## Energy efficient IM-DD OFDM-PON using dynamic SNR management and adaptive modulation |

Optics Express, Vol. 22, Issue 2, pp. 1789-1795 (2014)

http://dx.doi.org/10.1364/OE.22.001789

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### Abstract

This paper describes the demonstration of an energy efficient orthogonal frequency division multiplexing passive optical network using the dynamic signal to noise ratio (SNR) management and adaptive modulation. Controlling the calculation precision and modulation format minimizes the energy consumption of digital signal processor while satisfying the requirements of bit error ratio. We show that the calculation precision and modulation format can be optimized according to the optical received power, and realize a 58.7% effective energy efficiency per bit in an FPGA-based receiver experimentally.

© 2014 Optical Society of America

## 1. Introduction

2. N. Cvijetic, “OFDM for Next-Generation Optical Access Networks,” J. Lightwave Technol. **30**(4), 384–398 (2012). [CrossRef]

5. H. Kimura, H. Nakamura, S. Kimura, and N. Yoshimoto, “Numerical Analysis of Dynamic SNR Management by Controlling DSP Calculation Precision for Energy-Efficient OFDM-PON,” IEEE Photon. Technol. Lett. **24**(23), 2132–2135 (2012). [CrossRef]

## 2. Dynamic SNR management and adaptive modulation

_{OLT}-bit and X

_{ONU}-bit, according to the transmission loss and receiver noise, to reduce power consumption.

## 3. Experimental results of signal transmission

_{OLT}-bit IFFT creates an OFDM signal, which contains the quantization and rounding errors of the IFFT calculation. The IFFT matrix size was set at 256 to transmit OFDM signal using 96 (<256/2) subcarriers. The OFDM transmitter generates an OFDM frame digitally by adding a cyclic prefix (CP) and a preamble. Then, an arbitrary waveform generator (AWG) behaves as a D/A with a sampling rate of 10 GSample/s at QPSK, and 5 GSample/s at 16QAM to achieve 10-Gbit/s with a Hermitian overhead. The OFDM frame is transmitted by using a 1556.23 nm narrow-linewidth DFB-LD, which spectral width is 69 kHz, and an LN intensity modulator.

_{ONU}-bit FFT demodulates the OFDM signal with quantization and rounding errors. We varied X

_{OLT}-bit and X

_{ONU}-bit from 8 to 16, and set both with the same calculation precision.

- (1) A calculation with a large number of bits improves the BER for the same optical received power. The constellation becomes satisfactory even for the same optical received power by increasing the number of bits used for the FFT and IFFT calculation.
- (2) 8 bit FFT and IFFT calculations with 16QAM could not achieve the forward error correction (FEC) limit, which is a BER of 3.8x10
^{−3}for hard decision FEC with a 7% overhead [8], because the dominant characteristics of this transmission are the quantization and rounding errors caused by FFT and IFFT calculation. - (3) In particular, the increase in the number of bits significantly enhances the BER in a domain with a small number of bits. On the other hand, increasing the number of bits improves the BER characteristics slightly in a domain with a large number of bits, e.g. more than 10 bits with QPSK and 12 bits with 16QAM.
- (4) Several bit number and optical received power combinations satisfy the BER requirement. For example, a ≥10 bit calculation with 16QAM at −17 dBm optical received power, a ≥12 bit calculation with 16QAM at −20 dBm, and a 16 bit calculation with 16QAM at −21 dBm meet the FEC limit. These transmission results suggest that the calculation precision can be reduced for an ONU with a high optical received power, in other words, an ONU located at a short distance from the OLT.
- (5) Decreasing the number of bits for FFT and IFFT calculation degrades the BER with both 16QAM and QPSK. The dynamic SNR management can be applied for some multi-level modulation.

## 4. Experimental results for energy efficiency

## 5. Conclusions

## References and links

1. | K. Kitayama, Y. Yoshida, and A. Maruta, “Green, elastic coherent IFDMA-PON for next-generation access network,” in |

2. | N. Cvijetic, “OFDM for Next-Generation Optical Access Networks,” J. Lightwave Technol. |

3. | K. Kanonakis and I. Tomkos, “Energy-Efficient OFDMA-PON Exploiting Modular OLT/ONU Digital Signal Processing,” in |

4. | N. Iiyama, S.-Y. Kim, T. Shimada, S. Kimura, and N. Yoshimoto, “Co-existent Downstream Scheme between OOK and QAM Signals in an Optical Access Network using Software-defined Technology,” in |

