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25 September 2012, Volume 10 Issue 3

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The whole issue of ZTE Communications September 2012, Vol. 10 No. 3

2012, 10(3):  0. 

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Special Topic

Guest Editorial of 100G and Beyond: Trends in Ultrahigh-Speed Communications (Part II)

Gee-Kung Chang and Jianjun Yu

2012, 10(3):  1-1. 

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This is the second part of a special issue on “100G and Beyond: Trends in Ultrahigh-speed Communications.”The first part of this special issue contained nine fpapers written by service providers, telecommunications equipment manufacturers, and top universities and research institutes. This special issue includes comprehensive reviews as well as original technical contributions covering the rapid advances and broad scope of ultrahigh-speed technologies in optical fiber communications. All papers in this issue have been invited. After peer review, five papers were selected to be published. We hope this issue serves as a timely and high-quality networking forum for scientists and engineers.

The first paper,“FSK Modulation Scheme for High-Speed Optical Transmission,”by Nan Chi et al. from Fudan University, describes the generation, detection, and performance of frequency-shift keying (FSK) for high-speed optical transmission and label switching.

The second paper,“Computationally Efficient Nonlinearity Compensation for Coherent Fiber-Optic System,”by Li et al. from the University of Central Florida, describes how split-step digital backward propagation (DBP) can be combined with coherent detection to compensation for fiber nonlinear impairments.

The third paper,“Flipped-Exponential Nyquist Pulse Technique to Optimize the PAPR in Optical Direct Detection OFDM System,”by Xiao et al. from Hunan University, describes the use of advanced coding to reduce peak-to-average power ratio of the OFDM signal and extend the transmission distance.

The fourth paper,“100Gb/s Nyquist-WDM PDM-16QAM Transmission over 1200-km SMF-28 with Ultrahigh Spectrum Efficiency,”by Dong et al. from ZTE USA, describes the use of pre- and post-equalization to improve transmission system performance and realize ultrahigh spectrum efficiency.

The fifth paper,“Field Transmission of 100G and Beyond: Multiple Baud Rates and Mixed Line Rates Using Nyquist-WDM Technology,”by Jia et al. from ZTE USA, describes a field trial experiment of mixed 100G, 400G, and 1 Tbit/s signal transmission. Joint experiments between ZTE and Deutsche Telecom (DT) have been conducted on long-haul transmission of 100G and beyond over standard single-mode fiber (SSMF) and inline EDFA-only amplification.

We would like to thank all authors for their valuable contributions and all the reviewers for their timely and constructive feedback on all submitted papers. We hope that the contents of this issue are informative and useful for all readers.

FSK Modulation Scheme for High-Speed Optical Transmission

Nan Chi, Wuliang Fang, Yufeng Shao, Junwen Zhang, and Li Tao

2012, 10(3):  2-11. 

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In this paper, we describe the generation, detection, and performance of frequency-shift keying (FSK) for high-speed optical transmission and label switching. A non-return-to-zero (NRZ) FSK signal is generated by using two continuous-wave (CW) lasers, one Mach-Zehnder modulator (MZM), and one Mach-Zehnder delay interferometer (MZDI). An RZ-FSK signal is generated by cascading a dual-arm MZM, which is driven by a sinusoidal voltage at half the bit rate. Demodulation can be achieved on 1 bit rate through one MZDI or an array waveguide grating (AWG) demultiplexer with balanced detection. We perform numerical simulation on two types of frequency modulation schemes using MZM or PM, and we determine the effect of frequency tone spacing (FTS) on the generated FSK signal. In the proposed scheme, a novel frequency modulation format has transmission advantages compared with traditional modulation formats such as RZ and differential phase-shift keying (DPSK), under varying dispersion management. The performance of an RZ-FSK signal in a 4 × 40 Gb/s WDM transmission system is discussed. We experiment on transparent wavelength conversion based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) and in a highly nonlinear dispersion shifted fiber (HNDSF) for a 40 Gb/s RZ-FSK signal. The feasibility of all-optical signal processing of a high-speed RZ-FSK signal is confirmed. We also determine the receiver power penalty for the RZ-FSK signal after a 100 km standard single-mode fiber (SMF) transmission link with matching dispersion compensating fiber (DCF), under the post-compensation management scheme. Because the frequency modulation format is orthogonal to intensity modulation and vector modulation (polarization shift keying), it can be used in the context of the combined modulation format to decrease the data rate or enhance the symbol rate. It can also be used in orthogonal label-switching as the modulation format for the payload or the label. As an example, we propose a simple orthogonal optical label switching technique based on 40 Gb/s FSK payload and 2.5 Gb/s intensity modulated (IM) label.

