CONSTANT ENVELOPE Meaning and
Definition
-
Constant envelope refers to a signaling scheme or modulation technique in digital communications, where the amplitude of the transmitted signal remains constant over time. In other words, the envelope of the signal does not vary, regardless of the data being transmitted. This is in contrast to other modulation techniques where the amplitude of the signal changes to carry information.
In constant envelope modulation, information is conveyed through variations in the phase or frequency of the carrier signal, rather than changes in the signal's amplitude. Examples of constant envelope modulation schemes include frequency shift keying (FSK), phase shift keying (PSK), and differential phase shift keying (DPSK).
A key advantage of constant envelope modulation is its resilience to non-linear distortion in radio frequency (RF) power amplifiers. RF power amplifiers often exhibit non-linear characteristics that can cause undesired distortion, leading to signal degradation. By using constant envelope modulation, the signal can tolerate these nonlinearities without significant distortion, making it more robust and reliable in practical communication systems.
Constant envelope modulation techniques are commonly employed in applications where power efficiency and spectral efficiency are critical, such as satellite communication, wireless communication, and mobile networks. By maintaining a constant amplitude, these modulation schemes enable efficient utilization of the available power and spectrum, allowing for higher data rates and improved system performance.
Etymology of CONSTANT ENVELOPE
The etymology of the term "constant envelope" can be understood by breaking down the individual words:
1. Constant: This word comes from the Latin word "constans", which means "standing firm, steadfast". It is derived from the verb "constare", meaning "to stand firm, to be consistent". In English, "constant" refers to something that remains unchanged or remains the same over time.
2. Envelope: In this context, the term "envelope" is used in a technical sense rather than its usual meaning. It stems from the Middle French word "enveloppe", which means "a covering". Its ultimate origin is the Latin word "involucrum", meaning "wrapper" or "covering". In the field of signal processing, the envelope refers to the shape or amplitude variations of a signal.
