通信英文文献
『壹』 通信方面的英文文献翻译！！
本翻译符合专业要求，请明鉴，不过赏分有点少了。
Spatial Compressive Sensing Approach For Field
Directionality Estimation.
用于场方向性估计的空间压缩传感方法
I. INTRODUCTION
1. 引言
Variety of techniques for field directionality estimation were
studied in literature [1]-[5]. Thus, a theoretical analysis of
the relationship between the hydrophone array output and the
noise field was concted in [1]-[5]. 用于场方向性估计的多种技术在文献中做了研究[1]-[5]。因此，对水听器阵列输出和噪声场之间的关系进行了理论的分析[1]-[5]。The developed techniques were based on the array beamformer output or the cross spectral
matrix between outputs of array elements [4]-[5]. 所开发的技术是基于阵列波束形成器的输出或阵列单元输出之间的互功率谱矩阵[4]-[5]。The problem of a field directionality estimation in ocean, using horizontal line towed array was also addressed in literature [5]-[8]. 用水平线拖曳阵列在海洋中的场方向性估计问题，在文献中也用水平线拖曳阵列着重做了研究[5]-[8]。Recently, problems of direction of arrival and field directionality
estimation for moving sensors arrays have attracted
renewed interest [9]-[12]. 近年来，移动的传感器阵列的到达方向问题和场方向性估计问题已重新引起人们的兴趣[9]-[12]。It was shown that an array motion
can improve an array performance assuming temporal coherence
of successive samples [10]-[11]. 已经证明，假设相继的样本的时间相干性，那么一个阵列的运动可以改善一个阵列的性能[10]-[11]。In [12], the wavefield
sampling method that exploits the linear relationship between
the noise field and the collection of beamformer outputs over
various array orientations was proposed.在文献[12]中，提出了探索噪声场和在各个不同阵列取向上采集波束形成器输出之间线性关系的波场取样方法。 It was shown that
the wavefield sampling (WS) method outperforms other tested methods. This algorithm was implemented via the recursive estimation method and its convergence to the unique solution was promised for a specific set of array orientations and beamformer look directions. 已经证明，波长取样方法（WS）胜过其他被试验的方法。这一算法通过递推估计法实施，并且它对唯一解的收敛有望用于一组特定阵列取向和波束形成器观察方向。However, a method for a proper array orientation and beamformer look direction sequence selection remains an open question. 然而，一种用于完美阵列取向和波束形成器观察方向顺序选择的方法仍然是一个公开的问题。
The quality of the field directionality estimation is determined by the angular resolution. The higher angular resolution is, the more accurate estimation of the far field sources,
and better detection performance can be achieved. 场方向性估计的质量由角度分辨率决定。角度分辨率越高，远场源的估计精度就越高，并能达到越好的检测性能。One of
fundamental relations in the array signal processing is that the angular resolution is directly proportional to the number of the array elements [13]. 在阵列信号处理中的基本关系之一就是角度分辨率与阵列元件数成正比[13]。This relation motivates the desire
for longer arrays that can achieve higher resolution. Unfortunately,
the requirement contradicts the implementation and installation limitations that motivate shorter arrays. 这一关系激发了采用能达到较高分辨率的较长阵列的欲望。不幸的是，这一要求与促进较短阵列的实施和敷设是矛盾的。Moreover, implementation of longer arrays for maneuvering platforms such as unmanned underwater vehicles (UUV) can even be
impossible [14]. 而且，对操纵平台（例如无人潜水器（UUV））实施较长阵列甚至会是不可能的[14]。These contradictions motivate the quest for alternative array signal processing methods. Usually, the field directionality is modeled as a finite set of strong far-field narrow-band sources and an isotropic lowpower noise [1]. 这些矛盾激发了人们对可供选择的阵列信号处理方法的寻找。通常，场方向性被建模为一组有限的强远场窄带源和一个各向同性的低功率噪声[1]。In this work, the model of the field directionality
is adopted in the following way. 在本文中，场方向性的模型以以下方式被采用。First, the bearing angle space is uniformly sampled into a large number of discrete
angles. 首先，象限角空间被均匀取样成大量分离的角度。Next, it is assumed that ether the high energy that corresponds to the far-field strong sources or the low-energy
that corresponds to the isotropic noise is received at the sensor
array from every of these discrete azimuth angles. 其次，假设与远场强源相应的高能量及与各向同性噪声相应的低能量都在传感器阵列处被从这些分离的方位角的每一个角度被接收。（译注：这里的ether漏字了，现按either翻译，如实neither则意思相反）
『贰』 求关于通信方面的 英文论文
1
Wireless technology was little more than just a distant idea for the majority of ordinary consumers ten years ago. However, it has exploded over recent years with the use of 3G phones and wireless home computing increasingly commonplace.
