What is baseband

Baseband refers to the inherent frequency band of the original electrical signal that has not been modulated; the baseband bandwidth of a signal is its front bandwidth modulation and multiplexing, or demultiplexing and demodulation; the composite video signal is in the video recorder , game consoles and DVD players are a commonly used baseband signal; baseband is a signal with a very narrow frequency range, which means that the amplitude spectrum is non-zero only near the origin, and other frequencies can be almost ignored; in telecommunications and signal processing , the baseband signal is transmitted without modulation, that is, the frequency range of the signal does not have any shift, and the frequency is very low.

#The operating environment of this tutorial: Windows 10 system, Dell G3 computer.

What is baseband?

Baseband: Baseband The inherent frequency band (frequency bandwidth) of the original electrical signal emitted by the information source (information source, also called the transmitter) without modulation (spectrum shifting and transformation), is called Basic frequency band, referred to as baseband.

Baseband corresponds to frequency band. Frequency band: the frequency bandwidth occupied by the baseband signal after modulation (the difference from the lowest frequency to the highest frequency occupied by a signal).

The baseband bandwidth of a signal is its pre-bandwidth modulation and multiplexing, or demultiplexing and demodulation. Composite video signal is a commonly used baseband signal in video recorders, game consoles and DVD players.

Basic information

The baseband is a signal with a very narrow frequency range, which means that the amplitude spectrum is non-zero only near the origin (f= 0), and other frequencies It can almost be ignored. In telecommunications and signal processing, baseband signals are transmitted without modulation, that is, the frequency range of the signal does not have any shift, and the frequency is very low, including the frequency band from close to 0Hz to a higher cutoff frequency or maximum bandwidth.

In the current Chinese context, the word "baseband" is also commonly used to refer to the communication module (modem) of a mobile phone and to the corresponding control software (firmware).

Baseband is a circuit in a mobile phone that is responsible for demodulating, descrambling, despreading and decoding wireless signals in mobile networks, and passing the final decoded digital signal to the upper-layer processing system For processing, the baseband is commonly known as BB, and Baseband can be understood as a communication module.

Our mobile phones usually consist of two major circuits. One part is the high-level processing part, which is equivalent to the computer we use; the other part is the baseband, which is equivalent to the Modem we use. What kind of circuits does the mobile phone support? The network standard (GSM, CDMA, WCDMA, TD-SCDMA, etc.) is determined by it, just like the difference between ADSL Modem and ordinary narrowband Modem.

When we use mobile phones to make calls, surf the Internet, send text messages, etc., all instructions (usually standard AT instructions) are issued to the baseband part through the upper-layer processing system, and are processed and executed by the baseband part, and the baseband part completes the processing Afterwards, a logical channel will be established between the mobile phone and the wireless network. Our voice, text messages or Internet data packets are transmitted through this logical channel.

Baseband signal

Usually it is necessary to modulate a baseband signal to a higher frequency carrier to facilitate wireless transmission. As a result, the modulation signal is moved to a higher frequency (RF). For double-sideband modulation, the bandwidth of the modulation signal becomes twice as large. That is, the distance from the lowest frequency (not the 0 frequency point) to the highest frequency is twice the baseband bandwidth. Single sideband modulation can be used to reduce this effect. The highest frequency of a bandpass signal generally far exceeds the baseband bandwidth. Some signals are baseband depending on the situation. For example, an analog telephone switched network connection would use a bandpass filter to filter out waveforms below 300 Hz and above 3400 Hz. Because no signal is very close to zero frequency, it may not be considered a baseband signal, but at the telephone system frequency Within the multiplexing hierarchy, it is usually treated as a baseband signal.

The baseband signal is a signal that directly expresses the information to be transmitted. For example, the sound waves we speak are baseband signals. (If a signal contains an AC component with an infinite frequency and a possible DC component, the signal is a baseband signal.)

Since the attenuation of the baseband signal is not large in the short range, the signal content will not changes occur. Therefore, when the transmission distance is short, computer networks all use baseband transmission. For example, signals from computers to peripherals such as monitors and printers are transmitted via baseband. Most LANs use baseband transmission, such as Ethernet and Token Ring. The common network design standard 10BaseT uses baseband signals.

Frequency band signal

In communications, since the baseband signal has a spectrum component with a very low frequency, it is generally not suitable to be transmitted directly for the sake of anti-interference and improving the transmission rate. It needs to be Convert the baseband signal into a signal whose frequency band is suitable for transmission in the channel. The converted signal is a frequency band signal (if a signal contains only one frequency AC component or a limited number of frequency AC components, we call this signal called frequency band signal).

It is mainly used for video broadcasting on Internet TV and cable TV.

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