In today’s world, communication technology is developing rapidly. With the rapid growth of the Internet and the increasing demand for data communication, the global communication industry is showing three major trends: wireless, broadband, and IP-based. The development of Internet services has driven the market demand for broadband networks, with the number of broadband users experiencing significant growth worldwide. Among various broadband technologies, wireless technology, especially mobile communication technology, has become the biggest highlight in the communication technology market in recent years and is an important component of future communication technology.
ZigBee is a low-power personal area network protocol based on the IEEE802.15.4 standard. The technology defined by this protocol is a short-range, low-power wireless communication technology. The name comes from the zigzag dance of bees, as bees communicate the location of pollen by flying and buzzing (zig) their wings, forming a communication network within the group. Its characteristics include short-range, low complexity, self-organization, low power consumption, and high data rates. It is mainly suitable for automatic control and remote control fields and can be embedded in various devices. In short, ZigBee is a cheap, low-power, short-range wireless networking communication technology.
The Origin and Development of ZigBee Technology
Before introducing ZigBee, it is important to mention its predecessor—Bluetooth. During the use of Bluetooth technology, people found that despite its many advantages, it still had many drawbacks. For industrial and home automation control and industrial telemetry, Bluetooth technology is too complex, consumes too much power, has a short range, and a small network scale. However, the demand for wireless data communication in industrial automation is becoming increasingly strong, and for industrial sites, this wireless data transmission must be highly reliable and resistant to various electromagnetic interferences in the industrial environment. Therefore, after long-term efforts, the ZigBee protocol was officially launched in the United States in 2003.
The predecessor of ZigBee was the “Homerflite” technology initiated by industry giants such as INTEL and IBM in 1998.
In December 2000, a working group was established to draft the IEEE802.154 standard, and the ZigBee Alliance was established in August 2001.
In the second half of 2002, four major companies—UK’s Vensys, Japan’s Mitsubishi Electric, America’s Motorola, and Netherlands’ Philips Semiconductor—jointly announced their membership in the ZigBee Alliance to develop the next-generation wireless communication standard named “ZigBee,” marking a milestone in the development of this technology.
In December 2004, the ZigBee 1.0 standard (also known as ZigBee 2004) was finalized, establishing the basic development standards for ZigBee.
In September 2005, the ZigBee 1.0 standard was published and made available for download. During this year, Huawei Technologies and IBM joined the ZigBee Alliance. However, applications based on this version were few and incompatible with later versions.
In December 2006, the standard was revised, and ZigBee 1.1 (also known as ZigBee 2006) was released. Although named ZigBee 1.1, it was not compatible with ZigBee 1.0.
In October 2007, another revision was completed (referred to as ZigBee 2007/PRO), which was compatible with the previous ZigBee 2006 version and included the ZigBee Pro part. At this time, the ZigBee Alliance focused more on three areas: home automation, commercial building automation, and advanced metering infrastructure.
The Technical Principles of ZigBee
ZigBee is a wireless data transmission network platform composed of up to 65,000 wireless data transmission modules, very similar to existing mobile communication CDMA or GSM networks. Each ZigBee network data transmission module is similar to a base station in a mobile network, allowing mutual communication within the entire network range; the distance between each network node can range from the standard 75 meters to several hundred meters or even kilometers after expansion. Additionally, the entire ZigBee network can connect with various existing networks. For example, you can monitor a ZigBee control network in Yunnan from Beijing via the Internet.
The ZigBee network is primarily established for automated control data transmission, while mobile communication networks are mainly established for voice communication. Each mobile base station generally costs over one million RMB, while each ZigBee “base station” costs less than 1,000 RMB. Each ZigBee network node can not only connect directly with monitoring targets, such as sensors, for data collection and monitoring, but it can also automatically relay data from other network nodes. Furthermore, each ZigBee network node (FFD) can wirelessly connect with multiple isolated sub-nodes (RFD) within its signal coverage area that do not undertake network information relay tasks.
Each ZigBee network node (FFD and RFD) can support up to 31 sensors and controlled devices, with each sensor and controlled device capable of having eight different interface methods. It can collect and transmit both digital and analog signals.
