my world...~~~

my world...~~~

Friday, 11 May 2012


What is Unbound or 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:
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)
There are different types of antennas used for radio waves. Radio waves transmission can be divided into following categories.

1              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.
§  Low cost
§  Simple installation with pre-configured
§  1 M bps to 10 M bps capacity
§  High attenuation
§  Low immunity to EMI

This is similar to low power single frequency. These devices can communicate over greater distances.
§  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 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.

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.


(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.


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.
Parabolic antennas are used as high-gain antennas for point-to-point communication, in applications such as microwave relay links that carry telephone and television signals between nearby cities, wireless WAN/LAN links for data communications, satellite and spacecraft communication antennas, and radio telescopes. Their other large use is in radar antennas, which need to emit a narrow beam of radio waves to locate objects like ships and airplanes. With the advent of home satellite television dishes, parabolic antennas have become a ubiquitous feature of the modern landscape.

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. Horns are widely used as antennas at UHF and microwave frequencies, above 300 MHz.[1] 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."
Communications satellite
A communications satellite (sometimes abbreviated to COMSAT) is an artificial satellite stationed in space for the purpose of telecommunications. Modern communications satellites use a variety of orbits including geostationary orbits, Molniya orbits, other elliptical orbits and low (polar and non-polar) Earth orbits.

For fixed (point-to-point) services, communications satellites provide a microwave radio relay technology complementary to that of communication cables. They are also used for mobile applications such as communications to ships, vehicles, planes and hand-held terminals, and for TV and radio broadcasting, for which application of other technologies, such as cable television, is impractical or impossible.

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:
      o   A scanning antenna
      o   A transceiver with a decoder to interpret the data
      o   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
  • It provides the RFID tag with the energy to communicate (in the case of passive RFID tags).
-This is an absolutely key part of the technology; RFID tags do not need to contain batteries, and can therefore remain usable for very long periods of time (maybe decades).
-The scanning antennas can be permanently affixed to a surface; handheld antennas are also available. They can take whatever shape you need; for example, you could build them into a door frame to accept data from persons or objects passing through.
-When an RFID tag passes through the field of the scanning antenna, it detects the activation signal from the antenna. That "wakes up" the RFID chip, and it transmits the information on its microchip to be picked up by the scanning antenna.
-In addition, the RFID tag may be of one of two types. Active RFID tags have their own power source; the advantage of these tags is that the reader can be much farther away and still get the signal. -Even though some of these devices are built to have up to a 10 year life span, they have limited life spans. Passive RFID tags, however, do not require batteries, and can be much smaller and have a virtually unlimited life span.
-RFID tags can be read in a wide variety of circumstances, where barcodes or other optically read technologies are useless.
-The tag need not be on the surface of the object (and is therefore not subject to wear)
The read time is typically less than 100 milliseconds
-Large numbers of tags can be read at once rather than item by item.
In essence, that's how RFID works.


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.

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
@ Send or receive e-mail
@ Get information (news, entertainment, stock quotes) from the Internet
@ Play games
@ Watch TV
@ Integrate other devices such as PDAs, MP3 players and GPS receivers


- 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.

In telecommunications, 4G is the fourth generation of cell phone mobile communications standards. It is a successor of the third generation (3G) standards. A 4G system provides mobile ultra-broadband Internet access, for example to laptops with USB wireless modems, to smartphones, and to other mobile devices. Conceivable applications include amended mobile web access, IP telephony, gaming services, high-definition mobile TV, video conferencing and 3D television.
epresenting the third and fourth generations of mobile technology respectively, 3G and 4G networks have many differences. Most notably, their rates of data transfer and signal quality are highly divergent. However, the implementation of 4G networks has faced many hurdles. Unlike 3G, 4G technology is not fully defined by governing bodies in charge of wireless technology. 

  • -          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.
  • -          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.
  • -          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

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.