A: In the process of using Bluetooth technology, people find that Bluetooth technology has many advantages, but it also has many defects. For industrial, home automation control and industrial telemetry and remote control fields, Bluetooth technology is too complicated, with high power consumption, short distance and small networking scale ... The demand for wireless data communication in industrial automation is increasingly strong. Moreover, for the industrial site, this wireless data transmission must have high reliability and can resist all kinds of electromagnetic interference in the industrial site. Therefore, after people's long-term efforts, ZigBee protocol was officially announced in mid-2003. In addition, ZigBee uses home RF Lite, which is the home network communication protocol it studied before.
2. What is 2.ZigBee?
A: First of all, ZigBee is synonymous with the IEEE802. 15.4 protocol. According to this protocol, this technology is a short-distance, low-complexity, low-power, low-data-rate and low-cost two-way wireless communication technology, which is mainly suitable for automatic control and remote control, and can be embedded in various devices to support geographic positioning. Because bees communicate with their companions in the way of flying and flapping their wings to "dance", that is, bees rely on this way to form a communication "network" in the group, so the inventor of ZigBee vividly describes this wireless information transmission technology with this behavior of bees.
3. What are the characteristics of 3.Zigbee technology?
A: The characteristics of ZigBee mainly include the following eight aspects:
(1) Low power consumption: In low power standby mode, two No.5 dry batteries can support 1 node to work for 6-24 months or even longer. This is the outstanding advantage of ZigBee. In contrast, Bluetooth can work for several weeks and WiFi can work for several hours.
(2) Low cost: By greatly simplifying the protocol, the cost is reduced (less than Bluetooth's110), and the requirements for communication controllers are also reduced. According to the prediction and analysis, based on the 8-bit microcontroller of 805 1, the full-function master node needs 32KB code, and the sub-function node only needs 4KB code, and the protocol patent of ZigBee is free.
(3) Low rate: ZigBee works at a communication rate of 250kbps to meet the application requirements of low-rate data transmission;
(4) Close range: the transmission range is generally between 10 ~ 100m, and it can be increased to 1-3km after increasing the RF transmission power, which refers to the distance between adjacent nodes. If through the routing and communication between relay nodes, the transmission distance will be further;
(5) Short delay: The response speed of ZigBee is relatively fast. Generally, it only takes 15ms to switch from sleep to work, and it only takes 30ms for nodes to connect to the network, which further saves electricity. Comparatively speaking, Bluetooth needs 3- 10s and WiFi needs 3s;
(6) Large capacity: ZigBee can adopt star, sheet and mesh network structure, one master node can manage multiple child nodes, and one master node can manage up to 254 child nodes; At the same time, the master node can also be managed by the upper network nodes, which can form a large network with up to 65,000 nodes;
(7) High security: ZigBee provides a three-level security mode, including no security settings, using access control list (ACL) to prevent illegal access to data, and using symmetric password of advanced encryption standard (AES 128) to flexibly determine its security attributes;
(8) Unauthorized frequency band: The 2.4GHz (global) frequency band of industrial science and medical treatment adopts direct sequence spread spectrum.
4. Why is ZigBee produced to meet the growing demand of industrial automation for reliable wireless data transmission?
Answer: ZigBee technology itself is produced because Bluetooth technology can't meet the wireless data communication requirements of low data volume, low cost, low power consumption and high reliability in industrial automation. Because, for the industrial site, this wireless data transmission must have high reliability and be able to resist all kinds of electromagnetic interference in the industrial site. ZigBee technology adopts mesh topology, automatic routing, dynamic networking and direct sequence spread spectrum to meet the needs of industrial automation control field.
5. Which protocol does 5.ZigBee use?
A: Zigbee uses the IEEE802. 15.4 protocol, which is a low transmission rate protocol of infinite PAN. In standardization, the IEEE802. 15.4 working group is mainly responsible for formulating the protocols of physical layer and MAC layer, while other protocols mainly refer to and adopt existing standards. The ZigBee Alliance will be responsible for high-level application, testing and marketing.
At present, there are roughly four types of WPAN wireless personal area networks formulated by IEEE:
1) IEEE 802.15.1Bluetooth, Bluetooth V1.1;
2) The supplementary specification of Bluetooth, IEEE 802. 15.2 Bluetooth, reduces the mutual interference when it is used in the same category as WiFi;
3)IEEE 802. 15.3WiMEDIA, standard speed and high speed WPAN；; ; IEEE 802. 15.3a ultra-wideband and high-speed WPAN；; ;
4)IEEE 802. 15.4ZigBee, low-speed WPAN (also known as WSAN, s stands for sensor).
