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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 10 — May. 7, 2012
  • pp: 10552–10561
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109.92-Gb/s WDM-OFDMA Uni-PON with Dynamic Resource Allocation and Variable Rate Access

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


Optics Express, Vol. 20, Issue 10, pp. 10552-10561 (2012)
http://dx.doi.org/10.1364/OE.20.010552


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Abstract

This paper proposes a novel wavelength division multiplexing-orthogonal frequency multiple access (WDM-OFDMA) union passive optical network (uni-PON) architecture with dynamic resource allocation and variable rate access. It can offer an infrastructure with different access solutions. According to the quality of service (QoS) requirement of different services, the optical local terminal (OLT) can dynamically assign different resources as well as the access rates to different services. An experiment has been demonstrated with 4 wavelengths achieving combined signal at 109.92-Gb/s. A physical-layer adaptive algorithm is employed for the resource allocation and variable rate access. The different services with different resource allocations and variable access rates are also demonstrated in the experiment.

© 2012 OSA

1. Introduction

In this paper, we propose and demonstrate a novel WDM-OFDMA uni-PON architecture for the future broadband access, which can offer both ONU and RRU access with dynamic resource allocation and variable rate. In the proposed scheme, we further adopt an adaptive algorithm by leading symbol at physical-layer for the dynamic allocation and variable access rate. In our experiment, the access rate can vary from 13.74 Gb/s to 27.48 Gb/s with a total 5GHz bandwidth per wavelength. A total bit rate of 109.92-Gb/s consisting of three services with 4 wavelengths has successfully been reached in the experiment.

2. System configuration

When the traffic is transmitted to the remote node (RN), a flexible wavelength blocker (FWB) is adopted to route the optical carriers for different ONUs/RRUs according to their requirements as illustrated in Fig. 1. There we group the ONUs/RRUs into three types: type A contains only radio services (wireless signal), type B contains only baseband services and type C includes both services. The FWB is consisting of an arrayed waveguide grating (AWG), an optical switcher (SW) and some optical couplers. In Fig. 1, the input signal of FWB is a group of optical carriers spaced around 33GHz, and the total number of the optical carriers is 3 × N, where N equals the number of wavelength channel. The input optical carriers are firstly demultiplexed by the AWG and then fed into the SW with 3 × N inputs and 3 × N outputs. According to the RRU/ONU requirement, the SW can deliver different optical carriers to them. The SW can be controlled by the programmable module and the control information comes from the OLT through a control channel. The granularity of the FWB depends on the channel space of AWG, which is 33GHz in our scheme. The optical couplers after the SW are used to combine the chosen optical carriers. For example, in type A case, the AWG separates all the optical carriers and the SW will choose the dedicated couple carriers for RRU to generate the wireless signal. The ONUs or RRUs extract their own information from different OFDM subcarriers.

In order to realize the dynamic bandwidth allocation and variable access rate, we employ a physical-layer adaptive algorithm for the OFDM signal which is shown in Fig. 2
Fig. 2 The block of adaptive algorithm: (a) transmitter; (b) receiver; (c) structure of leading symbol (P/S: parallel to serial; IFFT: inverse fast Fourier transform).
. To illustrate the algorithm, we assume there are three kinds of services and four kinds of m-QAM mapping formats. Figures 2(a) and 2(b) show the transmitter and receiver diagrams for the dynamic allocation which is realized through the leading symbol. The structure of the leading symbol is shown in Fig. 2(c) and it is also with OFDM modulation format. The subcarriers of leading symbol are consisting of two parts: resource label and speed label. The resource label is used to record the bandwidth allocation for different services; the speed label is used to record the different access bit rates for different services, which are realized through different mQAM mappings. The speed label contains several subcarriers which represent different QAM mapping formats as shown in Fig. 2(c). When one QAM mapping format is chosen (e.g. 16QAM), the power value of the corresponding subcarrier will be set to the root mean square of 16QAM and the other subcarriers would be set to zero. At the transmitter, the resource label stores the starting subcarrier index of each service and the speed label stores the mQAM mapping adopted for each services. At the receiver, the ONU/RRU extracts the subcarrier and mQAM mapping information from the leading symbol. When the bandwidth and access rate are changed, the OLT and ONU can automatically adapt the variety through the leading symbol which is transparent to the media access control (MAC) layer.

