Foreword
The world's development is a speed, look back, now China has a major breakthrough, so that the Chinese and even foreigners look at each other, and also prove China It is unbearable, and the sleeping lion has awake.
In our lives, when people refer to communication, they will naturally think of the most common, most convenient and fastest calls, e-mail, mobile phones, etc. In these communication methods, it is to transmit messages with an electrical signal, which is called telecommunications. These generation, transmission electrical signals, and devices that restore it to the original messages in the receiving end constitute a communication system ...
We can see that communication is important in our lives. It brings us a variety of news. If one day it disappears, I can't imagine what the world will become.
Classification
in actual communication, due to the diversity of communication services, the source of the message is also varied, but it is basically divided into two categories: continuous And discrete. Continuous messages such as voice, the amplitude of sound wave vibration varies over time. The signal amplitude is a time consecutive function when converting it to a voltage signal that is continuously changed over time. Such a signal is called an analog signal; and the discrete message, such as the message generated by the type of type, the number of messages output is limited. If the parameters of the signal correspond to the discrete message, the discrete value is discrete, which is a digital signal.
Therefore, communication can be divided into analog communication and digital communication depending on the signal mode.
Simulation communication
What is analog communication? For example, in telephone communication, the electrical signal transmitted on the user line varies with the change in the size of the user. This changed electrical signal is continuous in times of time or amplitude, which is called an analog signal. The communication mode of transmitting an analog signal on the user line is called "simulation communication."
Digital communication
Different digital signals are different from the analog signal, which is a discrete, pulsed combination, is a signal of load digital information. The telegraph signal is a digital signal. The most common digital signal is now the waveform of only two (0 and 1), called "binary signals". "Digital Communication" refers to a communication method that transmits information as a carrier as a carrier, or uses a digital signal to digitally modulate the communication mode after digital modulation.
The simulation communication has occupied dominant position in history. However, in the past 20 years, with the maturity of the oversized scale integrated circuit process and the full development of computer and digital signal processing technology, digital communication has developed rapidly, and most analog communication systems have been replaced by digital communication systems. Although the digital communication system does not completely replace the analog communication system in the next period of time, communication is not changed toward the digital direction, which is determined by digital communication and analog communication itself.
Compared with the digital communication with analog communication with analog communication:
first is anti-interference, strong anti-noise ability. The analog signal is difficult to separate during transmission and superimposed noise, and the noise will be transmitted, amplified, and seriously affect communication quality. For example, 1 is expressed in a high level, 0 is represented by a low level.
An analog signal If the signal is attenuated 20%, then it is seriously distorted. When a high level signal is attenuated 20%, it still represents 1. Because digital communication is a regenerative relay mode, it is possible to eliminate noise, regenerated digital signals, and the original digital signal, can continue to transmit, so communication quality is not affected by distance, high quality, long-distance communication. The information in digital communication is included in the pulse, as long as the noise absolute value does not exceed a certain limit, the receiving end can determine the pulse of the pulse to ensure the reliability of the communication. Second, the digital signal is easy to encrypt, and the information transmission is relatively secure. Special forms of digital signals make information encryption make it easy. For example, the information bit rate is packetized in a certain length, and the encryption of the information is completed with these packets with these packets with a bit rate (called key). At the receiving end, use the same key to the received sequence mode, and restore the original information sequence. Digital mobile communication GSM system is encrypted by this method. Although the analog signal can also be encrypted, it is much more complicated. In addition, the reproducibility of digital communication devices is good, which is conducive to production and communication development and popularity.
Even if it is, the analog communication system has its own better side compared to the digital communication system, the design is simple, and the power consumption of the circuit is generally relatively low.
So the difference between digital communication and simulation communication is that the modulation method is different. Simulation communication, technology is mature, is to modulate the analog signal with the carrier to bring a certain carrier characteristic, and the uniqueness of the analog signal, the receiving end is passed through a low pass filter, and the initial analog signal is reduced. The digital signal is first sampled, and the sampling amplitude is encoded (0, 1 encoding), then modulation, phase shift keying, etc., the receiving end is reduced, the signal transmission rate is high. Relatively, digital communication is superior to analog communication.
Analog communication is analog signal, which is a continuous undulating waveform to transmit signals. Digital communication is the same as the computer, 1 follow 0 constitutes a signal. The simulated signal can be smooth, and the digital signal is even close to smoothing it is a stepped shape.
From a macro-view, the world communication method is still calling, in telephone communications, the fastest development of the transforcement exchange and mobile phone development. At present, the simulation communication system is still in use, but because people have increased rapidly to various communication services, digital communication is growing towards miniaturization, intelligence, and high-speed large capacity, and will eventually replace simulation.