Realistic end-to-end simulation of the optoelectronic links andcomparison with the electrical interconnections for system-on-chipapplications

A detailed comparison of optoelectronic versus electrical interconnections for system-on-chip applications is performed in terms of signal latency and power consumption. Realistic end-to-end models of both interconnection schemes are employed in order to evaluate critical performance parameters. A variety of electrical and optoelectronic interconnection configurations are implemented and simulated using accurate optical device and electronic circuit models integrated under an integrated circuit (IC) design computer-aided design tool. Two commercial complementary metal-oxide-semiconductor (CMOS) technologies (0.8 μm and 0.25 μm) are used for the estimation of the signal latency and the power consumption as a function of the interconnection length for the different link configurations. It was found that optoelectronic interconnects outperform their electrical counterparts, under certain conditions, especially for relatively long lines and multichannel data links     

IP/MPLS网络与GMPLS网络互联的研究

文章研究了网际协议／多协议标签交换（IP／MPLS）网络升级为通用多协议标签交换（GMPLS）网络的过程中存在的几种演进模型，并重点分析了岛式模型。同时，还分析了MPLS网络和GMPLS网络互联时存在的问题、两种协议问的差异以及解决这些问题所采用的路由、信令和通道计算技术。     

Flexible optical wireless links and networks

The worldwide demand for broadband communications is being met in many places by installed single-mode fiber networks. However, there is still a significant "first-mile" problem, which seriously limits the availability of broadband Internet access. Free-space optical wireless communications has emerged as a viable technology for bridging gaps in existing high-data-rate communications networks, and as a temporary backbone for rapidly deployable mobile wireless communication infrastructure. In this article we describe research designed to improve the performance of such networks along terrestrial paths, including the effects of atmospheric turbulence, obscuration, transmitter and receiver design, and topology control.     

OCDMA-coded free-space optical links for wireless optical-mesh networks

We propose a wireless optical-mesh network based on optical code-division multiple-access (OCDMA)-coded free-space optical links. The performance of the proposed network under intermediate and strong turbulence channel conditions is investigated for synchronous and asynchronous OCDMA. We show that synchronous OCDMA using complementary Walsh-Hadamard codes operating at a raw bit rate of 622 Mb/s per user can achieve a bit-error rate of 10/sup -9/. This is achievable in channels with strong turbulence and high temporal correlation, or in channels with intermediate turbulence conditions; reasonable conditions based on channel characteristics inferred from the refractive index spectrum. For asynchronous OCDMA using optical orthogonal codes (OOCs), using a lower bound, we show that asynchronous OCDMA using OOCs cannot achieve acceptable performance for the same channel conditions, due to interference limitations.     

Transmitter optimization and theoretical bounds for dispersion-limited optical fiber links

In this paper, we present a novel mathematical investigation on the dispersion-limited optical communication channel. We tackle the problem using a comprehensive approach that is based on the optimization of the energy transfer from the input to the output of the channel. We solve the optimization problem deriving a fundamental integral equation, which we are able to solve analytically. We show that the dispersion-limited optical channel has a very interesting equivalence to the ideal lowpass filter. This equivalence allows us to derive new bounds on the maximum achievable bit rate on the channel with limited intersymbol interference (ISI). In particular, we demonstrate that by suitably increasing the memory of the modulator and using the optimal pulses derived in this paper, one can transmit with limited ISI over a channel with arbitrarily high dispersion.     

Routing for cognitive radio networks consisting of opportunistic links

Cognitive radio (CR) has been considered a key technology to enhance overall spectrum utilization by opportunistic transmissions in CR transmitter–receiver link(s). However, CRs must form a cognitive radio network (CRN) so that the messages can be forwarded from source to destination, on top of a number of opportunistic links from co‐existing multi‐radio systems. Unfortunately, appropriate routing in CRN of coexisting multi‐radio systems remains an open problem. We explore the fundamental behaviors of CR links to conclude three major challenges, and thus decompose general CRN into cognitive radio relay network (CRRN), CR uplink relay network, CR downlink relay network, and tunneling (or core) network. Due to extremely dynamic nature of CR links, traditional routing to maintain end‐to‐end routing table for ad hoc networks is not feasible. We locally build up one‐step forward table at each CR to proceed based on spectrum sensing to determine trend of paths from source to destination, while primary systems (PSs) follow original ways to forward packets like tunneling. From simulations over ad hoc with infrastructure network topology and random network topology, we demonstrate such simple routing concept known as CRN local on‐demand (CLOD) routing to be realistic at reasonable routing delay to route packets through. Copyright © 2009 John Wiley & Sons, Ltd.     

On the analysis of active networks containing voltage, operational, and differential-input operational amplifiers

A method of drawing by inspection the signal-flow graph of an active network containing voltage, operational, and differential-input operational amplifiers is given and it is shown that the network functions can easily be determined from the signal-flow graph.     

光缆线路的防护及其故障的检测

论述了光缆线路故障的现象、原因及防护方法，结合OTDR(光时域反射计)的使用经验，总结了光缆线路故障的定位方法和排除技巧。     

Modeling and simulation of next-generation multimode fiber links

This paper describes an advanced multimode-fiber-link model that was used to aid the development of Telecommunication Industry Association standard specifications for a next-generation 50-/spl mu/m-core laser-optimized multimode fiber. The multimode-link model takes into account the interactions of the laser, the transmitter optical subassembly, and the fiber, as well as effects of connections and the receiver preamplifier. We present models for each of these components. Based on these models, we also develop an efficient and simple formalism for the calculation of the fiber transfer function and the signal at the link output in any link configuration. We demonstrate how the model may be used to develop specifications on transmitters and fibers that guarantee any desired level of performance.     

