Baseband signal, carrier signal, and wideband signal

Baseband signal
Source (information source, also known as the terminal) emitted by the non-modulated (for spectral removal and transformation) of the original electrical signal, characterized by a low frequency, the signal spectrum from the zero frequency near the beginning, with a low-pass form. According to the characteristics of the original signal, baseband signal can be divided into digital baseband signal and analog baseband signal (correspondingly, the source is also divided into digital sources and analog sources. ) is determined by the source of the letter. In a more popular sense, baseband signaling is a signal that directly conveys the information to be transmitted, such as the sound waves we speak are baseband signals. (If a signal contains an infinite AC component and a possible DC component, the signal is a baseband signal.) ）
The signal content does not change because the attenuation of the baseband signal is small in the near range. Therefore, when the transmission distance is close, the computer network uses the baseband transmission mode. such as from the computer to the monitor, printer and other peripheral signal is the baseband transmission. Most LANs use baseband transmission, such as Ethernet, Token Ring network. The common network design standard 10BaseT uses the baseband signal. The signals on the parallel bus inside the computer are all baseband signals, which is not suitable for long-distance transmission because of the extremely rich AC components in the baseband signal.

　　Simply put, the baseband signal is the low-frequency signal, which is the signal that needs to be transmitted, the equivalent of the goods. But because the baseband signal frequency is low, the transmission loss is large, so the signal needs to be modulated to high frequency. Modulation to the high frequency (that is, the carrier frequency, equivalent to the van) after transmission loss can be accepted.
Carrier Signal
A carrier is a waveform that is modulated to transmit a signal. Baseband signal Band is very wide (theoretically infinite width), but because of the band-pass reason, there is almost no infinite bandwidth of the transmission media, so the baseband signal can not be transmitted on the ordinary medium long-distance, or inter-code interference and attenuation can not make the signal recovery, so the carrier to the baseband signal modulation, reduce the bandwidth, Can make the signal reliable transmission, reduce attenuation, the receiver and then demodulation to restore the original digital signal. The carrier frequency is relatively single, so the modulated signal has a smaller bandwidth.
Wideband Signal
Wideband signal is a relative concept, it refers to its transmission medium has a wide band-pass capability, the advantage is that it can be used in the transmission of a large number of signals on the medium, saving the cost of line laying, the signal transmitted on the broadband medium is called broadband signal. The current bandwidth of the widest medium when single-mode fiber.

Baseband signal, carrier signal, and wideband signal