As an application-oriented research field, wireless sensor networks have achieved rapid development in recent years. In the research and development of key technologies, the academic community has carried out a lot of research from network protocols, data fusion, test and measurement, operating system, service quality, node positioning, time synchronization, etc., and achieved fruitful results; the industry is also in environmental monitoring, military Application exploration in target tracking, smart home, automatic meter reading, lighting control, building health monitoring, power line monitoring and other fields. With the promotion of applications, wireless sensor network technology has begun to expose more and more problems. Devices from different vendors need to achieve interoperability and avoid mutual interference with the current system. Therefore, different chip manufacturers, solution providers, product providers and associated device providers are required to reach a certain tacit agreement and work together to achieve the goal. This is the background to the standardization of wireless sensor networks. In fact, because the standardization work is related to many economic interests and even social interests, it is often valued by the relevant industries. How to coordinate the interests of all parties and reach a consensus requires the participants to have sufficient understanding and patience. So far, the standardization work of wireless sensor networks has received widespread attention from many national and international standards organizations, and a series of drafts and even standard specifications have been completed. The most famous of these is the IEEE 802.15.4/zigbee specification, which has even been considered a standard by some researchers and industry. IEEE 802.15.4 defines the physical layer and link layer specifications for short-range wireless communications, and zigbee defines network interconnection, transport, and application specifications. Although the IEEE802.15.4 and zigbee protocols have been introduced for many years, with the promotion of the application and the development of the industry, the basic protocol content can not fully meet the needs, and the protocol only defines the content of the network communication, and no standard is proposed for the sensor components. The protocol interface, so it is difficult to carry the dream and mission of wireless sensor network technology; in addition, when the standard is in different countries, it is bound to be bound by the current standards in the country. To this end, people began to introduce more versions based on the IEEE 802.15.4/zigbee protocol to adapt to different applications, different countries and regions. Despite the imperfections, IEEE 802.15.4/zigbee is still the best combination of the industry's development of wireless sensor network technology. This article will focus on the IEEE 802.15.4/zigbee protocol specification, with due regard to other relevant standards of sensor network technology. Of course, the standardization of wireless sensor networks has a long way to go: First, wireless sensor networks are still an emerging field, and their research and applications are still quite young, and the industry's demand is still unclear. Second, IEEE 802.15/zigbee is not aimed at wireless sensing. The network is tailor-made, and some problems need to be further solved in the wireless sensor network environment. In addition, the international standardization work for wireless sensor network technology has just begun, and the domestic standardization working group has just been established. To this end, we must be fully prepared for the smooth completion of the standardization work. 1. PHY/MAC layer standard The underlying standards for wireless sensor networks generally follow the relevant standard portion of the wireless personal area network (IEEE 802.15). The Wireless Personal Area Network (WPAN) appears earlier than the sensor network and is usually defined as a wireless short-range private network that provides interconnection between personal and consumer electronic devices. The wireless personal area network focuses on the two-way communication technology problem between portable mobile devices (such as personal computers, peripheral devices, PDAs, mobile phones, digital products and other consumer electronic devices), and its typical coverage is generally within 10 meters. The IEEE 802.15 working group was specifically set up to accomplish this mission and has completed the development of a series of related standards, including the underlying standard IEEE 802.15.4, which is widely used in sensor networks. (1) IEEE 802.15.4b specification The IEEE 802.15.4 standard is mainly developed for the Low-Rate Wireless Personal Area Network (LR-WPAN). The standard targets low energy consumption, low-rate transmission, and low cost (which is consistent with wireless sensor networks) and is designed to provide a unified interface for low-speed interconnection between different devices within an individual or home range. Since the characteristics of the LR-WPAN network defined by IEEE 802.15.4 and the intra-cluster communication of the wireless sensor network have many similarities, many research institutions regard it as the physical and link layer communication standard of the sensor network node. The IEEE 802.15.4 standard defines the physical layer and media access control