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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 7 — Mar. 26, 2012
  • pp: 8071–8077
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Energy-efficient WDM-OFDM-PON employing shared OFDM modulation modules in optical line terminal

Xiaofeng Hu, Liang Zhang, Pan Cao, Kongtao Wang, and Yikai Su  »View Author Affiliations


Optics Express, Vol. 20, Issue 7, pp. 8071-8077 (2012)
http://dx.doi.org/10.1364/OE.20.008071


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Abstract

We propose and experimentally demonstrate a scheme to improve the energy efficiency of wavelength division multiplexing - orthogonal frequency division multiplexing - passive optical networks (WDM-OFDM-PONs). By using an N × M opto-mechanic switch in optical line terminal (OLT), an OFDM modulation module is shared by several channels to deliver data to multiple users with low traffic demands during non-peak hours of the day, thus greatly reducing the number of operating devices and minimizing the energy consumption of the OLT. An experiment utilizing one OFDM modulation module to serve three optical network units (ONUs) in a WDM-OFDM-PON is performed to verify the feasibility of our proposal. Theoretical analysis and numerical calculation show that the proposed scheme can achieve a saving of 23.6% in the energy consumption of the OFDM modulation modules compared to conventional WDM-OFDM-PON.

© 2012 OSA

1. Introduction

Recent studies show that the amount of energy dissipated by the industry of information and communication technologies (ICT) is growing fast at a rate of ~2 dB/year [1

1. S. J. Ben Yoo, “Energy efficiency in the future internet: the role of optical packet switching and optical-label switching,” IEEE J. Sel. Top. Quantum Electron. 17(2), 406–418 (2011). [CrossRef]

] with the rapid increase of global data traffic [2

2. Cisco systems white paper, “Cisco visual networking index: Forecast and methodology, 2010-2015” (Cisco systems, 2011). http://www.cisco.com/en/US/hmpgs/index.html.

,3

3. A report of the TeleGeography Research, “Global internet geography” (PriMetrica, Inc., 2010). http://www.telegeography.com/research-services/global-internet-geography/index.html.

] and massive deployment of new network equipments and devices, leading to unsustainable power requirement [4

4. T. Asami and S. Namiki, “Energy consumption targets for network systems,” in Proc. ECOC2008, Brussels, Belgium, paper Tu.4.A.3.

]. Moreover, the ever-increasing energy consumption by ICT causes a series of issues, such as the emission of greenhouse gases and high operation cost of networks [5

5. Working Groups of the Intergovernmental Panel on Climate Change (IPCC), Climate change 2007: Synthesis report (IPCC, 2007).

,6

6. C. Lange, D. Kosiankowski, C. Gerlach, F.-J. Westphal, and A. Gladisch, “Energy consumption of telecommunication networks,” in Proc. ECOC2009, Vienna, Austria, Paper 5.5.3.

]. Therefore, great efforts have been dedicated to improving the energy efficiency in all aspects of ICT in the past few years [7

7. X. Dong, T. El-Gorashi, and J.-M. Elmirghani, “Green IP over WDM networks with data centers,” J. Lightwave Technol. 29(12), 1861–1880 (2011). [CrossRef]

10

10. R. S. Tucker, “Green optical communications – Part II: Energy limitations in networks,” IEEE J. Sel. Top. Quantum Electron. 17(2), 261–274 (2011). [CrossRef]

].

According to Ref [11

11. The Climate Group, SMART 2020: Enabling the low carbon economy in the information age (Global eSustainablity Initiative, 2008).

], network equipments dissipate roughly one third of the total energy consumed by ICT every year. Among this, it is estimated that the contribution of access networks is as high as 70% due to the presence of a huge number of active elements [12

12. C. Lange and A. Gladisch, “On the energy consumption of FTTH access networks,” in Proc. OFC2009, San Diego, CA, paper JThA79.

]. However, current access networks exhibit poor energy efficiency [13

13. K. J. Christensen, C. Gunaratne, B. Nordman, and A. D. George, “The next frontier for communications networks: Power management,” Comput. Commun. 27(18), 1758–1770 (2004).

