Real-time FPGA prototyping of Doppler frequency shift compensation using DSP-assisted automatic frequency control

Area of Science:

• Optical communications
• Digital signal processing
• Coherent optical systems

Background:

• Doppler frequency shift (DFS) poses a significant challenge in high-speed optical communication systems, degrading signal quality.
• Existing methods for DFS compensation may lack the real-time processing capabilities required for advanced optical networks.

Purpose of the Study:

• To present a novel real-time coherent receiver design.
• To demonstrate the effectiveness of digital signal processing (DSP)-assisted automatic frequency control (AFC) in compensating for Doppler frequency shifts (DFS).

Main Methods:

• Implementation of a real-time coherent receiver employing DSP-assisted AFC.
• Testing the system in a field-programmable gate array (FPGA)-based 2.5 Gbaud Quadrature Phase Shift Keying (QPSK) coherent optical system.
• Evaluation of DFS compensation range and frequency shifting rate.

Main Results:

• Achieved a DFS compensation range of ±8 GHz and a frequency shifting rate of 33 MHz/s.
• Demonstrated a receiver sensitivity of -47 dBm at a bit error rate (BER) of 2E-4.
• The power penalty induced by DFS compensation was found to be less than 1 dB.

Conclusions:

• The proposed DSP-assisted AFC scheme effectively compensates for DFS in real-time coherent optical systems.
• The system exhibits excellent sensitivity and minimal power penalty, making it suitable for high-performance optical communication.
• This approach offers a robust solution for mitigating DFS impairments in advanced optical networks.