The hottest new wireless network communication tec

A new wireless network communication technology ZigBee

Introduction

for embedded system applications, it is often necessary to communicate with each other to exchange measurement data and control instructions. At present, most of the methods used are wired connection, including point-to-point or bus methods, such as RS485, can, MODBUS, etc. With the development of wireless network communication technology, wireless communication technology has its place in some occasions that are not convenient or need to eliminate wired connections

at present, many companies in the market have launched RF chip products applied to short-range communication, such as nRF24E1 (Nordic) working at 2.4GHz, cc1020/2500 (Chipcon), max7044/7033 (Maxim) working at 300 ~ 450MHz, etc. Many embedded applications also use this kind of technology, but most of them only provide RF channels to solve wireless communication, and there is no standard specification (or their own special standard) to formulate the communication protocols of MAC layer, link layer and network layer, so they are not compatible; The control software for communication completely depends on the design of the target system and is completed by the user himself, which not only increases the workload, but also reduces the reliability and efficiency of coding, and is more likely to have problems in group application; The products of different manufacturers do not have interoperability and versatility

zigbee is a wireless network communication technology standard rising in recent years. It has appeared for a short time. At the end of 2004, ZigBee alliance released version 1.0 specification, which has not yet entered large-scale commercial production and application; However, its rising momentum is very obvious. Chipcon, Freescale, compxs and ember have passed the test and compatibility verification of their products by ZigBee alliance in April this year. It is expected that since 2006, wireless communication products and applications based on ZigBee will be popularized and developed rapidly

1 ZigBee technology and application

1.1 main technical features

zigbee comes from the honey group. When finding the location of pollen, it tells its partners by dancing zigzag dance, so as to achieve the purpose of exchanging information. It can be said that a small animal realizes "wireless" communication through a simple way. People call it a short-range communication technology that focuses on low power consumption, low cost, low complexity and low rate, because it is strong enough to eliminate the load limitation of bridge users, and it also contains implication

ZigBee technology is not a completely unique and brand-new standard. Its physical layer, MAC layer and link layer adopt IEEE802.15.4 (wireless personal area) protocol standard, but on this basis, it has been improved and expanded. Its network layer, application convergence layer and high-level application specification (API) are formulated by ZigBee alliance. The entire protocol architecture is shown in Figure 1

zigbee is based on independent working nodes and forms star shaped, sheet-shaped or shaped networks through wireless communication. Therefore, the functions of each node are not the same. In order to reduce costs, most of the nodes in the system are sub nodes. From the perspective of group communication, it is only a subset of its functions, which is called reduced function equipment; In addition, there are some nodes that are responsible for communicating with the controlled child nodes, collecting data and issuing control, or playing the role of communication routing, which are called full-function devices (also known as coordinators), as shown in Figure 2

zigbee has outstanding characteristics, especially in low power consumption and low cost, mainly in the following aspects:

① low power consumption. In the low power standby mode, two No. 5 dry batteries can support one node to work for 6 to 24 months, or even longer. This is the outstanding advantage of ZigBee. In contrast, Bluetooth can work for weeks and WiFi can work for hours

② low cost. By greatly simplifying the protocol (less than 1/1 of Bluetooth, both the experimental belt and the transmission belt slip 0 during the experimental process), the requirements for the communication controller are reduced. According to the prediction analysis, based on the 8-bit microcontroller of 8051, the full-function master node needs 32KB code, and the sub function node needs as little as 4KB code, and ZigBee is free of protocol patent fees

③ low speed rate. ZigBee works at a low rate of 20 ~ 250kbps, providing raw data throughput of 250kbps (2.4GHz), 40kbps (915MHz) and 20kbps (868mhz) respectively, meeting the application requirements of low-speed data transmission

④ close range. The transmission range is generally between 10 ~ 100m. After increasing the RF transmission power, it can also be increased to 1 ~ 3km. This refers to the distance between adjacent nodes. If the relay of routing and communication between nodes, the transmission distance will be longer

⑤ short delay. ZigBee's response speed is fast. Generally, it takes only 15ms from sleep to work, and only 30ms for nodes to connect into the network, which further saves power. Compared with Bluetooth, it takes 3 ~ 10s, and WiFi takes 3S

⑥ high capacity. ZigBee can adopt star, sheet and shape network structures. One master node manages several sub nodes, and at most one master node can manage 254 sub nodes; At the same time, the master node can also be managed by the upper network node; Up to 65000 nodes can be formed

⑦ high safety. 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 the use of symmetric passwords of the advanced encryption standard (AES-128) to flexibly determine its security attributes

⑧ license free frequency band. Direct sequence spread spectrum is used in the industrial scientific medical (ISM) band. 2.4GHz (global), 915MHz (US) and 868mhz (Europe)

1.2 ZigBee product application

zigbee is mainly used between various electronic devices with short distance, low power consumption and low transmission rate. Typical transmission data types include periodic data, intermittent data and low reaction time data. According to the assumption, its application goals are mainly: industrial control (such as automatic control equipment, wireless sensor network), medical care (such as monitoring and sensing), home intelligent control (such as lighting, water and electricity measurement and alarm), remote control device of consumer electronic equipment, wireless connection of PC peripherals and other fields

generally speaking, the application occasions that meet the following characteristics are the places where ZigBee applications have great advantages:

