Design Concepts and Performance Analysis of Multicarrier CDMA for Indoor Visible Light Communications

In this paper, we present a design methodology with implementational insight and evaluate the performance of a multicarrier code-division multiple access (MC-CDMA) system using intensity modulation/direct detection scheme suitable for an indoor visible light communication (VLC) environment. The proposed system is a CDMA system based on an orthogonal frequency division multiplexing (OFDM) platform. To overcome the light-dimming issue, we use a newly proposed methodology, namely, polarity reversed optical OFDM (PRO-OFDM). A unipolar signal is either added to the minimum current or subtracted from the maximum current in the LED linear current range to provide various amounts of dimming. The CDMA part employs Hadamard sequences to provide synchronous resource sharing. Combining the robustness of orthogonal modulation with the flexibility of CDMA schemes makes the proposed system a viable candidate for future indoor wireless communications such as VLC. The performance of the proposed MC-CDMA is evaluated, and mathematical formulations for the proposed system are derived. For example, closed-form equations for the signal-to-interference-plus-noise ratio and bit error rate (BER) performance are obtained. Furthermore, the analytical formulations are used in numerical analysis to verify the BER performance achieved in simulation results.