A wireless network is any type of computer network that uses
wireless data connections for connecting network nodes.
Wireless networking is a method by which homes,
telecommunications networks and enterprise (business) installations avoid the
costly process of introducing cables into a building, or as a connection
between various equipment locations. Wireless telecommunications networks are
generally implemented and administered using radio communication. This
implementation takes place at the physical level (layer) of the OSI model
network structure.
Examples of wireless networks include cell phone networks,
Wi-Fi local networks and terrestrial microwave networks.
Wireless links
Computers are very often connected to networks using
wireless links
Terrestrial
microwave – Terrestrial microwave communication uses Earth-based transmitters
and receivers resembling satellite dishes. Terrestrial microwaves are in the
low-gigahertz range, which limits all communications to line-of-sight. Relay
stations are spaced approximately 48 km (30 mi) apart.
Communications
satellites – Satellites communicate via microwave radio waves, which are not
deflected by the Earth's atmosphere. The satellites are stationed in space,
typically in geosynchronous orbit 35,400 km (22,000 mi) above the equator.
These Earth-orbiting systems are capable of receiving and relaying voice, data,
and TV signals.
Cellular and PCS
systems use several radio communications technologies. The systems divide the
region covered into multiple geographic areas. Each area has a low-power
transmitter or radio relay antenna device to relay calls from one area to the
next area.
Radio and spread
spectrum technologies – Wireless local area networks use a high-frequency radio
technology similar to digital cellular and a low-frequency radio technology.
Wireless LANs use spread spectrum technology to enable communication between
multiple devices in a limited area. IEEE 802.11 defines a common flavor of
open-standards wireless radio-wave technology known as Wifi.
Free-space optical
communication uses visible or invisible light for communications. In most
cases, line-of-sight propagation is used, which limits the physical positioning
of communicating devices.
Types of wireless networks
Wireless PAN
Wireless personal area networks (WPANs) interconnect devices
within a relatively small area, that is generally within a person's reach. For
example, both Bluetooth radio and invisible infrared light provides a WPAN for
interconnecting a headset to a laptop. ZigBee also supports WPAN applications.
Wi-Fi PANs are becoming commonplace (2010) as equipment designers start to
integrate Wi-Fi into a variety of consumer electronic devices. Intel "My
WiFi" and Windows 7 "virtual Wi-Fi" capabilities have made Wi-Fi
PANs simpler and easier to set up and configure.
Wireless LAN
Wireless LANs are often used for connecting to local
resources and to the Internet
A wireless local area network (WLAN) links two or more
devices over a short distance using a wireless distribution method, usually
providing a connection through an access point for Internet access. The use of
spread-spectrum or OFDM technologies may allow users to move around within a
local coverage area, and still remain connected to the network.
Products using the IEEE 802.11 WLAN standards are marketed
under the Wi-Fi brand name. Fixed wireless technology implements point-to-point
links between computers or networks at two distant locations, often using dedicated
microwave or modulated laser light beams over line of sight paths. It is often
used in cities to connect networks in two or more buildings without installing
a wired link.
Wireless mesh network
A wireless mesh network is a wireless network made up of
radio nodes organized in a mesh topology. Each node forwards messages on behalf
of the other nodes. Mesh networks can "self heal", automatically
re-routing around a node that has lost power.
Wireless MAN
Wireless metropolitan area networks are a type of wireless
network that connects several wireless LANs.
WiMAX is a type of
Wireless MAN and is described by the IEEE 802.16 standard.
Wireless WAN
Wireless wide area networks are wireless networks that typically
cover large areas, such as between neighboring towns and cities, or city and
suburb. These networks can be used to connect branch offices of business or as
a public internet access system. The wireless connections between access points
are usually point to point microwave links using parabolic dishes on the 2.4
GHz band, rather than omnidirectional antennas used with smaller networks. A
typical system contains base station gateways, access points and wireless
bridging relays. Other configurations are mesh systems where each access point
acts as a relay also. When combined with renewable energy systems such as
photo-voltaic solar panels or wind systems they can be stand alone systems.
