Intelecommunications andsignal processing,baseband is the range of frequencies occupied by asignal that has not beenmodulated to higher frequencies.^[1] Baseband signals typically originate fromtransducers, 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 conventionalanalogradio broadcasting, the baseband audio signal is used tomodulate anRF carrier signal of a much higher frequency.

A baseband signal may have frequency components going all the way down to theDC bias, or at least it will have a highratio bandwidth. A modulated baseband signal is called apassband signal. This occupies a higher range of frequencies and has a lower ratio andfractional bandwidth.

Abaseband signal orlowpass 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]

Abasebandbandwidth is equal to the highest frequency of a signal or system, or an upper bound on such frequencies,^[3] for example the uppercut-off frequency of alow-pass filter. By contrast,passband bandwidth is the difference between a highest frequency and a nonzero lowest frequency.

Abaseband channel orlowpass channel (orsystem, ornetwork) is acommunication channel that can transfer frequencies that are very near zero.^[4] Examples are serial cables andlocal area networks (LANs), as opposed topassband channels such as radio frequency channels and passband filtered wires of the analog telephone network.Frequency division multiplexing (FDM) allows an analog telephone wire to carry a baseband telephone call, concurrently as one or several carrier-modulated telephone calls.

Digital baseband transmission, also known asline coding,^[5] aims at transferring a digital bit stream over baseband channel, typically an unfiltered wire, contrary topassband transmission, also known ascarrier-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]

The word "BASE" inEthernet physical layer standards, for example10BASE5,100BASE-TX and1000BASE-SX, implies baseband digital transmission (i.e. that aline code and an unfiltered wire are used).^[8][9]

Abaseband 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 inGNSS receivers is responsible for providing observable data: that is, code pseudo-ranges and carrier phase measurements, as well as navigation data.^[7]

Anequivalent baseband signal orequivalent lowpass signal is a complex valued representation of the modulated physical signal (the so-calledpassband signal orRF signal). It is a concept within analog and digital modulation methods for (passband) signals with constant or varyingcarrier frequency (for exampleASK,PSKQAM, andFSK). The equivalent baseband signal is${\displaystyle Z(t)=I(t)+jQ(t)}$ where${\displaystyle I(t)}$ is the inphase signal,${\displaystyle Q(t)}$ the quadrature phase signal, and${\displaystyle j}$ the imaginary unit. This signal is sometimes calledIQ data. In a digital modulation method, the${\displaystyle I(t)}$ and${\displaystyle Q(t)}$ signals of each modulation symbol are evident from theconstellation diagram. The frequency spectrum of this signal includes negative as well as positive frequencies. The physical passband signal corresponds to

${\displaystyle I(t)\cos (\omega t)-Q(t)\sin (\omega t)=\mathrm{R}\mathrm{e}\{Z(t)e^{j\omega t}\}}$

where${\displaystyle \omega }$ is the carrier angular frequency in rad/s.^[10]

A signal at baseband is often used tomodulate a higher frequencycarrier signal in order that it may be transmitted via radio. Modulation results in shifting the signal up to much higher frequencies (radio frequencies, or RF) than it originally spanned. A key consequence of the usualdouble-sidebandamplitude modulation (AM) is that the range of frequencies the signal spans (its spectralbandwidth) 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 assingle-sideband modulation. Conversely, some transmission schemes such asfrequency modulation use even more bandwidth.

The figure below shows AM modulation:

Look upbaseband in Wiktionary, the free dictionary.

• Complex envelope
• Broadband
• In-phase and quadrature components
• Narrowband
• Wideband

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• Signal processing

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