Self-Clocking Constant-Power Multi-Level Scheme for Optical Camera Communication

Self-clocking line codes are commonly used in Optical Camera Communication (OCC) links to ensure accurate synchronization of data transmission without the need for an explicit clock signal. In OCC links where the light is used both for illumination and communication, some of these codes (e.g., Manchester) can also help minimize the perceptibility of flickering by ensuring rapid transitions and a consistent signal pattern. When considering multi-level line codes, the same self-clocking and constant power characteristics are desirable, which has led to the recent proposal of a Constant-Power Pulse Amplitude Modulation (CP-PAM) scheme for OCC. However, much like in Manchester coding, there is a significant trade-off associated with its use - the overall spectral efficiency is cut in half. This paper presents an alternative multi-level coding scheme that offers the same self-clocking and similar constant power properties, with a significantly improved spectral efficiency compared to CP-PAM (from 0.75 to 1 bps/Hz). Experimental results showcase its merits when used in a multi-level sub-pixel OCC link.