6. Why is the 2.4G frequency band used in 6.ZigBee wireless communication free?
A: In China and most other countries in the world, the use of radio equipment, including mobile phone communication, generally requires the payment of frequency usage fees, but mobile operators have already paid this fee to the country and charged users through the number occupation fee. When using other wireless devices, you must first apply for a frequency license from the relevant state departments, and then charge fees according to the frequency, power and quantity of your wireless devices. This is not a small expense, and the average equipment often costs several thousand yuan a year.
Free frequency band refers to a frequency band divided by countries according to their own actual conditions and considering the consistency with the regulations of other countries in the world as much as possible. It is specially used for industry, medical care and scientific research (ISM frequency band) and can be used free of charge without application. The 2.4G frequency band in our country is such a frequency band. However, in order to ensure that everyone can use it reasonably, the state has made corresponding restrictions on the use power of wireless transceiver equipment in this frequency band in different environments. For example, in urban environment, the transmission power cannot exceed 100mW.
7. Is 7.ZigBee only suitable for short-distance communication?
Answer: ZigBee LAN can not only expand the network by improving the transmitting power and receiving sensitivity of each node module and increasing the number of nodes, but also monitor the long-distance ZigBee control network through the traditional Internet.
However, during the expansion, it should be noted that:
1) With the increase of transmission power, the power consumption will naturally increase, and as long as the power consumption is high, the advantage of low power consumption of ZigBee itself will be lost;
2) Although 2)2.4 GHz is a free frequency band, it cannot exceed the maximum power limit in the radio wave method.
8. What are the advantages of 8.ZigBee using direct sequence spread spectrum communication?
Answer: In the same frequency band, if different communication methods are adopted, the results may be very different, such as ASK, FSK, FHSS, DSSS and other anti-interference capabilities, and the communication is safe, confidential and reliable. Like CDMA system, ZigBee system adopts direct sequence spread spectrum technology (DSSS), which is a communication mode with strong anti-interference ability, high confidentiality and reliability. If you have used the communication products of these two technologies, you will find that their reliability is remarkable.
Because the signal-to-noise ratio required by spread spectrum technology in normal communication can be very low, that is to say, it can still work normally in strong interference environment. According to calculation and experiment, this is equivalent to an increase of 7dBm in receiving sensitivity, and it is not easy to interfere with others. In other words, it can transmit longer distances with lower power.
9. What are the characteristics of 9.ZigBee compared with existing digital radio stations?
A: Its advantages are as follows:
(1) High reliability: Because the integration of ZigBee module is much higher than that of ordinary digital radio stations, there are fewer separated components, so the reliability is higher;
(2) Convenient and safe to use: Due to high integration, compared with the general digital radio station, the ZigBee receiving module can be made very small, with low power consumption, and the maximum emission current is much smaller than that of a CDMA mobile phone, so it is easy to be integrated or directly put into equipment, which is not only convenient to use, but also not easy to be damaged when carried outdoors;
(3) Strong anti-interference, good confidentiality and low bit error rate: ZigBee transceiver module adopts 2.4G direct sequence spread spectrum technology, which has stronger anti-interference ability and longer transmission distance than ordinary FSK, ASK and frequency hopping digital radio stations;
(4) Free frequency band: ZigBee uses free frequency band, and many digital radio stations not only need to apply for frequency band, but also need to pay a considerable frequency usage fee to the State Committee every year;
(5) Low price: The price of ZigBee digital transmission module is only a fraction of that of similar digital transmission radio stations.
10, what kind of wireless data transmission network does ZigBee have?
A: Simply put, ZigBee is a highly reliable wireless data transmission network, similar to CDMA and GSM networks, and the ZigBee data transmission module is similar to a mobile network base station. The communication distance ranges from the standard 75 meters to hundreds of meters and kilometers, which supports wireless expansion.
ZigBee is a wireless data transmission network platform composed of as many as 65,000 wireless data transmission modules, which is very similar to the existing mobile communication CDMA network or GSM network. Each ZigBee network data transmission module is similar to a base station of a mobile network, and they can communicate with each other in the whole network. The distance between each network node can range from the standard 75 meters to the extended several hundred meters or even several kilometers.
Different from CDMA network or GSM network for mobile communication, ZigBee network is mainly established for automatic data transmission in industrial field, so it must be simple, convenient, reliable and low-cost. The mobile communication network is mainly established for voice communication, and the value of each base station is generally more than one million yuan, while each ZigBee "base station" is less than 1000 yuan. Each ZigBee network node can not only be used as a monitoring object, for example, its connected sensors can directly collect and monitor data, but also can automatically transmit data from other network nodes.
In addition, each ZigBee network node (FFD) can also wirelessly connect a number of isolated child nodes (RFD), which do not undertake the task of network information transmission within their own signal coverage. Each ZigBee network node (FFD and RFD) can support as many as 365,438+0 sensors and controlled devices, and each sensor and controlled device can finally have 8 different interface modes. Can collect and transmit digital quantity and analog quantity.