Spectral-Efficient PAM Modulations for Dimmable Visible Light Communication Systems

In visible light communications (VLC), the bulbs are used to provide communication and illumination simultaneously. Therefore, it is important to design modulation schemes, which are capable of adjusting the illumination level. The simplest approach to achieve this is compensating an all-one or an all-zero sequence, which however is spectrally inefficient. In this letter, we propose to use the constant sum codes to construct spectral-efficient dimmable pulse amplitude modulation (PAM) for VLC. We also present an efficient algorithm based on graph expanding to design the mapping for the proposed dimmable PAM. Numerical results show that the spectral efficiencies of the proposed dimmable PAM are higher than those of the state-of-the-arts. Numerical results also show that the proposed dimmable PAM performs better than the state-of-the-arts in coded VLC. These results show the potential advantages of the proposed dimmable PAM.

I. Introduction

Visible light communications (VLC) is an emerging optical wireless communication scheme supporting short-range and high-speed data transmission [1]–[4]. It has been viewed as an important complementary technique of traditional cellular communications. In VLC, the light emitting diode (LED) bulbs are used to support communication service and illumination service simultaneously. From the communication perspective, the VLC systems should be spectrally efficient. From the illumination perspective, the VLC systems should support dimming control. Hence, it is important to design spectral-efficient and dimmable transmission schemes for VLC.