basebandsignal

A baseband signal is a signal whose spectrum lies in the low-frequency region, typically starting at or near DC, and that is transmitted without shifting its energy to a higher carrier frequency. In other words, it is the original signal before modulation onto a carrier for transmission on a particular channel. The term distinguishes signals that can be sent directly over a medium from those that require modulation to a passband.

Baseband signals can be analog or digital. Analog baseband includes signals such as audio from microphones or seismic data that can be transmitted directly over suitable media. Digital baseband refers to encoded digital data represented by voltage or current levels, as found in baseband Ethernet networks where information is transmitted without an RF carrier.

Bandwidth and channel considerations: The baseband bandwidth equals the highest frequency component present (for signals that extend from 0 Hz, the bandwidth is the maximum frequency). Transmitting baseband signals requires a channel that supports frequencies from near 0 up to that maximum with acceptable attenuation and dispersion. In practice, DC offsets are often removed by coupling techniques, and equalization or timing recovery may be needed to mitigate distortion and intersymbol interference.

Relation to modulation: To send a baseband signal over channels that cannot support low frequencies or over wireless media, the baseband content must be modulated onto a higher-frequency carrier (passband modulation). At the receiver, demodulation and baseband processing recover the original signal spectrum.

Examples: Baseband signaling is common in wired local networks such as Ethernet over twisted pair, and in audio and other low-frequency transmission systems where the medium supports the required low-frequency spectrum. In wireless contexts, baseband processing remains inside the radio transceiver before upconversion to a carrier.