DSP Algorithms for DP-QPSK Systems in OptiSystem

In optical communication systems, DP-QPSK (Dual-Polarization Quadrature Phase Shift Keying) technology has become the core solution for high-speed transmission due to its high spectral efficiency and strong interference resistance. When combined with the OptiSystem simulation platform, this system significantly enhances performance reliability through Digital Signal Processing (DSP) algorithms.

The core DSP algorithm workflow can be divided into the following stages: Polarization Demultiplexing: Implements Constant Modulus Algorithm (CMA) or pilot-based blind equalization techniques to separate X/Y polarization signals and eliminate polarization disturbances during transmission. Code implementation typically involves iterative weight updates using gradient descent methods. Carrier Phase Recovery: Employs Viterbi-Viterbi algorithm or maximum likelihood estimation to compensate for laser frequency offset and phase noise, ensuring QPSK constellation point stability. The algorithm processes phase increments through arctangent operations and phase unwrapping functions. Clock Synchronization: Utilizes Gardner algorithm or polynomial interpolation to correct sampling clock deviations, reducing inter-symbol interference. Implementation requires timing error detection and interpolation filter design with fractional interval calculations. Channel Equalization: Applies adaptive filters (e.g., LMS/RLS) to compensate for linear impairments such as chromatic dispersion and polarization mode dispersion. The code structure includes tap weight adaptation loops and error signal computation modules.

When implementing in OptiSystem, parameter linkage design must be considered, such as optimizing CMA step size in relation to system OSNR to improve convergence speed. Future extensions could explore machine learning-assisted nonlinear impairment compensation or low-complexity DSP architectures with reduced computational overhead.