Browsing by Author "Tsai, Hsin-Mu"

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Augmenting Indoor Inertial Tracking with Polarized Light
(2018-01-01)
Tian, Zhao
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Wei, Yu-Lin
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Chang, Wei-Nin
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Xiong, Xi
;
Zheng, Changxi
Inertial measurement unit (IMU) has long suffered from the problem of integration drift, where sensor noises accumulate quickly and cause fast-growing tracking errors. Existing methods for calibrating IMU tracking either require human in the loop, or need energy-consuming cameras, or suffer from coarse tracking granularity. We propose to augment indoor inertial tracking by reusing existing indoor luminaries to project a static light polarization pattern in the space. This pattern is imperceptible to human eyes and yet through a polarizer, it becomes detectable by a color sensor, and thus can serve as fine-grained optical landmarks that constrain and correct IMU's integration drift and boost tracking accuracy. Exploiting the birefringence optical property of transparent tapes - a low-cost and easily-accessible material - we realize the polarization pattern by simply adding to existing light cover a thin polarizer film with transparent tape stripes glued atop. When fusing with IMU sensor signals, the light pattern enables robust, accurate and low-power motion tracking. Meanwhile, our approach entails low deployment overhead by reusing existing lighting infrastructure without needing an active modulation unit. We build a prototype of our light cover and the sensing unit using off-the-shelf components. Experiments show 4.3 cm median error for 2D tracking and 10 cm for 3D tracking, as well as its robustness in diverse settings.
CELLI - Indoor Positioning using Polarized Sweeping Light Beams
(2017-01-01)
Wei, Yu-Lin
;
Huang, Chang-Jung
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Tsai, Hsin-Mu
;
Lin, Kate Ching-Ju
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資訊工程學系
CELLI: Indoor Positioning Using Polarized Sweeping Light Beams
(2017-01-01)
Wei, Yu-Lin
;
Huang, Chang-Jung
;
Tsai, Hsin-Mu
;
Lin, Kate Ching-Ju
;
資訊工程學系
Existing visible light positioning (VLP) systems leverage the high image resolution of a receiving camera to support high positioning accuracy. However, power-hungry cameras might not always be applicable for many scenarios, such as smart factories, in which small objects require to be accurately localized and tracked. In this paper, we introduce CELLI, an indoor VLP system that only uses a single luminary as the transmitter and requires only a simple light sensor to achieve an extremely high accuracy with centimeter-level error. The key idea is to provide the spatial resolution capability from the transmitter instead of the receiver, so that the complexity of the receiver can be minimized. In particular, a small LCD is installed at the transmitter to project a large number of narrow and interference-free polarized light beams to different spatial cells. A receiving light sensor identifies its located cell by detecting the unique polarization-modulated signals projected to that cell. CELLI further incorporates a number of novel designs to overcome the technical challenges such as reducing the positioning latency, which is typically limited by the long optical response time of an LCD, and transforming a cell coordinate to the global 3D position using only a single light. We have prototyped our design using off-the-shelf optical and electrical components, and experimentally shown that CELLI achieves a median 3D positioning error less than 11.8 cm and a median 2D positioning error to less than 2.7 cm.
LiCompass: Extracting Orientation from Polarized Light
(2017-01-01)
Wei, Yu-Lin
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Wu, Hsin-I
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Wang, Han-Chung
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Tsai, Hsin-Mu
;
Lin, Kate Ching-Ju
Accurate orientation information is the key in many applications, ranging from map reconstruction with crowdsourcing data, location data analytics, to accurate indoor localization. Many existing solutions rely on noisy magnetic and inertial sensor data, leading to limited accuracy, while others leverage multiple, dense anchor points to improve the accuracy, requiring significant deployment efforts. This paper presents LiCompass, the first system that enables a commodity camera to accurately estimate the object orientation using just a single optical anchor. Our key idea is to allow a camera to observe varying intensity level of polarized light when it is in different orientations and, hence, perform estimation directly from image pixel intensity. As the estimation relies only on pixel intensity, instead of the location of the anchor in an image, the system performs reliably at long distance, with low resolution images, and with large perspective distortion. LiCompass' core designs include an elaborate optical anchor design and a series of signal processing techniques based on trigonometric properties, which extend the range of orientation estimation to full 360 degrees. Our prototype evaluation shows that LiCompass produces very accurate estimates with median errors of merely 2.5 degrees at 5 meters and 7.4 degrees at 2.5 meters with an irradiance angle of 55 degrees.
POLI: Long-Range Visible Light Communications Using Polarized Light Intensity Modulation
(2017-01-01)
Chan, Chun-Ling
;
Tsai, Hsin-Mu
;
Lin, Kate Ching-Ju
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資訊工程學系
;
Department of Computer Science
Recent studies have demonstrated the potential of light-to-camera communications for realizing applications such as localization, augmented reality and vehicle-to-vehicle communications. However, the fundamental requirement of visible light communications, flicker-free illumination, becomes a key limitation hindering existing technologies from serving a camera at larger distances. To break this limitation, this paper presents POLI, a light-to-camera communication system that exploits a novel POlarized Light Intensity modulation scheme to provide reliable communications for a wide range of distances. The key idea of POLI is to hide the information with the polarization direction of the light, to which human eyes are insensitive. Taking advantage of this, POLI can change the intensity of the polarized light as slowly as possible, at a rate determined by the range the system would support, but does not generate flickers. By using an optical component to "transform polarization directions to colors", POLI allows a camera to leverage its received RGB values as the three spatial dimensions to recover the information carried in different data streams. POLI further incorporates a number of designs to tackle the non-linearity effect of a camera, which is especially critical for an intensity-based modulation scheme. We implemented a prototype using the USRP N200 combined with off-the-shelf optical components. The experimental results show that POLI delivers to its camera receiver a throughput proportional to the dynamic channel conditions. The achievable throughput can be up to 71 bytes per second at short distances, while the service range can be up to 40 meters.