## None pilot-tones and training sequence assisted OFDM technology based on multiple-differential amplitude phase shift keying |

Optics Express, Vol. 20, Issue 20, pp. 22878-22885 (2012)

http://dx.doi.org/10.1364/OE.20.022878

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### Abstract

This paper proposes a novel none pilot-assisted orthogonal frequency division multiplexing (OFDM) technology based on multi-differential amplitude phase shift keying (mDAPSK) for optical OFDM system. It doesn’t require any bandwidth-consuming pilot tones or training sequence for channel estimation due to the differential detection during demodulation. In the experiment, a 41.31 Gb/s 64DAPSK-OFDM signal without pilot tones is successfully transmitted over 160-km single mode fiber (SMF). The performance comparison between multi-quadrature amplitude modulation (mQAM) and mDAPSK is also given in the experiment, and the results indicate a prospect of this technology in optical OFDM system.

© 2012 OSA

## 1. Introduction

1. W. Shieh, “OFDM for flexible high-speed optical networks,” J. Lightwave Technol. **29**(10), 1560–1577 (2011). [CrossRef]

8. X. Liu, F. Buchali, and R. W. Tkach, “Improving the nonlinear tolerance of polarization-division-multiplexed CO-OFDM in long-haul fiber transmission,” J. Lightwave Technol. **27**(16), 3632–3640 (2009). [CrossRef]

11. A. Sano, E. Yamada, H. Masuda, E. Yamazaki, T. Kobayashi, E. Yoshida, Y. Miyamoto, R. Kudo, K. Ishihara, and Y. Takatori, “No-Guard-Interval coherent optical OFDM for 100-Gb/s long-haul WDM transmission,” J. Lightwave Technol. **27**(16), 3705–3713 (2009). [CrossRef]

## 2. Principle

_{a,i}and m

_{p,i}respectively, and then go through differential modulation. The format of m

_{a,i}or m

_{p,i}can be written as (

*d*), where

_{j}…d_{2}d_{1}d_{0}*d*denotes the input bits data. In our scheme, the data is differentially encoded between different subcarriers in the same OFDM symbol.

_{j}*m*

^{th}sample of baseband mDAPSK-OFDM signal in the n

^{th}symbol interval can be expressed aswhere

*k*is the index of the OFDM subcarrier, N is the total number of the subcarriers, T

_{s}is the time duration of each sample and X

_{i, k}means the mDAPSK modulated data symbol on the k

^{th}subcarrier. X

_{i, k}is represented asHere,

*i*is i

^{th}data symbol, α

_{ik}and θ

_{ik}are the amplitude and absolute phase of data symbol respectively, which can be expressed as

_{k}and

*Δθ*are the differential parameters of amplitude and phase, M

_{k}_{a}and M

_{p}are the bit numbers of m

_{a,i}and m

_{p,i}, A is a constant value and α

_{ik}∈(1, A, A

^{2}, …,

_{a}= 1 and M

_{p}= 3 are for 16DAPSK modulation, and M

_{a}= 2 and M

_{p}= 4 are for 64DAPSK modulation. The mapping rule from m

_{p,i}to

*Δθ*obeys the Gray coding for phase differential coding. For example, when m

_{k}_{p,i}= (000),

*Δθ*= π/8; when m

_{k}_{p,i}= (011),

*Δθ*= 5π/8. For amplitude differential coding, m

_{k}_{a,i}can choose different γ

_{k}according to the values of α

_{i(k-1)}and m

_{a,i}. We also adopt Gray coding for the input bits of m

_{a,i}. The status transition diagrams for m

_{a,i}= (

*d*) and m

_{0}_{a,i}= (

*d*) are illustrated in Fig. 2 .

_{1}d_{0}^{th}subcarrier can be expressed aswhere H

_{i,k}is the channel transfer function of the subcarrier, S

_{i,k}is the frequency domain information of transmitted signal and N

_{i,k}is the noise. There we assume the channel in the optical fiber is a kind of slow time-varying channel, and the differential factor can be expressed asHere, α’

_{i,k}is the received amplitude parameter and θ’

_{i,k}is the received phase parameter. We can get the original bits stream with the two parameters. Due to the differential coding, there is no need to know the channel function H

_{i,k}, which can reduce the complexity and redundancy of the receiver.

## 3. Experimental setup and results

_{2}(64)х6.94х(254/256)). The output I/Q parts from AWG are used to drive the optical I/Q modulator to produce the modulated optical signal. We employ a couple of DFB lasers at 1550.92nm with a linewidth of 5kHz as the optical source and local oscillator (LO). Transmission is performed through a 160 km single mode fiber (SMF), and the fiber loss, dispersion and dispersion slope is 0.22 dB/km, 16 ps/(nm∙km) and 0.06ps/(nm

^{2}∙km) respectively. The optical 64DAPSK-OFDM signal is set to −6 dBm before launching into the transmission link.

