4-ary CSK Modulation Scheme Better than RGBW for LCD-Screen Camera Communications

The extended adoption of portable computing equipment allows cheap and effortless access a screen and a camera, which can be exploited to suggest a wireless optical communications structure for specific applications. However, it faces low data rate performance because of the camera and screen physical limitations. Color shift keying (CSK) arises as a modulation alternative to circumvent this problem and the particular case of 4-ary CSK is addressed in this paper. We focus our attention on how machines perceive color and identify two 4-ary sets of equidistant colors employing communications theory. We emphasize the use of a LCD screen as a transmitter and an off-the-shelf smartphone camera as a receiver. Our results show that color set formed by aqua, fuchsia, yellow and black outperforms the color set comprising red (R), green (G), blue (B) and white (W) in a 4-CSK modulation scheme. In addition, we found that the mean value of the received pixels color components is adequate for detection when a LCD screen is the transmitter. Moreover, we identify some optical distortions that degrade the system performance when distance between transmitter and receiver is 18.2 cm.