What is baseband used for?

What is baseband?

Baseband in the transmission of communications signals means only one path is available to send and receive digital signals between devices. Baseband communication systems have been in use for many years and is still used in technologies such as Ethernet and wireless communications.

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Baseband technology is used in several ways:

• Information is carried in digital form on a single signal channel that isn't multiplexed and uses a transmission medium, such as copper twisted-pair wires. Baseband network technology is used in various types of networks, including Ethernet and token ring local area networks.
• With multiplexing, a transmission channel derives additional paths over a baseband channel.
• A baseband signal transmits data streams as analog signals using modulation technology.
• With any frequency band on which information is superimposed, baseband can be used whether or not the band is multiplexed and information is sent on subbands. In this application, it's assumed that the carrier frequency band used isn't shifted to a different frequency band but remains at its original place in the electromagnetic spectrum.

Baseband vs. broadband

A broadband transmission and signal processing system supports multiple frequency bands, whereas baseband transmission uses only one transmission band. Both telecommunications technologies support multiple concurrent transmissions, but they use different equipment at each end to accommodate different signal transmission methods.

A baseband network is designed with only one communication channel, while broadband has several.

10BASE-T and its derivatives

Baseband technology is used in Ethernet networks. Ethernet is typically deployed in a star network configuration with the network hub and device connections radiating from the hub. The Institute of Electrical and Electronics Engineers (IEEE) defines current Ethernet transmission specifications as follows:

• 10BASE-T. The initial IEEE Ethernet standard, 10BASE-T provides 10 megabits per second (Mbps) of transmission bandwidth over a baseband channel using twisted-pair copper wiring.
• 100BASE-T. This standard supports transmission speeds up to 100 Mbps.
• BASE-T. The BASE-T standard supports transmission speeds up to 1,000 Mbps or 1 gigabit per second (Gbps). It is also referred to as Gigabit Ethernet.
• 10GBASE-T. The 10GBASE-T standard supports transmission speeds up to 10 Gbps.

Star networks use a hub and spoke topology.

In addition to twisted-pair copper cable, providers use coaxial cable and fiber optic cable as transmission media. The following are IEEE standards for each of these media:

• 10BASE-2. This standard is for thin-wire coaxial cable with a maximum transmission distance of 607 feet, or 185 meters.
• 10BASE-5. This is the thick-wire coaxial cable standard with a maximum transmission distance of 1,640 feet, or 500 meters.
• 10BASE-F. This is the standard for fiber optic transmission cables.
• 10BASE-36. The standard for broadband coaxial cable that supports transmission of multiple baseband channels over a maximum distance of 11,800 feet, or 3,600 meters.

Strengths and limitations of baseband

Baseband is a cost-effective technology that's easy to use and inexpensive to install using twisted pair cable. It's also simple to maintain, and its simple structure makes it easy to understand and work with.

However, baseband can only be used for voice and data communications. It isn't generally used for video, and it has a limited transmission range.

Learn more about the evolution of Ethernet as the standard has evolved over the last half century.

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 telecommunications and signal processing, baseband is the range of frequencies occupied by a 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 analog radio 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 DC bias, or at least it will have a high ratio bandwidth. A modulated baseband signal is called a passband signal. This occupies a higher range of frequencies and has a lower ratio and fractional bandwidth.

Various uses

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Baseband signal

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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]

A baseband bandwidth is equal to the highest frequency of a signal or system, or an upper bound on such frequencies,[3] 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

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

Digital baseband transmission

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Digital baseband transmission, also known as 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 network local-loop or a band-limited wireless channel.[7]

Related links:
What are the Different Types of Self-Supporting Towers and Their Structural Characteristics?
Understanding the Essence of Voice Verification Code
Why is Voice Verification Code used?
Orthophoto Data Processing: Challenges and Solutions

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Baseband transmission in Ethernet

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The word "BASE" in Ethernet physical layer standards, for example 10BASE5, 100BASE-TX and BASE-SX, implies baseband digital transmission (i.e. that a line code and an unfiltered wire are used).[8][9]

Baseband processor

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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]

Equivalent baseband signal

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On the left is a part of the transmitter, which will take in a stream of baseband IQ data, and use this to amplitude modulate a Local Oscillator's signal, both the standard sine wave from the LO, and also a version which phase shifted by 90° (in-phase and quadrature) - these modulated signals are combined, to form the Intermediate frequency IF representation. In a typical transmitter, the IF would get up-converted, filtered, amplified, then transmitted from an antenna. (These are not shown)
On the right we see an aspect of the receiver. After some low-noise amplification, filtering and down-conversion (not shown) to an IF, the signal is mixed with the in-phase sine from the LO, and also the quadrature version of the LO, giving a complex (or 2-dimensional) representation of the signal. This IQ data could then be supplied to a digital signal processor to extract symbols or data.

An equivalent baseband signal or equivalent lowpass signal is a complex valued representation of the modulated physical signal (the so-called passband signal or RF signal). It is a concept within analog and digital modulation methods for (passband) signals with constant or varying carrier frequency (for example ASK, PSK QAM, and FSK). The equivalent baseband signal is Z ( t ) = I ( t ) + j Q ( t ) {\displaystyle Z(t)=I(t)+jQ(t)\,} where I ( t ) {\displaystyle I(t)} is the inphase signal, Q ( t ) {\displaystyle Q(t)} the quadrature phase signal, and j {\displaystyle j} the imaginary unit. This signal is sometimes called IQ data. In a digital modulation method, the I ( t ) {\displaystyle I(t)} and Q ( t ) {\displaystyle Q(t)} 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

I ( t ) cos &#; ( ω t ) &#; Q ( t ) sin &#; ( ω t ) = R e { Z ( t ) e j ω t } {\displaystyle I(t)\cos(\omega t)-Q(t)\sin(\omega t)=\mathrm {Re} \{Z(t)e^{j\omega t}\}\,}

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

Modulation

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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 (radio frequencies, or RF) than it originally spanned. A key consequence of the usual 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

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References

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