改进的PON网络监测方案对业务通信性能的影响

针对无源光网络(PON)的传统监测方案存在的成本高、系统复杂,以及无法实现在线监测等问题,提出了一种改进的基于调频连续波的PON网络监测方案.采用VIP和Matlab协同仿真,研究了该方案对业务通信性能的影响,结果表明:调频连续波频率变化基本对下行业务信号无影响,调制指数越高对下行业务信号的影响越大,如果调制指数控制在0.05以内,则可忽略其对下行业务信号的影响.     

一种改进的PON保护组解决方案

无源光网络(PON)无疑是下一代接入网的一种主流方案。由于该技术一般采用点到多点(P2MP)的树形拓扑结构,因此从局端设备OLT的PON MAC到ONU的PON MAC之间的链路可靠性就显得极为重要。文章提供了一种快速、稳定、成本低、易扩展且与PON系统其他软件模块兼容的光纤保护倒换的整体方案。     

Computer simulation of optical crosstalk in linear imaging arrays

Computer simulation is utilized to predict crosstalk in linear imaging arrays. The simulation is based on analysis which includes the effects of focusing the input light, the use of Kettleer's equations to describe propagation in a lossy medium, and a solution of the generalized diffusion equation for excited carriers. Crosstalk for a conventional linear image array and one employing a fan-out channel waveguide array are evaluated and compared. The fan-out channel waveguide array concept allows for high resolution imaging without requiring very small photodetector array elements, and calculations presented show that it should have superior performance with regard to crosstalk.     

Performance of WDM ring and bus networks in the presence ofhomodyne crosstalk

This paper examines the effects of coherent and incoherent homodyne crosstalk in wavelength division multiplexed (WDM) ring and bus networks using reconfigurable optical add-drop multiplexers (OADM's). It is widely understood that incoherent homodyne crosstalk causes power penalties at the receivers in these networks. We show that coherent homodyne crosstalk causes a range of possible received powers, and that coherent and incoherent crosstalk together lead to a range of possible power penalties. A Monte Carlo simulation is used to examine the probability distribution of power penalties due to homodyne crosstalk under various conditions. We find that increasing the switch and multiplexer crosstalk within each OADM, and increasing the number of WDM channels, all produce increased probabilities of large power penalties. However, the number of nodes through which a signal is transmitted does not affect the power penalty distribution     

Numerical and theoretical analysis of the crosstalk in linear optical amplifiers

The dynamic characteristics, including the crosstalk and relaxation oscillation, of linear optical amplifiers (LOAs) are investigated by small-signal analysis under an averaging carrier density approximation and compared with the results of numerical simulation. The good agreement between the numerical simulation and the small-signal analysis indicated the averaging carrier density is an appropriate approximation for analyzing LOAs. Theoretical analyzes also show that the dynamic properties of the vertical laser fields dominate the dynamic performance of LOAs. Based on the small-signal analysis, a concise equation for the crosstalk under high bit rate was derived, which can be applied to measure the differential gain of LOAs.     

Characteristics of an elliptical ring antenna excited by a linear electric probe

This paper presents the characteristics of an elliptical ring antenna excited by a linear electric probe. Based on the waveguide principle, the suitable cross-sectional dimension of the ring that yields the dominant mode (TE_C11 mode) will be formulated in terms of the cut off wavelength. The variation of the antenna characteristics, depending on cross-sectional dimension, ring length and probe length, were investigated using numerical electromagnetic code (NEC) based on the method of moments (MoM). From the experiment, the prototype antenna provides bidirectional pattern with HPBW in E-plane and H-plane of 83 and 46 degrees, respectively, and the gain of 5.1?dBi with SWR?相似文献   

