Throughput optimization for IR-LEDs in an optical wireless link

This paper addresses the question of whether an optical wireless communication (OWC) LiFi system preferably uses LEDs near their most efficient operating point, which is preferred for environmentally-friendly highly efficient illumination, or that one should preferably drive the LED into its droop regime to speed up its response. In fact, additional non-radiative recombination speeds up the LED response to modulation but spoils efficiency. We introduce the differential (Internal and External) Quantum Efficiency (dIQE; dEQE), as a particular derivative of quantum efficiencies. It quantifies the efficiency at which a current modulation translates into an optical signal.
We optimize the current density, thus how deeply the LED is to be driven into droop, using DC-offset (DCO) OFDM throughput expressions for the first--order low-pass LED response. Short-range small-coverage systems prefer high current densities to achieve very high throughputs. LiFi with wide opening angles, e.g. covering tens of square meters are better off with a high dIQE, thus lower current densities.