It would be foolish to suggest that wireless communication has reached its peak. Whilst mobile phones and home computing will continue to be the major focus in the quest for ever increasing sophistication within the technology, new applications are emerging daily.
One company, Securecom Technologies, based in Ireland, have been at the forefront of harnessing wireless technologies in the area of personal safety. They already have a number of procts in the marketplace designed to enable users to activate an alarm signal to a remote emergency centre wirelessly. Their Benefon range of applications are used by vulnerable elderly people, lone workers and VIPs to increase their sense of security and ability to effortlessly get in touch with help at the touch of the button.
They are now in the process of developing PERUSE1, which stands for 'Personal Safety System Utilising Satellite combined with Emerging Technologies'. The Peruse project will develop a Wireless Personal Alarm (WPA) solution which will be carried by or worn on a person and will allow the user to summon help at the touch of a button. When the alarm has been activated, the WPA will transmit a low power signal to a satellite communications headset which will forward a message to an authorised number. This will include the identity of the person in distress, as well as their current location. However, the ingenuity of the technology goes further as it will also have the potential to transmit the user's current state of health and local environmental parameters.
It is envisaged that the recipient of the users SOS signal will be a fully equipped Emergency Monitoring Centre to whom the user will have previously given full instructions as to the steps they would wish to have the Centre take on their behalf in the event of an emergency.
There are two core components that are in the development phase. The wireless personal alarm (WPA) and a 'dongle' which provides the handset for satellite communication use which will have a low power wireless link to the WPA.
The important issues here are that the two components will need to take into account size, cost, accuracy of location and battery autonomy. The main benefits will be that the device will be able to be worn or carried on a person discreetly. This makes it ideal for professions such as personal security, where the ability to communicate a message quickly and without fuss can often be of paramount importance. It will herald a new era in satellite communication. No longer will the user have to tap a keypad to enter a number nor will they have to move the handset for optimal signal strength prior to sending an emergence message. This technology will be invaluable to professions such as mountain rescue and will also be a tremendous benefit to those who enjoy hiking and climbing in the course of their leisure pursuits where conventional mobile phone technology can often be rendered useless.
There are currently no known competitors for this potentially life saving technology for which Securecom has filed for both Irish and European Patent Applications. Prototypes have already been manufactured and pilot programmes and laboratory tests are well under way.
UWB (Ultra Wide Band)2 is another example of emerging wireless technology. Alongside traditional wireless uses, UWB can also detect images through solid objects, such as people on the opposite side of a wall. This has led to an equal number of supporters and opponents.
Although UWB can be used for consumer applications in a similar fashion to Bluetooth technology such as cable elimination between a PC and its peripheral equipment, the more interesting applications focus on its 'radar 'like imagery. These applications could be used to find people trapped in a burning building, locating hostages and captors behind a thick wall and finding objects such as those that might be buried in the ground. Heightened security at airports and other public buildings can use UWB technology to detect weapons on people and bombs in luggage and packages. In this age of heightened security, post 9/11, the benefits of this emerging technology should not be understated.
A few companies have started to develop UWB procts, including XtremeSpectrum, Time Domain and Aether Wire. XtremeSpectrum is developing procts to enable the sending and receiving of multiple streams of digital audio and video for both battery powered and other consumer devices such as digital cameras, DVDs, DVRs, camcorders, MP3 players and set top boxes. Time Domain has developed a UWB chip set targeting three core technologies: wireless communication, precision location and tracking, and high definition portable radar whilst Aether Wire is working on miniature, distributed-position location and low data-rate communication devices. One of its goals is to develop coin sized devices that are capable of localisation to centimetre accuracy over kilometre distances.
