## Physical secure enhancement in optical OFDMA-PON based on two-dimensional scrambling |

Optics Express, Vol. 20, Issue 26, pp. B32-B37 (2012)

http://dx.doi.org/10.1364/OE.20.000B32

Acrobat PDF (1241 KB)

### Abstract

This paper proposes a novel physical-enhanced chaotic secure strategy for optical OFDMA-PON based on two-dimensional (2-D) scrambling. In order to enhance the physical security, a multi-layer chaotic mapping is proposed to generate the scrambling vectors. It can enhance the chaotic characteristic of Logistic mapping and increase the key space. Furthermore, the 2-D scrambling jointly utilizing frequency subcarriers and time-slots can improve the system resistance to eavesdropper. The feasibility of 15.6 Gb/s 2-D encrypted 64QAM-OFDM downstream signal has been successfully demonstrated in the experiment. The robustness of the proposed method shows its prospect in future OFDM access network.

© 2012 OSA

## 1. Introduction

1. N.-C. Tran, E. Tangdiongga, C. Okonkwo, H. Jung, and T. Koonen, “Flexibility level adjustment in reconfigurable WDM-TDM optical access networks,” J. Lightwave Technol. **30**(15), 2542–2550 (2012). [CrossRef]

3. R. Schmogrow, M. Winter, D. Hillerkuss, B. Nebendahl, S. Ben-Ezra, J. Meyer, M. Dreschmann, M. Huebner, J. Becker, C. Koos, W. Freude, and J. Leuthold, “Real-time OFDM transmitter beyond 100 Gbit/s,” Opt. Express **19**(13), 12740–12749 (2011). [CrossRef] [PubMed]

2. N. Cvijetic, “OFDM for next-generation optical access networks,” J. Lightwave Technol. **30**(4), 384–398 (2012). [CrossRef]

5. 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]

6. X. Q. Jin, E. Hugues-Salas, R. P. Giddings, J. L. Wei, J. Groenewald, and J. M. Tang, “First real-time experimental demonstrations of 11.25Gb/s optical OFDMA PONs with adaptive dynamic bandwidth allocation,” Opt. Express **19**(21), 20557–20570 (2011). [CrossRef] [PubMed]

7. N. Cvijetic, M.-F. Huang, E. Ip, Y. Shao, Y.-K. Huang, M. Cvijetic, and T. Wang, “1.92 Tb/s coherent DWDM-OFDMA-PON with no high-speed ONU-side electronics over 100 km SSMF and 1:64 passive split,” Opt. Express **19**(24), 24540–24545 (2011). [CrossRef] [PubMed]

8. M. P. Fok, Z. Wang, Y. Deng, and P. R. Prucnal, “Optical layer security in fiber-optic networks,” IEEE Trans. Inf. Forensics and Security **6**(3), 725–736 (2011). [CrossRef]

10. S.-L. Chen, T. T. Hwang, and W.-W. Lin, “Randomness enhancement using digitalized modified logistic map,” IEEE Trans. Circuits Syst., II Express Briefs **57**(12), 996–1000 (2010). [CrossRef]

11. L. Zhang, X. Xin, B. Liu, and J. Yu, “Physical-enhanced secure strategy in an OFDM-PON,” Opt. Express **20**(3), 2255–2265 (2012). [CrossRef] [PubMed]

## 2. Principle

10. S.-L. Chen, T. T. Hwang, and W.-W. Lin, “Randomness enhancement using digitalized modified logistic map,” IEEE Trans. Circuits Syst., II Express Briefs **57**(12), 996–1000 (2010). [CrossRef]

*μ*= 3.94 in this paper. For the bottom layer, it also adopts controlled Logistic map, and the control from upper layer is realized through numerical mapping. The chaos model can be expressed aswhere λ* and

_{1}and ε

_{2}are two constant values which ensure the chaotic nature of bifurcation parameters, and we choose ε

_{1}= 1/16 and ε

_{2}= 3.35 in our following experiment. The control from upper layer is opened every G × CP period, where CP is the time length of OFDM cyclic prefix and G is a constant number. It endows the chaotic mapping a random change at the bottom layer. To the illegal ONU, the upper layer is an indirect parameter and it can enhance the security.

