New metric for IQ imbalance compensation in optical QPSK coherent systems
- 64 Downloads
We report on a simple alternative method for the compensation of quadrature imbalance in optical quadrature phase-shift-keying (QPSK) coherent systems. By introducing a new metric, the phase imbalance can be determined and compensated. The proposed method is theoretically and numerically analyzed. In particular, it is shown that the method exhibits a small bias of estimated phase imbalance value. Thanks to its deterministic property, this bias can be simply compensated by incorporating at the receiver a phase rotator (or phase shift) whose value can be determined based on an analytical analysis. Moreover, the algorithm is also experimentally validated through bit-error-rate and error vector magnitude (EVM) measurements. A good agreement on the performance of the proposed method with that of the Gram–Schmidt orthogonalization procedure is shown in a 20-Gbit/s optical QPSK experiment. The robustness of both methods was verified with up to \(30^\circ \) phase imbalance by comparing the signal with and without phase imbalance compensation. A 10% reduction in EVM is achieved with our method for a high phase imbalance of \(30^\circ \), while the implementation complexity can be reduced owing to the suppression of the use of square-root operators.
KeywordsCoherent communications Fiber optical communications IQ imbalance Modulation
This work was supported by the French National Research Agency (ANR) in the frame of the OCELOT Project (Ref. ANR-10-VERS-0015), the Contrat de plan Etat-Région Ponant and the French Ministry of Research.
- 1.Raybon, G., Adamiecki, A., Winzer, P.J., Randel, S., Salamanca, L., Konczykowska, A., Jorge, F., Dupuy, J.-Y., Buhl, L.L., Chandrashekhar, S., Xie, C., Draving, S., Grove, M., Rush, K., Urbanke, R.: High symbol rate coherent optical transmission systems: 80 and 107 Gbaud. J. Lightwave Technol. 32, 824–831 (2014)CrossRefGoogle Scholar
- 4.Liu, X.: Receiver sensitivity improvement in optical DQPSK and DQPSK/ASK through data-aided multi-symbol phase estimation. In: Proceeding of ECOC, p. Th.4.4.5 (2006)Google Scholar
- 8.Schenk, T.C.W., Smulders, P.F.M., Fledderus, E.R.: Estimation and compensation of frequency selective TX/RX IQ imbalance in MIMO OFDM systems. In: Proceedings of IEEE International Conference on Communications, pp. 251–256 (2006)Google Scholar
- 9.Liu, C.-H.: Joint Tx and Rx IQ imbalance compensation of OFDM transceiver in mesh network. In: Proceedings of Globel Telecommunications Conference, pp. 704–708 (2008)Google Scholar
- 17.Nguyen, T.-H., Gomez-Agis, F., Gay, M., Anet-Neto, L., Scalart, P., Peucheret, C., Joindot, M., Sentieys, O., Simon, J.-C., and Bramerie, L.: IQ imbalance compensation based on maximum SNR estimation in coherent QPSK systems. In: Proceedings of IEEE International Conference on Transparent Optical Network, p. Tu.C1.3 (2014)Google Scholar
- 22.OIF: Implementation agreement for integrated dual polarization intradyne coherent receiver. IA# OIF-DPC-RX-01.2Google Scholar
- 23.Proakis, J.: Digital Communications (Chap. 5 and 11), 4th edn. McGraw-Hill, New York (2000)Google Scholar
- 25.McKinley, M.D., Remley, K.A., Myslinski, M., Kenney, J.S., Schreurs, D., Nauwelaers, B.: EVM calculation for broadband modulated signals. In: Proceedings of 64th ARFTG Conf. Dig., pp. 45–52 (2004)Google Scholar