Abstract

Offset quadrature amplitude modulation (offset-QAM) orthogonal frequency division multiplexing (OFDM) exhibits enhanced net data rates compared to conventional OFDM, and reduced complexity compared to Nyquist FDM (N-FDM). However, channel estimation in discrete-Fourier-transform (DFT) based offset-QAM OFDM is different from that in conventional OFDM and requires particular study. In this paper, we derive a closed-form expression for the demultiplexed signal in DFT-based offset-QAM systems and show that although the residual crosstalk is orthogonal to the decoded signal, its existence degrades the channel estimation performance when the conventional least-square method is applied. We propose and investigate four channel estimation algorithms for offset-QAM OFDM that vary in terms of performance, complexity, and tolerance to system parameters. It is theoretically and experimentally shown that simple channel estimation can be realized in offset-QAM OFDM with the achieved performance close to the theoretical limit. This, together with the existing advantages over conventional OFDM and N-FDM, makes this technology very promising for optical communication systems.

© 2014 Optical Society of America

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References

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  1. X. Q. Jin, R. P. Giddings, and J. M. Tang, “Real-time transmission of 3 Gb/s 16-QAM encoded optical OFDM signals over 75 km SMFs with negative power penalties,” Opt. Express 17(17), 14574–14585 (2009).
    [Crossref] [PubMed]
  2. B. Liu, L. Zhang, X. Xin, and J. Yu, “None pilot-tones and training sequence assisted OFDM technology based on multiple-differential amplitude phase shift keying,” Opt. Express 20(20), 22878–22885 (2012).
    [Crossref] [PubMed]
  3. Q. Yang, Z. He, Z. Yang, S. Yu, X. Yi, and W. Shieh, “Coherent optical DFT-spread OFDM transmission using orthogonal band multiplexing,” Opt. Express 20(3), 2379–2385 (2012).
    [Crossref] [PubMed]
  4. E. Giacoumidis, A. Tsokanos, C. Mouchos, G. Zardas, C. Alves, J. L. Wei, J. M. Tang, C. Gosset, Y. Jaouen, and I. Tomkos, “Extensive comparison of optical fast OFDM and conventional OFDM for local and access networks,” J. Opt. Commun. Netw. 4(10), 724–733 (2012).
    [Crossref]
  5. J. Zhao, S. K. Ibrahim, D. Rafique, P. Gunning, and A. D. Ellis, “Symbol synchronization exploiting the symmetric property in optical fast OFDM,” IEEE Photon. Technol. Lett. 23(9), 594–596 (2011).
    [Crossref]
  6. X. Zhou, L. Nelson, P. Magill, B. Zhu, and D. Peckham, “8x450-Gb/s, 50-GHz-spaced, PDM-32QAM transmission over 400km and one 50GHz-grid ROADM,” in Proc. Optical Fiber Communications Conference (2012), post-deadline paper PDPB3.
  7. G. Bosco, A. Carena, V. Curri, P. Poggiolini, and F. Forghieri, “Performance limits of Nyquist WDM and CO-OFDM in high-speed PM-QPSK systems,” IEEE Photon. Technol. Lett. 22(15), 1129–1131 (2010).
    [Crossref]
  8. J. Zhao and A. D. Ellis, “Electronic impairment mitigation in optically multiplexed multicarrier systems,” J. Lightwave Technol. 29(3), 278–290 (2011).
    [Crossref]
  9. Z. Dong, X. Li, J. Yu, and N. Chi, “6×144 Gb/s Nyquist WDM PDM-64QAM generation and transmission on a 12-GHz WDM grid equipped with Nyquist band pre-equalization,” J. Lightwave Technol. 30(23), 3687–3692 (2012).
    [Crossref]
  10. B. R. Saltzberg, “Performance of an efficient parallel data transmission system,” IEEE Trans. Commun. Technol. 15(6), 805–811 (1967).
    [Crossref]
  11. J. Zhao and A. D. Ellis, “Offset-QAM based coherent WDM for spectral efficiency enhancement,” Opt. Express 19(15), 14617–14631 (2011).
    [Crossref] [PubMed]
  12. S. Randel, A. Sierra, X. Liu, S. Chandrasekhar, and P. J. Winzer, “Study of multicarrier offset-QAM for spectrally efficient coherent optical communications,” in Proc. European Conference on Optical Communication (2011), paper Th.11.A.1.
    [Crossref]
  13. F. Horlin, J. Fickers, P. Emplit, A. Bourdoux, and J. Louveaux, “Dual-polarization OFDM-OQAM for communications over optical fibers with coherent detection,” Opt. Express 21(5), 6409–6421 (2013).
    [Crossref] [PubMed]
  14. Z. Li, T. Jiang, H. Li, X. Zhang, C. Li, C. Li, R. Hu, M. Luo, X. Zhang, X. Xiao, Q. Yang, and S. Yu, “Experimental demonstration of 110-Gb/s unsynchronized band-multiplexed superchannel coherent optical OFDM/OQAM system,” Opt. Express 21(19), 21924–21931 (2013).
    [Crossref] [PubMed]
  15. M. Xiang, S. Fu, M. Tang, H. Tang, P. Shum, and D. Liu, “Nyquist WDM superchannel using offset-16QAM and receiver-side digital spectral shaping,” Opt. Express 22(14), 17448–17457 (2014).
    [Crossref] [PubMed]
  16. J. Zhao, “DFT-based offset-QAM OFDM for optical communications,” Opt. Express 22(1), 1114–1126 (2014).
    [Crossref] [PubMed]
  17. L. Liu, X. Yang, and W. Hu, “Chromatic dispersion compensation using two pilot tones in optical OFDM systems,” in Proc. Asia Communications and Photonics Conference (2011), PDP 830937.1–6.
    [Crossref]
  18. X. Liu and F. Buchali, “Intra-symbol frequency-domain averaging based channel estimation for coherent optical OFDM,” Opt. Express 16(26), 21944–21957 (2008).
    [Crossref] [PubMed]
  19. A. Tolmachev and M. Nazarathy, “Filter-bank based efficient transmission of reduced-guard-interval OFDM,” Opt. Express 19(26), B370–B384 (2011).
    [Crossref] [PubMed]

