Smartphone Positioning Using an Ambient Light Sensor and Reflected Visible Light

In this paper, we propose a method for the 2D positioning of a smartphone by receiving sinusoidally modulated light signals emitted by ceiling-mounted LEDs. An ambient light sensor (ALS) mounted on the smartphone measures the reflected illumination from the floor. The advantage of this combination is that it consumes very little power, does not require the implementation of additional devices, and removes constraints on the placement of the LEDs caused by the field of view. To the best of our knowledge, this method of using the ALS on a smartphone with reflected light from the floor has not been proposed before. We conducted several experiments to investigate the effectiveness and limitations of our method for visible-light positioning. One experiment with different LED frequencies and floor materials showed that, for multiple LEDs emitting modulated light at around 60 Hz and highly reflective floor materials, positioning is possible with a 90th-percentile error of 35.5 cm. Other experiments involved different types of ambient light and different LED arrangements. Based on the results of these experiments, we can show how to improve the positioning performance. We also discuss future developments in real environments.