Wireless communication (data) transmission method and technical principle:
Wireless communication is a communication method that exchanges information using electromagnetic wave signals in a free space. Wireless communication technology has many advantages and low cost. Wireless communication technology does not need to establish physical lines, and does not require a lot of manpower to lay cables. Moreover, wireless communication technology is not restricted by industrial environment, and it has strong ability to resist environmental changes. It is also relatively easy. Compared with the traditional wired communication setup and maintenance, the maintenance of the wireless network can be completed by remote diagnosis, which is more convenient; the scalability is strong, when the network needs to be expanded, the wireless communication does not need to be expanded and wired; the flexibility is strong, wireless The network is not limited by the environmental terrain, and when the usage environment changes, the wireless network can adapt to the requirements of the new environment with only a few adjustments.
Common wireless communication (data) transmission methods and technologies are divided into two types: “near-range wireless communication technology” and “long-range wireless transmission technology.”
- Short-range wireless communication technology
The short (near) distance wireless communication technology refers to the communication between the two parties through radio waves, and the transmission distance is in a relatively close range, and its application range is very wide. In recent years, short-range wireless communication standards that are widely used and have good development prospects include Zig-Bee, Bluetooth, Wi-Fi, Ultra-Wideband (UWB), and Near Field Communication (NFC).
(1) Zig-Bee: Zig-Bee is a short-range, low-power wireless communication technology based on the IEEE802.15.4 standard. Zig-Bee is derived from the communication method of the bee colony. Because Bee is relying on flying and ‘Zig’ to shake the wings and companions to determine the direction, position and distance of the food source, etc. Group of communication networks. It is characterized by a close distance, and its usual transmission distance is 10-100m. With low power consumption, in the low-power standby mode, two No. 5 dry batteries can support one terminal for 6-24 months or even longer; its cost Zig-Bee is free of protocol fees, and the chip price is cheap; low rate, Zig-Bee often works at a lower rate of 20-250 kbps; short delay, Zig-Bee’s response speed is faster. It is mainly used in home and building control, industrial field automation control, agricultural information collection and control, public place information detection and control, intelligent labeling, etc., and can be embedded in various equipment.
(2) Bluetooth: It can realize point-to-point or point-to-multipoint wireless data and sound transmission within a radius of 10 meters. Its data transmission bandwidth can reach 1Mbps. The communication medium has a frequency between 2.402GHz and 2.480GHz. Electromagnetic waves. Bluetooth technology can be widely used in various data and voice devices in the local area network, such as PC, dial-up network, notebook computers, printers, fax machines, digital cameras, mobile phones and high-quality headphones, etc. Communication.
Bluetooth technology is widely used in wireless office environments, automotive industry, information appliances, medical equipment, and school education and factory automation. The main problems of Bluetooth are the high chip size and price; the anti-interference ability is weak.
(3) Wireless Broadband (Wi-Fi): It is a wireless LAN access technology based on the 802.11 protocol. The outstanding advantage of (Wi-Fi) technology is that it has a wide range of LAN coverage, and its coverage radius can reach about 100 meters. Compared with Bluetooth technology, (Wi-Fi) has a wide coverage; the transmission speed is very fast, Transmission speed can reach 11mbps (802.11b) or 54mbps (802.11.a), suitable for high-speed data transmission services; no wiring, can be free from the constraints of wiring conditions, very suitable for mobile office users. In some densely populated places, such as train stations, bus stations, shopping malls, airports, libraries, campuses, etc., ‘hot spots’ can be set up, and the Internet can be connected to the above places through high-speed lines. Users only need to connect wireless devices to the Internet in this area, and they can access the Internet at high speed. Health and safety, WiFi-enabled products have a transmission power of less than 100 mW, and the actual transmit power is about 60-70 mW. WiFi products have less radiation than communication devices such as handheld walkie-talkies.
(4) Ultra-wideband (UWB): UWB is a carrier-free communication technology that uses non-sinusoidal narrow pulses of nanoseconds to picoseconds to transmit data. The transmission distance is usually within 10M, and the communication speed can be more than 1GHz. Up to several hundred megabits/s, UWB operates from 3.1 GHz to 10.6 GHz with a minimum operating bandwidth of 500 MHz.