2014 (2)

2013 (2)

2012 (4)

2011 (4)

2010 (1)

G. Bosco, A. Carena, V. Curri, P. Poggiolini, and F. Forghieri, “Performance limits of Nyquist WDM and CO-OFDM in high-speed PM-QPSK systems,” IEEE Photon. Technol. Lett. 22(15), 1129–1131 (2010).
[Crossref]

2009 (1)

2008 (1)

1967 (1)

B. R. Saltzberg, “Performance of an efficient parallel data transmission system,” IEEE Trans. Commun. Technol. 15(6), 805–811 (1967).
[Crossref]

Alves, C.

Bosco, G.

G. Bosco, A. Carena, V. Curri, P. Poggiolini, and F. Forghieri, “Performance limits of Nyquist WDM and CO-OFDM in high-speed PM-QPSK systems,” IEEE Photon. Technol. Lett. 22(15), 1129–1131 (2010).
[Crossref]

Bourdoux, A.

Buchali, F.

Carena, A.

G. Bosco, A. Carena, V. Curri, P. Poggiolini, and F. Forghieri, “Performance limits of Nyquist WDM and CO-OFDM in high-speed PM-QPSK systems,” IEEE Photon. Technol. Lett. 22(15), 1129–1131 (2010).
[Crossref]

Chi, N.

Curri, V.

G. Bosco, A. Carena, V. Curri, P. Poggiolini, and F. Forghieri, “Performance limits of Nyquist WDM and CO-OFDM in high-speed PM-QPSK systems,” IEEE Photon. Technol. Lett. 22(15), 1129–1131 (2010).
[Crossref]

Dong, Z.

Ellis, A. D.

Emplit, P.

Fickers, J.

Forghieri, F.

G. Bosco, A. Carena, V. Curri, P. Poggiolini, and F. Forghieri, “Performance limits of Nyquist WDM and CO-OFDM in high-speed PM-QPSK systems,” IEEE Photon. Technol. Lett. 22(15), 1129–1131 (2010).
[Crossref]

Fu, S.

Giacoumidis, E.

Giddings, R. P.

Gosset, C.

Gunning, P.

J. Zhao, S. K. Ibrahim, D. Rafique, P. Gunning, and A. D. Ellis, “Symbol synchronization exploiting the symmetric property in optical fast OFDM,” IEEE Photon. Technol. Lett. 23(9), 594–596 (2011).
[Crossref]

He, Z.

