International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 6, June 2012)83
Comparison of CSRZ, DRZ and MDRZ Modulation Formats
for High Bit Rate WDM-PON System using AWG
Malti
1, Meenakshi Sharma
2, Anu Sheetal
31Sai Institute of Engg. & Tech., Amritsar, Punjab, India 2Sri Sai College of Engg. & Tech., Pathankot, Punjab, India
3GNDU, Regional Campus, Gurdaspur, Punjab, India
Abstract--In this paper, we have simulated 8 channel
WDM-PON system for downstream signals using carrier suppressed return-to-zero (CSRZ), duobinary return-to-zero (DRZ) and the modified duobinary return-to-zero (MDRZ) modulation formats. WDM-PON system has been analyzed by varying input power from 0 to 20dBm for different modulation formats in order to find the optimum modulation format for a high bit rate optical transmission system. Further, the system is evaluated 2.5Gb/s & 5Gb/s bit rates upto 130km in terms of Q value and eye opening for CSRZ, DRZ and MDRZ data formats. It is found that CSRZ is superior to DRZ and MDRZ and system gives optimum performance at input power Pin=15dBm.
Keywords: WDM-PON, CSRZ, DRZ, MDRZ, OLT, ONU.
I. INTRODUCTION
Passive optical networks are receiving much interest because they represent the cheapest way to provide fiber to the home [1]. Wavelength Division Multiplexed Passive Optical Networks (WDM-PONs) are expected to play a key role in realizing the next generation scalable and flexible access networks. A WDM-PON receives a dedicated wavelength for each Optical network Unit (ONU) thus providing better privacy, scalability. A WDM-PON solution provides scalability because it can support multiple wavelengths over the same fiber infrastructure, is inherently transparent to the channel bit rate, and it does not suffer power-splitting losses [2,3].
The bandwidth demand in the access networks has been increasing rapidly over the past several years. Residential subscribers demand first-mile access solutions that have high bandwidth and offer media-rich services. Similarly, corporate users demand broadband infrastructure through which they can connect their local-area networks to the internet backbone. The predominant broadband access solutions deployed today are the digital subscriber line (DSL) and community antenna television (CATV) / (cable TV) based networks.
International Journal of Emerging Technology and Advanced Engineering
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The AWG is a passive optical device with the special property of periodicity, which is the cyclic nature by which multiple spectral orders are routed to the same output port from an input port.
Bock et al. [4] described WDM/TDM-PON architecture by using Free Spectral Range (FSR) periodicity and AWG. In this a shared tunable laser, photo receiver, DBA and remote modulation were used for transmitter and receiver. Transmission test showed correct operation at 2.5Gb/s up to 30km. By mean of optical transmission test the authors demonstrated that this architecture was feasible and offered good performance with low optical losses as compared to other PON architectures.
Calabretta et al. [5] presented an innovative architecture to realize a single feeder bidirectional WDM/TDM-PON on modified NRZ (DPSK) downstream signals at 20kb/s and narrowband AWG. AWG was used as channel distributor and simultaneously demodulator for all the DPSK channels. Semiconductor Optical Amplifier (SOA) was used for bidirectional amplification and compensated splitter losses. In this remodulated upstream signals were obtained at 1Gb/s. The experimental result showed error free transmission for both upstream and downstream signals.
Feny et al. [6] discussed a scheme in which modified NRZ format was used to realize multicast WDM-PON by adjusting downstream extinction ratio and achieved good BER rate performance for upstream signals.
Han et al. [7] proposed a WDM-PON model with multicast capability like high scalability multi-wavelength converter and single copy broadcast capability by employing multistage AWGs at remote node. The result of this architecture was evaluated in terms of cost, scalability, link capacity and bandwidth per user in both upstream and downstream signals. In this architecture, the existing passive star coupler was replaced by a special passive optical device.
Bosco et al. [8] demonstrated the use of NRZ, RZ and CSRZ modulation formats in an ultra dense wavelength-division multiplexing (UDWDM) scenario at 40 Gb/s with 50GHz channel spacing. They showed that, due to the narrow transmission filtering, the RZ pulse becomes NRZ-like, and the CSRZ modulation is duobinary coded. Furthermore, they established that NRZ modulation does not benefit from the introduction of a transmission optical filter, while it takes advantage of the orthogonal polarization launch of adjacent channels, but its performance is still worse than the RZ and CSRZ performance in a UDWDM scenario.
Dahan and Eisenstein et al. [9] compared the performance of three different modulation formats non return-to-zero (NRZ), return-to-zero (RZ) and carrier-suppressed RZ (CS-RZ) for 40-Gb/s channels spaced at 100GHz using backward-pumped distributed Raman amplification over transmission distance of 375 km.
They proved that the CS-RZ format achieves good performances in forward-pumped Raman amplification and backward pumped configuration because of the high nonlinear regime.
