Code Division-based Sensing of Illumination Contributions in Solid-State Lighting

In recent years, light-emitting diode (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 can be enabled through tagging of the light of each LED with unique embedded IDs. To this end, we propose a new family of modulation and multiple access schemes in this paper and show how they can be applied to accurately estimate the local light contributions. First we will introduce code-time division multiple access pulse position modulation (CTDMAPPM): a form of PPM which is keyed according to a spreading sequence, and in which the duty cycle is compatible to any pulse width modulation (PWM) set by the required lighting setting. Another scheme proposed is CTDMA-PWM, where, in contrast to CTDMA-PPM, we modulate only the start position of a pulse, but not the end position. Our schemes satisfy luminary-dependent illumination constraints, in addition to the multi-signal separation requirements for simultaneous (hence CDMA) measurement of illumination strength. To our best knowledge, this combination has not been addressed previously by other optical modulation methods, which mainly aimed at high downlink throughout for a common data stream. Based on the proposed modulation methods and multiple access schemes, we develop a system structure, which includes PWM illumination sources, a sensor receiver and a control system. Performance analyses show that even for a very large number of LEDs, the sensing performance of the system satisfies the posed requirements up to an adequate range.