Simplex Communication refers to the working mode in which messages can only be transmitted in one direction.
In simplex communication, the communication channel is unidirectional, and the sender and receiver are fixed, that is, the sender can only send information and cannot receive information;The receiving end can only receive information and cannot send information.In this case, the data signal is transmitted from one end to the other, and the signal flow is unidirectional.
For example, broadcasting in life is a way of simplex communication.The broadcasting station is the sending end, and the audience is the receiving end.The broadcasting station sends information to the audience, and the audience receives and obtains information.The broadcasting station cannot obtain the information of the audience as the receiving end, and the audience cannot send signals to the broadcasting station as the sending end.
The "Push To Talk" (PTT) simplex communication between the two communication parties is a point-to-point communication.Simplex communication can be divided into the same frequency communication and the different frequency communication according to the similarities and differences of the receiving and transmitting frequencies[1]。
Half duplex communication
Announce
edit
Half duplex communication can realize two-way communication, but it cannot be carried out in two directions at the same time, and must be carried out alternately in turn.
In this working mode, the sending end can be transformed into the receiving end;Accordingly, the receiving end can also be transformed into the sending end.But at the same time, information can only be transmitted in one direction.Therefore, half duplex communication can also be understood as a simplex communication of switching direction.
For example, the walkie talkie is the most common half duplex communication mode in daily life. Both sides of the walkie talkie can communicate with each other, but at the same time, only one side can speak.
Full duplex communication
Announce
edit
Full duplex communication(Full duplex Communication) refers to the two-way signal transmission from A to B and from B to A on the line at any time of communication.Full duplex communication allows data to be transmitted in two directions at the same time, also known as two-way simultaneous communication, that is, both sides of the communication can send and receive data at the same time.In the full duplex mode, each end of the communication system is equipped with a transmitter and a receiver, so that data can be controlled to be transmitted in both directions at the same time.The full duplex mode does not require direction switching, so there is no time delay generated by switching operation, which is very beneficial to interactive applications (such as remote monitoring and control systems) that cannot have time delay.This method requires that both communication parties have transmitters and receivers, and two data lines are required to transmit data signals.(You may also need control lines, status lines, and ground wires).
In theory, full duplex transmission can improve the network efficiency, but it is still useful with other related equipment.For example, twisted pair network cables must be selected for full duplex transmission, and the hub (HUB) connected in the middle must also be capable of full duplex transmission;Finally, the adoptedNetwork operating systemIt must also support full duplex operations, so as to truly exert the power of full duplex transmission.
For example, the computer host connects the display terminal with a serial interface, and the display terminal is equipped with a keyboard.In this way, on the one hand, the characters entered on the keyboard are sent to the host memory;On the other hand, the information of host memory can be sent to the screen for display.Usually, after a character is typed into the keyboard, it will not be displayed first. After the computer host receives the character, it will send it back to the terminal immediately, and then the terminal will display the character again.In this way, the echo process of the previous character and the input process of the next character are carried out at the same time, that is, working in full duplex mode[2]。
Modern communication mode
Announce
edit
Postal
On the basis of physical transmission, although there are fewer and fewer people writing letters nowadays, they are simpler and more authentic, more simple and more sincere. Letters are the simplest and simplest way of information transmission, not to mention the information leakage caused by too fast transmission speed;Express delivery is the need for the development of human society. The main reason is that with the improvement of human material living standards, the service demand is also getting higher and higher, but its development is restricted by transportation. The transportation that is not convenient can not be fast.
Telephone
The telephone is divided into fixed line telephone, mobile telephone and network telephone. The advantages and disadvantages of its transmission mode are basically the same as that of the network mode. The difference with the network mode is that the telephone cannot directly transmit text and pictures, and the difference with the mail mode is that the physical object cannot be transmitted.
Fax
Fax is the fastest growing non voice telecommunication service in the past 20 years.The still image recorded on paper, such as text, chart and photo, is transformed into an electrical signal by scanning and photoelectric transformation, and then transmitted to the destination through various channels. At the receiving end, through a series of inverse transformation processes, the communication mode similar to the transmission of the original copy of the record is obtained, which is called fax.
The main technologies of fax include scanning technology, recording technology, synchronous in-phase technology and transmission technology.The communication process of fax includes scanning, photoelectric transformation, image signal transmission, recording transformation, receiving scanning and synchronous in-phase.
Fax is a PSTN based telecommunication signal that transfers fax signals through equipment.Due to the rapid development of science and technology, electronic network fax has gradually become a new generation of communication tools to replace fax machines.
