Theory And Application Of Error Correction Codes In High-speed Coherent Optical Communication Systems

With the explosive development of Internet area, construction of information increasingly deepens, which urges the backbone network to achieve larger capacity and further development. Under this circumstance,researchers domestic and abroad pay much more attention to high speed optical communication with larger capacity and longer distance. During the past decades, research in optical fiber telecommunication systems has been developed rapidly. And considerable research findings have been achieved by researchers domestic and abroad.In this paper, several research works round codes in high speed coherent optical communication systems have been done. Our work focus on the theory and application of codes in high speed coherent optical communication systems, which contains designing and simulation of Trellis Coded Modulation, Pilot Aided carrier phase estimation scheme combining with forward error correction to improving bit error rate and mitigation cycle slip, experiment of the forgoing scheme.First of all, with the development of channel coding in coherent optical communication systems, trellis coded modulation is a kind of code that gain much net code gain neither expanding band width nor lowering transmission rate. This is a kind of innovative code that combines code with modulation. After doing a large scale of investigation,simulation of Trellis coded modulation based on Quaternary Phase Shift Keying (QPSK) have been done. Compared with BPSK which has the same spectrum efficiency, TCM-QPSK achieve 2.6 dB coding gain at BER = 10-6. While compared with QPSK which possesses the same bandwidth, TCM-QPSK achieves 3.6 dB coding gain at BER = 10-6. At the cost of spectrum efficiency, trellis coded modulation achieve much more coding gain with low computing complexity.Secondly, a coherent optical simulation of 25Gbaud/s QPSK has been established by matlab. A analyzation of a carrier phase estimation based on pilot-aided phase unwrapping which is proposed by our group has been done. A comparison between PAPU+LDPC scheme and Turbo+LDPC scheme has been finished at the same coding overhead.There is a slightly advantage of Turbo scheme over PAPU scheme.However, the phenomenon of error floor of PAPU is much better than Turbo. And the shorter the length of filter is, the more superiority PAPU gets, which is significant in application.At last, a back to back experiment of modified PAPU scheme based on 28Gbaud/s QPSK in coherent optical system has been done. Laser line width of 100k Hz and 300k Hz have been used in experiment.Different length of CPE filter have been set during signal processing.Under different conditions, a comparison of ber has been done between PAPU algorithm used and VVPE algorithm used only (PAPU algorithm unused). With PAPU algorithm using, required Eb/N0 of error free is lower, and the falling range is becoming bigger while the length of filter is becoming longer, which verified the effectiveness of the algorithm. In the meantime, an experimental comparison of post-fec between modified PAPU+LDPC scheme and Turbo deferential decoding based on LDPC scheme has been done at different laser linewidths and different CPE filter length. Under different circumstance, Turbo scheme achieve a 3 dB Eb/NO gain.