OECC / ACOFT 2014
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6-10 July 2014
Melbourne, Australia
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Direct Detection SCFDE for Passive Optical Network Based on TDM and Polarization Interleaving Bangjiang Lin, Juhao Li, Hui Yang, Yuanbao Luo, Yangsha Wan, Yongqi He, Zhangyaun Chen State Key Laboratory of Advanced Optical Communication Systems and Networks, School of Electronics Engineering and Computer Science, Peking University, Beijing, 100871, China.
[email protected];
[email protected]
OFDM and SCFDM both on upstream transmission and downstream transmission.
Paper Summary We present TDM-SCFDE-PON architecture for colorless upstream transmission and polarization interleaving SCFDE-PON for high-speed downstream transmission. Compared with OFDM and SCFDM, SCFDE achieves the best receiver sensitivity.
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Introduction Passive optical network (PON) based on orthogonal frequency division multiplexing access (OFDMA) and single carrier frequency division multiplexing access (SCFDMA) are promising candidates for nextgeneration optical access network, due to their resilience to both chromatic and polarization mode dispersion (PMD), spectral efficiency, and natural compatibility with digital signal processing (DSP)-based implementation [1, 2]. OFDMA-PON and SCFDMAPON enable resource allocation both in time and frequency domains, achieving extreme flexibility on both multiple services access and dynamic bandwidth allocation. However, upstream signals from multiple optical network units (ONUs) will interfere each other if they are simultaneously received by one photodiode with direct detection, so the wavelengths of ONUs should be carefully managed. SCFDM/OFDM-PON based on time division multiplexing (TDM) architecture in which upstream or downstream bandwidth resources are allocated with time slots have been proposed and experimentally demonstrated, achieving colorless upstream transmission and maximum compatibility with conventional TDM scheme [3,4]. Compared with OFDM and SCFDM, SCFDE has simple transmitter structure and low peak-to-average power ratio (PAPR), which can reduce the cost of access network. Performance comparisons of coherent optical (CO)-OFDM and COSCFDE have showed that the CO-SCFDE system has similar chromatic dispersion (CD) tolerance while has better nonlinear transmission performance than the COOFDM system [5]. In this paper, we present TDM-SCFDE-PON architecture for colorless upstream transmission and polarization interleaving (PI) [6, 7] SCFDE-PON for high-speed downstream transmission. The PI scheme is a modified approach of polarization division multiplexing (PDM) [8], which has much less computational complexity than PDM at the cost of slightly-decreased spectrum efficiency. The experiment results show that the SCFDE achieves better receiver sensitivity than
978-1-922107-21-3 © 2014 Engineers Australia
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Fig. 1. Transmitter structure for OFDM, SCFDM and SCFDE Remove CP
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Fig. 2. Receiver structure for OFDM, SCFDM and SCFDE
Fig. 1 and Fig. 2 respectively show the transmitter and receiver DSP block diagrams for OFDM, SCFDM and SCFDE. As a modified form, the baseband DSP method of the SCFDM has much in common with that of the OFDM. We can see that the major differences between OFDM and SCFDM are the presences of the discrete Fourier transform (DFT) in the SCFDM transmitter and the inverse DFT (IDFT) in the SCFDM receiver. For this reason, SCFDM is sometimes referred to as DFT-spread OFDM. Because of its inherent single carrier transmission characteristics, SCFDM has lower PAPR than OFDM at the cost of increased computational complexity both at the transmitter and receiver. SCFDE and OFDM have many similarities except SCFDE requires an additional IDFT operation before data demodulation while OFDM requires IDFT at the transmitter. Due to single carrier transmission, SCFDE
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Fig. 3. Experiment setup for direct detection SCFDE-PON based on TDM and PI (EA: electrical amplifier, LD: laser diode, SSMF: standard single mode fiber, PBC: polarization beam combiner, PBS: polarization beam splitter)
has much lower PAPR than SCFDM and OFDM, which reduces nonlinear distortion induced by fiber nonlinearity and components nonlinearity. Experiment setup and results Fig. 3 shows the experimental setup for direct detection SCFDE-PON based on TDM and PI. In the upstream direction, the baseband 3.33-GBaud/s quadrature phase shift keying (QPSK) SCFDE signals are three times upsampled and then up-converted to 2.5-GHz via digital inphase-quadrature (I-Q) modulation. The RF SCFDE signals are uploaded into 10-Gsamples/s Tektronix AWG7122B arbitrary waveform generator (AWG) and converted to optical double sideband (DSB) signals by two intensity Mach-Zehnder modulators (MZM). Due to the low frequency of RF carriers, the power fading of DSB is negligible [9]. A pulse generator outputs opposite pulses to drive two optical switches, so that the two ONUs transmit in different time slots. At the receiver, the optical signals are detected by a 20-GHz photodiode. Then the RF SCFDE signals are amplified by an electrical amplifier (EA) before sampled