Everything about the ZigBee protocol is in this article.
In the field of intelligent hardware and the Internet of Things, the now famous ZigBee is no one knows, no one knows. In addition to wifi and Bluetooth, ZigBee is one of the most important wireless communication protocols, mainly used in the fields of Internet of Things and intelligent hardware. Regarding ZigBee, the following questions and answers are used to introduce you to all aspects. It is not a boast that everything you need to know about ZigBee is here!
Origin history
What technology does ZigBee originate from?
During the use of Bluetooth technology, Bluetooth technology has been found to have many drawbacks despite its many advantages. For industrial, home automation control and industrial telemetry and remote control, Bluetooth technology is too complicated, power consumption, distance is too close, network size is too small, etc., and industrial automation, the demand for wireless data communication is getting stronger and stronger. Moreover, for industrial sites, such wireless data transmission must be highly reliable and resistant to various electromagnetic interferences in the industrial field. Therefore, after long-term efforts, the ZigBee protocol was officially released in 2003. In addition, ZigBee uses Home RF Lite, a communication protocol for home networks that it has studied before.
What is ZigBee?
First of all, ZigBee is synonymous with the IEEE802.15.4 protocol. The technology specified in this protocol is a two-way wireless communication technology with close proximity, low complexity, low power consumption, low data rate and low cost. It is mainly suitable for automatic control and remote control, and can be embedded in various devices. Support for geolocation. Because bees rely on flying and "zig" to shake the wings of the "dance" to communicate the position and near-far information of the pollen with the companion, that is, the bees rely on this way to form the communication in the group. "Network", so the inventors of ZigBee visually use this behavior of bees to visually describe this wireless information transmission technology.
What are the characteristics of ZigBee technology?
The characteristics of ZigBee mainly include the following aspects:
(1) Low power consumption: In the low power standby mode, 2 No. 5 dry batteries can support 1 node 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 hours;
(2) Low cost: By greatly simplifying the protocol, the cost is very low (less than 1/10 of Bluetooth), and the requirements for the communication controller are reduced. According to the prediction analysis, the 8051 8-bit microcontroller is used to calculate the full-featured master. Nodes require 32KB of code, sub-function nodes as little as 4KB of code, and ZigBee's protocol patents are free;
(3) Low rate: ZigBee works at a communication rate of 250 kbps, meeting the application requirements of transmitting data at a low rate;
(4) Close range: The transmission range is generally between 10 and 100 m. After increasing the RF transmission power, it can also be increased to 1-3 km. This refers to the distance between adjacent nodes. If the relay is used by routing and communication between nodes, the transmission distance will be farther;
(5) Short delay: ZigBee's response speed is faster. Generally, it takes only 15ms from sleep to working state, and the node connection enters the network only takes 30ms, which further saves energy. In comparison, Bluetooth requires 3-10s, WiFi requires 3s;
(6) High capacity: ZigBee can adopt star, patch and mesh network structure. One master node manages several child nodes, and at most one master node can manage 254 child nodes. At the same time, the master node can also be managed by the upper layer network node. , can form a large network of up to 65,000 nodes;
(7) High security: ZigBee provides a three-level security mode, including no security settings, the use of access control lists (ACLs) to prevent illegal access to data, and symmetric passwords using the Advanced Encryption Standard (AES128) for flexible determination of security attributes. ;
(8) License-free frequency band: Direct sequence spread spectrum is used in the 2.4 GHz (global) frequency band of Industrial Science Medical.
Why is ZigBee compliant with the growing demand for reliable wireless data transmission from industrial automation?
The ZigBee technology itself is due to the fact that the Bluetooth technology cannot meet the demand for low data volume, low cost, low power consumption and high reliability wireless data communication in industrial automation. Because, for industrial sites, this wireless data transmission must be highly reliable and resistant to various electromagnetic interferences in the industrial field. In ZigBee technology, mesh topology, automatic routing, dynamic networking, and direct sequence spread spectrum are used. It is to meet the needs of industrial automation control sites.
