This paper mainly considers the space-division-multiplexing multiplexing elastic optical data center network (SDM-EODCN) as the application scenario and proposes a link resource-aware virtual optical network (VON) mapping approach. It not only maximizes spectrum utilization but also enhances the success rate of VON mapping. We define link spectrum fragment awareness (LSFA) and link resource contribution (LRC), and present the mapping calculation formulas of virtual links and physical links. In order to improve the spectrum efficiency, an integer linear programming (ILP) model is proposed to minimize the total number of the occupied frequency slots and two heuristic VON mapping approaches achieve more efficient resource allocation. Simulation results show that the proposed LSFA VON mapping approach yields results closest to those solutions from the ILP model, demonstrating better performance compared to other approaches. Therefore, the formulated ILP model and the proposed LSFA VON mapping approach can effectively reduce the average rejection rate and spectrum fragmentation rate of VON mapping, and improve the availability of spectrum resources in SDM-EODCNs.

In this paper, we proposed a resource-level classification and modulation-adaptive (RLC-MA) algorithm to reduce the latency and improve the network resource efficiency in cloud-edge data center optical networks. Simulation results show that the proposed RLC-MA algorithm can effectively reduce blocking probability, spectrum occupancy, and latency compared to existing task offloading approaches.

An impairment-aware spectrum allocation scheme with dedicated path protection was proposed to reduce blocking probability and enhance transmission quality in the C+L band elastic optical networks. Simulation results verify the effectiveness of the proposed scheme.

Timing synchronization is challenging under severe bandwidth limitations due to the requisite high-frequency components are suppressed, rendering conventional clock recovery (CR) algorithms ineffective. In such cases, clock tones (CTs) become indistinguishable from noise or are entirely masked. To overcome this challenge, we propose a novel phase detector (PD), the normalized interpolated-power Gardner (NIP-Gardner), which employs nonlinear normalization of interpolated power to enhance the CT and improve timing extraction. Compared with the interpolated-power Gardner (IP-Gardner) and fourth-power Gardner (FP-Gardner) PDs, the NIP-Gardner PD achieves lower residual jitter and enhanced phase-locked-loop (PLL) bandwidth robustness. We experimentally validate its effectiveness in a 60-GBd polarization-division-multiplexed quaternary phase-shift keying (PDM-QPSK) system with a limited 3-dB transmitter bandwidth reduced to 7.5 GHz, which is 1/8 of the baud rate. Results indicate that the NIP PD outperforms existing schemes in terms of clock-to-noise ratio (CNR), residual timing jitter performance, and residual chromatic dispersion (rCD) tolerance. In back-to-back (BTB) experiments, the NIP scheme achieves optical signal-to-noise ratio (OSNR) gains of 1.2 dB and 3.6 dB relative to the IP and FP schemes, respectively. In 300 km fiber transmission experiments, it demonstrates an improvement in rCD tolerance of 125.22 ps/nm (150%) over the IP scheme and 166.96 ps/nm (400%) over the FP scheme.

【Objective】With the continuous development of Artificial Intelligence (AI), a wide range of AI-driven applications is rapidly emerging. The growing service requirements have progressively surpassed the capacity of the existing network bandwidth resources, thus making spectrum expansion an essential avenue for capacity enhancement. Therefore, introducing C+L band optical networks can effectively address the problem of limited bandwidth capacity.【Methods】To reduce blocking probability and ensure network survivability, this paper considers the impact of spectrum allocation on both the C and L bands, employing different strategies for the selection of the working path and protection path, spectrum resource assignment, and modulation format selection. We propose an Impairment-Aware Spectrum Allocation method with Dedicated Protection (IASADP) in C+L band elastic optical networks. For comparison, three dedicated protection strategies are introduced: the Kth Shortest-Path First-Fit with Dedicated Protection method (KSPFFDP), Revalidated Signal-to-Noise Ratio with Dedicated Protection method (RSNRDP), and Maximize Signal-to-Noise Ratio with Dedicated Protection method (MSNRDP). The performance of these methods is analyzed under different network loads in terms of blocking probability and spectrum utilization.【Results】Simulation results show that, compared with KSPFFDP, RSNRDP, and MSNRDP, the proposed method significantly reduces the blocking probability, improves the spectrum utilization, and achieves higher transmission quality.【Conclusion】Therefore, the IASADP effectively achieves the goal of optimizing spectrum resources in C+L band optical networks.

This study demonstrates the effectiveness of a simplified maximum likelihood sequence estimation (MLSE) approach in enhancing the performance of coherent optical fiber transmission systems, particularly under conditions of linear and nonlinear symbol correlation. To counter the high complexity of traditional MLSE in high-speed systems, we introduce what we believe to be a novel simplification method. This approach replaces the conventional channel impulse response (CIR) convolution with a look-up table (LUT) and simplifies the Euclidean distance (ED) calculations. Additionally, we provide a detailed analysis of algorithmic operations, complementary metal oxide semiconductor (CMOS) transistor count, and power consumption across various technology nodes. The proposed simplified MLSE scheme has the potential to reduce implementation complexity to approximately 5% of the conventional approach. The proposed low-complexity approach was verified with both simulations and experiments. The results show that the performance loss is less than 0.3 dB in Q-factors for both linear and nonlinear bandwidth-constrained transmission scenarios. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

To extend a fiber-optic transmission system from traditional C band to C+L band, it is necessary to place Raman amplifiers to improve the optical signal-to-noise ratios (OSNR) of lightpaths. We develop a heuristic algorithm for optimal Raman amplifier placement. Simulations show that the proposed algorithm is efficient to require up to 50% fewer Raman amplifiers compared with benchmark schemes.

