Abstract
This paper analyzes the impact of high order light reflections on indoor optical wireless communication
(IOWC) channel models. Based on observing the results of computer simulations, a calibration method is proposed to
reduce model errors. Channel models are generated by tracing and adding up diffuse light reflections and sequential
sub-reflections along its traveling path. As computation complexity increases significantly with the number of
reflection orders considered, researchers traditionally, though incorrectly, take the contribution of first a few
reflection orders, most commonly three, to represent the complete channel. Discarded high-order reflections bring no
significant performance difference to low-speed transmission systems; however, major contemporary IOWC research
institutions focus on high-speed Gigabits per second (Gbps) communications and the model errors resulting from
discarded high-order reflections are no longer negligible. This is where the importance of our proposed method lies.
root-mean-square (RMS) delay-spread, for instance, is severely underestimated by neglecting higher-order reflections.
We simulate an IOWC system in an ordinary 6 m × 6 m × 3 m room and calculate the
contributions of each order of reflections at 841 locations. It shows the RMS delay-spread estimation using the first
three orders underestimates the true value by 15.3% on the average and by at most 26.6% as maximum. To
limit error within half a symbol period, 1 Gbps and 10 Gbps systems tolerate underestimations up to 13.7% and
1.4%, respectively. These must be achieved by applying first five and nine orders. To maintain the computation
efficiency of low-order reflection models and improve their accuracies, we propose a statistical calibration method.
It reduces average model error of first three reflection orders from 15.7% to 4.3%. The numbers of
orders required by 1 and 10 Gps systems are individually reduced to 3 and 7.
© 2014 IEEE
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