Communication technology
What kind of protocol does ZigBee use?
IEEE 802.15.4 protocol, which is a protocol for an infinite PAN with a low transfer rate. In terms of standardization, the IEEE802.15.4 working group is mainly responsible for the development of the physical layer and MAC layer protocols. The remaining protocols mainly refer to and adopt existing standards. The work of high-level applications, testing and marketing will be handled by the ZigBee Alliance.
Why is ZigBee wireless communication using the 2, 4G band as a free band?
In China and most other countries in the world, the general use of radio equipment is subject to frequency usage fees, including mobile communication, but the mobile operator has already paid the fee to the state and has provided the user with the number occupancy fee. This fee was charged. When using other wireless devices, you must first apply for a frequency license from the relevant national authorities, and then charge the amount and amount of power according to the frequency, amount and amount of wireless devices used by your wireless device. This is not a small fee. Generally, equipment costs a few thousand dollars a year. The free frequency band refers to a frequency band that each country divides according to its actual situation and considers the consistency with other countries in the world as much as possible. It is used exclusively for industrial, medical and scientific research (ISM band). A frequency band that can be used free of charge if required. The 2.4G band in our country is such a band. However, in order to ensure that everyone can use it reasonably, the state has limited the use of wireless transceiver equipment in this frequency band in different environments. For example, in an urban environment, the transmission power cannot exceed 100 mW.
Is ZigBee only suitable for near field communication?
ZigBee local area network can not only expand the network by increasing the transmit power and receiving sensitivity of each node module and increasing the number of nodes, but also can monitor the remote ZigBee control network through the traditional Internet. However, it is necessary to pay attention to the expansion: (1) As the transmission power increases, the power consumption naturally increases, and only requires a large amount of power consumption, which will lose the advantage of ZigBee's own low power consumption; (2) Although 2.4Ghz is a free band, it cannot exceed the maximum power limit in the radio wave method.
What are the benefits of ZigBee's direct-sequence spread spectrum communication?
In the same frequency band, different communication methods may have different results. For example, ASK, FSK, FHSS, DSSS, etc., anti-interference ability, communication security confidentiality, and reliability are all different. Like the CDMA system, the ZigBee system uses Direct Sequence Spread Spectrum (DSSS), which is a communication method with strong anti-interference ability, high confidentiality and high reliability. If you have used communication products for these two technologies, you will find that the two are exceptionally reliable.
Since the spread spectrum technology can achieve a low signal-to-noise ratio during normal communication, that is, it can still work normally in a highly interference environment. According to calculations and experiments, this is equivalent to an increase in receiving sensitivity of 7 dBm. It is also not easy to interfere with others. In other words, it can transmit longer distances with lower power. The following references some of the advantages of the spread spectrum technology for reference:
CDMA is a new digital cellular technology introduced in 1995 after the introduction of digital communication technology in the world. It uses digital transmission method and spread spectrum communication technology to greatly improve the frequency utilization. It has large capacity and coverage. The outstanding advantages of wide power consumption, low power consumption and high voice quality have pushed mobile communication technology to a new stage of development. CDMA (Code Division Multiple Access) cellular systems have the following outstanding advantages over FDMA (Frequency Division Multiple Access) and TDMA (Time Division Multiple Access) systems:
(1) Good anti-interference performance Because CDMA has spread spectrum processing, it has good anti-interference performance and can coexist with narrowband in the same frequency band without affecting its normal operation.
(2) Anti-multipath fading ability Strong multipath fading is a prominent problem affecting the quality of mobile communication. It usually must be overcome by techniques such as spatial diversity and adaptive equalization, and there is a large fading margin. CDMA systems can use multipath signals to provide path diversity, which not only mitigates Rayleigh fading, but also mitigates slow fading caused by physical occlusion, thereby greatly improving the high communication quality of Qualcomm.html 'target='_blank'.
