What is terrestrial microwave technology?

Terrestrial microwave technologies share with satellite microwave technologies many of the scientific and technical improvements used to accomplish microwave transmissions. They are different in that satellite microwave technolgies seek to neutralize the effects of the atmosphere in the microwave transmissions. On the other hand, terrestrial micowave technologies seek the aid of atmospheric effects on microwaves to extend the range limitations imposed by the Earth's curvature. Examples of these terrestrial technologies include those used to exploit troposcattering and meteor-burst in microwave communications--not used at all in satellites.

What is Unbound or Unguided media? 

UNBOUNDED / UN GUIDED 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:

• 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

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

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.

1. Point to point
2. 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.

radio frequency (RF, rf, orr.f.)

Radio frequency (abbreviated RF, rf, orr.f.) is a term that refers to alternating current (AC) havingcharacteristics such that, if the current is input to an antenna, an electromagnetic (EM) field is generated suitable for wireless broadcastingand/or communications. These frequencies cover asignificant portion of the electromagnetic radiation spectrum, extending from nine kilohertz (9 kHz),the lowest allocated wireless communications frequency (it's within the range of human hearing), to thousands of gigahertz(GHz).

When an RF current is supplied to an antenna, itgives rise to an electromagneticfield that propagates through space. This field is sometimescalled an RF field; in less technical jargon it is a "radiowave." Any RF field has a wavelength that is inverselyproportional to the frequency. In the atmosphere or in outerspace, if f is the frequency in megahertz and sis the wavelength in meters, then

s = 300/f

The frequencyof an RF signal is inversely proportional to the wavelengthof the EM field to which it corresponds. At 9 kHz, the free-spacewavelength is approximately 33 kilometers (km) or 21 miles (mi). At the highestradio frequencies, the EM wavelengths measure approximately one millimeter (1 mm). As the frequency isincreased beyond that of the RF spectrum, EM energy takes the form ofinfrared (IR), visible, ultraviolet (UV), X rays, and gamma rays.

Many types of wireless devices makeuse of RF fields. Cordless and cellular telephone, radio andtelevision broadcast stations, satellite communications systems,and two-way radio services all operate in the RF spectrum. Somewireless devices operate at IR or visible-light frequencies,whose electromagnetic wavelengths are shorter than those of RFfields. Examples include most television-set remote-controlboxes, some cordless computer keyboards and mice, and a fewwireless hi-fi stereo headsets.

The RF spectrum is divided into several ranges, orbands. With theexception of the lowest-frequency segment, each band represents an increaseoffrequencycorresponding to an order of magnitude (power of 10). The tabledepictsthe eightbands in the RF spectrum, showing frequency and bandwidth ranges. TheSHF and EHFbands are often referred to as themicrowave spectrum.

Wi-Fi (wireless fidelity)

Wi-Fi (short for "wireless fidelity") is a term for certain types of wireless local area network (WLAN) that use specifications in the 802.11 family. The term Wi-Fi was created by an organization called the Wi-Fi Alliance, which oversees tests that certify product interoperability. A product that passes the alliance tests is given the label "Wi-Fi certified" (a registered trademark).

Originally, Wi-Fi certification was applicable only to products using the 802.11b standard. Today, Wi-Fi can apply to products that use any 802.11 standard. The 802.11 specifications are part of an evolving set of wireless network standards known as the 802.11 family. The particular specification under which a Wi-Fi network operates is called the "flavor" of the network. Wi-Fi has gained acceptance in many businesses, agencies, schools, and homes as an alternative to a wired LAN. Many airports, hotels, and fast-food facilities offer public access to Wi-Fi networks. These locations are known as hot spots. Many charge a daily or hourly rate for access, but some are free. An interconnected area of hot spots and networkaccess points is known as a hot zone.

Unless adequately protected, a Wi-Fi network can be susceptible to access by unauthorized users who use the access as a free Internet connection. The activity of locating and exploiting security-exposed wireless LANs is called war driving. An identifying iconography, called war chalking, has evolved. Any entity that has a wireless LAN should use security safeguards such as the Wired Equivalent Privacy (WEP) encryption standard, the more recent Wi-Fi Protected Access (WPA), Internet Protocol Security (IPsec), or a virtual private network (VPN).