Analytical construction of a multidimensional carrierless amplitude-phase filter basis

Area of Science:

• Optical communications
• Signal processing
• Digital modulation

Background:

• Carrierless amplitude-phase (CAP) modulation is crucial for optical transmission, enabling signal constellations beyond 2D.
• Analytical expressions for CAP pulse-shaping filters are limited to 2D cases.
• Existing methods for N>2 dimensional CAP filters rely on minimax optimization, which can yield degenerate solutions.

Purpose of the Study:

• To address the limitations of existing methods for constructing multidimensional CAP filters.
• To propose an alternative analytical approach for N>2 dimensional CAP.
• To enhance the robustness of CAP modulation against synchronization errors.

Main Methods:

• Developed an analytical, low-numerical-complexity construction for multidimensional CAP basis.
• Utilized a superposition of frequency-overlapping filters satisfying interference-free conditions.
• Presented a method for DC suppression in CAP signals.

Main Results:

• The proposed method provides an analytical construction for multidimensional CAP filters.
• Filters exhibit ideal characteristics for N as powers of two, with minor non-uniformity for other N.
• The new formulation demonstrates improved immunity to synchronization errors compared to conventional CAP.

Conclusions:

• The proposed analytical construction offers a viable alternative for multidimensional CAP filter design.
• The method overcomes the convergence issues associated with minimax optimization.
• The enhanced robustness to synchronization errors and DC suppression capability are significant advantages for optical transmission systems.