Abstract
The spot-diffusing geometry is one of the attractive configurations considered in
the literature. It provides a better signal-to-noise ratio (SNR) than the conventional
diffuse system (CDS), but its SNR can be degraded due to shadowing, signal blockage and
mobility. Three methods: imaging reception, beam angle and beam power adaptation are
introduced to the design of spot-diffusing OW systems to effectively mitigate the
degradation due to mobility in the presence of ambient light noise, multipath
propagation, and shadowing. The performance of our systems was evaluated through channel
and noise modeling. The CDS SNR performance improves by more than 20 dB when an imaging
receiver with maximum ratio combining (MRC) replaces a non-imaging receiver. A 24 dB SNR
gain can be achieved when spot-diffusing is employed with an imaging MRC receiver
instead of the imaging MRC CDS. In an imaging spot-diffusing system, the SNR is
independent of the transmitter position and can be maximized at all receiver locations
when our new methods (beam angle and beam power adaptation) are implemented. Regardless
of the transmitter position, beam angle adaptation can target the spots at the optimum
location that yields the best SNR at the receiver. A significant SNR improvement of 36
dB in the imaging spot-diffusing performance can be achieved when angle adaptation is
introduced. Further SNR improvement of 4 dB can be obtained if the power is adaptively
distributed among the spots. Furthermore, an increase in the channel bandwidth from 43
MHz (non-imaging CDS) to 8.19 GHz can be achieved through the combination of these
methods (imaging reception, spot-diffusing, beam angle and beam power adaptation). The
increase in channel bandwidth and SNR can enable the OW system to achieve higher data
rates and 2.5 Gbit/s and 5 Gbit/s mobile OW systems are shown to be feasible. The
results also prove that the influence of shadowing and signal blockage can be
sufficiently combated through the use of these methods.
© 2010 IEEE
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