], wasting more than 80% of the total power when the network devices are idle [14

14. P. Chowdhury, M. Tornatore, S. Sarkar, and B. Mukherjee, “Building a green wireless-optical broad band access netwok (WOBAN),” J. Lightwave Technol. 28(16), 2219–2229 (2010). [CrossRef]

]. This is mainly because that the access networks are designed to meet the peak traffic load requirement while the users do not fully utilize the network capacity all the time. Of all kinds of access network schemes, passive optical network (PON) is an energy-saving technique installing passive components at remote node [15

15. C. Lange, D. Kosiankowski, and A. Gladisch, “Power and energy consumption in broadband fixed access network migration,” in Proc. ECOC 2011, paper We.8.C.2.

].

In this paper, we propose and experimentally demonstrate a new scheme to improve the energy efficiency in a WDM-OFDM-PON. In our scheme, an N × M opto-mechanic switch in the OLT is employed to dynamically assign OFDM modulation modules consisting of E/O modulators and electrical OFDM signal generators to different users. Several users can share one OFDM modulation module through flexible and adaptive OFDM subcarrier allocation when they have low data bandwidth requirements. Thus, a number of OFDM modulation modules can be turned off, resulting in great reduction of energy consumption.

2. Operation principle

It is well known that the traffic load of access networks fluctuates at different hours of the day. In a conventional WDM-OFDM-PON, all OFDM modulation modules have to be running regardless of the current traffic condition. This leads to high energy consumption and low energy efficiency. In our proposal, most under-utilized OFDM modulation modules can be turned off while rerouting their traffic to a few OFDM modulation modules by the N × M opto-mechanic switch reconfiguration during low-load hours. According to real-time traffic loads of different ONUs, an optimum strategy can be achieved to use minimum number of OFDM modulation modules to deliver the data of all ONUs. On the other hand, the additional energy cost incurred by the switch reconfiguration is negligible owing to the low energy consumption of the opto-mechanic switch [21

21. J. Zhang, T. Wang, and N. Ansari, “Designing energy-efficient optical line terminal for TDM passive optical networks,” in Proc. Sarnoff2011, pp. 1–5.

]. Therefore, the energy efficiency of WDM-OFDM-PON is largely improved by the proposed scheme. The numerical analysis will be discussed in detail in section 4.

3. Experimental setup and results

4. Numerical analysis for energy efficiency

In order to quantitatively analyze the improvement of the energy efficiency in the proposed scheme, we consider a WDM-OFDM-PON with 32 channels to support 32 users. For the conventional WDM-OFDM-PON, all OFDM modulation modules are required to be active all the time. In contrast, the number of running OFDM modulation modules depends on the traffic demands of ONUs in our proposal. Here, we first develop an appropriate traffic model for the access system. The total transport capacity of the network is Cm and the current traffic in a certain time is Cc. We define a parameter R as offered load (R = Cc/Cm). Each ONU has a maximum transport capacity of cm = Cm/32 and a current transmission speed of cc. The normalized traffic (r = cc/cm) of ONUs is assumed to be independent and obey normal distribution N(R, σ), where R is the offered load and σ is the variance of the traffic of customers. When r ≤ 0, we suppose the ONU has no data to receive; when 0 < r ≤ 1, the ONU has a certain load and can share an OFDM modulation module with other ONUs; when r ≥ 1, congestion occurs in the ONU and one OFDM modulation module has to be used to transmit data for it. An OFDM modulation module has a maximum transmission capability of Cm/32 and can serve as many as F ONUs. F is defined as the DOF of the network as aforementioned in section 2. Figure 4(a)
Fig. 4 The calculated mathematical expectations of the number of running OFDM modulation modules with (a) different degrees of flexibility, (b) different variances; (c) The offered load over the course of an average day in North America [24]; (d) Required OFDM modulation modules for energy-efficient (F = 4, σ = 0.1) and conventional WDM-OFDM-PONs versus time in an average day.
depicts the calculated mathematical expectations of the number of running OFDM modulation modules with the variation of the offered load while F equals 2, 4, 8, 16, and 32. The parameter σ is assumed to be 0.1 to moderate the congestion probability of ONU as R is high. From the figure, it is clearly observed that the energy-efficient WDM-OFDM-PON can significantly reduce the number of operating OFDM modulation modules, allowing for large energy savings. Also, the energy efficiency improves with the decrease of the offered load and the increase of the DOF of the network. However, the improvement is quite small while F ≥ 8. Therefore, the optimum value of the DOF of the energy-efficient WDM-OFDM-PON is set to be 4 in consideration of the system complexity and energy efficiency, which is irrelevant to the number of ONUs. Figure 4(b) shows the number of running OFDM modulation modules with the variation of the offered load while σ has different values. The energy efficiencies of the network are almost the same when σ = 0.05 and 0.1. But the network with σ = 0.5 saves more energy. This is mainly because that the variance of the traffic load of customers becomes larger and the congestion probability increases. It is worth noting that the improvement of the energy efficiency is also determined in part by the behavior patterns of the customers in addition to the DOF and the offered load of the proposed scheme.

