04-07-2016, 04:37 PM
From DC-Biased to DC-Informative Optical OFDM
Abstract
We propose a novel modulation scheme for intensity modulation and direct detection (IM/DD)
based optical communication system employing orthogonal frequency division multiplexing (OFDM).
This method utilizes the DC-bias, which typically is discarded at the receiver-end, to carry information
to achieve higher power efficiency. By formulating and solving a convex optimization problem, a
constellation in high dimensional space is designed offline for the input of the transmitter-side inverse
fast Fourier transform (IFFT) block. We point out that one can choose partial or full DC power for
information transmission. Under the condition that the spectrum efficiency is fixed and attainable, this
method bears notable power gain over traditional DC-biased optical OFDM (DCO-OFDM).
INTRODUCTION
Optical communication using visible light, infrared, or ultraviolet are promising candidates to
provide high-speed indoor/outdoor wireless access on non-regulated frequency bands [1], [2].
Unlike the radio frequency communication (RFC) systems, the light intensity is controlled to
convey information in optical communications. The baseband signals are required to be positive
and real, which impose some constraints on applying existing radio-frequency modulation
schemes, such as the orthogonal frequency division multiplexing (OFDM). Among plenty of
schemes proposed for Optical OFDM (O-OFDM), the asymmetrically-clipped optical OFDM
(ACO-OFDM) and DC-biased optical OFDM (DCO-OFDM) proposed by J. Armstrong etc. are
the most popular [3]. However, the ACO-OFDM scheme suffers from reduced spectral efficiency
since only 1/4 of the subcarriers carry information, and the DCO-OFDM scheme suffers from
low power efficiency due to use of a large DC-bias to compensate for the negative peak.
CONCLUSION AND FUTURE WORKS
We have proposed a novel IFFT-based optical OFDM scheme which uses the DC-bias to carry
information. In a high dimensional space including the DC and multiple subcarriers, optimized
constellation is obtained through solving a convex optimization problem. Further, a BSA scheme
is adopted to further reduce the system BER. Non-negligible power gains are observed from
simulations. We believe that the idea of proposed DC-informative constellation design can be
adopted to other optical modulation schemes.
Abstract
We propose a novel modulation scheme for intensity modulation and direct detection (IM/DD)
based optical communication system employing orthogonal frequency division multiplexing (OFDM).
This method utilizes the DC-bias, which typically is discarded at the receiver-end, to carry information
to achieve higher power efficiency. By formulating and solving a convex optimization problem, a
constellation in high dimensional space is designed offline for the input of the transmitter-side inverse
fast Fourier transform (IFFT) block. We point out that one can choose partial or full DC power for
information transmission. Under the condition that the spectrum efficiency is fixed and attainable, this
method bears notable power gain over traditional DC-biased optical OFDM (DCO-OFDM).
INTRODUCTION
Optical communication using visible light, infrared, or ultraviolet are promising candidates to
provide high-speed indoor/outdoor wireless access on non-regulated frequency bands [1], [2].
Unlike the radio frequency communication (RFC) systems, the light intensity is controlled to
convey information in optical communications. The baseband signals are required to be positive
and real, which impose some constraints on applying existing radio-frequency modulation
schemes, such as the orthogonal frequency division multiplexing (OFDM). Among plenty of
schemes proposed for Optical OFDM (O-OFDM), the asymmetrically-clipped optical OFDM
(ACO-OFDM) and DC-biased optical OFDM (DCO-OFDM) proposed by J. Armstrong etc. are
the most popular [3]. However, the ACO-OFDM scheme suffers from reduced spectral efficiency
since only 1/4 of the subcarriers carry information, and the DCO-OFDM scheme suffers from
low power efficiency due to use of a large DC-bias to compensate for the negative peak.
CONCLUSION AND FUTURE WORKS
We have proposed a novel IFFT-based optical OFDM scheme which uses the DC-bias to carry
information. In a high dimensional space including the DC and multiple subcarriers, optimized
constellation is obtained through solving a convex optimization problem. Further, a BSA scheme
is adopted to further reduce the system BER. Non-negligible power gains are observed from
simulations. We believe that the idea of proposed DC-informative constellation design can be
adopted to other optical modulation schemes.