Characteristics of ZigBee Technology
ZigBee technology is a bidirectional wireless communication technology characterized by short-range, low complexity, low power consumption, low data rate, and low cost. It is mainly used for data transmission between various electronic devices that require short distances, low power consumption, and low transmission rates, as well as typical applications involving periodic data, intermittent data, and low response time data transmission.
Since Marconi invented radio, wireless communication technology has been continuously developing towards higher data rates and transmission distances. For example, the third-generation mobile communication network (3G) in wide area networks aims to provide multimedia wireless services, while local area network standards have evolved from IEEE802.11’s 1Mbit/s to IEEE802.11g’s 54Mbit/s data rates. ZigBee technology, on the other hand, aims to provide a low-complexity, low-cost, and low-power low-rate wireless communication technology for fixed, portable, or mobile devices.
This wireless communication technology has the following characteristics:
Low Power Consumption
In working mode, ZigBee technology has a low transmission rate and transmits a small amount of data, resulting in short signal send/receive times. Additionally, in non-working mode, ZigBee nodes are in sleep mode. The device search delay is generally 30ms, the sleep activation delay is 15ms, and the active device channel access delay is 15ms. Due to the short working time, low information transmission power consumption, and the use of sleep mode, ZigBee nodes are very energy-efficient, with battery life ranging from 6 months to 2 years. Moreover, since battery life depends on many factors, such as battery type, capacity, and application scenarios, ZigBee technology has also optimized battery usage in its protocol. For typical applications, alkaline batteries can last for several years, and in cases where the working time and total time (working time + sleep time) ratio is less than 1%, battery life can even exceed 10 years.
Reliable Data Transmission
The media access control layer (MAC layer) of ZigBee adopts a talk-when-ready collision avoidance mechanism. In this fully acknowledged data transmission mechanism, when there is a need for data transmission, it is sent immediately, and each data packet must wait for acknowledgment from the receiver. If acknowledgment is not received, it indicates a collision, and the data will be retransmitted. This method improves the reliability of system information transmission. Additionally, dedicated time slots are reserved for communication services requiring fixed bandwidth, avoiding competition and conflicts during data transmission. ZigBee has also optimized for delay-sensitive applications, resulting in very short communication delays and sleep state activation delays.
Large Network Capacity
The low data rate, low power consumption, and short-range transmission characteristics of ZigBee make it very suitable for supporting simple devices. ZigBee defines two types of devices: full-function devices (FFD) and reduced-function devices (RFD). Full-function devices are required to support all 49 basic parameters, while reduced-function devices only need to support 38 basic parameters at minimum configuration. A full-function device can communicate with reduced-function devices and other full-function devices and can operate in three modes: personal area network coordinator, coordinator, or device. Reduced-function devices can only communicate with full-function devices and are used for very simple applications. A ZigBee network can include up to 255 ZigBee network nodes, with one being the master device and the others being slave devices. If connected through a network coordinator, the entire network can support over 64,000 ZigBee network nodes, and since various network coordinators can connect with each other, the total number of ZigBee network nodes can be quite substantial.
Compatibility
ZigBee technology seamlessly integrates with existing control network standards. The network is automatically established through a network coordinator, using carrier sense multiple access/collision avoidance (CSMA-CA) for channel access. A full handshake protocol is also provided for reliable transmission.
Security
ZigBee provides data integrity checks and authentication functions, offering three levels of security during data transmission. The first level is essentially a non-secure mode, which can be chosen for applications where security is not critical or where sufficient security protection is already provided at a higher level. For the second level of security, devices can use an access control list (ACL) to prevent unauthorized devices from accessing data, without encryption measures. The third level of security employs symmetric encryption based on the Advanced Encryption Standard (AES) during data transfer. AES can be used to protect data payloads and prevent attackers from impersonating legitimate devices, allowing applications to flexibly determine their security attributes.
Low Implementation Cost
The initial cost of modules is estimated to be around $6, quickly dropping to $1.5-$2.5, and the ZigBee protocol incurs no patent fees. Currently, low-speed, low-power UWB chipsets cost at least $20. In contrast, ZigBee’s price target is only a few cents. Low cost is also a key factor for ZigBee.
