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Circular Modulation Formats and Carrier Phase Estimation for Coherent Optical Systems
KTH, School of Information and Communication Technology (ICT).
2014 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Digital coherent receivers stand today as a promising technology for the next generation of high-capacity optical systems. Coherent systems enable the use of multilevel modulation formats which increase the spectral efficiency of a system. Key challenges of multilevel coherent systems are the strict laser linewidth requirements and receiver complexity which prevent a cost-effective implementation. The goal of this thesis is to address these challenges by investigating a novel approach to implement phase noise tolerant optical systems. The performance of a phase recovery scheme, normalized Viterbi-Viterbi carrier phase estimation (V-V CPE), is investigated for circular m-level quadrature amplitude modulation (C-mQAM) signals. C-mQAM provides inherent characteristics for phase noise mitigation, while V-V CPE enables an efficient hardware implementation in a blind feed-forward receiver. A coherent C-mQAM system was simulated in VPItransmissionMaker with phase recovery implemented with MATLAB.

Phase noise tolerance was analyzed for C-16QAM and C-64QAM signals. Results show an enhanced phase noise tolerance at a low sensitivity penalty. The achieved linewidth tolerance shows an enhanced performance over available CPE schemes for square mQAM signals, and enables the use of cost-effective lasers. C-mQAM signals allow a straightforward employment of V-V CPE, which can be easily upgraded for higher order circular modulations without adding significant complexity. By combining the power of normalized V-V CPE with C-mQAM inherent characteristics, the phase noise tolerance is enhanced with an efficient implementation. These results show that C-mQAM implemented with V-V CPE is a viable and promising alternative for phase noise tolerant high-speed optical coherent systems.

Place, publisher, year, edition, pages
2014. , 49 p.
TRITA-ICT-EX, 2014:167
National Category
Computer and Information Science
URN: urn:nbn:se:kth:diva-177439OAI: diva2:872741
Available from: 2015-12-18 Created: 2015-11-20 Last updated: 2015-12-18Bibliographically approved

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