3. Experimental setup and results

The experimental setup is shown in Fig. 3
Fig. 3 Experimental setup for the proposed uni-PON architecture (IL: interleaver; SMF: single mode fiber; LPF: low pass filter; TDS: real time domain sampling scope)
, where we adopt four wavelength channels for the demonstration. At the OLT, four DFB lasers at 1549.32nm, 1550.12 nm, 1550.92nm and 1551.72nm (λ1 to λ4) are employed as the light sources which satisfy the ITU-T standard grid. In Ref [22

22. C. H. Yeh, C. W. Chow, H. Y. Chen, and B. W. Chen, “Using adaptive four-band OFDM modulation with 40 Gb/s downstream and 10 Gb/s upstream signals for next generation long-reach PON,” Opt. Express 19(27), 26150–26160 (2011). [CrossRef] [PubMed]

], a four-band OFDM-PON with variable access rate is proposed which realized 40Gb/s wired access with 10 GHz bandwidth. However, the four bands are electrical signal bands and it lacks physical-layer adaptive algorithm for variable rate. The four bands are multiplexed through electrical I/Q modulation and the rate for each electrical band is fixed at the OLT. In our experiment, we adopt four optical wavelengths for both wired and wireless access and a physical-layer adaptive algorithm is proposed for automatic allocation of the bandwidth and access rate. To reduce the system complexity and cost, we adopt one electrical band with total bandwidth of 5 GHz for each wavelength. It can be extended to more bands if higher rate is required. At the OLT, the four wavelengths are firstly sliced by a 30 GHz radio frequency (RF) clock to generate the optical carriers and the optical spectrums are shown in Fig. 4(a)
Fig. 4 The corresponding optical spectra in Fig. 3 with resolution bandwidth of 0.02nm: (a) after the MZM; (b) after IM for radio signal; (c) after IM for baseband signal; (d) after EDFA; (e) before Rx-1; (f) before Rx-2.
where we can see that the center frequency of mm-wave optical carrier for the radio signal is 60 GHz. OFDM is a kind of an analog signal and the ROF is also analog. A 100 GHz inter-leaver (IL) is adopted to separate the odd and even wavelength channels. After that, two 25 GHz ILs are employed to divide the central carriers and couple carriers. The central carriers are used to carry the baseband data and the couple carriers are used to carry the radio data. They are both directly modulated through the IMs which are working in the linear area at 1.7V with half-wave voltage of 3.5V. The corresponding optical spectra after modulation are shown in Figs. 4(b)-4(c).

In the experiment, the ONUs/RRUs are of three types: type A, type B and type C. After transmission, the FWB is used to separate the optical carriers from the OLT and delivered the corresponding optical carriers to different RRU/ONUs through another 5km SMF: the central carrier for wired access users and the couple carriers for wireless access users. The FWB is consisting of an AWG and a 12x12 SW. The SW is controlled through programmable module in the experiment. The granularity of the FWB is 33GHz. The total insert loss of the element is about 4.5dB (1.3dB for SW and 3.2dB for AWG). If the number of wavelength increases, AWG and SW with larger scale would be needed and it will increase the system complexity and cost.

For the type A case, a 60 GHz PD is adopted for the generation of the wireless OFDM signal, which utilizes the optical up-conversion theory [23

23. J. Ma, J. Yu, C. Yu, X. Xin, and Q. Zhang, “Transmission performance of the optical mm-wave generated by double-sideband intensity-modulation,” Opt. Commun. 280(2), 317–326 (2007). [CrossRef]

