MIMO-diversity switching techniques for digital transmission in visible light communication

In this work, we propose two decision techniques that interchange between MIMO and diversity schemes for improving shadowing and alignment problems. In a visible-light communication (VLC) system, the transmission nature can be of two types: (1) all LEDs transmit the same signal stream simultaneously; or (2) each LED transmits different parts of a signal stream independently. The MIMO-diversity technique detects and computes the transmitted signal power during reception and conditionally informs the transmitter to switch between Type (1) and Type (2) transmission. Two experimental models have been tested to show the feasibility of such a technique. In the first model, we constructed a full transceiver and uses a switch IC to switch between MIMO and diversity. The second model uses a microcontroller and software decision to switch between two COM ports, each of them dedicated to MIMO and diversity output respectively. Results suggest that shadowing and alignment problems commonly encountered in visible-light communication systems can be readily solved using these methods. A focusing equation has also been formulated to predict signal intensity more accurately. The focusing gap between the concentrator and the photodiode is taken into consideration during channel computation.