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Communications and Sensing of Illumination Contributions in a Power LED Lighting System

N 1. N 2. Communications and Sensing of Illumination Contributions in a Power LED Lighting System. Jean-Paul Linnartz, Lorenzo Feri, Hongming Yang , Sel Colak and Tim Schenk. Intelligent lighting control system. Abstract

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Communications and Sensing of Illumination Contributions in a Power LED Lighting System

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  1. N1 N2 Communications and Sensing of Illumination Contributions in a Power LED Lighting System Jean-Paul Linnartz, Lorenzo Feri, Hongming Yang, Sel Colak and Tim Schenk Intelligent lighting control system • Abstract • LED technology emerged as a prime candidate for the future illumination light source. • LEDs offer a superior flexibility in terms of colors and shapes: immense variety of available light patterns. • Patterns creation via easy user interaction requires sensing of local light contribution of each LED. • Enabled through tagging of the light of each LED with an unique embedded IDs. • To this end, we propose a new modulation and multiple access scheme, named as code-time division multiple access - pulse position modulation (CTDMA-PPM). • Our new scheme considers illumination constraints in addition to the communication requirements. • Propose system structure, which includes illumination sources, a sensor receiver and a control system. • Illumination sources illuminate the environment and transmit information at the same time. • This system structure could support a number of luminaries equal to the size of the CDMA codebook times the dimming range. CTDMA-PPM decoding signal structure. • Analytical performance results for detection and estimation derived. Numerical Results • Scenario: 30 white LEDs/m2, square grid, 0.5 W optical power/LED. Code length = 256, dimming length 1024, time resolution 1 μs. • Visible light communications with LEDs over “light link”, allows for: • communication of individual data per light source • estimation of localized light contributions. • Key requirements: Modulation should be invisible and based on pulse-width modulation (PWM) dimming. • Analytical performance results worked out for this scenario. Modulation and Multiple Access • We propose the CTDMA-PPM scheme: a form of PPM which is keyed according to a spreading sequence, and the duty cycle is subject to PWM light dimming. Description of the binary PPM modulation format. Bit-error rate vs. PD-LED distance for different mode numbers μ of the LEDs. • Data is embedded in prefix and inversely in the postfix of PPM block. • Identifer: combination of assigned CDMA code γand start point of the pulse τ. • Walsh-Hadamard orthogonal codes are used. Channel model • Electro-optical conversion in LED has exponential on- and off-switching slopes, with different time constants. • Light propagation modeled using generalized Lambertian law. Depends on position of LED and photodiode (PD) and mode number LED μ. • Speed PD is much higher than of LEDs. • Noise sources are thermal noise and shot noise. Normalized MSE in intensity estimation vs. PD-LED distance. Conclusions • A new modulation and multiple access scheme for power LED systems has been proposed, named CTDMA-PPM, and analyzed. • Required performance is achieved up to distances of 10 meters. • A very large number of LEDs can be supported in this communications concept. Receiver design • Integrate-and-dump receiver followed by a code despreader. • Bit detection using maximum-ratio combiner and threshold detector. • Least squares and MMSE intensity estimator designed.

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