OFDMA-PON链路关键技术及优化设计研究
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摘要
在宽带业务对速率的需求不断增长和40 Gb/s以太网技术已走向应用的推动下,如何实现可提供“面向未来”的超高宽带的下一代接入网系统,成为当前无源光网络(PON)技术的发展趋势和研究热点。在带宽提升的同时,下一代PON (NGPON)系统还必须能够保持低成本的接入以及实现细粒度的资源分配,才能够有效地承载运营商提供的多元化应用业务。
光学正交频分复用(OFDM),作为面向未来光通信的最具吸引力的候选方案,可高效地支持各种先进调制格式,具有良好的抗色度色散和偏振模色散(PMD)能力、频谱效率高和基于数字信号处理(DSP)实现的自然兼容性等优势。将基于OFDM的高效多址技术与PON结合,所构建的大容量OFDMA-PON系统能够透明地支持多样化业务应用,并可实现时域和频域二维的动态带宽分配,已成为业界积极研究的新热点。
为了实现NGPON单波长40Gb/s的超高速率下行链路,需要引入偏振复用(POLMUX)技术以缓解数模转换(DAC)的速率瓶颈,使得信道利用率和系统容量翻倍。现有的POLMUX系统研究,基本都利用相干检测以实现接收信号偏振解复用,其收发机复杂度较高,不符合PON系统的应用要求。
本文提出了一种低硬件复杂度的基于直接检测和光学单边带调制(OSSB)的POLMUX-OFDMA-PON下行链路方案。在光线路终端(OLT),应用厄米对称映射、希尔伯特变换以及优化偏置的MZ调制器,实现了OSSB信号的产生,之后两路单边带OFDM信号被分别调制到偏振正交双光载波的上下边带,以产生可有效抵抗交叉偏振干涉的POLMUX光信号。在光网络单元(ONU),通过采用偏振分束直接检测、引入新型的MIMO信道估计方法和偏振解复用算法,实现POLMUX-OFDM信号的高效恢复。在光信噪比为40dB时,仿真结果显示本架构下采用16QAM调制的信号传输20km后的误码率可在前向纠错(FEC)门限之内。与POLMUX相干接收方案相比,本方案在成倍提高系统的频谱效率的同时,通过数字信号处理技术有效地简化了OLT/ONU端的光学结构。
Fueled by an exponentially growing demand for broadband services and the advent of 40 Gb/s Ethernet technologies, the R&D focus for passive optical networks (PON) has shifted toward next-generation access systems that are capable of providing a "future-proof" broadband solution. Moreover, it is also critical that these optical access systems be highly flexible and cost-efficient to readily accommodate emerging services and applications. Unlike long-haul networks, practical access networks (<20 km) generally focus on low hardware, low operational complexity and easily reconfiguration.
Optical orthogonal frequency-division multiplexing (OFDM), is natural compatible with advanced modulation formats, resilient to both chromatic and polarization-mode dispersion, spectral efficient, and fit for signal processing (DSP)-based implementation. As such, O-OFDM has been viewed as a emerged as an attractive candidate for future optical transmission systems.
Recent researches have proposed the effective application of orthogonal frequency division multiple access (OFDMA) technologies in PON system, which could simply support heterogeneous applications and dynamic bandwidth allocation with small granularity.
To meet further increase spectral efficiency at ultrahigh speeds, using the two polarization modes, which supported in the SSMF, each to be carried a high-speed OFDM signal present an attractive avenue to enables high-speed transmission systems with lower speed electronics.
In this manuscript, we propose a low complexity OFDMA-PON architecture using POLMUX based on direct detection (DD) and optical single sideband (OSSB) modulation. In the OSSB signal generation, we utilize Hermitian symmetry mapping, Hilbert transformations and the optimized dual-drive MZ modulators to reduce the hardware requirement at the optical line terminal (OLT). Then, two OSSB-OFDM signals are modulated onto two frequency-orthogonal optical carriers to reduce the cross-polarization interference. At the optical network unit (ONU), we introduce a corresponding MIMO channel estimation to recover the POLMUX-OFDM signals with direct detection. This architecture could simplify hardware facilities while increasing spectral efficiency to achieve 40 Gb/s data transmission. Moreover, we discuss the system factors that would affect the performance of the proposed OFDMA-PON architecture based on the simulation results.