]. The generated RF signal centered at 60 GHz can be set into the air through antenna directly. At the users’ terminal, the RF signal can be down-converted with a 60 GHz local oscillator (LO). The down-converted OFDM signal is fed into a real time domain sampling scope (TDS) with 20Gs/s sample rate to capture the waveform for offline DSP processing. The demodulation process includes the software down-conversion, synchronization, leading symbol extraction, FFT processing, equalization and QAM de-mapping. For the type B case, the optical OFDM signal is directly detected by a photodiode (PD) with 3 dB bandwidth of 5 GHz. Then the detected electrical wired signal is also sampled by a TDS for offline DSP processing. For the type C case, additional 25 GHz IL is employed to separate the central carrier and couple carriers. The optical spectra of λ1 after separation are shown in Figs. 4(e) and 4(f). After separation, the detections of couple carriers and central carrier are same as of type A and type B respectively. Considering that both wired and wireless signals are included in type C case, we have measured the performance of this case for demonstration. We have measured OFDM signals with different QAM mapping varying from 8QAM to 64QAM, the total measured bits are 0.7 to 1.41 million each time.

Figure 5
Fig. 5 Measured BER curves of baseband and radio signals with 64QAM constellation mapping and total rate of 109.92 Gb/s.
illustrates the measured BER curves for both baseband and radio 64QAM-OFDM signals at back to back (b2b) and 30 km transmission which results a net data rate of 109.92 Gb/s. In this case, all the services are modulated with 64QAM mapping formats. The receiver sensitivities are about −21.6 dBm and −17.2 dBm for baseband and radio signals respectively and the performances of the four-wavelength channels are almost the same. We also compare the four-wavelength system performance with single wavelength case. For the baseband signals, it can be seen that the power penalty is about 0.2dB at BER of 10−3 which indicates a good performance if FEC technology is used. Comparing with the one wavelength case, there is about less than 0.1dB power penalty in the WDM case which almost can be ignored. Because in the one wavelength case, the central carrier and couple carriers are spaced at 30GHz and the interference from the couple carriers can be equivalent to that in WDM case. For the radio signals, the power penalty at BER of 10−3 is about 0.4dB after fiber link, which is mainly due to the fiber dispersion during transmission. For the WDM case, the power penalty is a little deteriorated as compared to the single wavelength and can also be ignored. For the radio signal, the main interference comes from the fiber dispersion due to the couple carriers spaced at 60-GHz instead of WDM neighbor channel.

From Fig. 5, we can see that the system performances of the four-wavelength channels are almost the same, so we only take λ2 (1550.12 nm) for the following analysis. According to the service demand, the speed modes in the leading symbol would be different to each other. Here we demonstrate by setting 16QAM, 32QAM and 64QAM respectively for the three services and all the services adopt the same QAM mapping each time which means the three services averagely share the total access rate. Figure 6
Fig. 6 Measured BER curves of the baseband and radio signals with access rate of 18.32 Gb/s, 22.9 Gb/s and 27.48 Gb/s respectively (for λ2 channel).
shows the measured BER curves of the three services with access rate of 18.32 Gb/s (12.83 Gb/s for baseband and 5.49 Gb/s for radio), 22.9 Gb/s (16.03 for baseband and 6.87 Gb/s for radio) and 27.48 Gb/s (19.24 Gb/s for baseband and 8.24 Gb/s for radio) respectively. The bandwidth is 3.5 GHz for the baseband signal and 1.5GHz for the radio signal. The receiver sensitivities at BER of 10−3 are −24.3 dBm, −23 dBm and −21.8dBm for baseband signals, and −20.4 dBm, −18.8 dBm and −17.5 dBm for radio signals. Figure 7
Fig. 7 Constellation diagrams of the baseband and radio signals with different access rates.
shows the constellation diagrams for baseband and radio signals with different access rates respectively. The radio signals seem to suffer more due to the fading effect and fiber dispersion.

Besides the above scene, the three kinds of services can take different access rates. There we assume service-1 is 8QAM mapped, service-2 is 16QAM mapped and service-3 is 32QAM mapped respectively. Figure 8
Fig. 8 The measured BER curves of the baseband and radio signals with different services and access rates after 30km transmission.
illustrates the measured BER curves when different services are chosen and the cases are shown in Table 1

Table 1. System Parameters for Experiment

table-icon
View This Table
. The total bandwidth is also 5GHz during measurement. Figure 8 shows the BER performances of baseband and radio signals for the three cases. It can be observed that the receiver sensitivities are −25 dBm, −24.48 dBm and −24dBm for baseband signals and −22.4 dBm, −21.7 dBm and −21.1 dBm for radio signals at BER of 10−3.

