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Encyclopedia > Baseband

Baseband is an adjective that describes signals and systems whose range of frequencies is measured from 0 to a maximum bandwidth or highest signal frequency; it is sometimes used as a noun for a band of frequencies starting at 0. It can often be considered as synonym to lowpass, and antonym to passband. In telecommunications, passband is the portion of spectrum, between limiting frequencies (or, in the optical regime, limiting wavelengths), that is transmitted with minimum relative loss or maximum relative gain. ...

• A baseband bandwidth is equal to a highest frequency of a signal or system, or an upper bound on such frequencies. By contrast, a non-baseband (passband) bandwidth is the difference between a highest frequency and a nonzero lowest frequency.
• A baseband signal or lowpass signal is a signal that can include frequencies that are equal to or 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 is not).
• A baseband channel or lowpass channel (or system, or network) is a channel (e.g. a telecommunications system) that can transfer frequencies that are equal to or very near zero. Examples are serial cables and local area networks (LANs).
• Baseband modulation, also known as line coding, aims at transferring a digital bit stream over an analog baseband channel.
• An equivalent baseband signal or equivalent lowpass signal is – in analog and digital modulation methods with constant carrier frequency (for example ASK, PSK and QAM but not FSK) – a complex valued representation of the modulated physical signal (the so called passband signal or RF signal). The equivalent baseband signal is
Z(t) = I(t) + jQ(t),

where I(t) is the inphase signal, Q(t) the quadrature phase signal, and j the imaginary unit. In a digital modulation method, the I(t) and Q(t) signals of each modulation symbol are evident from the constellation diagram. The physical passband signal corresponds to
I(t)cos(ωt) + Q(t)sin(ωt) = real(Z(t)ejωt),

where ω is the carrier angular frequency in rad/s.
• A signal "at baseband" is usually considered to include frequencies from near 0 Hz up to the highest frequency in the signal with significant power.

In general, signals can be described as including a whole range of different frequencies added together. In telecommunications in particular, it is often the case that those parts of the signal which are at low frequencies are 'copied' up to higher frequencies for transmission purposes, since there are few communications media that will pass low frequencies without distortion. Then, the original, low frequency components, are referred to as the baseband signal. Typically, the new, high-frequency copy is referred to as the 'RF' (radio-frequency) signal. Local area network scheme A local area network (LAN) is a computer network covering a local area, like a home, office, or group of buildings[1]. Current LANs are most likely to be based on switched IEEE 802. ... In telecommunication, a line code is a code chosen for use within a communications system for transmission purposes. ... In telecommunications, passband is the portion of spectrum, between limiting frequencies (or, in the optical regime, limiting wavelengths), that is transmitted with minimum relative loss or maximum relative gain. ... Rough plot of Earths atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including radio waves. ... A constellation diagram is a representation of a digital modulation scheme in the complex plane. ... The hertz (symbol: Hz) is the SI unit of frequency. ... In information theory, a signal is the sequence of states of a communications channel that encodes a message. ... Sine waves of various frequencies; the lower waves have higher frequencies than those above. ... In applied mathematics and physics, the spectral density is a general concept applied to a signal which may have any physical dimensions or none at all. ... Copy of the original phone of Graham Bell at the MusÃ©e des Arts et MÃ©tiers in Paris Telecommunication is the transmission of signals over a distance for the purpose of communication. ... In telecommunications, transmission is the act of transmitting electrical messages (and the associated phenomena of radiant energy that passes through media). ... Rough plot of Earths atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including radio waves. ...

The concept of baseband signals is most often applied to real-valued signals, and systems that handle real-value signals. Fourier analysis of such signals includes a negative-frequency band, but the negative-frequency information is just a mirror of the positive-frequency information, not new information. For complex-valued signals, on the other hand, the negative frequencies carry new information. In that case, the full two-sided bandwidth is generally quoted, rather than just the half measured from zero; the concept of baseband can be applied by treating the real and imaginary parts of the complex-valued signal as two different real signals.

