## Phase noise suppression of optical OFDM signals in 60-GHz RoF transmission system |

Optics Express, Vol. 19, Issue 11, pp. 10423-10428 (2011)

http://dx.doi.org/10.1364/OE.19.010423

Acrobat PDF (974 KB)

### Abstract

The dispersion-induced phase noise (PN) in an OFDM RoF system at 60 GHz leads to not only subcarrier phase rotation (PRT) but also intercarrier interference (ICI) to severely degrade the transmission performance, when a commercial cost-effective DFB laser with the linewidth of several MHz is adopted. To mitigate both PRT and ICI, a post PN suppression algorithm is proposed, and it does not require any bandwidth-consuming pilot tone. For a 25.78-Gbps 16-QAM OFDM RoF signal using the laser with 1.8-MHz linewidth, employing the algorithm can extend the maximum transmission distance which corresponds to 3-dBm power penalty at the BER of 2×10^{−3} from 75 km to more than 115 km, i.e. 50% increment of transmission distance.

© 2011 OSA

## 1. Introduction

1. M. Sauer, A. Kobyakov, and J. George, “Radio over fiber for picocellular network architectures,” J. Lightwave Technol. **25**(11), 3301–3320 (2007). [CrossRef]

3. C. T. Lin, J. Chen, P.-T. Shih, W. J. Jiang, and S. Chi, “Ultra-hgh data-rate 60 GHz radio-over-fiber systems employing optical frequency multiplication and OFDM formats,” J. Lightwave Technol. **28**(16), 2296–2306 (2010). [CrossRef]

4. Z. Jia, J. Yu, Y. T. Hsueh, A. Chowdhury, H. C. Chien, J. A. Buck, and G. K. Chang, “Multiband signal generation and dispersion-tolerant transmission based on photonic frequency tripling technology for 60-GHz radio-over-fiber systems,” IEEE Photon. Technol. Lett. **20**(17), 1470–1472 (2008). [CrossRef]

3. C. T. Lin, J. Chen, P.-T. Shih, W. J. Jiang, and S. Chi, “Ultra-hgh data-rate 60 GHz radio-over-fiber systems employing optical frequency multiplication and OFDM formats,” J. Lightwave Technol. **28**(16), 2296–2306 (2010). [CrossRef]

6. W. R. Peng, J. Chen, and S. Chi, “On the phase noise impact in direct-detection optical OFDM transmission,” IEEE Photon. Technol. Lett. **22**(9), 649–651 (2010). [CrossRef]

6. W. R. Peng, J. Chen, and S. Chi, “On the phase noise impact in direct-detection optical OFDM transmission,” IEEE Photon. Technol. Lett. **22**(9), 649–651 (2010). [CrossRef]

8. C. C. Wei and J. J. Chen, “Study on dispersion-induced phase noise in an optical OFDM radio-over-fiber system at 60-GHz band,” Opt. Express **18**(20), 20774–20785 (2010). [CrossRef] [PubMed]

10. S. Wu, P. Liu, and Y. Bar-Ness, “Phase noise estimation and mitigation for OFDM systems,” IEEE Trans. Wirel. Comm. **5**(12), 3616–3625 (2006). [CrossRef]

^{−3}after 100-km transmission, and the extension of transmission distance is more than 40 km using the laser with 1.3 or 1.8-MHz linewidth.

## 2. PN suppression algorithm

*H*denotes Hermitian transpose. Then,

10. S. Wu, P. Liu, and Y. Bar-Ness, “Phase noise estimation and mitigation for OFDM systems,” IEEE Trans. Wirel. Comm. **5**(12), 3616–3625 (2006). [CrossRef]

- i. making hard decision on the received signal to “guess” what the transmitted signal is
- ii. estimating the PN from the received signal and the guessed transmitted signal by Eq. (5)
- iii. removing the PN from the received signal by Eq. (6)

*L*is generally small compared with

*N*as a result of very limited computational complexity.

## 3. Experimental results and discussion

13. C.-T. Lin, P.-T. Shih, J. Chen, W.-Q. Xue, P.-C. Peng, and S. Chi, “Optical millimeter-wave signal generation using frequency quadrupling technique and no optical filtering,” IEEE Photon. Technol. Lett. **20**(12), 1027–1029 (2008). [CrossRef]

^{®}AWG7102 arbitrary waveform generator (AWG). The sampling rate and D/A resolution of the AWG are 10 GHz and 8 bits, respectively, and the OFDM signal contains 176 subcarriers of 16-QAM format to occupy 7-GHz bandwidth with the fast-Fourier transform size of 256 and the CP of 1/16, yielding the data rate of 25.78 Gbps. After single mode fiber transmission, the electrical 7GHz-wide OFDM signal at 60 GHz is generated after square-law photo- detection in the 67-GHz photodiode. The generated OFDM signal is then amplified by a low noise amplifier (LNA) with 38-dB gain. After the LNA, the 60-GHz OFDM signal is fed into a rectangular waveguide-based standard gain horn antenna with ~23-dBi gain, and transmitted over 3-m wireless distance which is fixed and irrelevant to fiber length. After transmission over the air, the 60-GHz signal is received by another horn antenna and down-converted by a 55-GHz local oscillator, an electrical 25.78-Gbps signal at 5 GHz is obtained and captured by a Tektronix

^{®}DPO 71254 with the 50-GS/s sampling rate and the 3-dB bandwidth of 12.5 GHz. The off-line DSP program is applied to demodulate the signal and carry out the PNS algorithm, and BER is measured by error counting.

