Standardization progress and protocol analysis of wireless sensor network

Wireless sensor network has been developing rapidly in recent years as a research field of application.
In key technology research and development, academia from the network protocol, data fusion, test and measurement, operating system, service quality, the node localization, the respect such as time synchronization has carried out extensive research, achieved fruitful results;
The industry is also in the field of environmental monitoring, military target tracking, smart home, automatic meter reading, lighting control, building health monitoring, power line monitoring and other fields.
With the promotion of application, wireless sensor network technology has begun to expose more and more problems.
Equipment of different manufacturers need to implement the interconnection, and want to avoid interference with the current system, so require different chip manufacturer and solution provider, product providers and associated equipment providers to achieve a certain tacit understanding, a concerted effort to achieve goals.
This is the background of the standardization of wireless sensor networks.
In fact, because of the standardization work is related to the economic interests of the parties and even social interests, tend to be paid attention to by the relevant industry, how to coordinate the interests of all parties, agreement, need to have enough understanding and patience.
So far, the standardization of wireless sensor networks has received wide attention from many countries and international standards organizations, and has completed a series of drafts and even standard specifications.
One of the most famous is the IEEE 802.15.4/zigbee specification, which has even been considered by some research and industry figures.
IEEE 802.15.4 defines the physical layer and link layer specification for short-range wireless communication, and zigbee defines network interconnection, transmission and application specification.
Although IEEE802.15.4 and zigbee protocol has been introduced for years, but along with the application of the promotion and the development of industry, its basic agreement cannot fully adapt to the demand, coupled with the agreement only defines the content of network communication, there is no standard protocol for sensor component interface, so it is difficult to carry the dream of wireless sensor network technology and mission;
In addition, the standard is bound to be subject to existing standards in different countries.
To this end, people began to launch more versions of the IEEE 802.15.4/zigbee protocol to adapt to different applications, countries and regions.
Despite its imperfections, IEEE 802.15.4/zigbee is still the best combination for the industry to develop wireless sensor networks.
This article will focus on the IEEE 802.15.4/zigbee protocol specification, and take care of other relevant standards of sensor network technology.
Has a long way, of course, the standardization of wireless sensor network: first, the wireless sensor network is still an emerging field, its research and application were also look very young, industrial demand is unclear;
Secondly, IEEE 802.15/zigbee is not designed for wireless sensor network, and some problems need to be solved in the environment of wireless sensor network.
In addition, the international standardization of wireless sensor network technology has just begun, and the standardization working group in China has just been established.
To this end, we should prepare well for the smooth completion of standardization work.
1. PHY/MAC standards
The underlying standards of wireless sensor networks are generally used in the relevant standard parts of the wireless domain network (IEEE 802.15).
The emergence of the Wireless Personal Area Network (WPAN) is earlier than the sensor Network, which is often defined as a Wireless, short-range, dedicated Network that provides an interconnection between Personal and consumer electronics.
Zigbee focuses on portable mobile devices (such as personal computers and peripherals, consumer electronics devices such as PDA, mobile phones, digital products) two-way communication between technical issues, the typical coverage generally within 10 meters.
IEEE 802.15 working group is to complete the mission and dedicated, and has completed a series of related standards, including the bottom of the standard IEEE 802.15.4 is widely used in sensor networks.
(1) IEEE 802.15.4b specification
The IEEE 802.15.4 standard is mainly aimed at Low-Rate Wireless Personal Area Network (lr-wpan).
The standard of low energy consumption, low transmission rate, low cost as the key target (which, and wireless sensor networks), aimed at individuals or families within the scope of low speed interconnection between different devices to provide a unified interface.
Defined by IEEE 802.15.4 LR - the characteristics of WPAN network and wireless sensor network for communications within the cluster has many similarities, many research institutions put it as a physical sensor network node and link layer communication standards.
The IEEE 802.15.4 standard defines the physical layer and the media access control sublayer, which conforms to the open system interconnection model (OSI).
The physical layer includes the radio frequency transceiver and the underlying control module, and the media access control sub-layer provides the service interface to access the physical channel at the top level.
Figure 1 shows the relationship between IEEE 802.15.4 layer and layer and the protocol architecture of IEEE 802.15.4/ zigbee.

IEEE 802.15.4 in the physical (PHY) layer design for lower cost and higher level of integration requirements, the working frequency is divided into 868 MHZ, 915 MHZ and 2.4 GHz three, can use the spectrum channel respectively 1, 10, 16, each 20 KB/s, 40 KB/s and the 250 KB/s transmission rate, its transmission range between 10 meters to 100 meters.
Due to the specification to use three frequency bands are the international Telecommunication union Telecommunication Standardization group (ITUT, ITU Telecommunication Standardization Sector), which is used in the definition of Scientific research and Medical treatment of ISM (Industrial Scientific and Medical) open band, all kinds of wireless communication system widely used.
In order to reduce intersystem interference, the protocol specifies that Direct Sequence Spread Spectrum (DSSS, Direct Sequence Spread Spectrum) coding technology is adopted in each frequency band.
Compared with other digital coding methods, direct sequence spread spectrum technology can simplify the design of analog circuit of physical layer, and it has higher fault tolerant performance and suitable for low-end system implementation.
IEEE 802.15.4 defines two access modes in the media access control layer.
One is Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA).
This approach refers to the DCF model defined by the IEEE802.11 standard in the Wireless LAN (WLAN), which can easily coexist with the channel level of Wireless LAN (WLAN, Wireless LAN).