However, privacy violation is one of the major concerns of the technology's opponents. Any technology that can 'see' through solid objects can be used for illegal purposes as well as legitimate ones. In theory, a UWB-enabled system could 'look through' the walls of a house to locate valuable objects and could detect when the occupants are not at home. Supporters, however, could rightly point out that this is a dilemma shared by many technologies that are used to enhance public safety - the juggling act between increased security versus decreased personal freedom. It could be argued that baggage searches at airports via x-ray and metal detection are common examples of us giving up privacy for better security, a price most people are willing to pay.
No other area is more at the forefront of the emergence of innovation in wireless technology than space exploration. Future missions to nearby planets like Mars will require space communication technologies that can provide an interplanetary satellite and navigation infrastructure via space systems that are far more compact and efficient than seen ever before. A longer term commitment will be necessary to resolve the challenges of efficient planetary communication e to the increase in distances involved as space exploration ventures further out into the solar system. To support planetary exploration, techniques developed for Earth-bound usage will be transferred to other planets as well. Exploration of Mars, for example, will require a high accuracy positioning capability such as a 'Martian GPS' as an aid to exploratory roving vehicles.
This very day, the 'Mars Spirit' space rover continues to send data back to Earth, almost 18 months after it touched down on the red planet, surviving more than 4 times its expected mission length. One day it is highly likely that we may see astronauts walking on Mars carting around wi-fi enabled PCs. In a remote Arizona meteor crater, NASA has already begun testing a mobile wi-fi system that could enable those on a Mars mission to easily deploy wireless data connectivity at a transmission rate of just more than a megabit per second over a 2 square mile area, and then change that coverage area at will through the use of mobile access points, making it entirely feasible to explore different terrain on any given day.
Tropos Networks3 developed the technology which NASA has adopted whereby the astronauts could have inter-connectivity via a three node mesh network. They would first establish a base communications station near their spacecraft and then set up an Ethernet connection between that base and a main access point. Then each node in the network would pick up its wireless connectivity from the access point.
Testing is still in its infancy and there is some way to go before astronauts would be strutting their stuff on Mars and communicating wirelessly with one and other and with mission control in this way.
However, the Mars Spirit space rover is still sending back images and data from the red planet today, relying heavily on wireless technology to do so. It may appear that these vehicles have been designed solely for the purpose of space exploration but closer scrutiny reveals applications that could also be modified and used on Earth. Unlike, say, a car manufacturing robot which knows where and when the engine or body appears on the assembly line, the Mars rovers are working in an unstructured and unknown environment. As a result, the rovers have had to learn about their new home through their own sensors, including a set of nine cameras on each rover. The rovers have two navigation cameras for a 3D view of their surroundings, two hazard avoidance cameras for a 3D view of nearby terrain and panoramic cameras to capture the images of the planet's surface. However, the rovers cannot just look around them, process the images and know where to go. Neither can the mission controllers on Earth grab a joystick and start steering the rovers whilst watching images being beamed back from thousands of miles away. A key reason is processing power. The central processor in each rover has a top speed of 20 MHz. Instead, ring the Martian night, while a rover is 'asleep', a team on Earth with much more powerful computers programs its activities for the day ahead, and then sends basic instructions on where to go and how to get there. Along with taking pictures, each rover is examining the planet with several instruments on a robotic arm. The arms have 'shoulder', 'elbow' and 'wrist' joints for manoeuvrability and are equipped with four sensors: a microscopic camera for close up pictures of rocks, an alpha particle x ray spectrometer for determining the mineral content of rocks, another spectrometer for detecting iron and a rock abrasion tool for cutting through the layer of oxidation that forms on the surfaces of Martian rocks. As with the movement of the rovers, the arms are controlled mostly via prepared commands from mission control.
Some observers have noted that some of these applications may prove useful here on Earth. For example, a robotic arm that doesn't require real time human control might be good for disabled people who use wheelchairs and can't control a joystick with their hands. Using its own sensors, it could reach out and get things for the person in the wheelchair, for example.
