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.

in principle

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

Code element transmission rate RB

Information transmission rate Rb

Band utilization

Bit error rate Pe

False belief rate Pb

is a carrier of information

Classification

is the valid content contained in the message

It is a message transmission carrier

Classification

Message is the physical manifestation of information, and information is the connotation of the message. Signal is the transmission carrier of the message.

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 message → Original electrical signal (baseband) Baseband signal → Modulated signal (bandpass)

advantage

shortcoming

Classified by communication business

Classified by reuse method

Classified by channel characteristics

Classified by transmission media

Classified by transmission method

Classified by working band

Divided by transmission direction and time

Divided according to digital symbol transmission timing