MIMO system with multi-directional receiver in optical wireless communications

The performance of different multiple-input multiple-output (MIMO) techniques, i.e., spatial multiplexing (SMX), spatial modulation (SM) and spatial repetition coding (SRC), are studied in this paper considering a number of possible receiver designs for handheld devices for Light-Fidelity (LiFi) applications. It is demonstrated that the multi-directional receiver (MDR), as a simple yet effective and practical receiver structure, significantly improves the performance compared to a conventional benchmark receiver design, called screen receiver (SR). In MDR, multiple photodetectors (PDs) are placed on different sides of a handheld device, e.g., a smartphone. The channel condition number, defined as the ratio of maximum to minimum eigenvalues of the channel matrix, is statistically studied for MDR and SR. It is observed that the highly reduced values of channel condition numbers for MDR result in more than 16 dB reduction of required signal-to-noise ratio (SNR) for SMX and SM at a target bit error ratio (BER). It is shown that, particularly for a high target spectral efficiency, incorporating MDR in conjunction with an appropriate MIMO technique can be a effective solution for future LiFi applications.