Wireless networking technology

By Abbas Izadpanah

January 2007

ContentsThe components of Wires-WLAN

►Wireless stations►Access points►Ad hoc mode►Infrastructures mode►Roaming

►How wireless LANs work►ISM band►FHSS►DSSS►HR/DSSS►COFDM►Some other physical layers►MIMO

Wireless Local Area Network

A local area network that use wireless technology to connected computers in the network is called a wireless local area network (WLANs).

The components of Wires-WLAN

WLAN Stations-It Takes TwoWireless networking requires at least two radios. Each computer or device containing a radio that transmits and/or receives data over the wireless network is called a station. And station can be client or a server.

The components of Wires-WLAN

►Access points– Wireless access point (APs), also called

wireless stations, have become a crucial component for any wireless network that goes beyond simple ad hoc status.

– There are two kinds of access points:Software Access Pointshardware access points

►Access points– Wireless access point (APs), also called

wireless stations, have become a crucial component for any wireless network that goes beyond simple ad hoc status.

– There are two kinds of access points:Software Access Pointshardware access points

Software Access Points

• Software Access Points which run on a computer equipped with a wireless network interface card as used in an ad-hoc or peer-to-peer wireless network.

Hardware Access Point

• Dedicated hardware access points (HAP) such as Lucent's WaveLAN, Apple's Airport Base Station or WebGear's AviatorPRO.

Hardware Access Point cont…

• Access points come in many shapes, size, and configuration. However, no matter how else they might differ, all APs share the following components:• Antenna• Ethernet Port• LED Indicators• Reset Button• Power cord

• Note• Both wireless adapters and access

points must be the same brand.

Extension point

• Some manufacturers produce extension points, which act as wireless relays, extending the range of a single access point. Multiple extension points can be strung together to provide wireless access to far away locations from the central access point.

An ad-hoc, or peer-to-peer wireless network

• An ad-hoc, or peer-to-peer wireless network consists of a number of computers each equipped with a wireless networking interface card. Each computer can communicate directly with all of the other wireless enabled computers.

Wireless

pc

Wireless

pc

Wireless

pc

A

C

B

BSS 1

BSS 2

Infrastructures Wireless Network

• Infrastructures mode refer to a wireless network controlled through their wireless network access point that generate the signal for individual devices to read through their wireless network adapter.

PC

PC

PC

PC

PC

LAN

AP

Portal

BSS 1

BSS 2

ESS

DS

Roaming

• A wireless computer can "roam" from one access point to another, with the software and hardware maintaining a steady network connection by monitoring the signal strength from in range access points and locking on to the one with the best quality.

A user can move from Area 1 to Area 2 transparently. The Wireless networking hardware automatically swaps to the Access Point with the best signal.

USER

How wireless LANs work

• The IEEE 802.11 wireless networking standard define five ways that data can be transmitted between two wireless devices. These transmission method are called physical layers. Each physical layer is independent of other physical layers. Each pair of 802.11 complain radios uses of these physical layers to communicate.

The ISM Band

• In 1985 the Federal Communication commission (FCC) made change radios the radio spectrum regulation and assigned three bands designated as the industrial, scientific, and medical (ISM). These frequency bands are :♦ 902 MHz-928 MHz, a 26 MHz bandwidth♦ 2.4 GHz-2.4835 GHZ , a 83.5 MHz

bandwidth♦ 5.725 GHz-5.850 GHz, a 125 MHz

bandwidth

Frequency Hopping Spread Spectrum

• The Frequency Hopping Spread Spectrum physical layer is one of five available physical layers in 802.11.

Direct sequence Spread Spectrum

Direct-sequence spread-spectrum (DSSS) is another technique include in the IEEE 802.11 physical layer that uses DSSS can also transmit data at up to two Mbps.

It operates in the 2.4 MHz ISM band.

High Rate Direct Sequence Spectrum

• The High Rate Direct Sequence Spectrum physical layer is the most widely used 802.11 IEEE physical layer (1999).

• This layer specified by IEEE 802.11b supplement to the initial standard, uses an extension of IEEE 802.11 DSSS standard.

• It operates in the 2.4 MHz ISM band.

Coded Orthogonal Frequency Division Multiplexing

• Coded Orthogonal Frequency Division Multiplexing (COFDM) layer, specified in 802.11a supplement to the 802.11 standard. It operates in the 5 GHz ISM band.

Some other physical layers

• The IEEE 802.11 group is defining a physical layer that use OFDM in 2.4 GHz band. This allows 802.11a data rate (up to 54 Mbps) in the band used by 802.11b.

MIMO• (Multiple Input Multiple Output) Pronounced “

my-mo," it is the use of multiple transmitters and receivers (multiple antennas) on wireless devices for improved performance. When two transmitters and two or more receivers are used, two simultaneous data streams can be sent, which double the data rate. Multiple receivers alone allow greater distances between devices. The upcoming IEEE 802.11n wireless standard uses MIMO to, at a minimum, double the 54 Mbps speed of 802.11a and 802.11g to 108 Mbps.

Thank you

Tanks fromHooman ReisiAmin mahdavian