Figure 4(c) depicts the network traffic profile in the course of an average day in the fixed access networks of North America [24

24. Sandvine, “Global Internet Phenomena Spotlight – North America, Fixed Access, Spring 2011” (Sandvine, 2011). http://www.sandvine.com/news/global_broadband_trends.asp.

]. From it, an evident phenomenon is observed that the traffic demands of the users fluctuate during different hours of the day. The lowest traffic of the network is only about 29%, occurring at 6 am in the early morning. This implies that the energy-efficient WDM-OFDM-PON can make great improvement on the energy efficiency of the access networks. Figure 4(d) shows the number of OFDM modulation modules required to be up in energy-efficient and conventional WDM-OFDM-PONs, respectively. Here, the DOF of the energy-efficient WDM-OFDM-PON is set to be 4 as aforementioned. The conventional network requires the 32 OFDM modulation modules be running all the time, which is quite energy-inefficient and consumes lots of power. Exploiting the proposed scheme, quite a few OFDM modulation modules can be turned off as shown in Fig. 4(d). The numerical calculation shows that about 23.6% energy saving in the OFDM modulation modules can be achieved by using our scheme compared to the conventional WDM-OFDM-PON.

5. Conclusion

We have proposed an energy-efficient WDM-OFDM-PON using shared OFDM modulation modules to achieve energy saving. A proof-of-concept experiment employing one OFDM modulation module to serve three ONUs is performed and negligible power penalty is introduced compared to conventional WDM-OFDM-PON, validating the feasibility of the proposed scheme. Numerical analysis shows that up to 23.6% of energy consumed by OFDM modulation modules in the OLT can be saved by using our proposal.

Acknowledgments

This work was supported in part by NSFC (61077052/61125504), MoE (20110073110012), and Science and Technology Commission of Shanghai Municipality (11530700400).

References and links

1.

S. J. Ben Yoo, “Energy efficiency in the future internet: the role of optical packet switching and optical-label switching,” IEEE J. Sel. Top. Quantum Electron. 17(2), 406–418 (2011). [CrossRef]

2.

Cisco systems white paper, “Cisco visual networking index: Forecast and methodology, 2010-2015” (Cisco systems, 2011). http://www.cisco.com/en/US/hmpgs/index.html.

3.

A report of the TeleGeography Research, “Global internet geography” (PriMetrica, Inc., 2010). http://www.telegeography.com/research-services/global-internet-geography/index.html.

4.

T. Asami and S. Namiki, “Energy consumption targets for network systems,” in Proc. ECOC2008, Brussels, Belgium, paper Tu.4.A.3.

5.

Working Groups of the Intergovernmental Panel on Climate Change (IPCC), Climate change 2007: Synthesis report (IPCC, 2007).

6.

C. Lange, D. Kosiankowski, C. Gerlach, F.-J. Westphal, and A. Gladisch, “Energy consumption of telecommunication networks,” in Proc. ECOC2009, Vienna, Austria, Paper 5.5.3.

7.

X. Dong, T. El-Gorashi, and J.-M. Elmirghani, “Green IP over WDM networks with data centers,” J. Lightwave Technol. 29(12), 1861–1880 (2011). [CrossRef]

8.

D. Kilper, “Energy efficient networks,” in Proc. OFC2011, paper OWI5.

9.

R. S. Tucker, “Green optical communications – Part I: Energy limitations in transport,” IEEE J. Sel. Top. Quantum Electron. 17(2), 245–260 (2011). [CrossRef]

10.

R. S. Tucker, “Green optical communications – Part II: Energy limitations in networks,” IEEE J. Sel. Top. Quantum Electron. 17(2), 261–274 (2011). [CrossRef]

11.

The Climate Group, SMART 2020: Enabling the low carbon economy in the information age (Global eSustainablity Initiative, 2008).

12.