Horlin, F.

Hu, R.

Ibrahim, S. K.

J. Zhao, S. K. Ibrahim, D. Rafique, P. Gunning, and A. D. Ellis, “Symbol synchronization exploiting the symmetric property in optical fast OFDM,” IEEE Photon. Technol. Lett. 23(9), 594–596 (2011).
[Crossref]

Jaouen, Y.

Jiang, T.

Jin, X. Q.

Li, C.

Li, H.

Li, X.

Li, Z.

Liu, B.

Liu, D.

Liu, X.

Louveaux, J.

Luo, M.

Mouchos, C.

Nazarathy, M.

Poggiolini, P.

G. Bosco, A. Carena, V. Curri, P. Poggiolini, and F. Forghieri, “Performance limits of Nyquist WDM and CO-OFDM in high-speed PM-QPSK systems,” IEEE Photon. Technol. Lett. 22(15), 1129–1131 (2010).
[Crossref]

Rafique, D.

J. Zhao, S. K. Ibrahim, D. Rafique, P. Gunning, and A. D. Ellis, “Symbol synchronization exploiting the symmetric property in optical fast OFDM,” IEEE Photon. Technol. Lett. 23(9), 594–596 (2011).
[Crossref]

Saltzberg, B. R.

B. R. Saltzberg, “Performance of an efficient parallel data transmission system,” IEEE Trans. Commun. Technol. 15(6), 805–811 (1967).
[Crossref]

Shieh, W.

Shum, P.

Tang, H.

Tang, J. M.

Tang, M.

Tolmachev, A.

Tomkos, I.

Tsokanos, A.

Wei, J. L.

Xiang, M.

Xiao, X.

Xin, X.

Yang, Q.

Yang, Z.

Yi, X.

Yu, J.

Yu, S.

Zardas, G.

Zhang, L.

Zhang, X.

Zhao, J.

IEEE Photon. Technol. Lett. (2)

J. Zhao, S. K. Ibrahim, D. Rafique, P. Gunning, and A. D. Ellis, “Symbol synchronization exploiting the symmetric property in optical fast OFDM,” IEEE Photon. Technol. Lett. 23(9), 594–596 (2011).
[Crossref]

G. Bosco, A. Carena, V. Curri, P. Poggiolini, and F. Forghieri, “Performance limits of Nyquist WDM and CO-OFDM in high-speed PM-QPSK systems,” IEEE Photon. Technol. Lett. 22(15), 1129–1131 (2010).
[Crossref]

IEEE Trans. Commun. Technol. (1)

B. R. Saltzberg, “Performance of an efficient parallel data transmission system,” IEEE Trans. Commun. Technol. 15(6), 805–811 (1967).
[Crossref]

J. Lightwave Technol. (2)

J. Opt. Commun. Netw. (1)

Opt. Express (10)

X. Liu and F. Buchali, “Intra-symbol frequency-domain averaging based channel estimation for coherent optical OFDM,” Opt. Express 16(26), 21944–21957 (2008).
[Crossref] [PubMed]

A. Tolmachev and M. Nazarathy, “Filter-bank based efficient transmission of reduced-guard-interval OFDM,” Opt. Express 19(26), B370–B384 (2011).
[Crossref] [PubMed]

F. Horlin, J. Fickers, P. Emplit, A. Bourdoux, and J. Louveaux, “Dual-polarization OFDM-OQAM for communications over optical fibers with coherent detection,” Opt. Express 21(5), 6409–6421 (2013).
[Crossref] [PubMed]

Z. Li, T. Jiang, H. Li, X. Zhang, C. Li, C. Li, R. Hu, M. Luo, X. Zhang, X. Xiao, Q. Yang, and S. Yu, “Experimental demonstration of 110-Gb/s unsynchronized band-multiplexed superchannel coherent optical OFDM/OQAM system,” Opt. Express 21(19), 21924–21931 (2013).
[Crossref] [PubMed]

M. Xiang, S. Fu, M. Tang, H. Tang, P. Shum, and D. Liu, “Nyquist WDM superchannel using offset-16QAM and receiver-side digital spectral shaping,” Opt. Express 22(14), 17448–17457 (2014).
[Crossref] [PubMed]

J. Zhao, “DFT-based offset-QAM OFDM for optical communications,” Opt. Express 22(1), 1114–1126 (2014).
[Crossref] [PubMed]