① low-cost devices that need wireless communication to exchange information

② the exchange volume of data is small and the transmission rate is not high

③ the power consumption requirement is extremely low, and battery power supply is used and needs to be maintained for a long time

④ occasions that require multiple (especially a large number) devices to form a wireless communication network, mainly for monitoring and control

according to the basic assumption of ZigBee's alliance and the major manufacturers participating in the alliance, the product should provide a one-stop solution to facilitate application, so that those who are not familiar with RF technology can get started quickly. Therefore, its products not only provide RF wireless channel solutions, but also its built-in protocol stack has completely realized ZigBee's communication, group and other wireless communication work by products. Users only need to program application software according to the standard interface provided by the protocol. Due to the simplification of the protocol stack, the embedded processor that completes the ZigBee protocol can generally use 8-bit MCU with low cost and low power consumption

the highly integrated system launched by Chipcon "therefore, it also meets the requirements of many automotive applications, such as automotive internal parts. As shown in Figure 3, the class RF transceiver CC2430 integrates RF front-end, 128KB flash memory, 8kbram and 8051 eight bit MCU core; in addition, it also integrates analog-to-digital converter (ADC) , timer, AES-128 coprocessor, watchdog, 32kHz crystal oscillator sleep timer, power on reset and power off detection circuit, and 21 programmable i/o pins; This wide product is a SoC with ZigBee function, which can be used in various ZigBee wireless network nodes, including coordinators, routers, terminal devices, etc

in addition, many manufacturers have also launched ZigBee products and a full range of solutions. For example, the low-power 2.45GHz integrated RF device mc13192 released by Freescale company includes 802.15.4 physical layer, supports star and shape networks, and implements ZigBee protocol stack on a supporting MCU; The transmission rate is 250kbps. It adopts quadrature QPSK modulation and direct sequence spread spectrum coding, and communicates with MCU through a four wire serial interface. The IP link 1200 ZigBee development tools and products launched by Helicomm company include 2.4GHz RF components conforming to 802.15.4 standard, low-power 8-bit microcontroller, ZigBee network software and full wavelength antenna. Each relay communication can provide a rate of 250kbps within 75m; It supports the latest RS232 mesh transparent serial mode, and can support serial data routing in shape and multi hop infinite networks, with a maximum rate of 38.4kbps

it can be seen that some internationally renowned semiconductor manufacturers have actively launched ZigBee products, which is expected to greatly expand the application of ZigBee products through commercialization in the future. At the same time, some RF manufacturers are developing their own proprietary products, such as zensys, which actively promotes its Z-Wave wireless protocol, especially in the field of home automation; In addition, dust insists on using its own technology; Although ember has entered the ZigBee field on a large scale, it also plans to continue to provide its own proprietary embernet technology. It can be said that the application of ZigBee is not a smooth road, which requires the continuous efforts of ZigBee alliance and manufacturers and the wide recognition of the market

2 comparison with other wireless communication technologies

at present, the short-range wireless communication technologies in the market mainly include wireless local WiFi, Bluetooth and some special standards (such as ad hoc, etc.). 1. Conscientiously implement social responsibility. In order to expand the market and application fields, some large companies are also actively studying and formulating some new wireless group communication technology standards, Such as wireless (USB, UWB, WiMAX, etc., these technologies are briefly introduced and compared below.

the development of Bluetooth technology has experienced many years since 1999, and has been plagued by problems such as high chip price, insufficient manufacturer support, limited transmission distance and poor anti-interference ability. At present, it is mainly used in wireless headphones and other fields that do not need very high transmission bandwidth, and there are also problems in interoperability.

WiFi in With the strong support of Intel, it quickly occupied the market with Centrino processors; IEEE802.11b standard is adopted, 2.4GHz direct sequence spread spectrum is used, the maximum data transmission rate is 11Mbps, and the transmission rate can be adjusted to 5.5mbps, 2Mbps and 1Mbps bandwidth according to the signal strength; When using the latest 802.11g, the rate can reach 54Mbps, which is the most widely used wireless network transmission protocol at present

with the wide application of USB in PC, wireless USB has also been promoted by Intel, HP, Microsoft and other major companies in the PC field, and has recently formulated the wireless USB specification. Using the MB-OFDM UWB Mac and PHY layers of Wimedia alliance, the communication distance is 3 ~ 10m, and the maximum rate is 480mbps. It is expected to be widely used in the wireless connection of PC peripheral devices in the short term

uwb is a short-range broadband wireless transmission technology in the future. Because it does not use the carrier modulation technology in common wireless transceiver, it does not need mixing, filtering and RF/if conversion modules, and realizes low cost, low power consumption and high bandwidth performance. At present, there are two technical camps competing for technical standards. The expected communication distance is 5 ~ 10m, and the rate can even be as high as 1Gbps, which is very suitable for high-capacity data transmission between household consumer electronics products

as the next generation of WiFi technology, WiMAX is conceived as a wireless metropolitan area access technology, which outperforms WiFi in transmission distance and speed, with a maximum access rate of 70mbps