Range of frequencies occupied by an unmodulated signal
Spectrum of a baseband signal, energy E per unit frequency as a function of frequency f. The total energy is the area under the curve.
In
signal that has not been modulated to higher frequencies.[1] Baseband signals typically originate from transducers, converting some other variable into an electrical signal. For example, the electronic output of a microphone is a baseband signal that is analogous to the applied voice audio. In conventional analogradio broadcasting, the baseband audio signal is used to modulate an RF carrier signal
of a much higher frequency.
A baseband signal may have frequency components going all the way down to the
fractional bandwidth
.
Various uses
Baseband signal
A baseband signal or lowpass signal is a signal that can include frequencies that are very near zero, by comparison with its highest frequency (for example, a sound waveform can be considered as a baseband signal, whereas a radio signal or any other modulated signal is not).[2]
line coding,[5] aims at transferring a digital bit stream over baseband channel, typically an unfiltered wire, contrary to passband transmission, also known as carrier-modulated transmission.[6] Passband transmission makes communication possible over a bandpass filtered channel, such as the telephone network local-loop or a band-limited wireless channel.[7]
Baseband transmission in Ethernet
The word "BASE" in
1000BASE-SX, implies baseband digital transmission (i.e. that a line code and an unfiltered wire are used).[8][9]
Baseband processor
A baseband processor also known as BP or BBP is used to process the down-converted digital signal to retrieve essential data for a wireless digital system. The baseband processing block in GNSS receivers is responsible for providing observable data: that is, code pseudo-ranges and carrier phase measurements, as well as navigation data.[7]
An equivalent baseband signal or equivalent lowpass signal is a complex valued representation of the modulated physical signal (the so-called
carrier frequency (for example ASK, PSKQAM, and FSK
). The equivalent baseband signal is where is the inphase signal, the quadrature phase signal, and the imaginary unit. This signal is sometimes called
IQ data
. In a digital modulation method, the and signals of each modulation symbol are evident from the constellation diagram. The frequency spectrum of this signal includes negative as well as positive frequencies. The physical passband signal corresponds to
where is the carrier angular frequency in rad/s.[10]
Modulation
A signal at baseband is often used to
double-sideband amplitude modulation (AM) is that the range of frequencies the signal spans (its spectral bandwidth) is doubled. Thus, the RF bandwidth of a signal (measured from the lowest frequency as opposed to 0 Hz) is twice its baseband bandwidth. Steps may be taken to reduce this effect, such as single-sideband modulation. Conversely, some transmission schemes such as frequency modulation
use even more bandwidth.
The figure below shows AM modulation:
Comparison of the equivalent baseband version of a signal and its AM-modulated (double-sideband) RF version, showing the typical doubling of the occupied bandwidth.
See also
Look up baseband in Wiktionary, the free dictionary.