^{−3}are 19.87 dB and 22.5 dB respectively. An additional penalty of 2.63 dB is incurred in Fig. 5, which is mainly due to the fiber dispersion as well as nonlinearity during transmission. Although the CP of 1/32 can resolve the channel dispersion-induced inter-carrier interference (ICI) and inter-symbol interference (ISI), the phase noise on each subcarrier cannot be eliminated; furthermore, the signal suffers both nonlinearity and fiber dispersion, and no equalization is adopted for signal demodulation.

^{−3}(FEC limit), while the mDAPSK-OFDM signals can get a good performance without equalization, which indicates the robustness to the phase noise due to differential modulation. After equalization, the performances of mQAM-OFDM signals become better than mDAPSK-OFDM signals. Although the BER of mQAM-OFDM signals are obviously improved after channel estimation and signal equalization, it would increase the complexity and cost at the receiver. From Fig. 6, we can see that the OSNR penelties at BER of 10

^{−3}between mQAM-OFDM and mDAPSK-OFDM signals is about 4.3 dB for the three cases. It is because the mQAM-OFDM signal has a maximized average Euclidean distance between each constellation point compared with mDAPSK-OFDM. On the other hand, due to the absence of channel estimation and equalization, the demodulation of mDAPSK-OFDM signal can be simplified, but leading to loss of OSNR. The OSNR penalties become smaller as the BER increases. If EFEC is adopted, the OSNR penalties in Fig. 6(a)-6(c) would reduce to 3.55 dB, 2.82 dB and 1.49 dB respectively. In the experiment, we adopt offline processing for signal demodulation and the performance has been shown in Fig. 6. In real OFDM receiver, there might be about an additional penalty of 1.5 dB existing during channel estimation and equalization [14

14. T. May, H. Rohling, and V. Engels, “Performance analysis of Viterbi decoding for 64-DAPSK and 64-QAM modulated OFDM signals,” IEEE Trans. Commun. **46**(2), 182–190 (1998). [CrossRef]

## 4. Conclusion

## Acknowledgment

## References and links

1. | W. Shieh, “OFDM for flexible high-speed optical networks,” J. Lightwave Technol. |

2. | N. Cvijetic, M. Cvijetic, M.-F. Huang, E. Ip, Y.-K. Huang, and T. Wang, “Terabit optical access networks based on WDM-OFDMA-PON,” J. Lightwave Technol. |

3. | J. L. Wei, C. Sánchez, R. P. Giddings, E. Hugues-Salas, and J. M. Tang, “Significant improvements in optical power budgets of real-time optical OFDM PON systems,” Opt. Express |

4. | D. Qian, M.-F. Huang, E. Ip, Y.-K. Huang, Y. Shao, J. Hu, and T. Wang, “High capacity/spectral efficiency 101.7-Tb/s WDM transmission using PDM-128QAM-OFDM over 165-km SSMF within C- and L-bands,” J. Lightwave Technol. |

5. | N. Kaneda, Q. Yang, X. Liu, W. Shieh, and Y.-K. Chen, “Realizing real-time implementation of coherent optical OFDM receiver with FPGAs,” in Proc. ECOC’2009, paper.5.4.4 (2009). |

6. | A. J. Lowery and L. B. Du, “Optical orthogonal division multiplexing for long haul optical communications: A review of the first five years,” Opt. Fiber Technol. |

7. | J. Zhao and A. Ellis, “Transmission of 4-ASK optical fast OFDM with chromatic dispersion compensation,” IEEE Photon. Technol. Lett. |

8. | X. Liu, F. Buchali, and R. W. Tkach, “Improving the nonlinear tolerance of polarization-division-multiplexed CO-OFDM in long-haul fiber transmission,” J. Lightwave Technol. |

9. | Q. Zhuge, M. Morsy-Osman, and D. V. Plant, “Analysis of dispersion-enhanced phase noise in CO-OFDM systems with RF-pilot phase compensation,” Opt. Express |

10. | S. L. Jansen, I. Morita, N. Takeda, and H. Tanaka, “Pre-emphasis and RF-pilot tone phase noise compensation for coherent OFDM transmission systems,” in Proc. CLEO 2007, paper. MA1.2 (2007). |

11. | A. Sano, E. Yamada, H. Masuda, E. Yamazaki, T. Kobayashi, E. Yoshida, Y. Miyamoto, R. Kudo, K. Ishihara, and Y. Takatori, “No-Guard-Interval coherent optical OFDM for 100-Gb/s long-haul WDM transmission,” J. Lightwave Technol. |

12. | N. Toender and H. Rohling, “DAPSK schemes for low-complexity OFDM systems,” IEEE 16th International Symposium on Personal, Indoor and Mobile Radio Communications, 735–739 (2006). |

