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Abstract: We propose a scalable metro-access integrated network system enabled by reconfigurable wavelength-division multiplexing ring and high-quality ...
AF4A.29.pdf

ACP Technical Digest © 2012 OSA

A Scalable Metro-Access Integrated Network System with Reconfigurable WDM Central Ring and High-quality OFDMA Access Trees Chen Chen*, Chongfu Zhang, Qiongli Zhang, and Kun Qiu

Key lab of optical fiber sensing and communication networks, Ministry of Education, University of Electronic Science and Technology of China, 611731, Chengdu, China [email protected]

Abstract:

We

propose

a

scalable

metro-access

integrated

network

system

enabled

by

reconfigurable wavelength-division multiplexing ring and high-quality orthogonal frequency­

division multiple access trees. Simulation results successfully verify its feasibility. OC]S codes: (060.2330) Fiber optics communications; (060.2360) Fiber optics links and subsystems 1.

Introduction

With the ever-increasing number of remote end-users, the access capacity of metropolitan area network is soon exhausted meanwhile its access quality is inevitably difficult to be guaranteed. In consequence, the integration of independent metro and access networks is a certain evolution trend. In recent years, many investigations focused on the integration of metro/access networks have been reported. For example, the SARDANA network which integrates the wavelength-division multiplexing (WDM) metro with time-division multiplexing (TDM) access so as to keep the compatibility with existing standards or the MARIN architecture which employs dynamic wavelength allocation to provide a flexible metro-access interface [1,2]. In the above-mentioned two schemes, the WDM-based ring is commonly adopted to increase the access capacity for the integrated network while two different access technologies, namely TDM-based access and WDM-based access, are utilized to connect remote end-users. Nevertheless, the TDM access needs extremely accurate time synchronization to obtain an acceptable performance while the WDM access needs a mass of costly lasers to support multiple end-users [3]. It is obvious that these two access approaches are either too complicated or not cost-effective enough. In comparison, orthogonal frequency-division multiple access (OFDMA) technology is a better solution for the remote access of the metro/access integrated network owing to its high spectrum efficiency, robustness to chromatic dispersion and flexibility of dynamic bandwidth allocation [4,5]. In order to construct a cost-effective and performance-enhanced metro/access integrated network, we propose a

reconfigurable WDM central ring and high-quality OFDMA access tree enabled scalable metro-access integrated network (MAIN) system for the first time. In our simulation verification, the WDM central ring with three central nodes (CNs) is considered and both downstream (DS) and upstream (US) transmissions are demonstrated. 2.

Fig. 1. Architecture of the proposed

MAIN system with three eNs.

Fig. 1 shows the architecture of the proposed MAIN system where three CNs are configured. A central office (CO) is setup to generate the DS WDM comb of single side-band (SSB) OFDM signal. In the central office (CO), three DS lasers are aggregated by an arrayed waveguide grating (A WG) to form the WDM comb source. Then it is modulated with DS-OFDM signal in an intensity modulator

(lM)

to generate the double side-band (DSB) OFDM

signal. An optical filter (OF) is used to generate DS WDM-SSB-OFDM signal. After 20km fiber, DS WDM-SSB­ OFDM signal reaches the first CN and likewise, signal coming out from the first CN arrives at the second CN after passing through another 20km fiber. In the second CN, DS-SSB-OFDM signal at A. grating (FBG) and a circulator while DS-SSB-OFDM signals centered at A.

DS3

DS2

andA.

is reflected by a fiber Bragg USl

are directly transmitted.

AF4A.29.pdf

ACP Technical Digest © 2012 OSA

After amplification, DS-SSB-OFDM signal at A DS2 is combined with US seeding laser centered at A US2 and then the combined signal is launched into lOkm fiber after a circulator for remote access. In one of the multiple remote nodes (RNs) connected with the second CN, the combined signal is firstly sent into another OF to separate the DS­ SSB-OFDM signal at A DS2 and US laser at A US2 as two parts. The DS-SSB-OFDM signal at A DS2 is directly detected by a photodiode (PD) to generate the DS OFDM signal, while the US laser at A US2 is re-used as the US carrier to modulate with US-OFDM signal. Then the US-SSB-OFDM signal at A US2 is sent back to the second CN after lOkm fiber. The US-SSB-OFDM signal at A US2 is combined with DS-SSB-OFDM signals centered at A DS3 andA USl and then the combined signal is amplified and sent to the third CN. All the US-SSB-OFDM signals are received in CO to get the US transmission performance. In our proposed MAIN system, every CN shares the same structure and the only differences between them are

the central wavelength of FBG reflecting band and the wavelength of US seeding laser. Due to its principle of operation, the CN in WDM central ring is reconfigurable on the condition of employing more DS lasers in the CO. Furthermore, every RN also has the same colorless structure for the reason that the US laser shared by each RN is initially installed in their corresponding RN. Therefore, our proposed MAlN system is cost-effective and scalable. 3.

Simulation setup and results

In order to evaluate the performance of our proposed MAlN system, we perform the simulation via VPI

transmission-Maker Version 8.3. In the CO, three DS lasers are centered at 193.ITHz, 193.115THz and 193.13THz, respectively.lOGb/s DS-16QAM-OFDM signal is generated with 64 subcarriers and 0.2 cyclic prefix (CP), while the baseband OFDM signal is up-converted to 7.5GHz. A Mach-Zehnder modulator (MZM) with 30dB extinction ratio (ER) is driven by the 7.5GHz OFDM signal to modulate three DS lasers and thus generate the DS WDM-DSB­ OFDM signal, as shown in Fig. 2(a). A WDM de-multiplexer is used to generate the DS WDM-SSB-OFDM signal as given in Fig. 2(b). The fiber adopted in the simulation is standard single-mode fiber (SSMF) with the attenuation 2 of 0.2e-3dB/m and the dispersion of 16e-6s/m • The adjacent CNs in the WDM central ring are connected with 20km SSMF and the CNs adjacent to CO are also connected with 20km SSMF. Each CN is equipped with a narrowband FBG filter and a circulator to reflect the DS-SSB-OFDM signal at a certain wavelength for remote OFDMA access. The FBG filter used in each CN has 30GHz bandwidth and 20dB rejection. Take the second CN for example, DS-SSB-OFDM signal at 193.1l5THzis reflected and then combined with US seeding laser centered at 193. 16THz. After that, the combined signal is launched into lOkm SSMF for remote access. The second RN is one of the end-users in the OFDMA access tree and an OF is used to separate the DS-SSB-OFDM signal and the US laser. A PlN with 1.0AlW responsivity is utilized to detect the DS-SSB-OFDM signal, while the US laser is modulated by lOGb/s DS-16QAM-OFDM signal which is generated with 64 subcarriers and 0.2 CP and up­ converted to 7.5GHz via a MZM. An OF with 12GHz bandwidth is employed to generate the US-SSB-OFDM signal at 193.16THz and the it is transmitted back along the lOkm SSMF to the second CN. Likewise, each CN drops the DS-SSB-OFDM required by its connected RNs from the signal in the WDM central ring and adds the US­ SSB-OFDM signal from its connected RNs to the WDM central ring. Finally, all the US-SSB-OFDM signals form all the CNs are received in the CO to analyze the US transmission performance.

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