光学正交频分复用(OFDM),作为面向未来光通信的最具吸引力的候选方案,可高效地支持各种先进调制格式,具有良好的抗色度色散和偏振模色散(PMD)能力、频谱效率高和基于数字信号处理(DSP)实现的自然兼容性等优势。将基于OFDM的高效多址技术与PON结合,所构建的大容量OFDMA-PON系统能够透明地支持多样化业务应用,并可实现时域和频域二维的动态带宽分配,已成为业界积极研究的新热点。
为了实现NGPON单波长40Gb/s的超高速率下行链路,需要引入偏振复用(POLMUX)技术以缓解数模转换(DAC)的速率瓶颈,使得信道利用率和系统容量翻倍。现有的POLMUX系统研究,基本都利用相干检测以实现接收信号偏振解复用,其收发机复杂度较高,不符合PON系统的应用要求。
本文提出了一种低硬件复杂度的基于直接检测和光学单边带调制(OSSB)的POLMUX-OFDMA-PON下行链路方案。在光线路终端(OLT),应用厄米对称映射、希尔伯特变换以及优化偏置的MZ调制器,实现了OSSB信号的产生,之后两路单边带OFDM信号被分别调制到偏振正交双光载波的上下边带,以产生可有效抵抗交叉偏振干涉的POLMUX光信号。在光网络单元(ONU),通过采用偏振分束直接检测、引入新型的MIMO信道估计方法和偏振解复用算法,实现POLMUX-OFDM信号的高效恢复。在光信噪比为40dB时,仿真结果显示本架构下采用16QAM调制的信号传输20km后的误码率可在前向纠错(FEC)门限之内。与POLMUX相干接收方案相比,本方案在成倍提高系统的频谱效率的同时,通过数字信号处理技术有效地简化了OLT/ONU端的光学结构。
Fueled by an exponentially growing demand for broadband services and the advent of 40 Gb/s Ethernet technologies, the R&D focus for passive optical networks (PON) has shifted toward next-generation access systems that are capable of providing a "future-proof" broadband solution. Moreover, it is also critical that these optical access systems be highly flexible and cost-efficient to readily accommodate emerging services and applications. Unlike long-haul networks, practical access networks (<20 km) generally focus on low hardware, low operational complexity and easily reconfiguration.
Optical orthogonal frequency-division multiplexing (OFDM), is natural compatible with advanced modulation formats, resilient to both chromatic and polarization-mode dispersion, spectral efficient, and fit for signal processing (DSP)-based implementation. As such, O-OFDM has been viewed as a emerged as an attractive candidate for future optical transmission systems.
Recent researches have proposed the effective application of orthogonal frequency division multiple access (OFDMA) technologies in PON system, which could simply support heterogeneous applications and dynamic bandwidth allocation with small granularity.
To meet further increase spectral efficiency at ultrahigh speeds, using the two polarization modes, which supported in the SSMF, each to be carried a high-speed OFDM signal present an attractive avenue to enables high-speed transmission systems with lower speed electronics.
In this manuscript, we propose a low complexity OFDMA-PON architecture using POLMUX based on direct detection (DD) and optical single sideband (OSSB) modulation. In the OSSB signal generation, we utilize Hermitian symmetry mapping, Hilbert transformations and the optimized dual-drive MZ modulators to reduce the hardware requirement at the optical line terminal (OLT). Then, two OSSB-OFDM signals are modulated onto two frequency-orthogonal optical carriers to reduce the cross-polarization interference. At the optical network unit (ONU), we introduce a corresponding MIMO channel estimation to recover the POLMUX-OFDM signals with direct detection. This architecture could simplify hardware facilities while increasing spectral efficiency to achieve 40 Gb/s data transmission. Moreover, we discuss the system factors that would affect the performance of the proposed OFDMA-PON architecture based on the simulation results.
