Telecommunications Systems and Transmission Media
1. Definitions:
- System of Telecommunications: A technique for transmitting a message from one point to another, typically bidirectional.
- Channel of Communication: Used to route messages from the sender to the receiver.
- Means of Transmission: A physical support on which one or more communication channels can be created. A single means of transmission can be shared by several communication channels.
2. Types of Transmission Media:
Guided transmission media and unguided transmission media.
3. Sinusoidal Periodic Signal vs. Random Signal:
- Sine Wave: A signal that repeats cyclically, defined by three parameters (e.g., a tuning fork).
- Random Signal: A signal that does not repeat cyclically (e.g., the human voice).
4. Bandwidth Definition:
Bandwidth covers the frequency range within which its spectrum is limited.
5. Guided Communication Media:
A) Characteristics of Copper Cables:
Copper cables are now divided into two groups:
B) Types of Copper-Wire Cables:
- Coaxial Cable: Consists of a central conductor covered with insulation and lined with mesh-wire, encased in a protective plastic coating.
- Twisted-Pair Cable: Consists of sets of paired cables grouped by an outer shell, each encased in a plastic sleeve.
C) Electromagnetic Wave:
An electromagnetic wave is a combination of oscillating electric and magnetic force fields that propagate through space.
6. Wireless Communication Definition:
Wireless communications use air or vacuum as a means of transmitting information via electromagnetic waves.
7. Electromagnetic Wave Generation and Characteristics:
Electromagnetic waves are generated by the oscillation or acceleration of electric charges (e.g., in a transmitting antenna). They need a medium to propagate.
8. Electromagnetic Spectrum Definition:
Includes all existing electromagnetic waves.
A) Three Ranges:
Radio waves, microwaves, and infrared. Two of these are divided into bands, each intended for different applications according to ITU criteria.
9. Types of Links in Wireless Communications:
Definition: Wireless communications using air or vacuum as a means of transmitting information through electromagnetic waves.
10. Features of Digital Radio:
- Provides sound quality equivalent to that of a CD.
- Has a more reliable air system.
- Received information can be varied by adding additional text or images to the program, maps, etc.
A) Characteristics of Fiber Optics:
Serve to guide light, allowing travel through its interior, even on curves, by total internal reflection of light.
B) Applications of Optical Fiber:
Can be plastic or glass. They can be monomode (very fine) fibers.
11. Digital TV:
Definition: Digital television signals are transmitted in binary form, making possible the use of interactive applications.
12. Digital Mobile Phone Operation:
Each digital mobile phone uses two microwave channels (one for transmitting and one for receiving) at different frequencies to communicate with a base station connected to the operator’s switching network.
13. Mobile Phone Network Operation:
Different groups of base stations are connected to a base station controller, which manages communications in the cells under its control. It controls the occupation of channels in each cell and acts as an intermediary between the cell and the mobile switching center. The mobile switching center manages the connection between two subscribers during a call.