Semi-Blind Cancellation of IQ-Imbalances

International audienceThe technical realization of modern wireless receivers yields significant interfering IQ-imbalances, which have to be compensated digitally. To cancel these IQ-imbalances, we propose an algorithm using iterative blind source separation (IBSS) as well as information about the modulation scheme used (hence the term semi-blind). The novelty of our approach lies in the fact that we match the nonlinearity involved in the IBSS algorithm to the probability density function of the source signals. Moreover, we use approximations of the ideal non-linearity to achieve low computational complexity. For severe IQ-mismatch, the algorithm leads to 0.2 dB insertion loss in an AWGN channel and with 16-QAM modulation

Orthogonal Extended Infomax Algorithm

The extended infomax algorithm for independent component analysis (ICA) can separate sub- and super-Gaussian signals but converges slowly as it uses stochastic gradient optimization. In this paper, an improved extended infomax algorithm is presented that converges much faster. Accelerated convergence is achieved by replacing the natural gradient learning rule of extended infomax by a fully-multiplicative orthogonal-group based update scheme of the unmixing matrix leading to an orthogonal extended infomax algorithm (OgExtInf). Computational performance of OgExtInf is compared with two fast ICA algorithms: the popular FastICA and Picard, a L-BFGS algorithm belonging to the family of quasi-Newton methods. Our results demonstrate superior performance of the proposed method on small-size EEG data sets as used for example in online EEG processing systems, such as brain-computer interfaces or clinical systems for spike and seizure detection.Comment: 17 pages, 6 figure

An alternative perspective on adaptive independent component analysis algorithms

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An Alternative Perspective on Adaptive Independent Component Analysis Algorithms

This article develops an extended independent component analysis algorithm for mixtures of arbitrary subgaussian and supergaussian sources. The gaussian mixture model of Pearson is employed in deriving a closed-form generic score function for strictly subgaussian sources. This is combined with the score function for a unimodal supergaussian density to provide a computationally simple yet powerful algorithm for performing independent component analysis on arbitrary mixtures of nongaussian sources

Exploring Gustatory Neural Coding and the Influence of Appetite and Expectancy

The purpose of this thesis was to explore human gustatory processing and how it is influenced by appetite and expectancy. The initial two years of the doctorate were dedicated to developing a gustometer mechanism and taste stimulus set to employ in the experimental investigations. Event-related potentials (ERPs), source-localised ERPs and event-related de-synchronisations and synchronisations (ERD/S) were then evaluated in response to taste characteristics under a variety of conditions. The first experiment assessed the ERP, source-localisation and ERD/S components associated with the processing of taste quality (sweet, salt, bitter, water), intensity (neutral, weak, medium, strong) and hedonicity (pleasant, unpleasant, neutral). Gustatory stimulation evoked activations within the primary gustatory cortex (PGC) and intensity was represented in early ERP epochs and by alpha- and beta-band ERD. Hedonicity was coded in late ERP epochs and by alpha-band ERD. Taste quality coding was difficult to determine from the EEG data. The second experiment compared the processing of pleasant sweet and unpleasant bitter tastes during states of hunger following overnight fasting and satiety induced by a standardised liquid meal. Hunger and satiety evoked maximal responses to tastes from limbic regions. Hunger greatly enhanced ERP and beta-band ERS responses to tastes in general. However, responses to sweet tastes were dependent on hunger state; with enhanced neural signals in response to sweet taste after satiating on a sweet meal - suggesting differential attentional and evaluative mechanisms employed under fasted and fed conditions. A final experiment examined the influence of cue-elicited expectancy on the processing of sweet tastes. Participants were validly or invalidly cued to expect a low- or high-concentration of sweet taste; both behavioural and neural responses to invalidly cued tastes assimilated to those that were produced by the taste the participants were cued to receive. These effects began ~100 ms after the onset of the tastes, suggesting that expectancy influences the early perceptual processing of taste. The overall findings of this thesis provide some of the first accounts of the temporal, source-localised and oscillatory dynamics of gustatory coding. The results also provide important implications for understanding how people’s experience of taste and food can be modified by appetite and expectancy