Spatial frequency-based angular behavior of a short-range flicker-free MIMO–OCC link

In this paper, we provide a solution based on spatial frequency f_sf to study the angular behavior of a flicker-free, short-range indoor multiple–input multiple–output (MIMO) optical camera communications (OCC) link. We focus on the experimental investigation of OCC’s performance for the transmitters (Txs) [i.e., light-emitting diode (LED) based arrays] located at the same and different distances from the receiver (Rx) with the off-axis rotation angle θ. We have used two 8 × 8 distributed LED arrays and a commercial low-cost complementary metal-oxide-semiconductor (CMOS) Raspberry Pi camera with the rolling-shutter capturing mode as the Tx and Rx, respectively. The image and the respective communications link quality metrics are measured in terms of the peak signal-to-noise ratio (PSNR) and the rate of successfully received bits with respect to f_sf for different camera shutter speeds (SS). A CMOS image sensor noise characterization is carried in terms of the signal-to-noise ratio (SNR) and PSNR. The proposed study provides a 100% success rate in data reception at the optimum θ of 50^◦ at lower captured values of f_sf, which is projected onto the image sensor in the form of pixels. Moreover, the effect of channel saturation over f_sf is studied with respect to θ and SS and we show that, for θ exceeding the optimum value along transmission range, the f_sf area of the Txs reduces to less than ∼50% of the captured Tx units at θ of 0^◦, where no data can be fully recovered.