Wireless Communication
A
wired medium provides a reliable, guided link that conducts an electric signal
associated with the transmission of information from one fixed terminal to
another. There are a number of
alternatives for wired connection that include twisted pair (TP) telephone
wiring for high-speed LANs, coaxial cables used for television distribution,
and optical fiber used in the backbone of long-haul connections.
Wires
act as filters that limit the maximum transmitted data rate of the channel
because of band limiting frequency response characteristics. The signal passing through a wire also
radiates outside of the wire to some extent which can cause interference to
close-by radios or other wired transmissions.
These characteristics differ from one wired medium to another. Laying additional cables in general can
duplicate the wired medium, and thereby increase the bandwidth.
Wireless
Transmission:
Compared with wired media, the
wireless medium is unreliable, has a low bandwidth, and is of broadcast nature;
however, it supports mobility due to its tetherless nature. Different signals through wired media are
physically conducted through different wires, but all wireless transmissions
share the same medium – air. Thus it is
the frequency of operation and the legality of access to the band that
differentiates a variety of alternative for wireless networking.
Wireless networks operate around 1
GHz (cellular), 2 GHz (PCS and WLANs), 5 GHz (WLANs), 28-60 GHz (Local
Multipoint Distribution Service [LMDS] and point-to-point base station
connections), and IR frequencies for optical communications. These bands are either licensed, like cellular
and PCS bands, or unlicensed, like the ISM bands or U-NII bands. As the frequency of operation and data rates
increase, the hardware implementation cost increases, and the ability of a
radio signal to penetrate walls decreases.
The electronic cost has
become less significant with time, but in-building penetration and licensed
versus unlicensed frequency bands have become an important
differentiation. For frequencies of up
to a few GHz, the signal penetrates through the walls, allowing indoor
applications with minimal wireless infrastructure inside a building. At higher frequencies a signal that is
generated outdoors does not penetrate into buildings, and the signal generated
indoors stays confined to a room. This phenomenon
imposes restrictions on the selection of a suitable band for a wireless
application.
Difference
between Wired and Wireless Medium:
Wired media provide us
an easy means to increase capacity – we can lay more wires where required if it
affordable. With the wireless medium, we
are restricted to a limited available band for operation, and we cannot obtain
new bands or easily duplicate the medium to accommodate more users. As a result, researchers have developed a
number of techniques to increase the capacity of wireless networks to support
more users with a fixed bandwidth.
The simplest method,
comparable to laying new wires in wired networks, is to use a cellular
architecture that reuses the frequency of operation when two cells are at an
adequate distance from one another.
Then, to further increase the capacity of the cellular network, one may
reduce the size of the cells.
In a wired network,
doubling the number of wired connections allows twice the number of users at
the expense of twice the wired connections to the terminals. In a wireless network, reducing the size of
the cells by half allows twice as many users as in one cell. Reduction of the size of the cell increases
the cost and complexity of the infrastructure that interconnects the cells.
Wireless
Networks:
A wireless
network, which uses high-frequency radio waves rather than wires to communicate
between nodes, is another option for home or business networking. Individuals and organizations can use this
option to expand their existing wired network or to go completely
wireless. Wireless allows for devices to
be shared without networking cable which increases mobility but decreases
range. There are two main types of
wireless networking; peer to peer or ad-hoc and infrastructure. (Wi-fi.com)
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. They can share files and printers this
way, but may not be able to access wired LAN resources, unless one of the
computers acts as a bridge to the wired LAN using special software.
An infrastructure wireless network
consists of an access point or a base station.
In this type of network the access point acts like a hub, providing
connectivity for the wireless computers. It can connect or bridge the wireless
LAN to a wired LAN, allowing wireless computer access to LAN resources, such as
file servers or existing Internet Connectivity. (compnetworking.about.com)
There
are four basic types of transmissions standards for wireless networking. These types are produced by the Institute of
Electrical and Electronic Engineers (IEEE).
These standards define all aspects of radio frequency wireless
networking. They have established four
transmission standards; 802.11, 802.11a, 802.11b, 802.11g.
The
basic differences between these four types are connection speed and radio
frequency. 802.11 and 802.11b are the
slowest at 1 or 2 Mbps and 5.5 and 11Mbps respectively. They both operate off of the 2.4 GHz radio
frequency. 802.11a operates off of a 5
GHz frequency and can transmit up to 54 Mbps and the 802.11g operates off of
the 2.4 GHz frequency and can transmit up to 54 Mbps. Actual transmission speeds vary depending on
such factors as the number and size of the physical barriers within the network
and any interference in the radio transmissions. (Wi-fi.com)
Wireless
networks are reliable, but when interfered with it can reduce the range and the
quality of the signal. Interference can
be caused by other devices operating on the same radio frequency and it is very
hard to control the addition of new devices on the same frequency. Usually if your wireless range is
compromised considerably, more than likely, interference is to blame. (Laudon)
A major cause of interference with
any radio signals are the materials in your surroundings, especially metallic
substances, which have a tendency to reflect radio signals. Needless to say, the potential sources of
metal around a home are numerous--things like metal studs, nails, building
insulation with a foil backing and even lead paint can all possibly reduce the
quality of the wireless radio signal. Materials with a high density, like
concrete, tend to be harder for radio signals to penetrate, absorbing more of
the energy. Other devices utilizing the same frequency can also result in
interference with your wireless. For example, the 2.4GHz frequency used by
802.11b-based wireless products to communicate with each other. Wireless devices don't have this frequency
all to themselves. In a business environment, other devices that use the 2.4GHz
band include microwave ovens and certain cordless phones. (Laundon)
On
the other hand, many wireless networks can increase the range of the signal by
using many different types of hardware devices. A wireless extender can be used
to relay the radio frequency from one point to another without losing signal
strength. Even though this device extends the range of a wireless signal it has
some drawbacks. One drawback is that it extends
the signal, but the transmission speed will be slowed.
There
are many benefits to a wireless network.
The most important one is the option to expand your current wired
network to other areas of your organization where it would otherwise not be cost
effective or practical to do so. An
organization can also install a wireless network without physically disrupting
the current workplace or wired network. (Wi-Fi.org) Wireless networks are far
easier to move than a wired network and adding users to an existing wireless
network is easy. Organizations opt for a
wireless network in conference rooms, lobbies and offices where adding to the
existing wired network may be too expensive to do so.