Its main features are: high transmission rate; low transmission power, low power consumption; strong confidentiality; UWB communication uses time-modulation sequence, which can resist multipath fading; UWB requires few RF and microwave devices, which can reduce the system’s Complexity. Due to the high bandwidth occupied by the UWB system, the UWB system may interfere with other existing wireless communication systems. UWB is mainly used in high-resolution “small range” to penetrate walls and radars and image systems such as ground and other obstacles.
This device can be used to inspect defects in concrete and asphalt structures in buildings, bridges, roads, etc., as well as to locate fault locations in underground cables and other pipelines, as well as in disease diagnosis. In addition, it is useful in areas such as rescue, public security, fire and medical, and medical image processing.
(5) NFC: NFC is a new short-range wireless communication technology with an operating frequency of 13.56MHz, which is developed by 13.56MHz radio frequency identification (RFID) technology. It is compatible with the currently popular non-contact smart card ISO14443. The same frequency is used, which provides a convenient means of communication for all consumer electronics. NFC adopts amplitude shift keying (ASK) modulation, and its data transmission rate is generally 106kbit/s and 424kbit/s. The main advantages of NFC are: close distance, high bandwidth, low energy consumption, and compatibility with non-contact smart card technology, which has broad application value in the fields of access control, public transportation and mobile payment.
The application scenarios of NFC can be basically divided into the following five categories:
A contact-pass, mainly used in conference admissions, traffic checkpoints, access control and event tickets;
B contact-confirmation/payment, mainly used in mobile wallet, mobile and bus payment;
C contact-connection, this application can realize two point-to-point transmission of data by NFC-enabled devices;
DContact-Browse, users can understand and use the functions and services provided by the system through NFC mobile phones;
E-download-contact, through NFC-enabled terminal devices, use GPRS/CDMA networks to receive or download relevant information for access control or payment functions.
- Long-distance wireless transmission technology
Long-distance wireless transmission technology: At present, wireless communication technologies widely used in remote areas mainly include GPRS/CDMA, digital radio, spread spectrum microwave, wireless bridge and satellite communication, and short-wave communication technology. It is mainly used in areas that are more remote or unsuitable for laying lines, such as coal mines, seas, polluted areas or areas with harsh environments.
(1) GPRS/CDMA wireless communication technology: GPRS (General Wireless Packet Service) is a wireless packet switching technology based on GSM communication system developed and operated by China Mobile. It is a technology between the second generation and the third generation. , commonly referred to as 2.5G, is a wireless transmission method developed using the concept of packet exchange. Packet exchange encapsulates the data into a number of independent packages, and then transmits the packets one by one. The form is somewhat similar to sending a package. The advantage is that the bandwidth is occupied when the data needs to be transmitted, and it is validated by the amount of data. Improve the utilization of the network. The GPRS network supports both circuit type data and packet switched data, so that the GPRS network can be easily connected to the Internet. Compared with the original GSM network circuit switched data transmission mode, the GRRS packet switching technology has real-time online “quantity by volume”. High-speed transmission and other advantages.
CDMA (in English abbreviation for Code Division Multiple Access) is a new wireless communication system based on code division technology and multiple access technology operated by China Telecom. The principle is based on spread spectrum technology.
(2) Digital radio communication: Digital radio is the abbreviation of digital wireless data transmission station. It is a wireless data transmission station that uses digital signal processing, digital modulation and demodulation, forward error correction, and equalization soft decision. The working frequency of digital radio station mostly uses 220–240MHz or 400–470MHz frequency band, with digital compatibility, good real-time data transmission, dedicated data transmission channel, one investment, no running fee, suitable for harsh environment and stability. Good and so on. The effective coverage radius of digital radio stations is about tens of kilometers, covering a city or a certain area. Digital radio usually provides a standard RS-232 data interface, which can be directly connected to computers, data collectors, RTUs, PLCs, data terminals, GPS receivers, digital cameras, etc. It has been widely used in various industries, and has been applied in various fields such as aerospace, railway, electric power, petroleum, meteorology, earthquake, etc., and has made great progress and development in SCADA fields such as remote control, telemetry, shaking letter, and remote sensing.
