Page 112 - DCAP311_DCAP607_WIRELESS_NETWORKS

Wireless Networks

Notes z z Discuss the SOHO application Notes

z z Describe about public wireless LAN network
z z Explain the ad hoc wireless LAN network
Introduction

Wireless LAN technology is evolving at a rapid pace. Within just a few years the industry has
seen the highest data rates provided by products based on the 802.11 standards migrate from 2
Mbps (802.11) to 11 Mbps (802.11b) and now to 54 Mbps (802.11a/g). Currently, active efforts
are underway within the IEEE to define a next generation standard to be known as 802.11n that
will enable rates potentially as high as 600 Mbps in a 40 MHz channel. In addition, efforts are
also underway to define the 802.11s standard for mesh networking. These developments, as well
as potential future technologies such as cooperative diversity, are creating new challenges and
opportunities in the design of low power wireless LAN products.

7.1 History of Wireless LAN

Heinrich Herz discovered and first produced radio waves in 1888 and by 1894 the modern way
to send a message over telegraph wires was first conducted. Marconi sent and received signals
up to two miles using radio waves. Marconi became known as the “father of radio”. By 1899,
Marconi sent a signal nine miles across the Bristol Channel and 31 miles across the English
Channel to France. In 1901 he was able to transmit across the Atlantic Ocean.
During World War II, the United States Army first used radio signals for data transmission.
This inspired a group of researchers in 1971 at the University of Hawaii to create the first packet
based radio communications network called ALOHNET. ALOHNET was the very first wireless
local area network (WLAN). This first WLAN consisted of 7 computers that communicated in a
bi-directional star topology. The first generation of WLAN technology used an unlicensed band
(902-928 MHz ISM), which later became crowded with interference from small appliances and
industrial machinery. A spread spectrum was used to minimize this interference, which operated
at 500 kilobits per second. The second generation of WLAN technology was four times faster
and operating at 2Mbps per second. Third generation WLAN technology operates on the same
band as the second generation and we currently use it today.
!
Caution In 1990, the IEEE 802 Executive Committee established the 802.11 Working Group
to create a wireless local area network (WLAN) standard. The standard specified an
operating frequency in the 2.4GHz ISM band. In 1997 the group approved IEEE 802.11 as
the world’s first WLAN standard with data rates of 1 and 2 Mbps.

7.2 Wireless Local Area Network

A wireless LAN (WLAN) provides network connectivity between devices, also known as
stations, by using radio as the communication medium. Devices that communicate over the
WLAN conform to the interfaces and procedures defined through the IEEE 802.11 standards.
The basic building block of the WLAN network is the 802.11 basic service set (BSS). A BSS defines
a coverage area where all stations within the BSS remain fully connected.
There are two BSS network topologies:
1. Infrastructure BSS Networks: In this topology, all stations within the BSS communicate
with each other through an access point (AP). In this situation, the AP establishes the BSS
network. In addition, an infrastructure BSS can consist of more than one interconnected
APs that establishes an extended service set (ESS) network.

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