Transmission mode of analog transmission, digital transmission and analog transmission

Classification of analog signals according to the signals transmitted in the channel: where a certain parameter of the signal (such as the amplitude, frequency, and phase of the continuous wave, the amplitude, width, and position of the pulse wave) can take an infinite number of values, and directly corresponds to the message, the analog signal is sometimes called a continuous signal.

1.Principles of Digital Communication - An Introduction

Digital communication is a communication method that uses digital signals as carriers to transmit messages, or uses digital signals to digitally modulate the carrier and then transmit them. It can transmit digital signals such as telegrams and digital data, as well as analog signals such as voice and images that have been digitized. The early history of digital communication is linked to the development of the telegraph.

2.Principles of digital communication - structural composition.

The communication system is generally composed of several parts: information source, transmitting equipment, channel, receiving equipment, receiver and noise source. The functions of each section are as follows:

Source Message: A person or machine that generates information that sends out and receives information;

Source encoding and decoding: digitize the analog signal sent by the source or transform the digital signal output from the source to improve the effectiveness, a d conversion, compression and coding;

Channel encoding and decoding: improve the reliability of digital communication, also known as anti-interference coding, such as error control coding;

Modulation: Move the signal spectrum to a higher frequency band to increase the transmission rate of the signal on the channel, achieve the purpose of signal multiplexing, and improve the anti-interference performance.

Synchronous rent: The sender and receiver should have a unified time standard, so that the "pace" or "beat is consistent", which is the premise of digital communication;

Channel: The path of the signal, that is, the medium used to transmit the signal, can be divided into narrow channel and broad channel in the digital communication system model.

Noisy noise: additional harmful signals crammed between transmission and reception, also known as channel noise, such as undulating noise, impulse interference, thermal noise, etc.;

3.Principles of digital communication – advantages:

With the rapid development and wide application of microelectronics technology and computer technology, digital communication will gradually replace analog communication and dominate in the future communication mode. Outstanding advantages compared to analog communication systems:

1) The anti-interference ability of digital transmission is strong, especially in the frame relay, the digital signal can be regenerated and the accumulation of noise can be eliminated;

2) High communication reliability, controllable transmission error, can effectively improve transmission quality;

3) It is convenient to use modern digital signal processing technology to process digital information;

4) Digital information is easy to be encrypted with high confidentiality;

5) Digital communication can comprehensively transmit various messages, so that the function of the communication system is enhanced, and it is convenient to form an ISDN network.

4.Principles of Digital Communication - Applications.

Application of digital communication technology:

1) Used: trunking communication system, cellular mobile**, CT2 cordless communication;

2) Under development: satellite broadband access system, broadband CDMA cellular system, wireless LAN and other systems.

The transmission medium can support the propagation of acoustic, electromagnetic and light wave signals. These media are often able to confine these signals to metal wires or fiber optic cables inside them. Radio transmission is provided via linear microwave and satellite communications.

The type of medium, its shielding, and even the number of stranded wires in the copper wire pair determine the possible data transfer rate on this cable.

Transmission lines can be "balanced" or "unbalanced". A balanced cable is usually a twisted pair or stranded cable that contains two conductors. An unbalanced cable is usually a coaxial cable.

In a balanced line, both wires are connected to the generator (sender) and receiver, and they both have the same current, but the current is in the opposite direction. In an unbalanced cable, current flows through a conductor and returns through the earth.

Analog transmission, in which information is transmitted in the form of an analog signal in a transmission medium.

Analog signals are a way of conducting energy, such as sound waves that travel by vibrating air. The sound waves of a studio line and volume changes can be mapped on paper.

A machine is a conversion device that converts analog sound waves into corresponding electrical signals. At the receiving end of the ** or audio system, the amplitude (volume) and pitch of the speaker's vibrating signal are received. The tone reflects the vibrational frequency of the torsion wave.

Frequency is usually measured in cycles per second (cps) or hertz (Hz). One hertz is a kilohertz) is 1,000 Hz, 1 MHz (megahertz) is 1, 000 kHz, and 1 GHz is 1,000 MHz. The range that humans can hear is between 20Hz and 20,000Hz, and this is also the operating range of Chainbend Hi-Fi.

Analog waveforms can be very simple or very complex. A sound wave produced by a single piano timpani consists of only a single frequency. A complex waveform—such as the sound of a human voice or the sound of a pipe organ—contains many combinations of different frequencies.

**The system uses analog switched lines for audio communication. In general, data communication over analog lines has a number of problems that limit its usefulness. Modulation is required to convert a digital signal to an analog signal, and the transmission rate is limited due to the narrow frequency band of the audio line.

Moreover, analog signals must be amplified in the first order over long distances, so the distortion in these signals will also be amplified. Some applications that need to transmit large amounts of information, such as graphics processing and speech processing, require more bandwidth than analog services can handle.