Rapid and Accurate Time Synchronization using LED and General Purpose Video Camera

  LED illuminations are showing signs of wider acceptance in our society. By using a general purpouse video camera, such as a smartphone built-in camera, we propose a rapid and accurate timesynchronization technique. Optimally modulated illumination as a function of camera exposure time is investigated through theoretical analyses and its mathematical representation is derived. Experiments in real environments with a single LED and 60 fps camera show that the proposed technique can achieve time synchronization to within a 26.3 μ s error at the 90th percentile using only four frames (a measurement time of 0.067 s). Comparative experiments with computer simulations prove that the proposed technique using optimally modulated illumination to camera exposure time needs less CPU time than that using nonoptimally modulated illumination. Applications utilizing features of the proposed technique, such as high-speed visible light communication, indoor localizaion, multi-camera synchronization for motion capture are being implemented.



(NEW) Rapid and Selective Visible Light Communication using Rolling-shutter Camera

  We developed a flicker-free and high-speed visible light communication (VLC) system by using optimally modulated signals emitted from illumination devices. The proposed system achieved 75 kbps at maximum through experiments using a commercially-available camera (60 fps, 1080 line sensors), which goes beyond the theoretical upper limit of existing VLC systems implementing the on-off keying modulation. We clarified the performance of VLC systems using OFDM modulated multicarrier signals through theoretical analyses. Based on them, we devised a system for selective communication between multiple cameras whose exposure time ratios are mutually different.



Indoor 3D Localization Technique for Smartphones

  For rapid indoor 3D localization of smartphones, a new method called Frequency Division Multiplexing Phase Accordance Method (FDM-PAM) is proposed. The method uses a beat called a sync pattern composed of a pair of sinusoidal waves whose frequencies are slightly different, which is the same way as our original ultrasound ranging technique called the Phase Accordance Method (PAM). By generating multiple sync patterns whose central frequencies are different and transmitting each of them from different speakers, FDM-PAM conducts time-difference-of-arrival (TDOA) multilateration. In the current implementation of FDM-PAM, four sync patterns are generated by using two out of eight sinusoidal waves whose frequencies range from 14.75 kHz to 18.25 kHz (frequency interval: 500 Hz). Through experiments using four speakers in short baseline intervals (10-14 cm), it is confirmed that FDM-PAM achieves accuracy range around 10 to 30 centimeters using only a transmission of a short burst (4 ms), which indicates a sufficiently rapid indoor localization technique for smartphones.



Rapid Optical Ranging Technique

  The proposed optical ranging technique called LT-PAM (Long-Term Phase Accordance Method) transmits multiple sync patterns composed of two sinusoidal waves with different frequencies. Unlike chirp modulation techniques, LT-PAM transmits the two waves simultaneously and thus enables the shortening of measurement time. We have conducted experiments using two types of light sources, collimated and diffused light.
The experimental results indicated that the proposed method showed a moderate level of accuracy by adjusting the measurement time.



Compact 3D Tracking System

  We propose a novel technique for 3D localization that integrates a single camera and ultrasound. We use the Extended Phase Accordance Method and the ultrasound to measure accurately the distance to a moving target and we use the camera to identify the target’s 2D position on the image plane. A prototype system consists of a transmitter unit mounting one ultrasound transmitter and three infrared LEDs around it, and a receiver unit with one inexpensive camera and one ultrasound receiver.



Ultrasound Motion Capture System

  We propose an innovative motion capture system using ultrasonic communications. Compared with existing commercial motion-capture systems that use optical or magnetic sensing, the proposed system can provide a cost effective solution for industrial and entertainment applications. To improve the capture rate of the proposed system, the EPAM algorithm was implemented in a field-programmable gate array (FPGA).



A Relative Positioning Technique by Using Ultrasonic Communication

  We have been developing an innovative relative positioning technique by using ultrasonic sensors, in order to accurately and rapidly identify distances and orientations among multiple people and electronic devices in an indoor environment.