Performance Analysis of Aperture-Based Receivers for MIMO IM/DD Visible Light Communications

Aperture-based receivers are a new form of receiver for multiple-input multiple-output (MIMO) intensity-modulated direct-detection visible light communication (VLC). These receivers provide a wide field of view and excellent angular diversity using a compact planar structure and so are ideally suited for integration in hand-held devices such as smartphones. It is shown that in typical scenarios to achieve similar performance the photodiodes in a conventional receiver based on spatial diversity would have to be separated by distances greater than 30 cm. An in-depth analysis of the performance of aperture-based receivers is presented. Expressions are derived for the channel gain between an optical transmitter and each receiving element (RE) as a function of the transmission pattern of the transmitter, the design of the RE, and the relative positions of the transmitter and receiver. It is shown that a well-designed receiver consisting of multiple REs can separate signals received from different directions with low-multistream interference and that the associated MIMO channel matrices are well conditioned. Simulations are performed for a typical indoor VLC scenario in which light-emitting diode luminaires transmit information using asymmetrically clipped optical orthogonal frequency division multiplexing. Results are presented for receivers using both linear and nonlinear equalizers and for both line of sight (LOS) and LOS plus diffuse reception. The diffuse component is shown to improve the bit error rate (BER) performance slightly. It is shown that the BER depends on the receiver position. When a zero-forcing (ZF) linear receiver is used, the BER is dominated by the most attenuated signal, so the performance degrades at the corners of the room. In contrast, the receivers with nonlinear equalizers based on ZF followed by successive interference cancelation achieve low BER throughout the scenario.