Dual-Codeword Allocation Scheme for Dimmable Visible Light Communications

This letter proposes a practical scheme for LED dimming control in visible light communications (VLC). The scheme entails the allocation of a set of codewords to a symbol. Here, the set is usually composed of two codewords with different average intensities. For dimming control, one of two codewords is selectively transmitted and the dimming control capability of the proposed scheme increases when the symbol distribution is not uniform. The proposed VLC scheme is applied to text transmission, where the distribution of alphabets is nonuniform. For the transmission of the 128 ASCII characters using the proposed scheme through UART ports, a dimming range 23.1%-76.9% is guaranteed and the transmission rate is maintained. The proposed scheme can provide existing LED lighting systems with an efficient dimmable VLC feature.