*N*number of subcarriers is given bywhere C

_{k}is the input QAM mapped symbols on k

^{th}subcarrier and

*T*is time-slot. Before scrambling, the QAM symbols are scrambled by an exchange vector M

_{E}with size of 2 × 2, and the scrambled symbols can be expressed aswhereHere c

_{i,k}denotes the i

^{th}symbol on k

^{th}subcarriers, and the elements of a and b are generated through Logistic iteration in Eq. (1). It can mask the original information and improve the security. Then the scrambled QAM symbols are fed into the OFDM modulation block where frequency and time domain scrambling are executed. The generation of exchange vector has been originally demonstrated in our previous work [11

11. L. Zhang, X. Xin, B. Liu, and J. Yu, “Physical-enhanced secure strategy in an OFDM-PON,” Opt. Express **20**(3), 2255–2265 (2012). [CrossRef] [PubMed]

_{k}is the scrambled QAM symbols by Eq. (5), M

_{F}and M

_{T}are frequency scramble vector and time domain scramble vector. At the ONU, the received signal goes through a reverse processing to recover the information. The correct information can be obtained only by its own secure key.

## 3. Experiment and results

_{E}. It can be treated as part of secure key for physical layer encryption. Figure 5 illustrates the statistical histograms of the QAM symbols before and after scrambling. It can be observed that the distribution is averaged after QAM symbol scrambling, which is able to cover the statistical characteristic of original symbols and resist the statistical analysis attack.

_{E}, scrambling sizes of M

_{F}and M

_{T}and the period of numerical mapping. Assuming the scrambling sizes of M

_{F}and M

_{T}are L, the secure key can be written as (

*μ*,

_{1}, ε

_{2}, a, b, L,

*G*). Considering there would be (L!)

^{2}possible trial number to get the correct M

_{F}and M

_{T}for 2-D scrambling, the key space would be as large as 4.831 × (L!)

^{2}× 10

^{170}if double-precision float value is adopted. In the experiment, we have L = 128 and the key space would be 7.16 × 10

^{601}compared with 3 × 10

^{215}of 1-D scrambling. It is efficient to resist the brute-force attack. In real practice, if assuming the hardware resolution is 12-bit, the key space would be 3.24 × (L!)

^{2}× 10

^{32}. We have L = 128 in the experiment and the key space is 4.82 × 10

^{463}.

^{5}~3 × 10

^{6}are adopted to calculate BER by error counting for each case. At the regular ONU, an optical power penalty less than 0.2 dB was observed at the BER of 10

^{−3}when compared to back-to-back (b2b) measurement. It is clear that the illegal ONU has got a BER of 0.5, which indicate a good resistance to eavesdropping. If 1-D scrambling (only at frequency domain) is adopted, the measured BER at illegal ONU is about 0.42, which is also shown in Fig. 6. Due to the limitation of the scrambling size and lack of time domain scrambling, the 1-D scrambling method cannot get a BER value of 0.5. For 2-D scrambling, it can get better resistance with same scrambling size. Figure 6 also shows the BER curve of conventional 64QAM-OFDM signal at b2b case. The optical power penalty is about 0.1 dB compared with the 2-D scrambled signal. Although the hardware resolution would result in extra power penalty for the chaos scrambling, the digital quantification has been made during generation of scrambling matrix. It can mitigate the effect from the hardware performing. In order to investigate the power budget of the system, we have also measured the BER curves with a 10G avalanche photodiode (APD). The receive sensitivity at BER of 10

^{−3}is about −21.5 dBm, which leads to an optical power budget of 25.5 dB.

## 4. Conclusion

^{601}and BER of 0.5 are obtained at the illegal ONU with 2-D scrambling size of 128 × 128. The experiment results show a good resistance against illegal ONU.

## Acknowledgments

## References and links

1. | N.-C. Tran, E. Tangdiongga, C. Okonkwo, H. Jung, and T. Koonen, “Flexibility level adjustment in reconfigurable WDM-TDM optical access networks,” J. Lightwave Technol. |

2. | N. Cvijetic, “OFDM for next-generation optical access networks,” J. Lightwave Technol. |

3. | R. Schmogrow, M. Winter, D. Hillerkuss, B. Nebendahl, S. Ben-Ezra, J. Meyer, M. Dreschmann, M. Huebner, J. Becker, C. Koos, W. Freude, and J. Leuthold, “Real-time OFDM transmitter beyond 100 Gbit/s,” Opt. Express |

4. | H.-Y. Chen, C. C. Wei, D.-Z. Hsu, M. C. Yuang, J. Chen, Y.-M. Lin, P.-L. Tien, S. S. W. Lee, S.-H. Lin, W.-Y. Li, C.-H. Hsu, and J.-L. Shih, “A 40-Gb/s OFDM PON system based on 10-GHz EAM and 10-GHz direct-detection PIN,” IEEE Photon. Technol. Lett. |

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

6. | X. Q. Jin, E. Hugues-Salas, R. P. Giddings, J. L. Wei, J. Groenewald, and J. M. Tang, “First real-time experimental demonstrations of 11.25Gb/s optical OFDMA PONs with adaptive dynamic bandwidth allocation,” Opt. Express |