(3) Spread spectrum microwave communication: Spread spectrum communication, that is, spread spectrum communication technology refers to a communication technology in which the bandwidth of the signal used for transmitting information is much larger than the bandwidth of the information itself. It was first used for military communications. The basic principle of its transmission is to modulate the transmitted information with a pseudo-random code sequence (spreading code). The rate of the pseudo-random code is much larger than the rate at which the information is transmitted. At this time, the bandwidth occupied by the transmitted signal is much larger than that required by the information itself. The bandwidth achieves spectrum spreading, while the radio power spectral density transmitted to the space is also greatly reduced. At the receiving end, the same spreading code is used for correlation demodulation and information data recovery! Its main features are: strong anti-noise ability; strong anti-interference ability; strong anti-fading capability; strong anti-multipath interference capability; easy multimedia Communication networking; has good security communication capabilities; does not interfere with other systems of the same type, and has the characteristics of long transmission distance and wide coverage, especially suitable for field networking applications.
(4) Wireless Bridge: The wireless bridge is a combination of wireless radio frequency technology and traditional wired bridge technology. Wireless bridges are designed for point-to-point inter-network interconnection using wireless (microwave) for long-distance data transmission. It is a kind of storage and forwarding device that implements LAN interconnection at the link layer. It can be used for fixed long-distance (up to 50Km) and high-speed (up to 100 megabits) wireless networking between digital devices and other fixed digital devices. Both spread spectrum microwave and wireless bridge technology can be used to transmit large data volume signal transmission services such as video surveillance with relatively high bandwidth requirements.
(5) Satellite communication: Satellite communication refers to a technology that uses artificial earth satellites as relay stations to forward radio signals, thereby realizing communication between multiple ground stations. It is the inheritance and development of terrestrial microwave communication. The satellite communication system usually consists of two parts, the satellite end and the ground end. The satellite is in the air and is mainly used to amplify and forward the signal sent by the ground station to other ground stations. Ground stations are mainly used for satellite control, tracking, and access to terrestrial communication systems to access satellite communication systems.
Satellites can be divided into synchronous satellites and non-synchronous satellites. The direction and period of synchronization satellites in the air are the same as the direction and period of rotation of the Earth. From any position on the ground, the satellites are stationary; the operation of asynchronous satellites The period is greater or less than the earth’s operating cycle, and its orbital height “tilt” shape can be adjusted as needed.
The characteristics of satellite communication are: wide coverage, working frequency bandwidth, good communication quality, no geographical restrictions, and cost and communication distance. It is mainly used in international communications, domestic communications, military communications, mobile communications and broadcast television. The main disadvantage of satellite communications is that communications have certain delays. For example, when satellite phones are used, they cannot immediately hear each other’s calls. The main reason is satellites. The transmission distance of communication is long, and there is a certain delay in the transmission of radio waves in the air.
(6) Short-wave communication: According to the division of the International Radio Consultative Committee, short-wave refers to electromagnetic waves with a wavelength of 100m – 10m and a frequency of 3MHZ-30MHZ. Short-wave communication refers to radio communication using short-wave, also known as high-frequency (HF) communication. Short-wave communication can be divided into ground wave propagation and sky wave propagation. The attenuation of ground wave propagation increases with increasing operating frequency. Under the same ground conditions, the higher the frequency, the greater the attenuation. The ground wave is only suitable for short-range communication, and its working frequency is generally selected below 5MHZ. The ground wave propagation is less affected by the weather and is relatively stable. The channel parameters do not change with time, so the channel can be regarded as a constant reference channel. Sky wave propagation is a method in which radio waves are reflected by the ionosphere for long-distance communication. After obliquely projected electromagnetic waves are reflected by the ionosphere, they can be transmitted to the ground thousands of kilometers away. The propagation loss of the sky wave is much smaller than that of the ground wave. After multiple reflections between the ground and the ionosphere, it can reach a very far place. Therefore, the sky wave can be used for global communication. Sky wave propagation is extremely unstable due to the severe effects of ionospheric changes and multipath propagation, and its channel parameters change abruptly with time, so it is called a variable-parameter channel. The characteristics of short-wave communication are: low construction and maintenance costs, short cycle, simple equipment, easy circuit scheduling, strong anti-destructive capability, narrow frequency band, small communication capacity, and poor signal transmission stability of sky-wave channel.