*L*with the received power of −6 dBm after 115-km fiber transmission and the proposed iterative PNS algorithm. The optimized

*L*after three iterations is around 12~14, and further increasing

*L*does not help the reduction of BER due to error propagation from

*L*may vary with different iteration time, transmission distance and laser parameters, and it can be optimized by long training symbols in advance. Therefore,

*L*is optimized for each time as the proposed algorithm is applied throughout our experiment, and it lies in between 10 and 16. Furthermore, Fig. 4 depicts the BER curves after 115-km fiber with and without the iterative PNS algorithm. Without any PNS, the signal cannot reach the FEC threshold (BER of 2×10

^{−3}), but the BER is improved to lower than 2×10

^{−3}with the proposed algorithm for both cases of 10.5-dBm and 8.5-dBm laser output power. Since the third iteration only provides little improvement as show in Fig. 4, three iterations approximately reach the best performance. Furthermore, the results employing ideal PNS with the perfect knowledge of

**S**

*are also plotted for comparison, and the applied values of*

_{m}*L*are identical to those used in the first iteration. The further improvement by ideal PNS comes from the absence of error propagation, compared with the other iterative cases. However, the BERs employing ideal PNS are still worse than the case without dispersion-induced PN (B-to-B, with only air transmission), because of two assumptions made in the algorithm: 1) the bandwidth of ICI is limited to

*L*, and 2) OFDM subcarriers are completely coherent after transmission. Therefore, the performance gap between the signals without PN and with PN suppressed by iterative PNS comes from both the incomplete knowledge of

**S**

*and the assumptions of the algorithm.*

_{m}## 4. Conclusions

## Acknowledgment

## References and links

1. | M. Sauer, A. Kobyakov, and J. George, “Radio over fiber for picocellular network architectures,” J. Lightwave Technol. |

2. | Y. X. Gu, B. Luo, C. S. Park, L. C. Ong, M.-T. Zhou, and S. Kato, “60 GHz Radio-over-Fiber for Gbps Transmission,” in Proceedings of Global Symp. Millimeter Waves (GSMM), pp. 41–43,(2008). |

3. | C. T. Lin, J. Chen, P.-T. Shih, W. J. Jiang, and S. Chi, “Ultra-hgh data-rate 60 GHz radio-over-fiber systems employing optical frequency multiplication and OFDM formats,” J. Lightwave Technol. |

4. | Z. Jia, J. Yu, Y. T. Hsueh, A. Chowdhury, H. C. Chien, J. A. Buck, and G. K. Chang, “Multiband signal generation and dispersion-tolerant transmission based on photonic frequency tripling technology for 60-GHz radio-over-fiber systems,” IEEE Photon. Technol. Lett. |

5. | H. C. Chien, A. Chowdhury, Z. Jia, Y. T. Hsueh, and G. K. Chang, “Long-Reach, 60-GHz Mm-Wave Optical-Wireless Access Network Using,” European Conference on Optical Communication (ECOC’08), paper Tu.3.F.3, 2008. |

6. | W. R. Peng, J. Chen, and S. Chi, “On the phase noise impact in direct-detection optical OFDM transmission,” IEEE Photon. Technol. Lett. |

7. | D. Qian, N. Cvijetic, J. Hu, and T. Wang, “Optical OFDM Transmission in Metro/Access Networks,” Optical Fiber Communication (OFC’09), paper OMV1, 2009. |

8. | C. C. Wei and J. J. Chen, “Study on dispersion-induced phase noise in an optical OFDM radio-over-fiber system at 60-GHz band,” Opt. Express |

9. | R. Lin, “Next Generation PON in Emerging Networks,” Optical Fiber Communication (OFC’09), paper OWH1, 2008. |

10. | S. Wu, P. Liu, and Y. Bar-Ness, “Phase noise estimation and mitigation for OFDM systems,” IEEE Trans. Wirel. Comm. |

11. | W.-R. Peng, I. Morita, and H. Tanaka, “Digital Phase Noise Estimation and Mitigation Approach for Direct-Detection Optical OFDM Transmissions,” European Conference on Optical Communication (ECOC’10), paper Tu.3.C.3, 2010. |

