Optimizing LED Performance for LiFi: Bandwidth versus Efficiency

Optical transmission is attractive for future wireless communication because signals can be confined in a specific coverage area. In designing a system based on LEDs, the trade-off between transmission bandwidth and optical power is important. As a common practice with micro-LEDs, one may drive the LED at a high current density, beyond the optimum efficiency point, to boost the bandwidth. Bit rates of multiple gigabit/s have been demonstrated, but coverage is small. However, using high current densities is discouraged by self-heating, as only a part of the electrical power is converted to optical power. A rising temperature reduces efficiency, causing a degradation of the SNR. We combine multiple models, not only the ABC photon generation and the LED dynamic responses subject to a rapidly varying current but also, the junction voltage method to estimate its temperature. We quantify the achieved throughput in a DCO-OFDM link at different temperatures. This leads to the insight that there is an optimal size of the active region and an optimal current density that maximizes the throughput of the wireless link at different temperatures. The work presented here builds upon work that we published earlier, and we place this in the perspective of a combined system model.