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Introduction to Communication Principles
Information and its measurement, main performance indicators of communication systems, basic concepts of communication, communication system models, digital communication system models, classification of communication systems and communication methods are introduced.
Edited at 2024-02-18 11:26:23- One Hundred Years of Solitude Character Relationship Chart
One Hundred Years of Solitude is the masterpiece of Gabriel Garcia Marquez. Reading this book begins with making sense of the characters' relationships, which are centered on the Buendía family and tells the story of the family's prosperity and decline, internal relationships and political struggles, self-mixing and rebirth over the course of a hundred years.
- One Hundred Years of Solitude Character Relationship Chart
One Hundred Years of Solitude is the masterpiece of Gabriel Garcia Marquez. Reading this book begins with making sense of the characters' relationships, which are centered on the Buendía family and tells the story of the family's prosperity and decline, internal relationships and political struggles, self-mixing and rebirth over the course of a hundred years.
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Project management is the process of applying specialized knowledge, skills, tools, and methods to project activities so that the project can achieve or exceed the set needs and expectations within the constraints of limited resources. This diagram provides a comprehensive overview of the 8 components of the project management process and can be used as a generic template for direct application.
Introduction to Communication Principles
- One Hundred Years of Solitude Character Relationship Chart
One Hundred Years of Solitude is the masterpiece of Gabriel Garcia Marquez. Reading this book begins with making sense of the characters' relationships, which are centered on the Buendía family and tells the story of the family's prosperity and decline, internal relationships and political struggles, self-mixing and rebirth over the course of a hundred years.
- One Hundred Years of Solitude Character Relationship Chart
One Hundred Years of Solitude is the masterpiece of Gabriel Garcia Marquez. Reading this book begins with making sense of the characters' relationships, which are centered on the Buendía family and tells the story of the family's prosperity and decline, internal relationships and political struggles, self-mixing and rebirth over the course of a hundred years.
- Project Management Process Template
Project management is the process of applying specialized knowledge, skills, tools, and methods to project activities so that the project can achieve or exceed the set needs and expectations within the constraints of limited resources. This diagram provides a comprehensive overview of the 8 components of the project management process and can be used as a generic template for direct application.
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- Outline
introduction
Information and its measurement
information
Information is the content of the message
The purpose of communication is to transmit the information contained in the message
It is the uncertain content of the message that constitutes information
Information content is a quantitative description of this uncertainty.
measure
in principle
The measurement method is independent of the type of message
Regardless of the importance of the message
The amount of information I can be measured by probability P: I = f [P(x)]
Information content of discrete message x
The average information content of discrete sources of statistically independent M symbols is
A message consisting of m symbols has a total information amount of: Itotal=m×H
Main performance indicators of communication systems
effectiveness
Code element transmission rate RB
The number of transmitted symbols per unit time
Unit: Baud
RB=1/TB
Information transmission rate Rb
bits transferred per second
Unit: bit/second (b/s)
Rb=RB·H（Rb=RB·log2M）
Band utilization
Transmission rate per unit bandwidth
reliability
Bit error rate Pe
False belief rate Pb
Basic concepts of communication
information
is a carrier of information
Classification
Continuous messages: refers to messages whose status changes continuously or is uncountable.
Discrete message: refers to a message that has a countable, finite number of states.
information
is the valid content contained in the message
Signal
It is a message transmission carrier
Classification
Analog signal: The value of the signal parameter of the payload message is continuous
Digital signal: The signal parameters of the payload message have only a limited number of values.
The relationship between the three
Message is the physical manifestation of information, and information is the connotation of the message. Signal is the transmission carrier of the message.
Communication system model
General model
1. Information source: The function of the information source (referred to as the information source) is to convert various messages into original electrical signals. According to the type of message, different sources can be divided into analog sources and digital sources. Analog sources output continuous analog signals, such as microphones (sound → audio signal), cameras (image-view signals); digital sources output discrete digital signals, such as telex machines (keyboard character-digit signals), computers, etc. Various digital terminals. Moreover, the signal sent by the analog source can also be sent out as a digital signal after digitization. 2. Transmitting equipment: The function of the transmitting equipment is to generate signals suitable for transmission in the channel, so that the characteristics of the transmitted signal match the characteristics of the channel, and are resistant to Channel interference capability and sufficient power to meet the needs of long-distance transmission. Therefore, the sending equipment covers a lot of content, which may include transformation, amplification, filtering, coding, modulation and other processes. For multiplex transmission systems, multiplexers are also included in the sending equipment. 3. Channel: A channel is a physical medium used to transmit signals from the sending device to the receiving end. In wireless channels, the channel can be free space; in wired channels, it can be open wires, cables, and optical fibers. Both wired and wireless channels have multiple physical media. The channel not only provides a path for the signal, but also produces various interference and noise to the signal. The inherent characteristics of the channel and the interference and noise introduced are directly related to the quality of communication. 4. Receiving equipment: The function of the receiving equipment is to amplify and inversely transform the signal (such as decoding, demodulation, etc.). Its purpose is to correctly recover the original electrical signal from the damaged received signal. For multiplexed signals, the receiving equipment also includes the function of demultiplexing and achieving correct demultiplexing. In addition, it must minimize the impact of noise and interference during the transmission process. 5. Information destination: Information destination is the destination for transmitting messages. Its function is opposite to that of the information source, that is, it restores the original electrical signal into the corresponding message such as a speaker, etc.
