier spectrum analysis of optical feedback self-mixing signal under weak and moderate feedback

The spectrum characteristics of self-mixing signals observed in optical feedback self-mixing interferometry (OFSMI) is studied in this paper. The purpose is to provide guidance for the design of pre-processing techniques for eliminating noise or disturbance. The influence of two important parameters of the OFSMI system on the spectrum, that is, the optical feedback factor and the linewidth enhancment factor, are measured by means of Discrete Fourier transform (DFT). The simulated results show that, at a weak feedback, the OFSMI signals are strictly band limited in nature, with the cut-off frequencies being the vibration frequency and the fringe frequency respectively. Also increasing broadens the bandwidth but has little influence on the bandwidth of the signal. At moderate feedback, the OFSMI signals are still band limited with much higher cut-off frequencies, and there is a considerable spectrum spread over a very wide range in the high frequency end. The presented analysis provides sufficient information for applying signal processing to OFSMI signals such as the filter design

Improved Three-step Phase Shifting Profilometry Using Digital Fringe Pattern Projection

In this paper, an improved method for three-step phase shifting profilometry (PSP) is presented to eliminate the errors introduced by the second order harmonic when digital projection are used to generate fringe patterns. Firstly, the error caused by the second order harmonic is theoretically analyzed. Then based on the error analysis and principle of PSP, we propose a novel approach, called improved threestep phase shifting profilometry (I3PSP), to eliminate the influence of the second order harmonic. Finally, simulations are performed to verify the effectiveness of the proposed I3PSP, which demonstrate that the reconstruction accuracy of using three-step PSP has been significantly improved by the proposed I3PSP

Optimisation of triangulation based optical profilometers utilising digital video projection technology

Fast, high precision and automated optical noncontact surface profile and shape measurement has been an extensively studied research area due to its many potential applications including 3D sensing, industrial monitoring, mechanical engineering, medicine, robotics, machine vision,animation, virtual reality, dressmaking, prosthetics, ergonomics. Among others, structured light approaches including fringe profilometry have proven to be one of the most promising techniques. In such profilometry techniques a structured light pattern, generally composed of parallel lines is projected onto a diffuse surface to be measured and viewed from an offset angle. The observed pattern is distorted by the object in such a way that represents information about the height of the object perpendicular to the plane of observation. The distorted structured light pattern is recorded, commonly by a CCD camera and through computer analysis of the recorded image the object can be recreated in 3D space, typically with a high degree of precision