ZigBee related applications and advantages analysis

I. Introduction

For a long time, the wireless communication market with low price, low transmission rate, short distance and low power has always existed. Since the advent of Bluetooth, industrial control, home automation, toy manufacturers and other manufacturers have been excited, but the price of Bluetooth has been high, which has seriously affected the willingness of these manufacturers to use. Today, these companies have participated in the IEEE802.15.4 group, responsible for the development of ZigBee's physical layer and media intervention control layer. The IEEE802.15.4 specification is an economical, efficient, low data rate (250 kbps), working in 2.4 GHz and 868/915 MHz wireless technology for personal area networks and peer-to-peer mesh networks. It is the basis of ZigBee application layer and network layer protocols. ZigBee is an emerging wireless network technology with close range, low complexity, low power consumption, low data rate, and low cost. It is a technical proposal between wireless tag technology and Bluetooth. Mainly used for short-range wireless connection. According to the 802.15.4 standard, thousands of tiny sensors coordinate and communicate with each other. These sensors require very little energy, relaying data from one sensor to another through radio waves, so their communication efficiency is very high.

Generally speaking, as the communication distance increases, the complexity, power consumption, and system cost of the device increase. Compared with the existing various wireless communication technologies, ZigBee technology will be the technology with the lowest power consumption and cost. At the same time, due to the low data rate and small communication range of ZigBee technology, it also determines that ZigBee technology is suitable for carrying small data traffic services. Therefore, the main application areas predicted by the ZigBee Alliance include industrial control, consumer electronics, automotive automation, agricultural automation, and medical equipment control.

2. Introduction to IEEE 802.15.4 and ZigBee

The IEEE 802.15.4 technical standard of the IEEE Wireless Personal Area Network (PAN) Working Group is the foundation of ZigBee technology. The 802.15.4 standard aims to provide low-speed connections with a simple coverage of about 10 meters for simple devices with low energy consumption, and can be widely used in consumer and commercial applications such as interactive toys and inventory tracking and monitoring. Sensor network is its main market object.

2.1 802.15.4 protocol architecture and its technical characteristics

IEEE802.15.4 meets the International Standards Organization (ISO) Open System Interconnection (OSI) reference model. It defines a single MAC layer and multiple physical layers. The MAC layer of IEEE802.15.4 can support a variety of LLC standards, and bear the IEEE802.2 type 1 LLC standard through the SSCS (Service-Specific Convergence Sublayer) protocol, while allowing other LLC standards to use IEEE802.15.4 directly MAC layer service.

IEEE802.15.4 defines two physical layer standards, namely 2.4GHz physical layer and 868 / 915MHz physical layer. They are all based on DSSS (Direct Sequence Spread Spectrum, direct sequence spread spectrum), using the same physical layer packet format, the difference is the operating frequency, modulation technology, spreading chip length and transmission rate. The 2.4GHz band is a globally uniform ISM frequency band that does not require application, which helps to promote ZigBee equipment and reduce production costs. The 2.4GHz physical layer can provide a transmission rate of 250kb / s by adopting high-order modulation technology, which helps to obtain higher throughput, smaller communication delay and shorter duty cycle, thereby saving more power. 868MHz is the ISM frequency band in Europe, and 915MHz is the ISM frequency band in the United States. The introduction of these two frequency bands avoids the mutual interference of various wireless communication devices near 2.4GHz. The transmission rate of 868MHz is 20kb / s, and 916MHz is 40kb / s. The propagation loss of the wireless signal in these two frequency bands is small, so the requirement for receiver sensitivity can be reduced to obtain a longer effective communication distance so that a given area can be covered with less equipment.

2.2 ZigBee technology overview

ZigBee is a set of technical standards related to networking, security and application software developed based on the 802.15.4 wireless standard approved by IEEE. It's not just the name of 802.15.4. IEEE only deals with low-level MAC and physical layer protocols, and the ZigBee Alliance standardizes its network layer protocols and APIs. The complete protocol is used for 4K bytes that can be directly connected to the basic node of one device at a time or 32K bytes as the coordinator of Hub or router. Each coordinator can connect up to 255 nodes, and several coordinators can form a network, there is no limit to the number of routing transmissions. The ZigBee Alliance has also developed a security layer to ensure that such portable devices will not accidentally leak their identity, and that this long-distance transmission using the network will not be obtained by other nodes.

The complete Zigbee protocol suite consists of high-level application specifications, application convergence layer, network layer, data link layer, and physical layer. The protocol above the network layer is formulated by the ZigBee Alliance, and IEEE802.15.4 is responsible for the physical layer and link layer standards.

The application convergence layer will be mainly responsible for mapping different applications to the ZigBee network, specifically including:

(1) Security and authentication;

(2) Convergence of multiple business data streams;

(3) Device discovery;

(4) Business discovery.

The network layer will mainly consider the network protocol based on ad hoc technology, which should include the following functions:

(1) General network layer functions: construction and maintenance of topological structure, naming and associated services, including addressing, routing and security;
(2) Same as IEEE802.15.4 standard, very power-saving;

(3) It has self-organization and self-maintenance functions to minimize consumer expenses and maintenance costs.

Compared with common wireless communication standards, Zigbee protocol suite is compact and simple, and its specific implementation requirements are very low.

(1) 8-bit processor, such as 80c51;

(2) The protocol suite software requires 32kbytes of ROM;

(3) The minimum protocol suite software is about 4kbytes of ROM;

(4) The network master node needs more RAM to accommodate the device information, data packet forwarding table, device association table, and security-related key storage of all nodes in the network.

2.3 The entire protocol framework

The division of labor in the formulation of standards was jointly formulated by the ZigBee Alliance and the IEEE 802.15.4 task team. The development of the physical layer, MAC layer, data link layer, and data encryption mechanism during transmission was led by IEEE To discuss the development of ZigBee Protocol Stack, and in the future, according to the needs of system customers, we can modify the required application interface for different applications (as shown in Figure 2):

2.4 IPV6 Over 802.15.4

The ZigBee Alliance hopes to establish a wireless network that can connect to every electronic device. It predicts that ZigBee will soon become a global high-end wireless technology, reaching 3 billion nodes by 2007. A network with billions of nodes will quickly exhaust the compressed IPv4 address space, but ZigBee's routing does not depend on IPv6. IPv6 uses a 128-bit address length and can provide addresses almost without restrictions. According to conservative methods, IPv6 can actually allocate more than 1,000 addresses per square meter of the entire earth. In the design process of IPv6, in addition to solving the problem of address shortage once and for all, other problems that are not well solved in IPv4 are also considered, such as end-to-end IP connection, quality of service (QoS), security, multicast, and mobility , Plug and Play, etc. Therefore, the combination of IPV6 and 802.15.4 will be the direction of future research and development. At present, the IETF is also actively drafting Draft for V6over15.4, and its standard will be released soon.

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