by Chris Woodford. Last updated: March 15, 2016.
Imagine for a moment if all the wireless connections in the world were instantly replaced by cables. You'd have cables stretching through the air from every radio in every home hundreds of miles back to the transmitters. You'd have wires reaching from every cellphone to every phone mast. Radio-controlled cars would disappear too, replaced by yet more cables. You couldn't step out of the door without tripping over cables. You couldn't fly a plane through the sky without getting tangled up. If you peered through your window, you'd see nothing at all but a cats-cradle of wires. That, then, is the brilliance of wireless: it does away with all those cables, leaving our lives simple, uncluttered, and free! Let's take a closer look at how it works.
Photo: A typical wireless router. This one, made by Netgear, can connect up to four different computers to the Internet at once using wired connections, because it has four ethernet sockets. But—in theory—it can connect far more machines using wireless. The white bar sticking out of the back is the wireless antenna.
From wireless to radio
Wireless started out as a way of sending audio programs through the air. Pretty soon we started calling it radio and, when pictures were added to the signal, TV was born. The word "wireless" had become pretty old-fashioned by the mid-20th century, but over the last few years it's made a comeback. Now it's hip to be wireless once again thanks to the Internet. By 2007, approximately half of all the world's Internet users were expected to be using some kind of wireless access—many of them in developing countries where traditional wired forms of access, based on telephone networks, are not available. Wireless Internet, commonly used in systems called Wi-Fi®, WAP, and i-mode, has made the Internet more convenient than ever before. But what makes it different from ordinary Internet access?
From radio to Wi-Fi
Radio is an invisible game of throw-and-catch. Instead of throwing a ball from one person to another, you send information, coded as a pattern of electricity and magnetism, from a transmitter (the thrower) to a receiver (the catcher)—both of which are kinds of antennas. The transmitter is a piece of equipment that turns electrical signals (such as the sound of someone speaking, in radio, or a picture, in TV) into an oscillating electromagnetic wave that beams through the air, in a straight line, at the speed of light (300,000 km 186,000 miles per second). The receiver is a mirror-image piece of equipment that catches the waves and turns them back into electrical signals—so we can recreate the radio sounds or TV pictures. The more powerful the transmitter and receiver, the further apart they can be spaced. Radio stations use gigantic transmitters, and that's why we can pick up radio signals from thousands of miles away on the opposite side of Earth. Wireless Internet is simply a way of using radio waves to send and receive Internet data instead of radio sounds or TV pictures. But, unlike radio and TV, it is typically used to send signals only over relatively short distances with low-power transmitters.
Artwork: The basic concept of radio: sending messages from a transmitter to a receiver at the speed of light using radio waves. In wireless Internet, the communication is two-way: there's a transmitter and receiver in both your computer (or handheld device) and the piece of equipment (such as a router) that connects you to the Internet.
If you have wireless Internet access at home, you probably have a little box called a router that plugs into your telephone socket. This kind of router is a bit like a sophisticated modem: it's a standalone computer whose job is to relay connections to and from the Internet. At home, you might use a router to connect several computers to the Internet at once (saving on the need for several separate modems). In other words, the router does two jobs: it creates a wireless computer network, linking all your computers together, and it also gives all your machines a shared gateway to the Internet.
You can connect a router to all your different computers using ordinary network-connecting cables (for the technically minded, these are called RJ-45, Cat 5, or Ethernet cables). This creates what's called a LAN (local area network) linking the machines together. A computer network is a very orderly affair, more like an organized committee meeting, with carefully agreed rules of behavior, than a free-for-all cocktail party. The machines on the network have to be hooked up in a standard way and they communicate in a very orderly fashion. The rules that govern the network setup and the communication are based on an international standard called Ethernet (also known as IEEE 802.3).
Photo: Left: If your laptop doesn't have a built-in Wi-Fi card, you can plug in a PCMCIA adapter card like this one. They're relatively inexpensive, especially if you get them on eBay. But beware: older PCMCIA cards may not support newer forms of wireless security such as WPA.
A wireless router is simply a router that connects to your computer (or computers) using radio waves instead of cables. It contains a very low-power radio transmitter and receiver, with a maximum range of about 90 meters or 300 ft, depending on what your walls are made of and what other electrical equipment is nearby. The router can send and receive Internet data to any computer in your home that is also equipped with wireless access (so each computer on the wireless network has to have a radio transmitter and receiver in it too). Most new laptops come with wireless cards built in. For older laptops, you can usually plug a wireless adapter card into the PCMCIA or USB socket. In effect, the router becomes an informal access point for the Internet, creating an invisible "cloud" of wireless connectivity all around it, known as a hotspot. Any computer inside this cloud can connect into the network, forming a wireless LAN. Just as computers connected to a wired LAN use Ethernet, machines on a wireless LAN use the wireless equivalent, which is called Wi-Fi (or, more technically, IEEE 802.11). Wireless Internet is improving all the time, so better forms of Wi-Fi are constantly evolving. You may see wireless equipment marked 802.11a, 802.11b, 802.11g or 802.11n: these are all broadly compatible variants of 802.11, with 802.11n, 802.11g and 802.11a somewhat faster than 802.11b. Other more recent variants are named 802.11a with an extra letter added on the end (such as 802.11ax, 802.11ay, and so on). For example, 802.11ah is designed to work with the so-called Internet of Things, 802.11ax is for high-efficiency LANs, and 802.11az is concerned with "location services" (finding the accurate position of mobile devices).
Wi-Fi is where the expression Wi-Fi hotspot comes from. A Wi-Fi hotspot is simply a public place where you can connect your computer wirelessly to the Internet. The hotspots you find in airports, coffee bars, bookshops, and college campuses use one or more wireless routers to create wireless Net access over a large area. The University of Twente in the Netherlands has one of the world's biggest hotspots. Using 650 separate access points, it has created a seamless hotspot that covers the entire 140 hectare (350 acre) campus. Cities like Philadelphia have also announced ambitious plans to turn huge areas into hotspots. Wi-Fi hotspots are now popping up all over the world. By 2007, there were estimated to be around 180,000 in the United States alone; in October 2012, the JWire directory was listing over 793,049 hotspots in 145 countries worldwide; and in 2015, according to the Wi-Fi Alliance, the number of worldwide hotspots exceeded five million.
Charts: Right: There's been huge worldwide growth in cellphones (mobile phones) and wireless Internet access over the last decade, particularly in developing countries. In 2000, there were 0.7 billion cellphone subscriptions worldwide and 71 percent of them were in high-income (developed) countries. By 2010, there were 5.9 billion subscriptions and 77 percent of them were in developing countries. The implications for Internet access are obvious: more and more people are going online from wireless mobile devices, especially in the developing world. 2012 Information and Communications for Development: Maximizing Mobile, World Bank, 2012.