Wireless LANs are similar to television, cordless phones, and cellular phones in that they use radio frequency (RF) technology to transmit and receive data over the air, minimizing the need for wired connections. The radio signals are converted into digital data (actually small packets of information) that can be understood and processed.

In 1997, a standards committee of the IEEE defined a wireless networking service with the musical name "802.11." Standard 802.11b uses frequencies in the 2.4-GHz band to transmit data at up to 11 Million bits per second (Mbps), though lower rates of 5.5, 2 and 1 Mbps are defined in the standard for situations in which the signal conditions won't allow full network speed.

The growth of the Internet and online services has created a need for users to gain access without looking for a place to plug in, using conventional wires and networks. Wireless LANs offer the following advantages over traditional wired networks:

• Convenience: Always on connection without the delays and hassle of dialup.
• Standards based, not proprietary: Based on the IEEE 802.11b standard.
• Installation Speed and Simplicity: Installing a wireless LAN is fast and easy.
• Flexibility: Allows the user and network to go where wires cannot.
• Scalability: Configurations are easily changed to meet the needs of the user.
• Reliable and secure: Uses encryption techniques for secure data transmission.

Wireless is wireless
There's no wiring involved in a wireless networking infrastructure. Instead, data is sent over radio airwaves from PCs via wireless PCMCIA or PCI cards; the data is then received and transmitted from radio access points.

Spread Spectrum Technology
Spread spectrum products are so named because they "spread" their transmitted signal over a wide range of the radio frequency (RF) spectrum. They avoid concentrating power in a single narrow frequency band. Most wireless local area network (LAN) systems use spread-spectrum technology. Spread-spectrum technology is a wideband radio frequency technique, developed by the military, for use in reliable, secure communications systems. Spread-spectrum is designed to trade off bandwidth efficiency for reliability, integrity, and security. In other words, more bandwidth is consumed than in the case of narrowband transmission. The tradeoff of using wideband transmission produces a signal that is, in effect, louder and thus easier to detect.

There are two types of spread spectrum radio: Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS). Direct Sequence Spread Spectrum or Frequency Hopping Spread Spectrum technologies both operate in the unlicensed 2.4 Giga-hertz (GHz) Industrial, Scientific, and Medical (ISM) band frequencies. Let's look at each of these.

Frequency-Hopping Spread Spectrum Technology
There are products today that support the Frequency Hopping Spread Spectrum (FHSS) technology, which adheres to either the 802.11 or OpenAir standards. Frequency-hopping spread-spectrum (FHSS) uses a narrowband carrier that changes frequency in a pattern known to both transmitter and receiver. Properly synchronized, the net effect is to maintain a single logical channel.

Direct-Sequence Spread Spectrum Technology
There are products today that support the Direct Sequence Spread Spectrum (DSSS) technology, which adheres to the 802.11b standard. Direct-sequence spread-spectrum (DSSS) generates a redundant bit pattern for each bit to be transmitted. This bit pattern is called a "chip" (or chipping code). The longer the chip, the greater the probability that the original data can be recovered (and, of course, the more bandwidth required). Even if one or more bits in the chip are damaged during transmission, statistical techniques embedded in the radio can recover the original data without the need for retransmission.

How Wireless LANs Work
Wireless LANs use electromagnetic airwaves (radio or infrared) to communicate information from one point to another without relying on any physical connection. Radio waves are often referred to as radio carriers because they simply perform the function of delivering energy to a remote receiver. The data being transmitted is superimposed on the radio carrier so that it can be accurately extracted at the receiving end.

Multiple radio carriers can exist in the same space at the same time without interfering with each other if the radio waves are transmitted on different radio frequencies. To extract data, a radio receiver tunes in one radio frequency while rejecting all other frequencies.

In a typical wireless LAN configuration, a transmitter/receiver (transceiver) device, called an "access point", connects to the wired network from a fixed location using standard Ethernet cabling. The access point receives, buffers, and transmits data between the wireless LAN and the wired Ethernet network. A single access point can support a group of users.

Users access the wireless LAN through wireless-LAN adapter devices. These devices can be implemented as PCMCIA cards (slightly larger than credit cards) in notebook or laptop computers, as plug-in PC cards in desktop computers, or integrated within a USB device. These wireless-LAN adapter devices provide an interface between the computer's operating system and the airwaves via an antenna. The wireless connection is transparent to the computer's operating system. Radio signals are converted into digital data (actually small packets of information) the computer can understand and process.

Wireless LAN Configurations
Wireless LANs can be simple or complex. A simple LAN configuration would be two PCs equipped with wireless LAN adapter cards setup as an independent network whenever they are within range of one another. This is called a peer-to-peer or ad-hoc network. Networks such as in this example require no administration or pre-configuration. A complex LAN configuration can use a hardware access point to communicate with the wireless LAN adapter card. This is called an infrastructure network. The hardware access point is connected to a wired network using a standard Ethernet connection. The hardware access points acts like a wireless hub or gateway for the wireless LAN adapter card.