sublayers, in line with the Open Systems Interconnection Model (OSI). The physical layer includes a radio frequency transceiver and an underlying control module, and the medium access control sublayer provides a service interface for the upper layer to access the physical channel. Figure 1 shows the relationship between IEEE 802.15.4 layers and layers and the IEEE 802.15.4/zigbee protocol architecture. Refer to [1] for details. IEEE 802.15.4 is designed for low-cost and higher-level integration in the physical (PHY) layer design. The operating frequency is divided into three types: 868MHz, 915MHz and 2.4GHz. The channels that can be used in each frequency band are 1, 10 respectively. And 16 each providing a transmission rate of 20 kb/s, 40 kb/s and 250 kb/s, and the transmission range is between 10 meters and 100 meters. The three frequency bands used in the specification are the open bands of the ISM (Industrial ScienTIfic and Medical) for scientific research and medical treatment defined by the ITU Telecommunication Standardization Group (ITUT), and are widely used by various wireless communication systems. In order to reduce inter-system interference, the protocol specifies direct sequence spread spectrum (DSSS) coding techniques in each frequency band. Compared with other digital coding methods, direct sequence spread spectrum technology can make the analog circuit design of the physical layer simple and has higher fault tolerance performance, which is suitable for the implementation of low-end systems. IEEE 802.15.4 defines two access modes for the medium access control layer. One is Carrier Sense MulTIple Access with Collision Avoidance (CSMA/CA). In this way, referring to the DCF mode defined by the IEEE802.11 standard in the wireless local area network (WLAN), it is easy to achieve channel level coexistence with a wireless local area network (WLAN, Wireless LAN). The so-called CSMA/CA is to listen to whether there is a co-channel carrier in the medium before transmission. If it does not exist, it means that the channel is idle and will enter the data transmission state directly; if there is carrier, it will be randomly evacuated. The channel is re-detected after a period of time. This medium access control layer scheme simplifies the process of implementing self-organizing (Ad Hoc) network applications, but it brings troubles to improve bandwidth utilization in high-traffic transmission applications. At the same time, because there is no power management design, it is implemented. Low-power network applications based on sleep mechanisms require more work. Another communication mode defined by IEEE 802.15.4 is similar to the PCF mode defined by the 802.11 standard. It is easy to implement low power control by using a synchronized superframe mechanism to improve channel utilization and by defining a sleep period within a superframe. The PCF mode defines two devices: a Full-Function Device (FFD) and a Reduced-Function Device (RFD). The FFD device supports all 49 basic parameters, while the RFD device requires only 38 basic parameters for its minimum configuration. In the PCF mode, the FFD device acts as a coordinator to control the synchronization and data transceiving processes of all associated RFD devices, and can communicate with any device in the network. The RFD device can only interwork with the FFD device associated with it. In PCF mode, there is at least one FFD device in the IEEE 802.15.4 network as the PAN Coordinator, which acts as the network master controller, and performs inter-cluster and intra-cluster synchronization, packet forwarding, network establishment, and membership. Management and other tasks. The IEEE 802.15.4 standard supports both star and peer-to-peer network topologies, with 16-bit and 64-bit address formats. The 64-bit address is the only extended address in the world, and the 16-bit segment address is used for small network construction or as the identification address of the device in the cluster. The IEEE 802.15.4b standard has several variants, including IEEE 802.15.4a for low-speed ultra-wideband, and IEEE 802.15.4c and IEEE 802.15.4e, which are currently being promoted in China, and IEEE 802.15.4d, which is mainly promoted in Japan. I won't discuss it in depth. (2) Bluetooth technology In May 1998, just after the establishment of the IEEE 802.15 wireless personal area network working group, five world-renowned IT companies: Ericsson, IBM, Intel, Nokia and Toshiba jointly announced A research and development program called "Bluetooth". In July 1999, the Bluetooth Working Group introduced the Bluetooth protocol version 1.0, which was updated to version 1.1 in 2001, which is known as the IEEE 802.15.1 protocol. The agreement is designed to design a common international standard for the Radio Air Interface and its software, enabling the further integration of communications and computers, enabling portable devices from different manufacturers to achieve close-range interoperability without cables. ability. As soon as the plan was announced, it received extensive support from nearly 2,000 vendors including Motorola, Lucent, Compaq, Simens, 3Com, TDK and Microsoft. And adoption. Bluetooth technology also works in the 2.4GHz ISM band. It uses fast frequency hopping and short packet technology to reduce co-channel interference, ensure the reliability and security of physical layer transmission, has certain networking capabilities, and supports 64Kbps real-time voice. Bluetooth technology is becoming more and more popular, and related products in the market are also increasing. However, with the emergence of ultra-wideband technology, wireless LAN and zigbee technology, especially its security, price, power consumption and other issues are increasingly apparent, and its competitive advantage. begin descending. In 2004, the Bluetooth working group launched version 2.0, which tripled the bandwidth and reduced power consumption by half, rebuilding the confidence of the industry to a certain extent. Because of the commonality between Bluetooth technology and zigbee technology, they are often used in wireless sensor networks. 