Unipolar-pulse amplitude modulation frequency division multiplexing for visible light communication systems

Abstract

Asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) has been proposed in visible light communication (VLC) systems to overcome the DC-biased optical OFDM (DC-OFDM) power consumption issue at the cost of the available electrical spectral efficiency. Due to the implementation of inverse fast Fourier transform (IFFT), all the optical OFDM schemes including ACO-OFDM suffer from large peck to average power ratio (PAPR), which degrade the performance in VLC systems as the light emitting diodes used as the transmitter have a limited optical power-current linear range. To address the PAPR issue in ACO-OFDM, in this work we introduce a unipolar-pulse amplitude modulation frequency division multiplexing (U-PAM-FDM) by adopting the single carrier frequency division multiple access (SC-FDMA). This is achieved by considering a PAM as an SC-FDMA data symbols and inserting a conjugate copy of the middle and first SC-FDMA FFT output subcarriers after the middle and last subcarriers, respectively. Simulation results show that, for the proposed scheme the PAPR is 3.6 dB lower compared with ACO-OFDM. The PAPR improvement is further analyzed with the simulation results demonstrating that the proposed scheme offers 2.5 dB more average transmitted power compared to ACO-OFDM.

DFT Spread-Optical Pulse Amplitude Modulation for Visible Light Communication Systems

“…Since the AWGN power (𝑃 𝑎𝑤𝑔𝑛 ) (i.e., the noise power of the VLC system) increases the EVM, 𝑃 𝑚𝑎𝑥 will be affected by the amount of 𝑃 𝑎𝑤𝑔𝑛 present in the system. Note in [30][31], the 𝑃 𝑎𝑤𝑔𝑛 was set to -10 dBm. However, the noise power in VLC systems varies within a range as it depends on numerous parameters [1][2][3].…”

“…Such signal has almost the same features as OFDM (i.e., bit and power loading and reduce inter-symbol interference) but a low PAPR signal such as an SCM signal [25][26][27][28]. However, the SC-IFDMA is mainly proposed as a means to improve the OFDM PAPR signal in the RF domain and has recently been modified to make it suitable for IM/DD based VLC systems [29][30][31][32][33][34][35].…”

“…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]. To make the SC-IFDMA signal a real signal, its FFT output subcarriers at its Tx should be symmetrically conjugated.…”

“…This was achieved in the U-PAM-FDM by considering a PAM as an SC-IFDMA data symbol which results in a symmetrically output FFT conjugated subcarriers excluding the first and the middle ones. To make all the U-PAM-FDM output FFT subcarriers are symmetrically conjugated, a subcarrier conjugate (SCG) block is added after the FFT implementation at the U-PAM-FDM Tx where a copy of the first and the middle subcarriers are respectively inserted after the middle and the last ones [31]. On the other hand, the output FFT subcarriers of the ACO-SCFDE are imposed to HS at the Tx to satisfy the condition for the values to be real [29][30].…”

“…On the other hand, the output FFT subcarriers of the ACO-SCFDE are imposed to HS at the Tx to satisfy the condition for the values to be real [29][30]. However, the implementation of the HS and the SCG at the Tx of the ACO-SCFDE and the U-PAM-FDM leads to the increase in their PAPR values in comparison to the traditional SC-IFDMA [31][32].…”