混合链路光纤喇曼放大器研究

对由普通单模光纤 (SMF) ,色散补偿光纤 (DCF)作为喇曼增益介质的两种结构的混合链路光纤喇曼放大器进行了实验研究 ,并对实验情况下的实际传输系统中的混合喇曼放大链路进行了理论数值模拟 ,比较和分析了两种链路结构的增益和噪声特性     

具有不同色散分布链路的高速CO-OFDM系统中非线性损伤的研究

由于相干光正交频分复用(CO-OFDM)系统很高的峰均功率比(PAPR)以及非常近的子载波间隔,使得链路色散导致的子载波走离对光纤非线性损伤的影响更加明显。研究了不同色散分布、不同残余色散情况下,无色散补偿光纤(DCF)和有色散补偿光纤的光纤链路时CO-OFDM系统的非线性损伤以及系统性能。针对单信道40 Gb/s CO-OFDM系统,无DCF链路比完全补偿DCF链路,Q因子高5.1 dB;对于DCF链路,当残余色散从0变为到1200ps/nm时,最大Q因子提高了4dB,非线性阈值提高了4 dBm,1200ps/nm时性能几乎和无色散补偿系统相同。     

基于物理地址编码的光纤链路智能识别

光纤链路的质量直接影响电力通信系统的工作性能,针对当前光纤链路识别方法存在识别误差大、实时性差等缺陷,为了降低光纤链路识别误差,设计了一种基于物理地址编码的光纤链路智能识别方法。首先对光纤链路识别原理进行分析,找到与光纤链路识别效果有关的重要因素,然后采用光纤物理地址编码技术对光纤链路节点进行编码,并构建光纤链路智能识别模型,最后在相同仿真环境下,与经典光纤链路识别方法进行对比实验,结果显示,方法较好地克服了当前光纤链路识别方法存在的局限性,光纤链路识别的智能化程度更高,改善了光纤链路识别效果,获得了比经典方法更优的光纤链路识别结果,实际应用价值更高。     

双向时分复用光纤时间传递链路噪声分析

研究分析了双向时分复用(BTDM)光纤时间传递链路 的主要噪声及产生机理,建立了基于BTDM光纤时间传递 的链路噪声模型。仿真分析了激光器强度噪声、光放大器增益与个数、接收机带宽等对BTDM 光纤时间传 递接收信噪比(SNR)的影响。结果表明,BTDM光纤时间传递 接收SNR在光放大器达到最优增益时最大,且最 大SNR随光放大器个数的增加而增加并趋于稳定;相同长度光纤链路,光放大器个数越多 ,在一定范围 内,激光器相对强度噪声对BTDM光纤时间传递链路接收SNR 影响更大,接收机带宽对BTDM光纤时 间传递接收信号抖动的影响越小;BTDM光纤时间传递接收SNR随定时信号前 光持续时间的增加而减小,并趋于WDM方案的SNR。     

多段光纤链路中的FWM效率

通过推导由多段光纤构成的光纤链路中的四波混频(FWM)效率,找出了影响全光波长变换的FWM效率的因素,进而利用MATLAB软件成功模拟出任意多段光纤链路中的FWM效率.以由7段光纤组成的光纤链路为例,通过调节影响混频效率的各种参数的值,得到了获取最佳混频效率的参数取值范围,并可进一步获得稳定的波长变换效率.     

光传输链路高速自动增益控制研究

分析了光纤传输链路信号波动来源,得出引起信号波动的两种关键因素,针对该两种因素设计了一套高速自动增益控制系统(AGC)以及一套针对该系统的计算机软件效标方案,在光纤链路中通过引入该系统,使得光纤传输链路输出射频功率波动由以前的11 dB降低为0.5 dB以内。     

一种基于OPM和FBG滤波器的新型双工ROF系统

提出了一种采用光相位调制器(OPM)和光纤布 拉格光栅(FBG)滤波器实现的双向光纤无线通信(ROF)系统。在中心站,系统采用OPM和FBG滤波器产生抑制一阶边带的多边带光信号 ,而2.5Gbit/s 的下行链路信号只调制在中心光载波上同时经过光纤进行传输。在基站,未被调制的边带信 号用来重新调 制上行链路信号。建立了产生光载毫米波的理论模型,分析了光纤色散导致的相位影响,并 通过仿真实验 验证了系统的可行性。结果显示,经过60km光纤传输后,上、下行 链路信号的眼图都清晰可见,上行链 路功率代价小于0.2dB,下行链路功率代价小于1.8dB,系统具有较好的抗色散能力。     

光载信息能量同传方案及其通信检测应用

基于光纤的大传输带宽、微型传能通道、抗电磁干扰等优势,本文设计了一种光载信息能量同传方案.它基于光纤一体化分布式链路,结合微波光子模拟收发前端,同步实现能量远程配送与高频宽带信号的采集传输.首先,设计并测试了光纤传能(Power over Fiber,PoF)链路:高功率激光经多模光纤链路传输2 km后转换为百毫瓦级电...     

