Baseband


Baseband is a signal that has a near-zero frequency range, i.e. a spectral magnitude that is nonzero only for frequencies in the vicinity of the origin and negligible elsewhere. In telecommunications and signal processing, baseband signals are transmitted without modulation, that is, without any shift in the range of frequencies of the signal. Baseband has a low-frequency—contained within the bandwidth frequency close to 0 hertz up to a higher cut-off frequency. Baseband can be synonymous with lowpass or non-modulated, and is differentiated from passband, bandpass, carrier-modulated, intermediate frequency, or radio frequency.

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.
A baseband bandwidth is equal to the highest frequency of a signal or system, or an upper bound on such frequencies, for example the upper cut-off frequency of a low-pass filter. By contrast, passband bandwidth is the difference between a highest frequency and a nonzero lowest frequency.

Baseband channel

A baseband channel or lowpass channel is a communication channel that can transfer frequencies that are very near zero. Examples are serial cables and local area networks, as opposed to passband channels such as radio frequency channels and passband filtered wires of the analog telephone network. Frequency division multiplexing allows an analog telephone wire to carry a baseband telephone call, concurrently as one or several carrier-modulated telephone calls.

Digital baseband transmission

Digital baseband transmission, also known as line coding, aims at transferring a digital bit stream over baseband channel, typically an unfiltered wire, contrary to passband transmission, also known as carrier-modulated transmission. Passband transmission makes communication possible over a bandpass filtered channel, such as the telephone network local-loop or a band-limited wireless channel.

Baseband transmission in Ethernet

The word "BASE" in Ethernet physical layer standards, for example 10BASE5, 100BASE-TX and 1000BASE-SX, implies baseband digital transmission.

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 the wireless digital system. The baseband processing block in GNSS receivers is usually responsible for providing observable data: code pseudo-ranges and carrier phase measurements, as well as navigation data.

Equivalent baseband signal

An equivalent baseband signal or equivalent lowpass signal is—in analog and digital modulation methods for signals with constant or varying carrier frequency —a complex valued representation of the modulated physical signal. The equivalent baseband signal is where is the inphase signal, the quadrature phase signal, and the imaginary unit. 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.

Modulation

A signal at baseband is often used to modulate a higher frequency carrier signal in order that it may be transmitted via radio. Modulation results in shifting the signal up to much higher frequencies than it originally spanned. A key consequence of the usual double-sideband amplitude modulation is that the range of frequencies the signal spans is doubled. Thus, the RF bandwidth of a signal is twice its baseband bandwidth. Steps may be taken to reduce this effect, such as single-sideband modulation. Some transmission schemes such as frequency modulation use even more bandwidth.
The figure shows what happens with AM modulation: