Engineering Science, School of

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Error Concealment for 5/3 Motion Compensated Temporal Filtering with Lifting

Author: 
Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2007-10-09
Abstract: 

5/3 Motion Compensated Temporal Filtering (MCTF) is a tool for highly scalable video coding which has been recently studied by many researchers. This thesis presents several error concealment algorithms for 5/3 MCTF with lifting, which can be used to improve the quality of compressed video damaged by packet losses. In MCTF video, the low frequency subband frame, abbreviated as L-frame, contains most of the signal energy in any given Group-of-Pictures (GOP). We assume that one of these L-frames is lost. The proposed error concealment algorithms use the available data to reconstruct the missing L-frame. The simplest error concealment method considered in the thesis is Zero Motion Error Concealment. This method simply assumes zero motion through the damaged GOP, and averages the neighboring L-frames to reconstruct the missing L-frame. Another method called Motion Concatenation finds temporal pathways through the damaged GOP by connecting motion vectors available at the decoder, and copies the corresponding pixel values from the neighboring L-frames to the missing L-frame. Finally, Motion Re-estimation uses motion estimator at the decoder to find a motion vectors between two neighboring L-frames of the missing L-frame, and synthesizes the missing L-frame halfway between its neighboring L-frames. The overall error concealment system combines these three methods to maximize visual performance, as well as the Peak Signal-to-Noise-Ratio (PSNR).

Document type: 
Thesis
File(s): 
Senior supervisor: 
Ivan V. Bajic
Department: 
School of Engineering Science
Thesis type: 
BASc

Comparison of Regression Models for Estimation of Isometric Wrist Joint Torques Using Surface Electromyography

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2011
Abstract: 

Background: Several regression models have been proposed for estimation of isometric joint torque using surfaceelectromyography (SEMG) signals. Common issues related to torque estimation models are degradation of modelaccuracy with passage of time, electrode displacement, and alteration of limb posture. This work compares theperformance of the most commonly used regression models under these circumstances, in order to assistresearchers with identifying the most appropriate model for a specific biomedical application.Methods: Eleven healthy volunteers participated in this study. A custom-built rig, equipped with a torque sensor,was used to measure isometric torque as each volunteer flexed and extended his wrist. SEMG signals from eightforearm muscles, in addition to wrist joint torque data were gathered during the experiment. Additional data weregathered one hour and twenty-four hours following the completion of the first data gathering session, for thepurpose of evaluating the effects of passage of time and electrode displacement on accuracy of models. AcquiredSEMG signals were filtered, rectified, normalized and then fed to models for training.Results: It was shown that mean adjusted coefficient of determination (R2a) values decrease between 20%-35% fordifferent models after one hour while altering arm posture decreased mean R2avalues between 64% to 74% fordifferent models.Conclusions: Model estimation accuracy drops significantly with passage of time, electrode displacement, andalteration of limb posture. Therefore model retraining is crucial for preserving estimation accuracy. Data resamplingcan significantly reduce model training time without losing estimation accuracy. Among the models compared,ordinary least squares linear regression model (OLS) was shown to have high isometric torque estimation accuracycombined with very short training times.

Document type: 
Article

A Preliminary Investigation Assessing the Viability of Classifying Hand Postures in Seniors

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2011
Abstract: 

Background: Fear of frailty is a main concern for seniors. Surface electromyography(sEMG) controlled assistive devices for the upper extremities could potentially be usedto augment seniors’ force while training their muscles and reduce their fear of frailty.In fact, these devices could both improve self confidence and facilitate independentleaving in domestic environments. The successful implementation of sEMG controlleddevices for the elderly strongly relies on the capability of properly determining seniors’actions from their sEMG signals. In this research we investigated the viability ofclassifying hand postures in seniors from sEMG signals of their forearm muscles.Methods: Nineteen volunteers, including seniors (70 years old in average) andyoung people (27 years old in average), participated in this study and sEMG signalsfrom four of their forearm muscles (i.e. Extensor Digitorum, Palmaris Longus, FlexorCarpi Ulnaris and Extensor Carpi Radialis) were recorded. The feature vectors werebuilt by extracting features from each channel of sEMG including autoregressive (AR)model coefficients, waveform length and root mean square (RMS). Multi-classsupport vector machines (SVM) was used as a classifier to distinguish between fifteendifferent essential hand gestures including finger pinching.Results: Classification of hand gestures both in the pronation and supination positionsof the arm was possible. Classified hand gestures were: rest, ulnar deviation, radialdeviation, grasp and four different finger pinching configurations. The obtained averageclassification accuracy was 90.6% for the seniors and 97.6% for the young volunteers.Conclusions: The obtained results proved that the pattern recognition of sEMGsignals in seniors is feasible for both pronation and supination positions of the armand the use of only four EMG channel is sufficient. The outcome of this studytherefore validates the hypothesis that, although there are significant neurologicaland physical changes occurring in humans while ageing, sEMG controlled handassistive devices could potentially be used by the older people.

Document type: 
Article

Two-Way Relaying Using Constant Envelope Modulation and Phase-Superposition-Phase-Forward

Author: 
Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2011
Abstract: 

In this article, we propose the idea of phase-superposition-phase-forward (PSPF) relaying for 2-way 3-phasecooperative network involving constant envelope modulation with discriminator detection in a time-selectiveRayleigh fading environment. A semi-analytical expression for the bit-error-rate (BER) of this system is derived andthe results are verified by simulation. It was found that, compared to one-way relaying, 2-way relaying with PSPFsuffers only a moderate loss in energy efficiency (of 1.5 dB). On the other hand, PSPF improves the transmissionefficiency by 33%. Furthermore, we believe that the loss in transmission efficiency can be reduced if power isallocated to the different nodes in this cooperative network in an ‘optimal’ fashion. To further put the performanceof the proposed PSPF scheme into perspective, we compare it against a phase-combining phase-forwardtechnique that is based on decode-and-forward (DF) and multi-level CPFSK re-modulation at the relay. It wasfound that DF has a higher BER than PSPF and requires additional processing at the relay. It can thus beconcluded that the proposed PSPF technique is indeed the preferred way to maintain constant envelope signalingthroughout the signaling chain in a 2-way 3 phase relaying system.

Document type: 
Article

A Receiver for Differential Space-Time -Shifted BPSK Modulation Based on Scalar-MSDD and the EM Algorithm

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2005
Abstract: 

In this paper, we consider the issue of blind detection of Alamouti-type differential space-time (ST) modulation in static Rayleighfading channels. We focus our attention on a π/2-shifted BPSK constellation, introducing a novel transformation to the receivedsignal such that this binary ST modulation, which has a second-order transmit diversity, is equivalent to QPSK modulation withsecond-order receive diversity. This equivalent representation allows us to apply a low-complexity detection technique specificallydesigned for receive diversity, namely, scalar multiple-symbol differential detection (MSDD). To further increase receiver performance,we apply an iterative expectation-maximization (EM) algorithm which performs joint channel estimation and sequencedetection. This algorithm uses minimum mean square estimation to obtain channel estimates and the maximum-likelihood principleto detect the transmitted sequence, followed by differential decoding.With receiver complexity proportional to the observationwindow length, our receiver can achieve the performance of a coherent maximal ratio combining receiver (with differentialdecoding) in as few as a single EM receiver iteration, provided that the window size of the initialMSDD is sufficiently long. To furtherdemonstrate that the MSDD is a vital part of this receiver setup, we show that an initial ST conventional differential detectorwould lead to a strange convergence behavior in the EM algorithm.

Document type: 
Article

Facile Fabrication of Super-Hydrophobic Nano-Needle Arrays via Breath Figures Method

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2011
Abstract: 

Super-hydrophobic surfaces which have been fabricated by various methods such as photolithography, chemicaltreatment, self-assembly, and imprinting have gained enormous attention in recent years. Especially 2D arrays ofnano-needles have been shown to have super-hydrophobicity due to their sharp surface roughness. These arrayscan be easily generated by removing the top portion of the honeycomb films prepared by the breath figuresmethod. The hydrophilic block of an amphiphilic polymer helps in the fabrication of the nano-needle arraysthrough the production of well-ordered honeycomb films and good adhesion of the film to a substrate.Anisotropic patterns with water wettability difference can be useful for patterning cells and other materials usingtheir selective growth on the hydrophilic part of the pattern. However, there has not been a simple way togenerate patterns with highly different wettability. Mechanical stamping of the nano-needle array with apolyurethane stamp might be the simplest way to fabricate patterns with wettability difference. In this study,super-hydrophobic nano-needle arrays were simply fabricated by removing the top portion of the honeycombfilms. The maximum water contact angle obtained with the nano-needle array was 150°. By controlling the poresize and the density of the honeycomb films, the height, width, and density of nano-needle arrays weredetermined. Anisotropic patterns with different wettability were fabricated by simply pressing the nano-needlearray at ambient temperature with polyurethane stamps which were flexible but tough. Mechanical stamping ofnano-needle arrays with micron patterns produced hierarchical super-hydrophobic structures.