一种基于光载波抑制的ROF双工系统

为克服远距离光纤传输系统中色散效应的影响,研究了一种基于光载波抑制的单工ROF(光纤无线电)系统,并提出改进的双工ROF系统传输方案。在中心站,采用20GHz的射频信号将下行链路信号耦合至光载波抑制频段处,通过单模光纤传输50km至基站,并重复利用未调制边带传输上行链路信号。通过仿真得到的系统光谱图和误码率曲线表明:加入上行链路信号传输后,下行链路的光纤能量损耗降低,上、下行链路同时具有较好的抗色散能力。     

基于程控的光纤链路自动交换设计

针对当前光纤链路交换的特点,提出了一种基于程控的光纤链路自动交换技术,该技术利用程序控制发送光纤链路旋转,实现与其它光纤链路的对接,完成光纤链路的自动化交换,为全光网的实现提供了另一种途径。     

Improving routing performance in wireless ad hoc networks using cross-layer interactions

This article presents a combined layer two and three control loop, which allows prediction of link breakage in wireless ad hoc networks. The method monitors the physical layer transmission mode on layer two and exploits the gained knowledge at layer three. The mechanism bases on link adaptation, which is used in IEEE 802.11a WLAN to select the transmission mode according to the link quality. The process of link adaptation contains information that is useful to predict link stability and link lifetime. After introducing the IEEE 802.11a Medium Access Control (MAC) and PHY layer, we present insight to the IEEE 802.11a link adaptation behaviour in multi-hop ad hoc networks. The link adaptation algorithm presented here is derived from Auto Rate Fallback (ARF) algorithm. We survey the performance gain of two newly developed route adaptation approaches exploding the prediction results. One approach is Early Route ReArrangement (ERRA) that starts a route reconstruction procedure before link breakage. Hence, an alternative route is available before connectivity is lost. Early Route Update (ERU) is a complementing approach that enhances this process, by communications among routing nodes surrounding the breaking link. The delay caused by route reconstruction can be significantly reduced if prediction and either of our new route discovery processes is used.     

Reachable and stabilizable area of an underactuated manipulator without state feedback control

The reachable and stabilizable area of a two-link underactuated manipulator is clarified theoretically and experimentally. The manipulator consists of an active (first) link attached to an actuator and a free (second) link connected to the first link with a joint that lacks not only an actuator but also a sensor. In this circumstance the motion of the second (free) link can be controlled without state feedback of the free link, using the nonlinear characteristics of the bifurcations produced in the free link under the high-frequency excitation of the active (first) link attached to the actuator. It is theoretically shown according to the bifurcation theory that the stable equilibrium states of the free link vary depending on the configuration of the active link with respect to the direction of gravity. Then, the set of positions where the tip of the free link can reach and be stable, i.e., the reachable and stabilizable area, is theoretically clarified under the combination of the excitation frequency and the configuration of the active link. Furthermore, experimental results show the validity of the theoretically predicted reachable and stabilizable area.     

Optically coherent direct modulated FM analog link with phase noisecanceling circuit

This paper demonstrates a new phase noise canceling (PNC) circuit for use with an optically coherent analog frequency modulation (FM) link employing directly modulated distributed feedback (DFB) lasers. Direct frequency modulation of a semiconductor laser is a highly efficient optical-to-electrical conversion process, which can lead to very low noise figure (NF) and high dynamic range (DR). However, the large laser phase noise found in semiconductor lasers significantly degrades the FM link performance. The PNC circuit is a simple means for canceling the laser phase noise while extracting the modulated signal and taking advantage of the high FM conversion efficiency of semiconductor lasers. The theoretical performance of the PNC PM link is discussed in terms of the signal-to-noise ratio (SNR), NF, and DR, and is compared to a Mach-Zehnder modulated link which uses high-power, solid-state lasers. Phase noise cancellation is demonstrated in an experimental PNC FM link. Comparison of a PNC FM link to an externally modulated AM (coherent) link shows a 31 dB improvement in the NF of the FM link, and a 10 dB improvement in DR. However at higher received optical powers phase-to-intensity noise limits the performance of both links to well below the theoretical calculations     

Application of the Link Management Protocol to Discovery and Forwarding Adjacencies

The link management protocol (LMP) is used to maintain control channel connectivity, to verify the physical connectivity of data channels, to correlate link property information at both endpoints of a data link and to aggregate multiple data links into a single traffic engineering (TE) link. LMP also provides assistance in fault localization, both in opaque and transparent optical networks. In this paper, we show how LMP relates to the generalized multi-protocol label switching (GMPLS) suite of protocols and integrates into a distributed GMPLS control plane. We describe the role of LMP in two applications: data link (auto-)discovery and the establishment of forwarding adjacency label-switched paths (FA-LSPs) including their initiation, verification and bundling, and conclude that they can be built upon basic functions of LMP, namely control channel management, link verification and link property correlation.     

