OSA's Digital Library

Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 15 — Jul. 18, 2011
  • pp: 14542–14548
« Show journal navigation

Performance investigation and demonstration of colorless upstream transmission in ECDM-OFDM-PON

Bo Liu, Xiangjun Xin, Lijia Zhang, and Jianjun Yu  »View Author Affiliations


Optics Express, Vol. 19, Issue 15, pp. 14542-14548 (2011)
http://dx.doi.org/10.1364/OE.19.014542


View Full Text Article

Acrobat PDF (1018 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

This paper has experimentally demonstrated and analyzed the performance of 2.5-Gb/s × 3-channel upstream transmission in electrical code divided multiplexing-orthogonal frequency division multiplexing access (ECDM-OFDM) passive optical network (PON). The colorless upstream link can be realized in ECDM-OFDM-PON. The experimental results show that the performance degradation due to optical beating interference (OBI) noise can be well suppressed in this network when the three channels adopt the same upstream wavelength. Compared with the WDM-OFDM-PON upstream signals without ECDM, the error floor shows about three orders of magnitude improvement due to the code gain when the same wavelength is used for all upstream signals.

© 2011 OSA

1. Introduction

2. System model and operating principle

Figure 1
Fig. 1 A basic configuration of ECDM-OFDM-PON (down: downstream; up: upstream).
shows the basic configuration of the ECDM-OFDM-PON. After constellation mapping, the downstream or upstream data of each ONU is assigned to the given OFDM subcarriers and code chip. The optical line terminal (OLT) controls the code chips and subcarriers allocation for each ONU according to different service demands. For the upstream signal, since one photodiode (PD) is used at the OLT, the OBI noise will occur within the receiver bandwidth and cause the performance degradation. The employment of chip code can minimize interference between different ONUs due to the code gain, while maintaining the OFDM merits of convenient multi-service and dynamical bandwidth allocation. In this architecture, the spreading spectrum with code chip is executed accompanying with the subcarrier modulation of OFDM frame in the electrical domain. The electrical ECDM-OFDM frames are converted into optical OFDM signals through intensity modulation.

The time domain ECDM-OFDM signal is given by

s(t)=k=1N[u(k)wm+jv(k)wm]exp(j2πfkt),fk=(k1)/Ts
(1)

with

Cov(wm,wn)={0,mnN,m=n
(2)

where m is the m th ONU, and wm is the code chip for mth ONU. The optical OFDM signal at the receiver can be expressed as

E(t)=exp(j2πft)[1+γs(t)]
(3)

where f is the frequency of laser and γ is the modulation index. Assuming two optical signals (ONU-1 and ONU-2) are detected simultaneously, the photocurrent after the PD can be presented as

I(t)=|E1(t)+E2(t)|=|[1+γ1s1(t)]ej2πf1t+[1+γ2s2(t)]ej2πf2t|
(4)

If we assume that γ1 = γ2 = γ and ignore the double frequency of photocurrent due to the low-pass photo-detection, Eq. (4) can be represented as

I(t)=γ[s1(t)+s2(t)]+Re{exp[j2π(f1f2)t]}1+γs1(t)1+γs2(t)
(5)

where f 1-f 2 denotes the central frequency of the OBI noise. After subcarriers demodulation and decoding, the received signal for one ONU can be expressed as

s1'(t)=0TsI(t)w1dt=0Tsγ[s1(t)+s2(t)]w1dtsignal+0Tscos[2π(f1f2)t]1+γs1(t)1+γs2(t)w1dtOBI=0Tsγk=1Nb1kexp(j2πf1t)w1w1dt+0Tsγk=1Nb2kexp(j2πf2t)w2w1dt+nOBI
(6)

The first term is the data of ONU-1, the second term is the data of ONU-2 and the last term is the OBI noise, which comes from the DC components of optical sources and the spectrum itself. From Eq. (2), we can see that the second term equals zero. According to the spread spectrum theory [17

17. A. W. Lam and S. Tantaratana, Theory and Application of Spread-Spectrum Systems (IEEE, Piscataway, NJ, 1994).

], the maximum of the OBI noise comes to

Nbeatγ2+2GcBOFDM2
(7)

where Gc is the code gain and BOFDM is the bandwidth of baseband OFDM signal, which is denoted [18

18. W. Shieh, H. Bao, and Y. Tang, “Coherent optical OFDM: theory and design,” Opt. Express 16(2), 841–859 (2008). [CrossRef] [PubMed]

]

BOFDM=2Ts+Nsc1ts
(8)

If Gc is large enough, Nbeat can be suppressed to ensure the performance of the system.

