Wednesday, 2 May 2012

Unbounded /Unguided Media or Wireless Technology

The topic for this week’s lesson is unbounded /unguided media or as called as wireless technology. 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 sometimes it can be just across the rule. Wireless media is used when a physical obstruction or distance blocks are used with normal cable media.

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 microwaves:

1)       Moderate to high cost.
2)       Moderately difficult installation
3)       1 M bps to 10 M bps capacity
4)       Variable attenuation
5)       Low immunity to EMI
6)       The taller the antenna, the longer the sight distance

There are 2 types of antenna:
ü  Parabolic dish
ü  Horn

A parabolic dish 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 main advantage of a parabolic dish 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 dish has some of the highest gains, that is they can produce the narrowest beam width angles, of any antenna type.
Parabolic Dish

A horn antenna is used for the transmission and reception of microwave signals. It derives its name from the characteristic flared appearance. The flared portion can be square, rectangular, or conical. The maximum radiation and response corresponds with the axis of the horn. In this respect, the antenna resembles an acoustic horn. It is usually fed with a wave guide.


In order to function properly, a horn antenna must be a certain minimum size relative to the wavelength of the incoming or outgoing electromagnetic field. If the horn is too small or the wavelength is too large (the frequency is too low), the antenna will not work efficiently.

Satellite owns a similar principle as terrestrial microwave where it acts as a super tall antenna and repeater.
In general, a satellite is anything that orbits something else, as, for example, the moon orbits the earth. In a communications context, a satellite is a specialized wireless receiver/transmitter that is launched by a rocket and placed in orbit around the earth. There are hundreds of satellites currently in operation. They are used for such diverse purposes as weather forecasting, television broadcast, amateur radio communications, Internet communications, and the Global Positioning System, (GPS).
Transmission from earth to satellite----uplink
Transmission from satellite to earth---downlink


How Does it Work
Radio frequency use electrical oscillation to transmit its signal. When an RF current is supplied to an antenna, an electromagnetic field is created that then is able to propagate through space.
In order to receive radio signals an antenna must be used. 
Distance covered
Different forms of electromagnetic energy are categorized by their wavelengths and frequencies. The RF part of the electromagnetic spectrum is generally defined as that part of the spectrum where electromagnetic waves have frequencies in the range of about 3 kilohertz (3 kHz) to 300 gigahertz (300 GHz). 

Different Types of Radio Frequency

How Does it Work
Make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile phone operator, allowing access to the public telephone network. By contrast, a cordless telephone is used only within the short range of a single, private base station.
Cellular phone
Distance covered
 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.
Cellular Phone

How Does it Work
Wifi allows an electronic device to exchange data wirelessly (using radio waves) over a computer network, including high-speed Internet connections. The Wi-Fi Alliance 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.
A device that can use Wi-Fi (such as a personal computer, video game console, smartphone, tablet, or digital audio player) can connect to a network resource such as the Internet via a wireless network access point.
Distance covered
Access point (or hotspot) has a range of about 20 meters (65 feet) indoors and a greater range outdoors. Hotspot coverage can comprise an area as small as a single room with walls that block radio waves or as large as many square miles 

I would like to share a video with you all. It is an interesting video regarding to the difference between 3G and 4G… J