5. | H. Kimura, H. Nakamura, S. Kimura, and N. Yoshimoto, “Numerical Analysis of Dynamic SNR Management by Controlling DSP Calculation Precision for Energy-Efficient OFDM-PON,” IEEE Photon. Technol. Lett. |

6. | R. Bouziane, P. A. Milder, R. J. Koutsoyannis, Y. Benlachtar, J. C. Hoe, M. Glick, and R. I. Killey, “Dependence of Optical OFDM Transceiver ASIC Complexity on FFT Size,” in |

7. | H. Takahashi, A. A. Amin, I. Morita, and H. Tanaka, “Required Resolution of Digital-Analog-Converter for Optical OFDM,” in |

8. | ITU-T Recommendation G.975.1, Appendix I.9 (2004). |

9. | H. Kimura, K. Asaka, H. Nakamura, S. Kimura, and N. Yoshimoto, “First Demonstration of Energy Efficiency of Dynamic SNR Management for Adaptive Modulation in IM-DD OFDM-PON,” in |

10. | F. Vacondio, O. Bertran-Pardo, Y. Pointurier, J. Fickers, A. Ghazisaeidi, G. de Valicourt, J.-C. Antona, P. Chanclou, and S. Bigo, “Flexible TDMA access optical networks enabled by burst-mode software defined coherent transponders,” in |

**OCIS Codes**

(060.0060) Fiber optics and optical communications : Fiber optics and optical communications

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

**ToC Category:**

Access, Local Area and Data Center Networks

**History**

Original Manuscript: October 9, 2013

Revised Manuscript: January 9, 2014

Manuscript Accepted: January 10, 2014

Published: January 21, 2014

**Virtual Issues**

European Conference and Exhibition on Optical Communication (2013) *Optics Express*

**Citation**

Hideaki Kimura, Kota Asaka, Hirotaka Nakamura, Shunji Kimura, and Naoto Yoshimoto, "Energy efficient IM-DD OFDM-PON using dynamic SNR management and adaptive modulation," Opt. Express **22**, 1789-1795 (2014)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-22-2-1789

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### References

- K. Kitayama, Y. Yoshida, and A. Maruta, “Green, elastic coherent IFDMA-PON for next-generation access network,” in Proceedings of 14th International Conference on Transparent Optical Networks, paper Tu.B3.1 (2012).
- N. Cvijetic, “OFDM for Next-Generation Optical Access Networks,” J. Lightwave Technol. 30(4), 384–398 (2012). [CrossRef]
- K. Kanonakis and I. Tomkos, “Energy-Efficient OFDMA-PON Exploiting Modular OLT/ONU Digital Signal Processing,” in Proceedings of OFC 2013, paper OTh3A.4 (2013).
- N. Iiyama, S.-Y. Kim, T. Shimada, S. Kimura, and N. Yoshimoto, “Co-existent Downstream Scheme between OOK and QAM Signals in an Optical Access Network using Software-defined Technology,” in Proceedings of OFC 2012, paper JTh2A.53 (2012).
- H. Kimura, H. Nakamura, S. Kimura, N. Yoshimoto, “Numerical Analysis of Dynamic SNR Management by Controlling DSP Calculation Precision for Energy-Efficient OFDM-PON,” IEEE Photon. Technol. Lett. 24(23), 2132–2135 (2012). [CrossRef]
- R. Bouziane, P. A. Milder, R. J. Koutsoyannis, Y. Benlachtar, J. C. Hoe, M. Glick, and R. I. Killey, “Dependence of Optical OFDM Transceiver ASIC Complexity on FFT Size,” in Proceedings of OFC 2012, paper JW2A.58 (2012).
- H. Takahashi, A. A. Amin, I. Morita, and H. Tanaka, “Required Resolution of Digital-Analog-Converter for Optical OFDM,” in Proceedings of OFC 2010, paper JThA4, (2010).
- ITU-T Recommendation G.975.1, Appendix I.9 (2004).
- H. Kimura, K. Asaka, H. Nakamura, S. Kimura, and N. Yoshimoto, “First Demonstration of Energy Efficiency of Dynamic SNR Management for Adaptive Modulation in IM-DD OFDM-PON,” in Proceedings of ECOC 2013, paper We.4.F.5 (2013).
- F. Vacondio, O. Bertran-Pardo, Y. Pointurier, J. Fickers, A. Ghazisaeidi, G. de Valicourt, J.-C. Antona, P. Chanclou, and S. Bigo, “Flexible TDMA access optical networks enabled by burst-mode software defined coherent transponders,” in Proceedings of ECOC 2013, paper We.1.F.2 (2013).

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