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Proposal and Preliminary Experiments of Indoor Optical Wireless LAN Based on a CMOS Image Sensor with a High-Speed Readout Function Enabling a Low-Power Compact Module with Large Uplink Capacity
Keiichiro KAGAWA Tomohiro NISHIMURA Takao HIRAI Yasushi YAMASAKI Hiroaki ASAZU Tomoaki KAWAKAMI Jun OHTA Masahiro NUNOSHITA Kunihiro WATANABE
IEICE TRANSACTIONS on Communications
Publication Date: 2003/05/01
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Joint Special Issue on Recent Progress in Optoelectronics and Communications)
indoor optical wireless LAN, CMOS image sensor, free-space optical communication, space division multiple access, MEMS mirror,
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We propose a new scheme of indoor optical wireless LAN based on a special CMOS image sensor (CIS), which realizes a low-power compact communication module with large uplink capacity due to space division multiple access. In our scheme, all nodes and a hub utilize the CIS as a photoreceiver as well as a position-sensing device for finding the positions of the communication modules, while a single large photodiode is used in the conventional systems. Although conventional image sensors cannot detect modulated signals because they integrate photocurrents, our CIS has a high-speed readout function for receiving optical data from the specific pixels receiving optical signals. The advantages of the proposed scheme are 1) compact embodiment of the communication module due to no need of the bulky mechanical components for searching the other modules, 2) space division multiple access, which leads to 3) large capacity of uplink, and 4) applicability of simple modulation and coding schemes for optical signals. In our scheme, diffusive and narrow beam lights are complementally used for position detection and communication, respectively, which leads to the advantage 5) low power consumption of both light emitter and receiver circuits. To demonstrate two basic functional modes of our CIS: an IS (image sensor) mode and a COM (communication) mode, we fabricate an 88-pixel CIS by use of a 0.8µm BiCMOS technology. In the experiments, the image of a light source is successfully captured in the IS mode for integration time of 29.6msec and optical power of 1.1nW. After the functional mode of the pixel receiving the light is changed to the COM mode, the eye pattern of the modulated light is obtained from the pixel at frequency of 1MHz. We also fabricate a test pixel circuit with in-pixel amplifier, with which operation speed is improved to 100MHz.