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Novel survivable scheme for OFDM passive optical network
Optik 124 (2013) 4664–4666
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Novel survivable scheme for OFDM passive optical network Lei Tang ∗ , Shibao Wu, Yulong Li, Hongke Lu Key Laboratory of Special Fiber Optics and Optical Access Networks, Shanghai University, 149 Yanchang Road, Shanghai 200072, China
a r t i c l e
i n f o
Article history: Received 1 September 2012 Accepted 22 January 2013
Keywords: Self-surviving Orthogonal frequency division multiplexing (OFDM) Passive optical network (PON) Rayleigh backscattering
a b s t r a c t In this paper, we present a novel self-surviving architecture for orthogonal frequency division multiplexing (OFDM) passive optical network (PON) which can protect distribution and feeder fiber simultaneously. The proposed system uses two different frequency bands for paratactic OFDM-PON and the disrupt signals can be restored via the fiber links of the neighboring OFDM-PON without special protecting fibers. So Rayleigh backscattering and crosstalk can be alleviated in normal working mode. © 2013 Elsevier GmbH. All rights reserved.
1. Introduction Optical orthogonal frequency division multiplexing (O-OFDM) has emerged as a dominate R&D area in the field of high-speed optical communications in recent years [1–7]. Today, the gigabit passive optical network (GPON) offers downstream and upstream bit rates of 2.5 Gb/s and 1.25 Gb/s, respectively [4]. However as bandwidth hungry multimedia application like Internet protocol television (IPTV) and high-definition (HD) video continue to fuel the rise in bandwidth demand in multiuser access networks, the passive optical network (PON) in the various fiber-to-the-x (FTTx) architectures, continues to emerge as the most advanced ‘futureproof’ solution for addressing this need [4,5]. It is envision that in the future PON-based schemes that can both provide symmetric 10+ Gb/s rates [4–7] and can flexibly and cost-efficiently support simultaneous delivery of heterogeneous services over a common platform will form the core of the next-generation optical access network. In this paper, we propose and demonstrate a novel self-surviving architecture for OFDM-PON which can protect distribution and feeder fiber simultaneously. The proposed system uses two different frequency bands for paratactic OFDM-PON in and the disrupt signals can be restored via the fiber links of the neighboring OFDMPON without special protecting fibers. Power monitor (P/M) has been used for controlling the optical switch (OS). Because crossremodulation ONU Group has been employed in this scheme, downstream and upstream carriers are at different wavelength
∗ Corresponding author. Tel.: +86 18801931015. E-mail address: [email protected] (L. Tang). 0030-4026/$ – see front matter © 2013 Elsevier GmbH. All rights reserved. http://dx.doi.org/10.1016/j.ijleo.2013.01.093
bands in the upper or lower fiber links. So Rayleigh backscattering and crosstalk can be alleviated in normal working mode. 2. Network architecture Fig. 1 shows the proposed OFDM-PON architecture capable of protecting from both distribution and feeder fiber links. The proposed scheme consists of one CO (centre office), one RN (remote node) and N ONU groups (a ONU group consists of two ONUs). For the system self-protecting capability, we use N × 2 OSs (optical switches), N × 2 P/Ms (power monitors), N × 2 R/Bs (Red/Blue filters) in CO and 2 × N OSs, 2 × N R/Bs in the N ONU groups. The RN only consists of two cAWGs (array waveguide gratings with cyclic property) and easy to manage. The optical carrier frequency assignment plan as shown in Fig. 2. Here we use Red and Blue band that are spaced by the n free spectral range (nFSR) of the cAWG in the CO. The N × 2 CW (continue wave) lasers generate optical carriers in two bands (the upper part use Red band and lower part use Blue band) which are first fed into N × 2 MZMs (Mach-Zehnder modulators). The N × 2 MZMs are driven by downstream OFDM signals. For working mode, here we take optical carrier 1 and n+1 as example. When 1 which carries downstream signal comes into ONU 1, it is separated into two parts: one is for RX 1 to demodulate the downstream signal; the other is injecting RSOA (reflective semiconductor optical amplifiers) in ONU N + 1 for remodulating the upstream NRZ signal. So Red band for downstream signals and Blue bands for upstream signals in upper fiber link and is the opposite in lower fiber link. Rayleigh backscattering and crosstalk can be alleviated in normal working mode. However, in case of a fiber cut in distribution or in feeder fiber, the P/Ms in the CO or ONUs detect a transmission failure by moni-
L. Tang et al. / Optik 124 (2013) 4664–4666
4665
Table 1 Insert loss of components.