In addition, a robot that can deal with new and unknown environments might save manufacturers money. In current factories with 'robotic' workers, when the company shifts to making a new proct, the whole factory floor has to be reconfigured and the robots reprogrammed to deal with the new arrangement. A robot that could use feedback from sensors to figure out where things are could adapt to changes by itself, saving the company the time and effort of building a new structured environment and reprogramming the robots.
With all the emerging technologies around and, inevitably, with more to come, the inevitable hurdle will be one of convergence and integration as the IT instry seeks to develop the tools that will be most sought after. Inevitably, there will be winners and losers.
However, there is no doubt that the wireless phenomenon is reshaping enterprise connectivity worldwide and is definitely here to stay. Business needs information mobility for better customer interaction. Employees will be even more equipped to perform their job functions from their workplace of choice and, though this sounds like utopia, a societal change from office based to 'wherever they feel like being' based might conjure up an horrific vision of the future for company leaders who have enjoyed the traditions of having all their employees working from under the same roof.
Another major issue has to be one of security. There are many issues when it comes to security over wireless networks. Wireless networks do not follow the rules of traditional wired networks. Many times, the signals are carried far beyond the physical parameters they are meant to be controlled within making it easier to intercept signals and capture information.
There will also be the question posed of what happens to the have nots? - Those people and developing countries in particular that don't have the resources to wirelessly interact with others. The same thing could be said about the Internet itself but satellites could alleviate that problem far more quickly than the ability to put broadband connections in every office and home throughout the world.
Another major hurdle has to be that business and society can only adapt at a certain pace. Technology evolves far more quickly and there may be many a proct developed for which the demand is not yet there. But the mobile phone and PC market driven by what the consumer wants will determine what the future of wireless holds.
But there is no question that wireless communication is here to stay and will grow even more.
Signs of the new wireless technologies abound. Consumers are setting up wireless local area networks (WLANS) in their homes. These allow multiple computers to hook up to one fast internet connection or laptop users to connect from the comfort of their sofa or back garden patio. Away from home, 'Hotspots' that permit wireless connection to the internet are popping up everywhere, in book stores, coffee shops, airports and even pubs. Within the next year, airlines are expected to announce the availability of wi-fi ring flights. However, until there is increased competition in the market place, this new epoch will be there for the privileged few as opposed to the mass market who will still be relying solely on their mobile phones for wireless connectivity on the move. It remains to be seen whether the new generation of 3G phones has arrived too late to push aside wi-fi and it's even conceivable that mobile phone companies could one day find themselves obsolete unless they look for new ways to attract and retain customers.
But issues like security, along with the problems of cost, intrusion on privacy and identifying such things as hotspot locations is not going to hold wireless communication and technology back. In the end, there will always be solutions to problems and wi-fi is no different in this respect.
David Reed, an adjunct professor at MIT's Media Lab in Cambridge, Massachusetts has been studying the future of wireless communications. He draws a comparison with the new wi-fi revolution with that of the 'paperless society' which was often mooted in offices and homes all over the world with the advent of the PC. He said, The market will push us towards a wireless future. People love paper but I can't find a single person who can say that about wires.4
As more wi-fi systems are developed which will, in turn, drive the cost down it will become an increasingly less disruptive way to communicate in the future and it will become very difficult for anything else out there to compete with that.
2
It is used by millions of people every minute. For many people the Internet is a "room" that is situated somewhere behind their computer screens in a cyberspace. Though the Internet exists for about a decade it has become the medium of the new network society. The popular and commercial spreading of the Internet has been exceedingly significant - promoting changes in almost every sphere of human activity and society.
From the very beginning of the Internet in 1991, it has completely changed the way firms do business, as well as the way customers buy and use procts and services. The Internet gives extra opportunities for marketing. The spreading of the Internet has been so impetuous that it has been the point for well-grounded analysis. The Internet, virtual reality, can or cannot have negative effects on our culture and society? This paper is concentrated on the Internet phenomenon and on the spreading of the Internet culture and its effects on people.
