Signal characterization for indoor close-range free-space optical communications

In this paper, the characteristics of indoor close-range free-space optical communications are studied. A visible-light communication (VLC) prototype system using white light-emitting diodes (LEDs) is established. Signals are probed from the real-world conditions. Both the propagation model and the statistics of the background noise in different scenarios are analyzed thereupon. Various signal distortions are observed from the experiments over the established prototype. Such distortions have never been addressed in the existing literature, which has provided only the basic simple signal model for free-space optical communications. We devise a new comprehensive framework to analyze the LED transmitter, the receiver, and the free-space VLC channel. Accordingly, the theoretical system performance such as bit-error-rate (BER) can be analyzed accurately using our proposed analytical framework. In order to evaluate the effectiveness of our proposed new system analysis, the measured BERs from the prototype, the theoretical BERs based on the existing analysis, and the theoretical BERs based on our proposed new analysis are compared. It is proved that our new analysis can lead to much more reliable system performance measures.