DCT-OFDM based visible light communications

Visible light communication (VLC) is a short-range wireless transmission technique in which light emitting diodes (LEDs) are used as data transmitters. Because of non-coherent characteristics of LEDs, only intensity can be used in transmission, therefore, the signal driven to LEDs should be real valued and non-negative. The output of inverse discrete Fourier transform (IDFT) process in conventional orthogonal frequency division multiplexing (OFDM) is complex-valued. In VLC systems, to make the output of IDFT block real valued, Hermitian symmetry is applied at the input. This reduces spectral efficiency to half. In this paper, to prevent the decrease in spectral efficiency of VLC systems, discrete cosine transform (DCT)-based OFDM structure with real valued outputs is proposed. The error rate performance of the proposed system is compared with DFTbased OFDM system over indoor realistic VLC channel models.