The first ideas appeared in the 1950s. In the 1980s, technologies that became the basis of the modern Internet began to spread worldwide. In the 1990s the World Wide Web was used all over the world. The infrastructure of the Internet spread all over the world and the modern world wide network of computers have appeared. It spread amidst the western countries, then came into the developing countries and created a worldwide admittance to communications and data and a digital divide in admittance to this new infrastructure.
While studying the amount of Internet users, the Internet had 30 million users on 10 million computers linked to over 240,000 networks in about 100 states. The last figures indicate the fact that International Data Corp values that 40 million people are home web users in the USA in 1999, which consists of 15% of the population. “Le Monde” in 1998 published that 100 million people use the Internet all over the world. Jupiter Communications estimates that active Internet users - 4 to 5 million USA customers - shop regularly on the Internet by 2000, which represents 3% of grown-ups.
The Internet is a very attractive marketing tool with the possibility to customize pages, as well as new promotional systems, giving firms the possibility of communication and promotion effectively by adapting to consumers’ likings. Interactive traits of the Internet permit asking customers their likings, and then the firm can adapt proct offers and promotions to these likings. It provides the effective recruit of new customers. For instance, some car manufacturers ask Internet users for concrete information and in return give potential customers a $1,000 discount coupon or a free CD player coupon.
这里有很多，不知是通讯的具体什么方面，看看这里，找你想要的吧
http://www.ukessays.com/essays/communications/
『叁』 通信类英文论文、英文文献
基于WIN CE的ADSL线路参数研究
ADSL line parameters research based on WIN CE
http://books.google.com.sg/books?hl=en&id=jDmiKarm_EMC&dq=ADSL&printsec=frontcover&source=web&ots=oJXbatzNWO&sig=fyomvlADYeB7NRS2gjTJAfpSapQ
http://books.google.com.sg/books?hl=en&id=HsXaS5y6SZoC&dq=ADSL&printsec=frontcover&source=web&ots=EdCHuJT2WG&sig=QnNSogd7OIvYS7Z6Vr2UYal4iw8
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Windows CE (also known officially as Windows Embedded CE since version 6.0[2][3], and sometimes abbreviated WinCE) is a variation of Microsoft's Windows operating system for minimalistic computers and embedded systems. Windows CE is a distinctly different kernel, rather than a trimmed-down version of desktop Windows. It is not to be confused with Windows XP Embedded which is NT-based. It is supported on Intel x86 and compatibles, MIPS, ARM, and Hitachi SuperH processors.
Features
Windows CE is optimized for devices that have minimal storage—a Windows CE kernel may run in under a megabyte of memory. Devices are often configured without disk storage, and may be configured as a “closed” system that does not allow for end-user extension (for instance, it can be burned into ROM). Windows CE conforms to the definition of a real-time operating system, with a deterministic interrupt latency. It supports 256 priority levels and uses priority inheritance for dealing with priority inversion. The fundamental unit of execution is the thread. This helps to simplify the interface and improve execution time.
Microsoft has stated that the ‘CE’ is not an intentional initialism, but many people believe CE stands for ‘Consumer Electronics’ or ‘Compact Edition’; users often disparagingly called it “Wince”.[4] Microsoft says it implies a number of Windows CE design precepts, including “Compact, Connectable, Compatible, Companion, and Efficient.”[5] The first version, known ring development under the codename “Pegasus”, featured a Windows-like GUI and a number of Microsoft's popular applications, all trimmed down for smaller storage, memory, and speed of the palmtops of the day.
Since then, Windows CE has evolved into a component-based, embedded, real-time operating system. It is no longer targeted solely at hand-held computers. Many platforms have been based on the core Windows CE operating system, including Microsoft's AutoPC, Pocket PC 2000, Pocket PC 2002, Windows Mobile 2003, Windows Mobile 2003 SE, Windows Mobile 5.0, Windows Mobile 6, Smartphone 2002, Smartphone 2003 and many instrial devices and embedded systems. Windows CE even powered select games for the Sega Dreamcast, was the operating system of the controversial Gizmondo handheld, and can partially run on modified Microsoft Xbox game consoles.
