无线网卡是如何工作的

Hans Neleman/Getty Images

Walk into any coffee shop and you'll see scores of people pecking away at theirlaptopcomputers. If you feel like everywhere you go -- from college campuses and libraries to Starbucks and McDonald's -- haswireless connectivity, you're not alone. Currently, 241,506WiFi hot spotsare scattered throughout 134 countries, and some of those "spots" are entire cities [source:JiWire].

These hot spots usually connect to the largerInternetcommunity by wires or cables and broadcast the Internet signal wirelessly to individual computers usingradiofrequencies. Many personal computers pick up that signal using awireless Internet card, a small device about the size of a credit card.

Advertisement

Wi-Fi everywhere. See morelaptop pictures.

Wireless Internet cards, also known asLocal Area Network, orLAN,cards, are one of the many types ofadapter cardsthat add capabilities to your computer. Other adapter cards can enableteleconferencing, improve sound systems or download photos from adigital camera.

Wireless Internet cards come in several forms. Different cards exist for laptops, desktops andPDAs. Many computers come with one preinstalled, but they can also be purchased relatively inexpensively and self-installed or simply inserted into a slot on the side of the computer.

The sheer number ofWiFihot spots has made wireless Internet cards even more desirable. Initially used mostly in homes or businesses so that multiple people could share an Internet connection, they are a hot commodity for anyone with a computer, especially with entire cities going wireless. For more information, readHow Municipal WiFi Works.

In this article, you'll learn how wireless Internet cards communicate with hot spots to connect to the Internet. You'll also learn about the different wireless cards available and what you should look for when buying one, so that you too can check youre-mailwhile sipping a soy latte.

Find out how a device no bigger than your hand can detect a signal hundreds of feet away on the next page.

Advertisement

Wireless Internet Background

Wi-Fi routers communicate with wireless Internet cards using radio waves.
Marcus Williams/How Stuff Works

To understand the mechanism behindwireless Internetcards, you first have to grasp how the wireless Internet itself works. Rather than transmitting data through a phone line,digital subscriber line(DSL) or high-speed cable, a wireless Internet network transmits data the same way thatradiosandcell phonesdo: radio waves.

AWiFihot spot, usually a wirelessrouteroraccess point, first receives information from the Internet the old-fashioned way: through wires. It then translates that data from thebinary form(the computer code of 1s and 0s) into radio waves. Next it broadcasts those radio waves into the surrounding area. Wireless signals typically travel between 75 feet and 150 feet (23 meters and 46 meters). In a wide open area with no obstacles, however, they have been known to transmit up to 1,000 feet (305 meters) and, with optimal conditions, even a mile (1.6 kilometers) [source:Wi-Fi Alliance]. More on those optimal conditions in a little bit.

Advertisement

Wireless Internet cards within the range of the radio signal pick it up using a tiny antenna and translate it back into binary code for yourcomputerto read. The process also works in the opposite direction, with the card translating your computer's information into radio waves to send to the router, where it is put back into binary form and sent to the Internet over the wires.

The radio communication used by wireless networks is slightly different from that of radios and cell phones. For instance, wireless Internet cards are designed to work at higher frequencies to handle more data -- typically either 2.4 gigahertz or 5 gigahertz. In addition, the cards and the routers can communicate on one of three different frequency channels. In cases where many people are using the wireless signal, like an airport crowded with business travelers, the cards and the routers can also jump between channels to reduce interference.

Wireless cards operate under networking standards that are a variation of the basic 802.11 standard. These standards were developed by theInstitute of Electrical and Electronics Engineersto differentiate between the various technologies. The802.11band802.11gstandards are the most common, while the faster802.11n, which was recently released, is not as widespread.

Although WiFi radio signals have some benefits over regular radio signals, they are still subject to interference by physical obstacles.Interferencehappens when a signal is hampered by distance or a physical obstacle. For instance, microwaves and manycordless phonesoperate in the same frequency used by some WiFi networks, so you might notice a slowdown in your service if you're trying to warm your latte while you sign on. Likewise, if you move to another room or if an elephant comes to stand between you and the hot spot, the signal could be lost.

Don't worry if you don't have your own wirelessnetwork at homeor at work. You can purchase prepaid wireless Internet cards in the U.S. from companies such as T-Mobile, which allow you access to all the T-Mobile hot spots. This can get kind of pricey, though, so you may want to kick in the cash to set up your own network or find a local spot that advertises a free Wi-Fi connection.

If you're overwhelmed by computer acronyms, brace yourself. On the next page, you'll learn the difference betweenPCI, PCMCIA (PC) and WCF cards.

Advertisement

Wireless Internet Cards for Laptops, Desktops and PDAs

Some wireless Internet cards are installed internally, while others, like this one, protrude from a slot on the computer.
AFP/Getty Images

If you've ever gone into acomputerstore and looked in the section devoted to adapter cards, you're aware of how many different kinds await you. Cards labeled asPCIrefer to the specific language the card uses to communicate with the computer's centralprocessor.PCIstands forPeripheral Component Interconnect, which is an industry standard that refers to the way an attached device talks to the computer through a central pathway called thebus.