Comparison between various mainstream wireless communication technologies
Currently popular wireless communication technologies are: RFID, GPRS, Bluetooth, Wi-Fi, IrDA, UWB, Zig-Bee and NFC.
RFID is a simple wireless system with only two basic components for controlling, detecting, and tracking objects. The system consists of an interrogator and a number of transponders.
Transponder: consists of an antenna, a coupling element and a chip. Generally, the tag is used as a transponder. Each tag has a unique electronic code attached to the object to identify the target object.
Reader: A device consisting of an antenna, a coupling element, a chip, and reading (and sometimes writing) tag information. It can be designed as a handheld rfid.
Application software system: It is application layer software, which mainly processes the collected data and uses it for people.
Through the connection between the monitoring center and the Internet, it can support some more complex applications. In addition, there are more communication methods supported, so that users can monitor the actual application points in multiple communication modes anytime and anywhere. The solution also allows the monitoring center to communicate with multiple GPRS modules simultaneously to monitor multiple work sites.
The Bluetooth system consists of a wireless unit, a link controller, a link manager, and a support unit that provides functions to the host interface.
The Bluetooth wireless unit is a microwave frequency hopping spread spectrum communication system in which data and voice information packets are transmitted and received in a designated time slot with a specified frequency hopping frequency. The hopping sequence is determined by the address of the master device, and the channel connection is established by paging and inquiry. The link control (baseband control) includes the hardware portion of the baseband digital signal processing and performs the baseband protocol and other underlying link procedures. Link Manager (LM) software implements link establishment, verification, link configuration, and protocol. The link manager can discover other link managers and establish communication links through the connection management protocol LMP. The link manager implements the above functions through the services provided by the link controller.
The design of the Wi-Fi solution is relatively simple compared to other solutions. It only needs to control the WIFI module through the MCU, communicate with the motherboard through the CAN bus, and then transmit the message to the Internet through the WIFI module. By connecting to the server, the server processes the data.
Infrared communication mainly consists of three parts:
(1) Transmitter part: At present, information sources of infrared wireless digital communication systems include voice, data, images and the like.
(2) Channel parts: Their functions are: shaping, filtering, field of view conversion, frequency band division, and so on.
(3) Terminal part: The terminal part of the infrared wireless digital communication system includes a part of light receiving part, sampling, filtering, decision, quantization, equalization and decoding.
UWB (UltraWideband) is a carrierless communication technology that uses a non-sinusoidal narrow pulse of nanoseconds to picoseconds to transmit data. UWB can achieve data transmission rates of hundreds of Mbit/s to several Gbit/s in a range of about 10 meters by transmitting extremely low power signals over a wide spectrum.
Technology is a two-way wireless communication technology with close proximity, low complexity, low power consumption, low speed and low cost. It is mainly used for data transmission between various electronic devices with short distance, low power consumption and low transmission rate, and typical applications with periodic data, intermittent data and low response time data transmission.
Like RFID, NFC information is also transmitted by electromagnetic induction coupling of the radio frequency portion of the spectrum, but there is still a big difference between the two. First, NFC is a wireless connection technology that provides easy, secure, and fast communication with a smaller transmission range than RFID. Second, NFC is compatible with existing contactless smart card technology and has become the official standard supported by more and more major vendors. Again, NFC is a close-range connection protocol that provides easy, secure, fast, and automatic communication between devices. Compared to other connections in the wireless world, NFC is a close-range, private communication method.