SoftLight: Adaptive visible light communication over screen-camera links

Abstract

Screen-camera links for Visible Light Communication (VLC) are diverse, as the link quality varies according to many factors, such as ambient light and camera's performance. This paper presents SoftLight, a channel coding approach that considers the unique channel characteristics of VLC links and automatically adapts the transmission data rate to the link qualities of various scenarios. SoftLight incorporates two new ideas: (1) an expanded color modulation interface that provides soft hint about its confidence in each demodulated bit and establishes a bit-level VLC erasure channel, and (2) a rateless coding scheme that achieves bit-level rateless transmissions with low computation complexity and tolerates the false positive of bits provided by the soft hint enabled erasure channel. SoftLight is orthogonal to the visual coding schemes and can be applied atop any barcode layouts. We implement SoftLight on Android smartphones and evaluate its performance under a variety of environments. The experiment results show that SoftLight can correctly transmit a 22-KByte photo between two smartphones within 0.6 second and improves the average goodput of the stateof-the-art screen-camera VLC solution by 2.2¢.

Spectral Domain-Based Data-Embedding Mechanisms for Display-to-Camera Communication

“…The data bits were encoded using the three different embedding mechanisms described in Section 2.2. For M1, α was set in the range [10,50], and for M2 and M3, the α values were in the range [0.1, 0.3]. For error correction, we used the ½ convolution code in the experiment.…”

“…Previous D2C approaches [7][8][9][10] mainly considered data embedding in the image spatial domain. In [7], the alpha channel was used to embed data into the translucency change of image pixels; the pixel RGB values were kept unchanged.…”

“…Using a rolling shutter camera, transmitted messages were acquired by converting the temporally modulated incident light into a spatial flicker pattern. The SoftLight system [10] used a channel-coding approach that automatically adapts the data transmission rate to different scenarios; suggestions on how to exploit expanded color modulation and coding of bit-level rate-less transmissions of low computational complexity were provided. Quick response (QR) codes [11] and twodimensional (2D) color barcodes [12,13] are also considered as a D2C technology where barcoding can be used to embed data.…”

Complementary Color Barcode-Based Optical Camera Communications

“…RainBar [12] proposed code locator detection and localization scheme to provide robust color recognition and its updated version RainBar+ [13] is an online robust color barcode-based VLC system with real-time feedback. In [14,15], "SoftLight" scheme is presented over screen-camera links, which uses color modulation schemes with channel coding and "Soft hint" for data decoding through barcode layout. To the best of the authors' knowledge, the abovementioned techniques do not consider complementary color-based packetization of pilot and data symbols that are imperceptible to the human eye, along with optical channel estimation between a display device and a camera; thus, performance may vary depending on the ambient optical noise or the characteristics of the transceiver.…”

Energy efficient sensing and networking : a visible light perspective

“…As an important branch of camera based VLC, Screen-Camera Communication mainly focuses on designing sophisticated coded images to boost data rate [29,30,31,32,33], or to enhance link reliability [34,35,36]. To improve data rate, SBVLCD [29] and CO-BRA [30] exploit advanced barcode design, PixNet [31] leverages efficient modulation mechanism, SoftLight [32] employs channel coding, and NLE/LE [33] utilizes channel equalization and nonbinary channel coding. Reliability is addressed in terms of either frame synchronization [36] or barcode detection under a prolonged communication distance and device diversity [34,35].…”