Abatement of PAPR for ACO-OFDM deployed in VLC systems by frequency modulation of the baseband signal forming a constant envelope

• Published in: Optics communications 2017-06, Vol.393, p.258-266
• Main Authors: Kumar Singh, Vinay, Dalal, U.D.
• Format: Article
• Language: English
• Subjects: Constant envelope; LED; Optical OFDM; PAPR reduction; Visible light communication
• ISSN: 0030-4018; 1873-0310
• DOI: 10.1016/j.optcom.2017.02.065

To inhibit the effect of non-linearity of the LEDs leading to a significant increase in the peak to average power ratio (PAPR) of the OFDM signals in the Visible light communication (VLC) we propose a frequency modulated constant envelope OFDM (FM CE-OFDM) technique. The abrupt amplitude variations in the OFDM signal are frequency modulated before being applied to the LED for electro-optical conversion resulting in a constant envelope signal. The LED is maintained in the linear region of operation by this constant envelope signal at sufficient DC bias. The proposed technique reduces the PAPR to the least possible value ≈0dB. We theoretically analyze and perform numerical simulations to assess the enhancement of the proposed system. The optimal modulation index is found to be 0.3. The metrics pertaining to the evaluation of the phase discontinuity is derived and is found to be lesser for the FM CE-OFDM as compared to the phase modulated (PM) CE-OFDM. The receiver sensitivity is improved by 1.6dB for a transmission distance of 2m for the FM CE-OFDM as compared to the PM CE-OFDM at the FEC threshold. We compare the BER performance of the ideal OFDM (without the non linearity of LED), power back-off OFDM, PM CE-OFDM and FM CE-OFDM in an optical wireless channel (OWC) scenario. The FM CE-OFDM has an improvement of 2.1dB SNR at the FEC threshold as compared to the PM CE-OFDM. It also shows an improvement of 11dB when compared with the power back-off technique used in the VLC systems for 10dB power back-off. •A unique PAPR reduction technique based on FM of O-OFDM in VLC is proposed.•This constant envelope (CE) technique theoretically achieves PAPR ≈0dB.•The effect of non linearity of the LED is also reduced.•Derivation of mathematical model to assess performance and phase discontinuity.•The FM CE-OFDM has lesser phase discontinuity and is 2.1dB better than PM CE-OFDM.