Digitized radio-over-fiber transmission based on probabilistic quantization codeword shaping

Area of Science:

• Optical Communications
• Digital Signal Processing
• Information Theory

Background:

• Digitized radio-over-fiber (DRoF) systems are crucial for modern telecommunications.
• Receiver sensitivity is a key performance metric limiting system reach and data rates.
• Traditional quantization schemes can be suboptimal for advanced modulation formats like PAM-4.

Purpose of the Study:

• To propose and experimentally validate a novel vector quantization scheme, probabilistic quantization codeword shaping (PQCS), for DRoF systems.
• To enhance receiver sensitivity and improve the overall performance of DRoF transmission.
• To optimize the distribution of quantization bits (QBs) for 4-Pulse Amplitude Modulation (PAM-4).

Main Methods:

• A probabilistic quantization codeword shaping (PQCS) scheme is developed.
• PQCS involves rematching quantization bits (QBs) in the codebook.
• The proposed scheme is experimentally verified in a 16-Quadrature Amplitude Modulation (16-QAM) DRoF system using intensity-modulation/direct-detection.

Main Results:

• The PQCS method achieved a 1.45 dB shaping gain in system sensitivity at a bit error rate (BER) of 5 × 10⁻⁴ compared to traditional vector quantization.
• The experimental setup demonstrated the effectiveness of PQCS in improving receiver sensitivity.
• Error vector magnitude (EVM) below 2% was achieved for 64-QAM and 256-QAM with 6 and 7 QBs, respectively.

Conclusions:

• PQCS is an effective technique for enhancing receiver sensitivity in DRoF transmission systems.
• The proposed scheme offers a practical method for optimizing quantization for advanced modulation formats.
• This advancement contributes to more robust and efficient optical communication systems.