Fig. 1. Proposed OFDM-PON architecture against both distribution and feeder fiber links (P/M = power monitor; OS = optical switch; R/B = Red/Blue filter).
Fig. 2. Optical carrier frequency assignment plan.
toring the optical power of upstream on CO or downstream in ONUs and then trigger the OSs to transfer the disrupted signals via the other branch. For example, when the upper fiber link cut occurs, the OSs in the upper part of the CO and ONU 1–ONU N will trigger from the port 1 to port 2. The Red bands signals are coupled with Blue bands signals in R/Bs at lower part of CO and delivered to their corresponding ONUs through the distribution fibers, cAWG, OSs, B/Rs, and 3-dB splitter. The upstream signals of ONU 1–ONU N can also be transferred to CO by the opposite procedure. Thus, the proposed scheme can automatically protect the transmission failure caused by the fiber cut in feeder fiber link without duplicating another fiber links. The principle of protecting from distribution fiber cutting is the same as distribution fiber. 3. Simulation and results Fig. 3 shows the experimental setup of the proposed selfsurviving OFDM PON architecture. In this experiment, the wavelength bands of Red and Blue are chosen from 1550.12 to 1552.52 nm and 1542.12 to 1544.52 nm with a channel spacing of 0.8 nm, respectively. The output power of each CW laser is set to be 0 dBm. All the transmitters in Red and Blue bands are directly modulated with 10 Gb/s OFDM signals. The 10 GHz OFDM baseband signals were generated via VPI transmission Maker 7.6 with a sampling rate of 10 G symbols/s and 16-QAM used for symbol
Fig. 3. Experimental setup.
Components
Insert loss (dB)
OS R/B Circulator cAWG Fiber link/km Splitter
0.5 0.5 1 4 0.2 3.5
mapping. The lengths of feeder fibers with a chromatic dispersion 16 ps/nm/km and distribution fibers with a chromatic dispersion −160 ps/nm/km were 20 km and 2 km, respectively. At the ONU, an RSOA driven by a 2.5 Gb/s NRZ 27 − 1 pseudorandom binary sequence (PRBS) is used for upstream re-modulation. In addition, an erbium-doped fiber amplifier (EDFA) is also required and gain of the EDFA is set to be 10 dB. After passing into the CO, the upstream OOK signal is detected by a conventional receiver. The power budget is evaluated in latter paragraphs to prove the feasibility of the proposed scheme. Table 1 gives the insert loss of the components used in this article. In normal working mode, the downstream OFDM signals pass from CO to RN, the loss is: N LCO –RN = LCirculator + LOS + LRB + LcAWG + LFeeder
fiber link
(1)
Lastly, the downstream OFDM signals pass from the RN to ONU, the loss is as follows: N LRN –ONU = LDistribution
fiber link
+ LOS + LRB + LSplitter
(2)
So the total loss of the downstream OFDM signals pass from the CO to ONU is: N N N RN LCO –ONU = LCO–RN + LRN–ONU + LcAWG
(3)
In case of upper Fiber link in Fig. 3 cut, the total loss of the downstream OFDM signals pass from the CO to ONU is: P P P RN LCO –ONU = LCO–RN + LRN–ONU + LcAWG + LRayleigh P LCO –RN
N LCO –RN ,
P LRN –ONU
backscattering N LRN –ONU ,
(4)
where = = and LRayleigh backscattering is the loss caused by upstream signals in the same carrier frequency as downstream signals. Similarly, the upstream signals pass from ONU to CO, the loss is the same as downstream signals. Here, the insertion loss for EDFA is ignored. Fig. 4 shows the symbol error rate (SER) performance and 16-QAM OFDM constellation diagram of the downstream OFDM
Fig. 4. SER curve and 16-QAM diagram of downstream OFDM signals.
