Understanding Signal Polarization, COFDM, and Decibels

Understanding Signal Polarization

Signal polarization refers to the orientation of the electric and magnetic fields in space as an electromagnetic wave propagates.

Types of Electromagnetic Wave Polarization

Electromagnetic waves can exhibit different types of polarization, primarily categorized as linear or circular.

• Linear Polarizations: In linear polarization, the emitted signal maintains a constant orientation as it propagates. This type can be further differentiated into:
  • Vertical Polarization: The electric field oscillates along a vertical plane.
  • Horizontal Polarization: The electric field oscillates along a horizontal plane.
• Circular Polarizations: In circular polarization, the wave's electric field rotates as it moves through space. This means that depending on the point or time of observation, a different angle of polarization will be measured. Circular polarization can be:
  • Left-Handed Circular Polarization: The electric field rotates counter-clockwise when viewed along the direction of propagation.
  • Right-Handed Circular Polarization: The electric field rotates clockwise when viewed along the direction of propagation.

The COFDM Transmission System

The COFDM (Coded Orthogonal Frequency-Division Multiplexing) system is an advanced method for managing signal transmission, operating with modulated signals.

Unlike classical transmission systems, where each channel typically uses a single carrier frequency for all information, COFDM utilizes a large number of closely spaced, orthogonal carrier frequencies. Each of these carriers acts as an independent communication channel. Digital information is automatically and sequentially assigned to these individual carriers, resulting in a highly efficient frequency-multiplexed transmission.

The COFDM system is widely used in the transmission of Digital Terrestrial Television (DTT), enabling robust and high-quality digital broadcasting.

Understanding the Decibel (dB)

The decibel (dB) is a logarithmic unit used to express the ratio of two values of a physical quantity, most commonly power or intensity. It serves as a unit of relation, comparing a measured value against a reference value.

Decibels are widely applied in various fields, including electronics, acoustics, and telecommunications, to quantify ratios of power, voltage, or sound pressure. For instance:

• Decibel-milliwatt (dBm): This unit measures absolute power at a specific point, relating it to one milliwatt (1 mW) of power. It is commonly used in radio, microwave, and fiber optic communication networks.
• Relative Decibel (dB): Decibels are also used to indicate whether a signal has experienced gain (amplification) or attenuation (reduction) within a process. In this context, the output signal is compared to the input signal, and the unit is expressed simply as dB, without subscripts. A positive dB value indicates gain, while a negative dB value indicates attenuation.