引文
[1]张鹏,阎王阔,FTTxPON技术与应用,人民邮电出版社,北京,2010。
[2]Kazovsky L, Shaw W, Gutierrez D, Cheng N,et al. "Next-Generation Optical Access Networks.' Journal of Lightwave Technology,2007,25(11):3428-3442.
[3]Armstrong J. "OFDM for Optical Communications". Journal of Lightwave Technology,2009, 27(3):189-204.
[4]尹长川,罗涛,乐光新,多载波宽带无线通信技术,北京邮电大学出版社,北京,2004年。
[5]Shieh W, Djordjevic I. "OFDM for Optical Communications", USA:Elsevier (Singapore) Pte Ltd. 2010.389-393.
[6]Shieh W, Bao H, and Tang Y. "Coherent optical OFDM:theory and design". OPTICS EXPRESS, 2008,16(2):841-859.
[7]Djordjevic I, Vasic B. "Orthogonal frequency division multiplexing for high-speed optical transmission." Opt Express 2006; 14:3767-75.
[8]Lowery AJ, Du L, Armstrong J. "Orthogonal frequency division multiplexing for adaptive dispersion compensation in long haul WDM systems. In:Opt. Fiber Commun. Conf., paper no. PDP 39. Aneheim, CA; 2006.
[9]Chandrasekhar S., Xiang Liu, Peckham D. W, "Transmission of a 1.2-Tb/s 24 carrier no-guard-interval coherent OFDM superchannel over 7200-km of ultra-large-area fiber", Optical Communication,2009,1-2
[10]陈雪,无源光网络技术,北京邮电大学出版社,北京,2006年。
[11]顾畹仪,WDM超长距离光传输技术,北京邮电大学出版社,北京,2006年。
[12]周炯盘,庞沁华,通信原理,北京邮电大学出版社,北京,2005年。
[13]Jansen SL, Morita I, Tanaka H. "10*121.9-Gb/s PDM-OFDM transmission with 2-b/s/Hz spectral efficiency over 1000km of SSMF". In:Opt. Fiber Commun. Conf., paper no. PDP2. San Diego; 2008
[14]Shieh W, Yi X, Ma Y, Tang Y. "Theoretical and experimental study on PMD-supported transmission using polarization diversity in coherent optical OFDM systems". Optics Express,2007,15(16): 9936-9947.
[15]Xie C. "PMD Insensitive Direct-Detection Optical OFDM Systems Using Self-Polarization Diversity ". OFC2008, OMM2.
[16]Schmidt BJC, Lowery AJ, and Armstrong J. "Experimental demonstrations of electronic dispersion compensation for long-haul transmission using direct-detection optical OFDM". JOURNAL OF LIGHTWAVE TECHNOLOGY,26(1):196-203.
[17]Abuelmaatti M. "Large Signal Analysis of the Mach-Zehnder Modulator with Various BIAS". Proc. Natl.Sci. Counc. ROC(A),2001,25(4):254-258
[18]Qian D, Cvijetic N, Hu J, et al. "40-Gb/s MIMO-OFDM-PON Using Polarization Multiplexing and Direct-Detection". Optical Fiber Communication Conference (OFC),2009,OMV3
[19]Sander L. Jansen, Itsuro Morita, Tim C. W. Schenk, et al, "Long-haul transmission of 16*52.5 Gbits/s polarization-division-multiplexed OFDM enabled by MIMO processing," Journal of Optical Networking,7:173-182
[20]Xiang Liu, Fred Buchali, "Intra-symbol frequency-domain averaging based channel estimation for coherent optical OFDM," Optics Express,2008,16:21944-21957.
[21]W. Shieh, X. Yi, Y. Ma, et al, "Theoretical and experimental study on PMD-supported transmission using polarization diversity in coherent optical OFDM systems," Optics Express,2007,15: 9936-9947.
[22]Qian D, Cvijetic N, Hu J, et al. "108 Gb/s OFDMA-PON With Polarization Multiplexing and Direct Detection". Journal of Lightwave Technology,2010,28(4):484-493.
[2]Kazovsky L, Shaw W, Gutierrez D, Cheng N,et al. "Next-Generation Optical Access Networks.' Journal of Lightwave Technology,2007,25(11):3428-3442.
[3]Armstrong J. "OFDM for Optical Communications". Journal of Lightwave Technology,2009, 27(3):189-204.
[4]尹长川,罗涛,乐光新,多载波宽带无线通信技术,北京邮电大学出版社,北京,2004年。
[5]Shieh W, Djordjevic I. "OFDM for Optical Communications", USA:Elsevier (Singapore) Pte Ltd. 2010.389-393.
[6]Shieh W, Bao H, and Tang Y. "Coherent optical OFDM:theory and design". OPTICS EXPRESS, 2008,16(2):841-859.
[7]Djordjevic I, Vasic B. "Orthogonal frequency division multiplexing for high-speed optical transmission." Opt Express 2006; 14:3767-75.
[8]Lowery AJ, Du L, Armstrong J. "Orthogonal frequency division multiplexing for adaptive dispersion compensation in long haul WDM systems. In:Opt. Fiber Commun. Conf., paper no. PDP 39. Aneheim, CA; 2006.
[9]Chandrasekhar S., Xiang Liu, Peckham D. W, "Transmission of a 1.2-Tb/s 24 carrier no-guard-interval coherent OFDM superchannel over 7200-km of ultra-large-area fiber", Optical Communication,2009,1-2
[10]陈雪,无源光网络技术,北京邮电大学出版社,北京,2006年。
[11]顾畹仪,WDM超长距离光传输技术,北京邮电大学出版社,北京,2006年。
[12]周炯盘,庞沁华,通信原理,北京邮电大学出版社,北京,2005年。
[13]Jansen SL, Morita I, Tanaka H. "10*121.9-Gb/s PDM-OFDM transmission with 2-b/s/Hz spectral efficiency over 1000km of SSMF". In:Opt. Fiber Commun. Conf., paper no. PDP2. San Diego; 2008
[14]Shieh W, Yi X, Ma Y, Tang Y. "Theoretical and experimental study on PMD-supported transmission using polarization diversity in coherent optical OFDM systems". Optics Express,2007,15(16): 9936-9947.
[15]Xie C. "PMD Insensitive Direct-Detection Optical OFDM Systems Using Self-Polarization Diversity ". OFC2008, OMM2.
[16]Schmidt BJC, Lowery AJ, and Armstrong J. "Experimental demonstrations of electronic dispersion compensation for long-haul transmission using direct-detection optical OFDM". JOURNAL OF LIGHTWAVE TECHNOLOGY,26(1):196-203.
[17]Abuelmaatti M. "Large Signal Analysis of the Mach-Zehnder Modulator with Various BIAS". Proc. Natl.Sci. Counc. ROC(A),2001,25(4):254-258
[18]Qian D, Cvijetic N, Hu J, et al. "40-Gb/s MIMO-OFDM-PON Using Polarization Multiplexing and Direct-Detection". Optical Fiber Communication Conference (OFC),2009,OMV3
[19]Sander L. Jansen, Itsuro Morita, Tim C. W. Schenk, et al, "Long-haul transmission of 16*52.5 Gbits/s polarization-division-multiplexed OFDM enabled by MIMO processing," Journal of Optical Networking,7:173-182
[20]Xiang Liu, Fred Buchali, "Intra-symbol frequency-domain averaging based channel estimation for coherent optical OFDM," Optics Express,2008,16:21944-21957.
[21]W. Shieh, X. Yi, Y. Ma, et al, "Theoretical and experimental study on PMD-supported transmission using polarization diversity in coherent optical OFDM systems," Optics Express,2007,15: 9936-9947.
[22]Qian D, Cvijetic N, Hu J, et al. "108 Gb/s OFDMA-PON With Polarization Multiplexing and Direct Detection". Journal of Lightwave Technology,2010,28(4):484-493.