Suppression of near- and far-end crosstalk by linear pre- andpost-filtering

Full-duplex data communication over a multi-input/multi-output linear time-invariant channel is considered. The minimum mean square error (MMSE) linear equalizer is derived in the presence of both near- and far-end crosstalk and independent additive noise. The MMSE equalizer is completely specified in terms of the channel and crosstalk transfer functions by using a generalization of previous work due to Salz (1985). Conditions are given under which the equalizer can completely eliminate both near- and far-end crosstalk and intersymbol interference. The MMSE transmitter filter, subject to a transmitted power constraint, is specified when the channel and crosstalk transfer functions are bandlimited to the Nyquist frequency. Also considered is the design of MMSE transmitter and receiver filters when the data signals are arbitrary wide-sense stationary continuous or discrete-time signals, corresponding to the situation where the crosstalk is not phase-synchronous with the desired signal     

Improved tolerance in optical directional couplers

Tolerance requirements in conventional synchronous-mode directional couplers are examined. It is proposed that the tolerance situation can be improved considerably by tapering one, or both, of the propagation coefficients, so that they intersect at one position. This model is examined numerically, and suggestions are made for the practical realisation of a device.     

Dramatic reduction of optical crosstalk in deep-submicrometer CMOS imager with air gap guard ring

A dielectric structure, air gap guard ring, has been successfully developed to reduce optical crosstalk thus improving pixel sensitivity of CMOS image sensor with 0.18-/spl mu/m technology. Based on refraction index (RI) differences between dielectric films (RI = 1.4 /spl sim/ 1.6) and air gap (RI = 1), total internal reflection occurred at dielectric-film/air-gap interface, thus the incident light is concentrated in selected pixel. Excellent optical performances have been demonstrated in 3.0 /spl times/ 3.0 /spl mu/m pixel. Optical spatial crosstalk achieves 80% reduction at 20/spl deg/ incidence angle and significantly alleviates the pixel sensitivity degradation with larger angle of incident light.     

Improved Y-junction splitter for ring waveguides

The authors present a novel design for a Y-junction splitter for ring waveguides based on the principle of mode conversion by self-interference. Power in the device is diverted from an edge-guided ring mode into a straight guide with little loss to radiation modes. The power injected into the fundamental modes of both the straight and ring guides is maximised relative to higher order modes     

Analysis of linear crosstalk in photonic crossbar switches based onon/off gates

This paper presents expressions for the linear crosstalk and the resulting error rate degradation in a photonic switch based on on/off gates, considering cyclostationary interference among digital signals. The periodically time-varying interference accounts for the dependencies of error probability both on the spectrum of transmitted signals and on random bit-skews between channels. This paper quantitatively verifies the intuitions that bit-aligned channels increase the crosstalk power penalty, and that a sharp modulating pulse improves error probability. These dependencies on spectrum and bit-skews become noticeable at high crosstalk levels caused by either a low contrast ratio or a large switch size     

Impact of crosstalk in an arrayed-waveguide router on an opticaladd-drop multiplexer

The impact of crosstalk in an arrayed-waveguide (AWG) router on the performance of an N-channel optical add-drop multiplexer (OADM), with m add/drop channels and n-pass channels is theoretically investigated. A single arrayed-waveguide router is simultaneously used for multiplexing and demultiplexing. This results in crosstalk not only from the incoming channels, but from the outgoing channels as well. We show that the performance of the OADM degrades as either N or m are increased, suggesting that the number of channels in a network based on OADM's is limited by crosstalk in the AWG router. When an optical filter is added at the output of the OADM the digital signal-to-noise ratio Q is independent of N and m, and within a few tenths of a decibel of the perfect filtering case     

一种PON系统线路保护装置的研制

无源光网络(PON)系统普遍采用点到多点的树形拓扑结构,它的主干光纤的生存性问题关系到整个PON系统的可靠性,因此对主干光纤进行保护是非常必要的.文章介绍一种低成本并可自动切换的PON系统主干光线路保护装置(OLP-P),并用两个实验来验证OLP-P的自动倒换功能和倒换时间以及在PON系统中的自动倒换功能和倒换恢复时间.     

