  This paper presents a modulation scheme in the time domain based on
On-Off-Keying and proposes various compatible supports for different types of
image sensors. The content of this article is a sub-proposal to the IEEE
802.15.7r1 Task Group (TG7r1) aimed at Optical Wireless Communication (OWC)
using an image sensor as the receiver. The compatibility support is
indispensable for Image Sensor Communications (ISC) because the rolling shutter
image sensors currently available have different frame rates, shutter speeds,
sampling rates, and resolutions. However, focusing on unidirectional
communications (i.e., data broadcasting, beacons), an asynchronous
communication prototype is also discussed in the paper. Due to the physical
limitations associated with typical image sensors (including low and varying
frame rates, long exposures, and low shutter speeds), the link speed
performance is critically considered. Based on the practical measurement of
camera response to modulated light, an operating frequency range is suggested
along with the similar system architecture, decoding procedure, and algorithms.
A significant feature of our novel data frame structure is that it can support
both typical frame rate cameras (in the oversampling mode) as well as very low
frame rate cameras (in the error detection mode for a camera whose frame rate
is lower than the transmission packet rate). A high frame rate camera, i.e., no
less than 20 fps, is supported in an oversampling mode in which a majority
voting scheme for decoding data is applied. A low frame rate camera, i.e., when
the frame rate drops to less than 20 fps at some certain time, is supported by
an error detection mode in which any missing data sub-packet is detected in
decoding and later corrected by external code. Numerical results and valuable
analysis are also included to indicate the capability of the proposed schemes.