高带宽数据中心网络的动态光链接结构

信息传输对带宽的要求越来越高,采用密集波分复用等常规方法来提高系统容量会大大增加数据中心成本,针对这一问题提出了一种低成本、高带宽具有动态结构的光网络。分析结果表明,这种光网络可以适应未来通信模式的发展要求。     

Traffic modeling in packet switched networks for single links

To correctly model traffic in packet switched networks for single links with FC-FS discipline at each node, we introduce the influence of the phenomenon of short packets agglutinating behind long packets. It is then necessary to abandon the usual notions of local traffic sources and local G/G/1 queues in favor of the more realistic notion of traffic sources at the network input with local queues appearing as the consequence of a tandem queue whose parameters we define. The influence of the upstream transfer delay and the upstream network topology then appear. We compare theoretical results with those derived by traffic simulations.     

链路累积干扰（CIL）在无线Mesh网络中的应用

由于无线Mesh网络具有无线节点的静态性或半静态性以及共享无线媒介等特性,因此在无线Mesh网络中设计路由判据对网络的整体性能起着至关重要的作用。分析了现有的最小跳数（hop count）、期望传输次数（ETX）、加权累积ETT（WCETT）、MIC等4种路由判据,并指出它们的优缺点。最后提出了一种链路累积干扰（CIL）的路由判据方法,从理论上分析其优点,给出仿真结果。仿真结果说明,这种链路累积干扰路由判据能明显改善网络性能。     

为今天的光纤网选择合适的OTDR设备

工程师在选择试仪器时必须评估其特性和成本     

城域网用的新型光纤

简要介绍了城域网用的新型光纤的研究要点、光纤特点、光纤性能及其应用实例。     

Identification of faulty links in dynamic-routed networks

The authors present a maximum a posteriori method to identify faulty links in a communication network. A designated network node with management responsibilities determines a fault has occurred due to its inability to communicate with certain other nodes. Given this information as well as the information that it can communicate with another specified set of nodes, one would like to identify as quickly as possible a ranked list of the most probable failed network links. The authors also indicate how the method might be extended to the identification of most probable faulty network resources in a more abstract (higher level) model of a network, including, for example, an object-oriented model     

城域光缆线路系统障碍和隐含断纤的查修

对城域光缆线路的系统障碍和隐含的断纤查修问题进行了详细的讨论，强调在具体的障碍查修过程中，应把技术手段和实践经验结合起来，灵活应用。     

Realization of an analog predistortion circuit for RF optical fiber links

This paper presents an analog predistortion circuit for RF optical fiber links. The circuit consists of two source-coupled differential transconductance amplifiers which could provide linear and nonlinear transfer charac-teristics by adjusting the bias voltage and the transistor sizes. The circuit was designed and realized in a standard 0.18-μm CMOS technology of SMIC. The chip occupies 0.48 × 0.24 mm~2. The DC supply is 3.3 V. Using this circuit, the third-order intermodulation distortion (IMD) suppression of a directly modulated RF optical fiber link can be improved by 9-16 dBc at relatively low cost.     

A MAC layer protocol for wireless networks with asymmetric links

We introduce AsyMAC, a MAC layer protocol for wireless networks with asymmetric links and study a protocol stack consisting of AsyMAC and the A⁴LP routing protocol. The two protocols are able to maintain connectivity where the standard IEEE 802.11 MAC protocol coupled with either AODV or OLSR routing protocols may loose connectivity. A comparative study shows that AsyMAC improves on two previously proposed protocols’ accuracy in determining the nodes to be silenced to prevent collisions.     

A recommended error control architecture for ATM networks withwireless links

This paper provides performance results through analysis and simulation for key error control problems encountered in using wireless links to transport asynchronous transfer mode (ATM) cells. Problems considered include the forward-error correction (FEC) and interleaving at the physical layer, the impact of wireless links on the ATM cell header-error control (HEC) sand cell delineation (CD) functions, the application of data link automatic repeat-request (ARQ) for traffic requiring reliable transport, and the impact of the choice of end-to-end ARQ protocol for reliable service. We conclude that it is very important to make the physical layer as SONET-like as possible through the use of powerful FEC, interleaving, and ARQ. These additional error control measures are especially necessary for disturbed channels because of the degrading effects of the channel on higher-layer functions. A recommended error control architecture is given with tradeoffs     

射频光传输模拟预失真电路实现

This paper presents an analog predistortion circuit for RF optical fiber links. The circuit consists of two source-coupled differential transconductance amplifiers which could provide linear and nonlinear transfer characteristics by adjusting the bias voltage and the transistor sizes. The circuit was designed and realized in a standard 0,18-μm CMOS technology of SMIC. The chip occupies 0.48 × 0.24 mm^2. The DC supply is 3.3 V. Using this circuit, the third-order intermodulation distortion （IMD） suppression of a directly modulated RF optical fiber link can be improved by 9-16 dBc at relatively low cost.