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In this paper, we describe a visible-light positioning system that uses the ambient-light sensor assembly in a smartphone as a receiver for illumination signals from LED-based room lighting. After correcting for missing or inconsistently sampled data captured by the receiver, we can identify the source LEDs contributing to the received signal via Fourier analysis of its frequency distribution. Localization of the smartphone is then achieved by trilateration of the distances to the various LEDs, which are calculated from the received signal strength for each LED. Experiments using multiple LEDs were conducted to evaluate the signal reception and positioning performance of the system. We found that multiple LEDs modulated at frequencies of over 70 Hz could be correctly identified from the received signal pattern. The 90th-percentile 2D positioning errors using low frequency signals (3.951-7.902 Hz) were less than 0.21 meter for a room illuminated by four LEDs arranged in a 1-m square on the ceiling at 2.22 meters height, where the smartphone was placed parallel on the floor from 1.4 meters height. Those using high frequency signals (111.619-114.582 Hz) in the same room setting showed 50th-percentile 2D position errors of less than 0.44 meter. The position calculation was offline and not implemented on real time. Potential applications and limitations of the proposed method are discussed.

This paper describes a novel acoustic localization and communication methods using multiple speakers. Acoustic signals for localization are modulated by differential phase shift keying to contain some information. Therefore, localization and communication can be conducted simultaneously. Regarding the design of acoustic signals, short-time and narrow-band acoustic signals are ideal to save time and frequency resources. However, if such signals are used with conventional methods, the interference of signals can occur and cause errors of localization and communication. Additionally, this error changes depending on the phase value that corresponds to the modulation for communication. To reduce this error, in our proposed method, a noninterference region in the received signal was constituted by using dual-carrier acoustic signals, and localization and demodulation were processed using this region. In the evaluation experiments, we estimate the azimuth of the microphone from two speakers and demodulate each of the symbols at 9 locations. Through simulation and real-environment experiments, it was confirmed that our proposed method can reduce the error caused by the interference. In real-environment experiments, the demodulation performance of our proposed method was similar to that of conventional methods. We discussed this similarity and revealed the cause.

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.

This paper describes the Symphony-Q support system for learning music. This system integrates a sensing board and a computer, and is used for collaborative learning in a face-to-face setting. One of the aims of Symphony-Q is to enhance music experiences: children who do not have music skills can easily participate in music learning, enjoy making sounds, and play rhythmically to music in collaboration with others. The paper discusses comments and feedback from school children and their teachers, which were collected during experiments with Symphony-Q carried out in a Japanese public elementary school.