  In this paper, we present the first indoor light-based detection and
localization system that builds on concepts from radio detection and ranging
(radar) making use of the expected growth in the use and adoption of visible
light communication (VLC), which can provide the infrastructure for our LiDAL
system. Our system enables active detection, counting and localization of
people, in addition to being fully compatible with existing VLC systems. In
order to detect human (targets), LiDAL uses the visible light spectrum, it
sends pulses using a VLC transmitter and analyses the reflected signal
collected by a photodetector receiver. Although we examine the use of the
visible spectrum here, LiDAL can be used in the infrared spectrum and other
parts of the light spectrum. We introduce LiDAL with different
transmitter-receiver configurations and optimum detectors considering the
fluctuation of the received reflected signal from the target in the presence of
Gaussian noise. We design an efficient multiple input multiple output (MIMO)
LiDAL system with wide field of view (FOV) single photodetector receiver, and
also design a multiple input single output (MISO) LiDAL system with an imaging
receiver to eliminate the ambiguity in target detection and localization. We
develop models for the human body and its reflections and consider the impact
of the colour and texture of the cloth used as well as the impact of target
mobility. A number of detection and localization methods are developed for our
LiDAL system including cross correaltion, a background subtraction method and a
neural network based method. These methods are considered to distinguish a
mobile target from the ambient reflections due to background obstacles
(furniture) in a realistic indoor environment.