Satellite telephone
Telephones that transmit information based on satellite communication systems areSatellite telephone。Satellite telephone is the product of modern mobile communication, and its main function is to fill the existing communication (wired communicationwireless communication ）The area that cannot be covered by the terminal provides more sound services for people's work.In modern communication, satellite communication cannot be replaced by other communication methods. All communication functions provided by existing common communication have been applied in satellite communication.
telegraph
Telegraph is the written information transmitted by electric signal.Communication is becoming faster and faster, and the role of the telegraph is not very important. Maybe one day the telegraph will disappear from our life.
Telegraph is a kind of communication service, which is the earliest method of using electricity for communication.It uses current (wired) or electromagnetic wave (wireless) as the carrier, and realizes the communication mode of long-distance transmission and exchange of information through coding and corresponding electrical processing technology.
Telegraph has greatly accelerated the circulation of information and is one of the important inventions of industrial society.Early telegrams could only communicate on land. Later, submarine cables were used to carry out transoceanic services.At the beginning of the twentieth century, radio was used to send and send telegrams, and telegraph services had basically reached most parts of the earth.Telegraph is mainly used to transmit text messages, and the use of telegraph technology to transmit pictures is called fax.
data communication
The information transmitted in the computer network is digital data. The communication between computers is the data communication mode, and the data communication is the combination of computers and communication lines.In data communication, according to the number of data bits transmitted each time, communication modes can be divided into parallel communication and serial communication.
Parallel communication is to transmit 8-bit binary data at the same time, and 8 transmission lines are required from the sending end to the receiving end.Parallel mode is mainly used for short distance communication. For example, data communication within a computer is usually carried out in parallel mode.The advantages of this method are fast transmission speed and simple processing.
Serial communication only transmits one binary data at a time, and only one transmission line is needed from the sending end to the receiving end.Although the transmission rate of serial mode is low, it is suitable for long-distance transmission. In the network (such as public telephone system), serial communication mode is widely used[3]。
Advantages and disadvantages
Announce
edit
There are several communication modes adopted by the power grid, including optical fiber communication, ordinary microwave communication,Power line carrier communication, wired audio cable communication, UHF radio communication, wireless spread spectrum communication.
1. The biggest characteristic of optical fiber communication is its large communication capacity and high speed. It can transmit hundreds or even thousands of telephones in one optical fiber, and can transmit real-time images. Moreover, it has good anti electromagnetic interference, high communication quality, and long use duration.But the cost is high, especially the long-distance erection construction is expensive and limited by the terrain.
2. Ordinary microwave communication is a wireless communication mode with large transmission capacity, high quality and flexible configuration. It is widely used in substations above 220kv in power systems. This communication mode has high requirements for the environment. In addition, the construction of an ordinary microwave communication network requires site survey and design, so the total construction cost is also high.
3. The power line carrier communication mode is relatively common. The biggest advantage is that there is no need to set up special communication lines, and the communication can be carried out wherever the power extends. The investment is not large, but its disadvantages are, first, poor reliability, and second, small communication capacity, which results in poor voice call quality and low data transmission rate,Moreover, the communication from substation to dispatching needs to be solved by setting up audio cable.
4. Wired audio cable communication is widely used. It is a good communication mode when the distance is relatively short, and its communication channel is an analog channel. Therefore, when carrying out data communication, it needs to add a modem, which has poor anti-interference performance and is vulnerable to lightning strikes. In long-distance communication, it needs a thicker wire diameter and higher cost.Generally, it is not used to form a large communication network but only used locally.
5. UHF radio station has long communication transmission distance, convenient use, low equipment price and easy maintenance.But to meetUnattended substationIts communication requirements are far from enough, and its anti-interference ability is poor.The communication is unstable, and the communication index is also very low. It is an analog channel, and the data transmission rate is less than 300it/s, which can only be used as an auxiliary means of communication.
6. The wireless spread spectrum communication is a spread spectrum communication technology and a digital communication technology.The transmission power of the spread spectrum signal is low and has little impact on the electromagnetic environment, while the transmission data rate is high. In addition, the threshold signal-to-noise ratio of the spread spectrum borrowing phone is low and can work normally under negative signal-to-noise ratio.Spread spectrum communication has good anti co frequency interference performance. For all foreign interference signals with the same carrier frequency entering the receiver, the receiver has the ability to suppress them, and it has good anti fading performance.In general, the fading is selective when radio signals are propagated, and the spread spectrum communication will expand the signal power to a very wide bandwidth, which will not have too much impact on the reception.
Therefore, there are various communication modes at present. When selecting communication modes, the advantages of various modes should be maximized to achieve the purpose of cost saving and communication[2]。