by a realtime digital storage oscilloscope (Tektronix DPO72004B) operating at 25 GS/s. The sampled SCFDE signals are down converted to baseband and then decoded offline with synchronization, channel equalization and bit error rate (BER) calculation. In the downstream direction, two 3.33-Gbaud baseband QPSK SCFDE signals are three times up-sampled and then up-converted to 2.5 GHz by digital I-Q modulation. The generated waveforms are uploaded into the AWG operating at 10-GS/s. Two tunable lasers are used to facilitate the generation of the two optical carriers with the frequency spacing of 15GHz. Two MZM are utilized to convert the two SCFDE signals to DSB optical signals. Then the two DSB SCFDE signals are combined by a polarization beam combiner (PBC). At the receiver, the DSB PI-SCFDE signals are split by the polarization beam splitter (PBS) and detected by two 20-GHz linear photo-diodes. The electrical RF SCFDE signals are amplified by two EAs before sampled by a real-time digital storage
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oscilloscope operating at 25-GS/s. The sampled SCFDE signals are down-converted and decoded by 2×2 MIMO algorithm. Fig. 4 shows the BER performance for SCFDE, OFDM and SCFDM upstream transmission based on TDM. Each BER is calculated from the average of the two ONUs. For SCFDE modulation, the cyclic prefix (CP) size is 32 and the DFT size is 1024, in which 32 are used for phase estimation. For OFDM and SCFDM modulation, the CP size is 32 and the DFT size is 1024,
Fig. 4. BER performances for SCFDE, OFDM and SCFDM upstream transmission based on TDM
Fig. 5. BER performances for SCFDE, OFDM and SCFDM downstream transmission based on PI
in which 932 are used for data mapping. Comparing the back-to-back and 26.7km SSMF transmission curves, we can see that the chromatic dispersion induced penalty is negligible for all the three DSP based modulations. The received optical powers to achieve the BER of 10-3 are about -15-dBm, -14.3-dBm and -12.5-dBm for SCFDE, SCFDM and OFDM, respectively. Due to the low PAPR, SCFDE achieves the best receiver sensitivity. Fig. 5 shows the BER performances for SCFDE, OFDM and SCFDM downstream transmission based on PI. Each BER is calculated from the average of the two polarizations. For SCFDE modulation, the cyclic prefix (CP) size is 4 and the DFT size is 128, in which 124 are used for carrying data. For OFDM and SCFDM modulation, the CP size is 4 and the DFT size is 128, in which 104 are used for data mapping. The received optical powers to achieve the BER of 10-3 are about 11.5-dBm, -9.5-dBm and -8-dBm for SCFDE, SCFDM and OFDM, respectively. Due to the low PAPR, SCFDE performs better than OFDM and SCFDM. Conclusions We present TDM-SCFDE-PON architecture for colorless upstream transmission and PI-SCFDE-PON for high-speed downstream transmission. Compared with OFDM and SCFDM, SCFDE achieves better receiver sensitivity both on upstream and downstream transmission, due to its low PAPR. Acknowledgements This work was supported in part by the National Basic Research Program of China 973 Program under Grant 2010CB328201 and Grant 2010CB328202, in part by the National Hi-Tech Research and Development Program of China under Grant 60907030, Grant 60736003, and Grant 60931160439, and in part by the National Hi-Tech Research and Development Program of China under Grant 2011AA01A106. References 1. Dayou Qian, Junqiang Hu, Philip Ji, Ting Wang, and Milorad Cvijetic, “10-Gb/s OFDMA-PON for Delivery of Heterogeneous Services,” in OFC/NFOEC Proceeding 2008, paper OWH4. 2. Cheng Zhang, Juhao Li, Fan Zhang, Yongqi He, Hequan Wu, and Zhangyuan Chen, “Experimental demonstration of a single-carrier frequency division multiple address based PON (SCFDMA-PON) architecture,” Opt. Express, vol. 18, no. 24, pp. 24556–24564, 2010. 3. Hui Yang, Juhao Li, Bangjiang Lin, Yangsha Wan, Yong Guo, Lixin Zhu, Li Li, Yongqi He, and Zhangyuan Chen, "DSP-Based Evolution From Conventional TDM-PON to TDM-OFDM-PON," Journal of Lightwave Technology, VOL. 31, NO. 16, August 15, 2013. 4. Juhao Li, Hui Yang, Bangjiang Lin, Yongqi He and Zhangyuan Chen, “Juhao Li, Hui Yang, Bangjiang Lin, Yongqi He and Zhangyuan Chen,” in CLEO Proceeding 2012, paper JTh2A.120. 5. Juhao Li, Chunxu Zhao, Su Zhang, Fan Zhang, and Zhangyuan Chen, “Experimental Demonstration of 120-Gb/s PDM CO-SCFDE Transmission Over 317-km SSMF,”
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Photonics Technology Letters, VOL. 22, NO. 24, December 15, 2010. 6. Bangjiang Lin, JuhaoLi, HuiYang, SongJiang, LixinZhu, YongqiHe, ZhangyuanChen, “Experimental demonstration of optical MIMO transmission for SCFDM-PON based on polarization interleaving and direct detection,” Optics Communications, vol. 285, Issue 24, pp. 5163-5168, 2012. 7. Bangjiang Lin, Juhao Li, Yangsha Wan, Hui Yang, Yongqi He and Zhangyuan Chen, “Efficient MIMO Channel Estimation for OFDM-PON Based on Polarization Interleaving and Direct Detection,” in OFC/NFOEC Proceeding 2013, paper JW2A.70. 8. Dayou Qian, Neda Cvijetic, Junqiang Hu, Ting Wang, “40Gb/s MIMO-OFDM-PON Using Polarization Multiplexing and Direct-Detection,” in OFC/NFOEC Proceeding 2009, paper OMV.3. 9. Bangjiang Lin, Juhao Li, Hui Yang, Yangsha Wan, Yongqi He, Zhangyuan Chen, “Comparison of DSB and SSB transmission for OFDM-PON,” in OFC/NFOEC Proceeding 2012, paper NTu1J.7.
