Wireless sensor network coordinator of the research and design (1)

1 Overview

Wireless communication with a variety of ways, and Bluetooth, Wi-Fi, GSM mobile communication system, developed by the ZigBee ZigBee Alliance with low power consumption mode, data transmission reliability, compatibility, and achieve low costs and benefits of networking easy for low bit rate transmission of wireless sensor networks.

ZigBee Alliance was founded in 2001, 2002, Invensys company, Mitsubishi Electric, Motorola and Philips Semiconductor company franchise, now is growing rapidly. The Union based on the IEEE 802.15.4 PHY layer, MAC layer and data link layer, research and development for wireless sensor network layer protocols for the other.

Physical layer 2 standard is 2.4 GHz and 868/915 MHz, are based on direct sequence spread spectrum DSSS (Direct Sequence Spread Spec-trum) technology, use the same physical layer packet format.

2.4 GHz band for global unity does not need to apply for ISM band, contribute to the promotion of ZigBee devices and lower production costs. Its physical layer by using high-order 16-phase modulation technology to provide 250 kb/s transmission rate, help to achieve higher throughput and smaller communication delays and more short work cycle, thus more power.

ZigBee Alliance defines two physical device type: full-featured devices FFD (Full Function Device) and the concise functional device RFD (Re-duced Function Device).

ZigBee network star topology is typically used by some one FFD and RFD. FFD acts as a network coordinator, additional device simply communicate with the Coordinator, the Coordinator has decided to deal with things to do. If a terminal equipment needed to transmit data to another terminal equipment, it will send the data sent to the Coordinator, and then by the Coordinator will forward the data to the destination receiver terminal equipment. Delivered through the FFD relay, network and can be extended into other topologies, as shown in Figure 1.

Research and development with ZigBee, 2005, all major chip manufacturers have introduced in line with the ZigBee standard transceiver modules and communication suite, but at present, only Norway Chip-con company (CC2420/CC2430 and CC2500/CC2550, etc), Freescale Semiconductor company United States (MC13192 and MC13193), United States CompXs company (ML7065) and United States Ember Corporation (EM2420) four original equipment manufacturer (OEM) ZigBee kits meet Alliance standards.

2007 Texas instruments (TI) announced the launch of ZigBee protocol stack (Z-Stack) free download version.

2 design and debug

2.1 research objectives

Network Coordinator's primary function is to coordinate the establishment of networks, other features also include: transport network beacon, manage network nodes and storage network node information, and providing the associated node routing information between; in addition, network coordinator to store some basic information, such as node data equipment, data forwarding and equipment such as the associated table.

The question is, at present, the ZigBee protocol primarily at the low end of the 8-bit or 16-bit MCU.

For network coordinator node, the data processing is not strong, and limited to its own hardware resources, rarely achieve good human-computer interaction interface. On the feature request high ZigBee Coordinator, this framework is very difficult to meet application requirements. While the PC based node network coordinator, not only bulky, high prices and low power consumption, and for transfer of sensor networks are a waste of resources, the development of the embedded chip based on arm series as the core microprocessor network coordinator is very necessary. Experimental structure based on a star, in the realization of the RFD features, on the basis of the ARM9-based embedded network coordinator, provides 3.5 TFTLCD touch screen and man-machine interaction, show the work of other nodes, test parameters, to provide a platform for future advanced application.

2.2 Coordinator hardware structure

The design of RF chip select Norway Chipcon company CC2420 (2.4 GHz, support 250 kb/s data transfer rate).

Microprocessor with embedded industrial chip S3C2440. Hardware diagram as shown in Figure 2, ARM (left) + RFD (right) = ARM embedded network coordinator.

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