We review the progress of correlated multisymbol modulation scheme for coherent optical fiber transmissions, which treats inter-symbol-interference as symbol correlation to achieve high spectral efficiency. We discuss key digital signal processing algorithms for implementing the scheme.

Significance As cloud computing, the Internet of Things, and 5G technologies rapidly develop, global network traffic has experienced exponential growth. This surge in traffic, both within and between data centers, has fostered an ever increasing demand for high-speed and high-performance optical fiber transmission systems for short- and medium-reach distances. Currently, the intensity-modulation and direct-detection (IMDD) system employing four-level pulse amplitude modulation (PAM4) is the primary solution for cost-sensitive short- and medium-reach transmission scenarios. The IMDD system features a simple structure, low power consumption, and low cost. However, it utilizes only the amplitude dimension of the optical carrier to transmit information, leaving other optical domain dimensions untapped. Additionally, the IMDD system's limited receiver sensitivity poses a challenge when higher-order modulation formats are tried to improve spectral efficiency. Coherent detection systems with higher receiver sensitivity are characterized by utilizing the polarization, phase, and amplitude of optical carriers to transmit information, which leads to higher spectral efficiency. However, their practical implementation in short-to medium-reach transmission scenarios brings about challenges including increased system complexity, higher power consumption of digital signal processing (DSP) chips employed in coherent detection systems, and the need for a high-performance narrow linewidth laser as a local oscillator (LO). These factors limit the widespread adoption of coherent detection in such scenarios. To this end, researchers have explored simplified coherent schemes, including self-homodyne coherent detection (SHCD) and differential self-coherent detection (DSCD) schemes for new-generation short-and medium-reach transmission systems. These schemes strike a balance between system performance and complexity, with higher receiver sensitivity than IMDD systems, and less complexity and costs than standard coherent detection. Among these schemes, the SHCD scheme has caught considerable attention. The SHCD system eliminates the need for a narrow linewidth laser as an LO on the receiver side by splitting the laser power at the transmitter between the transmitted signal and a remote LO. This allows utilizing an uncooled large linewidth laser in SHCD systems while the receiver sensitivity remains high. Extensive research efforts have been devoted to advancing the development of this scheme. The DSCD scheme, based on a differential modulation format, provides an alternative approach. It utilizes the relative phase information between two adjacent signals for self-coherent signal demodulation. A notable advantage of this scheme is its high tolerance to laser linewidth, which eliminates the need for LO and carrier phase recovery at the receiver side. Consequently, it enables the utilization of large linewidth lasers for coherent detection to reduce system cost and improve receiver sensitivity. In contrast to the SHCD scheme, the DSCD scheme overcomes the performance degradation caused by mismatched transmission paths of the signal and the remote LO. Recent research findings presented in our paper highlight that, in systems where receiver electrical noise is the primary impairment, the theoretical performance of DSCD is equivalent to that of SHCD. Additionally, DSCD outperforms SHCD in systems dominated by optical noise introduced by optical amplifiers. As a result, the DSCD technology provides a promising solution for high-speed and high-performance optical fiber transmission systems. Its advantages include high receiver sensitivity, low-cost implementation, and low power consumption, thus making itself an appealing choice in the field. Progress In terms of receiver sensitivity, implementation complexity, and performance in optical power-limited and optical signal-to-noise (OSNR) limited regimes, we review and compare the optical transmission schemes, including IMDD employing PAM4, SHCD employing quadrature phase shift keying (QPSK) modulation, and DSCD employing differential quadrature phase shift keying (DQPSK) modulation. In recent years, the IMDD system faces challenges in improving system transmission rates, while the SHCD system has gained attention as a low-cost, and high-performance solution. Sowailem's group from McGill University demonstrates a bidirectional SHCD scheme employing optical circulators for short-reach systems. Deming Liu's research group from Huazhong University of Science and Technology presents an SHCD system leveraging a large linewidth distributed feedback ( DFB) laser as a downstream transmission solution for optical access networks. Ming Tang's research group from Huazhong University of Science and Technology proposes a real-time 400 Gbit/s bidirectional SHCD transmission by employing low-cost uncooled large linewidth DFB lasers for data center interconnects. However, the practical implementation of an SHCD system still encounters challenges. Bidirectional transmission of signals and remote LOs requires additional optical circulators in SHCD transceivers (Table 2). Furthermore, the sensitivity of the SHCD system to transmission path differences increases with the utilization of larger laser linewidth (Fig. 4). In contrast, the DSCD system exhibits high tolerance for laser linewidth and is unaffected by transmission path differences. In optical power-limited systems, the DSCD-DQPSK system yields comparable performance to the SHCDQPSK system with optimal power separation ratio (Fig. 6), which is significantly better than the IMDD-PAM4 system (Fig. 7). In OSNR-limited systems, the remote LO quality is inevitably affected by optical noise, which influences the optimal laser power separation ratio (Fig. 8) and the receiver sensitivity of the SHCD system (Fig. 9). Implementing a narrow bandwidth optical filter for the remote LO can filter out a portion of the noise and enhance system performance but at the expense of additional costs. Conversely, in OSNR-limited systems, the receiver sensitivity of the DSCD-DQPSK system is superior to that of the SHCD-QPSK system, and it does not require an additional narrow bandwidth optical filter. Conclusions and Prospects In conclusion, both the SHCD and DSCD schemes realize a significant improvement in receiver sensitivity compared to the IMDD scheme. However, the increased DSP complexity and power consumption for coherent detection is a price for this improvement. Additionally, the SHCD system faces challenges from transmission path differences and noise within the remote LO, and addressing the challenges will increase the system implementation costs. Thus, further reducing DSP power consumption, system complexity, and cost is an important direction for future research for simplified self-coherent schemes. However, compared with the IMDD-PAM4 system and the SHCD-QPSK system, the proposed DSCD-DQPSK system is inherently advantageous and promising for short-and medium-reach optical fiber transmissions.