C. Lange and A. Gladisch, “On the energy consumption of FTTH access networks,” in Proc. OFC2009, San Diego, CA, paper JThA79.

13.

K. J. Christensen, C. Gunaratne, B. Nordman, and A. D. George, “The next frontier for communications networks: Power management,” Comput. Commun. 27(18), 1758–1770 (2004).

14.

P. Chowdhury, M. Tornatore, S. Sarkar, and B. Mukherjee, “Building a green wireless-optical broad band access netwok (WOBAN),” J. Lightwave Technol. 28(16), 2219–2229 (2010). [CrossRef]

15.

C. Lange, D. Kosiankowski, and A. Gladisch, “Power and energy consumption in broadband fixed access network migration,” in Proc. ECOC 2011, paper We.8.C.2.

16.

B. Liu, X. Xin, L. Zhang, J. Yu, Q. Zhang, and C. Yu, “A WDM-OFDM-PON architecture with centralized lightwave and PolSK-modulated multicast overlay,” Opt. Express 18(3), 2137–2143 (2010). [CrossRef] [PubMed]

17.

M.-F. Huang, J. Yu, D. Qian, N. Cvijetic, and G.-K. Chang, “Lightwave centralized WDM-OFDM-PON network employing cost-effective directly modulated laser,” in Proc. OFC2009, San Diego, CA, paper OMV5.

18.

D. Qian, T. Kwok, N. Cviject, J. Hu, and T. Wang, “41.25 Gb/s real-time OFDM receiver for variable rate WDM-OFDMA-PON transmission,” in Proc. OFC2010, paper PDPD9.

19.

L. Shi, S.-S. Lee, and B. Mukherjee, “An SLA-based energy-efficient scheduling scheme for EPON with sleep-mode ONU,” in Proc. OFC2011, paper OThB4.

20.

R. Kubo, J. Kani, H. Ujikawa, T. Sakamoto, Y. Fujimoto, N. Yoshimoto, and H. Hadama, “Study and demonstration of sleep and adaptive link rate control mechanisms for energy efficient 10G-EPON,” IEEE J. Opt. Commun. Netw. 2(9), 716–729 (2010). [CrossRef]

21.

J. Zhang, T. Wang, and N. Ansari, “Designing energy-efficient optical line terminal for TDM passive optical networks,” in Proc. Sarnoff2011, pp. 1–5.

22.

A. Banerjee, Y. Park, F. Clarke, H. Song, S. Yang, G. Kramer, K. Kim, and B. Mukherjee, “Wavelength-division-multiplexed passive optical network (WDM-PON) technologies for broadband access: a review,” J. Opt. Netw. 4(11), 737–758 (2005). [CrossRef]

23.

B. Schmidt, A. Lowery, and J. Armstrong, “Experimental demonstrations of electronic dispersion compensation for long-haul transmission using direct-detection,” J. Lightwave Technol. 26(1), 196–203 (2008). [CrossRef]

24.

Sandvine, “Global Internet Phenomena Spotlight – North America, Fixed Access, Spring 2011” (Sandvine, 2011). http://www.sandvine.com/news/global_broadband_trends.asp.

OCIS Codes
(060.2330) Fiber optics and optical communications : Fiber optics communications
(060.4250) Fiber optics and optical communications : Networks

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: January 19, 2012
Revised Manuscript: February 24, 2012
Manuscript Accepted: February 28, 2012
Published: March 22, 2012

Citation
Xiaofeng Hu, Liang Zhang, Pan Cao, Kongtao Wang, and Yikai Su, "Energy-efficient WDM-OFDM-PON employing shared OFDM modulation modules in optical line terminal," Opt. Express 20, 8071-8077 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-7-8071