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L. Tang et al. / Optik 124 (2013) 4664–4666
4. Conclusion In this paper, we present a novel self-surviving architecture for orthogonal frequency division multiplexing (OFDM) passive optical network (PON) which can protect distribution and feeder fiber simultaneously. The proposed system uses two different frequency bands for paratactic OFDM-PON and the disrupt signals can be restored via the fiber links of the neighboring OFDM-PON without special protecting fibers. The power budget is evaluated to prove the feasibility of the proposed scheme. Moreover, as shown by the experimental results, the proposed architecture alleviated the effect of Rayleigh backscattering and crosstalk. Acknowledgements
Fig. 5. BER curve and eye diagram of upstream NRZ signals.
signals. After the transmission over 20 km feeder fiber and 2 km distribution fiber, the receiver sensitivity at the SER of 10−10 is −19.3 dBm. From (3), the total loss experienced by the downstream signal is around 15.3 dB. So the power margin for the downstream signal is 4 dB. From Fig. 4, it is showing clearly that the performance of proposed system in normal state is better than in protected state. The reason is that the downstream OFDM signals and upstream NRZ signals are at different frequency bands that can reduce the effect of Rayleigh backscattering and crosstalk in normal state. The bit error rate (BER) curve and eye diagram of the upstream RRZ data is shown in Fig. 5. The receiver sensitivity at BER of 10−10 is −19.25 dBm in normal state while that is about −18.64 dBm in protected state. So the performance degrades around 0.61 dB. Such a penalty attributed to crosstalk and Rayleigh backscattering effect on upstream transmission. From Figs. 4 and 5, when the receiver sensitivity at BER of 10−10 both for downstream and upstream signals in protect working state, the LRayleigh backscattering is about 0.6 dBm.
This work is supported by Key Program of Natural Science Foundation of China (No. 61132004), Shanghai Science and Technology Development Funds (Nos. 11511502501 and 11511502502), Shanghai Leading Academic Discipline Project, Postgraduate Innovation Foundation of Shanghai University (SHUCX120136). References [1] J. Armstrong, OFDM for optical communications, J. Lightwave Technol. 27 (February (3)) (2009) 189–204. [2] C.W. Chow, C.H. Yeh, C.H. Wang, F.Y. Shih, S. Chi, Signal remodulation of OFDMQAM for long reach carrier distributed passive optical networks, IEEE Photon. Technol. Lett. 21 (June (11)) (2009) 715–717. [3] J. Yu, M.-F. Huang, D. Qian, L. Chen, G.-K. Chang, Centralized lightwave WDM-PON employing 16-QAM intensity modulated OFDM downstream and OOK modulated upstream signals, IEEE Photon. Technol. Lett. 20 (September (18)) (2008) 1545–1547. [4] Y.-M. Linand, P.-L. Tien, Next-generation OFDMA-based passive optical network architecture supporting radio-over-fiber, IEEE J. Select. Areas Commun. 28 (August (6)) (2010) 791–799. [5] N. Cvijetic, D. Qian, J. Hu, T. Wang, Orthogonal frequency division multiple access PON (OFDMA-PON) for colorless upstream transmission beyond 10 Gb/s, IEEE J. Select. Areas Commun. 28 (August (6)) (2010) 781–790. [6] D. Qian, N. Cvijetic, J. Hu, T. Wang, 108 Gb/s OFDMA-PON with polarization multiplexing and direct detection, J. Lightwave Technol. 28 (February (4)) (2010) 484–493. [7] N. Cvijetic, OFDM for next-generation optical access networks, J. Lightwave Technol. 30 (February (4)) (2012) 384–398.
