Wireless Local Area Networks

Wireless Local Area Networks

A wireless local area network (LAN) is a flexible data communications system implemented as an extension to, or as an alternative for, a wired LAN. It uses radio frequency (RF) technology, to transmit and receive data over the air, minimizing the need for wired connections. A wireless LAN system can combine data connectivity with user mobility.

The data to be transmitted is modulated onto the radio waves, called carriers, and then are removed from the carriers at the other end by what is called a transceiver. End users in a wireless local area network access the network through adapters such as PC cards in laptop notebook computers. And PCI cards in desktop computers.

These cards provide the interface linking the network operating system (NOS) and the airwaves by means of an antenna. The wireless connection is clear to the network operating system as well as to those using the network, and it supports applications such as electronic mail (e-mail), access to shared peripherals, and access to multi-user databases and applications. Wireless LANs have gained popularity in areas such as the health-care, retail, manufacturing, warehousing and academia markets (Kurose, 2003).

Some widely known wireless technology in use in devices includes, cameras, automobiles, security systems, and kitchen appliances. Wireless LANs use electro magnetic airwaves (radio or infrared) to transmit information from one point to another without relying on any physical connection (Dean, 2000). Radio waves often are referred to as radio carriers because they simply perform the function to delivering energy to a remote receiver. Networking firms have a range of technologies to choose from when constructing wireless LANs. All technology comes with its own set of advantages and limitations. A narrowband radio system transmits and receives data on a specific radio frequency. Any unwanted crosstalk between communication channels is evaded by carefully designating different users on different channel frequencies. (Kurose, 2003)

The commonly used wireless systems used is the spread-spectrum technology, which is a wideband radio frequency technique developed by the military for use in reliable, secure communication systems. This technology is developed to substitute bandwidth effectiveness for security, reliability, and integrity (Dean, 2000). More bandwidth is consumed than in the case of narrowband transmission, but the end result produces a signal that is louder and easier to detect. If the receiver is not on the right frequency, a spread-spectrum signal looks like background noise. The two types of spread-spectrum radio are frequency hopping and direct sequence. (Behrouz, 2004)

Frequency-hopping spread-spectrum (FHSS) is a method that uses a narrow band carrier that changes frequencies in a distinct pattern. The signal hops to a variety of frequencies, with the exact sequence of changes, known as the hopping sequence. At any moment, the broadcast signal uses only one frequency, or even several frequencies is not enough to effectively affect the communication between devices. The FHSS is used between 2.4 GHz and 2.5 GHz and operates at a data rate of about 1.6 Mbs per channel. Direct sequence spread-spectrum (DSSS) generates a bit pattern for each bit to be transmitted. This bit pattern is called a chip or chipping code (Kurose, 2003).

Another technology that can be used in wireless networks is infrared light (IR). Infrared systems use very high frequencies, which are those just under visible light, to transfer data. IR cannot pass through dense objects. Therefore it must be used in line-of-sight or with diffused technology (Dean 2000). Line of sight, or directed, technologies have a very limited range, many times less than five feet, and are very unrealistic for people who work in environments clustered with things which would prevent line-of-sight between devices. Diffuse IR systems do not require line-of-sight, but units are still restricted to one individual room.

The simplest configuration for a wireless network is an independent LAN that connects a set of computers with wireless adapters. Any time two ore more of the wireless adapters are within range of each other, they can form a network. With such a network there is usually no administration or reconfiguration required.

Finally a wireless LAN can be connected to a standard wired backbone, and become an extension of that network, allowing users to share all the resources available on the network. This connection to the wired backbone is accomplished through Access points, which then acts as a bridge between the networks (Kurose, 2003). These access points are protocol free and work with networks using 10Base5, 2, and T connections. Wireless coverage