12th week:unbounded / unguided media

Different between bounded and unbounded media

·        Bounded media are those that use cables for transmitting electricity or light;

·        Unbounded media does not require cabling and includes satellite, microwave and radio transmission.

·        Wireless connections, including 802.11b and 802.11a, are examples of unbounded media.

·        Today, bounded media continue to be more common than unbounded.

Unbounded media / unguided media

-         Translate electromagnetic wave without physical conductor.

-         Signal = broadcasting thru air/water

-         Available for anyone who has a device capable of receiving them

-         2 type of microwave:

1.         Terrestrial Microwave

§  Require line-of-sight transmission and reception equipment

§  The taller the antennas, the longer the sight distance

§  The higher, the stronger

§  So…Usually built on hills / mountains

§  One way direction signal

§  Install system(repeater) with antennas to increase distance

§  2 type of antennas

1.         Parabolic dish

o   Same as it’s name, in a dish shape

o   good at catching a wide range of signal waves

o   directing to a common point(focus)

o   Every wave parallel to the line of sight reflects back to the focus on a common point

2.      Horn

o   looks like a gigantic scoop

o   broadcasts the assembled signals that are deflected outward in a series of narrow parallel beams by the curve head

o   signals are received in a manner are deflected down into the stem

2.      Satellite microwave

§  same principle as terrestrial microwave

§  acting as a super tall antenna and repeater

§  single bounce

§  capability = anywhere on earth

§  high quality communication without huge investment in ground-based infrastructure

§  same speed as earth

§  Geosynchronous satellite = orbit speed is based on distance from the planet

§  Minimum 3 satellites to provide full global transmissions

§  earth à satellite = uplink

§  satellite à earth = downlink

Something you might do not know….

Wireless technology

·        Technology that does not require any wires. (unbounded media)

·        The distances involved may be short such as a few meters as in television remote control

·        Long like thousands or millions of kilometers for radio communications.

Wifi

·        developed to be used for mobile computing devices

·        Transmit data use radio wave

·        IEEE802.11 – standard for implementing wifi

·        IEEE802.11b standard provides a transmit data size up to 11Mbps (Megabyte per second)

·        IEEE802.11a standard provides throughput rates up to 54Mbps

Radio frequency[RF] and cellular phones

·        Cellular phone is one of the wireless devices make use of RF

·        Cell phones work by sending signals to (and receiving them from) nearby cell towers (base stations) using RF waves

·        This is a form of electromagnetic energy that falls between FM radio waves and microwaves

·        RF waves are a form of non-ionizing radiation

·        RF waves are different from stronger (ionizing) types of radiation such as x-rays, gamma rays, and ultraviolet (UV) light, which can break the chemical bonds in DNA.

·        At very high levels, RF waves can heat up body tissues. (This is the basis for how microwave ovens work.)

·        But the levels of energy given off by cell phones are much lower, and are not enough to raise temperatures in the body.

Designation	Frequencies	Free-space Wavelengths
Very Low Frequency	9 kHz - 30 kHz	33 km - 10 km
Low Frequency	30 kHz - 300 kHz	10 km - 1 km
Medium Frequency	300 kHz - 3 MHz	1 km - 100 m
High Frequency	3 MHz - 30 MHz	100 m - 10 m
Very High Frequency	30 MHz - 300 MHz	10 m - 1 m
Ultra High Frequency	300 MHz - 3 GHz	1 m - 100 mm
Super High Frequency	3 GHz - 30 GHz	100 mm - 10 mm
Extremely High Frequency	30 GHz - 300 GHz	10 mm - 1 mm

By Mhui