7. | N. Cvijetic, M.-F. Huang, E. Ip, Y. Shao, Y.-K. Huang, M. Cvijetic, and T. Wang, “1.92 Tb/s coherent DWDM-OFDMA-PON with no high-speed ONU-side electronics over 100 km SSMF and 1:64 passive split,” Opt. Express |

8. | M. P. Fok, Z. Wang, Y. Deng, and P. R. Prucnal, “Optical layer security in fiber-optic networks,” IEEE Trans. Inf. Forensics and Security |

9. | C. E. Shannon, “Communication theory of secrecy systems,” Bell Syst. Tech. J. |

10. | S.-L. Chen, T. T. Hwang, and W.-W. Lin, “Randomness enhancement using digitalized modified logistic map,” IEEE Trans. Circuits Syst., II Express Briefs |

11. | L. Zhang, X. Xin, B. Liu, and J. Yu, “Physical-enhanced secure strategy in an OFDM-PON,” Opt. Express |

**OCIS Codes**

(060.4080) Fiber optics and optical communications : Modulation

(060.4250) Fiber optics and optical communications : Networks

(060.4510) Fiber optics and optical communications : Optical communications

**ToC Category:**

Access Networks and LAN

**History**

Original Manuscript: October 1, 2012

Revised Manuscript: October 29, 2012

Manuscript Accepted: November 7, 2012

Published: November 28, 2012

**Virtual Issues**

European Conference on Optical Communication 2012 (2012) *Optics Express*

**Citation**

Lijia Zhang, Xiangjun Xin, Bo Liu, and Xiaoli Yin, "Physical secure enhancement in optical OFDMA-PON based on two-dimensional scrambling," Opt. Express **20**, B32-B37 (2012)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-26-B32

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### References

- N.-C. Tran, E. Tangdiongga, C. Okonkwo, H. Jung, and T. Koonen, “Flexibility level adjustment in reconfigurable WDM-TDM optical access networks,” J. Lightwave Technol.30(15), 2542–2550 (2012). [CrossRef]
- N. Cvijetic, “OFDM for next-generation optical access networks,” J. Lightwave Technol.30(4), 384–398 (2012). [CrossRef]
- R. Schmogrow, M. Winter, D. Hillerkuss, B. Nebendahl, S. Ben-Ezra, J. Meyer, M. Dreschmann, M. Huebner, J. Becker, C. Koos, W. Freude, and J. Leuthold, “Real-time OFDM transmitter beyond 100 Gbit/s,” Opt. Express19(13), 12740–12749 (2011). [CrossRef] [PubMed]
- H.-Y. Chen, C. C. Wei, D.-Z. Hsu, M. C. Yuang, J. Chen, Y.-M. Lin, P.-L. Tien, S. S. W. Lee, S.-H. Lin, W.-Y. Li, C.-H. Hsu, and J.-L. Shih, “A 40-Gb/s OFDM PON system based on 10-GHz EAM and 10-GHz direct-detection PIN,” IEEE Photon. Technol. Lett.24(1), 85–87 (2012). [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. Q. Jin, E. Hugues-Salas, R. P. Giddings, J. L. Wei, J. Groenewald, and J. M. Tang, “First real-time experimental demonstrations of 11.25Gb/s optical OFDMA PONs with adaptive dynamic bandwidth allocation,” Opt. Express19(21), 20557–20570 (2011). [CrossRef] [PubMed]
- N. Cvijetic, M.-F. Huang, E. Ip, Y. Shao, Y.-K. Huang, M. Cvijetic, and T. Wang, “1.92 Tb/s coherent DWDM-OFDMA-PON with no high-speed ONU-side electronics over 100 km SSMF and 1:64 passive split,” Opt. Express19(24), 24540–24545 (2011). [CrossRef] [PubMed]
- M. P. Fok, Z. Wang, Y. Deng, and P. R. Prucnal, “Optical layer security in fiber-optic networks,” IEEE Trans. Inf. Forensics and Security6(3), 725–736 (2011). [CrossRef]
- C. E. Shannon, “Communication theory of secrecy systems,” Bell Syst. Tech. J.28, 656–715 (1949).
- S.-L. Chen, T. T. Hwang, and W.-W. Lin, “Randomness enhancement using digitalized modified logistic map,” IEEE Trans. Circuits Syst., II Express Briefs57(12), 996–1000 (2010). [CrossRef]
- L. Zhang, X. Xin, B. Liu, and J. Yu, “Physical-enhanced secure strategy in an OFDM-PON,” Opt. Express20(3), 2255–2265 (2012). [CrossRef] [PubMed]

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