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:
RADIO WAVES
MICRO WAVES
INFRARED WAVES
1. RADIO WAVES:-
It has frequency between 10 K Hz to1 G Hz. Radio waves has the following types.
Short waves
VHF (Very High Frequency)
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
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
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:-
Moderate to high cost.
Moderately difficult installation
1 M bps to 10 M bps capacity
Variable attenuation
Low immunity to EMI
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 in line 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:
High cost
Extremely difficult and hare installation.
Variable attenuation.
Low immunity to EMI
High security needed because a signal send to satellite is broadcasts through all receivers with in satellite.
WIFI :-
Fairly recently the IEEE 802.11 standard became more popular as it suites mobile computing devices really well. The IEEE 802.11 standard is another term for WiFi essentially is wireless networking. This standard allows two computers that have wireless NICs to communicate with one another with no strings (wires) attached. This standard makes use of radio waves that are transmitted through the air to communicate. Speeds of either 54 Mbps or 108 Mbps are supported but higher speeds are in the pipeline.
IEEE (Institute of Electrical and Electronics Engineers)
IEEE is the world’s largest professional association dedicated to advancing technological innovation and excellence for the benefit of humanity. IEEE and its members inspire a global community through IEEE's highly cited publications, conferences, technology standards, and professional and educational activities.
IEEE, pronounced "Eye-triple-E", stands for the Institute of Electrical and Electronics Engineers. The association is chartered under this name and it is the full legal name. To learn more about association's name
Difference Between 3G And 4G
Cellular phone
Cellular telephone, sometimes called mobile telephone, is a type of short-wave analog ordigital 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 acell. 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).
Uplink and downlink
In satellite telecommunication, a downlink is the link from a satellite down to one or more ground stations or receivers, and an uplink is the link from a ground station up to a satellite. Some companies sell uplink and downlink services to television stations, corporations, and to other telecommunication carriers. A company can specialize in providing uplinks, downlinks, or both.
The following table shows the main frequency bands used for satellite links.
The C band is the most frequently used. The Ka and Ku bands are reserved exclusively for satellite communication but are subject to rain attenuation. Some satellites carry transponders for both C and Ku bands.
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
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
(i) 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.
