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In this paper, we construct the spot communication method using a stereo speaker. In our proposed method, one speaker transmits differential binary phase-shift keying (DBPSK) symbols for communication, and the other speaker transmits sine waves whose frequency is close to that of the DBPSK symbols for jamming. Inside the spot, the jamming signal is canceled by the orthogonality of the communication symbols and jamming signals. Outside the spot, the jamming signal inverts the differential phase of the communication symbols, which prevents normal DBPSK demodulation rendering the communication symbols concealed in the area. This enables correct demodulation only inside the spot. In the conventional method using a stereo speaker, the effect of the jamming signal is weak; thus, transmitting at least 11 symbols is required. In our proposed method, the effective jamming using the interference between sine waves of close frequencies enables spot communication by transmitting only 3 symbols. In the evaluation experiments, we generate the spot from −10 to 20 degrees in a real environment and measure the signals at 9 positions inside and outside the spot, from −40 to 40 degrees at 10 degree intervals. The measurements were conducted 100 times at each position. Through these experiments, we confirmed that demodulation errors occur only outside the spot. In the measurement results, some systematic errors of the differential phase were observed inside the spot, where theoretically this error should not occur. To discuss this error, we conducted additional experiments and revealed the causes. [ABSTRACT FROM AUTHOR]

In this paper, we describe a novel method for the five-degrees-of-freedom (5-DoF) pose estimation of a smartphone using the acoustic signal from only one external speaker. To obtain the smartphone’s 5-DoF pose using this speaker, we apply the concept of “mirror-image” speakers to effectively obtain a multiplicity of signals. Here, the primary reflected signals from the wall or floor are captured as signals transmitted from “virtual speakers” located at (wall or floor) mirror-image positions with respect to the real speaker’s location. By using the smartphone built-in stereo microphones, we can obtain not only its three-dimensional (3-D) position but also its yaw and pitch angles, giving a 5-DoF pose estimation. Holding the smartphone sideways, we can calculate arrival angles for each speaker using the two microphones, and identify which (real or mirror-image) speaker is the signal source. We can then robustly identify the 5-DoF pose by utilizing the information obtained from arrival angles and an acceleration-based pitch angle. For our experiments, we located the speaker and estimated the smartphone’s 5-DoF pose at several places along a 2-m wide corridor. Its measurement range was $2.0\times 2.0\times 1.9\,\,\text{m}^{3}$. The results within the effective operating range gave 90th-percentile errors of less than 114.35 mm for the 3-D position, less than 7.96° for the yaw angle, and 7.09° for the pitch angle. We also clarified the effectiveness of the proposed method which can extend speakers’ baselines beyond the physical limit of the corridor via dilution-of-precision measures. Moreover, we identified limitations of the proposed method using simulations. [ABSTRACT FROM AUTHOR]

This paper presents a rapid and accurate time-synchronization technique using an LED and an off-the-shelf camera. We discuss optimally modulated illumination as a function of camera exposure time through theoretical analysis and derive its mathematical representation. Experiments in real environments with a single LED and 60 fps camera show that the proposed technique can achieve time synchronization within a 17.4 $\mu$ 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. The performance of the proposed technique derived from the noise distribution of intensities in captured images agrees closely with the experimental results, enabling time synchronization to be estimated within a confidence interval at a given confidence level. Possible applications to be developed by utilizing features of the proposed technique are described. [ABSTRACT FROM PUBLISHER]