Dispersion tolerance enhancement using an improved offset-QAM OFDM scheme

Area of Science:

• Optical Communications
• Digital Signal Processing
• High-Speed Data Transmission

Background:

• Conventional cyclic prefix (CP) based OFDM systems require significant overhead for dispersion compensation.
• Discrete-Fourier transform (DFT) based offset-QAM OFDM without CP offers comparable dispersion tolerance to conventional OFDM with CP.
• A fundamental limitation in conventional schemes involves signal and crosstalk becoming in-phase due to dispersion.

Purpose of the Study:

• To analytically investigate the mechanism limiting dispersion tolerance in CP-free offset-QAM OFDM.
• To propose a novel scheme to overcome this limitation and enhance dispersion tolerance.
• To improve the dispersion tolerance of offset-QAM OFDM systems significantly.

Main Methods:

• Analytical study of the dispersion tolerance limitations in DFT-based offset-QAM OFDM.
• Development and simulation of a novel scheme to enhance dispersion tolerance.
• Performance evaluation using a 224-Gb/s polarization-division-multiplexed offset-4QAM OFDM signal.

Main Results:

• The proposed scheme significantly improves dispersion tolerance, approaching that of a single subcarrier.
• Simulations demonstrate support for a 224-Gb/s signal over 160,000 ps/nm without CP using 128 subcarriers.
• Dispersion tolerance scales with the square of the number of subcarriers.

Conclusions:

• The novel scheme effectively overcomes the in-phase limitation caused by dispersion in CP-free offset-QAM OFDM.
• This approach offers substantial improvements in spectral efficiency, dispersion tolerance, and reduced complexity.
• It presents a promising solution for future high-capacity, long-haul optical communication systems.