Cellular network
Example of frequency reuse factor or pattern 1/4
A cellular network or mobile network is a radio network
distributed over land areas called cells, each served by at least one
fixed-location transceiver, known as a cell site or base station. In a cellular
network, each cell characteristically uses a different set of radio frequencies
from all their immediate neighbouring cells to avoid any interference.
When joined together these cells provide radio coverage over
a wide geographic area. This enables a large number of portable transceivers
(e.g., mobile phones, pagers, etc.) to communicate with each other and with
fixed transceivers and telephones anywhere in the network, via base stations,
even if some of the transceivers are moving through more than one cell during
transmission.
Although originally intended for cell phones, with the
development of smartphones, cellular telephone networks routinely carry data in
addition to telephone conversations:
Global System for
Mobile Communications (GSM): The GSM network is divided into three major
systems: the switching system, the base station system, and the operation and
support system. The cell phone connects to the base system station which then
connects to the operation and support station; it then connects to the
switching station where the call is transferred to where it needs to go. GSM is
the most common standard and is used for a majority of cell phones.
Personal
Communications Service (PCS): PCS is a radio band that can be used by mobile
phones in North America and South Asia. Sprint happened to be the first service
to set up a PCS.
D-AMPS: Digital
Advanced Mobile Phone Service, an upgraded version of AMPS, is being phased out
due to advancement in technology. The newer GSM networks are replacing the
older system.
Global area network
A global area network (GAN) is a network used for supporting
mobile across an arbitrary number of wireless LANs, satellite coverage areas,
etc. The key challenge in mobile communications is handing off user
communications from one local coverage area to the next. In IEEE Project 802,
this involves a succession of terrestrial wireless LANs.
Space network
Space networks are networks used for communication between
spacecraft, usually in the vicinity of the Earth. The example of this is NASA's
Space Network.
Different uses
Some examples of usage include cellular phones which are
part of everyday wireless networks, allowing easy personal communications.
Another example, Inter-continental network systems, use radio satellites to
communicate across the world. Emergency services such as the police utilize
wireless networks to communicate effectively as well. Individuals and
businesses use wireless networks to send and share data rapidly, whether it be
in a small office building or across the world.
Properties
General
In a general sense, wireless networks offer a vast variety
of uses by both business and home users.
"Now, the
industry accepts a handful of different wireless technologies. Each wireless
technology is defined by a standard that describes unique functions at both the
Physical and the Data Link layers of the OSI Model. These standards differ in
their specified signaling methods, geographic ranges, and frequency usages,
among other things. Such differences can make certain technologies better
suited to home networks and others better suited to network larger
organizations."
Performance
Each standard varies in geographical range, thus making one
standard more ideal than the next depending on what it is one is trying to
accomplish with a wireless network. The performance of wireless networks
satisfies a variety of applications such as voice and video. The use of this
technology also gives room for expansions, such as from 2G to 3G and, most
recently, 4G technology, which stands for fourth generation of cell phone
mobile communications standards. As wireless networking has become commonplace,
sophistication increases through configuration of network hardware and
software, and greater capacity to send and receive larger amounts of data,
faster, is achieved.
Space
Space is another characteristic of wireless networking.
Wireless networks offer many advantages when it comes to difficult-to-wire
areas trying to communicate such as across a street or river, a warehouse on
the other side of the premise or buildings that are physically separated but
operate as one. Wireless networks allow for users to designate a certain space
which the network will be able to communicate with other devices through that
network. Space is also created in homes as a result of eliminating clutters of
wiring. This technology allows for an alternative to installing physical
network mediums such as TPs, coaxes, or fiber-optics, which can also be
expensive.
Home
For homeowners, wireless technology is an effective option
compared to ethernet for sharing printers, scanners, and high speed internet
connections. WLANs help save the cost of installation of cable mediums, save
time from physical installation, and also creates mobility for devices
connected to the network. Wireless networks are simple and require as few as
one single wireless access point connected directly to the Internet via a
router.
