Codierte vierdimensionale Modulationsverfahren für die kohärente optische OFDM-Übertragung
Zusammenfassung der Projektergebnisse
We have recapitulated the 4D constellations PDM-QPSK, 2PolSK-QPSK, 16opt and I6PolSK-QPSK in PDM systems for uncoded tranmission over AWGN channels and have discussed the assignment in BICM systems. It was shown that with iterative demapping the advantages of the 4D constellations can be preserved. We further discussed SDM in MMF in terms of capacity. Thereby we illustrated the benefits to consider the additional multiplexing dimensions among the spatial modes as higher-dimensional signal-space, in which further optimizations can be performed. 2PolSK-QPSK was analyzed and compared to PDM-QPSK as subcarrier modulation scheme in a coherent 20 Gbit/s OFDM system by an experimental setup. Thereby, the resilence of 2PolSK-QPSK against nonlinear fiber effects was found to be comparable with respect to PDM-QPSK. In addition, the generation and detection of 2PolSK-QPSK and 6PolSK-QPSK was experimentally demonstrated. This was enabled by a lab setup with a new 28 Gbaud 4D tranmitter working with a 4 channel digital to analog converter driving a dual-polarization IQ modulator. For offline processing a modification of a PDM-QPSK algorithm was required by implementing a 8th-power phase estimation by defining a new cost function for the CMA algorithm. The cost function exploits that 6PolSK-QPSK can be regarded as a composite of PDM-QPSK and 2PolSK-QPSK and implements a pre-decision on whether the actual signal sample is more likely one of these two symbol sets. Successful back-to-back BER measurements were possible for 6PolSK-QPSK as well as for PS-QPSK. Aremaining1 dB penalty of 6PolSK-QPSK with respect to PDM-QPSK indicated the potential for further improvement. We demonstrated experimentally the generation and detection of the 16opt signal constellation. The performance of 16opt was compared to 6PolSK-QPSK and PDM-QPSK by a tranmission over 480 km uncompensated SSMF. The nonlinear threshold of 16opt was the same as for PM-QPSK. However, a comparison of experimental OSNR sensitivity with theoretically predicted linear tranmission performance indicates that a refinment of lab implementation is mandatory to achieve potential performance gains of 4D formats.
Projektbezogene Publikationen (Auswahl)
- Coded Modulation of Polarization- and Space-Multiplexed Signals. In Proceedings of Communications and Photonics Conference and Exhibition, Shanghai, China, November 2011
H. Bülow, Ü. Abay, A. Schenk, J. B. Huber
- Experimental Study of Polarization-Switched-QPSK Subcarrier Modulation and Iterative Demapping on Optical OFDM Systems. In Proceedings of Optical Fiber Communication Conference (OFC), Los Angeles, United States, March, 2011
E. Masalkina, R. Dischler, H. Bülow
- Experimental Transmission with POLQAM and PS-QPSK Modulation Format Using a 28-Gbaud 4-D Transmitter. In Proceedings of European Conference and Exhibition on Optical Communication (ECOC), Amsterdam, Netherlands, 2012
F. Buchali, H. Bülow
- Tranmsmission of 4-D Modulations Formats at 28-Gbaud. In Proceedings of Optical Fiber Communication Conference (OFC), Anaheim, United States, March, 2013
H. Bülow, T. Rahman, F. Buchali, W. Idler, W. Kuebart