Emerging correlated multi-symbol modulation (CMSM) techniques require sequence detection to effectively increase spectral efficiency. A simplified sequence detection algorithm with low implementation complexity is proposed for CMSM-enhanced high-speed optical fiber transmissions. ©2023 The Author(s)

结合《计算机网络》课程特点和教学中存在的问题,借鉴先进的学习范式教学理念,以子网划分与网络互联为例探索实验教学改革.文章重点阐述实验原理、项目设计、仿真实现与测试分析等教学过程.实践表明,教学改革在教学模式、学生思维和教学方法等方面取得重大转变,学生学习效果显著,是高校本科教育改革的有益探索.

NAT技术能够解决IP地址资源紧张的问题,在实际网络建设中得到广泛应用.文章首先完成某企业网的NAT实验项目设计,然后利用思科模拟器实现了仿真设计,最后进行连通性测试、NAT地址转换表分析以及IP数据报分析等结果分析,直观地阐述了NAT的工作原理.该研究能够为学生提供自我探究的机会,帮助学生深入地理解理论知识,是高校本科教育改革的有益探索.

掺铒光纤放大器(EDFA)是波分复用(WDM)系统必不可少的器件,可以通过放大信号补偿由于器件和电路造成的损耗,在高速光纤通信系统发展中发挥至关重要的作用.文章基于OptiSys-tem仿真平台建立EDFA模型,对影响EDFA增益系数的因素进行分析.研究结果表明,掺铒光纤中铒离子浓度、掺铒光纤长度、泵浦功率、泵浦波长和输入信号功率等因素均能影响EDFA增益系数.研究结果对EDFA的产品设计和实际应用有一定参考价值.

A network is not always fully loaded during operation and may have idle capacity which is neither carrying any network services nor providing protection for working capacities. This idle capacity may be used to pre-plan as many additional paths as possible to enhance service connection availability with only some extra pre-planning in the network central controller. Our proposed adaptive multi-pat...

以OBE理念为依据的工程教育认证是新工科建设的一种重要手段.CDIO工程教育模式是实现OBE理念的有效途径,本文将CDIO工程教育模式应用在"关系数据库"课程中进行教学探索,以"员工信息管理系统"项目的设计与实现贯穿教学始终,学生以项目组形式完成信息系统开发,采用多元评价方式.实践表明,教学改革在提高教学质量、培养学生能力方面效果显著.

首先完成基于Matlab/Simulink的基带传输系统的仿真设计,经显示器观察发现各点波形与原理一致.在仿真基础上,对双极性码和双相码两种传输码系统进一步研究系统误码率,分析信息传输速率、不同传输码型和系统传输特性对系统可靠性的影响,仿真结果表明,降低信息速率、提高系统信噪比、增加系统滤波器滚降系数和选用高效的传输码型均可以降低系统误码率,提高系统的可靠性.

主要研究循环冗余校验码(CRC)交织级联编码在正交相移键控(QPSK)通信系统的应用.首先完成了基于MAT-LAB/Simulink的QPSK通信系统的仿真设计,然后在QPSK系统中采用CRC进行信道编码,通过测试发现,系统接收和发送的信号波形一致,说明系统仿真设计合理有效.进一步将CRC编码和交织编码进行级联应用到QPSK系统.对比误码率数据发现,CRC编码能够有效降低系统误码率、改善系统的性能,编码增益能达到3dB,级联编码较CRC编码性能有进一步提高.这给出了通信系统仿真设计的一种新方法,为实验教学提供一种新思路.