Document type: 
Article

Surface EMG Pattern Recognition for Real-Time Control of a Wrist Exoskeleton

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2010
Abstract: 

Background: Surface electromyography (sEMG) signals have been used in numerousstudies for the classification of hand gestures and movements and successfullyimplemented in the position control of different prosthetic hands for amputees.sEMG could also potentially be used for controlling wearable devices which couldassist persons with reduced muscle mass, such as those suffering from sarcopenia.While using sEMG for position control, estimation of the intended torque of the usercould also provide sufficient information for an effective force control of the handprosthesis or assistive device. This paper presents the use of pattern recognition toestimate the torque applied by a human wrist and its real-time implementation tocontrol a novel two degree of freedom wrist exoskeleton prototype (WEP), whichwas specifically developed for this work.Methods: Both sEMG data from four muscles of the forearm and wrist torque werecollected from eight volunteers by using a custom-made testing rig. The featuresthat were extracted from the sEMG signals included root mean square (rms) EMGamplitude, autoregressive (AR) model coefficients and waveform length. SupportVector Machines (SVM) was employed to extract classes of different force intensityfrom the sEMG signals. After assessing the off-line performance of the usedclassification technique, the WEP was used to validate in real-time the proposedclassification scheme.Results: The data gathered from the volunteers were divided into two sets, one withnineteen classes and the second with thirteen classes. Each set of data was furtherdivided into training and testing data. It was observed that the average testingaccuracy in the case of nineteen classes was about 88% whereas the averageaccuracy in the case of thirteen classes reached about 96%. Classification and controlalgorithm implemented in the WEP was executed in less than 125 ms.Conclusions: The results of this study showed that classification of EMG signals byseparating different levels of torque is possible for wrist motion and the use of onlyfour EMG channels is suitable. The study also showed that SVM classificationtechnique is suitable for real-time classification of sEMG signals and can be effectivelyimplemented for controlling an exoskeleton device for assisting the wrist.

Document type: 
Article

Signal Processing with Teams of Embedded Workhorse Processors

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2006
Abstract: 

Advanced signal processing for voice and data in wired or wireless environments can require massive computational power. Dueto the complexity and continuing evolution of such systems, it is desirable to maintain as much software controllability in the fieldas possible. Time to market can also be improved by reducing the amount of hardware design. This paper describes an architecturebased on clusters of embedded “workhorse” processors which can be dynamically harnessed in real time to support a wide rangeof computational tasks. Low-power processors and memory are important ingredients in such a highly parallel environment.

Document type: 
Article

A New Reduced-Complexity Detection Scheme for Zero-Padded OFDM Transmissions

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2006
Abstract: 

Recently, zero-padding orthogonal frequency division multiplexing (ZP-OFDM) has been proposed as an alternative solution to the traditional cyclic prefix (CP)-OFDM, to ensure symbol recovery regardless of channels nulls. Various ZP-OFDM receivers have been proposed in the literature, trading off performance with complexity. In this paper, we propose a novel low-complexity (LC) receiver for ZP-OFDM transmissions and derive an upper bound on the bit error rate (BER) performance of the LC-ZP-OFDM receiver. We further demonstrate that the LC-ZP-OFDM receiver brings a significant complexity reduction in the receiver design, while outperforming conventional minimum mean-square error (MMSE)-ZP-OFDM, supported by simulation results. A modified (M)-ZP-OFDM receiver, which requires the channel state information (CSI) knowledge at the transmitter side, is presented. We show that the M-ZP-OFDM receiver outperforms the conventional MMSE-ZP-OFDM when either perfect or partial CSI (i.e., limited CSI) is available at the transmitter side.Index Terms-Zero-padding, orthogonal frequency division multiplexing (OFDM), equalization.

Document type: 
Article

An FPGA-Based MIMO and Space-Time Processing Platform

Author: 
Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2006
Abstract: 

Faced with the need to develop a research unit capable of up to twelve 20MHz bandwidth channels of real-time, space-time,and MIMO processing, the authors developed the STAR (space-time array research) platform. Analysis indicated that the possibledegree of processing complexity required in the platform was beyond that available from contemporary digital signal processors,and thus a novel approach was required toward the provision of baseband signal processing. This paper follows the analysis andthe consequential development of a flexible FPGA-based processing system. It describes the STAR platform and its use throughseveral novel implementations performed with it. Various pitfalls associated with the implementation of MIMO algorithms in realtime are highlighted, and finally, the development requirements for this FPGA-based solution are given to aid comparison withtraditional DSP development.

Document type: 
Article