UNBOUNDED
/ UNGUIDED MEDIA:-
Unbounded / Unguided media or wireless media doesn't
use any physical connectors between the two devices communicating. Usually the
transmission is send through the atmosphere but sometime it can be just across
the rule. Wireless media is used when a physical obstruction or distance blocks
are used with normal cable media. The three types of wireless media are:
v RADIO WAVES
v MICRO WAVES
v INFRARED WAVES
1. RADIO WAVES:-
It has frequency between 10 K Hz to 1 G Hz. Radio
waves has the following types.
I.
Short
waves
II.
VHF
(Very High Frequency)
III.
UHF
(Ultra High Frequency)
SHORT WAVES:-
There are different types of antennas used for radio
waves. Radio waves transmission can be divided into following categories.
-
LOW POWER,
SINGLE FREQUENCY.
-
HIGH POWER,
SINGLE FREQUENCY
1.
LOW POWER , SINGLE FREQUENCY:-
As the name shows this system transmits from one
frequency and has low power out. The normal operating ranges on these devices
are 20 to 25 meter.
CHARACTERISTICS LOW POWER , SINGLE
FREQUENCY:-
§ Low cost
§ Simple installation with pre-configured
§ 1 M bps to 10 M bps capacity
§ High attenuation
§ Low immunity to EMI
2. HIGH POWER,
SINGLE FREQUENCY:-
This is similar to low power single frequency. These
devices can communicate over greater distances.
CHARACTERISTICS HIGH POWER, SINGLE
FREQUENCY:-
§ Moderate cost
§ Easier to install than low power single frequency
§ 1 Mbps to 10 Mbps of capacity
§ Low attenuation for long distances
§ Low immunity to EMI
2. MICRO WAVES
Micro waves travels at high frequency than radio
waves and provide through put as a wireless network media. Micro wave
transmission requires the sender to be inside of the receiver.
Following are the types of Micro waves.
· Terrestrial Micro waves
· Satellite Micro waves
1. Terrestrial Micro waves:-
Terrestrial Micro waves are used are used to
transmit wireless signals across a few miles. Terrestrial system requires that
direct parabolic antennas can be pointed to each other. These systems operate
in a low Giga Hertz range.
Characteristics Of Terrestrial
Micro Waves:-
o Moderate to high cost.
o Moderately difficult installation
o 1 M bps to 10 M bps capacity
o Variable attenuation
o Low immunity to EMI
2. Satellite Micro waves
The main problem with aero wave communication is the
curvature of the earth, mountains & other structure often block the line of
side. Due to this reason, many repeats are required for long distance which
increases the cost of data transmission between the two points. This problem is
recommended by using satellites.
Satellite micro wave transmission is used to
transmit signals through out the world. These system use satellites in orbit
about 50,000 Km above the earth. Satellite dishes are used to send the signals
to the satellite where it is again send back down to the receiver satellite.
These transmissions also use directional parabolic antenna’ with inline of
side.
In satellite communication micro wave signals at 6
GHz is transmitted from a transmitter on the earth through the satellite
position in space. By the time signal reaches the satellites becomes weaker due
to 50,000 Km distance. The satellite amplifies week signals and transmits it
back to the earth at the frequency less than 6 GHz.
Characteristics Satellite Micro
waves:
o High cost
o Extremely difficult and hare installation.
o Variable attenuation.
o Low immunity to EMI
o High security needed because a signal send to
satellite is broadcasts through all receivers with in satellite.
3. INFRARED
Infrared frequencies are just below visible light.
These high frequencies allow high sped data transmission. This technology is
similar to the use of a remote control for a TV. Infrared transmission can be
affected by objects obstructing sender or receiver. These transmissions fall
into two categories.
-
POINT TO POINT
- BROADCAST
(i) Point to Point: - Point to point infrared transmission signal
directly between two systems. Many lap top system use point to pint
transmission. These systems require direct alignment between many devices.
Characteristics
of Point to point:-
+ Wide range of cost
+ Moderately easy installation.
+ 100 k bps to 16 Mb of capacity.
+ Variable attenuation.
+ High immunity to EMI
(ii) Broad Cast: - These infrared transmission use sprayed signal, one
broad cast in all directions instead of direct beam. This help to reduce the
problems of proper alignment and abstraction. It also allows multiple receiver
of signal
Characteristics
of Broad Cast:-
+ In expensive.
+ Single installation.
+ 1M bps capacity.
+ Variable attenuation.
PARABOLIC
ANTENA
@ A parabolic antenna is an antenna that uses a parabolic
reflector, a curved surface with
the cross-sectional shape of a parabola, to direct the radio waves.
@ The
most common form is shaped like a dish and is popularly called a dish antenna or parabolic
dish.
@ The main advantage of a parabolic antenna is that
it is highly directive; it functions similarly to a searchlight or flashlight reflector to direct the radio waves in a narrow
beam, or receive radio waves from one particular direction only.
@ Parabolic antennas have some of the highest gains, that is they can produce the narrowest beam width angles, of any antenna type.
HORN
ANTENA
= A horn antenna or microwave horn is an antenna that consists of a flaring metal waveguide shaped like a horn to direct radio waves in a beam.