12. | W. J. Jiang, C. T. Lin, L. Y. Wang He, C. C. Wei, C. H. Ho, Y. M. Yang, P. T. Shih, J. Chen, and S. Chi, “32.65-Gbps OFDM RoF Signal Generation at 60GHz Employing an Adaptive I/Q Imbalance Correction,” European Conference on Optical Communication (ECOC’10), paper Th.9.B.5, 2010. |

13. | C.-T. Lin, P.-T. Shih, J. Chen, W.-Q. Xue, P.-C. Peng, and S. Chi, “Optical millimeter-wave signal generation using frequency quadrupling technique and no optical filtering,” IEEE Photon. Technol. Lett. |

**OCIS Codes**

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

(060.5625) Fiber optics and optical communications : Radio frequency photonics

(060.3510) Fiber optics and optical communications : Lasers, fiber

**ToC Category:**

Fiber Optics and Optical Communications

**History**

Original Manuscript: April 1, 2011

Revised Manuscript: May 9, 2011

Manuscript Accepted: May 9, 2011

Published: May 11, 2011

**Citation**

Chun-Ting Lin, Chia-Chien Wei, and Ming-I Chao, "Phase noise suppression of optical OFDM signals in 60-GHz RoF transmission system," Opt. Express **19**, 10423-10428 (2011)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-11-10423

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### References

- M. Sauer, A. Kobyakov, and J. George, “Radio over fiber for picocellular network architectures,” J. Lightwave Technol. 25(11), 3301–3320 (2007). [CrossRef]
- Y. X. Gu, B. Luo, C. S. Park, L. C. Ong, M.-T. Zhou, and S. Kato, “60 GHz Radio-over-Fiber for Gbps Transmission,” in Proceedings of Global Symp. Millimeter Waves (GSMM), pp. 41–43,(2008).
- C. T. Lin, J. Chen, P.-T. Shih, W. J. Jiang, and S. Chi, “Ultra-hgh data-rate 60 GHz radio-over-fiber systems employing optical frequency multiplication and OFDM formats,” J. Lightwave Technol. 28(16), 2296–2306 (2010). [CrossRef]
- Z. Jia, J. Yu, Y. T. Hsueh, A. Chowdhury, H. C. Chien, J. A. Buck, and G. K. Chang, “Multiband signal generation and dispersion-tolerant transmission based on photonic frequency tripling technology for 60-GHz radio-over-fiber systems,” IEEE Photon. Technol. Lett. 20(17), 1470–1472 (2008). [CrossRef]
- H. C. Chien, A. Chowdhury, Z. Jia, Y. T. Hsueh, and G. K. Chang, “Long-Reach, 60-GHz Mm-Wave Optical-Wireless Access Network Using,” European Conference on Optical Communication (ECOC’08), paper Tu.3.F.3, 2008.
- W. R. Peng, J. Chen, and S. Chi, “On the phase noise impact in direct-detection optical OFDM transmission,” IEEE Photon. Technol. Lett. 22(9), 649–651 (2010). [CrossRef]
- D. Qian, N. Cvijetic, J. Hu, and T. Wang, “Optical OFDM Transmission in Metro/Access Networks,” Optical Fiber Communication (OFC’09), paper OMV1, 2009.
- C. C. Wei and J. J. Chen, “Study on dispersion-induced phase noise in an optical OFDM radio-over-fiber system at 60-GHz band,” Opt. Express 18(20), 20774–20785 (2010). [CrossRef] [PubMed]
- R. Lin, “Next Generation PON in Emerging Networks,” Optical Fiber Communication (OFC’09), paper OWH1, 2008.
- S. Wu, P. Liu, and Y. Bar-Ness, “Phase noise estimation and mitigation for OFDM systems,” IEEE Trans. Wirel. Comm. 5(12), 3616–3625 (2006). [CrossRef]
- W.-R. Peng, I. Morita, and H. Tanaka, “Digital Phase Noise Estimation and Mitigation Approach for Direct-Detection Optical OFDM Transmissions,” European Conference on Optical Communication (ECOC’10), paper Tu.3.C.3, 2010.
- W. J. Jiang, C. T. Lin, L. Y. Wang He, C. C. Wei, C. H. Ho, Y. M. Yang, P. T. Shih, J. Chen, and S. Chi, “32.65-Gbps OFDM RoF Signal Generation at 60GHz Employing an Adaptive I/Q Imbalance Correction,” European Conference on Optical Communication (ECOC’10), paper Th.9.B.5, 2010.
- C.-T. Lin, P.-T. Shih, J. Chen, W.-Q. Xue, P.-C. Peng, and S. Chi, “Optical millimeter-wave signal generation using frequency quadrupling technique and no optical filtering,” IEEE Photon. Technol. Lett. 20(12), 1027–1029 (2008). [CrossRef]

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