Communication Channels and Technologies
Communication Channels
A communication channel routes messages from sender to receiver. Channels can be guided (e.g., copper wires, optical fiber) or unguided (e.g., air, vacuum).
Types of Communication Channels
- Dedicated Links: Establish an exclusive channel between two interlocutors.
- Point-to-Point: One sender and one receiver.
- Multipoint: Multiple callers at either end.
- Shared Networks: Callers connect to a network node to contact others.
- Dissemination (Broadcast): Transmitter sends data to multiple receivers (e.g., TV).
- Switching (Circuit-Switched/Packet-Switched): A temporary channel is established for communication (e.g., telephone, internet).
Signal Transmission
Information is converted into electrical signals for transmission. These signals can be:
- Periodic Sinusoidal: Characterized by amplitude, period, and frequency.
- Random: Amplitude changes over time (e.g., voice).
Modulation
Modulation is used to transmit baseband signals by modifying a carrier signal. Common types include:
- Amplitude Modulation (AM): Carrier amplitude varies with the modulating signal.
- Frequency Modulation (FM): Carrier frequency varies with the modulating signal.
Digital Modulation
Analog signals are sampled and quantized, with each sample encoded in binary for transmission.
Transmission Media
Copper Cables
- Coaxial: Central conductor insulated and shielded by a metallic mesh.
- Twisted Pair: Pairs of wires twisted together.
Optical Fibers
- Single Mode: Small core diameter, minimal signal distortion.
- Multimode: Larger core diameter, more distortion, shorter transmission distances.
Electromagnetic Waves
Electromagnetic waves are used in wireless communication. Wavelength is related to frequency and the speed of light.
Wireless Communication Links
- Proximity: Short-range communication (e.g., Wi-Fi, Bluetooth).
- Terrestrial: Long-range communication between ground stations (e.g., TV, radar).
- Space: Communication via satellites (e.g., meteorology, telephony).
Satellite Orbits
- LEO (Low Earth Orbit)
- MEO (Medium Earth Orbit)
- HEO (Highly Elliptical Orbit)
- GEO (Geostationary Orbit)
Applications of Communication Technologies
- Telecommunications and Navigation
- Positioning and Location
- Observation and Meteorology
- Cartography and Research