Impact of the IR LED Temperature on the Throughput of Optical Wireless Communication Links

In an optical wireless communication system, the LEDs require high bandwidth to achieve data rates compare to RF communications. Therefore, it is preferred to use high current densities to drive the LED, even beyond its maximum efficiency point. Nevertheless, the LED is a self-heating device where part of the electrical power is converted to optical power and the rest into heat. This increment of temperature in the LED will reduce its optical power and efficiency, causing a degradation of the optical system SNR. Firstly, we start by derivingthe relationship between the LED voltage with its junction temperature using the Shockley equation. Then, we measure the forward voltage at different temperatures to prove a linear relation between them. The optical power, LED bandwidth, and efficiency can be calculated using the ABC parameters from the rate equation. Therefore, we propose a method to obtain these parameters by measuring the emitted optical power and its rise time when varying the driving current. Finally, the ABC parameters are calculated by solving an MMSE problem with the measurements previously done. The throughput of an optical wireless link depends on the efficiency and the LED bandwidth, thus it is temperature dependent. We calculate the degradation of the rate caused by the temperature increment.