Photonic Network Communications

, Volume 31, Issue 2, pp 294–304 | Cite as

DFT-based optical offset-QAM OFDM: analytical, numerical, and experimental studies

  • Jian ZhaoEmail author


We investigate discrete Fourier transform-based offset quadrature amplitude modulation (offset-QAM) orthogonal frequency division multiplexing (OFDM) technology. We derive a closed-form expression for the de-multiplexed signal and analyze the influence of crosstalk on implementation algorithms and system performance. It is found that channel estimation in offset-QAM OFDM is different from that in conventional OFDM (C-OFDM) due to the residual crosstalk terms and requires particular study. We propose simple and efficient channel estimation algorithms and show, in a 38-Gbit/s offset-16QAM OFDM experiment with 840-km single-mode fiber, that these algorithms can enable the system performance close to the theoretical limit. By using these algorithms, we compare this technology with C-OFDM and Nyquist FDM (N-FDM) and numerically and experimentally show that DFT-based offset-QAM OFDM can greatly enhance the net data rate for fiber transmissions compared to C-OFDM and exhibit lower complexity than N-FDM. These advantages together with the successfully developed implementation algorithms make this technology very promising for optical communication systems.


Optical orthogonal frequency division multiplexing Coherent detection Dispersion Crosstalk 



This work was supported by the Science Foundation Ireland under Grant Number 11/SIRG/I2124 and 13/TIDA/I2718, and EU \(7\mathrm{th}\) Framework Program under grant agreement 318415 (FOX-C).


  1. 1.
    Jin, X.Q., Giddings, R.P., Tang, J.M.: Real-time transmission of 3Gb/s 16QAM encoded optical OFDM signals over 75 km SMFs with negative power penalty. Opt. Express 17, 14574–14585 (2009)CrossRefGoogle Scholar
  2. 2.
    Liu, B., Zhang, L., Xin, X., Yu, J.: None pilot-tone and training sequence assisted OFDM technology based on multiple-differential amplitude phase shift keying. Opt. Express 20, 22878–22885 (2012)CrossRefGoogle Scholar
  3. 3.
    Yang, Q., He, Z., Yang, Z., Yu, S., Yi, X., Shieh, W.: Coherent optical DFT-spread OFDM transmission using orthogonal band multiplexing. Opt. Express 20, 2379–2385 (2012)CrossRefGoogle Scholar
  4. 4.
    Giacoumidis, E., Ibrahim, S.K., Zhao, J., Tang, J.M., Ellis, A.D., Tomkos, I.: Experimental and theoretical investigations of intensity modulation and direct detection optical fast OFDM over MMF links. IEEE Photon. Technol. Lett. 24, 52–54 (2012)Google Scholar
  5. 5.
    Zhao, J., Shams, H.: Fast dispersion estimation in coherent optical 16QAM fast OFDM systems. Opt. Express 21, 2500–2505 (2013)CrossRefGoogle Scholar
  6. 6.
    Zhou, X., Nelson, L., Magill, P., Zhu, B., Peckham, D.: \(8\times 450\)-Gb/s, 50-GHz-spaced, PDM-32QAM transmission over 400 km and one 50 GHz-grid ROADM. In: Proceedings of the Optical Fiber Communications Conference (2012), post-deadline paper PDPB3Google Scholar
  7. 7.
    Bosco, G., Carena, A., Curri, V., Poggiolini, P., Forghieri, F.: Performance limits of Nyquist WDM and CO-OFDM in high-speed PM-QPSK systems. IEEE Photon. Technol. Lett. 22, 1129–1131 (2010)CrossRefGoogle Scholar
  8. 8.
    Zhao, J., Ellis, A.D.: Electronic impairment mitigation in optically multiplexed multicarrier systems. IEEE J. Lightwave Technol. 29, 278–290 (2011)CrossRefGoogle Scholar
  9. 9.
    Dong, Z., Li, X., Yu, J., Chi, N.: \(6\times 144\) Gb/s Nyquist WDM PDM-64QAM generation and transmission on a 12-GHz WDM grid equipped with Nyquist band pre-equalization. IEEE J. Lightwave Technol. 30, 3687–3692 (2012)CrossRefGoogle Scholar
  10. 10.
    Saltzberg, B.R.: Performance of an efficient parallel data transmission system. IEEE Trans. Commun. Technol. 15, 805–811 (1967)CrossRefGoogle Scholar
  11. 11.
    Zhao, J., Ellis, A.D.: Offset-QAM based coherent WDM for spectral efficiency enhancement. Opt. Express 19, 14617–14631 (2011)CrossRefGoogle Scholar
  12. 12.
    Randel, S., Sierra, A., Liu, X., Chandrasekhar, S., Winzer, P.J.: Study of multicarrier offset-QAM for spectrally efficient coherent optical communications. In: Proceedings of the European Conference on Optical Communication (2011), paper Th.11.A.1Google Scholar
  13. 13.
    Horlin, F., Fickers, J., Emplit, P., Bourdoux, A., Louveaux, J.: Dual-polarization OFDM-OQAM for communications over optical fibers with coherent detection. Opt. Express 21, 6409–6421 (2013)CrossRefGoogle Scholar
  14. 14.
    Li, Z., Jiang, T., Li, H., Zhang, X., Li, C., Li, C., Hu, R., Luo, M., Zhang, X., Xiao, X., Yang, Q., Yu, S.: Experimental demonstration of 110-Gb/s unsynchronized band-multiplexed superchannel coherent optical OFDM/OQAM system. Opt. Express 21, 21924–21931 (2013)CrossRefGoogle Scholar
  15. 15.
    Zhao, J.: DFT-based offset-QAM OFDM for optical communication. Opt. Express 22, 1114–1126 (2014)CrossRefGoogle Scholar
  16. 16.
    Xiang, M., Fu, S., Tang, M., Tang, H., Shum, P., Liu, D.: Nyquist WDM superchannel using offset-16QAM and receiver-side digital spectral shaping. Opt. Express 22, 17448–17457 (2014)CrossRefGoogle Scholar
  17. 17.
    Zhao, J.: Channel estimation in DFT-based offset-QAM OFDM systems. Opt. Express 22, 25651–25662 (2014)CrossRefGoogle Scholar
  18. 18.
    Zhao, J., Ibrahim, S.K., Rafique, D., Gunning, P., Ellis, A.D.: Symbol synchronization exploiting the symmetric property in optical fast OFDM. IEEE Photon. Technol. Lett. 23, 594–596 (2011)CrossRefGoogle Scholar
  19. 19.
    Liu, L., Yang, X., Hu, W.: Chromatic dispersion compensation using two pilot tones in optical OFDM systems. In: Proceedings of the Asia Communications and Photonics Conference (2011), PDP 830937.1-6Google Scholar
  20. 20.
    Liu, X., Buchali, F.: Intra-symbol frequency-domain averaging based channel estimation for coherent optical OFDM. Opt. Express 16, 21944–21957 (2008)CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media New York 2015

Authors and Affiliations

  1. 1.Photonic Systems Group, Tyndall National Institute and Department of PhysicsUniversity College CorkCorkIreland

Personalised recommendations