$M$-Point Combinatory for Parallel Transmission Image Sensor-Based Visible Light Communications

$M$
-point combinatory (MC) modulation is proposed for parallel transmission (PT) image sensor (IS)-based visible light communication (VLC). In the conventional PT system,
$M_{0}$
discrete signals which incorporate
$N=(M_{0}-1)/2$
spatial frequencies are transmitted in parallel with
$M_{0}$
transmitting regions of liquid crystal display (LCD). When each of spatial frequencies is modulated with
$P$
-ary phase shift keying (
$P$
-PSK), the number of bits transmitted in one frame is given by
$k=N \log _{2} P$
bits.
$k$
increases when the number of spatial frequencies
$N$
increases with
$M_{0}$
, but at the same time, the peak-to-average power ratio (PAPR) becomes high because the signal of the PT system is essentially orthogonal frequency modulation, thus remaining at a very low number of spatial frequencies
$N$
that the system accommodates without any error. In this paper, we propose MC modulation, which is combined with the PT system to increase the number of bits per frame that the system carries without any error. In the MC PT system,
$M$
out of the
$M_{0}$
transmitting regions are used for transmitting
$M$
discrete signals related to
$M$
-point DFT, where
$M \leq M_{0}$
. Since there are
$\binom{M_{0}}{M}$
ways in choosing
$M$
out of the
$M_{0}$
ones, we map them to
$\ell = \lfloor \log _{2} \binom{M_{0}}{M} \rfloor$
bits. In addition
$k$
bits, the total number of bits per frame is
$k+\ell$
bits. According to
$\ell$
bits,
$M$
transmitting regions are chosen for a frame, and then the
$M$
chosen ones are used to transmit
$M$
discrete signals of the PT system which carries
$k$
bits. Our experimental results show that our proposed MC PT system with 8-PSK achieves 697 bits per frame with keeping no error being observed, while the conventional PT system does only 180 bits per frame.