OFDM based visible light broadcasting systems

Visible light communication (VLC) involves the use of light emitting diode (LED)- based illumination infrastructure for communication purposes [1]. Recent experimental studies on VLC have demonstrated data speeds more than 3 Gigabits per second [2]. Although indoor spaces usually have more than one light source, most of the existing works on VLC in the current literature consider point-topoint communication and few efforts have been made on the scenarios with multiple transmitters. In this work, we consider a broadcasting scenario in which multiple transmitters (light sources) simultaneously emit the same information using orthogonal frequency division multiplexing (OFDM)

OFDM based visible light broadcasting systems

Visible light communication (VLC) involves the use of light emitting diode (LED)- based illumination infrastructure for communication purposes [1]. Recent experimental studies on VLC have demonstrated data speeds more than 3 Gigabits per second [2]. Although indoor spaces usually have more than one light source, most of the existing works on VLC in the current literature consider point-topoint communication and few efforts have been made on the scenarios with multiple transmitters. In this work, we consider a broadcasting scenario in which multiple transmitters (light sources) simultaneously emit the same information using orthogonal frequency division multiplexing (OFDM)

Link adaptation for MIMO OFDM visible light communication systems

In this paper, we investigate link adaptation for an orthogonal frequency division multiplexing (OFDM)-based multiple-input multiple-output (MIMO) visible light communication (VLC) system. The proposed adaptive OFDM VLC system supports both repetition coding (RC) and spatial multiplexing (SM) as MIMO modes and allows spatial mode switching based on channel conditions. Regarding to the instantaneous signal-to-noise ratio for both RC and SM modes, the maximum constellation size that can be supported for each MIMO mode on each subcarrier is determined. The MIMO mode that gives the highest spectral efficiency (SE) is then selected. The proposed joint MIMO mode selection and bit loading scheme maximizes the SE while satisfying a target bit error rate. Our numerical results reveal that a peak data rate up to 18.3 Gb/sec can be achieved in a 16 × 16 MIMO setting using light emitting diodes with cut-off frequency of 10 MHz in typical indoor environments.Nazarbayev University ; TÜBİTAKPublisher versio

A comprehensive score reflecting memory-related fMRI activations and deactivations as potential biomarker for neurocognitive aging

Older adults and particularly those at risk for developing dementia typically show a decline in episodic memory performance, which has been associated with altered memory network activity detectable via functional magnetic resonance imaging (fMRI). To quantify the degree of these alterations, a score has been developed as a putative imaging biomarker for successful aging in memory for older adults (Functional Activity Deviations during Encoding, FADE; Düzel et al., Hippocampus, 2011; 21: 803–814). Here, we introduce and validate a more comprehensive version of the FADE score, termed FADE-SAME (Similarity of Activations during Memory Encoding), which differs from the original FADE score by considering not only activations but also deactivations in fMRI contrasts of stimulus novelty and successful encoding, and by taking into account the variance of young adults' activations. We computed both scores for novelty and subsequent memory contrasts in a cohort of 217 healthy adults, including 106 young and 111 older participants, as well as a replication cohort of 117 young subjects. We further tested the stability and generalizability of both scores by controlling for different MR scanners and gender, as well as by using different data sets of young adults as reference samples. Both scores showed robust agegroup-related differences for the subsequent memory contrast, and the FADE-SAME score additionally exhibited age-group-related differences for the novelty contrast. Furthermore, both scores correlate with behavioral measures of cognitive aging, namely memory performance. Taken together, our results suggest that single-value scores of memory-related fMRI responses may constitute promising biomarkers for quantifying neurocognitive aging

Novelty-Related fMRI Responses of Precuneus and Medial Temporal Regions in Individuals at Risk for Alzheimer Disease

BACKGROUND AND OBJECTIVES: We assessed whether novelty-related fMRI activity in medial temporal lobe regions and the precuneus follows an inverted U-shaped pattern across the clinical spectrum of increased Alzheimer disease (AD) risk as previously suggested. Specifically, we tested for potentially increased activity in individuals with a higher AD risk due to subjective cognitive decline (SCD) or mild cognitive impairment (MCI). We further tested whether activity differences related to diagnostic groups were accounted for by CSF markers of AD or brain atrophy. METHODS: We studied 499 participants aged 60-88 years from the German Center for Neurodegenerative Diseases Longitudinal Cognitive Impairment and Dementia Study (DELCODE) who underwent task-fMRI. Participants included 163 cognitively normal (healthy control, HC) individuals, 222 SCD, 82 MCI, and 32 patients with clinical diagnosis of mild AD. CSF levels of β-amyloid 42/40 ratio and phosphorylated-tau181 were available from 232 participants. We used region-based analyses to assess novelty-related activity (novel > highly familiar scenes) in entorhinal cortex, hippocampus, and precuneus as well as whole-brain voxel-wise analyses. First, general linear models tested differences in fMRI activity between participant groups. Complementary regression models tested quadratic relationships between memory impairment and activity. Second, relationships of activity with AD CSF biomarkers and brain volume were analyzed. Analyses were controlled for age, sex, study site, and education. RESULTS: In the precuneus, we observed an inverted U-shaped pattern of novelty-related activity across groups, with higher activity in SCD and MCI compared with HC, but not in patients with AD who showed relatively lower activity than MCI. This nonlinear pattern was confirmed by a quadratic relationship between memory impairment and precuneus activity. Precuneus activity was not related to AD biomarkers or brain volume. In contrast to the precuneus, hippocampal activity was reduced in AD dementia compared with all other groups and related to AD biomarkers. DISCUSSION: Novelty-related activity in the precuneus follows a nonlinear pattern across the clinical spectrum of increased AD risk. Although the underlying mechanism remains unclear, increased precuneus activity might represent an early signature of memory impairment. Our results highlight the nonlinearity of activity alterations that should be considered in clinical trials using functional outcome measures or targeting hyperactivity

