可见光通信 与光共舞

作者:未知 来源:经济学人 2013-07-05

    Science and technology
    科学技术

    Visible-light communication
    可见光通信

    Tripping the light fantastic
    与光共舞

    A fast and cheap optical version of Wi-Fi is coming
    一个高速而廉价的光学Wi-Fi即将问世

    AMONG the many new gadgets unveiled at the recent Consumer Electronics Show in Las Vegas was a pair of smartphones able to exchange data using light.
    最近,在拉斯维加斯国际消费电子展上首次展出的电子产品中,有一对能利用光交换数据的智能手机。

    These phones, as yet only prototypes from Casio, a Japanese firm, transmit digital signals by varying the intensity of the light given off from their screens.
    目前,这两部不过是日本卡西欧公司的样机,它们能通过改变自身屏幕的光强来传传输数字信号。

    The flickering is so slight that it is imperceptible to the human eye, but the camera on another phone can detect it at a distance of up to ten metres.
    这样的闪光很微弱,人眼无法感知,但另一部手机的摄像头能够在十米的范围内检测得到。

    In an age of Wi-Fi and Bluetooth, flashing lights might seem like going back to sending messages with an Aldis lamp.
    在这个Wi-Fi和蓝牙横行的时代里,使用闪光可能有点像回到用奥尔迪斯手提信号灯发送信息的年代。

    In fact, they are the beginning of a fast and cheap wireless- communication system that some have labelled Li-Fi.
    事实上,它们正是有人称之为Li-Fi的高速、廉价的无线通讯系统的鼻祖。

    The data being exchanged by Casio’s phones were trifles:
    两部卡西欧手机交换的数据量非常小:

    message balloons to be added to pictures on social-networking sites.
    不过是添加在社交网站图片中的虚拟对话框。

    But the firm sees bigger applications , such as pointing a smartphone at an illuminated shop sign to read information being transmitted by the light:
    但卡西欧公司发现这项技术有更大的应用前景,比如将智能手机对准发光的商店招牌读取通过灯光传送的信息:

    opening times, for example, or the latest bargains.
    如营业时间或最新优惠。

    Yet that is still only a flicker of what is possible.
    但是,这项技术可能有万千功能,以上不过是冰山一角。

    Last October a number of companies and industry groups formed the Li-Fi Consortium, to promote high-speed optical wireless systems.
    去年十月,多家公司及实业集团共同成立了Li-Fi联盟,以推广高速无线光学通信系统。

    The idea is that light can help with a looming capacity problem.
    他们的想法是可见光通信将有助于解决即将来临的数据传输瓶颈问题。

    As radio-based wireless becomes ubiquitous, more and more devices transmitting more and more data are able to connect to the internet, either through the mobile-phone network or through Wi-Fi.
    随着无线电通讯的普及,越来越多的数据传输量越来越大的设备能够通过移动网络或Wi-Fi与互联网连接。

    But there is only a limited amount of radio spectrum available.
    但可用于通信的无线电频段是有限的。

    Using light offers the possibility of breaking out of this conundrum by exploiting a completely different part of the electromagnetic spectrum, one that is already ubiquitous because it is used for another purpose: illumination.
    运用一个完全不同的电磁波段—可见光,就有可能解决这个难题;这个波段其实早已相当常用,因为它有另一个作用:照明。

    Lighten the darkness
    照亮黑暗

    To turn a light into a Li-Fi router involves modulating its output, to carry a message, and linking it with a network cable to a modem that is connected to a telephone or cable-broadband service, just like a Wi-Fi router.
    要将一个可见光源变成能够携带信息的Li-Fi路由器,需要调制其光强以及用网线将其与一个调制解调器连接,一如Wi-Fi路由器。

    Incandescent light bulbs and fluorescent tubes are not really suitable for modulation,
    白炽灯和日光灯的光其实并不适合调制,

    but they are yesterday’s lighting technology.
    不过它们已是旧式的照明技术了。

    Tomorrow’s is the light-emitting diode.
    新式的照明技术是发光二极管,

    LEDs are rapidly replacing bulbs and tubes because they are more efficient.
    LED正凭借其更高的能量利用率迅速取代电灯泡和灯管。

    And because they are semiconductor devices, tinkering with their electronics to produce the flickering signals required for data transmission is pretty straightforward, according to Gordon Povey,
    歌登·波文在英国爱丁堡大学与哈拉尔德?哈斯及其同事一起研究光通信;他说,因为LED是半导体器件,

    who is working on light communication with Harald Haas and his colleagues at the University of Edinburgh, in Britain.
    调整一下其电路就能很轻易地产生传输数据所需的闪光信号。

    The rate of data transfer is also good. Dr Povey’s group is already up to 130 megabits a second over a distance of about two metres, using standard LEDs.
    用可见光传输数据的速度也相当可观。波文博士的研究小组已能利用标准LED在约两米内以最高每秒130兆位的速度传输数据。

    Dr Povey, who is also the boss of VLC, a firm set up to commercialise the technology, thinks such devices should be able to reach 1 gigabit per second, and do so over greater range.
    同时也是VLC公司的老板的波文博士认为这种器件应能达到每秒1千兆比特的传输速度,且传输距离可以更远。

    Specially constructed LEDs would be even faster.
    采用特制LED所达到的速度将会更高。

    The Li-Fi consortium reckons more than 10 Gbps is possible.
    Li-Fi联盟估计传输速度可能达到10 Gbps以上。

    In theory, that would allow a high-definition film to be downloaded in 30 seconds.
    理论上,这个速度意味着不到30秒就能下载一部高清电影。

    Dr Povey believes that adapting existing LEDs to work with the sensors and light sources—cameras, ambient-light detectors, screens, flashbulbs, torches and so on.
    波文博士认为,改造现在的LED使之适应智能手机及类似设备上已有的感应器及光源,如摄像头、环境光感应器、屏幕、闪光灯泡、手电筒等,

    already found in smartphones and similar devices will be the fastest way to bring Li-Fi to market.
    是将Li-Fi推向市场最快的方法。

    VLC has already produced a smartphone app which allows low-speed data transmission between a pair of iPhones.
    VLC已设计了一款智能手机软件,两部iPhone能用此软件以低速传输数据。

    It has also made an experimental optical transceiver that plugs into a laptop to receive and send light signals.
    该公司也制造了一台用作试验的光收发器,可插入笔记本电脑以收发光信号。

    Later this year it will bring out Li-Fi products for firms installing LED-lighting systems.
    今年再过不久,VLC将面向安装了LED照明系统的企业推出Li-Fi产品。

    There are limitations to using light, of course.
    当然,利用可见光通信也存在局限性。

    Unlike radio, light waves will not penetrate walls.
    可见光不同于无线电波,无法穿透墙壁。

    Yet for secure applications that could be a bonus.
    但对于安全应用而言这可能是个意外的优点。

    And light bulbs—some 14 billion of them around the world—are almost everywhere and often on.
    而全球大约共有一百四十亿个灯泡,它们几乎随处可见,而且经常亮着。

    As they are gradually replaced by LEDs, every home, office, public building and even streetlight could become a Li-Fi hotspot.
    随着电灯泡逐渐被LED所取代,每家每户、办公室、公共建筑物、甚至路灯都可能成为一个Li-Fi热点。

    Having a line-of-sight connection with the LED in question would undoubtedly improve the signal,
    若你正在使用的LED光源处于视线范围内,信号强度无疑会有所增加,

    but light reflected from walls or ceilings might often be enough.
    不过仅靠墙壁或天花板的反射光可能往往也足够了。

    In any case, having a good line of sight helps Wi-Fi as well.
    同样,不论如何,若在视线之内有Wi-Fi信号源,信号当然也会更强。

    And spotting a nearby light in order to sit next to it is certainly easier than finding the location of a Wi-Fi router.
    而在身边找一个光源就近使用之当然要比寻找Wi-Fi路由器来得容易。

    Communication, though, is a two-way street.
    不过通信是双向的。

    That means the LEDs involved in Li-Fi would need photodetectors to receive data.
    这意味着Li-Fi中的LED需要有光电探测器来接收数据。

    Some LED systems have such sensors already.
    一些LED系统已经配备这种探测器了。

    But even if LEDs are not modified Dr Povey reckons hybrid systems are possible:
    但即使不对LED进行改造,波文博士认为混合系统也可能行得通:

    data could be downloaded using light but uploaded using radio.
    通过光下载数据,而上传数据则使用无线电波。

    In an office, for example, an LED-powered desk lamp could work as a Li-Fi router, able to link up with any networked device placed on the desk.
    例如在一个办公室里,一盏LED台灯也可以是一个Li-Fi路由器,它能连接桌上任何一个已经联网的设备。

    A big advantage of light is that it can be used in areas which contain sensitive equipment that radio signals might interfere with, such as aircraft and operating theatres.
    可见光通信的一大好处在于:它在装有可能会受无线电信号干扰的敏感设备的场所能派上用场,如飞机上及手术室内。

    LEDs in the ceiling of an airliner would not only allow internet access but could also transmit films on demand to individual seats, removing the need for lots of expensive and heavy cabling, thus saving airlines fuel.
    将LED安装在大型客机的舱顶,不仅能提供网络服务,还能将旅客点播的电影传送至他们的座位上,这样就不必安装许多昂贵而又笨重的线缆,如此一来也会节省燃油。

    That alone could be enough to, as it were, make this idea fly.
    光是这一点,似乎就足以令这项技术腾飞。

    词语解释

    1.fantastic a.极好的;巨大的;奇异的

    We watched a fantastic play yesterday evening.
    昨天晚上我们看了一场非常精彩的演出。

    2.imperceptible a.感觉不到的;细微的

    The pulse is almost imperceptible.
    脉搏几乎摸不清。

    3.communication n.交流;通讯;传达

    Most important of all, computers create wide communication around the world.
    最重要的是,计算机在世界范围内建立了广泛的交流。

    4.application n.应用;申请;专心

    I didn't receive an acknowledgement of my application.
    对我的申请,我还没有收到复信告知收悉。

    5.flicker v.闪动;闪烁;摇动

    She is read by the flicker light of the candle.
    她借著闪烁的烛光读书。

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