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Novel survivable scheme for OFDM passive optical network Lei Tang ∗ , Shibao Wu, Yulong Li, Hongke Lu Key Laboratory of Special Fiber Optics and Optical Access Networks, Shanghai University, 149 Yanchang Road, Shanghai 200072, China
a r t i c l e
i n f o
Article history: Received 1 September 2012 Accepted 22 January 2013
Keywords: Self-surviving Orthogonal frequency division multiplexing (OFDM) Passive optical network (PON) Rayleigh backscattering
a b s t r a c t In this paper, we present a novel self-surviving architecture for orthogonal frequency division multiplexing (OFDM) passive optical network (PON) which can protect distribution and feeder fiber simultaneously. The proposed system uses two different frequency bands for paratactic OFDM-PON and the disrupt signals can be restored via the fiber links of the neighboring OFDM-PON without special protecting fibers. So Rayleigh backscattering and crosstalk can be alleviated in normal working mode. © 2013 Elsevier GmbH. All rights reserved.
1. Introduction Optical orthogonal frequency division multiplexing (O-OFDM) has emerged as a dominate R&D area in the field of high-speed optical communications in recent years [1–7]. Today, the gigabit passive optical network (GPON) offers downstream and upstream bit rates of 2.5 Gb/s and 1.25 Gb/s, respectively [4]. However as bandwidth hungry multimedia application like Internet protocol television (IPTV) and high-definition (HD) video continue to fuel the rise in bandwidth demand in multiuser access networks, the passive optical network (PON) in the various fiber-to-the-x (FTTx) architectures, continues to emerge as the most advanced ‘futureproof’ solution for addressing this need [4,5]. It is envision that in the future PON-based schemes that can both provide symmetric 10+ Gb/s rates [4–7] and can flexibly and cost-efficiently support simultaneous delivery of heterogeneous services over a common platform will form the core of the next-generation optical access network. In this paper, we propose and demonstrate a novel self-surviving architecture for OFDM-PON which can protect distribution and feeder fiber simultaneously. The proposed system uses two different frequency bands for paratactic OFDM-PON in and the disrupt signals can be restored via the fiber links of the neighboring OFDMPON without special protecting fibers. Power monitor (P/M) has been used for controlling the optical switch (OS). Because crossremodulation ONU Group has been employed in this scheme, downstream and upstream carriers are at different wavelength
∗ Corresponding author. Tel.: +86 18801931015. E-mail address: [email protected] (L. Tang). 0030-4026/$ – see front matter © 2013 Elsevier GmbH. All rights reserved. http://dx.doi.org/10.1016/j.ijleo.2013.01.093
bands in the upper or lower fiber links. So Rayleigh backscattering and crosstalk can be alleviated in normal working mode. 2. Network architecture Fig. 1 shows the proposed OFDM-PON architecture capable of protecting from both distribution and feeder fiber links. The proposed scheme consists of one CO (centre office), one RN (remote node) and N ONU groups (a ONU group consists of two ONUs). For the system self-protecting capability, we use N × 2 OSs (optical switches), N × 2 P/Ms (power monitors), N × 2 R/Bs (Red/Blue filters) in CO and 2 × N OSs, 2 × N R/Bs in the N ONU groups. The RN only consists of two cAWGs (array waveguide gratings with cyclic property) and easy to manage. The optical carrier frequency assignment plan as shown in Fig. 2. Here we use Red and Blue band that are spaced by the n free spectral range (nFSR) of the cAWG in the CO. The N × 2 CW (continue wave) lasers generate optical carriers in two bands (the upper part use Red band and lower part use Blue band) which are first fed into N × 2 MZMs (Mach-Zehnder modulators). The N × 2 MZMs are driven by downstream OFDM signals. For working mode, here we take optical carrier 1 and n+1 as example. When 1 which carries downstream signal comes into ONU 1, it is separated into two parts: one is for RX 1 to demodulate the downstream signal; the other is injecting RSOA (reflective semiconductor optical amplifiers) in ONU N + 1 for remodulating the upstream NRZ signal. So Red band for downstream signals and Blue bands for upstream signals in upper fiber link and is the opposite in lower fiber link. Rayleigh backscattering and crosstalk can be alleviated in normal working mode. However, in case of a fiber cut in distribution or in feeder fiber, the P/Ms in the CO or ONUs detect a transmission failure by moni-
L. Tang et al. / Optik 124 (2013) 4664–4666
4665
Table 1 Insert loss of components.