3. Experiment and results

Firstly, we evaluate the performance of the WDM-OFDM-PON without ECDM in different optical channel space from 0 GHz to 50 GHz. The experimental setup of WDM-OFDM-PON without ECDM is similar to Fig. 2, and the difference is that the code chip at ONU and correlator at OLT are canceled compared with Fig. 2. Figure 3
Fig. 3 BER curves of WDM-OFDM-PON upstream signals with and without ECDM (w/o: without, w/: with).
illustrates the measured average bit rate error (BER) curves of the upstream signals from three ONUs. The corresponding error floors are about 2.26 × 10−3, 3.22 × 10−5 and 3.44 × 10−6 when the channel space is 0 GHz, 10 GHz and 50 GHz respectively. We can see that the error floor of upstream signal at 0 GHz channel space is beyond the FEC limit and cannot be recovered due to the high OBI noise. For the case of 50 GHz, the channel space seems large enough so as to neglect the effect from the OBI noise. The power penalties of the signals with different channel space can almost be ignored. Figure 3 also shows the performance comparison between ECDM-OFDM-PON and WDM-OFDM-PON with variable channel spacing. After adopting ECDM, there is about 2dB and 1.6dB receive sensitivity improved for 10GHz and 50GHz channel spaces respectively. The error floors are also improved in both 10GHz and 50GHz cases. As the number of ONUs increases, the OBI noise would also increase and the performance would even be worse. Figure 4
Fig. 4 BER curves of WDM-OFDM-PON upstream signal with different numbers of ONUs and channel space.
shows the BER performance with different ONU number and channel space. We can see that for the case of 50GHz, even the number of ONUs is 8, the performance has little deterioration, which indicates a robust resistance to OBI noise. But for the case of 10GHz, when the number of ONUs increases to 6, the OBI noise is large enough to worsen the BER performance and the error floor is observed above 10−3.

Next, we investigate the BER performances of upstream OFDM signals of ECDM-OFDM-PON. Figure 5
Fig. 5 Two types of multiplexing for ONUs. (a) case-a: all subcarriers assigned to every ONU; (b) case-b: part of subcarriers assigned to every ONU.
shows our experiment within two cases: in case-a, all the OFDM subcarriers are assigned to every ONUs, which will produce a maximum upstream rate; in case-b, only parts of the OFDM subcarriers are assigned to every ONU. The transmitter wavelengths of the three ONUs are set to 1557.37 nm. Figure 6
Fig. 6 The BER curves and constellation of OFDM upstream signals with CDM coding.
depicts the average BER curves of ONUs and the constellations of received signals at the OLT under the two cases. The performance deterioration due to the OBI noise is well suppressed, and there is nearly no power penalty before and after 25-km transmission. Compared with case-a, case-b gets a better receive sensitivity in the same BER performance. This is mainly because the OFDM subcarriers are not totally overlapped as in case-a, which results in a lower OBI noise from Eq. (6). The error floor of the system is almost the same as the WDM-OFDM-PON without ECDM in 50-GHz channel space. In our experiment, we just adopt three ONUs for demonstration. Similarly, the OBI noise would enlarge as the number of ONUs increases. However, the OBI noise can still be suppressed through extending the length of code chip. The complexity scaling is proportioned to N × (N-1), where N is the chip length, and it mainly attributes to the shift register executing the encoding part. For upstream signals with fixed bandwidth, both the chip length and number of ONUs will affect the OBI noise and system performance in ECDM-OFDM-PON. According to the Q-factor definition [19

19. G. P. Agrawal, Fiber-Optic Communication Systems (Wiley-Interscience, New York, 1997).

] and Eqs. (3)-(7), the Q-factor of the upstream can be expressed as

Q=1NONUγ10logN2+γ2
(9)

where Nonu is the number of ONUs and N is the chip length. Equation (9) indicates a number of tolerable OBI noise sources and the corresponding chip length.

4. Conclusion

We have experimentally demonstrated a 2.5-Gb/s × 3 colorless upstream transmission in ECDM-OFDM-PON. We investigated the BER performances of WDM-OFDM-PON without ECDM system in different channel space as well as ECDM-OFDM-PON. The experimental results show that the ECDM-OFDM-PON can improve the error floor of the system by three orders of magnitude when the same wavelength is used for all upstream signals. This paper also suggests some guidance on number of ONUs and chip length for ECDM-OFDM-PON.

Acknowledgments

The financial support from National Basic Research Program of China with No. 2010CB328300, National Natural Science Foundation of China with No. 61077014, 61077050, 60932004, BUPT Young Foundation with No. 2009CZ07 are gratefully acknowledged. The project is also supported by the Fundamental Research Funds for the Central Universities and the open foundation of state key laboratory of optical communication technologies and networks (WRI) with No. 2010OCTN-02.

References and links

1.