(3) Increase in system capacity For FDMA and TDMA, if the frequency or time slot of the cell is allocated, the cell cannot receive a new call, and the capacity is hard limited. While CDMA is an interference-limited system, at a given interference level, even if the number of users has reached a limited number, individual users are allowed to be added, which has the disadvantage of causing a drop in voice quality. Service providers can balance capacity and voice quality. CDMA's precise power control and soft handoff techniques greatly reduce the strength of the interfering signal and the required signal to noise ratio requirements, and effectively employ such things as voice activated or variable rate voice coding, diversity reception, power control. According to reports, the CDMA signal-to-noise ratio is 3.7 times that of DAMPS and TDMA, 11.2 times that of TACS, 13.6 times that of AMPS, and 20 times that of FM/FDMA.
(4) Good communication quality CDMA system adopts direct sequence spread spectrum technology, comprehensively applies time diversity, frequency diversity, space diversity, path diversity and other diversity techniques to overcome multipath effects, and can obtain strong anti-interference ability, plus it In the handover, the soft handover technology that establishes the post-interruption is adopted to ensure the communication quality of CDMA, especially in the handover. The system is a broadband low noise ratio, and the waveform allows high redundancy error correction coding and efficient digital modulation techniques to ensure high quality voice and data transmission.
(5) High frequency utilization The same frequency of CDMA system can be reused in all cells with a frequency reuse rate of 2/3 (FDMA and TDMA frequency reuse rate is 1/7), without FDMA and TDMA Frequency configuration in that way greatly simplifies cell splitting and microcell introduction.
(6) Multiple access capability Strong CDMA system multiple access capability determines the size of multiple access interference between spread spectrum codes, which is related to the spread spectrum coding scheme used, and multiple access interference between users transmitting signals simultaneously (ie, spread spectrum coding) Related characteristics) related to the allowed reception quality (output signal-to-noise ratio), so the lower the multiple access interference between working users, the lower the acceptable reception quality, the stronger the multi-access capability of CDMA technology.
(7) Highly reliable security CDMA mobile communication system is a secure communication system. If a certain encryption algorithm technology is added, the communication security performance can be greatly improved, which is unmatched by FDMA and TDMA systems. Analysis of the spread spectrum system used by it is almost impossible to intercept other people's communication content. For example, as long as the lithium battery in the machine is not discharged, it changes the instantaneous state of the sequence with a clock frequency of 512KHz, even if it is continuously working. Its spread spectrum address sequence period is also up to 7 years. It can also easily set and change the master key, sub-key, spreading code table, standard encryption algorithm, etc. in the CDMA system to make the confidentiality of communication more reliable.
(8) Mobile phone power consumption After power control, CDMA only increases the transmit power level during fading, thus reducing the average transmit power. The minimum power of FDMA is 5mW, the average transmit power is 794 mW, and the peak power is 3W. The CDMA has a minimum power of 2.3 mW, an average transmit power of 5 mW, and a peak power of 100 mW. It can be seen that the average transmit power and the maximum transmit power of CDMA are lower than FDMA, thereby increasing the system capacity, reducing the number of cells and reducing the equipment cost.
What are the characteristics of ZigBee compared with existing digital radio stations?
The advantages are as follows:
(1) High reliability: Since the integration of ZigBee modules is much higher than that of general digital radio stations, there are fewer separate components, so the reliability is higher;
(2) Easy to use and safe: Because of the high integration, the ZigBee receiving module can be made smaller than the general digital radio, and the power consumption is low. The maximum emission current is much smaller than that of a CDMA mobile phone. Easy to integrate or directly placed in the device, not only easy to use, but also not easily damaged when carried outdoors.
(3) Strong anti-interference ability, good confidentiality and low bit error rate: ZigBee transceiver module uses 2.4G direct sequence spread spectrum technology, which is better than general FSK, ASK and frequency hopping digital radio. Anti-interference ability, and longer transmission distance;
(4) Free frequency band: ZigBee uses the free frequency band, and the frequency bands used by many digital radio stations not only need to apply, but also need to pay a considerable frequency usage fee to the national committee every year;
(5) Low price: The price of the ZigBee digital transmission module is only a fraction of that of a digital radio station with similar functions.
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