Abstract
DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) has been proposed in visible light communication (VLC) to overcome the limited modulation bandwidth of light emitting diode (LED). Due to the implementation of the inverse fast Fourier transform at the DCO-OFDM transmitter, DCO-OFDM suffers from its high peak-to-average power ratio (PAPR), which restricts its use in some VLC applications, especially where the optical power efficiency is a crucial requirement. That is because the LEDs used in VLC systems have a limited optical power-current linear range. To this end, a novel discrete Fourier transform spread-optical pulse amplitude modulation (DFTS-OPAM) signal scheme based on the single carrier-interleaved frequency division multiple access (SC-IFDMA) signal is introduced in this paper to address the high PAPR issue of OFDM. DFTS-OPAM is achieved by considering a PAM as an SC-IFDMA data symbol and duplicate the output vector of the fast Fourier transform at the SC-IFDMA transmitter side. Simulation results show that the PAPR of the proposed scheme is 7 dB lower than that of DCO-OFDM. Furthermore, this significant PAPR improvement is experimentally investigated where the practical results show that the proposed scheme can provide more 2.5 dB reduction in the average transmitted power requirement compared to DCO-OFDM and can subsequently increase the maximum achieved distance between the transmitter and the receiver up to 44%.
Highlights
Visible light communications (VLCs) have received a great deal of research attention as a promising candidate for future broadband networks by utilizing white light emitting diodes (LEDs) in the existing solid-state lighting (SSL) infrastructure
The reduction of the peak-to-average power ratio (PAPR) value of orthogonal frequency division multiplexing (OFDM) in intensity modulation and direct detection (IM/DD) systems was mathematically established in the previous section by implementing the FFT and repeating mapping (RM) processes before the implementation of the inverse fast Fourier transform (IFFT) method
To obtain fair comparison between DFTS-OPAM and DCO-OFDM in terms of the signal-to-noise ratio (SNR), bit error rate (BER), and error vector magnitude (EVM) as well as the PAM symbols of DFTS-OPAM are generated by separating the real and the imaginary parts of quadrature amplitude modulation (QAM) symbols [i.e., QAM symbol (a + ib) is separated into ‘a’ and ‘b’ PAM symbols], where these symbols are combined at the Rx to reconstruct the QAM
Summary
Visible light communications (VLCs) have received a great deal of research attention as a promising candidate for future broadband networks by utilizing white light emitting diodes (LEDs) in the existing solid-state lighting (SSL) infrastructure. The IFFT properties have been again exploited to make the OFDM signal unipolar without any DC-bias requirements [20,21] This comes at the cost of halving the spectral efficiency in comparison to the DCO-OFDM scheme which is achieved by keeping the real part of the data symbols to be blank in the pulse amplitude modulated discrete multitone (PAM-DMT) or by modulating only the odd subcarriers in asymmetrically clipped optical OFDM (ACO-OFDM). The ACO-single carrier frequency-domain equalization (ACO-SCFDE) and the unipolar pulse amplitude modulation frequency division multiplexing (UPAM-FDM) are the two SC-IFDMA modified schemes that have recently been proposed to make the SC-IFDMA suitable for VLC systems [29,30,31].
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