Microwave –Terrestrial & Satellite

Microwave transmission uses very-high frequency signals

Frequency range:300MHz-300GhzWavelengths range in air:100cm-

1mm The two types of microwave transmission

Microwaves are electromagnetic waves

Microwave

Terrestrial

Satellite

1

2

• Unidirectional• Propagation is line-of sight.• Repeaters are needed for long distance communication.• Very high frequency microwaves cannot penetrate walls.• Wave band is relatively wide almost 299GHZ → a high data rate• Use of certain portion of the band requires permission from

authorities.

Microwave

Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless

LANs.

Terrestrial Microwave

• Terrestrial microwave transmissions are sent between two microwave stations on the earth (earth station).

• It is the most common form of long-distance communication.

• Terrestrial microwave systems operate in the low-gigahertz range

• Use a parabolic dish to focus a narrow beam onto a receiver antenna

Terrestrial Microwave

Used for long-distance telephone service Parabolic dish transmitter, mounted high Used for both voice and TV transmission Used by common carriers as well as private

networks

Terrestrial Microwave cont.

Applications

fewer repeaters but requires line of sight transmission

Higher frequencies give higher data rates• common frequencies used for transmission

are in the range 1 to 40GHz. main source of loss is attenuation

caused mostly by distance, rainfall and interference

Terrestrial Microwave cont.

Transmission characteristics

Satellite Microwave

A communication satellite is a microwave relay station Used to link two or more ground stations Receives on one frequency (uplink), amplifies or repeats signal and

transmits on another frequency (downlink) eg. uplink 5.925-6.425 GHz & downlink 3.7-4.2 GHz frequency bands are called transponder channels

Requires geo-stationary orbit rotation match occurs at a height of 35,863 km at the equator need to be spaced at least 3° - 4° apart to avoid interfering with each other spacing limits the number of possible satellites

Satellite Microwave

Satellite Microwave cont.

Most communications satellites are placed into orbit 22,300 miles above the earth's surface. The earth's gravity keeps the satellite in orbit at the same rate as the earth (geosynchronous orbit). Such satellites are called geosynchronous orbiting satellites (GEOS).

Low earth orbiting satellites (LEOS) orbit the earth at a height of 325-1,000 miles and they orbit around the poles (not in a fixed position relative to the earth).

Medium earth orbiting satellites (MEOS) are similar to LEOS but are positioned at 6,000-10,000 miles above the earth.

Because microwaves use line-of-sight, the satellite signal can only reach a part of the earth. This area is called a footprint.

At a glance, categories of satellites

dish dish

uplink station downlink station

satellitetransponder

22,300 miles

Satellite Transmission Process

Satellite Microwave cont.

Private business networks satellite providers can divide capacity into channels to lease to individual business

users Television distribution

programs are transmitted to the satellite then broadcast down to a number of stations which then distributes the programs to individual viewers

Direct Broadcast Satellite (DBS) transmits video signals directly to the home user Long-distance telephone transmission

high-usage international trunks Global positioning

Navstar Global Positioning System (GPS)

Applications

Satellite Microwave cont.

the optimum frequency range for satellite transmission is 1 to 10 GHz

lower has significant noise from natural sources higher is attenuated by atmospheric absorption and

precipitation satellites use a frequency bandwidth range of

5.925 to 6.425 GHz from earth to satellite (uplink) and a range of 3.7 to 4.2 GHz from satellite to earth (downlink)

this is referred to as the 4/6-GHz band because of saturation the 12/14-GHz band has been

developed (uplink: 14 - 14.5 GHz; downlink: 11.7 - 12.2 GHz

Transmission characteristics

Microwave Transmission advantages

No cables needed

Multiple channels available

Wide bandwidth

Microwave Transmission Disadvantages

line of sight requirement They require no obstacle is

present in the transmission path expensive towers and repeaters

subject to interference such as passing airplanes and rain

a presentation by-

Farhana Mishufp.mishu@gmail.com

Thank you