Analog communication system model
Analog message → Original electrical signal (baseband) Baseband signal → Modulated signal (bandpass)
Digital communication system model
1. Source coding and decoding: Source coding has two basic functions: one is to improve the effectiveness of information transmission, that is, to reduce the number of symbols through some compression coding technology to reduce the symbol rate. The second is to complete analog/digital (A/D) conversion, that is, when the information source gives an analog signal, the source encoder converts it into a digital signal to achieve digital transmission of the analog signal. Source decoding is the reverse process of source encoding. 2. Channel coding and decoding: The function of channel coding (Channel Coding) is to perform error control. Digital signals will be affected by noise and other errors during transmission. In order to reduce errors, the channel encoder adds protection components (supervision symbols) to the transmitted information symbols according to certain rules to form the so-called "anti-interference coding". The channel decoder at the receiving end decodes according to the corresponding inverse rules to discover or correct errors and improve the reliability of the communication system. 3. Encryption and decryption: When confidential communication is required, in order to ensure the security of the transmitted information, the transmitted digital sequence is artificially scrambled, that is, a password is added. This process is called encryption. The receiving end uses the reverse process of the sending end to decrypt the received digital sequence and restore the original information. 4. Digital modulation and demodulation: Digital modulation moves the spectrum of the digital baseband signal to a high frequency to form a bandpass signal suitable for transmission in the channel. The basic digital modulation methods include amplitude keying (ASK), frequency shift keying (FSK), absolute phase shift keying (PSK), and relative (differential) phase shift keying (DPSK). At the receiving end, coherent demodulation or non-coherent demodulation can be used to restore the digital baseband signal. Modulation: Putting information on the carrier Demodulation: Unloading information from the modulated signal 5. Synchronization: Synchronization (Synchronization) is to keep the signals at the sending and receiving ends consistent in time, and to ensure that the digital communication system is orderly, accurate and reliable Prerequisites for work. According to the different functions of synchronization, it is divided into carrier synchronization, bit synchronization, group (frame) synchronization and network synchronization.
Features
advantage
Strong anti-interference ability and no noise accumulation
Controllable transmission errors
It is convenient to use modern digital signal processing technology to process, transform and store digital information.
Easy to integrate, miniaturizing and reducing the weight of communication equipment
Easy to encrypt and maintain confidentiality
shortcoming
May require larger transmission bandwidth
High requirements for synchronization
Communication system classification and communication methods
Classification
Classified by communication business
Telephone, data, image communication, etc.
Classified by reuse method
time division multiplexing
frequency division multiplexing
code division multiplexing
Classified by channel characteristics
Analog communication
Digital communications
Classified by transmission media
wired communication
Wireless communication
Classified by transmission method
baseband transmission
bandpass transmission
Classified by working band
long wave
medium wave
shortwave
microwave
infrared
Laser communications, etc.
way of communication
Divided by transmission direction and time
simplex
Messages can only be transmitted in one direction
half duplex
It refers to a working method in which both communicating parties can send and receive messages, but cannot send and receive messages at the same time.
duplex
It refers to a working method in which both communicating parties can send and receive messages at the same time.
Divided according to digital symbol transmission timing
Parallel input
It is to transmit a sequence of digital symbols representing information in groups on two or more parallel channels simultaneously.
advantage
Save transfer time, fast
shortcoming
N communication lines are required and the cost is high
application
Generally only used for short-range communication between devices
serial input
It is to transmit a sequence of digital symbols on a channel in a serial manner one symbol after another.
advantage
Only one communication channel is required, and the cost of laying the required lines is low
shortcoming
The speed is slow and additional synchronization measures are needed to solve the synchronization problem of code groups or characters between the receiving and transmitting parties.
application
Generally used for long-distance digital transmission