Wireless Network Elements
The telecommunications network at the physical layer also
consists of many interconnected wireline Network Elements (NEs). These NEs can
be stand-alone systems or products that are either supplied by a single
manufacturer, or are assembled by the service provider (user) or system
integrator with parts from several different manufacturers.
Wireless NEs are products and devices used by a wireless
carrier to provide support for the backhaul network as well as a Mobile
Switching Center (MSC).
Reliable wireless service depends on the network elements at
the physical layer to be protected against all operational environments and
applications (see GR-3171, Generic Requirements for Network Elements Used in
Wireless Networks - Physical Layer Criteria).
What are especially important are the NEs that are located
on the cell tower to the Base Station (BS) cabinet. The attachment hardware and
the positioning of the antenna and associated closures/cables are required to
have adequate strength, robustness, corrosion resistance, and rain/solar
resistance for expected wind, storm, ice, and other weather conditions.
Requirements for individual components, such as hardware, cables, connectors,
and closures, shall take into consideration the structure to which they are
attached.
Difficulties
Interference
Compared to wired
systems, wireless networks are frequently subject to electromagnetic
interference. This can be caused by other networks or other types of equipment
that generate radio waves that are within, or close, to the radio bands used
for communication. Interference can degrade the signal or cause the system to
fail.
Absorption and reflection
Some materials
cause absorption of electromagnetic waves, preventing it from reaching the
receiver, in other cases, particularly with metallic or conductive materials
reflection occurs. This can cause dead zones where no reception is available.
Multipath fading
In multipath
fading two or more different routes taken by the signal, due to reflections,
can cause the signal to cancel out at certain locations, and to be stronger in
other places (upfade).
Hidden node problem
The hidden node
problem occurs in some types of network when a node is visible from a wireless
access point (AP), but not from other nodes communicating with that AP. This
leads to difficulties in media access control.
Shared resource problem
The wireless
spectrum is a limited resource and shared by all nodes in the range of its
transmitters. Bandwidth allocation becomes complex with multiple participating
users. Often users are not aware that advertised numbers (e.g., for IEEE 802.11
equipment or LTE networks) are not their capacity, but shared with all other
users and thus the individual user rate is far lower. With increasing demand,
the capacity crunch is more and more likely to happen. User-in-the-loop (UIL)
may be an alternative solution to ever upgrading to newer technologies for
over-provisioning.
Capacity
Channel
Understanding of SISO, SIMO, MISO and MIMO. Using multiple
antennas and transmitting in different frequency channels can reduce fading,
and can greatly increase the system capacity.
The maximum data rate of any single wireless link can be
described by the Shannon's theorem which is related to the bandwidth in hertz,
and the noise on the channel.
Network
[icon] This section
requires expansion. (April 2013)
The total network bandwidth depends on how dispersive the
medium is (more dispersive medium generally has better total bandwidth because
it minimises interference), how many frequencies are available, how noisy those
frequencies are, how many aerials are used and whether directional antenna are
in use, whether nodes employ power control and so on.
Cellular wireless networks generally have good capacity, due
to their use of directional aerials, and their ability to reuse radio channels
in non-adjacent cells. Additionally, cells can be made very small using low
power transmitters, and this fact is used in cities to give network capacity
that scales linearly with population density.
Safety
Wireless access points are also often close to humans, but
the drop off in power over distance is fast, following the inverse-square law.
The position of the United Kingdom's Health Protection Agency (HPA) is that
“...radio frequency (RF) exposures from WiFi are likely to be lower than those
from mobile phones.” It also saw “...no reason why schools and others should
not use WiFi equipment.” In October 2007, the HPA launched a new “systematic”
study into the effects of WiFi networks on behalf of the UK government, in
order to calm fears that had appeared in the media in a recent period up to
that time". Dr Michael Clark, of the HPA, says published research on mobile
phones and masts does not add up to an indictment of WiFi.
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