Analysis of forward error correction schemes for colour shift keying modulation

Abstract

Colour shift keying (CSK) is a visible light communication (VLC) modulation scheme, designed for multi-colour light emitting diodes (LEDs), standardised in IEEE 802.15.7. The standard specifies a Reed-Solomon (RS) encoder for the CSK physical layer (PHY). Currently, no investigations have been made to analyse the performance of the RS coded CSK. This paper details, that the CSK systems yield to soft de-mapping, allowing the soft-decision binary convolutional (SD-BC) coding to be used, and evaluates the performance of RS, SD-BC and hard-decision binary convolutional (HD-BC) coded CSK systems. The throughputs of the three colour (TLED) and four colour (QLED) based, coded and uncoded, CSK systems are compared over the additive white Gaussian noise (AWGN) and wireless VLC channels, with colour crosstalk and insertion losses (CIL). A throughput vs operating-range analysis is also presented. The results show that the SD-BC scheme proves to be the most efficient of the coded systems investigated and that the HD-BC coded CSK systems will outperform the RS coded CSK as the SNR increases. The SD-BC coded TLED and QLED systems, when compared to RS coded equivalents, provide up to 2 and 6 dB optical SNR gain over AWGN channel, and up to 2.3 and 5.7 dB optical SNR gain over the indoor VLC channel, respectively. The performance of the uncoded CSK systems has also been approximated analytically for the AWGN channel.