A distinctive feature of Windows CE compared to other Microsoft operating systems is that large parts of it are offered in source code form. First, source code was offered to several vendors, so they could adjust it to their hardware. Then procts like Platform Builder (an integrated environment for Windows CE OS image creation and integration, or customized operating system designs based on CE) offered several components in source code form to the general public. However, a number of core components that do not need adaptation to specific hardware environments (other than the CPU family) are still distributed in binary form only.
Development tools
Visual Studio
Late versions of Microsoft Visual Studio support projects for Windows CE / Windows Mobile, procing executable programs and platform images either as an emulator or attached by cable to an actual mobile device. A mobile device is not necessary to develop a CE program. The .NET Compact Framework supports a subset of the .NET Framework with projects in C# and VB.NET, but not Managed C++.
Platform Builder
This programming tool is used for building the platform (BSP + Kernel), device drivers (shared source or custom made) and also the application. This is a one step environment to get the system up and running. One can also use Platform Builder to export an SDK (standard development kit) for the target microprocessor (SuperH, x86, MIPS, ARM etc.) to be used with another associated tool set named below.
Embedded Visual C++ (eVC)
The Embedded Visual C++ tool is for development of embedded application for Windows CE based devices. This tool can be used standalone using the SDK exported from Platform Builder or using the Platform Builder using the Platform Manager connectivity setup.
Relationship to Windows Mobile, Pocket PC, and SmartPhone
Often Windows CE, Windows Mobile, and Pocket PC are used interchangeably. This practice is not entirely accurate. Windows CE is a molar/componentized operating system that serves as the foundation of several classes of devices. Some of these moles provide subsets of other components' features (e.g. varying levels of windowing support; DCOM vs COM), others which are mutually exclusive (Bitmap or TrueType font support), and others which add additional features to another component. One can buy a kit (the Platform Builder) which contains all these components and the tools with which to develop a custom platform. Applications such as Excel Mobile/Pocket Excel are not part of this kit. The older Handheld PC version of Pocket Word and several other older applications are included as samples, however.
Windows Mobile is best described as a subset of platforms based on a Windows CE underpinning. Currently, Pocket PC (now called Windows Mobile Classic), SmartPhone (Windows Mobile Standard), and PocketPC Phone Edition (Windows Mobile Professional) are the three main platforms under the Windows Mobile umbrella. Each platform utilizes different components of Windows CE, as well as supplemental features and applications suited for their respective devices.
Pocket PC and Windows Mobile is a Microsoft-defined custom platform for general PDA use, and consists of a Microsoft-defined set of minimum profiles (Professional Edition, Premium Edition) of software and hardware that is supported. The rules for manufacturing a Pocket PC device are stricter than those for procing a custom Windows CE-based platform. The defining characteristics of the Pocket PC are the digitizer as the primary Human Interface Device and its extremely portable size.
The SmartPhone platform is a feature rich OS and interface for cellular phone handsets. SmartPhone offers proctivity features to business users, such as email, as well as multimedia capabilities for consumers. The SmartPhone interface relies heavily on joystick navigation and PhonePad input. Devices running SmartPhone do not include a touchscreen interface. SmartPhone devices generally resemble other cellular handset form factors, whereas most Phone Edition devices use a PDA form factor with a larger display.
Windows Mobile 5 supports USB 2.0 and new devices running this OS will also conform to the USB Mass Storage Class, meaning the storage on PPC can be accessed from any USB-equipped PC, without requiring any extra software, except requiring a compliant host. In other words, you can use it as a flash drive.
Competing procts
Competitors to consumer CE based PDA platforms like Pocket PC – the main application of Windows CE – are Java, Symbian OS, Palm OS, iPhone OS and Linux based packages like Qtopia Embedded Linux environment from Trolltech, Convergent Linux Platform from a La Mobile, and Access Linux Platform from Orange and Access.
The secondary usage of CE is in devices in need of graphical user interfaces, (point of sale terminals, media centers, web tablets, thin clients) as the main selling point CE is the look and feel being similar to desktop Windows. The competition is Windows XP, Linux and graphical packages for simpler embedded operating systems.