J. Zhao and A. D. Ellis, “Offset-QAM based coherent WDM for spectral efficiency enhancement,” Opt. Express 19(15), 14617–14631 (2011).
[Crossref] [PubMed]

X. Q. Jin, R. P. Giddings, and J. M. Tang, “Real-time transmission of 3 Gb/s 16-QAM encoded optical OFDM signals over 75 km SMFs with negative power penalties,” Opt. Express 17(17), 14574–14585 (2009).
[Crossref] [PubMed]

B. Liu, L. Zhang, X. Xin, and J. Yu, “None pilot-tones and training sequence assisted OFDM technology based on multiple-differential amplitude phase shift keying,” Opt. Express 20(20), 22878–22885 (2012).
[Crossref] [PubMed]

Q. Yang, Z. He, Z. Yang, S. Yu, X. Yi, and W. Shieh, “Coherent optical DFT-spread OFDM transmission using orthogonal band multiplexing,” Opt. Express 20(3), 2379–2385 (2012).
[Crossref] [PubMed]

Other (3)

X. Zhou, L. Nelson, P. Magill, B. Zhu, and D. Peckham, “8x450-Gb/s, 50-GHz-spaced, PDM-32QAM transmission over 400km and one 50GHz-grid ROADM,” in Proc. Optical Fiber Communications Conference (2012), post-deadline paper PDPB3.

S. Randel, A. Sierra, X. Liu, S. Chandrasekhar, and P. J. Winzer, “Study of multicarrier offset-QAM for spectrally efficient coherent optical communications,” in Proc. European Conference on Optical Communication (2011), paper Th.11.A.1.
[Crossref]

L. Liu, X. Yang, and W. Hu, “Chromatic dispersion compensation using two pilot tones in optical OFDM systems,” in Proc. Asia Communications and Photonics Conference (2011), PDP 830937.1–6.
[Crossref]

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Figures (7)

Fig. 1
Fig. 1 Principle of DFT-based implementation for offset-16QAM OFDM.
Fig. 2
Fig. 2 Experimental setup of coherent optical offset-16QAM OFDM. Inset shows its spectrum.
Fig. 3
Fig. 3 BER versus the received OSNR using different channel estimation methods when (a) a SRRC function and (b) a 3rd-order Gaussian function are used as the signal spectrum.
Fig. 4
Fig. 4 (a) Amplitude and (b) phase responses of the system at 0 km obtained using the M-LMS-1 method under −10-ps (dashed), 0-ps (solid), and 10-ps (dotted) time delays.
Fig. 5
Fig. 5 (a) BER versus roll-off coefficient of the receiver filter for different channel estimation method when the roll-off coefficient of the transmitter filter is 0.5. (b) BER versus the memory length of the pulse-shaping filter when a SRRC function with a roll-off coefficient of 0.5 is used as the signal spectrum. In (a) and (b), the OSNR is 14 dB.
Fig. 6
Fig. 6 (a) BER versus the received OSNR (dB) for M-LS-2 and M-LMS-1 at different fiber lengths. (b) BER versus the fiber length for LS, M-LS-2, and M-LMS-1 methods. The OSNR values for 0, 120, 240, 360, 480, 600, 720 km are 15.9, 15.2, 16.1, 15.4, 15.7, 16.1, and 15.5 dB, respectively.
Fig. 7
Fig. 7 (a) BER versus residual dispersion at 600 km. (b) BER versus timing error at 600 km. In (a) and (b), the OSNR is 15.1 dB.

Equations (16)