From Fig. 8, we can see that the receiver sensitivities at BER of 10−3 for baseband and radio 8QAM-OFDM signals are −22.4dBm and −25dBm respectively. The optical path loss is about 13.5dB. For the baseband signal, the margin budget is 16.5dB, which is abundant for a 1:32 split ratio; for the radio signal, the margin budget is 13.9dB, which is close to the split loss of a 1:32 splitter. The maximum number of users for one wavelength can be 64, and the number can be up to 256 in our experiment.

4. Conclusion

Acknowledgments

The financial supports from National Basic Research Program of China with No. 2010CB328300, National Natural Science Foundation of China with No. 60932004, 61077050, 61077014, 61177085, BUPT Excellent Ph. D. Students Foundation with No.CX201112. The project is also supported by the Fundamental Research Funds for the Central Universities with No.2012RC0311, 2011RC0307.

References and links

1.

G. Chang, Z. Jia, J. Yu, A. Chowdhury, T. Wang, and G. Ellinas, “Super-Broadband Optical Wireless Access Technologies,” in Proc. OFC, paper OThD1 (2008).

2.

J. Chen, L. Wosinska, C. Machuca, and M. Jaeger, “Cost vs. reliability performance study of fiber access network architectures,” IEEE Commun. Mag. 48(2), 56–65 (2010). [CrossRef]

3.

F. Effenberger, “The XG-PON system: cost effective 10Gb/s access,” J. Lightwave Technol. 29(4), 403–409 (2011). [CrossRef]

4.

J. Kani, F. Bourgart, A. Cui, A. Rafel, M. Campbell, R. Davey, and S. Rodrigues, “Next-generation PON part I—Technology roadmap and general requirements,” IEEE Commun. Mag. 47(11), 43–49 (2009). [CrossRef]

5.

10-Gigabit-Capable Passive Optical Network (XG-PON) Systems: Definitions, Abbreviations, and Acronyms, ITU-T G.987 (2009).

6.

S. Jain, F. Effenberger, A. Szabo, Z. Feng, A. Forcucci, W. Guo, Y. Luo, R. Mapes, Y. Zhang, and V. O’Byrne, “The world’s first XG-PON field trial,” J. Lightwave Technol. 29(4), 524–528 (2011). [CrossRef]

7.

D. Kilper, “Energy Efficient Networks,” in Proc. OFC, USA, paper OWI5 (2011).

8.

Y. Ma, Q. Yang, Y. Tang, S. Chen, and W. Shieh, “1-Tb/s single-channel coherent optical OFDM transmission over 600-km SSMF fiber with subwavelength bandwidth access,” Opt. Express 17(11), 9421–9427 (2009). [CrossRef] [PubMed]

9.

J. L. Wei, A. Hamié, R. P. Gidding, E. Hugues-Salas, X. Zheng, S. Mansoor, and J. M. Tang, “Adaptively modulated optical OFDM modems utilizing RSOAs as intensity modulators in IMDD SMF transmission systems,” Opt. Express 18(8), 8556–8573 (2010). [CrossRef] [PubMed]

10.

C. Yeh, C. Chow, and C. Hsu, “40-Gb/s Time-Division-Multiplexed Passive Optical Networks Using Downstream OOK and Upstream OFDM Modulations,” IEEE Photon. Technol. Lett. 22(2), 118–120 (2010). [CrossRef]

11.

H. Zhang, G. Pickrell, Z. Morbi, Y. Wang, M. Ho, K. Anselm, and W. Hwang, “32-Channel, Injection-Locked WDM-PON SFP Transceivers for Symmetric 1.25 Gbps Operation,” in Proc. OFC, USA, paper NTuB4 (2011).

12.

E. Wong, “Current and Next-Generation Broadband Access Technologies,” in Proc. OFC, USA, paper NMD1 (2011).

13.

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

14.

“Cloud-Radio Access Network (C-RAN) White Paper,” website: http://labs.chinamobile.com/cran/.

15.

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]

16.