Rajniti et al. [10] compared the performance of two modulation formats non zero (NRZ), return-to-zero (RZ) for 2.5Gb/s bidirectional WDM/TDM-PON using narrowband AWG. They investigated the impact of extinction ratio (ζ) of Mach-Zehnder (MZ) amplitude modulator on the performance of WDM-PON for varying optical fiber lengths. The system performance had been analyzed by varying the value of ζ from 2 to 22dB. They found that the system gave optimum performance at extinction ratio (ζ) value 20dB. Further, the effect of variation in the input power (from 0 to 20dBm) and transmission distance upto 60km was observed in terms of Q value and eye opening for NRZ and RZ data formats. They found that NRZ was superior to RZ and system gave optimum performance at input power Pin=10dBm.
In this paper, we have extended the work of reference [10], they compared the performance of two modulation formats non return-to-zero (NRZ), return-to-zero (RZ) for 2.5Gb/s bidirectional WDM/TDM-PON using narrowband AWG by varying input power (from 0 to 20dBm) and transmission distance upto 60km. We have evaluated the system performance by using advanced modulation formats and transmission distance upto 130km has been observed in terms of Q value and eye opening factor. Here, in section 2, the system description and simulation parameters have been described. In section 3, the results of the simulated system have been reported for different modulation data formats, signal input power, bit rate and distance. Finally in section 4, conclusions are made.
II. SYSTEM DESCRIPTION AND SIMULATION
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Fig.1: Schematic of Simulation SetupThree different types of modulation formats carrier suppressed return to zero (CSRZ), duobinary return to zero (DRZ) and modified return to zero (MDRZ) has been used. An Erbium Doped Fiber Amplifier with gain 17dB and noise figure 6dB is used in the transmitter to boost the optical signal to the desired power level. The EDFA is followed by power splitter and upstream circulator with return loss and isolation of 60dB Array waveguide grating AWG (8×8) with frequency of 193.4THz and bandwidth = 10GHz is used for upstream and AWG (1×8) with frequency of 1550 nm and bandwidth of 10GHz is used for downstream. A bidirectional Single Mode Fiber SMF fiber with parameters attenuation of 0.24dB/km, dispersion slope of 0.075 ps/km-nm2 and dispersion at 1550nm is 16.75ps/km-nm has been used and the length of fiber has been varied up to 130km.
III. RESULTS AND DISCUSSION
Three modulation formats have been compared by varying input power and transmission distance up to 130km for WDM-PON system in terms of Q value [dB] and eye opening factor. The Fig. 2(a), 2(b) and 2(c) shows the graphical representation of Q value as a function of transmission distance at varied input power and bit rate of 2.5Gb/s for CSRZ, DRZ and MDRZ data formats for downstream data respectively.
10 20 30 40 50 60 70 80 90
0 20 40 60 80 100 120 140 160 180
Length(kms)
Q
.f
a
c
to
r(
d
B
)
Power = 10dBm & Bit rate = 2.5Gb/s
CSRZ DRZ MDRZ
(a)
10 20 30 40 50 60 70 80 90 100 110
0 50 100 150
Length(kms)
Q
.f
a
c
to
r(
d
B
)
Power = 15dBm & Bit rate = 2.5Gb/s
CSRZ DRZ MDRZ
(b)
0 20 40 60 80 100 120 140
0 10 20 30 40 50 60
Length(kms)
Q
.f
a
c
to
r(
d
B
)
Power = 20dBm & Bit rate = 2.5Gb/s
CSRZ DRZ MDRZ
(c)
Fig.2 Length Vs Q.factor for CSRZ, DRZ and MDRZ modulation formats at bit rate = 2.5Gb/s (a)Pin = 10dBm (b)Pin = 15dBm (c)Pin =
20dBm
It is cleared from the graphs with increase in power and length of fiber, the system performance has also been increased. But after Pin = 15dBm the system performance
has been degraded due to more dominance of non linear effects like Cross Phase Modulation (XPM) and Four Wave Mixing (FWM).
DFB Laser Array
WDM Multi-plexer
Circu-lators
CSRZ/DRZ or MDRZ Modulator
AWG 8*8
Circu-lators
3R-Regenerator Low Pass Bessel
Filter
Q measurement BER Analyser
PIN Detector
Optical Transmitter
Power Splitter EDFA
AWG 1*8
International Journal of Emerging Technology and Advanced Engineering
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It has been observed that the system give repeaterless transmission up to 128km. When bit rate = 2.5Gb/s, the CSRZ gives better performance as compared to DRZ and MDRZ modulation data formats.
