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Optoelectronics & Communications

A video-based spatial-optical system for wireless communication

A video camera can simultaneously detect a wearable terminal and user messages for data communication.
5 September 2006, SPIE Newsroom. DOI: 10.1117/2.1200608.0346

Radio and ray are complementary transmission media, and different applications favor the use of one medium or the other. Radio is favored for applications in which user mobility must be maximized or where transmission though walls or over long range is required. For indoor and wireless local-area networks, however, spatial optical communication is an attractive, safe alternative. A number of indoor wireless communications systems using infrared radiation have been proposed.1,2

We have constructed a novel location-based indoor spatial optical communications system for a wearable computing environment that is private and secure enough to enable users to obtain necessary information and services. Data transmission is based uniquely on user location and the time-series change of terminal intensities, unburdened by the need for private user data. To create such an environment, we have developed an information terminal with low power consumption that employs a spatial optical reflectivity modulation technique. We propose a method for location detection with information recognition of the terminal based on video signal analysis.

The video-based spatial optical communication system for a wearable computing environment is shown in Figure 1. It consists of three component subsystems. On the wearable side, one or more video cameras with LED rings and infrared bandpass filters are used to find and track terminal equipment, worn by users, and to transmit video image data. On the terminal side, a compact, low-power-consumption PDA (personal digital assistant) with a liquid-crystal display—equipped with a corner reflector—is employed to show the messages received, modulate reflectivity to carry data, and to upload user information. In order to turn the PDA into a corner-reflecting device, we remove its original light-scattering reflection sheet and embed a corner-reflection sheet behind the liquid crystal panel as shown in Figure 2 We have also developed application software to modulate PDA reflectivity for data transmission. On the processing side, we chose an image acquisition board with good-quality image-processing and pattern-recognition capabilities. We proposed a dynamic multipattern recognition method to simultaneously detect user locations and messages.

Figure 1. The video-based spatial optical communication system uses an infrared band-pass filter to track terminal equipment.

Figure 2. The terminal equipment consists of (a) a PDA with a liquid crystal display and (b) a corner-cube-array sheet that employs the imaging principle of a corner-cube prism.

This system requires that the wearable information environment pose two questions to the user: first, “Now, where are you?” and second, “Now, what do you want to do?” To answer the first question, a geometric matching algorithm based on optical pattern recognition can be developed that will measure the similarity of shape between an idealized representation of a feature, called a template image, and a feature that may be present in a terminal image. With this algorithm, pattern matching can take place regardless of poor lighting, noise, occlusion, or geometric transformations of the terminal object. On the other hand, because the terminal is a corner-reflection device, the signal light carried by the terminal will be reflected intensively to its source, making it easy to extract terminal patterns from background noise. Figure 3 is an example of program that can detect three terminals simultaneously. To answer the second question, “Now, what do you want to do?” we propose a method for terminal information recognition. When the terminal location is detected, control buttons on the terminal panel enable signal codes to modulate the reflectivity of the liquid crystal panel corresponding to user-determined messages. Figure 4 shows an application to multicontent recognition in an indoor information environment.

Figure 3. A program is implemented for terminal location detection.

Figure 4. The method has been applied to a multilanguage service.

We have constructed a video-based spatial optical communication system as described here, and employed it to conduct experiments for a multilanguage program. We plan to construct a ubiquitous computing environment with flexible multimedia information support, to be developed in tandem with a compact, smart, secure, and low-power-consumption information terminal.

We are grateful to Citizen Watch Co., Ltd. for providing the PDA (DataSlim2) used in our experiments.

Xin Lin, Hideo Itoh  
Information Technology Research Institute, AIST
Dr. Xin Lin received her PhD in optoelectronics from Shizuoka University, Japan, in 1996. She is currently a researcher at the National Institute of Advanced Industrial Science and Technology (AIST), Japan. Her research interests include optical wireless communications, optical information processing, optical neural networks, and pattern recognition. In addition, she is a member of SPIE, and has written numerous papers for SPIE journals and conferences.
Hideo Itoh is a senior researcher of the National Institute of Advanced Industrial Science and Technology (AIST), Japan. He received his BEng and MEng in electronic engineering from Tohoku University in 1982 and 1984, respectively, and received his PhD in computer science from Japan Advanced Institute of Science and Technology in 2005.