PCI network adapters come in many different shapes and sizes calledform factors. Two common form factors are themini PCI, which is a wireless network card that comes embedded inside alaptopcomputer, and thePCI wireless adapter cardfor desktops. Since a desktop computer's bus is located inside the computer, wireless Internet cards for desktops have to be installed inside the unit, and most computers come with one preinstalled. If you want an external Internet adapter, you need to look for one that connects through theUSB.

Advertisement

Other labels you might see are thePC CardorExpressCarddesignations. Whereas PCI wireless network adapters communicate through a computer's bus, PC Card adapters just fit into a slot on the side and are used mainly in laptops because of their thin design. The newer ExpressCard technology has gradually been replacing PC Card adapters.

The PC Card and ExpressCard designations come fromPCMCIA,Personal Computer Memory Card International Association, which is the organization that developed a standard network adapter using the PC form factor. You'll sometimes see these cards labeled as PCMCIA cards. Regardless of the name, they all insert into a slot on the laptop's side, and typically stick out a little bit to better transmit and receive signals with their built-in WiFi antennas.

You also can buyUSBkeys that plug in to use as wireless adapters. These devices, which resemble the memory sticks orflash drivesyou stick into an available USB port on the side of your computer, seem to be an increasingly popular choice.

我另一个类型的无线nternet card exists forPDAs. For people who haven't yet jumped on theBlackBerrybandwagon, there isWCF.Wireless CompactFlashcards, like PC Cards, fit into a slot on the side or back of a PDA and enable it to communicate with the Internet.

The variations in wireless Internet cards don't stop there. Learn about some of the other differences next.

Advertisement

Comparing Wireless Internet Connection Cards

Wireless Internet cards come in many different flavors, like this one for PDAs.
Getty Images

You'll need to pay attention to several things when purchasing a wireless Internet card, such as the networking standard that the card uses. For example,802.11b, which used to be the dominantWiFistandard, is meant for wireless networks operating in the 2.4-gigahertz range. It supports a bandwidth of 11 megabits of data per second. Thebandwidthrefers to how much data can be transferred in a set amount of time. The higher the number, the faster the rate of transfer. So802.11gand802.11n, which send data over theInternetat speeds of 54 and 140 megabits per second, respectively, are going to stream your video faster than the clunkier 802.11b standard.

Paying attention to the network standard on the card you purchase is important because you need it to be able to communicate with the other wireless products you'll be using. For instance, if your home network uses the 2.4-gigahertz frequency, and you buy a card that just works in the 5-gigahertz range, you'll be out of luck. However, if you buy a card that is WiFi-certified for the same frequency band and with the same features (such asencryptioncodes) of the other products you'll be using, you're good to go. If you want a card that works on different frequencies, you can get adual-bandone, which will be compatible with all WiFi-certified products.

Advertisement

In addition, don't forget to look at the card's transfer rate, range and theoperating systemit requires. Also, consider whether you want a card with an external or internal antenna. Last but not least is security. Wireless networks are notoriously easier to hack into than wired ones, which means you have to take extra measures to protect yourself. The Wi-Fi Alliance suggests always connecting through a trusted provider that uses encryption technologies, enabling security if you have your own network and buying products that are WiFi-certified forWiFi Protected Access (WPA).

Wireless technology shows no signs of stopping its quest to allow you to check youre-mailanytime, anywhere. Soon you may even be able to surf the net while flying at 30,000 feet (9,144 meters). For more on wireless technology, including where to find the nearest hot spot, try some of the links on the next page.

Advertisement

Frequently Answered Questions

How do Wi-Fi cards work?
wi - fi卡工作,允许设备连接a wireless network. The card includes a radio receiver and antenna that allow the device to receive and transmit data over the air. The device must be within range of the router or access point to connect to a Wi-Fi network.

Lots More Information

Related HowStuffWorks Articles

More Great Links

  • Brain, Marshall, and Tracy V. Wilson. "How WiFi Works." HowStuffWorks. 2008. (May 9, 2008) //www.feetulcer.com/wireless-network.htm
  • Buechner, Mary Anne Murray. "How To Set Up A Wireless Home Network." May 19, 2003. (May 9, 2008) http://www.time.com/time/techtime/200305/story.html
  • Ellison, Craig and Daniel S. Evans. "How to Set Up a Wireless Home Network." Oct. 14, 2003. (May 9, 2008) http://www.pcmag.com/article2/0,4149,1276145,00.asp
  • Indiana State University. "Wireless Internet Access." Aug. 4, 2006. (May 9, 2008) http://ithelp.indstate.edu/wireless/
  • JiWire. "Wi-Fi Finder." 2008. (May 9, 2008) http://www.jiwire.com/search-hotspot-locations.htm
  • PCMCIA. "Frequently Asked Questions." 2008. (May 9, 2008) http://www.pcmcia.org/faq.htm
  • Vicomsoft. "Wireless Networking Q&A." 2007. (May 9, 2008) http://www.vicomsoft.com/knowledge/reference/wireless1.html
  • Wi-Fi Alliance. "FAQ." 2007. (May 9, 2008) http://www.wi-fi.org/knowledge_center_overview.php?type=2#3272

Advertisement

Loading...