应用于无人机中继测控链路的微波前端设计

当前无人机测控数据链系统多为点对点视距传输,当遇到需要扩展通信距离或存在障碍物遮挡时往往限制了链路的正常工作。针对此问题,提出了一种应用于无人机中继测控链路的微波前端设计方案。其空空链路与空地链路采用频率倒置的频分双工体制,有效避免了前向链路与返向链路的收发干扰,并实现了机载设备的硬件统型;通过软件注入便可完成对终端模式的在线切换,提升了系统应用的灵活性与鲁棒性,为保证复杂环境下无人机测控链路的实时传输提供了一种有效的解决途径。     

全光网中的光信噪比估算与系统设计

指出了WDM光传送网中 ,级联光上下路节点或光交叉连接节点后 ,系统构成上与传统级联线路放大器情况下的差异以及常用光信噪比评估公式的近似性。对WDM光传送网中线路给出了一个等效模型 ,并详细推导了光信噪比的计算公式 ,同时计入了光放大器的自发辐射噪声引起的饱和效应。最后针对不同系统配置情况进行了光信噪比的估算 ,分析了估算结果及其对线路设计的指导意义     

Analysis of peak-to-average power ratio for IS-95 and thirdgeneration CDMA forward link waveforms

The peak-to-average power ratio (PAR) of IS-95-type code division multiple-access (CDMA) forward link waveforms is an important parameter which directly relates to system capacity performance. In this paper, analytical expressions are derived for the PAR. The probability that the instantaneous-to-average power ratio (IAR) exceeds a given value is also derived. The analysis is carried out parametric in 1) the number of active traffic channels; 2) the fractions of power allocated to different forward link channels; and 3) other parameters related to the forward link power budget. An analysis is also given for the distribution of the IAR for the forward link modulation planned for third generation (3G) versions of the IS-95 system and a simple modification to present and future IS-95 modulation schemes is shown that reduces the forward link PAR by up to 3 dB     

Stable Throughput of Cognitive Radios With and Without Relaying Capability

A scenario with two single-user links, one licensed to use the spectral resource (primary) and one unlicensed (secondary or cognitive), is considered. According to the cognitive radio principle, the activity of the secondary link is required not to interfere with the performance of the primary. Therefore, in this paper, it is assumed that the cognitive link accesses the channel only when sensed idle. Moreover, the analysis includes: (1) random packet arrivals; (2) sensing errors due to fading at the secondary link; (3) power allocation at the secondary transmitter based on long-term measurements. In this framework, the maximum stable throughput of the cognitive link (in packets/slot) is derived for a fixed throughput selected by the primary link. The model is modified so as to allow the secondary transmitter to act as a ldquotransparentrdquo relay for the primary link. In particular, packets that are not received correctly by the intended destination might be decoded successfully by the secondary transmitter. The latter can, then, queue and forward these packets to the intended receiver. A stable throughput of the secondary link with relaying is derived under the same conditions as before. Results show that benefits of relaying strongly depend on the topology (i.e., average channel powers) of the network.     

Performance analysis of weather-dependent satellite–terrestrial network with rate adaptation hybrid free-space optical and radio frequency link

Due to the rapid development of satellite laser communication technology, free-space optical (FSO) links present a promising alternative to traditional radio frequency (RF) links. In this paper, taking the influence of weather factors into consideration, we investigate the performance of the hybrid FSO/RF links where the feeder link operates in the FSO band and the user link operates in the hybrid FSO/RF band. Specifically, the FSO feeder link is modeled by the gamma–gamma distribution in the presence of beam wander and pointing error, and the detection method adopts either the intensity modulation with direct intensity (IM/DD) or heterodyne detection. The RF user link is assumed to follow the shadowed Rician model. In addition, in order to improve the transmission rate of the link under the time-varying satellite–terrestrial channel, a rate adaptation scheme is proposed. The performance of the system under study is evaluated in terms of the outage probability, average bit error rate (BER), and average transmission rate. Our results provide some important insights, for example, (1) due to the constraints of the feeder link and weather factors, there is an upper limit on the outage performance and bit error rate of the hybrid link; (2) the adaptive transmission strategy can significantly improve the transmission rate of the link compared with traditional design.     

Optical ISL tracking considerations in meeting ISDN requirements

Burst errors in an optical intersatellite link (ISL) are short term (of the order of a millisecond) degradations of the link due to antenna mistracking. These errors degrade the average bit error rate (BER), decrease coding gain, complicate calculations of tracking accuracy, and give rise to concern about the quality of the link for carrying digital signals. After reviewing previous work on these topics, the digital performance of the link is examined in terms of how these considerations affect the ability of an optical ISL to meet ISDN (Integrated Services Digital Network) criteria for an ISL. A link with on-board regeneration is assumed. Since no allocation has yet been made for an ISL, an allocation of 25 per cent of the degradation permitted for the satellite link by CCITT Rec. G.821 and CCIR Rec. 614 is assumed here. It is found (1) that if the requirement derived from Rec. 614 is met, the requirements derived from Rec. G.821 are also met and (2) that an optical ISL should have little difficulty in meeting these requirements.