การพัฒนาระบบระบุตำแหน่งภายในอาคารโดยใช้การสื่อสารไร้สายทางแสง

Abstract

In this thesis, we propose a three-dimensional visible light communication indoor positioning system using smart device camera receiver to reduce errors of other positioning systems inappropriate for the indoor environment. Instead of radio signal, light signal is used to communicate between transmitter and receiver. We use the rolling shutter effect of CMOS sensor in a mobile device to demodulate identification information from the LEDs, encoded by code division multiplexing technique. Each LED code consists of positions in world coordinate of the LED and distance between LEDs. For the receiver, additional equipment is not required since the demodulation can be performed by within the mobile application. From the obtained images of 4 LEDs, two techniques are used to estimate the distance between the camera and the LEDs. In the first technique, the distance is estimated by counting the number in pixels of the white area that appears in image, which is a function of the distance. In the second technique, the distance is estimated by finding the relationship between the world coordinate and the image coordinate of the distance between a pair of LEDs, together with the data from gyroscope sensors. For estimating receiver position, its distance toward 4 LEDs is required in the 3D trilateration algorithm. All processing in this method is done by the application on the smart device. The system can send and receive information to make an accurate estimation of the location. The result has shown similar position errors using the first and the second methods, within 10 and 11 centimeters, respectively.