D. Qian, N. Cvijetic, J. Hu, and T. Wang, “108 Gb/s OFDMA-PON with Polarization Multiplexing and Direct Detection,” J. Lightwave Technol. 28(4), 484–493 (2010). [CrossRef]

17.

J. Armstrong, “OFDM for Optical Communications,” J. Lightwave Technol. 27(3), 189–204 (2009). [CrossRef]

18.

X. Liu, F. Buchali, and R. W. Tkach, “Improving the Nonlinear Tolerance of Polarization-Division-Multiplexed CO-OFDM in Long-Haul Fiber Transmission,” J. Lightwave Technol. 27(16), 3632–3640 (2009). [CrossRef]

19.

Z. Jia, J. Yu, and G.-K. Chang, “A Full-Duplex Radio-Over-Fiber System Based on Optical Carrier Suppression and Reuse,” IEEE Photon. Technol. Lett. 18(16), 1726–1728 (2006). [CrossRef]

20.

P. T. Shih, C. T. Lin, W. J. Jiang, H. S. Huang, J. Chen, A. Ng’oma, M. Sauer, and S. Chi, “Transmission of 20-Gb/s OFDM signals occupying 7-GHz license-free band at 60 GHz using a RoF system employing frequency sextupling optical up-conversion,” Opt. Express 18(12), 12748–12755 (2010). [CrossRef] [PubMed]

21.

Y. Hsueh, M. Huang, S. Fan, and G. Chang, “A Novel Lightwave Centralized Bidirectional Hybrid Access Network: Seamless Integration of RoF With WDM-OFDM-PON,” IEEE Photon. Technol. Lett. 23(15), 1085–1087 (2011). [CrossRef]

22.

C. H. Yeh, C. W. Chow, H. Y. Chen, and B. W. Chen, “Using adaptive four-band OFDM modulation with 40 Gb/s downstream and 10 Gb/s upstream signals for next generation long-reach PON,” Opt. Express 19(27), 26150–26160 (2011). [CrossRef] [PubMed]

23.

J. Ma, J. Yu, C. Yu, X. Xin, and Q. Zhang, “Transmission performance of the optical mm-wave generated by double-sideband intensity-modulation,” Opt. Commun. 280(2), 317–326 (2007). [CrossRef]

OCIS Codes
(060.0060) Fiber optics and optical communications : Fiber optics and optical 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: February 29, 2012
Revised Manuscript: April 12, 2012
Manuscript Accepted: April 18, 2012
Published: April 23, 2012

Citation
Bo Liu, Xiangjun Xin, Lijia Zhang, and Jianjun Yu, "109.92-Gb/s WDM-OFDMA Uni-PON with Dynamic Resource Allocation and Variable Rate Access," Opt. Express 20, 10552-10561 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-10-10552


