Indoor positioning using a high-speed, fish-eye lens-equipped camera in Visible Light Communication

We propose a method for determining the indoor position based on a Visible Light Communication (VLC) system that uses a high-speed fish-eye lens-equipped camera. In VLC, lights are used as data transmitters and users can receive location information using a receiving device. Since the lights are configured to meet a pre-determined illumination level, the system requires neither space nor additional power. The lights serve their usual function as sources of illumination, and as a means of transmitting digitized information. Up to now, photo sensors or a normal lens-equipped camera have been used as receiving devices. However, the number of lights that can be received by a photo sensor is limited, and the receiving angle of the image that a normal lens-equipped camera takes is also limited. Since a camera with a fish-eye lens commands a 180-degree view of the ceiling, the number of detectable LED lights increases and positioning accuracy is improved. In terms of data transmission in VLC, the LED lights transmit data at 9.6 kbps. Thus, we use a high-speed complementary metal-oxide-semiconductor image sensor to receive the digitized information. The sampling frequency of the image sensor is up to 48 kHz. The LED lights send ID frames containing a prefix, ID, and Cyclic Redundancy Check (CRC) code. The ID and CRC are modulated with 4 Pulse-Position Modulation. The receiver detects the LED lights from the ceiling image. Then, variations in intensity at the center of the LED lights are stored as light signals. Since received data can be separated into two segments within a small buffer, according to the measurement period, received data are occasionally swapped. The receiver obtains the world coordinates of the LED light from the received ID. Finally, self-location estimation is performed using the relationship between the fish-eye image coordinates and the world coordinates. We conducted an experiment using the VLC platform in Niigata University, with the receiver position fixed at 24 measuring points. The platform area measures 5.4 m by 7.5 m, and the ceiling height is 3 m.The results show that the maximum horizontal error is 10 cm.We conclude that it is possible to determine a horizontal position within merely 10 cm, using the proposed method.