Unguided Transmission Media
Guided transmission media is also called unbounded or wireless media where the devices communicate with each other through space or air by using broadcast radio signals, microwave signals and infrared signals etc.
Types of guided transmission media are in following diagram
1. Radio Waves
- Radio waves are the electromagnetic waves that are transmitted in all the directions in free space.
- Radio waves are omnidirectional, i.e., the signals are propagated in all the directions.
- frequencies range of radio waves is from 3 Khz to 1 Khz.
- Radio transmission is mainly used for wide area networks and mobile cellular phones, FM radio, television etc.
- Radio waves can penetrate the walls and cover a large area.
- Radio transmission provides a higher transmission rate.
2. Microwave System
- Both voice and data is transmitted through microwaves over free space or air like radio waves.
- It uses the line of sight because signals travel in straight path and cannot bend.
- Microwave stations (antennas) are usually installed on high buildings and towers so that there should be no interference in-between the antennas.
- Distance between the towers is 20 to 30 miles to each other.
- Each station receives the signals from previous stations and transmits it to next station.
3. Satellite communication
- A satellite is a physical object that revolves around the earth at a known height almost 22300 miles.
- It receives microwave signals from earth based stations. After amplifications it retransmits them to different earth based stations
- Transmission from earth based stations to satellite is called uplink and transmission satellite to earth based station is called uplink.
- We can communicate with any point on the globe by using satellite communication.
- Satellite communication is more reliable nowadays as it offers more flexibility than cable and fiber optic systems.
- High data transmission
- Bad weather can affect the quality of satellite transmission.
How Does Satellite work?
The satellite accepts the signal that is transmitted from the earth station, and it amplifies the signal. The amplified-signal is again transmitted to another earth station.
It is used in a wide variety of applications such as weather forecasting, radio/TV signal broadcasting, mobile communication, internet, global positioning system etc.
Disadvantages of Satellite Microwave Communication
- Satellite designing and development requires more time and higher cost.
- The Satellite needs to be monitored and controlled on regular periods so that it remains in orbit.
- The life of the satellite is about 12-15 years after that it becomes non-functional.
4. Cellular Communication
It is a wireless communication system. It is used all over the world for mobile communications. In cellular communication, text, image, voice and video can be transmitted.
How cellular communication works?
Physical region (city) is divided into small units called cells. RBS (radio based station) provides the coverage within the entire cell. Each cell can transmit and receive the radio signals through RBS . These cells are close enough to one another so that the signals strength is maintained throughout the area. In this way a large number of cellular phones can communicate with each other.
Generations of Cellular Transmission
There are different generations of cellular transmissions such as 1G (1981), 2G(1991), 3G(2001), and 4G(2010-15).
Components of Cellular Communication System
- MU: It is mobile unit which consists of control unit and transceiver.
- RBS: RBS (radio based station) provides the coverage within the entire cell.
- PSTN: Public switched telephone network (PSTN) is worldwide telephone network for voice and data communication.
- MTSO: Mobile telephone switching office (MTSO) controls the entire operation of a cellular system. It control calls, provides billing information’s etc.
Infrared (IR) is wireless transmission medium. It sends signals using infrared light waves. It require a line-of-sight transmission.
Mouse, printer and digital camera have an irRA port. This ports is used to transfer data to another using infrared light waves.
It is alternative of Bluetooth.