P. P. Iannone and K. C. Reichmann, “Optical access beyond 10 Gb/s PON,” in 2010 36th European Conference and Exhibition on Optical Communication (ECOC) (2010), paper.Tu.3.B.1, pp. 1–5.

2.

M. Dueser, “Optical network architectures,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2011), paper OMN1.

3.

M. Cvijetic, “Advanced Technologies for Next-Generation Fiber Networks,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2010), paper OWY1.

4.

G. Chang, Z. Jia, J. Yu, A. Chowdhury, T. Wang, and G. Ellinas, “Super Broadband Optical Wireless Access Technologies,” in Optical Fiber Communication Conference and Exposition and The National Fiber Optic Engineers Conference, OSA Technical Digest (CD) (Optical Society of America, 2008), paper OThD1.

5.

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 18(20), 20732–20745 (2010). [CrossRef] [PubMed]

6.

Y.-M. Lin and P.-L. Tien, “Next-generation OFDMA-based passive optical network architecture supporting radio-over-fiber,” IEEE J. Sel. Areas Comm. 28(6), 791–799 (2010). [CrossRef]

7.

J. G. Lin Chen, J. G. Yu, J. Shuangchun Wen, Z. Lu, M. Dong, Huang, and G. K. Chang, “A novel scheme for seamless integration of ROF with centralized lightwave OFDM-WDM-PON system,” J. Lightwave Technol. 27(14), 2786–2791 (2009). [CrossRef]

8.

W. Wei, C. Wang, J. Yu, N. Cvijetic, and T. Wang, “Optical orthogonal frequency division multiple access networking for the future internet,” J. Opt. Commun. Netw. 1(2), A236–A246 (2009). [CrossRef]

9.

J. M. Tang, P. M. Lane, and K. A. Shore, “High-speed transmission of adaptively modulated optical OFDM signals over multimode fibers using directly modulated DFBs,” J. Lightwave Technol. 24(1), 429–441 (2006). [CrossRef]

10.

J. L. Wei, E. Hugues-Salas, R. P. Giddings, X. Q. Jin, X. Zheng, S. Mansoor, and J. M. Tang, “Wavelength reused bidirectional transmission of adaptively modulated optical OFDM signals in WDM-PONs incorporating SOA and RSOA intensity modulators,” Opt. Express 18(10), 9791–9808 (2010). [CrossRef] [PubMed]

11.

C.-W. Chow, C.-H. Yeh, C.-H. Wang, F.-Y. Shih, C.-L. Pan, and S. Chi, “WDM extended reach passive optical networks using OFDM-QAM,” Opt. Express 16(16), 12096–12101 (2008). [CrossRef] [PubMed]

12.

C. W. Chow, G. Talli, A. D. Ellis, and P. D. Townsend, “Rayleigh noise mitigation in DWDM LR-PONs using carrier suppressed subcarrier-amplitude modulated phase shift keying,” Opt. Express 16(3), 1860–1866 (2008). [CrossRef] [PubMed]

13.

D. Qian, J. Hu, P. Ji, T. Wang, and M. Cvijetic, “10-Gb/s OFDMA-PON for Delivery of Heterogeneous Services,” in Optical Fiber Communication Conference and Exposition and The National Fiber Optic Engineers Conference, OSA Technical Digest (CD) (Optical Society of America, 2008), paper OWH4.

14.

N. Cvijetic, D. Qian, J. Hu, and T. Wang, “44-Gb/s/λ Upstream OFDMA-PON Transmission with Polarization-Insensitive Source-Free ONUs,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2010), paper OTuO2.

15.

N. Cvijetic, D. Qian, and J. Hu, “100 Gb/s optical access based on optical orthogonal frequency division multiplexing,” IEEE Commun. Mag. 48(7), 70–77 (2010). [CrossRef]

16.

L. Zhang, X. Xin, B. Liu, J. Yu, and Q. Zhang, “A novel ECDM-OFDM-PON architecture for next-generation optical access network,” Opt. Express 18(17), 18347–18353 (2010). [CrossRef] [PubMed]

17.

A. W. Lam and S. Tantaratana, Theory and Application of Spread-Spectrum Systems (IEEE, Piscataway, NJ, 1994).

18.

W. Shieh, H. Bao, and Y. Tang, “Coherent optical OFDM: theory and design,” Opt. Express 16(2), 841–859 (2008). [CrossRef] [PubMed]

19.