A signal at baseband is often modulated in order that it may be transmitted. Modulation results in shifting the signal up to much higher (RF) frequencies than it originally spanned. A key consequence of the usual double-sideband amplitude modulation (AM) is that, usually, 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 usually twice its baseband bandwidth. Steps may be taken to reduce this effect, such as single-sideband modulation; the highest frequency of such signals greatly exceeds the baseband bandwidth. In telecommunications, modulation is the process of varying a periodic waveform, i. ... In radio communications, a sideband is a band of frequencies higher than or lower than the carrier frequency, containing energy as a result of the modulation process. ... [[Amplitude modulation]] (AM) is a technique used in electronic communication, most commonly for transmitting information via a carrier wave wirelessly. ... This article or section does not cite its references or sources. ... Single-sideband modulation (SSB) is a refinement of the technique of amplitude modulation designed to be more efficient in its use of electrical power and bandwidth. ...

Some signals can be treated as baseband or not, depending on the situation. For example, a switched analog connection in the telephone network has energy below 300 Hz and above 3400 Hz removed by bandpass filtering; since the signal has no energy very close to zero frequency, it may not be considered a baseband signal, but in the telephone systems frequency-division multiplexing hierarchy, it is usually treated as a baseband signal, by comparison with the modulated signals used for long-distance transmission. The 300 Hz lower band edge is this case is treated as "near zero", being a small fraction of the upper band edge. The frequency axis of this symbolic diagram would be logarithmically scaled. ... Frequency-division multiplexing (FDM) is a form of signal multiplexing where multiple baseband signals are modulated on different frequency carrier waves and added together to create a composite signal. ...

The figure shows what happens with AM modulation:

Comparison of the baseband version of a signal and its RF version, showing the typical doubling of the occupied bandwidth.

The simplest definition is that a signal's baseband bandwidth is its bandwidth before modulation and multiplexing, or after demultiplexing and demodulation. Picture of baseband signal compared to it RF equivalent. ... In telecommunications, modulation is the process of varying a periodic waveform, i. ... In telecommunications, multiplexing (also muxing or MUXing) is the combining of two or more information channels onto a common transmission medium using hardware called a multiplexer or (MUX). ... In telecommunications, multiplexing (also muxing or MUXing) is the combining of two or more information channels onto a common transmission medium using hardware called a multiplexer or (MUX). ... Demodulation is the act of removing the modulation from an analog signal. ...

The composite video signal created by devices such as most newer VCRs, game consoles and DVD players is a commonly used baseband signal. Composite video is the format of an analog television (picture only) signal before it is combined with a sound signal and modulated onto an RF carrier. ... The video cassette recorder (or VCR, less popularly video tape recorder) is a type of video tape recorder that uses removable cassettes containing magnetic tape to record audio and video from a television broadcast so it can be played back later. ... The Nintendo GameCube is an example of a popular video game console. ... DVD (commonly Digital Versatile Disc or Digital Video Disc) is an optical disc storage media format that can be used for data storage, including movies with high video and sound quality. ...

## Not to be confused with GA_googleFillSlot("encyclopedia_square");

• Broadband - generally refers to transmission of data over numerous frequencies
• Wideband - a communications medium or signal that spans a large (continuous) range of frequencies, or is wide compared to something else
• Narrowband - the opposite of wideband.

Broadband in telecommunications is a term which refers to a signaling method which includes or handles a relatively wide range of frequencies which may be divided into channels or frequency bins. ... Wideband is a relative term used to describe a wide range of frequencies in a spectrum. ... Narrowband (narrow bandwidth) refers to a signal which occupies only a small amount of space on the radio spectrum -- the opposite of broadband or wideband. ...

Results from FactBites:

 Baseband - Wikipedia, the free encyclopedia (338 words) More precisely, a signal "at baseband" is usually considered to comprise all relevant frequencies from 0Hz up to the highest frequency component in the signal with significant power. Thus, the RF bandwidth of a signal is usually twice its baseband bandwidth. The simplest definition is that a signal's baseband bandwidth is its bandwidth before modulation and multiplexing, or after demultiplexing and demodulation.
 Multiplex baseband - Wikipedia, the free encyclopedia (219 words) In frequency-division multiplexing, the frequency band occupied by the aggregate of the signals in the line interconnecting the multiplexing and radio or line equipment. This is the group-level baseband that results from combining 12 voice-frequency input channels, having a bandwidth of 4 kHz each, including guard bands. Ten super groups are in turn multiplexed into one master group, the output of which is a baseband that may be used to modulate a microwave-frequency carrier.
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