Joe F. Chicharo

A sliding Goertzel algorithm

Abstract This paper presents a sliding Goertzel algorithm to accurately estimate the Fourier coefficients of multifrequency (MF) sinusoidal signals buried in noise. The algorithm is based on second-order digital resonators that are tuned at the desired frequencies. The proposed method provides the following advantages when compared with the conventional Goertzel algorithm. Firstly, it computes Fourier coefficients in less than one signal period. Therefore, faster detection time is achieved, particularly when the greatest common divisor (GCD) of the input frequencies is small. Secondly, it is less prone to numerical overflow problems in fixed-point arithmetic implementation. Thirdly, the algorithm is quite suitable for time varying sinusoidal signal estimation. An analysis is undertaken to provide additional insight into the issue of required acquisition time versus the desired accuracy for the proposed algorithm. Extensive simulation tests are also included to demonstrate its performance.

Gradient-based adaptive IIR notch filtering for frequency estimation

The use of gradient-based algorithms with infinite impulse response (IIR) notch filtering for estimating sinusoids imbedded in noise is investigated. Two notch filter model structures are presented. The first is for applications where two signal sources with correlated noise components can be assessed. The second can be used in situations where only one composite signal source is available. Error surface analysis indicates that second-order modules are unimodal and result in guaranteed convergence. Higher-order modules are multimodal and require judicious choice of initial parameter estimates. Simulation results are included to demonstrate the performance characteristics of both filter structures. >

A new algorithm for improving the accuracy of periodic signal analysis

Digital periodic signal analysis often requires synchronized sampling with the signal being analyzed. In certain practical situations, however, this condition is difficult to satisfy. As a result, a number of undesirable effect such as the spectral leakage associated with the discrete Fourier transform (DFT), and the truncation errors in digital wattmeters arise and degrade system performance. This paper presents a new approach which attempts to remedy the underlying problem. The basic idea of the proposed method is to modify the actual sampled sequence such that it becomes an ideal sample sequence which is synchronized with the signal subjected to sampling. A simple algorithm for modifying the sampled sequence on-line is derived based on interpolation. The proposed approach requires quite modest additional computational burden which makes it suitable for real-time signal professing. To illustrate the practical applicability of the proposed algorithm, the paper considers two distinct but common cases. First, it shows how the proposed method can be used in the case of DFT analysis of harmonic signals, and secondly, it considers the digital wattmeter application area in electrical power-system measurement. Results show that the proposed algorithm is capable of reducing both the leakage effect in DFT analysis and truncation errors in digital wattmeters.

Improving the measurement performance for a self-mixing interferometry-based displacement sensing system

Approaches that are, to our knowledge, novel, are proposed in this paper to improve the accuracy performance of self-mixing interferometry (SMI) for displacement measurement. First, the characteristics associated with signals observed in SMI systems are studied, based on which a new procedure is proposed for achieving accurate estimation of the laser phase. The studies also revealed the reasons for the inherent errors associated with the existing SMI-based techniques for displacement measurement. Then, this paper presents a new method for estimating the optical feedback level factor (denoted by C) in real time. Combining the new algorithms for estimating the laser phase and updating C value, the paper finally presents a novel technique for displacement measurement with improved accuracy performance in contrast to existing techniques. The proposed technique is verified by both simulation and experimental data.

Unfairness and capture behaviour in 802.11 adhoc networks

We address issues with the performance of IEEE 802.11, when used in the adhoc mode, in the presence of hidden terminals. We present results illustrating the strong dependence of channel capture behavior on the SNR observed on contending hidden connections. Experimental work has illustrated that in a hidden terminal scenario, the connection having the strongest SNR is able to capture the channel, despite the use of the RTS-CTS-DATA-ACK 4-way handshake designed to alleviate this problem. Our results indicate that the near-far SNR problem may have a significant effect on the performance of an adhoc 802.11 network.

Multi-frequency and multiple phase-shift sinusoidal fringe projection for 3D profilometry

In this paper, we report on a laser fringe projection set-up, which can generate fringe patterns with multiple frequencies and phase shifts. Stationary fringe patterns with sinusoidal intensity distributions are produced by the interference of two laser beams, which are frequency modulated by a pair of acousto-optic modulators (AOMs). The AOMs are driven by two RF signals with the same frequency but a phase delay between them. By changing the RF frequency and the phase delay, the fringe spatial frequency and phase shift can be electronically controlled, which allows high-speed switching from one frequency or phase to another thus makes a dynamic 3D profiling possible.

Three-dimensional profilometry based on shift estimation of projected fringe patterns

This paper presents a new approach to fringe pattern profilometry. In this paper, a generalized model describing the relationship between the projected fringe pattern and the deformed fringe pattern is derived, in which the projected fringe pattern can be arbitrary rather than being limited to being sinusoidal, as are those for the conventional approaches. Based on this model, what is believed to be a new approach is proposed to reconstruct the three-dimensional object surface by estimating the shift between the projected and deformed fringe patterns. Additionally, theoretical analysis, computer simulation, and experimental results are presented, which show how the proposed approach can significantly improve the measurement accuracy, especially when the fringe patterns are distorted by unknown factors.

Universal multimedia access from wired and wireless systems

Personal computing and communication devices such as computers, personal digital assistants (PDAs), and mobile phones are moving to their next generation in which the end user will be able to access a multitude of information with a single device either locally or through a network. One likely trend in future personal computing and personal communication is that there will not be a single but several equivalent devices available to users allowing access to information in various forms. Each user, depending on his/her needs would access one or several among them depending on the situation and his/her preference. Using existing protocol mechanisms, in this case, a mapping and negotiation of resources during connection setup would be performed, which would remain in place throughout the life of the connection.This paper provides an overview of universal multimedia access (UMA), a concept for accessing multimedia content through a variety of possible schemes, and discusses some of the issues that arise regarding its deployment. In particular, UMA will provide a solution for adapting the delivered content when users attempt to access their choice irrespective of their terminal characteristics and communication infrastructure, as apposed to the assumption that the content remains fixed and the objective is to deliver the original content at all times. This recognition represents the impetus for the development of media descriptions and hence UMA; that is, the notion that valuable information can be derived from a variety of conversions of a multimedia content source.The issues discussed are future requirements on content servers and multimedia viewers, media conversions, UMA protocols, and UMA network architectures. The problems addressed are quality of service issues in network solutions for multimedia communications and reconfigurable architectures and network control based on source adaptations through media conversions and transcoding.

Estimating the parameters of semiconductor lasers based on weak optical feedback self-mixing interferometry

The paper presents a practical approach for measuring the linewidth enhancement factor /spl alpha/ of semiconductor lasers and the optical feedback level factor C in a semiconductor laser with an external cavity. The proposed approach is based on the analysis of the signals observed in an optical feedback self-mixing interferometric system. The parameters /spl alpha/ and C are estimated using a gradient-based optimization algorithm that achieves best data-to-theoretical model match. The effectiveness and accuracy of the method has been confirmed and tested by computer simulations and experiments, which show that the proposed approach is able to estimate /spl alpha/ and C with an accuracy of 6.7% and 4.63%, respectively.

Recovering the absolute phase maps of two fringe patterns with selected frequencies

Phase unwrapping is an important and challenging issue in fringe pattern profilometry. In this Letter we propose an approach to recover absolute phase maps of two fringe patterns with selected frequencies. Compared to existing temporal multiple frequency algorithms, the two frequencies in our proposed algorithm can be high enough and thus enable efficient and accurate recovery of absolute phase maps. Experiment results are presented to confirm the effectiveness of the proposed technique.