The so-called CSMA/CA is before transmission, whether there is a co-channel (co-channel) carrier in the medium, if it does not exist, it means that the channel is idle and will enter the data transmission state directly.
If the carrier is present, the channel will be re-detected after a period of random withdrawal.
This dielectric access control scheme simplifies the process of implementing Ad Hoc network applications, but causes problems for improving bandwidth utilization in the application of large traffic.
At the same time, because there is no power consumption management design, it is necessary to do more work to realize the low power network application based on sleep mechanism.
IEEE 802.15.4 definition of a different kind of communication mode is similar to 802.11 standard definition of PCF mode, through the use of synchronous mechanism of super frame to improve channel utilization, and through the definition in a super frame dormancy period, it is easy to achieve low power consumption control.
The PCF model defines two devices: full-function Device, FFD, and reduction-function Device (RFD).
The FFD device supports all 49 basic parameters, while the RFD device only requires that it support 38 basic parameters when minimum configuration.
In PCF mode, the FFD device is used as the coordinator to control the synchronization of all associated RFD devices, the data transceiver process, and can communicate with any device in the network.
The RFD device can only communicate with the FFD devices associated with it.
In PCF mode, an IEEE 802.15.4 network has at least one FFD equipment as the network Coordinator (PAN Coordinator), to play the role of a network master controller, take between clusters and cluster synchronization, packet forwarding, networking, members of management, and other tasks.
IEEE 802.15.4 standard supports star and point-to-point two network topologies, with 16 and 64-bit address formats.
The 64-bit addresses are the world's only extension addresses, and the 16-bit addresses are used for small network builds, or as the identification addresses for cluster devices.
IEEE 802.15.4 standard b has multiple variants, including the low speed ultra-wideband IEEE 802.15.4 a, and recently China is promoting the IEEE 802.15.4 c and IEEE 802.15.4 e, and Japan's main push IEEE 802.15.4 d, it is not discussed here.
(2) Bluetooth technology
In May 1998, the working group on the IEEE 802.15 zigbee founded soon, five world famous IT companies: Ericsson (Ericsson), IBM, Intel (Intel), Nokia (Nokia) and Toshiba (Toshiba) jointly announced a called "Bluetooth (Bluetooth)" development plan.
In July 1999, the bluetooth working group launched the bluetooth protocol version 1.0, which was updated in 2001 to version 1.1, known as the IEEE 802.15.1 protocol.
The agreement aims to design general wireless Air Interface (Radio Air Interface) and its software of international standard, make the communications and computer further combination, make different manufacturer production of portable equipment is realized in the absence of cable at close range in the ability of communication.
Plans were released, get the including Motorola (Motorola), Lucent (Lucent), Compaq (Compaq), Siemens (Simens), 3 com, TDK, and big companies such as Microsoft (Microsoft) wide support nearly 2000 companies and adoption.
The bluetooth technology is also working on 2.4 GHz ISM frequency band, fast frequency hopping and short package technology to reduce the same frequency interference, guarantee the physical transmission reliability and safety, have certain ability of network, support 64 KBPS real-time voice.
, becoming increasingly prevalent in bluetooth technology, the related products on the market are also increasing, but with the ultra broadband technology, the emergence of wireless local area network (LAN) and zigbee technology, especially its security, price, power consumption and so on the emerging problems, its competitive advantage began to decline.
In 2004, the bluetooth working group released version 2.0, which tripled the bandwidth and reduced the power consumption by half, restoring confidence in the industry to a certain extent.
Because bluetooth technology and zigbee technology have some common features, they are often used in wireless sensor networks.
2. Other wireless network standards
The wireless sensor network is to construct a complete network from the physical layer to the application layer, and the wireless domain network standard sets the specification for the physical layer and the media access control layer in advance.
In addition to the previously discussed IEEE 802.15.4 and bluetooth technology, zigbee technology solutions include: the ultra wideband (UWB) technology, infrared (IrDA) technology, household (HomeRF) of the radio frequency technology and so on, their common characteristic is short, low power consumption, low cost, personality, etc., they are in different application scenarios used in the underlying protocol of wireless sensor network (WSN), a simple introduction is as follows:
(1) ultra broadband (UWB) technology
UWB (Ultra Wide - Band, UWB) technology originated in the late 1950 s, is a use of broadband radio signals from a few Hz to several GHz technology, through the pulse emitter is short, and reflected signal receiving and analysis, information can be detected object.
UWB because USES the extremely high bandwidth, so its power spectral density is very flat, shown as at any frequency points of the output power is very small, even lower than ordinary equipment radiation noise, so it has good anti-interference and safety.
Ultra-wideband technology was originally used primarily as a military technology in radar detection and positioning applications, and the FCC granted the technology access to civilian applications in February 2002.
In addition to the low power consumption, ultra-wideband technology can easily reach more than 100Mbps and its second generation of products can reach more than 500 MBPS. This single index alone will leave many other technologies behind.
The standard debate around the UWB has been intense from the beginning, with Freescale's ds-uwb and the MBOA promoted by TI emerging from the top, and domestic research in this area has been very popular in recent years.
Due to its low power consumption, high bandwidth, strong anti-jamming capability, uwb technology has fantastic prospects for development, but has not listed ultra-wideband chip product, it leaves us a big regret.
In recent years, there have been reports of related products, but this deeply rooted technology needs to be promoted by the whole industry.
At present, ultra-wideband technology can be seen as an early stage, believing that it is a late, old and strong type, and it will make great use in wireless sensor network applications.