Being an RTOS, Windows CE is also theoretically a competitor to any realtime operating system in the embedded space, like VxWorks, ITRON or eCos. The dominating method, however, of mixing Windows look and feel with realtime on the same hardware, is to run double operating systems using some virtualization technology, like TRANGO Hypervisor from TRANGO Virtual Processors or Intime from TenAsys in the case of Windows, and OS Ware from VirtualLogix, Padded Cell from Green Hills Software, OKL4 from Open Kernel Labs, TRANGO Hypervisor from TRANGO Virtual Processors, RTS Hypervisor from Real-Time Systems or PikeOS from Sysgo, in case of the competition.
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Asymmetric Digital Subscriber Line (ADSL) is a form of DSL, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. It does this by utilizing frequencies that are not used by a voice telephone call. A splitter - or microfilter - allows a single telephone connection to be used for both ADSL service and voice calls at the same time. Because phone lines vary in quality and were not originally engineered with DSL in mind, it can generally only be used over short distances, typically less than 3mi (5.5 km) [William Stallings' book].
At the telephone exchange the line generally terminates at a DSLAM where another frequency splitter separates the voice band signal for the conventional phone network. Data carried by the ADSL is typically routed over the telephone company's data network and eventually reaches a conventional internet network. In the UK under British Telecom the data network in question is its ATM network which in turn sends it to its IP network IP Colossus.
The distinguishing characteristic of ADSL over other forms of DSL is that the volume of data flow is greater in one direction than the other, i.e. it is asymmetric. Providers usually market ADSL as a service for consumers to connect to the Internet in a relatively passive mode: able to use the higher speed direction for the "download" from the Internet but not needing to run servers that would require high speed in the other direction.
There are both technical and marketing reasons why ADSL is in many places the most common type offered to home users. On the technical side, there is likely to be more crosstalk from other circuits at the DSLAM end (where the wires from many local loops are close to each other) than at the customer premises. Thus the upload signal is weakest at the noisiest part of the local loop, while the download signal is strongest at the noisiest part of the local loop. It therefore makes technical sense to have the DSLAM transmit at a higher bit rate than does the modem on the customer end. Since the typical home user in fact does prefer a higher download speed, the telephone companies chose to make a virtue out of necessity, hence ADSL. On the marketing side, limiting upload speeds limits the attractiveness of this service to business customers, often causing them to purchase higher cost Digital Signal 1 services instead. In this fashion, it segments the digital communications market between business and home users
How ADSL works
On the wire
Currently, most ADSL communication is full plex. Full plex ADSL communication is usually achieved on a wire pair by either frequency division plex (FDD), echo canceling plex (ECD), or time division plexing (TDD). FDM uses two separate frequency bands, referred to as the upstream and downstream bands. The upstream band is used for communication from the end user to the telephone central office. The downstream band is used for communicating from the central office to the end user. With standard ADSL (annex A), the band from 25.875 kHz to 138 kHz is used for upstream communication, while 138 kHz – 1104 kHz is used for downstream communication. Each of these is further divided into smaller frequency channels of 4.3125 kHz. During initial training, the ADSL modem tests which of the available channels have an acceptable signal-to-noise ratio. The distance from the telephone exchange, noise on the copper wire, or interference from AM radio stations may introce errors on some frequencies. By keeping the channels small, a high error rate on one frequency thus need not render the line unusable: the channel will not be used, merely resulting in reced throughput on an otherwise functional ADSL connection.
Vendors may support usage of higher frequencies as a proprietary extension to the standard. However, this requires matching vendor-supplied equipment on both ends of the line, and will likely result in crosstalk issues that affect other lines in the same bundle.
There is a direct relationship between the number of channels available and the throughput capacity of the ADSL connection. The exact data capacity per channel depends on the molation method used.
[edit] Molation
ADSL initially existed in two flavours (similar to VDSL), namely CAP and DMT. CAP was the de facto standard for ADSL deployments up until 1996, deployed in 90 percent of ADSL installs at the time. However, DMT was chosen for the first ITU-T ADSL standards, G.992.1 and G.992.2 (also called G.dmt and G.lite respectively). Therefore all modern installations of ADSL are based on the DMT molation scheme.
