Abstract
The requirement of a DC-bias is known to make DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) less energy efficient. This can be improved by asymmetrically clipped optical OFDM (ACO-OFDM), pulse amplitude modulated OFDM (PAM-OFDM) or Flip-OFDM, but these variants use the bandwidth inefficiently. Our trade-off between energy and spectrum efficiency considers a given limited channel bandwidth of the light emitting diode (LED) and then attempts to get the highest throughput per unit of energy. We investigate previous findings that clipped OFDM can be more attractive in a low-SNR regime. More specifically, we consider visible light communication (VLC) in which the average light level, i.e., the bias, is prescribed by illumination requirements, thus comes for free. ACO/PAM/Flip-OFDM can convert the DC-bias into power for communication, but all variants of OFDM, including DCO-OFDM consume extra electrical power. We conclude that in this scenario, advantages attributed to ACO/PAM/Flip-OFDM vanish, as DCO-OFDM outperforms its variants in all SNR conditions, in terms of achieved throughput over a bandlimited channel as a function of extra electrical power required. For hybrid solutions, such as Asymmetrically clipped DC biased Optical OFDM (ADO-OFDM) and Hybrid ACO-OFDM (HACO-OFDM), we optimize a new adaptive power and rate splitting between odd (clipped) and even (biased/clipped) subcarriers to balance power and bandwidth efficiency.
Highlights
Orthogonal Frequency Division Multiplexing (OFDM) is widely considered as a modulation technique for an Intensity Modulated/Direct Detection (IM/DD) optical wireless system, because of its ability to transform the full bandwidth channel into smaller subchannels, each with a flat response within their subband
We witness a continuous effort in improving the energy and spectrum efficiency for basic DCO-OFDM in optimal wireless communications
We confirm that unipolar variants of OFDM outperform DCO-OFDM in low-Signal Noise Ratio (SNR) regions for IR communications
Summary
Orthogonal Frequency Division Multiplexing (OFDM) is widely considered as a modulation technique for an Intensity Modulated/Direct Detection (IM/DD) optical wireless system, because of its ability to transform the full bandwidth channel into smaller subchannels, each with a flat response within their subband. We take the position that the channel bandwidth often is a hard constraint [12], [13], while our design objective is to get the highest possible bit rate for a given power budget This calls for an optimization of the maximum throughput per available dimension, as a function of the link budget. Anticipating on results, with ACO/Flip/PAM-OFDM, the extra power for modulation can, depending on the LED and its operation, be significantly above 20% of the illumination only power. This would severely deteriorate the efficiency of LED lighting and may disqualify its energy star compliance [15].
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
