Optical wireless communication (OWC) is an alternative technology to meet the demands of the exponentially-growing high data rate applications run by broadband users. The implementation of single carrier modulation techniques in OWC is an age old technology, but for the last few years research is focused towards the multicarrier modulation techniques in OWC. In OWC, information is carried using intensity modulation and retrieved using direct detection. To perform intensity modulation, the baseband signal should be a unipolar signal. To obtain a unipolar signal, various techniques such as DC-biased orthogonal frequency division multiplexing (DCO-OFDM), Asymmetrically clipped orthogonal frequency division multiplexing (ACO-OFDM), Flip orthogonal frequency division multiplexing (Flip-OFDM) and Unipolar orthogonal frequency division multiplexing (U-OFDM) techniques are reported in the literature. Though the DCO-OFDM is spectrally efficient compared to other techniques it requires more power to achieve the targeted BER. In this article, a convolutional Coded DCO-OFDM (CDCO-OFDM) has been introduced by applying channel coding. A convolutional encoder and a hard-decision Viterbi decoder are considered in CDCO-OFDM. It has been observed that CDCO-OFDM requires less transmitted power than DCO-OFDM to attain the targeted BER. The performance of DCO-OFDM and CDCO-OFDM is evaluated for 4, 16, 64 QAM- 7dB and 13dB bias, in the presence of the additive white Gaussian noise (AWGN) channel. It is observed that CDCO requires less power to transmit than DCO-OFDM for the BER 10-4.
Low-PAPR Asymmetrically Clipped Optical OFDM for Intensity-Modulation/Direct-Detection Systems