Short Delay
Communication delays and activation delays from sleep states are very short, with typical device search delays of 30ms, sleep activation delays of 15ms, and active device channel access delays of 15ms. Therefore, ZigBee technology is suitable for wireless control applications with stringent delay requirements (such as industrial control scenarios).
Differences Between ZigBee and WiFi
Similarities:
1. Both are short-range wireless communication technologies;
2. Both use the 2.4GHz frequency band;
3. Both employ DSSS technology;
Differences:
1. Different transmission speeds. ZigBee’s transmission speed is low (<250Kbps), but it consumes very little power, typically lasting over 3 months on battery power; WiFi, commonly known as wireless local area network, has a high speed (11Mbps) but also high power consumption, generally requiring external power;
2. Different application scenarios. ZigBee is used in low-speed, low-power scenarios, such as wireless sensor networks, suitable for industrial control, environmental monitoring, smart home control, etc. WiFi is generally used for wireless network technology covering a certain range (such as a building) (coverage of about 100 meters). The typical implementation is a wireless router, where one router can provide wireless internet access for laptops (with wireless network cards) within the building.
3. Different market status. ZigBee, as an emerging technology, has been rapidly developing and promoting since the release of its first version in 2004; however, due to cost and reliability issues, it has not yet been widely adopted. WiFi, on the other hand, is a more mature technology with many applications. Overall, the differences between the two are significant, with different market positioning and limited competition between them. However, they do share some technical similarities, and there is considerable interference, especially from WiFi to ZigBee.
Comparison of hardware memory requirements: ZigBee: 32~64KB+; WiFi: 1MB+; ZigBee has lower hardware requirements.
Comparison of battery-powered operational duration: ZigBee: 100~1000 days; WiFi: 1~5 days; ZigBee has low power consumption. Comparison of transmission distances (general usage, without high-power antenna transmission devices): ZigBee: 1~1000M; WiFi: 1~100M; ZigBee has a longer transmission distance. ZigBee disadvantages: network bandwidth comparison: ZigBee: 20~250KB/s; WiFi: 11000KB/s; ZigBee has lower bandwidth and slower transmission.
Applications of ZigBee Technology
As a low-rate, short-range wireless communication technology, ZigBee has its own characteristics, leading to tailored applications, although there may be overlaps with other technologies in certain areas. Some potential applications of ZigBee include smart homes, industrial control, automatic meter reading, medical monitoring, sensor network applications, and telecommunications applications.
Smart Home
Homes may have many electrical and electronic devices, such as lights, televisions, refrigerators, washing machines, computers, air conditioners, etc., as well as smoke detectors, alarms, and cameras. Previously, we could only achieve point-to-point control, but with ZigBee technology, we can connect all these electronic devices into a network, even linking them to the Internet through a gateway. This allows users to conveniently monitor their home situation from anywhere, eliminating the hassle of wiring in the house.
Industrial Control
In factory environments, there are numerous sensors and controllers that can be connected into a network using ZigBee technology for monitoring, enhancing operational management, and reducing costs.
Automatic Meter Reading
Meter reading is something most people are familiar with, such as gas meters, electric meters, and water meters, which need to be read monthly or quarterly and reported to gas, electricity, or water companies for billing. Currently, most places still use manual methods for meter reading, which is inconvenient. ZigBee can be used in this field, utilizing sensors to convert meter readings into digital signals and directly sending them to the gas or water and electricity providers via the ZigBee network. Using ZigBee for meter reading also brings other benefits, such as allowing gas or water and electricity companies to send information directly to users or integrating with energy-saving measures to automatically reduce usage when energy consumption is detected to be too high.
Medical Monitoring
Electronic medical monitoring has recently become a research hotspot. Many sensors can be installed on the human body to measure pulse, blood pressure, and monitor health status, along with placing monitors and alarms in the surrounding environment, such as in hospital rooms, to continuously monitor a person’s physical condition. If a problem occurs, timely responses can be made, such as notifying hospital staff. These sensors, monitors, and alarms can form a monitoring network using ZigBee technology, and since it is a wireless technology, the sensors do not require wired connections, allowing the monitored person to move freely, which is very convenient.
Sensor Network Applications
Sensor networks are also a recent research hotspot, with promising applications in areas such as cargo tracking, building monitoring, and environmental protection. Sensor networks require low-cost, low-power nodes that can automatically form networks, are easy to maintain, and have high reliability. ZigBee’s advantages in networking and low power consumption make it a great technical choice for sensor network applications.
