Unguided or wireless media sends the data through air (or water), which is available to anyone who has a device capable of receiving them. Types of unguided/ unbounded media are discussed below :
- Radio Transmission
- MicroWave Transmission
Its frequency is between 10 kHz to 1GHz. It is simple to install and has high attenuation. These waves are used for multicast communications.
Types of Propogation
Radio Transmission utilizes different types of propogation :
- Troposphere : The lowest portion of earth’s atmosphere extending outward approximately 30 miles from the earth’s surface. Clouds, jet planes, wind is found here.
- Ionosphere : The layer of the atmosphere above troposphere, but below space. Contains electrically charged particles.
It travels at high frequency than the radio waves. It requires the sender to be inside of the receiver. It operates in a system with a low gigahertz range. It is mostly used for unicast communication.
There are 2 types of Microwave Transmission :
- Terrestrial Microwave
- Satellite Microwave
Advantages of Microwave Transmission
- Used for long distance telephone communication
- Carries 1000’s of voice channels at the same time
Disadvantages of Microwave Transmission
- It is Very costly
For increasing the distance served by terrestrial microwave, repeaters can be installed with each antenna .The signal received by an antenna can be converted into transmittable form and relayed to next antenna as shown in below figure. It is an example of telephone systems all over the world
There are two types of antennas used for terrestrial microwave communication :
1. Parabolic Dish Antenna
In this every line parallel to the line of symmetry reflects off the curve at angles in a way that they intersect at a common point called focus. This antenna is based on geometry of parabola.
2. Horn Antenna
It is a like gigantic scoop. The outgoing transmissions are broadcast up a stem and deflected outward in a series of narrow parallel beams by curved head.
This is a microwave relay station which is placed in outer space. The satellites are launched either by rockets or space shuttles carry them.
These are positioned 3600KM above the equator with an orbit speed that exactly matches the rotation speed of the earth. As the satellite is positioned in a geo-synchronous orbit, it is stationery relative to earth and always stays over the same point on the ground. This is usually done to allow ground stations to aim antenna at a fixed point in the sky.
Features of Satellite Microwave :
- Bandwidth capacity depends on the frequency used.
- Satellite microwave deployment for orbiting satellite is difficult.
Advantages of Satellite Microwave :
- Transmitting station can receive back its own transmission and check whether the satellite has transmitted information correctly.
- A single microwave relay station which is visible from any point.
Disadvantages of Satellite Microwave :
- Satellite manufacturing cost is very high
- Cost of launching satellite is very expensive
- Transmission highly depends on whether conditions, it can go down in bad weather