G. P. Agrawal, Fiber-Optic Communication Systems (Wiley-Interscience, New York, 1997).

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: May 31, 2011
Revised Manuscript: July 6, 2011
Manuscript Accepted: July 7, 2011
Published: July 13, 2011

Citation
Bo Liu, Xiangjun Xin, Lijia Zhang, and Jianjun Yu, "Performance investigation and demonstration of colorless upstream transmission in ECDM-OFDM-PON," Opt. Express 19, 14542-14548 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-15-14542


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. P. P. Iannone and K. C. Reichmann, “Optical access beyond 10 Gb/s PON,” in 2010 36th European Conference and Exhibition on Optical Communication (ECOC) (2010), paper.Tu.3.B.1, pp. 1–5.
  2. M. Dueser, “Optical network architectures,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2011), paper OMN1.
  3. M. Cvijetic, “Advanced Technologies for Next-Generation Fiber Networks,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2010), paper OWY1.
  4. G. Chang, Z. Jia, J. Yu, A. Chowdhury, T. Wang, and G. Ellinas, “Super Broadband Optical Wireless Access Technologies,” in Optical Fiber Communication Conference and Exposition and The National Fiber Optic Engineers Conference, OSA Technical Digest (CD) (Optical Society of America, 2008), paper OThD1.
  5. 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 18(20), 20732–20745 (2010). [CrossRef] [PubMed]
  6. Y.-M. Lin and P.-L. Tien, “Next-generation OFDMA-based passive optical network architecture supporting radio-over-fiber,” IEEE J. Sel. Areas Comm. 28(6), 791–799 (2010). [CrossRef]
  7. J. G. Lin Chen, J. G. Yu, J. Shuangchun Wen, Z. Lu, M. Dong, Huang, and G. K. Chang, “A novel scheme for seamless integration of ROF with centralized lightwave OFDM-WDM-PON system,” J. Lightwave Technol. 27(14), 2786–2791 (2009). [CrossRef]
  8. W. Wei, C. Wang, J. Yu, N. Cvijetic, and T. Wang, “Optical orthogonal frequency division multiple access networking for the future internet,” J. Opt. Commun. Netw. 1(2), A236–A246 (2009). [CrossRef]
  9. J. M. Tang, P. M. Lane, and K. A. Shore, “High-speed transmission of adaptively modulated optical OFDM signals over multimode fibers using directly modulated DFBs,” J. Lightwave Technol. 24(1), 429–441 (2006). [CrossRef]
  10. J. L. Wei, E. Hugues-Salas, R. P. Giddings, X. Q. Jin, X. Zheng, S. Mansoor, and J. M. Tang, “Wavelength reused bidirectional transmission of adaptively modulated optical OFDM signals in WDM-PONs incorporating SOA and RSOA intensity modulators,” Opt. Express 18(10), 9791–9808 (2010). [CrossRef] [PubMed]
  11. C.-W. Chow, C.-H. Yeh, C.-H. Wang, F.-Y. Shih, C.-L. Pan, and S. Chi, “WDM extended reach passive optical networks using OFDM-QAM,” Opt. Express 16(16), 12096–12101 (2008). [CrossRef] [PubMed]
  12. C. W. Chow, G. Talli, A. D. Ellis, and P. D. Townsend, “Rayleigh noise mitigation in DWDM LR-PONs using carrier suppressed subcarrier-amplitude modulated phase shift keying,” Opt. Express 16(3), 1860–1866 (2008). [CrossRef] [PubMed]
  13. D. Qian, J. Hu, P. Ji, T. Wang, and M. Cvijetic, “10-Gb/s OFDMA-PON for Delivery of Heterogeneous Services,” in Optical Fiber Communication Conference and Exposition and The National Fiber Optic Engineers Conference, OSA Technical Digest (CD) (Optical Society of America, 2008), paper OWH4.
  14. N. Cvijetic, D. Qian, J. Hu, and T. Wang, “44-Gb/s/λ Upstream OFDMA-PON Transmission with Polarization-Insensitive Source-Free ONUs,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2010), paper OTuO2.
  15. N. Cvijetic, D. Qian, and J. Hu, “100 Gb/s optical access based on optical orthogonal frequency division multiplexing,” IEEE Commun. Mag. 48(7), 70–77 (2010). [CrossRef]
  16. L. Zhang, X. Xin, B. Liu, J. Yu, and Q. Zhang, “A novel ECDM-OFDM-PON architecture for next-generation optical access network,” Opt. Express 18(17), 18347–18353 (2010). [CrossRef] [PubMed]
  17. A. W. Lam and S. Tantaratana, Theory and Application of Spread-Spectrum Systems (IEEE, Piscataway, NJ, 1994).
  18. W. Shieh, H. Bao, and Y. Tang, “Coherent optical OFDM: theory and design,” Opt. Express 16(2), 841–859 (2008). [CrossRef] [PubMed]
  19. G. P. Agrawal, Fiber-Optic Communication Systems (Wiley-Interscience, New York, 1997).

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.


« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited