Sniffing About the Urban Jungle
Most of us know about Wi-Fi, the popular name for wireless networking that lets us hook up to the Internet in a cafe, in our garden or in an airport lounge, without cables and with surprisingly little hassle. Many of us have even set up our own little Wi-Fi networks in our homes. But could all those Wi-Fi beacons throwing out their signals be put to some other use? Like, say, finding our way around the urban jungle? Or to locate our car in a parking lot, or one of our kids in the mall?
Yes, they could. And they are. Wi-Fi positioning, for want of a better term, has got some exciting potential, not least that we and our offspring need never be parted again.
But, wait, I hear you say. Isn't this what Global Positioning Systems -- GPS -- are supposed to do?
Well, yes. But GPS has major limitations. GPS uses a network of satellites whose signals are picked up by a GPS receiver in your hand, or in your car or yacht, which then does a few calculations to pinpoint your position. The GPS receiver knows where the satellites are at that time of day, so all it needs is to get signals from three or more of them and it can triangulate from that information its position. This works fine in the open air, where there's line of sight between receiver and satellite, but not so great when things get in the way -- say a mountain, or a building, or a tunnel. So GPS navigation is great in the desert, open countryside or at sea, but lousy where you're likely to need it just as much: inside or amid tall buildings.
This is where Wi-Fi comes in. Your home Wi-Fi network gives off a signal, just like a GPS satellite. Your computer connects to your Wi-Fi network by sniffing out all the Wi-Fi signals it can find first (before connecting to the one it recognizes from before, or giving you a list of potential connections). This sniffing process is not unlike a GPS receiver sniffing for satellite signals, only the sniffing computer, or receiver, is not looking up to the heavens for information. It's looking for Wi-Fi signals on the ground, in buildings, coffee shops: wherever someone has put up a Wi-Fi network. That makes it a perfect complement to GPS. Wi-Fi thrives in those urban nooks and crannies, indoors and outdoors; in fact, just the places where GPS has problems.
Sniffing Out a Position
There's only one snag: Until it knows where, exactly, the signals are coming from the sniffer can't pinpoint its own position. Triangulation isn't much good if you don't know the precise location of the points you're triangulating from. For Wi-Fi to be as useful as a GPS satellite, someone has to pinpoint the exact source of all those Wi-Fi networks.
That's where folks like Ted Morgan come in. Mr. Morgan realized he was onto something after finding 700 Wi-Fi signals, or access points, in his Boston neighborhood. "We were amazed at the sheer number of access points that were being purchased and deployed," he recalls. So he set up Skyhook Wireless and sent forth teams to map all these Wi-Fi access points by driving around every street in 40 major U.S. urban centers. So, say you have a Wi-Fi box in your house. By driving around your block, Skyhook's technician is able to get a close fix on where the signal is coming from, whether it's your bedroom, den or living room. Triangulating from other access points he finds and maps in the neighborhood, he can pinpoint his location to within 20 to 40 meters. Compare that to GPS, which in urban areas can only be accurate within a block or two, according to Mr. Morgan.
Once this is all done, all sorts of services can pop up. GPS Industries, for example, uses Wi-Fi and GPS to offer golfers detailed information on the course, hazards, distances and shot measurements. Skyhook plans to make money by selling its maps to, say, a taxi company, so cabbies can pinpoint exactly where you are waiting (or so you can know how far away the taxi is). As Internet search engines get more localized to your needs, Wi-Fi could locate your exact position and ensure you got much more accurate matches to your requests for the nearest pizza stop.
Keeping Tabs On Kids
Downsides? The most obvious one is that systems like Skyhook rely on an ad-hoc network of Wi-Fi access points set up by ordinary folk like you and me. And those signals move. We move house, we go on holiday and turn it off, we forget to turn it on. Aren't people relying on the signal going to get disappointed if it's not on, or, if we move it, get horribly confused and wind up in Nova Scotia? No, says Mr. Morgan, because there are safeguards built in. For one, the end-user's Skyhook software relies on a rich patchwork of access points -- between 10 and 15 in most areas, he says -- reducing the error rate. Secondly, it doesn't just find out where the user is, but reports anomalies back to head office, so if you've moved your Wi-Fi network across the house, it spots this and will update the database.
And what about security? Not everyone will be happy to have people sniffing their access points and using them to get around, surely? Mr. Morgan says the sniffing is no different to what your Wi-Fi card does when you search for an access point: No attempt is made to get inside the Wi-Fi network itself.
I like the idea of Wi-Fi positioning, not least because it's making use of something that's already there. And its potential extends way beyond merely figuring out where you are more accurately: You could cheaply keep a tab on your kids in the mall by giving them a small Wi-Fi beacon and then monitor their movements around the toy section; collar your pets with a Wi-Fi beacon so they don't go missing; wander around museums using Wi-Fi to figure out what exhibit you're standing in front of and access a commentary via your Wi-Fi-ready personal digital assistant or phone. You could know whether a Wi-Fi-ready colleague is still at their desk and able to take a call or is walking down the corridor to the bathroom.
Of course there are scary implications too: Will we all end up being mere Wi-Fi tags monitored endlessly as we wander the planet? Could be. We'll have to deal with the privacy implications as they come up. But, in the meantime, if it gets me a pizza quickly, I'm all for it.
Wi-Fi定位 前景广阔
大多数人对于无线保真(Wi-Fi)技术已经是耳熟能详了。这是一种能让人们在咖啡馆、自家的花园或者候机厅、无需借助网线就可轻而易举地接驳互联网的网络连接技术。许多人已经在家里搭建了自己的Wi-Fi小型网络。但Wi-Fi能不能应用于其他领域呢，例如，用它在钢筋水泥的都市从林中寻找道路，或者用它来寻找放在停车场里的车辆，或者用它来在购物中心里帮助我们寻找走散的孩子？
当然可以，而且Wi-Fi也正应用在一些领域里。用更准确的定义来说，应该把这项应用称之为“Wi-Fi定位”。它具有令人心动不已的应用前景，凭借这项应用，我们就可以掌握孩子的行踪，再也不用担心他们走散。
我知道你会说，这不是全球卫星定位系统(GPS)应该完成的任务么？
你说的不错。但GPS在应用上有著很大的局限性。用户需要凭借手持接收器或者在汽车或游艇上安装接收器接收卫星信号，接收器从卫星获得信号后进行一些计算来确定你的位置。GPS接收器知道一天某个时候卫星的位置，它至少要从3个卫星上获取信号，然后根据信号画出你的三角坐标。在空旷的场地上，接收器能够畅通无阻地收到卫星发出的信号，这时候GPS的接收效果就会很好，但如果有高山、建筑或者隧道挡在接收器和卫星之间，GPS的接收效果就会很差。因此，GPS在沙漠、空旷的乡间和海面能提供良好的导航效果，但如果是在高层建筑里面或者高楼大厦之间导航效果就会不尽人意。
这个时候，Wi-Fi就派上了用场。你家里面的Wi-Fi网络会像GPS卫星一样发出信号。你电脑上的Wi-Fi设备先是搜索信号，之后通过以前就识别出来的连接或者一系列可用连接来接驳到你家里的Wi-Fi网络。这个搜索过程和GPS接收器搜索卫星信号并无区别。不过，装有Wi-Fi设备的电脑不用像GPS接收器那样仰著头、接收空中的信号，它搜索的是地面上、建筑里、咖啡馆里面的Wi-Fi信号。在城市的犄角旮旯、不论是户内还是户外，总而言之，在GPS接收效果不佳的地方，Wi-Fi可是大有用武之地。
但Wi-Fi也有一个软肋：只有在知道信号源在哪里之后，用户才能使用Wi-Fi搜索器确定出自己的位置。如果你不知道信号源确切位置的话，即使进行三角定位效果也不会很好。要想让Wi-Fi发挥定位功效，使用者必须首先要确定自己到底是接驳到了Wi-Fi网络中的哪个接入点。
泰德?摩根(Ted Morgan)就在进行这方面的研究。当他在波士顿的家附近找到了700个Wi-Fi接入点之后，他意识到他有事干了。他回忆说，如此之多的接入点让他感到震惊。为此，他组建了自己的公司Skyhook Wireless。他派出的队伍为寻找Wi-Fi接入点几乎走遍了美国40座主要城市的每一条街道，然后把搜索结果绘制成地图。如果你的家里有一个Wi-Fi信号发射器，Skyhook的技术人员就能确定信号的源头，不论信号来自你的卧室、书房，还是客厅。利用其他信号源进行三角测量，然后比照街区的信号源地图，定位的精度可以控制在20至40米之内。而据摩根介绍，GPS在城市地区的定位精度只能限制在1、2个街区之内。
一旦所有的条件都成熟了，各种设备就会应运而生。例如，GPS产业可以把Wi-Fi和GPS结合起来使用，为高尔夫选手提供地面情况、障碍物、距离和击球策略等方面的具体信息。Skyhook准备把出售信号源地图作为盈利点。例如，它可以把地图出售给一家出租车公司，这样出租车就可以确定乘客的位置，乘客也可以知道出租车离他还有多远。随著互联网搜索引擎在满足具有本地特色的需求方面做得越来越好，Wi-Fi可以让你确切把握自己的位置；如果你想知道距离你最近的比萨店在哪里，Wi-Fi能够确保让你获得精准得多的信息。
当然，什么事物都不是完美的。最需要改进的地方在于Skyhook这样的系统依赖于你我这类的普通人搭建的信号源网络，而这些信号源是会发生移动的，比如，我们会搬家、休假。而且，我们会关掉网络，或者忘记打开。如果信号源关闭，依赖这些信号源进行定位的人们是不是会无所适从，或者如果我们移动信号源，会不会使定位出现严重的误差？摩根表示，不会这样的。这是因为Skyhook已经采取了防范措施。Skyhook终端用户的软件获取的是一批接入点发出的信号，在大多数地区选定的信号源通常有10-15个，这样就降低了出错的概率。此外，如果不能确定用户位置的话，Skyhook就会向总部汇报出现了异常情况。因此，如果你把你的Wi-Fi网络从房间的一头移动到另一头，Skyhook会发现这个变化，并及时地更新数据库。
安全性如何？肯定会有人对搜索他们的信号源并把这些信号源散播出去感到不满。摩根表示，这个搜索过程与Wi-Fi卡搜索接入点别无二致，并不会闯入个人搭建的Wi-Fi网络的内部。
我看好Wi-Fi定位这项应用，而且Wi-Fi定位也经在一些场合派上用场了。它未来的功能将不止仅仅指出你的准确位置这样简单：在购物时你可以给你的孩子一个小型Wi-Fi信号发射器，让他们去玩具区玩耍，而这样你就可以安心地购物，并且能随时随地地掌握他们在玩具区的行踪；给你的宠物带上一个能发射Wi-Fi信号的项圈，这样它们就不会跑丢了；在博物馆里，你可以利用Wi-Fi来判断你面前的是哪个出口，或者通过支持Wi-Fi功能的个人数字助理或手机来获得展品的有关信息。你还可以知道一个配备Wi-Fi信号发射器的同事是还在工作、能接听电话，还是他正穿过走廊去往洗手间。
当然，也有一些可怕的应用：我们在环游世界时，我们的行踪可能会时时刻刻都在别人的掌控之中。出现这种情况时，我们将不得不解决隐私权这个问题。不过，至于能够帮助用户迅速找到比萨店这个应用，我还是非常支持的。