= They are used as feeders (called feed horns) for larger antenna structures such as parabolic antennas, as standard calibration antennas to measure the gain of other antennas, and as directive antennas for
such devices as radar
guns, automatic
door openers, and microwave
radiometers
= A horn antenna serves the same function for electromagnetic
waves that an acoustical horn does for sound waves in a musical instrument such as a trumpet.
= It provides a gradual transition structure to match
the impedance of a tube to the impedance of free space, enabling
the waves from the tube to radiate efficiently into space.
A satellite is an object that goes around, or
orbits, a larger object, such as a planet. While there are natural satellites,
like the moon, hundreds of man-made satellites also orbit the Earth.
-
communication
capabilities with Earth
-
a power source
-
a control system
to accomplish its mission
Communications antennae, radio receivers and
transmitters enable the satellite to communicate with one or more ground
stations, called command centers. Messages sent to the satellite from a ground
station are "uplinked";
messages transmitted from the satellite to Earth are "downlinked."
RADIO FREQUENCY:-
Radio frequency (RF) is a rate of oscillation in the
range of about 3 kHz to 300 GHz,
which corresponds to the frequency of radio waves,
and the alternating
currents which carry radio
signals. RF usually refers to electrical rather than mechanical oscillations,
although mechanical RF systems do exist (see mechanical filter
and RF MEMS).
How does RFID work?
A
Radio-Frequency IDentification system has three parts:
·
A scanning
antenna
·
A transceiver
with a decoder to interpret the data
·
A transponder -
the RFID tag - that has been programmed with information.
The scanning antenna puts out radio-frequency
signals in a relatively short range. The RF radiation does two things:
It provides a means of communicating with the
transponder (the RFID tag) AND
EQUIPMENT USE ?
Radio waves operate at different frequencies and can
be transmitted and received through radio frequency equipment. Transmitters
broadcast the radio frequencies over the air and are then received through
radio receivers. These are some of the equipment used for the transmission and
reception of radio frequencies.
ü Dipole Antennas.
ü VHF FM dipole antenna.
ü Radio Receiver.
ü Communication Receivers.
-Radio frequency equipment can be found almost
everywhere in your homes, offices or out in the streets. They can be used for
entertainment purposes, communication or for other purposes that require
manipulation of radio frequencies like defrosting frozen food in microwaves.
CELULLAR
PHONE:-
Cellular telephone, sometimes called mobile
telephone, is a type of short-wave analog
or digital
telecommunication in which a subscriber has a wireless
connection from a mobile telephone to a relatively nearby transmitter. The
transmitter's span of coverage is called a cell.
Generally, cellular telephone service is available in urban areas and along
major highways. As the cellular telephone user moves from one cell or area of
coverage to another, the telephone is effectively passed on to the local cell
transmitter.
A cellular telephone is not to be confused with a
cordless telephone (which is simply a phone with a very short wireless
connection to a local phone outlet).
The first cellular telephone for commercial use was
approved by the Federal Communications Commission (FCC) in 1983. The phone, a Motorola DynaTAC 8000X, weighed 2 pounds, offered just a half-hour of talk
time for every recharging and sold for $3,995.
-
These days, cell
phones provide an incredible array of functions, and new ones are being added
at a breakneck pace. Depending on the cell-phone model, you can:
@
Store contact information
@
Make task or to-do lists
@
Keep track of appointments and set reminders
@
Use the built-in calculator for simple math
@
Play games
WIFI
??
The name of a popular wireless (WIRELESS FIDELITY ) networking technology that
uses radio waves to provide wireless high-speed Internet and network connections. The Wi-Fi Alliance,
the organization that owns the Wi-Fi (registered trademark) term specifically
defines Wi-Fi as any "wireless local area network (WLAN) products that are based on the Institute of
Electrical and Electronics Engineers' (IEEE) 802.11 standards."
Wi-Fi works with no physical wired connection
between sender and receiver by using radio frequency (RF) technology, a frequency within the electromagnetic
spectrum associated with radio wave propagation.
DIFFERENT 3G AND 4G ??
Misconceptions
-
4G networks do
not have a standard technology, minimizing the value of the label. Different
carriers apply the term to three basic technologies; HSPA+ 21/42, WiMAX and
LTE. However, the slow speed of some of these technologies make calling them a
4G technology disputable.
Function
-
3G and 4G
networks offer divergent levels of data transfer from sources to a device. In
general, 3G networks enable 144Kbps minimum for Internet transfer speed. No
specific standard exists for 4G networks.
Features
-
The basic difference
is that -- on the same network -- a 4G network is faster than a 3G network.
However, compared across multiple carriers, one carrier's 3G may be
significantly faster than another carrier's version of 4G.
Knowing What to Buy
-
When comparing
3G and 4G, compare data transmission speeds, not the label. AT&T's 3G, for
example, is faster than MetroPCS' 4G LTE, according to tests run by PCMag.com.
When to Move to 4G
-
Upgrading to 4G
requires a new phone. Before you make that upgrade, check the status of the 4G
coverage in your area. In some situations, 3G is the best available, with 4G
only in planning stages.
