Introduction to Wireless LAN
Wireless LAN stands for Wireless Local Area Network. It is also called LAWN (Local Area Wireless
Network). WLAN is one in which a mobile user can connect to a Local Area Network (LAN) through a
wireless connection.
The IEEE 802.11 group of standards defines the technologies for wireless LANs. For path sharing,
802.11 standard uses the Ethernet protocol and CSMA/CA (carrier sense multiple access with
collision avoidance). It also uses an encryption method i.e. wired equivalent privacy algorithm.
Wireless LANs provide high speed data communication in small areas such as building or an office.
WLANs allow users to move around in a confined area while they are still connected to the network.
In some instance wireless LAN technology is used to save costs and avoid laying cable, while in other
cases, it is the only option for providing high-speed internet access to the public. Whatever the
reason, wireless solutions are popping up everywhere.
Examples of WLANs that are available today are NCR's waveLAN and Motorola's ALTAIR.
Advantages of WLANs
o Flexibility: Within radio coverage, nodes can communicate without further restriction. Radio
waves can penetrate walls, senders and receivers can be placed anywhere (also non-visible,
e.g., within devices, in walls etc.).
o Planning: Only wireless ad-hoc networks allow for communication without previous
planning, any wired network needs wiring plans.
o Design: Wireless networks allow for the design of independent, small devices which can for
example be put into a pocket. Cables not only restrict users but also designers of small
notepads, PDAs, etc.
o Robustness: Wireless networks can handle disasters, e.g., earthquakes, flood etc. whereas,
networks requiring a wired infrastructure will usually break down completely in disasters.
o Cost: The cost of installing and maintaining a wireless LAN is on average lower than the cost
of installing and maintaining a traditional wired LAN, for two reasons. First, after providing
wireless access to the wireless network via an access point for the first user, adding
additional users to a network will not increase the cost. And second, wireless LAN eliminates
the direct costs of cabling and the labor associated with installing and repairing it.
o Ease of Use: Wireless LAN is easy to use and the users need very little new information to
take advantage of WLANs.
Disadvantages of WLANs
o Quality of Services: Quality of wireless LAN is typically lower than wired networks. The main
reason for this is the lower bandwidth due to limitations is radio transmission, higher error
rates due to interference and higher delay/delay variation due to extensive error correction
and detection mechanisms.
o Proprietary Solutions: Due to slow standardization procedures, many companies have come
up with proprietary solutions offering standardization functionality plus many enhanced
features. Most components today adhere to the basic standards IEEE 802.11a or 802.11b.
o Restrictions: Several govt. and non-govt. institutions world-wide regulate the operation and
restrict frequencies to minimize interference.
o Global operation: Wireless LAN products are sold in all countries so, national and
international frequency regulations have to be considered.
o Low Power: Devices communicating via a wireless LAN are typically power consuming, also
wireless devices running on battery power. Whereas the LAN design should take this into
account and implement special power saving modes and power management functions.
o License free operation: LAN operators don't want to apply for a special license to be able to
use the product. The equipment must operate in a license free band, such as the 2.4 GHz
ISM band.
o Robust transmission technology: If wireless LAN uses radio transmission, many other
electrical devices can interfere with them (such as vacuum cleaner, train engines, hair dryers,
etc.).Wireless LAN transceivers cannot be adjusted for perfect transmission is a standard
office or production environment.
Infrared vs Radio Transmission
Infrared Transmission
o Infrared technology uses diffuse light reflected at walls, furniture etc. or a directed light if a
line of sight (LOS) exists between sender and receiver.
o Infrared light is the part of the electromagnetic spectrum, and is an electromagnetic form of
radiation. It comes from the heat and thermal radiation, and it is not visible to the naked
eyes.
o In infrared transmission, senders can be simple light emitting diodes (LEDs) or laser diodes.
Photodiodes act as receivers.
o Infrared is used in wireless technology devices or systems that convey data through infrared
radiation. Infrared is electromagnetic energy at a wave length or wave lengths somewhat
longer than those of red light.
o Infrared wireless is used for medium and short range communications and control. Infrared
technology is used in instruction detectors; robot control system, medium range line of sight
laser communication, cordless microphone, headsets, modems, and other peripheral
devices.
o Infrared radiation is used in scientific, industrial, and medical application. Night vision
devices using active near infrared illumination allow people and animals to be observed
without the observer being detected.
o Infrared transmission technology refers to energy in the region of the electromagnetic
radiation spectrum at wavelength longer than those of visible light but shorter than those of
radio waves.
o Infrared technology allows computing devices to communicate via short range wireless
signals. With infrared transmission, computers can transfer files and other digital data
bidirectional.
Advantages of infrared
o The main advantage of infrared technology is its simple and extremely cheap senders and
receivers which are integrated into nearly all mobile devices available today.
o No licenses are required for infrared and shielding is very simple.
o PDAs, laptops, notebooks, mobile phones etc. have an infrared data association (IrDA)
interface.
o Electrical devices cannot interfere with infrared transmission.
Disadvantages of Infrared
o Disadvantages of infrared transmission are its low bandwidth compared to other LAN
technologies.
o Limited transfer rates to 115 Kbit/s and we know that even 4 Mbit/s is not a particular high
data rate.
o Their main disadvantage is that infrared is quite easily shielded.
o Infrared transmission cannot penetrate walls or other obstacles.
o Typically, for good transmission quality and high data rates a LOS (Line of site), i.e. direct
connection is needed.
Radio Transmission
o Almost all networks use radio waves for data transmission, e.g., GSM at 900, 1800, and 1900
MHz, DECT at 1880 MHz etc. Radio transmission technologies can be used to set up ad-hoc
connections for work groups, to connect, e.g., a desktop with a printer without a wire, or to
support mobility within a small area.
o The two main types of radio transmission are AM (Amplitude Modulation) and (FM)
Frequency Modulation.
o FM minimizes noise and provides greater reliability. Both AM and FM process sounds in
patterns that are always varying of electrical signals.
o In an AM transmission the carrier wave has a constant frequency, but the strength of the
wave varies. The FM transmission is just the opposite; the wave has constant amplitude but a
varying frequency.
o Usually the radio transmission is used in the transmission of sounds and pictures. Such as,
voice, music and television.
o The images and sounds are converted into electrical signals by a microphone or video
camera. The signals are amplified, and transmitted. If the carrier is amplified it can be
applied to an antenna.
o The antenna converts the electrical signals into electromagnetic waves and sends them out
or they can be received. The antenna consists commonly of a wire or set of wires.
Advantages of Radio Transmission
o Advantages of radio transmission include the long-term experiences made with radio
transmission for wide area networks (e.g. microwave links) and mobile cellular phones.
o Radio transmission can cover larger areas and can penetrate (thinner) walls, plants, furniture
etc.
o Additional coverage is gained by reflection.
o Radio typically does not need a LOS (Line of Site) if the frequencies are not too high.
o Higher transmission rates (e.g. 54 Mbit/s) than infrared (directed laser links, which offer data
rates well above 100 Mbit/s).
Disadvantages of Radio Transmission
o Radio transmission can be interfered with other senders, or electrical devices can destroy
data transmitted via radio.
o Bluetooth is simple than infrared.
o Radio is only permitted in certain frequency bands.
o Shielding is not so simple.
o Very limited ranges of license free bands are available worldwide and those that are available
are not the same in all countries.
o A lot harmonization is going on due to market pressure.
