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Channels of communicationdata transmissionIn computer network, the channel is divided into physical channel and logical channel.Physical channel refers to the physical channel used to transmit data signals, which is composed of transmission medium and relevant communication equipment;Logical channel refers to the logical path realized by both sending and receiving data signals through intermediate nodes on the basis of physical channels, which is the logical path formed by transmitting data signals.
Chinese name
communication channel
Foreign name
Channels of communication[1]
Definition
Digital and analog channels according to transmission data type
Logical channels can be connected or unconnected.Physical channels can also be divided into wired channels and wireless channels according to different transmission media, and can also be divided into digital channels and analog channels according to different transmission data types.
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The communication channel can be composed of one of the following transmission equipment or some combination of them:
1. Telephone line;
2. Telegraph line;
3. Satellite;
4. Laser;
5. Coaxial cable;
6. Microwave;
7. Optical fiber.
Data is stored and transmitted by bit (0, 1 signal). Channel speed refers to the number of bits that can be transmitted per second, also known as baud rate.Bit/s and baud rate are not identical, but they are common in actual use.According to the baud rate, channels can generally be divided into three categories: infrasound level, sound level and broadband level.
1. Infrasound level.The infrasound level of the line is one level lower than that of the telephone line.Usually, due to the limitation of hardware technology, this line can only be used when only 7 characters are output per second.
2. Sound level.This is a conventional telephone line with a rate between 600 baud (bits per second) and 9600 baud.A conventional telephone line can be "tuned" to transmit data at a rate of up to 9600 baud, and is quite accurate.Of course, with the increase of this capability, user costs will inevitably increase accordingly.If it depends on the speed of the sound level line, a line with a speed of 1200 baud can transmit about 120 characters per second.Sound level circuit is mainly used for high-speed link between computer and group controller, but it can also be used for low-speed, computer to computer communication.
3. Broadband level.The broadband channel has a capacity of more than 1 megabaud and is mainly used for computer to computer communication.
The channels in GSM communication can be divided into physical channels and logical channels.A physical channel is a time slot, which is usually defined as a time slot (TS) at a fixed position on a given TDMA frame.Logical channels are defined according to different types of messages transmitted between BTS (base station) and MS (terminal).These logical channels are mapped to different physical channels through BTS.
Technical characteristics
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Overview: Compared with other communication channels, mobile communication channels are the most complex.Multipath fading and complex and harsh radio environment are the most significant characteristics that distinguish mobile communication channels from other channels, which are determined by the way of wireless communication in motion itself.In a typical urban environment, the radio signal received by the mobile station on a fast moving vehicle can significantly fade for dozens of times within one second, and the fading depth can reach 20-30 dB.This fading phenomenon will seriously reduce the quality of the received signal and affect the reliability of communication.In order to effectively overcome the adverse effects of fading, variousAnti fading technology, including:diversity reception , equalization technology and error correction coding technology.
