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MALEKIZANDI, Mohammadreza Power budget extension for OFDM-TDM-WDM PON Mohammadreza Malekizandi*1 , Ali Emsia1 , Dieter Briggmann1 , Quang Trung Le1 , Ivan Djordjevic2 , and Franko K¨uppers1 1 TU 2 * Corresponding
Darmstadt, Merckstrasse 25, Darmstadt, Germany;
University of Arizona, 1401 E University Blvd, Tucson, USA;
Author:
[email protected] Abstract
In this paper we are going to transmit the Orthogonal Frequency Division Multiplexing (OFDM) modulated signal in a hybrid of Time Division Multiplexing (TDM) and Wavelength Division Multiplexing (WDM) for Passive Optical Network (PON) system to have the most efficient use of bandwidth. Furthermore in order to decrease the number of Central Offices (COs) and also increase the number of Optical Network Users (ONUs) we try to find a suitable power budget extension method.
I NTRODUCTION Due to progressive bandwidth demand for newfangled bandwidth intensive applications, spectrum efficiency in PONs will be an issue very soon. From the other side network operators are always interested to deFigure 1: OFDM treansmitter [3] crease the deployment costs and at the same time cover more users. Therefore, we propose to use the OFDM To receive the OFDM, as it is depicted in Fig. 2, which is one of the most bandwidth efficient candiOOFDM signal is received and down converted from dates for high data rate transmission and also power optical frequency to intermediate frequency, by an budget extension, which helps to decrease the number avalanche photo diode (APD) and then to the base of COs and increase the reach of the optical links [1]. band frequency, by an IQ mixer. After demodulating OFDM signal, DSP implementation is needed to estimate the effect of channel and correct the phase of OFDM T RANSCEIVER data before demapping and measuring the Bit Error Rate (BER). To generate the Optical OFDM (OOFDM), in the transmitter (Fig. 1), digital bits are generated and mapped to a higher order modulation format (for example DQPSK), and then passed through an OFDM modulator. After that, the baseband signal will be up converted to the intermediate frequency by IQ mixer and finally to the optical frequency with the use of a Figure 2: OFDM receiver [3] Mach Zender Modulator (MZM) and a laser. Conventional OOFDM consists of an optical carrier and two sidebands. Because of fiber dispersion and nonlinear- POWER BUDGET EXTENSION CONFIGURATIONS ity of optical devices, these sidebands would be moved into a different phase which causes self-cancellation As we mentioned we implement a WDM-TDM PON and signal degradation. Single Side Band (SSB) can to use the advantages of both of WDM and TDM. Hytreat this problem and combat the power [2]. There- brid PON attempts to combine the large aggregated fore we use an optical bandpass filter (OBPF) after capacity of WDM-PON with the efficient utilization MZM to filter out one of the sidebands and build SSB- of resources of TDM-PON. Hybrid PON also adopts OOFDM. multiple channels, as in WDM-PON, while allowing
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channel sharing among multiple ONUs, as in TDMPON. As it is depicted in Fig. 3 our WDM setup consists of four 10 Gbit/s OFDM channels with the 50 GHz channel spacing according to ITU-Grid. Channels are multiplexed and launched to the transmission line via an Arrayed Waveguide Grating (AWG) multiplexer. In the feeder line, we have 40 km SMF and a variable optical attenuator (VOA) to see how long the feeder line can be prolonged. In the RN, optical signal will be amplified by SOA or EDFA. Then the channels will be separated via AWG demux and each wavelength can serve many ONUs separately. At the end, in the access line there is 10 km fiber and a VOA to see how many ONUs can be served by splitting data into different paths. The data can be split into different paths by a 1:M splitter.
nel (1:64 splitters),which means 256 users in total and the remaining power is 9 dB for loss compensation.
Figure 4: Comparison of EDFA and SOA for OFDM WDM, without fiber [3]
Figure 3: OFDM-WDM Power budget extension [3] Simulation results are depicted in Fig. 4 & 5 in case of without and with fiber, respectively. The illustrated curves are called isoBER. In this paper we assume forward error correction FEC standard, therefore we consider bit error rate of 10−3 . As you can see from Fig. 5 in feeder line there is 13 dB power budget penalty, which means extending the feeder line up to 65 km is possible. In the access line in case of SOA we can use 18 dB power budget to split between 16 ONUs in each channel (1:16 splitters),which means 64 users in total and the remaining power is 6 dB for loss compensation, which can be used for RN demultiplexer and downstream/upstream circulators. But in case of EDFA in the access line we can use 27 dB power budget to split between 64 ONUs in each chan-
Figure 5: Comparison of EDFA and SOA for OFDM WDM, 40 km feederline & 10 km access line [3]
C ONCLUSION In this paper we used OFDM to improve the bandwidth efficiency in hybrid of TDM and WDM-PON and also tried to find a suitable power budget extension method in order to decrease the number of COs and increase the number of ONUs. We saw, although SOA is much cheaper than EDFA, but since EDFA has better performance and the number of severed users is almost four times more than SOA case, additional costs would be covered easily.
[1] A. Emsia, et al., IPC (2013). [2] C. Wang, et al., Photonics Technology Letters, IEEE 22, 820 (2010). [3] M. Malekizandi, Higher Order Modulation Formats for PON, Master’s thesis, TU Darmstadt (2013).
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