FFT-based Frequency Detection and Interference Analysis for NLOS MIMO-OCC

In this paper, we provide a solution based on fast Fourier Transform (FFT) for frequency detection and interference analysis in a non-line-of-sight (NLOS) multiple-input multiple-output (MIMO) optical camera communications (OCC) link. The proposed NLOS MIMO-OCC uses two organic light-emitting diodes (OLEDs) and a camera as transmitters (Txs) and the receiver, respectively, and reflections from various surfaces such as plain wall, paper and wooden surfaces. In this paper, for the first time, we analyze the performance of NLOS MIMO-OCC for two indoor scenarios utilizing two OLED Txs that are in phase and modulated at the same modulation frequency <italic>f_s</italic> and especially when they are out of phase and under different <italic>f_s</italic>. We carry out FFT for <italic>f_s</italic> detection and interference analysis for OLEDs operating at different phases and <italic>f_s</italic>. To analyze the performance of NLOS MIMO-OCC, first FFT-based <italic>f_s</italic> detection is performed to identify Txs followed by evaluation of the reception success rates <italic>R</italic>_rs for a range of camera exposure times <italic>t</italic>_exp and the gain <italic>G_v</italic> for a given <italic>f_s</italic>. The results show that for two OLEDs in phase and different phases at <italic>t</italic>_exp of 1500, <italic>G_v</italic> of 45 dB and a link span of 2 m, <italic>R_rs</italic> of 94% is achieved at <italic>f_s</italic> of 600 Hz for the plain wall and paper reflectors. For interference analysis, the proposed FFT analysis gives accurate, i.e., 100 % <italic>f_s</italic> detection in all the above cases.