Wireless visible light communications employing feed-forward pre-equalization and PAM-4 modulation

X. Li, N. Bamiedakis, X. Guo, J. J. D. McKendry, E. Xie, R. Ferreira, E. Gu, M. D. Dawson, R. V. Penty, I. H. White

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In this paper, feed-forward pre-equalization in conjunction with a PAM modulation scheme are proposed for use in wireless visible light communication (VLC) systems in order to enable the transmission of data rates > 1 Gb/s. Simulation results demonstrate that simple few-tap feed-forward pre-equalization is able to remove the inter-symbol-interference (ISI) caused by the limited link bandwidth of a line of sight (LOS) VLC link, providing up to 5 dB better receiver sensitivity compared with post-equalization. The pre-equalization scheme is implemented for a free-space VLC link using a PAM modulation scheme, which provides an enhanced spectral efficiency compared to NRZ modulation. Micro-pixelated LEDs (μLEDs) are used as the transmitter in this work, as they exhibit higher modulation bandwidth than conventional large-diameter LEDs. An avalanche photodiode (APD) is used at the receiver to provide an enhanced link power budget. Error-free (BER<10-12) 2 Gb/s freespace VLC transmission over 0.6 m is demonstrated experimentally using a simple 3-tap feed-forward pre-equalizer and a PAM-4 modulation scheme. The results show that feedforward pre-equalization with only a few taps can improve the μLED-based link performance greatly, providing a simple and cost-effective solution for high speed VLC links.
Original languageEnglish
Pages (from-to)2049-2055
Number of pages7
JournalJournal of Lightwave Technology
Issue number8
Early online date22 Jan 2016
Publication statusPublished - 3 Mar 2016


  • feed forward equalization
  • micro LED
  • pulse amplitude modulation
  • visible light communication


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