Takayuki Akiyama

Smart phone localization method using dual-carrier acoustic waves

We describe an indoor localization technique for smart phones. Our new method, called the Frequency Division Multiplexing Phase Accordance Method (FDM-PAM), uses a beat called a sync pattern composed of a pair of sinusoidal waves with slightly different frequencies, which is similar to our original ultrasound ranging technique called the Phase Accordance Method (PAM). By generating multiple sync patterns with different central frequencies and transmitting them from different speakers, FDM-PAM conducts time-difference-of-arrival (TDOA) multilateration for localizing smart phones. In the current implementation of FDM-PAM, the 2D indoor position of a smart phone can be estimated. Three sync patterns are generated by using two out of six sinusoidal waves with frequencies ranging from 14.75 kHz to 17.25 kHz. The transmission of the sync pattern from the speakers lasts 4 ms. Through experiments, we have confirmed that FDM-PAM achieves accuracy of around 10 cm using only a short burst transmission, which indicates that the localization technique is sufficiently rapid and accurate.

SyncSync: Time-of-arrival based localization method using light-synchronized acoustic waves for smartphones

In this paper we describe SyncSync, a novel time-of-arrival (ToA) localization method for smartphones. ToA measurements generally show better precision than time-difference-of-arrival measurements, but ToA systems require a synchronization mechanism between anchor and mobile nodes. For this synchronization, we employ modulated light with an acoustic signal for the time-of-flight distance measurement. These are detected by the smartphones video camera and microphone. The time resolution in consumer video cameras is typically only a few tenths of a second, but by utilizing a CMOS image sensors rolling shutter effect we obtain synchronization resolutions of a few microseconds, sufficient for precise acoustic ToA measurement. Experiments confirm operation of the system with localization errors within 10 mm.

3D FDM-PAM: rapid and precise indoor 3D localization using acoustic signal for smartphone

In this paper, we present an indoor 3D positioning method for smartphones using acoustic signals. In our proposed 3D Frequency Division Multiplexing--Phase Accordance Method (3D FDM--PAM), four speakers simultaneously emit burst signals comprising two carrier waves at different frequencies to enable the rapid calculation of the position of the smartphone. Through experiments, we show that 3D FDM--PAM can achieve a standard deviation of less than 2.8 cm at 7.8 measurements per second. The worst positioning error was 48.3 cm at the 95th percentile. We investigate the causes of error and discuss potential improvements to the localization performance.

Light-synchronized acoustic ToA measurement system for mobile smart nodes

We describe a novel time-synchronization technique for mobile smart nodes. We capture modulated LED light with a video camera, which is usually built into a smart node. The CMOS image sensor of a video camera does not take a snapshot at a certain time. Instead, the sensor captures data on a line-byline basis and the sensor output consists of lines taken at slightly different times. Therefore, we can extract time information from the image. This can be used for time synchronization for time-of-arrival (ToA) measurements. In this paper, we describe the fundamentals and an experiment using light-synchronized acoustic ToA measurements with mobile smart nodes. The acknowledged precision of the obtained time information is equivalent to 5.8 mm with an airborne sound wave.

Optimally Modulated Illumination for Rapid and Accurate Time Synchronization

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 μs 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.

OFDM Visible Light Communication using Off-the-shelf Video Camera

This paper describes a rapid and flicker-free visible light communication technique that uses an off-the-shelf video camera. Transfer rates at least 53% faster than existing methods were achieved in experiments. Features of the proposed method are discussed via theoretical analysis.

A rapid and accurate time-synchronization technique for acoustic localization using modulated illumination

This paper presents a rapid and accurate time-synchronization technique for acoustic localization. Two LED arrays for modulated illumination and an off-the-shelf camera are used. An equation that specifies the time difference between them accurately and precisely is proposed. Experiments in real environments show that the proposed technique using rectangular signals can achieve time synchronization to within 29.4 μs (5.94 μs standard deviation) and acoustic ranging to within 9.9 mm (2.01 mm standard deviation) for a measurement period of 0.1 s. Because of the smaller standard deviation in comparison with the error, it is indicated that there exist systematic errors to be removable. This technique will enable the implementation of an acoustic 3D localization system for mobile devices such as tablet PCs and smartphones based on time-of-arrival trilateration, which is more accurate than positioning taking a time-difference-of-arrival approach. Theoretical analyses for modulated illumination considering a camera exposure time clarify how an optimally modulated signal is designed for achieving rapid and accurate time synchronization.

Poster: Multicamera Synchronization for Smartphones using Optimally Modulated Illuminations

The paper describes a rapid and accurate time-synchronization technique for smartphones using their built-in cameras and its preliminary evaluations for application development.

Time-of-arrival-based smartphone localization using visible light communication

We describe a time-of-arrival-(ToA-) based localization system for smartphones. In this system, the transmitter emits modulated light-emitting diode (LED) light and sound waves, then the smartphone catches them. The smartphone measures the time of flight of sound waves and localizes its position using multilateration. The LED light is used for visible light communication, which also conveys the time reference of the sound emission. Using the time reference, we can synchronize between the transmitter and the receiver, then the ToA-based localization can be available. The precision of time synchronization is the key factor for localization based on ToA. Hence, we have proposed the SyncSync method using a modulated LED light and a smartphone video camera, which enables ToA localization by measuring the time of flight of sound waves. This method gives better results than those of time-difference-of-arrival localization. However, we had to use a dedicated light synchronization device for our method. Visible light communication (VLC) is becoming a popular application of smartphones. If VLC demodulation could be used for time synchronization in acoustic localization, VLC and indoor localization would be integrated into a single application. In this paper, we examined the feasibility of VLC time synchronization for localization. Then, ToA-based localization was performed using a smartphone application. The standard deviation of the 3D localization was around 100 mm in a dark room, which is sufficiently precise for practical applications.

A spot-controllable data transfer technique using COTS speakers

This paper describes a spot-controllable data-transfer method. The proposed method generates a beam-shaped spot using two commercial off-the-shelf speakers. In our method, a symbol consists of a pair of sinusoidal waves having different angular frequencies. The width and direction of a beam-shaped spot are controlled by the angular-frequency difference between the sinusoidal waves and the transmission-time difference between the two speakers. Multiple spots can be generated by transmitting multiple pairs of sinusoidal waves based on the principle of orthogonal frequency-division multiplexing. By over-lapping multiple beam-shaped spots, the locations and sizes of the areas enabled to receive data are controllable. Experiments using four speakers and computer simulation show that the proposed method can generate controllable spots. An analysis of the errors in a real indoor environment indicate that they are caused by multipath signals, radiation damping of transmitted signals, and the incident/output angle characteristics of the microphone and speakers.