Abstract
In this paper, we design linear precoders for the downlink of a visible light communication (VLC) system that simultaneously serves multiple users. Instead of using phosphor-coated white light-emitting diodes (PWLEDs), we focus on Red-Green-Blue light-emitting diodes (RGB-LEDs) that allow modulating three separate data streams on the three primary colors of the RGB-LEDs. For this system, we design a zero-forcing (ZF) precoder that maximizes the weighted sum rate for a multilevel pulse amplitude modulation (M-PAM). The precoding design in RGB-based systems presents some challenges due to the system constraints, such as the limited power, the non-negative amplitude constraints per light-emitting diode (LED), and the need to guarantee white light emission while transmitting with RGB-LEDs. For comparison purposes, we also consider the ZF design for a PWLED-based system and evaluate the performance of both a PWLED- and an RGB-based system.
Highlights
Due to the limitation in the availability of spectrum and the millimeter wave signals propagation problems, short-range Visible Light Communications (VLC) has received much attention from the research community, experiencing significant advances in the last years
MHz for the phosphor-coated white light-emitting diodes (PWLEDs), which could be achieved by suppressing the slow response of the phosphorescent component of the light-emitting diode (LED) but increasing the cost significantly [40]
We have focused on the design of ZF multi-user precoding techniques for VLC systems
Summary
Due to the limitation in the availability of spectrum and the millimeter wave (mmWave) signals propagation problems, short-range Visible Light Communications (VLC) has received much attention from the research community, experiencing significant advances in the last years. The PWLED is low cost and commercially available, the phosphor coating limits the LED’s velocity to switch between different light intensity levels. This limitation reduces the transmission bandwidth (BW) to a few MHz [12,13]. We focus on MU scenarios and precoding schemes for RGB-LEDs that can cancel MU interference and adapt the users’ rate to channel conditions. We design such strategies by formulating non-trivial optimization problems that we solve through convex optimization techniques. Working with RGB-based systems requires a new formulation of the precoding design problem, which is more general and challenging
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