How signals are actually transmitted

How signals are actually transmitted

Signal Channel

Capacity of the channel

　　Channel: generally refers to the medium for transmitting information in a certain direction. And the information is divided into analog and digital information.

　　Bandwidth: The maximum bandwidth of the signal that can effectively pass through the channel. Depending on the information transmitted is divided into analog bandwidth and digital bandwidth.

Analog bandwidth: For analog bandwidth also known as bandwidth, the highest frequency through which the channel can pass - the lowest frequency through which the channel can pass. Both are determined by the physical characteristics of the channel. When the circuit that makes up the channel is made, the bandwidth of the channel is determined. In order for the signal to be transmitted with less distortion, the channel should have sufficient bandwidth.

Digital Bandwidth: Bandwidth is the amount of data that can pass through a link per unit of time. The transmission of digital signals is accomplished by modulation of analog signals. In order to distinguish it from analog bandwidth, the bandwidth of digital channels is generally described directly in terms of baud rate or symbol rate.

Code element: In digital communication often use the same time interval of symbols to represent a binary number, such a time interval of the signal is called (binary) code element. And this interval is called the code element length. When the discrete state of the code element has more than 2 (such as M more than 2), then the code element is M binary code element.

Code element rate: indicates the number of transformations of the signal waveform per unit time, i.e., the number of code elements transmitted through the channel.

　　When using binary coding, there are only two different code elements, one representing the 0 state and the other representing the 1 state.

　　The higher the rate of code element transmission, or the farther the signal transmission distance, or the greater the noise interference, or the poorer the quality of the transmission media, the more serious the distortion of the waveform at the receiving end.

The waveform received at the receiving end thus loses the clear boundary between code elements, a phenomenon called inter-code crosstalk;

　　According to Nye's criterion: in any channel, there is an upper limit to the rate at which code elements can be transmitted, and when the transmission rate exceeds this limit, serious inter-code crosstalk problems will occur, making the identification of code elements at the receiving end impossible.

　　If the channel's bandwidth is wider, that is, the more high-frequency components of the signal can be passed, then the code elements can be transmitted at a higher rate without inter-code crosstalk. The bandwidth of a channel determines the highest rate at which a pulse train can be transmitted in the channel without distortion.

　　This explains why the greater the bandwidth of the network, the faster the transmission rate.

Signal-to-noise ratio:

  Noise: The energy field that interferes with signal transmission is called noise. The source of this energy field can come from internal systems or can be generated from the external environment. Noise is present in all electronic devices and communication channels. This will not be repeated here (for those who are curious to know, you can look up the information to learn), just remember.

　　Shannon's formula shows that the larger the bandwidth of the channel or the signal-to-noise ratio in the channel, the higher the ultimate transmission rate of information.

　　Therefore, for the band width has been determined for the channel, if the signal-to-noise ratio can no longer be increased, and the transmission rate of the code element has reached the upper limit, if you still want to increase the transmission rate of information, then you need to use the coding method, so that each code element to carry more bits of information.

Physical medium for signal transmission

Transmission media:

  As the physical path between the transmitter and the receiver, the transmission media is an essential part. There are two main categories:

Guided transmission media: electromagnetic waves are guided to propagate along a solid medium (copper or optical fiber).

   Twisted pair: A general purpose wiring made by winding two mutually insulated wires around each other according to certain specifications (usually clockwise). Twisted pair cable used to be mainly used for the transmission of analog signals, but is now also applicable to the transmission of digital signals.

  Principle: Two insulated copper wires are twisted together according to certain specifications to reduce the degree of signal interference, each wire in the transmission of radiated waves will be offset by the waves emitted on the other wire. Which the outer skin of the wire wrapped two by two twisted, forming a twisted pair.

   Coaxial cables: Coaxial cables consist of an inner conductor copper core (single stranded solid wire or multi-stranded stranded wire), an insulation layer, a mesh braided outer conductor shield (also single stranded) and a protective plastic outer layer.

　　Short distance coaxial cables are also used in home audio and video equipment and amateur radio equipment. It was also widely used for Ethernet connections until it was replaced by twisted pair cables.

　　Long distance coaxial cables are often used for TV signals in radio and TV networks. In the future it will be gradually replaced by other high-tech equipment, such as fiber optics, T1, satellite, etc. However, since coaxial cable is relatively cheap and has been laid for a long time, it is still in use today.

   Fiber optic cable: A cable containing optical fibers is called a fiber optic cable.

  Optical fiber, or optical fiber for short, is a fiber made of glass or plastic that uses light transmission in these fibers by the principle of total internal reflection as a means of light transmission. There are single-mode fibers and multimode fibers.

　　According to the latest research results, light is both a high-frequency electromagnetic wave and a stream of particles called elementary particles.

Light has both particle and fluctuation properties. Because of its fluctuating nature, this is why light can be used as a carrier for signal propagation.

Non-guided transmission media: free space, manifested as unlimited transmission.

  This part is actually radio transmission, through different bands of frequencies to transmit signals, the focus is to pay attention to the sender's equipment band to be consistent with the receiver, for example, A and B communication, A use the operating frequency of 2.4GHz, then B receive also to use the frequency of the equipment to receive, if the use of other frequency bands is not received.

Signal transmission method

Both serial and parallel transmission are common methods of data transmission in digital communications. Serial transmission involves transmitting data one after another in a sequence of bits, while parallel transmission involves splitting the data into several parts at the same time and transmitting them simultaneously.

1. Serial transmission

The main advantage of serial transmission is the high transmission rate, which allows for easy long-distance transmission. Specifically, because data is transmitted bit by bit with only a short time interval between each bit, fast transmission is possible using a high-speed clock. In addition, serial transmission can reduce the bit error rate during transmission because interference between different data bits cancels each other out during transmission, thereby improving transmission quality. In addition, serial transmission can easily support full duplex transmission, i.e., simultaneous sending and receiving of data, improving the efficiency of data transmission.

However, serial transmission also has disadvantages. First of all, the transmission distance is limited, because when transmitting over long distances, the impedance of the transmission line is not uniform, the signal-to-noise ratio and other factors can lead to distortion of the transmitted signal, thus affecting the quality of data transmission. In addition, serial transmission itself has a relatively large overhead because data is transmitted one by one, and each data bit requires the transmission of control information such as clock and synchronization signals, thus increasing transmission overhead.

2. Parallel transmission

The main advantage of parallel transmission is that the transmission speed is fast and multiple bits can be transmitted simultaneously, making it suitable for high-speed transmission over short distances. Specifically, because the data is divided into several parts, each part can be transmitted using a single transmission line, and there is no mutual interference between the different parts, so the transmission speed can be greatly increased. In addition, parallel transmission can support synchronous data transmission, during which there is no need to use special synchronous control signals, and thus control overhead can be reduced.

However, parallel transmission also has disadvantages. The first is the limited transmission distance, which may cause distortion of the transmitted signal and degrade the data transmission quality due to issues such as the length and impedance non-uniformity of the signal transmission lines over long distances. In addition, parallel transmission is expensive to implement and requires relatively complex hardware design and layout, including components such as DMA controllers, multiplexers, etc., thus increasing the overhead, as well as consuming more power.

By HornmicLink_Henry @230412 16:42