  In this paper, we design a dimming compatible visible light communication
(VLC) system in a standard office room according to illumination standards
under channel constraints. We use overlapping pulse position modulation (OPPM)
to support dimming control by changing the code weights. The system parameters
such as a valid interval for dimming together with an upper bound for bit rate
according to the channel delay spread are investigated. Moreover, considering
the dispersive VLC channel and using Monte Carlo (MC) simulations, a method is
proposed to determine the minimum code length in different dimming levels in
order to achieve a valid bit error rate (BER).
  Finally, trellis coded modulation (TCM) is suggested to be applied to OPPM in
order to take advantage of consequent coding gain which could be up to $3$ dB.