2. Other wireless personal area network standards The wireless sensor network needs to build a complete network from the physical layer to the application layer, and the wireless personal area network standard prescribes the physical layer and medium access control layer specifications. In addition to the IEEE 802.15.4 and Bluetooth technologies discussed above, the wireless personal area network technology solution also includes: ultra-wideband (UWB) technology, infrared (IrDA) technology, home radio frequency (HomeRF) technology, etc., and their common feature is short distance. Low power consumption, low cost, personal use, etc., which are used in the underlying protocol scheme of wireless sensor networks in different application scenarios, which are briefly described as follows: (1) Ultra-wideband (UWB) technology Ultra Wide-Band (UWB) technology originated in the late 1950s and is a technology that uses broadband electric wave signals from a few Hz to several GHz. It emits a very short pulse and receives and analyzes the reflected back. Signal, you can get the information of the detected object. UWB uses a very high bandwidth, so its power spectral density is very flat, showing that the output power at any frequency is very small, even lower than the noise emitted by ordinary equipment, so it has good anti-interference and security. Sex. Ultra-wideband technology was originally used primarily as a military technology in radar detection and location applications. The US FCC (Federal Communications Commission) granted the technology to the civilian sector in February 2002. In addition to low power consumption, the transmission rate of ultra-wideband technology can easily reach more than 100Mbps, and its second-generation products are expected to reach more than 500Mbps. Only this one indicator can make many other technologies far behind. The standard dispute surrounding UWB has been fierce since the beginning. Freescale's DS-UWB and MBOA advocated by TI have gradually emerged. In recent years, domestic research in this area has also been very popular. Due to its low power consumption, high bandwidth and strong anti-interference ability, UWB technology has undoubtedly a fantastic development prospect, but UWB chip products have not been available for a long time, which undoubtedly leaves us with a big regret. In recent years, reports on related products have begun to appear, but this deep-rooted technology also needs to be promoted by the entire industry. At present, the ultra-wideband technology can be said to be the first to show its edge. It is believed that it belongs to the type of late, old and strong, and it will have a lot to do in wireless sensor network applications. (2) Infrared (IrDA) technology Infrared technology is a technology for point-to-point communication using infrared rays. It was promoted by the IrDA (Infrared Data Association), a non-profit organization of the Infrared Data Standards Association established in 1993. The association is committed to establishing a world standard for wireless communication connections. Currently has more than 130 official corporate members. The transmission rate of infrared technology has increased from 4 Mbps of the initial FIR to 16 Mbps of the current VFIR, and the reception angle has also been extended from the original 30 to 120. Since it is only used for point-to-point communication and has a certain directionality, data transmission is less subject to interference. Due to its small size, low cost, low power consumption, and no need for frequency application, infrared technology has been widely used since its birth. It is an evergreen tree in the field of wireless personal area networks. After years of development, its hardware and supporting software technology are quite mature. At present, there are at least 50 million devices in the world using IrDA technology, and still growing at an annual rate of 50%. Today, 95% of laptops are equipped with an IrDA interface, while remote control devices (television, air conditioners, digital products, etc.) are more commonly used in infrared technology. However, IrDA is a line-of-sight transmission technology. The core components of infrared LEDs are not very durable, and it is impossible to build a stable network for long-term operation. As a result, infrared technology has not become the physical layer standard technology of wireless personal area networks. Attempts have been made in wireless sensor network applications (such as location tracking) and are used in conjunction with other wireless technologies. Diesel Generator Power Range,Single Phase Diesel Generator,Mobile Type Diesel Generator,Standby Power Diesel Generator Shanghai Kosta Electric Co., Ltd. , https://www.ksdgenerator.com