Solar cell operating point for joint LiFi communication and harvesting in battery-free devices

Abstract

Solar cells have shown promising performance for Simultaneous Lightwave Information and Power Transfer (SLIPT). Most of literature has focused on applying this concept to battery-powered high-data rate communication. Nevertheless, its application is also particularly advantageous in the low-data rate regime for battery-free systems. However, we find that using the same solar cell causes both communication and harvesting performances degradation. This problem is particularly critical in battery-free systems for its size and power constraints. This paper reveals that the reason behind this problem is that solar cells are typically operated at their Maximum Power Point (MPP), which optimizes energy harvesting but is inefficient for communication. In order to address this finding we introduce, for the first time, the Maximum Communication Point (MCP), a new operating point that complements the traditional MPP by optimizing communication performance. We then propose a transformer-based SLIPT design that enables an accurate control of the impedance at the solar cell's output and thereby allowing precise selection of its operating point. Extensive experiments show that our system provides communication gains of 5x in peak-to-peak received voltage when operating at the MCP, and harvested power gains of more than 3x when operating at the MPP, with respect to the best performing state-of-the-art design.