Multiuser MIMO Indoor Visible Light Communication System Using Spatial Multiplexing

Visible light communications is an energy efficient and cost-effective solution for indoor wireless access. In this paper, we propose a multiple input multiple output system using centralized or decentralized transmitted power allocation algorithms with multiple LEDs and photodetectors. The proposed system uses an optical code division multiple-access technique to support multiple users. Time-space minimum mean squared error filters at the receivers are designed to diminish the effect of multiple-access interference. In the centralized power allocation algorithm, all the LED lamps in the room are coordinated and controlled by a central controller; each LED lamp supports all the users within the indoor area. The decentralized power allocation algorithms we propose have similar bit error rate performance yet less computational burden compared to the centralized algorithm. In our decentralized algorithms, users are supported by a subset of the LEDs, and so the optimization problem size can be reduced by as much as 93%. For each receiver, multiple photodetectors with different orientations are employed to improve the signal to interference plus noise ratio. In addition, some practical considerations such as shadowing effects, illumination requirements, dimming control, and transmitted power quantization are taken into account.