Coding approaches to fault tolerance in linear dynamic systems

This paper discusses fault tolerance in discrete-time dynamic systems, such as finite-state controllers or computer simulations, with focus on the use of coding techniques to efficiently provide fault tolerance to linear finite-state machines (LFSMs). Unlike traditional fault tolerance schemes, which rely heavily-particularly for dynamic systems operating over extended time horizons-on the assumption that the error-correcting mechanism is fault free, we are interested in the case when all components of the implementation are fault prone. The paper starts with a paradigmatic fault tolerance scheme that systematically adds redundancy into a discrete-time dynamic system in a way that achieves tolerance to transient faults in both the state transition and the error-correcting mechanisms. By combining this methodology with low-complexity error-correcting coding, we then obtain an efficient way of providing fault tolerance to k identical unreliable LFSMs that operate in parallel on distinct input sequences. The overall construction requires only a constant amount of redundant hardware per machine (but sufficiently large k) to achieve an arbitrarily small probability of overall failure for any prespecified (finite) time interval, leading in this way to a lower bound on the computational capacity of unreliable LFSMs.     

一种实时无源光以太网的硬件设计与实现

设计了一种基于无源光网络结构的实时光纤以太网的硬件系统,在FPGA的基础上实现了相应的中心节点与接入节点的物理层功能;构建了一个包含16个接入节点、1个中心节点的试验系统,进行了CAN实时业务的测试.测试结果验证了试验系统的可行性和实时性,实时响应时间小于200μs.     

Logical topology design for linear and ring optical networks

The design of logical topologies in wavelength-routing multihop optical networks is a well-studied problem. We consider logical topology (LT) design over the popular ring and linear topologies. Our objective is the minimization of the electronic processing delay for the worst case traffic flow. For uniform traffic between nodes, this delay minimization corresponds to minimizing the number of hops on a shortest path between the farthest two nodes in the logical topology (the diameter of the logical topology). The simple structure of the physical topologies enables us to present a rigorous analysis of the problem. We present lower bounds for the achievable diameter wherever possible and propose practical logical topology design algorithms and corresponding upper bounds. We also present an application of the LT designs in the linear topology to the survivability of ring networks     

ATM PON中MAC算法的研究

ＡＴＭ ＰＯＮ网络属于分布式媒质共享拓扑结构，所承载业务的 ＱｏＳ要求各异，如何在保证系统传输效率的同时满足用户对服务质量的需求，是ＡＰＯＮ ＭＡＣ算法的关键。分析了 ＡＰＯＮ系统的特点，提出了分布式分层调度的方案。     

APON中MAC算法的研究

APON网络属于分布式媒质共享拓扑结构,所承载业务的QoS要求各异,如何在保证系统传输效率的同时满足用户对服务质量的需求,是APON MAC算法的关键。本文分析了APON系统的特点,提出了分布式分层调度的方案。     

一种改进的容差机制图像去雾算法

针对经典容差机制图像去雾算法存在的对部分明亮区域透射率提升力度不够,难以彻底消除色彩失真问题,本文提出一种改进算法。将原算法中对明亮区域透射率根据容差进行双曲线提升修正变为线性提升修正,使透射率平稳提升,并适当增大了透射率提升力度,有效消除色彩失真。以方差和色调还原度作为图像去雾的客观质量评测指标,与暗原色先验算法和经典容差机制算法进行对比实验。实验结果表明,本文算法在改善明亮区域色彩失真及提高图像去雾效果方面优于对比算法。     

Improved latch-up immunity in junction-isolated smart power ICswith unbiased guard ring

The performance of the unbiased guard ring structure is measured and the effects of high current, emitter area, and layout of unbiased guard rings are reported and explained. Measurements show a reduction in parasitic gain by up to six orders of magnitude, while also avoiding the cross talk and power consumption of biased rings. A comparative analysis of unbiased guard ring with biased guard ring shows up to 100 times better performance at low current levels. A modification to the unbiased guard ring is also implemented and successfully tested which shows an increase in the current handling capability of the structure by an order of magnitude