通信学毕业论文范文.docx

关键词：光纤通信，监测，案例摘要：论文介绍了光纤通信系统监测的发展、组成，简单介绍测试仪表OTDR原理及光纤通信系统的维护案例。1 光纤光缆的现状1.1规模及技术 由于光纤通信具有容量大、传送信息质量高、传输距离远、性能稳定、防电磁干扰、抗腐蚀能力强等优点，伴随“光进铜退”推进，以建设完成的八纵八横光缆传输网连接全国个省（自治区、直辖市），光纤光缆通信网络成为我国主要的传输网络。另一方面，随着光同步数字传输网（）、分组传送技术（PTN）和密集波分复用（）技术的飞速发展，光纤的传输容量也在以前所未有的速度发展着。1.2 故障原因 光纤是由很脆弱的玻璃制成，通常其外径为125um单模光纤的纤芯只有7-8um，多模光纤的纤芯也仅为50um，虽然光缆本身利用FBT加强芯、油膏和塑料外护套等保护光纤，使光缆具有了一定的抗外力强度。但由于大建设时期伴随的野蛮施工、强烈的外力的冲击、加之光缆自身的原因如接头盒的开裂、进水、腐蚀和光缆自然老化等因素，还会常常导致光缆传输系统的故障。光缆线路和铺设是通过地下直埋、架空和管道等方式，具有点多、线长、面广、高度分散的特点，受外力影响大，由于光缆自身的外界原因造成的阻断障碍，涉及光缆的扩容、迁、改、移时对光缆线路进行施工维护等，维护量多且难度大。如何快速检测光缆和故障定位成为通信工程师或技术人员必备技能。2 光纤系统监测 光缆线路自动监测系统主要由省监测中心PMC、区域监测中心LMC、现场监测站MS组成。监测中心负责对各监测站进行控制，是采集和处理数据的中心，由控制器（服务器、客户机、工作站）、路由器、集线器/交换型集线器、网络适配器、MODEM、打印机及相应的软件等组成。 在长途和市内中继光缆传输系统中，传输设备都配置有比特误码率（BER）的监测设备或监测单元。然而，传统的线路维护部门未配备监测手段，通常只能是出现BER告警时，首先由机务人员判断引起告警的原因，在查明其原因是传输线路-光缆后，机务人员再通知相关的线路维护部门和上报有关主管部门，然后线路维护部门根据得知的光缆线路传输性能劣化情况采取相应的维护措施。如果发生光纤断裂障碍，则立即派人员携带仪表（OTDR）查找光纤断裂的位置，同时组织人员、机具、器材等进行抢修，也就是通常所说的障碍抢修；如果是发生光纤通道总衰减增大，在其值可以容许时，则列入线路维修和改造计划，不可容许时，则组织人员对其进行抢修，以便改善其传输性能，提供可靠的电路。3 OTDR OTDR（光时域反射仪）是维护中测试光缆障碍的主要工具，用来测试光缆断点的位置，以便抢修人员能够及时到达现场进行抢修。它是采用后向散射发来测量光纤中的损耗。对于光纤损耗的测量，OTDR采用取样积分议和光脉冲激励的原理，对光纤中传输的光信号进行取样分析，可以判断出光纤中的接续点和损耗变化点，其原理如图1所示。图1 OTDR测试原理4光缆线路故障处理 由于光缆线路的复杂性，在光缆线路障碍中，对于不同性质的障碍采取不同的定位方法，。虽然都是使用OTDR对光缆故障点进行定位，但是测试定位时的参数设置、计算方式均有所区别。4.1部分系统阻断障碍 如果障碍是某一系统障碍，在排除设备故障的前提下，精确调整OTDR仪表的折射率、脉宽和波长，使之与被测纤芯的参数相同，尽可能减少测试误差。再将测出的距离信息与维护资料核对看障碍点是否在接头处。1、若通过OTDR曲线观察障碍点有明显的菲涅尔反射峰（菲涅尔反射是瑞利散射的特例，它是在光纤的折射率突变时出现的特殊现象），与资料核对和某一接头距离相近，可初步判断为盒内光纤障碍（光纤盒内断裂多为镜面性断裂，有较大的菲涅尔反射峰）。修复人员到现场后，可先与机房人员配合进一步进行判断，然后进行处理。2、若障碍点与接头距离相差较大，则为缆内障碍。这类障碍隐蔽性较强，如果定位不准，盲目查找就可能造成不必要的人力和物力的浪费，如直埋光缆大量土方开挖，架空光缆摘挂大量的挂钩等，延长障碍历时。4.2光缆全阻障碍 对于光缆线路全阻障碍，查找较为容易，一般为外力影响所致。可利用OTDR测出障碍点与局（站）间的距离，结合维护资料，确定障碍点的地理位置，指挥巡线人员沿光缆路由查看是否有建设施工，架空光缆是否有明显的拉伤、火灾等，一般可找到障碍点。若无法找到就需要用上面介绍的方法进行精确计算，确定障碍点。4.3由光纤衰耗过大引起的障碍 用OTDR测试系统障碍纤芯，如果发现障碍是衰耗空变引起的，可基本判定障碍点位于某接头出处，多是由于弯曲损耗造成的。盒内余留光纤盘留不当或热缩管脱落等形成小圈，使余纤的曲率半径过小。另外，接头盒进水也造成接头处障碍的主要原因。打开接头盒后，可进一步进行判断，将正常纤芯绕在手指上，使其曲率半径过小，此时用OTDR测试（1550nm）该处会有一大衰耗点，若该衰耗点与障碍光纤衰耗位置一致，则障碍点即为该点。再仔细查看障碍光纤有无损伤或盘小圈，若有小圈将其放大即可，否则进行重接处理。4.4机房线路终端障碍 如果障碍发生在终端机房内，在障碍端测试时，由于OTDR仪表净化不出规整曲线，在对端测试可以发现障碍纤芯测试曲线正常。为精确定位，需要加一段能避开仪表盲区的尾纤，一般长度不少于500m，先精确测出尾纤长度，再接入障碍光纤测试。5 案例分析 某光缆线路A站至B站段发生系统阻断，阻断的系统为80G和2.5G两个主干系统。技术人员赶赴A点无人站进行测试和抢修。在测试过程中，发现是光缆线路阻断，当即对光时域反射仪进行设置，针对光缆的线路参数，与线路参数相符，设置如下：=1550nm；Index=1.4690;Range=4Km。 测试界面虚线（B点）为光纤断点，定位距离为3.3730km。根据图纸（路由图和标石距离对照表校对），地面距离为956#-957#标石之间。到了现场之后，在光缆上方有一处施工的炕洞，判定为光缆线路路障碍点。组织人员对光缆进行开挖，并根据障碍情况制定修复方案。由于是外力施工造成，光缆外皮损伤严重，如果在障碍点进行处理，容易造成其他光纤的断裂并延发更多系统的阻断。所以只能在障碍点的两端进行光纤带业务割接的方式进行处理。工期紧操作人员只开挖接头坑，选择原厂生产的同期光缆100m。Key words: optical fiber communication, monitoring, caseAbstract: the paper introduces the optical fiber communication system to monitor the development, composition, introduces principle of OTDR test instrument and the maintenance of optical fiber communication system case.1 the current situation of the optical fiber cable1.1 size and technologyBecause the optical fiber communication has large capacity, high transmission information quality, long transmission distance, stable performance, the advantages of preventing electromagnetic interference, strong ability to resist corrosion, with light into the copper retreat to promote, to build complete eight vertical and eight horizontal cable transmission network connecting the national 31 provinces (autonomous regions and municipalities directly under the central government), optical fiber cable communication network become the main transmission network. On the other hand, as the light (SDH) and synchronous digital transmission network packet transmission technology (PTN) and the rapid development of dense wavelength division multiplexing (DWDM) technology, the transmission capacity of the fiber is developing at an unprecedented pace.1.2 the cause of the problemFiber is made from fragile glass, usually it is 125 um single-mode optical fiber in the fiber core diameter is only 7-8 um, multimode fiber in the fiber core is only 50 um, FBT fiber itself used to strengthen the core, ointment and plastic outer sheath protect optical fiber, the fiber optic cable has a certain external force strength. But due to the large construction period with the brutal construction, the impact of the strong force, combined with the fiber optic cables own reasons such as crack, water, corrosion and cable connector box natural aging factors, will often result in fiber optic cable transmission system fault. Optical cable lines and laid by buried, aerial and underground pipelines, has a long point, line, area wide, the characteristics of the highly fragmented, affected by external force is big, because the cables own external causes of blocking barrier, involving the expansion and fiber optic cables, move, change, move on optical cable line construction maintenance, maintenance amount is much and difficult. How to quickly detect cable and the fault location become engineers or technicians necessary skills.2 fiber optic monitoring systemOptical fiber cable line automatic monitoring system is mainly composed of the provincial monitoring center PMC, regional monitoring center LMC, on-site monitoring station of MS. Monitoring center is responsible for control of monitoring stations, is the center of the data acquisition and processing, by the controller (server, client, workstations, routers, the hub/exchange type, network adapter, MODEM, printer, and the corresponding software, etc.In long distance and local relay cable transmission system, transmission equipment configuration have bit error rate (BER) of the monitoring devices or monitoring unit. However, the traditional route maintenance department is not equipped with monitoring means, is usually only appears when BER alarm, first of all, determine the cause of the alarm by maintenance personnel, and find out the reason for this is that in transmission lines, cable, crew to inform the related lines and submitted to the competent department, maintenance department and line maintenance department according to know the maintenance of optical cable circuit transmission performance degradation take corresponding measures. If fiber fracture occur disorder, then immediately send personnel to carry instrument (OTDR) to find the location of the optical fiber fracture, organize personnel, machinery, equipment, etc to repair at the same time, known as the barriers to repair; If it is happened fibre channel attenuation increases in total, with its value can be allowed, are included in the line maintenance and transformation, do not allow, organize personnel to repair, in order to improve the transmission performance, provide reliable circuit.3 OTDROTDR (optical time domain reflectometer) is the main tool, maintenance of test cable barriers to test cables breakpoint position, so that emergency workers arrived at the scene to repair in time. After it is used to scattering from the measurement of optical fiber loss. For measuring optical fiber loss, OTDR USES the sampling points and the principle of optical pulse excitation, the optical transmission of light signal sampling analysis, can judge the connection point and loss change point in the fiber, the principle is shown in figure 1.Figure 1 OTDR test principle4 cable line fault processingBecause of the complexity of the fiber optic cable line, in the optical cable circuit obstacle, to the obstacles of