10 15 20 25 30 35 40 45 50 55 60
10 15 20 25 30 35 40 45 50 55
Length(kms)
Q
.f
a
c
to
r(
d
B
)
Power = 10dBm & Bit rate = 5Gb/s
CSRZ DRZ MDRZ
(a)
10 20 30 40 50 60 70 80 90 100
0 10 20 30 40 50 60 70 80
Length(kms)
Q
.f
a
c
to
r(
d
B
)
Power = 15dBm & Bit rate = 5Gb/s
CSRZ DRZ MDRZ
(b)
0 20 40 60 80 100 120
0 10 20 30 40 50 60 70
Length(kms)
Q
.f
a
c
to
r(
d
B
)
Power = 20dBm & Bit rate = 5Gb/s
CSRZ DRZ MDRZ
(c)
Fig.3 Length Vs Q.factor for CSRZ, DRZ and MDRZ modulation formats at bit rate = 5Gb/s.(a)Pin = 10dBm (b)Pin = 15dBm (c)Pin =
20dBm
The Fig. 3(a), (b) & (c) shows the graphical representation of Q value as a function of transmission distance at varied input power and bit rate of 5Gb/s for CSRZ, DRZ and MDRZ data formats for downstream data respectively.
It is clear from the graphs as the bit rate increases the system performance has been decreased. It has been observed that MDRZ gives better performance as compared to DRZ and CSRZ, when bit rate = 5Gb/s. It is also observed that at bit rate = 5Gb/s MDRZ shows optimum performance at input power Pin = 15dBm as compared to
CSRZ and DRZ.
We have evaluated the system performance by varying bit rate at 2.5Gb/s and Gb/s and it is observed that the system gives optimal transmission when the data is transmitted at the bit rate of 2.5Gb/s.
Fig.4.shows the eye diagrams for downstream data respectively for CSRZ, DRZ and MDRZ modulation formats at distance 60km. These results further endorse the results of earlier discussion. The results obtained are also consistent with the results reported in [8].
(a)
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(c)Fig.4. Received Eye diagrams at bit rate 5Gb/s for downstream over
transmission distance 60 km when input power Pin = 20dBm for
modulation formats (a) CSRZ (b) DRZ (c) MDRZ
IV. CONCLUSIONS
In this paper, we have simulated the WDM-PON system by varying input power Pin from 0 to 20dBm, bit rate at
2.5Gb/s, 5Gb/s and 10Gb/s and length of fiber up to 130km. It is observed that at bit rate 2.5Gb/s, the faithful transmission distance covered is 128km and at bit rate 5Gb/s, the faithful transmission distance covered is120km.Further, it is concluded that at bit rate 2.5Gb/s and 5Gb/s the CSRZ and MDRZ shows the optimum performance.
REFERENCES
[1] Asier Villafranca Velasco, Member, OSA, Juan Carlos Aguado, and María Ángeles Losada Binué Juan José Martínez, Juan Ignacio Garcés Gregorio, Member, IEEE, Alicia López Lucia, “Novel WDM-PON Architecture Based on a Spectrally Efficient IM-FSK Scheme Using DMLs and RSOAs” , journal of lightwave technology, vol. 26, no. 3, february 1, 2008.
[2] Zhaowen Xu, Yang Jing Wen, Wen-De Zhong, Attygalle, M, Xiaofei Cheng, Yixin Wang, Tee Hiang Cheng,Chao Lu “WDM-PON architecture with a single shared interferomatric filter for carrier reuse upstream,” Journal of Lightwave Technology, Vol.25 (2007).
[3] Manish Choudhary, Bipin Kumar “ Analysis of next generation PON architecture for optical broadcast access networks”IEEE Comm. Mag. (2006).
[4] Carlos Bock, Josep Prat, Stuart D. Walker “Hybrid WDM/TDM-PON using AWG FSR and featuring centralized light generation and dynamic bandwidth allocation,” Spanish ministerio technology project TIC2002-00053 (2005).
[5] N.Calabretta,M.Presi,R.Proietti,G.Contestabile and E.Ciaramella “ A bidirectional WDM/TDM-PON using DPSK downstream signals and a narrowband AWG,” IEEE Photonics Technology Letters. Vol.19.No.16 (2007).
[6] Hanlin Feny, Fengqing Liu “A novel scheme of multicast WDM-PON using modified NRZ signal format,” Proceedings of the IEEE INFOCOM (2009).
[7] Kyeong-Eun Han, Kyoung-Min Yoo, Won Hyuk Yang, Young-Chon Kim “Design of AWG based WDM-PON architecture with multicast capability,” Proceedings of the IEEE INFOCOM (2008). [8] G. Bosco, A. Carena, V. Curri, R. Gaudino, P. Poggiolini, On the
use of NRZ, RZ, and CSRZ Modulation at 40 Gb/s with narrow DWDM channel spacing, J. Lightwave Technol. 20 (9) (2002) 1694. [9] D. Dahan, G. Eisenstein, Numerical comparison between distributed and discrete amplification in a point-to-point 40-Gb/s 40-WDM-based transmission system with three different modulation formats, J. Lightwave Technol. 20(2002) 379.
