Angle diversity receiver for indoor MIMO visible light communications

In indoor visible light communication systems, transmitters are usually within the line of sight of the receiver. In order to enjoy the benefits of using multiple-input-multiple-output (MIMO) system, the technique for reducing channel correlation is important. This paper proposes a MIMO system using an angle diversity receiver (ADR) to achieve high spatial multiplexing gain. In our proposed system, receiver consists of multiple photodetectors (PDs) whose normals are pointing toward different directions. As a result, the incident angles from the same light emitting diode (LED) are different for different PDs and hence, channel correlation can be reduced. The spatial separation among PDs is small and no imaging lens is required. The proposed receiver is suitable for mounting on small devices like smartphones. Performance comparisons, in terms of analytical, simulated and experimental bit error rates (BER), are carried out for a MIMO system with 4 LED transmitters and 5 PD receivers. Results show that the proposed receiver performs better than other existing non-imaging receiver designs. Our proposed MIMO system is a practically feasible solution to enjoy low channel correlation and support mobility at receiver.