Annexes J and M shift the upstream/downstream frequency split up to 276 kHz (from 138 kHz used in the commonly deployed annex A) in order to boost upstream rates. Additionally, the "all-digital-loop" variants of ADSL2 and ADSL2+ (annexes I and J) support an extra 256 kbit/s of upstream if the bandwidth normally used for POTS voice calls is allocated for ADSL usage.
While the ADSL access utilizes the 1.1 MHz band, ADSL2+ utilizes the 2.2 MHz band.
The downstream and upstream rates displayed are theoretical maxima. Note also that because Digital subscriber line access multiplexers and ADSL modems may have been implemented based on differing or incomplete standards some manufacturers may advertise different speeds. For example, Ericsson has several devices that support non-standard upstream speeds of up to 2 Mbit/s in ADSL2 and ADSL2+.
[edit] Installation issues
Due to the way it uses the frequency spectrum, ADSL deployment presents some issues. It is necessary to install appropriate frequency filters at the customer's premises, to avoid interferences with the voice service, while at the same time taking care to keep a clean signal level for the ADSL connection.
In the early days of DSL, installation required a technician to visit the premises. A splitter was installed near the demarcation point, from which a dedicated data line was installed. This way, the DSL signal is separated earlier and is not attenuated inside the customer premises. However, this procere is costly, and also caused problems with customers complaining about having to wait for the technician to perform the installation. As a result, many DSL vendors started offering a self-install option, in which they ship equipment and instructions to the customer. Instead of separating the DSL signal at the demarcation point, the opposite is done: the DSL signal is "filtered off" at each phone outlet by use of a low pass filter, also known as microfilter. This method does not require any rewiring inside the customer premises.
A side effect of the move to the self-install model is that the DSL signal can be degraded, especially if more than 5 voiceband devices are connected to the line. The DSL signal is now present on all telephone wiring in the building, causing attenuation and echo. A way to circumvent this is to go back to the original model, and install one filter upstream from all telephone jacks in the building, except for the jack to which the DSL modem will be connected. Since this requires wiring changes by the customer and may not work on some household telephone wiring, it is rarely done. It is usually much easier to install filters at each telephone jack that is in use.
『肆』 光纤通信英文文献
直接点击下载
【图书】
Fiber-optic communication systems
GP Agrawal, GP Agrawal - 1997
http://www.master-photonics.org/uploads/media/Govind_Agrawal1.pdf
【期刊】
A receiver model for optical fiber communication systems with arbitrarily polarized noise
IT Lima Jr, AO Lima, Y Sun, H Jiao- Journal of Lightwave , 2005
http://www.photonics.umbc.e/home/members/publications/PdfPapers/PAJ187.pdf
Nonlinear loop mirror-based all-optical signal processing in fiber-optic communications
S Boscolo, SK Turitsyn- Optical Fiber Technology, 2008
http://www-users.aston.ac.uk/~turitssk/OFTNOLM2008.pdf
Capacity limits of fiber-optic communication systems
RJ Essiambre, G Foschini, P Winzer. Fiber Communication , 2009
http://ee.usc.e/~gkramer/Papers/OFC09tutorial.pdf
『伍』 求一个关于通信的英文文献
在数据库里找!
学校里有买的网上数据库,在里面有!
『陆』 有关通信工程的英文文献（2000字左右）有中英翻译来一篇，谢谢了
外文文献有，翻译没有，翻译得靠你自己了，如果需要直接网络Hi中留言贴出问题的链接地址及邮箱地址即可，希望能满足你的需要，能帮到你，并请及时知道评价，多多给点悬赏分吧，急用的话请多选赏点分吧，这样更多的知友才会及时帮到你，我找到也是很花时间的
『柒』 通信工程的外文文献有哪些
可以上网络文库查找
『捌』 跪求通信电子类的英文原版期刊或文献
外文文献可抄以用你们图书馆袭的外文数据库检索, 如www.sciencedirect.com, www.springerlink.com
自己去找吧 学校里面可以下载到的！英文关键词可以利用www.iciba.com网站翻译～