Polar coded probabilistic shaping PAM8 based on many-to-one mapping for short-reach optical interconnection

Area of Science:

• Optical communications
• Information theory
• Digital signal processing

Background:

• Short-reach optical interconnections require efficient modulation and coding schemes.
• Traditional probabilistic amplitude shaping (PAS) often involves complex distribution matchers and redundancy.
• Polar codes offer strong error correction capabilities, especially at short code lengths.

Purpose of the Study:

• To investigate a polar coded probabilistic shaping (PS) 8-ary pulse amplitude modulation (PAM8) scheme for short-reach optical interconnections.
• To develop a low-complexity PS scheme without extra redundancy or complex distribution matchers.
• To enhance the bit error rate (BER) performance by proposing an optimal clock recovery method.

Main Methods:

• A many-to-one (MTO) mapping was employed for PS PAM8.
• Parity bits were assigned to ambiguity positions to reduce complexity.
• Noise distributions were analyzed at various transmission distances.
• An optimal clock recovery method was proposed and evaluated.

Main Results:

• Shaping gains of up to 1.2 dB (back-to-back) and 0.8 dB (2-km SSMF) were achieved.
• The optimal clock recovery improved shaping gain from 0.15 dB to 0.4 dB after 10-km transmission.
• Polar coded PS-PAM8 provided an additional 2.2 dB coding gain over LDPC codes at a code length of 256.

Conclusions:

• The proposed polar coded PS-PAM8 scheme offers a low-complexity and high-performance solution for short-reach optical interconnections.
• Polar codes demonstrate superior performance over LDPC codes for short code lengths in this application.
• The scheme is a viable alternative for cost-sensitive short-reach optical interconnects.