  Visible light communications (VLC) is a promising technology to address the
spectrum crunch problem in radio frequency (RF) networks. A major advantage of
VLC networks is that they can use the existing lighting infrastructure in
indoor environments, which may have large number of LEDs for illumination.
While LEDs used for lighting typically have limited bandwidth, presence of many
LEDs can be exploited for indoor VLC networks, to serve each user by multiple
LEDs for improving link quality and throughput. In this paper, LEDs are grouped
and assigned to the users based on received signal strength from each LED, for
which different solutions are proposed to achieve maximum throughput,
proportional fairness and quality of service (QoS). Additionally, power
optimization of LEDs for a given assignment is investigated, and Jacobian and
Hessian matrices of the corresponding optimization problem are derived.
Moreover, for multi-element receivers with LED grouping at the transmitter, an
improved optimal combining method is proposed. This method suppresses
interference caused by simultaneous data transfer of LEDs and improves the
overall signal-to-interference-plus-noise-ratio (SINR) by 2 dB to 5 dB. Lastly,
an efficient calculation of channel response is presented to simulate multipath
VLC channel with low computational complexity.
