Particle filter-based parameter estimation in a model of the human circadian rhythm

Recent insights into the effects of light on human health call for a more human-centric approach in automatic lighting control systems. We contribute to the provisioning of lighting settings tailored to the needs of individuals by addressing the challenge of predicting the response of an individual’s circadian rhythm to light exposure. Existing models of the human circadian rhythm are not tailored to individual physiological characteristics such as intrinsic circadian period, light sensitivity and age. We propose to improve model accuracy by using Bayesian statistical inference to estimate the values of model parameters that reflect these physiological characteristics. We illustrate our generic method by applying to a combination of two popular models of the circadian rhythm. By processing individual light exposure- and actigraphy data recoded during a field trial with 20 human subjects with a Particle Filter, we estimate each subject’s intrinsic circadian period. When correlating these to the subjects’ Munich Chronotype Questionnaire Midsleep on Free Days time, a significant relationship was found: r > 0.6 and p < 0.01. This shows the proposed method has good potential for improving model accuracy

Wireless optical communication in illumination systems

Electric lighting is pervasive and with LED lighting the ability arises to modulate light. This paper will address some challenges in using illumination products for Optical Wireless Communication (OWC). Electronic LED drivers are going through extreme cost down and have to adhere to efficiency and other requirements that are not easily compatible with OWC. This paper also validates the use of traditional water pouring for OWC channels in which the transmit power consumed for modulation is a nonlinear function of the emitted energy per communication bit

Continuous phase Flip-OFDM in optical wireless communications

Intensity Modulated (IM) optical communication over an LED channel requires the use of a non-negative signal that can also cope with the low-pass nature of LEDs. For this purpose, dedicated schemes such as Flip-OFDM and Assymetrically Clipped Optical (ACO)-OFDM have been proposed. We derive a common mathematical description on which both schemes rely. Exploiting this insight, we propose Continuous Phase Flip-OFDM (CP-Flip-OFDM) as an enhancement to Flip-OFDM. It ensures phase continuity at the transition between the two successive copies of the OFDM blocks, thereby it obviates the Cyclic Midfix between the first OFDM block and its flipped copy. Simultaneously, we derive a less compute-intensive way to generate and detect ACO-OFDM. Instead of creating an Hermitian-symmetry at the transmit Inverse FFT input, which is common in optical IM OFDM, we use zero padding. After the transmit IFFT, a phase ramp-up, i.e., a multiplication with a complex-valued exponential, is applied before truncating to a real and non-negative signal

Collecting Road Traffic Data Using ALOHA Mobile Radio Channel

This report proposes a spectrum efficientsolution for transmitting link travel times from vehicles to a central infrastructure. The performance of an ALOHA mobile radio system for this application is studied analytically. The average number of new updates per minute and the expected time lapsed since the latest update of the road traffic situation in a particular street section is obtained. Results show that in an urban environment, a single (cellular) radio channel has sufficient capacity if receivers are located every 5 to 10 km

Some general methods for tampering with watermarks

Watermarks allow embedded signals to be extracted from audio and video content for a variety of purposes. One application is for copyright control, where it is envisaged that digital video recorders will not permit the recording of content that is watermarked as "never copy". In such a scenario, it is important that the watermark survive both normal signal transformations and attempts to remove the watermark so that an illegal copy can be made. In this paper, we discuss to what extent a watermark can be resistant to tampering and describe a variety of possible attacks.

Dynamic performance analysis of IEEE 802.15.4 networks under intermittent Wi-Fi interference

A ZigBee (802.15.4) lighting network is potentially vulnerable to interference by other wireless technologies that operate in the same Industrial, Scientific and Medical (ISM) frequency band, such as Wi-Fi (802.11). Therefore the study of coexistence between IEEE 802.15.4 and IEEE 802.11/Wi-Fi is becoming more relevant than ever. In this area, literature approaches to the co-existence issue currently fall into two main categories: experimental or simulation results and analytical models which are either asymptotic (e.g., using Bianchi's assumption) and/or stationary. In contrast, in this paper we present an analytical framework in which a comprehensive study of the dynamic influence of Wi-Fi interference on ZigBee networks of arbitrary size becomes possible. We first present an application of mean field approximation to an intractable Markov model of ZigBee networks. We use this modeling approach to investigate the effect of the Wi-Fi traffic pattern on the ZigBee network performance. By taking this dynamic interaction into account, we notice major performance differences depending on the type of traffic. It also reveals that even light traffic patterns, that offer long gaps of inactivity, can hamper the ZigBee performance significantly more than previously reported Wi-Fi coexistence studies suggest

