  Visible light communication (VLC) has the potential to supplement the growing
demand for wireless connectivity. In order to realise the full potential of
VLC, channel models are required Discrete channel models based on semi-hidden
Markov models (Fritchman model) for indoor VLC using low data rate LEDs are
presented. Each channel considered includes background noise and differing
types of interference from fluorescent lights and pulse-width modulated (PWM)
LEDs, which could be part of an indoor smart lighting system. Models were
developed based on experimental error sequences from a VLC system using an
on-off keying (OOK) modulation scheme. The error sequences were input into the
Baum-Welch algorithm to determine the model parameters by expectation
maximisation. Simulated error sequences generated by the models are compared to
and, in most cases, perform better than simpler models with a single bit error
rate. The models closely approximate the experimental errors sequences in terms
of error distribution. The models performed better in channels where there is
less interference. It was also found that periodic errors were introduced as a
results of the PWM modulated smart lighting LEDs. These models have use for
designing error control codes and simulating indoor VLC environments with
different types of interference.