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s ( i N + k ) = s r e a l ( i N + k ) + j s i m a g ( i N + k ) = p = + n = N / 2 + 1 N / 2 a p , n r e a l exp ( j π n / 2 ) exp ( 2 π j ( p N + k ) n / N ) h ( i N + k p N ) + p = + n = N / 2 + 1 N / 2 a p , n i m a g exp ( j π ( n + 1 ) / 2 ) exp ( 2 π j ( p N + k ) n / N ) h ( i N + k N / 2 p N ) k = N / 2 + 1 , N / 2 + 2... N / 2 1 , N / 2
b i , m r e a l = k = N / 2 + 1 N / 2 q = + exp ( 2 π j k m / N ) r ( ( i q ) N + k ) h r e c e i v e r , k ( q N )
b i , m r e a l = k 1 = + p = + a p , m r e a l exp ( j π m / 2 ) h ( ( i p ) N k 1 ) h ( k 1 ) + k 1 = + p = + a p , m + 1 r e a l exp ( j π ( m + 1 ) / 2 ) h ( ( i p ) N k 1 ) h ( k 1 ) exp ( 2 π j k 1 / N ) + k 1 = + p = + a p , m 1 r e a l exp ( j π ( m 1 ) / 2 ) h ( ( i p ) N k 1 ) h ( k 1 ) exp ( 2 π j k 1 / N ) + k 1 = + p = + a p , m i m a g exp ( j π ( m + 1 ) / 2 ) h ( ( i p ) N N / 2 k 1 ) h ( k 1 ) + k 1 = + p = + a p , m + 1 i m a g exp ( j π ( m + 2 ) / 2 ) h ( ( i p ) N N / 2 k 1 ) h ( k 1 ) exp ( 2 π j k 1 / N ) + k 1 = + p = + a p , m 1 i m a g exp ( j π ( m ) / 2 ) h ( ( i p ) N N / 2 k 1 ) h ( k 1 ) exp ( 2 π j k 1 / N )
k 1 = + p = + a p , m r e a l exp ( j π m / 2 ) h ( ( i p ) N k 1 ) h ( k 1 ) = a i , m r e a l exp ( j π m / 2 )
k 1 = + p = + a p , m + 1 r e a l exp ( j π ( m + 1 ) / 2 ) h ( ( i p ) N k 1 ) h ( k 1 ) exp ( 2 π j k 1 / N ) = j exp ( j π m / 2 ) ( 1 ) i p k 2 = + p = + a p , m + 1 r e a l h ( ( i p ) N / 2 k 2 ) h ( ( i p ) N / 2 + k 2 ) exp ( 2 π j k 2 / N ) = j c m + 1 r e a l exp ( j π m / 2 )
b i , m r e a l = ( a i , m r e a l + j c m + 1 r e a l + j c m 1 r e a l + j c m i m a g + j c m + 1 i m a g + j c m 1 i m a g ) exp ( j π m / 2 )
a i , m , e s t r e a l = r e a l { b i , m r e a l exp ( j π m / 2 ) } = a i , m r e a l
b i , m r e a l = exp ( j π m / 2 ) exp ( j φ i ) ( a i , m r e a l H ( ω m ) + j c m + 1 r e a l H ( ω m + 1 ) + j c m 1 r e a l H ( ω m 1 ) + j c m i m a g H ( ω m ) + j c m + 1 i m a g H ( ω m + 1 ) + j c m 1 i m a g H ( ω m 1 ) )
H e s t ( ω m ) = 1 M p = 1 M r e a l { b p , m r e a l exp ( j π m / 2 ) exp ( j β 2 L ω m 2 / 2 ) exp ( j τ ω m ) exp ( j φ p ) } / a p , m r e a l
H e s t ( ω 2 m 1 ) = 2 M p P 2 m 1 b p , 2 m 1 r e a l exp ( j π ( 2 m 1 ) / 2 ) exp ( j φ p ) / a p , 2 m 1 r e a l
H e s t ( ω 2 m ) = 2 M p P 2 m b p , 2 m r e a l exp ( j π ( 2 m ) / 2 ) exp ( j φ p ) / a p , 2 m r e a l
a i , m , e s t r e a l = r e a l { b i , m r e a l exp ( j π m / 2 ) H e s t , i ( ω m ) }
H e s t , i ( ω m ) = H e s t , i 1 ( ω m ) + e δ i ( ω m )
δ i ( ω m ) = 0.5 × δ i 1 ( ω m ) + 0.5 × ( a i 1 , m r e a l a i 1 , m , e s t r e a l ) ( a i , m , e s t r e a l r e a l { H e s t , i ( ω m ) } + j a i , m , e s t r e a l i m a g { H e s t , i ( ω m ) } )
h r e c e i v e r , k , i = h r e c e i v e r , k , i 1 + ε κ k , i
κ k , i = 0.5 × κ k , i 1 + 0.5 × ( a i 1 , m r e a l a i 1 , m , e s t r e a l ) c o n j ( H e s t , i 1 ( ω m ) r k , i 1 F m , k )

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