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Electromagnetic wave band division and typical application fields

Time:2018-04-23

Electromagnetic wave band division and typical application fields

  Today, one of the most important constraints affecting the development of electronic communication systems is non-renewable spectrum resources. Almost all new theories or new technologies have emerged, in essence, to transmit more information and accommodate morecommunication users under spectrum restrictions.

   Most of the spectrum resources are managed by the relevant departments of the governments of the countries and regions where they are located (China Radio Administration Bureau). These management departments of various countries have also formed the international telecommunications union, referred to as ITU. He is mainly responsible for the coordinated distribution and management of global spectrum resources. The frequency range of electromagnetic spectrum currently known is approximately 10 0 to 10 22 Hz. The most common frequency band division in the world today is established by theInstitute of Electrical and Electronics Engineers (IEEE).

       The division of frequency bands cannot give precise boundaries, they are forked. For electronic communication systems, a practical limit is whether the wavelength of the transmitted signal is equivalent to the actual size of the electronic system. The radio frequency band now usually refers to the VHF to X band, which is also the current working frequency band that most lumped components can reach.


Electromagnetic wave propagation characteristics

   In wireless communication, a very important part is the propagation part of radio waves, from the transmitting antenna to the receiving antenna. The propagation of electromagnetic waves in real media space can be considered as the free propagation plus the influence of the media.


Wireless channel characteristics and capacity

   Characteristics: After the signal is transmitted through the channel, it will suffer from different attenuation in Chengdu. Different channels have different degrees of signal attenuation. In wireless channels, the degree of attenuation of electrical signals is closely related to factors such as propagation path, propagation distance, atmospheric structure, ionosphere structure, atmospheric attenuation, and signal frequency.


Wireless communication modem

   The role of modulation in wireless communications is crucial. According to different modulation parameters of the carrier, the modulation can be divided into three basic methods: amplitude modulation (referred to as amplitude modulation), he uses the baseband signal to control the amplitude of the carrier, and frequency modulation (abbreviated as frequency modulation), he uses the baseband signal to control the frequency of the carrier; phaseModulation (referred to as phase modulation) He uses the baseband signal to control the phase of the carrier. These three methods are represented by AM, FM and PM respectively. When the modulation signal is a digital signal, the modulation is usually keyed. The three basic keying methods are ASK, FSK, and PSK. Demodulation is the inverse of modulation.


Typical wireless communication system

       Mobile Communication: The socalled mobile communication refers to the communication between the two parties at least one place in motion. Mobile communications are classified according to the environment in which they are used: land mobile communications, maritime mobile communications, aerospacemobile communications, and communications under special environments (such as mines, tunnels, submarines, etc.). According to the object categories of services: public telephone booths, dedicated mobile communications (communication systems established to ensure communication in a particular department). According to the network structure of mobile communications, there are: public networks and private networks.

   The development of mobile communications has experienced the first generation of analog mobile communication systems (1G), second-generation digital mobile communication systems (2G), third-generation mobile communication systems (3G), and fourth-generation communication systems (4G).

Satellite communication: In simple terms, satellite communication is the communication between satellites used as relays between the radio stations in the earth including the ground and the lower atmosphere. It consists of two parts: the satellite and the earth station.

   Wireless LAN: Wireless LAN refers to the application of wireless communication technology to interconnect computer devices and form a network system that can communicate with each other and share line-of-sight resources. Wireless LANs are essentially an extension of fixed LANs and are network links that do not have cable restrictions. For the user, the wireless LAN is completely transparent. The feature is that it no longer uses a communication cable to link the computer to the network, but links it wirelessly, making the construction of the network and the mobility of the terminal more flexible.


Composition of wireless communication system

   The purpose of communication is to deliver messages. The process from the sender to the receiver is called communication, and the system that implements this information transmission process is called the communication system, mainly by the source, the transmitter, the space channel media, the receiver, and the It consists of several parts.


Radio Transceiver RF Front-End Functions and Features

   When the channel medium of the electronic communication system is atmospheric space, it is called "wireless communication". At this moment, the communication system is mainly composed of a transmitter and a receiver.

   There are two types of transforms in wireless communication transceivers. At the transmitting end, the first transform is the input transformer, which transforms the information that needs to be transmitted into an electrical signal, the baseband signal; and the second transformer is the signal that the transmitter transforms the baseband into a band that is suitable for efficient transmission in the channel. Form - modulated signal, this process is called modulation. At the receiving end, the first transform is the modulated wave selected by the receiver from the channel and converted to a baseband signal. This conversion process is called demodulation; the second transform is the baseband signal that the output converter will demodulate. Transform into corresponding information.

   The most difficult part of the transmission system hardware circuit system lies in the frequency conversion and RF efficiency. The most difficult part for receiving systems is the RF front-end.


Composition of wireless communication system

   The purpose of communication is to deliver messages. The process from the sender to the receiver is called communication, and the system that implements this information transmission process is called the communication system, mainly by the source, the transmitter, the space channel media, the receiver, and the It consists of several parts.


Radio Transceiver RF Front-End Functions and Features

   When the channel medium of the electronic communication system is atmospheric space, it is called "wireless communication". At this moment, the communication system is mainly composed of a transmitter and a receiver.

   There are two types of transforms in wireless communication transceivers. At the transmitting end, the first transform is the input transformer, which transforms the information that needs to be transmitted into an electrical signal, the baseband signal; and the second transformer is the signal that the transmitter transforms the baseband into a band that is suitable for efficient transmission in the channel. Form - modulated signal, this process is called modulation. At the receiving end, the first transform is the modulated wave selected by the receiver from the channel and converted to a baseband signal. This conversion process is called demodulation; the second transform is the baseband signal that the output converter will demodulate. Transform into corresponding information.

   The most difficult part of the transmission system hardware circuit system lies in the frequency conversion and RF efficiency. The most difficultpart for receiving systems is the RF front-end.


Wireless communications and RF circuit technology trends

The development trends of wireless communication and RF circuit technology are as follows:

1 High Frequency: With the development of wireless communications, the amount of information that needs to be transmitted is increasing. The increase in the amount of information means that communication requires more bandwidth, and the absolute bandwidth of the line of sight at very low frequencies has become very large. Therefore, a development trend of wireless communication and RF circuit technology is that the operating frequency is getting higher and higher. Frequency, VHF, UHF, microwave, millimeter wave reach the purpose of effective communication bandwidth.

2 High speed: In order to meet people's requirements for communication quality and communication capacity, high-speed data transmission has become one of the trends in wireless communication. This also requires that the RF circuit technology can adapt to high-rate data transmission to meet real-time transmission of sound and data. The need for multimedia high-capacity information such as images.

3 Low power consumption: It is a development direction of wireless communication that it is convenient to carry, long work time and function are many, this must require the characteristic that the radio frequency circuit has low power consumption.

4 Digitization/Software: Software radios will be the main implementation of wireless communications. Therefore, radio frequency and digital hardware circuits are required to implement interconnection and interoperability among wireless communications systems at different frequencies, and use multiple devices.

5 Low price and humanity: Low price is one of the powerful competition means. With the development of component technology and the reduction of manufacturing cost, wireless communication equipment and RF circuits can further reduce costs. In addition, humanization and intelligence will be one of the trends in wireless communications and RF circuit technology.







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