Throughput of Optical WDM with Wide LED Spectra and Imperfect Color-detecting Filters

Plastic optical fiber (POF) is considered as an attractive candidate for next-generation networks, for fiber-to the-home or for fronthaul of wireless access points in offices. Inside such spaces, visible light communication (VLC) can be an attractive interference-free communication approach. Such system can offer high data rates with potential cost reduction compared to existing techniques. Wavelength division multiplexing (WDM) can not only increase the link capacity, but also offers the ability to share the POF media with multiple services. In VLC systems, WDM can increase capacity. However, the use of narrow emitters and narrow bandpass filters to demultiplex the WDM signals are relative costly components in such systems. This work focuses on inexpensive light emitting diodes (LEDs), to accelerate mass-market applications, and we explore the potential for relaxing the wavelength filters at the detector. In these scenarios, multiple-input multiple-output (MIMO) technology can efficiently suppress interference or automatically fall back to common signalling if the crosstalk is so large that parallel channels would be insufficiently independent. We calculate the MIMO crosstalk channel coefficients due to relatively wide LED spectra. We derive analytical expressions for the maximum achievable rate of the system and we conclude that relatively large amount of crosstalk can be tolerated without jeopardizing performance, provided that dedicated signal processing is used. We show that without such signal processing, the choice of optical filters is very critical

An LED Communication Model Based on Carrier Recombination in the Quantum Well

Optical Wireless Communication (OWC) is gaining popularity as it potentially offers interference-free communication in dense environments. By using LEDs, cells of very small size can be created with sharp boundaries thus bandwidth can be reused very densely. Building an effective communication systems starts from understanding the channel. In scientific literature, various models for the LED response are in use. This overview paper starts from the non-linear recombination of electrons and holes in the LED semiconductor junction, which then appears to lead to a very tractable and simple signal processing model. In fact, the LED channel substantially differs from a radio channel. The paper summarizes recent progress in developing an LED channel model, based on the physics of photon generation in the active region. The LED Quantum Well (QW) creates a first-order low-pass effect and the hole-electron re-combinations are inherently non-linear. Thereby the LED exhibits dynamic distortion, that is, non-linearities that are are intertwined with memory effects. The model can be used to reduce power consumption and to increase throughput of LED OWC systems

Compensating Dynamic Nonlinearities in LED Photon Emission to Enhance Optical Wireless Communication

LEDs can be modulated to support wireless optical data communication. However, particularly LEDs optimized for illumination act as a non-linear low-pass communication channel. In this paper, we translate the non-linear differential equations for the hole-electron recombination and photon emissions, into a discrete-time model with delay taps and non-linear coefficients. This LED model can be inverted, to actively eliminate or mitigate the non-linear dynamic LED distortion. We propose a further simplification of the compensation circuit that allows us to use a relatively simple structure with only a couple of parameters. We experimentally characterize and measure signals communicated via commercially available illumination LEDs that are also used for LiFi communication. In an Intensity Modulation Direct Detection (IM/DD) system employing Pulse Amplitude Modulation (PAM), we show that the proposed equalizer can effectively widen the measured eye diagram, thereby reduce the error rate or can allow a larger constellation. For Orthogonal Frequency Division Multiplexing (OFDM), the reduction in distortion allows at least a 50% increase in bit rate, even on measured noisy channels. This confirms the suitability of the LED model on which our non-linear equalizer is based. We show how non-linear time-constants can be estimated from electrical measurements on the LED signal. With the proposed parameter estimation, the equalizer converges to appropriate compensation settings, in Minimum Mean Square Error (MMSE) sense