Evaluation of large girth LDPC codes for PMD compensation by turbo equalization
Lyubomir L Minkov1, Ivan B Djordjevic, Lei Xu
1Department of Electrical and Computer Engineering, University of Arizona, Tucson, AZ 85721, USA. ljubo@email.arizona.edu
Optics Express
|August 20, 2008
Summary
Large-girth quasi-cyclic LDPC codes enhance optical transmission systems by improving PMD compensation. These codes offer significant coding gain, approaching channel capacity limits for 10 Gb/s systems.
Area of Science:
- Optical Communications
- Information Theory
- Error Correction Coding
Background:
- Polarization Mode Dispersion (PMD) in optical fibers degrades signal quality.
- Turbo equalization is a technique used to mitigate signal impairments.
- LDPC codes are advanced error-correcting codes known for their performance.
Purpose of the Study:
- To experimentally evaluate large-girth quasi-cyclic LDPC codes for PMD compensation.
- To assess the performance of these codes in a 10 Gb/s NRZ optical transmission system.
- To quantify the coding gain achieved by LDPC codes compared to traditional detectors.
Main Methods:
- Experimental setup simulating a 10 Gb/s NRZ optical transmission system with PMD.
- Implementation of turbo equalization utilizing girth-10 LDPC codes of varying rates and lengths.
- Bit Error Rate (BER) measurements at a BER of 10(-6) to determine coding gain.
Main Results:
- A girth-10, rate 0.906 LDPC code (length 11936) achieved a 6.25 dB coding gain over MAP detection for 125 ps differential group delay.
- A girth-10 LDPC code with rate 0.8 outperformed the rate 0.906 code by 2.75 dB, yielding a 9 dB coding gain.
- LDPC codes with lengths around 15000 approached the channel capacity limit within 1.25 dB.
Conclusions:
- Large-girth quasi-cyclic LDPC codes are effective for PMD compensation in high-speed optical systems.
- Code rate significantly impacts performance, with lower rates offering greater coding gain.
- Optimized LDPC codes demonstrate near-capacity performance, crucial for future optical network advancements.
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