Communication Channels: Types and Applications
Communication Channels
A communication channel is used to route messages from the sender to the receiver’s transmission components. A physical medium can support one or more communication channels. These can be:
- Guided: Such as copper wires or optical fiber (e.g., coaxial cable).
- Unguided: Such as air or a vacuum (e.g., wireless communications).
To establish a communication channel, the following are used:
- Dedicated Links: Establish an exclusive channel between two interlocutors.
- Point-to-Point: There is one communicator on each side.
- Multipoint: Many callers at either end.
- Shared Networks: Each caller is coupled to a network node that allows contact with others.
- Dissemination: The transmitter transmits data to receivers (e.g., TV).
- Switching: Temporarily sets the duration of the communication channel.
- Circuit Switching: Fixed path (e.g., telephone).
- Message Switching: Information is chopped, and each piece is sent on a network route (e.g., Internet).
Signal Transmission
To transmit any information, it needs to be converted into electrical signals. These can be:
- Sinusoidal Periodic: Its shape is repeated cyclically and is defined by:
- Amplitude (signal value, measured in mV).
- Period (one cycle, measured in seconds).
- Frequency (cycles per second, measured in Hz, representing pitch).
- Random: Its amplitude changes over time (e.g., voice).
When signals are sent from sender to receiver without changes in frequency, it is a baseband transmission. Modulation involves:
- Modulating Signal: Provides information.
- Carrier Signal: Often a high-frequency signal that receives the modulating signal.
- Modulated Signal: Will be transmitted and demodulated at the receiver to recover the original modulating signal.
Types of Modulation:
- AM (Amplitude Modulation): Changes in the carrier signal’s amplitude as a function of the modulating signal.
- FM (Frequency Modulation): Changes in the carrier signal’s frequency as a function of the modulating signal’s amplitude.
Digital Signal Modulation
Digital modulation involves taking samples of the analog signal and encoding each sample to quantify the value for each, which can then be transmitted in binary.
Transmission Media
Copper Cables
Signals take the form of voltages and electric currents. There are two types:
- Coaxial: A set sheathed in a protective layer containing a central conductor covered with insulation and a metallic mesh exterior.
- Peer-to-Peer: Sets of cable pairs grouped by an exterior cover.
Fiber Optics
Used to guide light, offering a wide transmission band, low signal attenuation, noise immunity, robustness, and lightness. There are two types:
- Single-Mode: They have a much smaller core diameter than the cladding; signals are hardly distorted.
- Multimode: Signals have more distortion and reach less than 2 km.
Wireless Communication
An electromagnetic wave is a combination of two oscillating force fields, one electric and one magnetic, spreading at the speed of light. Wavelength = speed of light / oscillation frequency.
Within the electromagnetic spectrum, there are different frequency paths. The one used in telecommunications is called radio waves (including radio waves, microwaves, and infrared).
There are three types of wireless communication links:
- Proximity: Communication over short distances (e.g., Wi-Fi, remote control).
- Terrestrial: Remote stations communicate with each other (e.g., TV, radar).
- Space: Communications via satellite, reaching millions of kilometers (e.g., meteorology, telephony).
Satellites and Orbits
There are four types of satellite orbits:
- LEO (Low Earth Orbit): Low orbit.
- MEO (Medium Earth Orbit): Around 10,000 km.
- HEO (Highly Elliptical Orbit): Inclined orbits that reach between 5,000 and 50,000 km.
- GEO (Geostationary Orbit): 36,000 km and travel at the Earth’s rotation speed.
Applications of Communications
- Telecommunications and navigation.
- Positioning and location.
- Observation and meteorology.
- Cartography and research.