Wireless Networks
The increase use of laptop computers and worker mobility has fuelled the
demand for wireless networks. The Wireless network is a technology that
enables two or more computers to communicate without using cables. [1]
All computers in the Wireless network will broadcast their information to one
another by using radio signals, that produce a number of wireless solutions in
the environments where cabling isn’t practical or impossible. Moreover
wireless networking makes it much simpler to move the connected computers
around. [2]
Also It is easier to use wireless laptop computers and they are less intrusive ,
Wireless networking can be used with fixed position computers when the
building’s walls is very cost effective or difficult to be wired.
WLAN can be used in different environments such as home, public
cooperates, and schools or business projects where the wireless LAN can be
easily established. [1]
There are two kinds of wireless networks:
1. Peer to peer WLAN:
Peer to peer, or ad-hoc wireless network is a network has no central
control and no connection to the outside world, it consists of two or more
computers that equipped with a wireless networking interface card. Each
computer in the ad-hoc WLAN can have a direct communication with
every other wireless enabled computer. [1]
Figure 1: Peer-to-Peer Networking [1]
2. Infrastructure WLAN:
This kind of wireless network is using an access point, or base station,
which is a wired controller that receives and transmits data to the wireless
adapters installed in each computer. Each access points acts like a hub
that provides connectivity for the wireless computers, and can connect the
wireless LAN to a wired LAN.
Multiple access points can be used together; they can be connected to a
wired LAN or even to another second wireless LAN. Some access points
support a limit of 10 wireless connections, others can support up to 100
wireless connections. Using more computers than recommended will badly
affect the performance of the access point.
Figure 2: Infrastructure WLAN [1]
There are two types of access points, Hardware access points (HAP) that
offers a very good support for most wireless features see figure 2, and
Software Access Points, which run on a computer equipped with a
wireless network interface card, the Software access point can be used in
Peer to peer wireless networks see figure 1. [1]
IEEE 802 LANs
Wireless networking hardware requires the use of underlying
technology to deals with radio frequencies and data
transmission. IEEE 802.11 is the basic slandered for WLANs that
define all aspects of Radio Frequency Wireless networking. IEEE
802.11 produced by the Institute of Electrical and Electronic
Engineers (IEEE). [1]
802.11 LAN architecture:
The fundamental building block of 802.11 WLAN is the cell, which known
as the Basic service set (BSS). A BSS contain one or more wireless
station, which can be fixed or mobile, and one access point (AP) as a
central base station. The access points communicate among themselves
using IEEE 802.11 wireless MAC protocol to form a distributed System
(DS).
IEEE 802.11 stations can also group themselves together to form an ad
hoc network. An ad hoc has neither a central point nor a connection to
the outside world. An example of where ad hoc network can be formed is
when people with their lab tops meet in a conference room and want to
exchange information in absence of centralize access point. [3]
{I Have to add the graph from the book here.}
Indoors positioning using WLAN:
To understand the Indoors positioning methods using WLAN we
have to know the definition of the received signal strength. The
received signal strength is a function of the signal’s amplitude
that transmitted from the access point to the mobile terminal.
The received signal strength in two indoor positions sufficiently
apart are different. Moreover, the received signal strengths in
the same position at different times are the same. [4]
There are two positioning methods based on the signal
strength, the Empirical model and the Propagation model.
The Empirical model is based on recorded measurements
stored in a database. Theses measurements are the signal
strength at each particular location of the area from all the
access points, which can read that area. The mobile device
sends the signal strength from all access points to the server
that holds the database; the server will search the database to
find the matched location and then response the mobile device
with the location. [5]
The propagation model is based on the fact that the radio wave
travelling through an environment it loses some of its signal
strength. The distance from a wireless device to an access
point can be determined by the lost in signal strength over a
space. By determining the wireless device distance to three or
more access points, triangulation method can be used to
determine the exact location of that device. [5]
Ref
[1]-“Wireless Networking Q&A“, Vicomsoft Ltd, 2003.
http://www.vicomsoft.com/knowledge/reference/wireless1.html
[2]- Jeff Tyson “Wireless Networking: How Wireless Networking Works”
http://computer.howstuffworks.com/wireless-network1.htm
[3]- James F. Kurose and Keith W. Ross “Computer Networking: A top
Down Approach Featuring the Internet”, Addison Wesley Longman, 2001.
[4]- John Aa. Sørensen ,”Global and Mobile Application: Mobile Positioning
Technique” ,IT University of Copenhagen, 2003.
[5]-“Indoor positioning file “ http://www.ul.ie/nlenihan/WLAN%20positioning.pdf