different nature take different positioning methods,. Although all is the use of OTDR cable fault point location, but the test parameter Settings when positioning and calculation are different.4.1 part of the system obstaclesThe barrier, if the obstacle is a system on the premise of exclusion of equipment failure, the refractive index of a precise adjustment of OTDR instrument, pulse width and wavelength, make it the same as the measured the parameters of the fiber core, as far as possible to reduce the test error. Then measure the distance of the information and maintenance data check to see if the barriers in the junction.1, if by OTDR curve Fresnel reflection peak of observation points have obvious obstacles (Fresnel reflex is a special case of Rayleigh scattering, it is a special phenomena when the refractive index of the fiber mutation), and data check and a joint distance close, can preliminary judgment for optical fiber barrier inside the box (fiber fracture more for mirror sexual fracture, inside the box has the larger Fresnel reflection peak). Repair personnel to the scene, can with the first room personnel further judgment, and then for processing.2, if the barriers and joint distance is large, for the cable in disorder. This kind of strong concealment of the barrier, if positioning, blind search is likely to cause unnecessary waste of manpower and material resources, such as directly buried cable of earthwork excavation, aerial cable to pick a peg to hang a lot of, extend the obstacle lasted.4.2 cable resistance barriersFor optical fiber cable line all resistance barriers and find easy, is commonly caused by outside influence. Available OTDR detect obstacle distance between the point and the bureau (station), combined with the maintenance data, determine the barriers of geography, command patrol personnel along the cable routing to see whether there is a construction, aerial cable if there is a obvious injury, fire, etc., can generally be found the barriers. If cant find you need using the precise calculation method mentioned above, determine the barriers.4.3 caused by fiber attenuation is too large obstaclesSystem obstacle by OTDR fiber core, if it is found that the disorder is caused by the attenuation space-variant, can judge barrier basic point is located in a joint source, mostly caused by bending loss. Remaining fiber optic disk remain inside the box or improper heat shrinkable tube falls off form small circle, such as more than make fiber curvature radius is too small. In addition, the connector box water is the main cause of joint disorder. After open the connector box, can further judgment, the normal fiber core around the fingers, and make its curvature radius is too small, this time by OTDR (1550 nm), there will be a big loss, if the loss point is consistent with the obstacle position of optical fiber attenuation, the barriers to that point. Check again carefully fiber without damage or plate of small circle, if have a small circle its amplification can, otherwise again processing.4.4 room line terminal barriers, if the obstacles in the terminal room on disorder test, because the OTDR instrument cleaning out neat curve, the obstacles will be found to end to test fiber core test curve is normal. For accurate positioning, it is necessary to add a section to avoid blind area of the tail fiber, generally not less than 500 m in length, to accurately measure the tail long first degrees, fiber access barriers to test again.5 case analysisA fiber optic cable line management system of A station to B block, block system is 80 G and 2.5 G two main systems. Technical personnel to point A unmanned station for te