A comparison between DCO-OFDMA and synchronous one-dimensional OCDMA for optical wireless communications

In this paper, a comparison between direct-current-biased optical orthogonal frequency-division multiple-access (DCO-OFDMA) and synchronous one-dimensional (1-D) optical code-division multiple-access (OCDMA) is performed for optical wireless communication (OWC). Line-of-sight (LOS) channel conditions are considered in an indoor downlink scenario. The bit-error ratio (BER) performance is investigated in an additive white Gaussian noise (AWGN) channel under the conditions of equal spectral and power efficiency. For DCO-OFDMA and 1-D OCDMA, the negative-level clipping effect and multiple-access interference (MAI) are considered, respectively. For the OCDMA scheme, the categories of optical orthogonal codes (OOCs) and unipolar Walsh-Hadamard codes (WHCs) are employed. The time-division multiple-access (TDMA) is also represented in the context of synchronous OCDMA by the use of identity matrices. In order to enhance the 1-D OCDMA spectral efficiency, unipolar M-ary pulse amplitude modulation (M-PAM) is employed. The BER performance versus the average electrical signal-to-noise ratio (SNR) per bit is illustrated both for the single and the multiple-user communication using Monte Carlo simulations.