Fig. 1. Proposed OFDM-PON architecture against both distribution and feeder fiber links (P/M = power monitor; OS = optical switch; R/B = Red/Blue filter).
Fig. 2. Optical carrier frequency assignment plan.
toring the optical power of upstream on CO or downstream in ONUs and then trigger the OSs to transfer the disrupted signals via the other branch. For example, when the upper fiber link cut occurs, the OSs in the upper part of the CO and ONU 1–ONU N will trigger from the port 1 to port 2. The Red bands signals are coupled with Blue bands signals in R/Bs at lower part of CO and delivered to their corresponding ONUs through the distribution fibers, cAWG, OSs, B/Rs, and 3-dB splitter. The upstream signals of ONU 1–ONU N can also be transferred to CO by the opposite procedure. Thus, the proposed scheme can automatically protect the transmission failure caused by the fiber cut in feeder fiber link without duplicating another fiber links. The principle of protecting from distribution fiber cutting is the same as distribution fiber. 3. Simulation and results Fig. 3 shows the experimental setup of the proposed selfsurviving OFDM PON architecture. In this experiment, the wavelength bands of Red and Blue are chosen from 1550.12 to 1552.52 nm and 1542.12 to 1544.52 nm with a channel spacing of 0.8 nm, respectively. The output power of each CW laser is set to be 0 dBm. All the transmitters in Red and Blue bands are directly modulated with 10 Gb/s OFDM signals. The 10 GHz OFDM baseband signals were generated via VPI transmission Maker 7.6 with a sampling rate of 10 G symbols/s and 16-QAM used for symbol
Fig. 3. Experimental setup.
Components
Insert loss (dB)
OS R/B Circulator cAWG Fiber link/km Splitter
0.5 0.5 1 4 0.2 3.5
mapping. The lengths of feeder fibers with a chromatic dispersion 16 ps/nm/km and distribution fibers with a chromatic dispersion −160 ps/nm/km were 20 km and 2 km, respectively. At the ONU, an RSOA driven by a 2.5 Gb/s NRZ 27 − 1 pseudorandom binary sequence (PRBS) is used for upstream re-modulation. In addition, an erbium-doped fiber amplifier (EDFA) is also required and gain of the EDFA is set to be 10 dB. After passing into the CO, the upstream OOK signal is detected by a conventional receiver. The power budget is evaluated in latter paragraphs to prove the feasibility of the proposed scheme. Table 1 gives the insert loss of the components used in this article. In normal working mode, the downstream OFDM signals pass from CO to RN, the loss is: N LCO –RN = LCirculator + LOS + LRB + LcAWG + LFeeder
fiber link
(1)
Lastly, the downstream OFDM signals pass from the RN to ONU, the loss is as follows: N LRN –ONU = LDistribution
fiber link
+ LOS + LRB + LSplitter
(2)
So the total loss of the downstream OFDM signals pass from the CO to ONU is: N N N RN LCO –ONU = LCO–RN + LRN–ONU + LcAWG
(3)
In case of upper Fiber link in Fig. 3 cut, the total loss of the downstream OFDM signals pass from the CO to ONU is: P P P RN LCO –ONU = LCO–RN + LRN–ONU + LcAWG + LRayleigh P LCO –RN
N LCO –RN ,
P LRN –ONU
backscattering N LRN –ONU ,
(4)
where = = and LRayleigh backscattering is the loss caused by upstream signals in the same carrier frequency as downstream signals. Similarly, the upstream signals pass from ONU to CO, the loss is the same as downstream signals. Here, the insertion loss for EDFA is ignored. Fig. 4 shows the symbol error rate (SER) performance and 16-QAM OFDM constellation diagram of the downstream OFDM
Fig. 4. SER curve and 16-QAM diagram of downstream OFDM signals.
