Channel Analysis for Passive Communication with Ambient Light

The idea of the internet of things (IoT) states that devices with embedded electronics will outnumber the devices operated by humans. All those ”things” will require connectivity to exchange information gathered from processed sensor data. A large part of the data will be sent through the air, such that mobile devices can be deployed without a need to connect any wire. Radio frequencies are widely used for wireless communication and include many systems like WiFi, Bluetooth, FM radio stations and mobile telephony. The capacity of radio channels is limited, thus IoT devices might require different methods for communication. In this work we study the behaviour of a relatively new communication channel, called the passive light channel. The passive light channel uses reflections of light to send information in the visible spectrum. It works a bit similar to barcode readers in stores, but it doesn’t require a laser. It is sufficient to reflect sunlight or light from other sources, providing a sustainable method of transmitting information. Patterns consisting of black and white parts, or barcodes in particular, are used to regulate the reflected light. A light sensor is used to detect the reflected light and read the information from the reflected light. The key question in this research is how much information we can convey in such manner. In this work we show our three main contributions. First, we show that the passive light channel works with barcodes and reflections of ambient light. Second, a mathematical model and simulation tools are presented that describe the behaviour of the channel. Finally, the performance of the passive light channel with ambient light is analysed using empirical testbeds and compared with results of optical simulations.