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Channel Ranking based Spread Code Optimization for Visible Light Communication OFDM-IDMA Systems

This paper proposes a novel code length optimization for improving the throughput performance on Orthogonal Frequency Division Multiple - Interleave Division Multiple Access (OFDM-IDMA) based Visible Light Communication (VLC). VLC is under the global spotlight, since Light Emitting Diode (LED) has recently become a part of building infrastructure and VLC functionality is fairly easy by adding communication components to LED lighting. To enhance the VLC capability, OFDM-IDMA has been proposed as a connection method in a multiuser environment. By applying an interleave pattern peculiar to the transmission signal of each user, signals are well separated and multiple access becomes possible in VLC-OFDM-IDMA. However, VLC-OFDM-IDMA necessitates a low coding rate error correction code as well as a long length spreading code which limits the throughput performance. To resolve this problem, we newly introduce a channel ranking and allocates the short length spreading code to a user in good channel state. Overall throughput performance can be improved while the compatible BER performance.