Baseband transmission, band transmission, and broadband transmission

An electrical signal is also called a signal. The number of changes in a signal per second is called a frequency, in Hz ). The signal frequency is high or low, just as the sound frequency is high or low. The frequency to high frequency ranges are called frequency bands. Different signals have different frequency bands.

Baseband transmission
In data communication, the binary digital signal directly sent by a computer or a terminal is called a square wave, that is, "1" or "0", respectively, with a high (or low) level or low (or high) level. people refer to the band inherent in the square wave as the band occupied by signals that are directly converted from messages into unmodulated signals, in theory, the spectrum of a baseband signal ranges from 0 to infinity. A Square Wave electrical signal is called a baseband signal.

In the digital signal spectrum, the frequency range from DC (zero frequency) to the energy concentration is called the basic frequency band (baseband for short. Therefore, digital signals are called digital baseband signals, which are directly transmitted over channels. In baseband transmission, the entire channel only transmits one signal, and the communication channel utilization is low. In general, it is necessary to convert the source data into directly transmitted digital baseband signals, which are completed by the encoder. At the sender end, the encoder implements encoding, and at the receiver end, the decoder decodes the original data sent by the sender. Baseband transmission is the simplest and most basic transmission method. It is a typical rectangular electrical pulse signal. Its spectrum includes various components, such as DC, low frequency, and high frequency.

Because the power attenuation of the baseband signal is not large within a close range, the channel capacity will not change. Therefore, the baseband transmission technology is usually used in the LAN.

In baseband transmission, digital signals must be encoded to represent data.

Band transmission
Long-distance communication channels are mostly analog channels. For example, traditional telephone channels (telephone channels) can only transmit analog signals in the audio range (300-3400Hz, it is not applicable to digital baseband signals with a wide direct transmission band but concentrated in low frequency segments.

In band transmission, the baseband signal is first transformed (modulated) into a analog signal (called band signal) with a high frequency range that facilitates transmission in the analog channel ), then, the band signal is transmitted in the analog channel.

Long-distance communication in computer networks usually uses band transmission.

The conversion between the baseband signal and the band signal is completed by the modulation and demodulation technology.

Broadband Transmission
Through band transmission, the link capacity can be divided into two or more channels, each channel can carry different signals, which is broadband transmission. All channels in broadband transmission can send signals at the same time. Such as CATV and ISDN.

Features of broadband transmission and baseband transmission

Baseband transmission:
The digital signal and spectrum generated by a computer or terminal start from scratch, the frequency range of this unmodulated signal is the basic frequency band (which can be up to several hundred kHz or even several megahertz from DC), referred to as the base band ). This digital signal is called a baseband signal. For example, in a wired channel, the signal transmitted when the communication is directly carried out using a telex printer is a baseband signal. When transmitting data, the baseband signal is sent to the line in the original form, which is called the baseband transmission. Baseband transmission does not require a modem, and the device cost is small. This method is suitable for short-distance data transmission. For example, a company or a factory can connect a large number of terminals to the master computer. In addition, it is the transmission medium. Generally, the baseband coaxial cable is used as the transmission medium in the LAN. However, if you plan to use the optical fiber, I have no objection.

Band transmission:
The above transmission method is applicable to the LAN transmission within a unit, but in addition to the local lines, long-distance lines cannot transmit components similar to 0, that is, in computer remote communication, the original electrical pulse signal cannot be directly transmitted (that is, the baseband signal ). Therefore, it is necessary to use band transmission, that is, to control certain parameters of the carrier waveform using a baseband pulse, so that these parameters change with the baseband pulse, Which is modulation. The modulated signal is called the tuned signal. The tuned signal is transmitted to the receiving end through a line and then demodulated to the original baseband pulse. This band transmission not only overcomes the disadvantages that many long-distance telephone lines cannot directly transmit baseband signals, but also achieves multiplexing, thus improving the utilization rate of communication lines. However, you must set a modem for both the transmission end and the receiving end.

However, in baseband transmission, we often have a deep understanding of the problem, that is, waiting and so on-in this case, we are very envious and eager for a kind of transmission, this type of transmission is called broadband transmission. The so-called Broadband refers to a frequency band that is wider than the audio (4 kHz) bandwidth. Simply put, it includes the frequency band of most electromagnetic spectrum. The system that uses this broadband for transmission is called a broadband transmission system. It can simply accommodate all-in-one broadcasts and transmit data at a high speed. For LAN, the term "Broadband" is specifically used to transmit analog signals over a coaxial cable. It can be seen that a broadband transmission system is a analog signal transmission system that allows digital information and analog information services on the same channel. The difference between baseband and broadband is that the data transmission rate is different. The baseband data transmission rate is 0 ~ 10 Mb/s, more typical: 1 Mb/s ~ 2.5 Mb/s, usually used to transmit digital information. Broadband is a transmission analog signal with a data transmission rate ranging from 0 ~ 400 Mb/s, and the transmission rate is usually 5 Mb/s ~ 10 Mb/s, and a broadband channel can be divided into multiple logical baseband channels. In this way, the transmission of sound, image and data information can be integrated in a physical channel to meet your network's excessive requirements. In short, broadband transmission must adopt the band transmission technology, but the band transmission is not necessarily broadband transmission.