Machine learning‐based classification of Alzheimer's disease and its at‐risk states using personality traits, anxiety, and depression

Background Alzheimer's disease (AD) is often preceded by stages of cognitive impairment, namely subjective cognitive decline (SCD) and mild cognitive impairment (MCI). While cerebrospinal fluid (CSF) biomarkers are established predictors of AD, other non-invasive candidate predictors include personality traits, anxiety, and depression, among others. These predictors offer non-invasive assessment and exhibit changes during AD development and preclinical stages. Methods In a cross-sectional design, we comparatively evaluated the predictive value of personality traits (Big Five), geriatric anxiety and depression scores, resting-state functional magnetic resonance imaging activity of the default mode network, apoliprotein E (ApoE) genotype, and CSF biomarkers (tTau, pTau181, Aβ42/40 ratio) in a multi-class support vector machine classification. Participants included 189 healthy controls (HC), 338 individuals with SCD, 132 with amnestic MCI, and 74 with mild AD from the multicenter DZNE-Longitudinal Cognitive Impairment and Dementia Study (DELCODE). Results Mean predictive accuracy across all participant groups was highest when utilizing a combination of personality, depression, and anxiety scores. HC were best predicted by a feature set comprised of depression and anxiety scores and participants with AD were best predicted by a feature set containing CSF biomarkers. Classification of participants with SCD or aMCI was near chance level for all assessed feature sets. Conclusion Our results demonstrate predictive value of personality trait and state scores for AD. Importantly, CSF biomarkers, personality, depression, anxiety, and ApoE genotype show complementary value for classification of AD and its at-risk stages

Relay-assisted OFDM transmission for indoor visible light communication

Due to copyright restrictions, the access to the full text of this article is only available via subscription.In this study, we investigate a relay-assisted visible light communication (VEC) system where an intermediate light source cooperates with the main light source. Specifically, we consider two light sources in an office space; one is the information source employed on the ceiling and the other one is a task light mounted on a desk. Our system builds upon DC biased optical orthogonal frequency division multiplexing (DCO-OFDM). The task light performs amplify-and-forward relaying to assist the communication and operates in half-duplex mode. We investigate the error rate performance of the proposed OFDM-based relay-assisted VEC system. Furthermore, we present joint AC and DC optimal power allocation in order to improve the performance. The DC power allocation is controlled by sharing the number of LED chips between the terminals and the AC power allocation decides the fraction of the information signal energy to be consumed at the terminals. Simulation results reveal that the VLC. system performance can be improved via relay-assisted transmission and the performance gain as much as 6 dB can be achieved

Non-orthogonal multiple access (NOMA) for indoor visible light communications

Due to copyright restrictions, the access to the full text of this article is only available via subscription.Providing multiple access support to visible light communication (VLC) systems requires new networking architecture. Non-orthogonal multiple access (NOMA) is a proposed multiple access technique for future cellular systems. In this work, based on a realistic indoor channel conditions, we apply NOMA to indoor VLC channels and demonstrate its superior performance over orthogonal frequency division multiple access (OFDMA)

Relay-assisted OFDM-based visible light communications over multipath channels

Due to copyright restrictions, the access to the full text of this article is only available via subscription.In this paper, we investigate the performance of relay-assisted visible light communication (VLC) system over multipath channels. We consider an indoor environment where the ceiling light serves as the information source and a desk light helps the source forward the information to the destination. The VLC system is built on orthogonal frequency division multiplexing (OFDM) with either amplify-and-forward or decode-and-forward relaying. A realistic channel impulse response of the indoor environment generated through ray tracing is used. Through simulations, we present the bit error rate performance of OFDM-based relay-assisted VLC system over indoor multipath channels and quantify the performance degradation with respect to idealistic single tap channels. We further discuss the impact of imperfect channel estimation on the performance.Qatar National Research Fun