Lorenzo Feri

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

In recent years, LED technology emerged as a prime candidate for the future illumination light source, due to high energy efficiency and long life time. In addition, LEDs offer a superior flexibility in terms of colors and shapes, which leads to a potentially infinite variety of available light patterns. In order to create these patterns via easy user interaction, we need to sense the local light contribution of each LED. This measurement could be enabled through tagging of the light of each LED with 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): a form of PPM which is keyed according to a spreading sequence, and in which the duty cycle is subject to pulse width modulation (PWM) according to the required lighting setting. Our scheme considers illumination constraints in addition to the communication requirements and, to our best knowledge, it has not been addressed by other optical modulation methods. Based on the proposed modulation method and multiple access schemes, we develop a system structure, which includes illumination sources, a sensor receiver and a control system. Illumination sources illuminate the environment and transmit information, simultaneously. According to our theoretical analysis, this system structure could support a number of luminaries equal to the size of the CDMA codebook times the dimming range.

Code Division-Based Sensing of Illumination Contributions in Solid-State Lighting Systems

Light-emitting diodes (LEDs) have emerged as a prime candidate for the light source of the future. To enable easy user interaction with a future lighting system consisting of many LEDs, this paper proposes a method to accurately measure and estimate the local light contributions of a large set of LEDs. This is enabled through tagging the light of each LED with an unique identifier. To this end, we propose a new family of modulation and multiple access schemes in this paper, named code-time division multiple access-pulse position modulation (CTDMA-PPM) and CTDMA-pulse width modulation (CTDMA-PWM). These schemes satisfy illumination constraints, are compatible with the commonly used PWM dimming of LEDs, and meet the multi-signal separation requirements for simultaneous measurement of illumination strengths. Based on these modulation methods, the paper develops algorithms to estimate illumination. Finally, performance analyses show that even for a very large number of LEDs, the sensing performance of the proposed system satisfies the requirements up to an adequate range.

Optical wireless CDMA employing solid state lighting LEDs

We show that optical wireless CDMA can successfully be applied for visible light communication with power LEDs. We detail how it meets the requirements of multiple access communication, particularly for positioning and illumination sensing.