Wireless Transmission Media - IT 709

Overview of Transmission Media

• Transmission methods fall into two main categories: guided and unguided media.
• Guided media include twisted pairs, coaxial cables, and fiber optics which direct electromagnetic waves along a physical path.
• Unguided media involve transmission through the atmosphere or outer space, without a physical guiding medium.

Wireless Transmission Media

• The electromagnetic spectrum includes various types of waves: radio, microwave, infrared, and visible light, essential for wireless communication.
• Higher frequency waves like ultraviolet, X-rays, and gamma rays could transmit data efficiently but are difficult to produce, modulate, and are harmful to health.
• Information capacity of a signal is proportional to its bandwidth and received power, making fiber optics favorable due to high bandwidth.

Electromagnetic Spectrum

• The spectrum includes bands like LF (Low Frequency), MF (Medium Frequency), and HF (High Frequency), denoting different ranges of wavelength and frequency.
• Recent bands are humorously labeled Very, Ultra, Super, Extremely High Frequencies, with the absence of names for frequencies beyond these.

Radio Transmission

• Radio waves are generated easily, travel long distances, and penetrate buildings, making them popular for communication.
• Radio waves are omnidirectional, allowing signal reception without precise transmitter-receiver alignment.
• VLF, LF, and MF bands are effective for indoor signal penetration, though they have low bandwidth, limiting data communication.

Microwave Transmission

• Microwaves travel in straight lines above 100 MHz, allowing for focused signals via parabolic antennas, which improves signal-to-noise ratio.
• They form the foundation for long-distance telephone transmission prior to optical fiber technology.
• Repeaters are necessary for maintaining signal over long distances, requiring precise tower placement to avoid obstacles.

Multipath Fading and Water Absorption

• Microwaves can experience multipath fading, resulting in signal cancellation when delayed waves arrive out of phase with direct waves.
• At frequencies around 4 GHz, water absorption becomes significant, particularly during rain, requiring alternate routing for affected links.

Lightwave Transmission

• Free-space optics allows unguided optical signaling, often used to connect LANs through rooftop lasers.
• Optical signals provide high bandwidth, enhanced security against tapping, and easy installation without licensing requirements.
• Environmental factors like heat-induced air turbulence can affect the stability of optical signals.

Communication Satellites

• Satellites act as relay stations, receiving signals on one frequency, amplifying them, and transmitting on another.
• Types of satellites include Geostationary (GEO), Medium-Earth Orbit (MEO), and Low-Earth Orbit (LEO), each with specific uses in television, phone networking, and business communications.
• Global coverage requires consideration of satellite altitude and round-trip delay times for operational efficiency.