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An optical wireless communication (OWC) system based on a light-emitting-diode (LED) transmitter and a camera receiver has been developed for use in the automotive area. The automotive OWC system will require Mb/s-class data rates and the ability to quickly detect LEDs from an image. The key to achieving this is improvements to the capabilities of the image sensor mounted on the camera receiver. In this paper, we report on a novel OWC system equipped with an optical communication image sensor (OCI), which is newly developed using CMOS technology. To obtain higher transmission rates, the OCI employs a specialized Bcommunication pixel (CPx)[ capable of responding promptly to optical intensity variations. Furthermore, a new quick LED detection technique, based on a 1-bit flag image which only reacts to high-intensity objects, is formulated. The communication pixels, ordinary image pixels, and associated circuits (including 1-bit flag image output circuits) are then integrated into the OCI. This paper describes the design, fabrication, and capabilities of the OCI, as well as the development of the LED and image sensor based OWC system, which boasts a 20-Mb/s/pixel data rate without LED detection and a 15-Mb/s/pixel data rate with a 16.6-ms real-time LED detection. Index Terms: Optical wireless communication (OWC), visible light communication (VLC), light-emitting diode (LED), complementary metal-oxide-semiconductor (CMOS) image sensor, image sensor based OWC, automotive communication system.

This paper introduces an optical vehicle-to-vehicle (V2V) communication system based on an optical wireless communication technology using an LED transmitter and a camera receiver, which employs a special CMOS image sensor, i.e., an optical communication image sensor (OCI). The OCI has a "communication pixel (CPx)" that can promptly respond to light intensity variations and an output circuit of a "flag image" in which only high-intensity light sources, such as LEDs, have emerged. The OCI that employs these two technologies provides capabilities for a 10-Mb/s optical signal reception and real-time LED detection to the camera receiver. The optical V2V communication system consisting of the LED transmitters mounted on a leading vehicle and the camera receiver mounted on a following vehicle is constructed, and various experiments are conducted under real driving and outdoor lighting conditions. Due to the LED detection method using the flag image, the camera receiver correctly detects LEDs, in real time, in challenging outdoor conditions. Furthermore, between two vehicles, various vehicle internal data (such as speed) and image data (320 Â 240, color) are transmitted successfully, and the 13.0-fps image data reception is achieved while driving outside.

As a new technology for next-generation vehicle-to-everything (V2X) communication, visible-light communication (VLC) using light-emitting diode (LED) transmitters and camera receivers has been energetically studied. Toward the future in which vehicles are connected anytime and anywhere by optical signals, the cutting-edge camera receiver employing a special CMOS image sensor, i.e., the optical communication image sensor (OCI), has been prototyped, and an optical V2V communication system applying this OCI-based camera receiver has already demonstrated 10-Mb/s optical signal transmission between real vehicles during outside driving. In this paper, to reach a transmission performance of 54 Mb/s, which is standardized as the maximum data rate in IEEE 802.11p for V2X communication, a more advanced OCI-based automotive VLC system is described. By introducing optical orthogonal frequency-division multiplexing (optical-OFDM), the new system achieves a more than fivefold higher data rate. Additionally, the frequency response characteristics and circuit noise of the OCI are closely analyzed and taken into account in the signal design. Furthermore, the forward-current limitation of an actual LED is also considered for long operational reliability, i.e., the LED is not operated in overdrive. Bit-error-rate experiments verify a system performance of 45 Mb/s without bit errors and 55 Mb/s with BER G 10 À5 .Index Terms: Visible light communication (VLC), intelligent transport system (ITS), vehicleto-vehicle (V2V) communication, infrastructure-to-vehicle (I2V) communication, light-emitting diode (LED), image sensor-based VLC, optical communication image sensor (OCI), optical orthogonal frequency division multiplexing (optical-OFDM).

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For low-noise complementary metal-oxide-semiconductor (CMOS) image sensors, the reduction of pixel source follower noises is becoming very important. Column-parallel high-gain readout circuits are useful for low-noise CMOS image sensors. This paper presents column-parallel high-gain signal readout circuits, correlated multiple sampling (CMS) circuits and their noise reduction effects. In the CMS, the gain of the noise cancelling is controlled by the number of samplings. It has a similar effect to that of an amplified CDS for the thermal noise but is a little more effective for 1/f and RTS noises. Two types of the CMS with simple integration and folding integration are proposed. In the folding integration, the output signal swing is suppressed by a negative feedback using a comparator and one-bit D-to-A converter. The CMS circuit using the folding integration technique allows to realize a very low-noise level while maintaining a wide dynamic range. The noise reduction effects of their circuits have been investigated with a noise analysis and an implementation of a 1Mpixel pinned photodiode CMOS image sensor. Using 16 samplings, dynamic range of 59.4 dB and noise level of 1.9 e− for the simple integration CMS and 75 dB and 2.2 e− for the folding integration CMS, respectively, are obtained.