Abstract
The performance of pixelated multiple-input mul-tiple-output optical wireless communication systems can
be impaired by vignetting, which is the gradual fall-off in illumination at the edges of a received image. This paper
investigates the effect of vignetting for a pixelated system using spatial orthogonal frequency division multiplexing
(OFDM). Our analysis shows that vignetting causes attenuation and intercarrier interference (ICI) in the spatial
frequency domain. MATLAB simulations indicate that for a given constellation size, spatial asymmetrically clipped
optical OFDM (SACO-OFDM) is more robust to vignetting than spatial dc biased optical OFDM (SDCO-OFDM). Moreover, for
the case of SDCO-OFDM, the very large zeroth subcarrier causes severe ICI in its neighbourhood causing flattening of
the bit error rate (BER) curves. We show that this BER floor can be eliminated by leaving some of the lower spatial
frequency subcarriers unused. The BER performance can also be improved by applying a vignetting estimation and
equalization scheme. Finally, it is shown that equalized SACO-OFDM with 16-QAM has the same overall data rate as
equalized SDCO-OFDM using 4-QAM, but requires less optical power.
© 2013 IEEE
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