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References

  1. G. Chang, Z. Jia, J. Yu, A. Chowdhury, T. Wang, and G. Ellinas, “Super-Broadband Optical Wireless Access Technologies,” in Proc. OFC, paper OThD1 (2008).
  2. J. Chen, L. Wosinska, C. Machuca, and M. Jaeger, “Cost vs. reliability performance study of fiber access network architectures,” IEEE Commun. Mag.48(2), 56–65 (2010). [CrossRef]
  3. F. Effenberger, “The XG-PON system: cost effective 10Gb/s access,” J. Lightwave Technol.29(4), 403–409 (2011). [CrossRef]
  4. J. Kani, F. Bourgart, A. Cui, A. Rafel, M. Campbell, R. Davey, and S. Rodrigues, “Next-generation PON part I—Technology roadmap and general requirements,” IEEE Commun. Mag.47(11), 43–49 (2009). [CrossRef]
  5. 10-Gigabit-Capable Passive Optical Network (XG-PON) Systems: Definitions, Abbreviations, and Acronyms, ITU-T G.987 (2009).
  6. S. Jain, F. Effenberger, A. Szabo, Z. Feng, A. Forcucci, W. Guo, Y. Luo, R. Mapes, Y. Zhang, and V. O’Byrne, “The world’s first XG-PON field trial,” J. Lightwave Technol.29(4), 524–528 (2011). [CrossRef]
  7. D. Kilper, “Energy Efficient Networks,” in Proc. OFC, USA, paper OWI5 (2011).
  8. Y. Ma, Q. Yang, Y. Tang, S. Chen, and W. Shieh, “1-Tb/s single-channel coherent optical OFDM transmission over 600-km SSMF fiber with subwavelength bandwidth access,” Opt. Express17(11), 9421–9427 (2009). [CrossRef] [PubMed]
  9. J. L. Wei, A. Hamié, R. P. Gidding, E. Hugues-Salas, X. Zheng, S. Mansoor, and J. M. Tang, “Adaptively modulated optical OFDM modems utilizing RSOAs as intensity modulators in IMDD SMF transmission systems,” Opt. Express18(8), 8556–8573 (2010). [CrossRef] [PubMed]
  10. C. Yeh, C. Chow, and C. Hsu, “40-Gb/s Time-Division-Multiplexed Passive Optical Networks Using Downstream OOK and Upstream OFDM Modulations,” IEEE Photon. Technol. Lett.22(2), 118–120 (2010). [CrossRef]
  11. H. Zhang, G. Pickrell, Z. Morbi, Y. Wang, M. Ho, K. Anselm, and W. Hwang, “32-Channel, Injection-Locked WDM-PON SFP Transceivers for Symmetric 1.25 Gbps Operation,” in Proc. OFC, USA, paper NTuB4 (2011).
  12. E. Wong, “Current and Next-Generation Broadband Access Technologies,” in Proc. OFC, USA, paper NMD1 (2011).
  13. N. Cvijetic, “OFDM for Next-Generation Optical Access Networks,” J. Lightwave Technol.30(4), 384–398 (2012). [CrossRef]
  14. “Cloud-Radio Access Network (C-RAN) White Paper,” website: http://labs.chinamobile.com/cran/ .
  15. 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]
  16. D. Qian, N. Cvijetic, J. Hu, and T. Wang, “108 Gb/s OFDMA-PON with Polarization Multiplexing and Direct Detection,” J. Lightwave Technol.28(4), 484–493 (2010). [CrossRef]
  17. J. Armstrong, “OFDM for Optical Communications,” J. Lightwave Technol.27(3), 189–204 (2009). [CrossRef]
  18. X. Liu, F. Buchali, and R. W. Tkach, “Improving the Nonlinear Tolerance of Polarization-Division-Multiplexed CO-OFDM in Long-Haul Fiber Transmission,” J. Lightwave Technol.27(16), 3632–3640 (2009). [CrossRef]
  19. Z. Jia, J. Yu, and G.-K. Chang, “A Full-Duplex Radio-Over-Fiber System Based on Optical Carrier Suppression and Reuse,” IEEE Photon. Technol. Lett.18(16), 1726–1728 (2006). [CrossRef]
  20. P. T. Shih, C. T. Lin, W. J. Jiang, H. S. Huang, J. Chen, A. Ng’oma, M. Sauer, and S. Chi, “Transmission of 20-Gb/s OFDM signals occupying 7-GHz license-free band at 60 GHz using a RoF system employing frequency sextupling optical up-conversion,” Opt. Express18(12), 12748–12755 (2010). [CrossRef] [PubMed]
  21. Y. Hsueh, M. Huang, S. Fan, and G. Chang, “A Novel Lightwave Centralized Bidirectional Hybrid Access Network: Seamless Integration of RoF With WDM-OFDM-PON,” IEEE Photon. Technol. Lett.23(15), 1085–1087 (2011). [CrossRef]
  22. C. H. Yeh, C. W. Chow, H. Y. Chen, and B. W. Chen, “Using adaptive four-band OFDM modulation with 40 Gb/s downstream and 10 Gb/s upstream signals for next generation long-reach PON,” Opt. Express19(27), 26150–26160 (2011). [CrossRef] [PubMed]
  23. J. Ma, J. Yu, C. Yu, X. Xin, and Q. Zhang, “Transmission performance of the optical mm-wave generated by double-sideband intensity-modulation,” Opt. Commun.280(2), 317–326 (2007). [CrossRef]

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