Computationally Efficient Nonlinearity Compensation for Coherent Fiber-Optic Systems

Likai Zhu and Guifang Li

2012, 10(3):  12-15. 

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Split-step digital backward propagation (DBP) can be combined with coherent detection to compensate for fiber nonlinear impairments. A large number of DBP steps is usually needed for a long-haul fiber system, and this creates a heavy computational load. In a trade-off between complexity and performance, interchannel nonlinearity can be disregarded in order to simplify the DBP algorithm. The number of steps can also be reduced at the expense of performance. In periodic dispersion-managed long-haul transmission systems, optical waveform distortion is dominated by chromatic dispersion. As a result, the nonlinearity of the optical signal repeats in every dispersion period. Because of this periodic behavior, DBP of many fiber spans can be folded into one span. Using this distance-folded DBP method, the required computation for a transoceanic transmission system with full inline dispersion compensation can be reduced by up to two orders of magnitude with negligible penalty. The folded DBP method can be modified to compensate for nonlinearity in fiber links with non-zero residual dispersion per span.

Flipped-Exponential Nyquist Pulse Technique to Optimize PAPR in Optical Direct-Detection OFDM Systems

Jiangnan Xiao, Zizheng Cao, Fan Li, Jin Tang, and Lin Chen

2012, 10(3):  16-21. 

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In this paper, we describe a novel technique based on the flipped-exponential (FE) Nyquist pulse method for reducing peak-to-average power ratio (PAPR) in an optical direct-detection orthogonal frequency-division multiplexing (DD-OFDM) system. The technique involves proper selection of the FE Nyquist pulses for shaping the different subcarriers of the OFDM. We apply this technique to a DD-OFDM transmission system to significantly reduce PAPR. We also investigate the sensitivity of a received OFDM signal with strong nonlinearity in a standard single-mode fiber (SMF).

100 Gbit/s Nyquist-WDM PDM 16-QAM Transmission over 1200 km SMF-28 with Ultrahigh Spectrum Efficiency

Ze Dong

2012, 10(3):  22-27. 

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Nyquist wavelength-division multiplexing (N-WDM) allows high spectral efficiency (SE) in long-haul transmission systems. Compared to polarization-division multiplexing quadrature phase-shift keying (PDM-QPSK), multilevel modulation, such as PDM 16 quadrature-amplitude modulation (16-QAM), is much more sensitive to intrachannel noise and interchannel linear crosstalk caused by N-WDM. We experimentally generate and transmit a 6 × 128 Gbit/s N-WDM PDM 16-QAM signal over 1200 km single-mode fiber (SMF)-28 with amplification provided by an erbium-doped fiber amplifier (EDFA) only. The net SE is 7.47 bit/s/Hz, which to the best of our knowledge is the highest SE for a signal with a bit rate beyond 100 Gbit/s using the PDM 16-QAM. Such SE was achieved by DSP pre-equalization of transmitter-side impairments and DSP post-equalization of channel and receiver-side impairments. Nyquist-band can be used in pre-equalization to enhance the tolerance of PDM 16-QAM to aggressive spectral shaping. The bit-error ratio (BER) for each of the 6 channels is smaller than the forward error correction (FEC) limit of 3.8 × 10^-3 after 1200 km SMF-28 transmission.

Field Transmission of 100G and Beyond: Multiple Baud Rates and Mixed Line Rates Using Nyquist-WDM Technology

Zhensheng Jia, Jianjun Yu, Hung-Chang Chien, Ze Dong, and Di Huo

2012, 10(3):  28-38. 

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In this paper, we describe successful joint experiments with Deutsche Telecom on long-haul transmission of 100G and beyond over standard single mode fiber (SSMF) and with in-line EDFA-only amplification. The transmission link consists of 8 nodes and 950 km installed SSMF in DT’s optical infrastructure. Laboratory SSMF was added for extended optical reach. The first field experiment involved transmission of 8 × 216.8 Gbit/s Nyquist-WDM signals over 1750 km with 21.6 dB average loss per span. Each channel, modulated by a 54.2 Gbaud PDM-CSRZ-QPSK signal, is on a 50 GHz grid, which produces a net spectral efficiency (SE) of 4 bit/s/Hz. We also describe mixed-data-rate transmission coexisting with 1T, 400G, and 100G channels. The 400G channel uses four independent subcarriers modulated by 28 Gbaud PDM-QPSK signals. This yields a net SE of 4 bit/s/Hz, and 13 optically generated subcarriers from a single optical source are used in the 1T channel with 25 Gbaud PDM-QPSK modulation. The 100G signal uses real-time coherent PDM-QPSK transponder with 15% overhead of soft-decision forward-error correction (SD-FEC). The digital post filter and 1-bit maximum-likelihood sequence estimation (MLSE) are introduced at the receiver DSP to suppress noise, linear crosstalk, and filtering effects. Our results show that future 400G and 1T channels that use Nyquist WDM can transmit over long-haul distances with higher SE and using the same QPSK format.

Research Paper

Open Augmented Reality Standards: Current Activities in Standards-Development Organizations

Christine Perey

2012, 10(3):  39-46. 

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Augmented reality (AR) has emerged from research laboratories and is now being accepted in other domains as an attractive way of visualizing information. Before AR can be used in the mass market, there are a number of obstacles that need to be overcome. Several of these can be overcome by adopting open standards. A global grassroots community seeking open, interoperable AR content and experiences began to take shape in early 2010. This community is working collaboratively to reduce the barriers to the flow of data from content provider to AR end user. Standards development organizations and industry groups that provide open interfaces for AR meet regularly to provide updates, identify complementary work, and seek harmonization. The community also identifies deployer and implementer needs, communicates requirements, and discusses emerging challenges that could be resolved with standards. In this article, we describe current activities in international standards-development organizations. We summarize the AR standards gap analysis and shed light on special considerations for using standards in mobile AR.

Mobile Cloud for Personalized Any-Media Services

Bhumip Khasnabish

2012, 10(3):  47-54. 

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In this paper, we define mobile cloud computing and describe how it can be used for delivering advanced any-media services to both nomadic and mobile users. We focus on service delivery that is localized and personalized and suggest that virtualization and tighter cross-layer communication allows for convergence and seamless transition of services. These are also creating new and never-before seen ways of developing and delivering personalized any-media services. We discuss current paradigms for implementing cloud-based any-media services that generate revenue. Future research topics and requirements for evolving network and service elements are also discussed.

Multiple-Constraint-Aware RWA Algorithms Based on a Comprehensive Evaluation Model: Use in Wavelength-Switched Optical Networks

Hui Yang, Yongli Zhao, Shanguo Huang, Dajiang Wang, Xuping Cao, and Xuefeng Lin

2012, 10(3):  55-61. 

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Because of explosive growth in Internet traffic and high complexity of heterogeneous networks, improving the routing and wavelength assignment (RWA) algorithm in underlying optical networks has become very important. Where there are multiple links between different the node pairs, a traditional wavelength-assignment algorithm may be invalid for a wavelength-switched optical networks (WSON) that has directional blocking constraints. Also, impairments in network nodes and subsequent degradation of optical signals may cause modulation failure in the optical network. In this paper, we propose an RWA algorithm based on a novel evaluation model for a WSON that has multiple constraints. The algorithm includes comprehensive evaluation model (CEM) and directional blocking constraint RWA based on CEM (DB-RWA). Diverse constraints are abstracted into various constraint conditions in order to better assign routing and wavelength. We propose using the novel CEM to optimize routing according to an assessed value of constraints on transmission performance. This eliminates the effects of physical transmission impairments in a WSON. DB-RWA based on CEM abstracts directional blocking conditions in multiple links between network nodes into directional blocking constraints. It also satisfies rigorous network specifications and provides flexibility, scalability, and first-fit rate for the backbone, especially in multiple links between WSON nodes.