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L. Tang et al. / Optik 124 (2013) 4664–4666
4. Conclusion In this paper, we present a novel self-surviving architecture for orthogonal frequency division multiplexing (OFDM) passive optical network (PON) which can protect distribution and feeder fiber simultaneously. The proposed system uses two different frequency bands for paratactic OFDM-PON and the disrupt signals can be restored via the fiber links of the neighboring OFDM-PON without special protecting fibers. The power budget is evaluated to prove the feasibility of the proposed scheme. Moreover, as shown by the experimental results, the proposed architecture alleviated the effect of Rayleigh backscattering and crosstalk. Acknowledgements
Fig. 5. BER curve and eye diagram of upstream NRZ signals.
signals. After the transmission over 20 km feeder fiber and 2 km distribution fiber, the receiver sensitivity at the SER of 10−10 is −19.3 dBm. From (3), the total loss experienced by the downstream signal is around 15.3 dB. So the power margin for the downstream signal is 4 dB. From Fig. 4, it is showing clearly that the performance of proposed system in normal state is better than in protected state. The reason is that the downstream OFDM signals and upstream NRZ signals are at different frequency bands that can reduce the effect of Rayleigh backscattering and crosstalk in normal state. The bit error rate (BER) curve and eye diagram of the upstream RRZ data is shown in Fig. 5. The receiver sensitivity at BER of 10−10 is −19.25 dBm in normal state while that is about −18.64 dBm in protected state. So the performance degrades around 0.61 dB. Such a penalty attributed to crosstalk and Rayleigh backscattering effect on upstream transmission. From Figs. 4 and 5, when the receiver sensitivity at BER of 10−10 both for downstream and upstream signals in protect working state, the LRayleigh backscattering is about 0.6 dBm.
This work is supported by Key Program of Natural Science Foundation of China (No. 61132004), Shanghai Science and Technology Development Funds (Nos. 11511502501 and 11511502502), Shanghai Leading Academic Discipline Project, Postgraduate Innovation Foundation of Shanghai University (SHUCX120136). References [1] J. Armstrong, OFDM for optical communications, J. Lightwave Technol. 27 (February (3)) (2009) 189–204. [2] C.W. Chow, C.H. Yeh, C.H. Wang, F.Y. Shih, S. Chi, Signal remodulation of OFDMQAM for long reach carrier distributed passive optical networks, IEEE Photon. Technol. Lett. 21 (June (11)) (2009) 715–717. [3] J. Yu, M.-F. Huang, D. Qian, L. Chen, G.-K. Chang, Centralized lightwave WDM-PON employing 16-QAM intensity modulated OFDM downstream and OOK modulated upstream signals, IEEE Photon. Technol. Lett. 20 (September (18)) (2008) 1545–1547. [4] Y.-M. Linand, P.-L. Tien, Next-generation OFDMA-based passive optical network architecture supporting radio-over-fiber, IEEE J. Select. Areas Commun. 28 (August (6)) (2010) 791–799. [5] N. Cvijetic, D. Qian, J. Hu, T. Wang, Orthogonal frequency division multiple access PON (OFDMA-PON) for colorless upstream transmission beyond 10 Gb/s, IEEE J. Select. Areas Commun. 28 (August (6)) (2010) 781–790. [6] D. Qian, N. Cvijetic, J. Hu, T. Wang, 108 Gb/s OFDMA-PON with polarization multiplexing and direct detection, J. Lightwave Technol. 28 (February (4)) (2010) 484–493. [7] N. Cvijetic, OFDM for next-generation optical access networks, J. Lightwave Technol. 30 (February (4)) (2012) 384–398.