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References

  1. S. J. Ben Yoo, “Energy efficiency in the future internet: the role of optical packet switching and optical-label switching,” IEEE J. Sel. Top. Quantum Electron. 17(2), 406–418 (2011). [CrossRef]
  2. Cisco systems white paper, “Cisco visual networking index: Forecast and methodology, 2010-2015” (Cisco systems, 2011). http://www.cisco.com/en/US/hmpgs/index.html .
  3. A report of the TeleGeography Research, “Global internet geography” (PriMetrica, Inc., 2010). http://www.telegeography.com/research-services/global-internet-geography/index.html .
  4. T. Asami and S. Namiki, “Energy consumption targets for network systems,” in Proc. ECOC2008, Brussels, Belgium, paper Tu.4.A.3.
  5. Working Groups of the Intergovernmental Panel on Climate Change (IPCC), Climate change 2007: Synthesis report (IPCC, 2007).
  6. C. Lange, D. Kosiankowski, C. Gerlach, F.-J. Westphal, and A. Gladisch, “Energy consumption of telecommunication networks,” in Proc. ECOC2009, Vienna, Austria, Paper 5.5.3.
  7. X. Dong, T. El-Gorashi, J.-M. Elmirghani, “Green IP over WDM networks with data centers,” J. Lightwave Technol. 29(12), 1861–1880 (2011). [CrossRef]
  8. D. Kilper, “Energy efficient networks,” in Proc. OFC2011, paper OWI5.
  9. R. S. Tucker, “Green optical communications – Part I: Energy limitations in transport,” IEEE J. Sel. Top. Quantum Electron. 17(2), 245–260 (2011). [CrossRef]
  10. R. S. Tucker, “Green optical communications – Part II: Energy limitations in networks,” IEEE J. Sel. Top. Quantum Electron. 17(2), 261–274 (2011). [CrossRef]
  11. The Climate Group, SMART 2020: Enabling the low carbon economy in the information age (Global eSustainablity Initiative, 2008).
  12. C. Lange and A. Gladisch, “On the energy consumption of FTTH access networks,” in Proc. OFC2009, San Diego, CA, paper JThA79.
  13. K. J. Christensen, C. Gunaratne, B. Nordman, A. D. George, “The next frontier for communications networks: Power management,” Comput. Commun. 27(18), 1758–1770 (2004).
  14. P. Chowdhury, M. Tornatore, S. Sarkar, B. Mukherjee, “Building a green wireless-optical broad band access netwok (WOBAN),” J. Lightwave Technol. 28(16), 2219–2229 (2010). [CrossRef]
  15. C. Lange, D. Kosiankowski, and A. Gladisch, “Power and energy consumption in broadband fixed access network migration,” in Proc. ECOC 2011, paper We.8.C.2.
  16. B. Liu, X. Xin, L. Zhang, J. Yu, Q. Zhang, C. Yu, “A WDM-OFDM-PON architecture with centralized lightwave and PolSK-modulated multicast overlay,” Opt. Express 18(3), 2137–2143 (2010). [CrossRef] [PubMed]
  17. M.-F. Huang, J. Yu, D. Qian, N. Cvijetic, and G.-K. Chang, “Lightwave centralized WDM-OFDM-PON network employing cost-effective directly modulated laser,” in Proc. OFC2009, San Diego, CA, paper OMV5.
  18. D. Qian, T. Kwok, N. Cviject, J. Hu, and T. Wang, “41.25 Gb/s real-time OFDM receiver for variable rate WDM-OFDMA-PON transmission,” in Proc. OFC2010, paper PDPD9.
  19. L. Shi, S.-S. Lee, and B. Mukherjee, “An SLA-based energy-efficient scheduling scheme for EPON with sleep-mode ONU,” in Proc. OFC2011, paper OThB4.
  20. R. Kubo, J. Kani, H. Ujikawa, T. Sakamoto, Y. Fujimoto, N. Yoshimoto, H. Hadama, “Study and demonstration of sleep and adaptive link rate control mechanisms for energy efficient 10G-EPON,” IEEE J. Opt. Commun. Netw. 2(9), 716–729 (2010). [CrossRef]
  21. J. Zhang, T. Wang, and N. Ansari, “Designing energy-efficient optical line terminal for TDM passive optical networks,” in Proc. Sarnoff2011, pp. 1–5.
  22. A. Banerjee, Y. Park, F. Clarke, H. Song, S. Yang, G. Kramer, K. Kim, B. Mukherjee, “Wavelength-division-multiplexed passive optical network (WDM-PON) technologies for broadband access: a review,” J. Opt. Netw. 4(11), 737–758 (2005). [CrossRef]
  23. B. Schmidt, A. Lowery, J. Armstrong, “Experimental demonstrations of electronic dispersion compensation for long-haul transmission using direct-detection,” J. Lightwave Technol. 26(1), 196–203 (2008). [CrossRef]
  24. Sandvine, “Global Internet Phenomena Spotlight – North America, Fixed Access, Spring 2011” (Sandvine, 2011). http://www.sandvine.com/news/global_broadband_trends.asp .

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