13. | C.-C.Fang, Y.-J. Lin, S.-W. Wei, and J.-F. Chang, “Performance analyses of DAPSK in a very high mobility environment,” in Proc.WIRLES 2005, 570–575 (2005). |

14. | T. May, H. Rohling, and V. Engels, “Performance analysis of Viterbi decoding for 64-DAPSK and 64-QAM modulated OFDM signals,” IEEE Trans. Commun. |

**OCIS Codes**

(060.2330) Fiber optics and optical communications : Fiber optics communications

(060.4080) Fiber optics and optical communications : Modulation

(060.4250) Fiber optics and optical communications : Networks

**ToC Category:**

Fiber Optics and Optical Communications

**History**

Original Manuscript: July 25, 2012

Revised Manuscript: September 14, 2012

Manuscript Accepted: September 18, 2012

Published: September 20, 2012

**Citation**

Bo Liu, Lijia Zhang, Xiangjun Xin, and Jianjun Yu, "None pilot-tones and training sequence assisted OFDM technology based on multiple-differential amplitude phase shift keying," Opt. Express **20**, 22878-22885 (2012)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-20-22878

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### References

- W. Shieh, “OFDM for flexible high-speed optical networks,” J. Lightwave Technol.29(10), 1560–1577 (2011). [CrossRef]
- N. Cvijetic, M. Cvijetic, M.-F. Huang, E. Ip, Y.-K. Huang, and T. Wang, “Terabit optical access networks based on WDM-OFDMA-PON,” J. Lightwave Technol.30(4), 493–503 (2012). [CrossRef]
- J. L. Wei, C. Sánchez, R. P. Giddings, E. Hugues-Salas, and J. M. Tang, “Significant improvements in optical power budgets of real-time optical OFDM PON systems,” Opt. Express18(20), 20732–20745 (2010). [CrossRef] [PubMed]
- D. Qian, M.-F. Huang, E. Ip, Y.-K. Huang, Y. Shao, J. Hu, and T. Wang, “High capacity/spectral efficiency 101.7-Tb/s WDM transmission using PDM-128QAM-OFDM over 165-km SSMF within C- and L-bands,” J. Lightwave Technol.30(10), 1540–1548 (2012). [CrossRef]
- N. Kaneda, Q. Yang, X. Liu, W. Shieh, and Y.-K. Chen, “Realizing real-time implementation of coherent optical OFDM receiver with FPGAs,” in Proc. ECOC’2009, paper.5.4.4 (2009).
- A. J. Lowery and L. B. Du, “Optical orthogonal division multiplexing for long haul optical communications: A review of the first five years,” Opt. Fiber Technol.17(5), 421–438 (2011). [CrossRef]
- J. Zhao and A. Ellis, “Transmission of 4-ASK optical fast OFDM with chromatic dispersion compensation,” IEEE Photon. Technol. Lett.24(1), 34–36 (2012). [CrossRef]
- X. Liu, F. Buchali, and R. W. Tkach, “Improving the nonlinear tolerance of polarization-division-multiplexed CO-OFDM in long-haul fiber transmission,” J. Lightwave Technol.27(16), 3632–3640 (2009). [CrossRef]
- Q. Zhuge, M. Morsy-Osman, and D. V. Plant, “Analysis of dispersion-enhanced phase noise in CO-OFDM systems with RF-pilot phase compensation,” Opt. Express19(24), 24030–24036 (2011). [CrossRef] [PubMed]
- S. L. Jansen, I. Morita, N. Takeda, and H. Tanaka, “Pre-emphasis and RF-pilot tone phase noise compensation for coherent OFDM transmission systems,” in Proc. CLEO 2007, paper. MA1.2 (2007).
- A. Sano, E. Yamada, H. Masuda, E. Yamazaki, T. Kobayashi, E. Yoshida, Y. Miyamoto, R. Kudo, K. Ishihara, and Y. Takatori, “No-Guard-Interval coherent optical OFDM for 100-Gb/s long-haul WDM transmission,” J. Lightwave Technol.27(16), 3705–3713 (2009). [CrossRef]
- N. Toender and H. Rohling, “DAPSK schemes for low-complexity OFDM systems,” IEEE 16th International Symposium on Personal, Indoor and Mobile Radio Communications, 735–739 (2006).
- C.-C.Fang, Y.-J. Lin, S.-W. Wei, and J.-F. Chang, “Performance analyses of DAPSK in a very high mobility environment,” in Proc.WIRLES 2005, 570–575 (2005).
- T. May, H. Rohling, and V. Engels, “Performance analysis of Viterbi decoding for 64-DAPSK and 64-QAM modulated OFDM signals,” IEEE Trans. Commun.46(2), 182–190 (1998). [CrossRef]

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