Telecommunications Applications
In early 2006, Telecom Italia announced that it had developed a SIM card integrated with ZigBee technology, named “ZSIM.” This SIM card is essentially a means of integrating ZigBee into telecommunications terminals. The ZigBee Alliance also announced in April 2007 that its members were developing telecommunications-related applications. If ZigBee technology can indeed be developed in the telecommunications field, users will be able to use their mobile phones for mobile payments and receive interesting information, such as news and discount information, in hotspot areas. Users can also know their location through location services. Although GPS location services are already well-developed, they struggle with indoor positioning, and ZigBee’s positioning capabilities can fill this gap.
Current Issues with ZigBee Technology
Despite being listed in 2004 as one of the ten fastest-developing and most market-promising new technologies in the world, and despite extensive discussions about the advantages of ZigBee technology, many manufacturers both domestically and internationally have developed various ZigBee products and made significant efforts in application promotion. However, realistically speaking, there are very few meaningful cases where ZigBee technology has been fully utilized to solve specific practical problems.
ZigBee seems to have become a fashionable but not yet truly practical new technology. The reasons for this include the need for technical improvements and maturity, as well as market cultivation processes for this new technology. Additionally, in the long-term application of ZigBee technology to solve practical problems, we have identified several important issues that we believe are difficult to resolve in the short term:
1. One of the core technologies of ZigBee is dynamic networking and dynamic routing, which considers the changes in the number of nodes in the network. Each node in the network needs to communicate wirelessly at intervals to re-establish the network, and every time information is sent from one node to another, various possible paths must be scanned, starting from the shortest route. This involves managing the wireless network, which requires significant bandwidth resources and increases data transmission delays, especially as the number of network nodes and relay times increase. Therefore, although ZigBee’s RF transmission rate is 250kbps, the actual usable rate after multiple relays will be significantly reduced, and data transmission delays will also increase, making wireless network management more complicated. This is currently the main issue with data transmission in ZigBee networks.
2. The word “ZigBee” is composed of “Zig” and “bee.” The former means a zigzag path, while the latter refers to bees. Our understanding is that ZigBee network technology mimics the way bees transmit information, relaying information between network nodes to transfer data from one node to another. According to general standards, a ZigBee node in open space increases the straight-line transmission distance by an average of 50 meters for each data relay. To transmit a straight-line distance of 500 meters, ten relays are needed. Indoors, due to the 2.4 GHz transmission frequency used by ZigBee, transmission is often achieved through signal reflection. Due to building obstructions, transmitting over a certain distance often requires many network nodes for data relaying, as analyzed in the first point. This is not a simple task for a ZigBee network. Of course, we can use amplifiers to increase the transmission distance of ZigBee network nodes, but this will significantly increase the power consumption and cost of network nodes, defeating the original purpose of ZigBee’s low cost and low power consumption. Moreover, using this method indoors to increase transmission distance has limited effectiveness. Clearly, a star network communication structure with a central point outdoors and terminal modules outdoors would be more reasonable.
3. One of the core technologies of ZigBee is that each network node, in addition to serving as an information collection point and executing commands from the center, also undertakes data relay tasks from the network at any time. This means that the transceiver of the network node must always be in a send/receive state, which implies a minimum power consumption of at least 20mA. Generally, network nodes using amplifiers for long-distance communication consume around 150mA. This makes it challenging to use battery power to ensure the normal operation of network nodes.
4. Since each node in ZigBee participates in automatic networking and dynamic routing, the microcontroller of each network node is relatively complex, leading to higher costs. Additionally, the amount of development work required for specific applications based on ZigBee networks is also greater.
In summary, we believe that ZigBee networks often sacrifice network transmission efficiency, bandwidth, and node module power consumption to achieve dynamic networking and dynamic routing functions, which may not be significant in many practical applications. In general, our network nodes and data transmission paths are often fixed. Therefore, the unresolved issues of node power consumption, low efficiency of network data transmission, long delays, and limited data transmission distances are fundamental reasons why ZigBee technology has not been well promoted.
Reprinted from: Sensor Technology
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