To increase symbol rate and security at the physical layer for uplink optical camera communication from a smartphone screen to indoor camera at a distance of 3.5 m, space division multiplexing by adaptive thresholding is proposed and experimentally verified. The adaptive thresholding sets the optimal threshold for a center cell with each outer 8cell pattern in 3x3 cells. Although the outer 8-cell pattern is estimated from conventional fixed threshold, the pattern helps to determine the threshold adaptively. The adaptive thresholding achieved 216.75 and 168.75 kilo symbol per second using 85x85 and 75x75 cells at luminance of 255 and 95, respectively.

Secure uplink from smartphone screen to camera communication (SCC) needs to increase the throughput and simultaneously reduce the screen luminance. To realize low-luminance wavelength division multiplexing / space division multiplexing (WDM/SDM) transmission, 2wavelength adaptive thresholding that categorizes both inter-wavelength and spatial inter-symbol interferences (ISIs) is proposed and experimentally verified. The camera images are categorized into 3×3 cells and the symbol of the center cell is determined. The inter-wavelength ISIs are categorized by the pixel value of the center cell of the other wavelength. The spatial ISIs are categorized by the outer 8-cell symbol pattern estimated at the same wavelength.

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