Khanh Tuan Le, RFIC system architect, ChipCon
Nov 08, 2005 (1:46 PM)
Wireless Net DesignLine
In a near future, our homes and workplaces will have wireless networks that control and monitor daily tasks autonomously or on command enhancing our comfort and safety. Several of these networks will be based on the ZigBee wireless technology and the underlying IEEE 802.15.4 standard.
IEEE 802.15.4 and ZigBee basics
The IEEE 802.15.4 standard and ZigBee wireless network technology are ideal for the implementation of a wide range of low cost, low power and reliable control and monitoring applications within the private home and industrial environment. The working model of the IEEE 802.15.4 and ZigBee is illustrated in Figure 1.
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1. IEEE 802.15.4 and ZigBee working model.
The IEEE 802.15.4 standard specifies the physical (PHY) and media access control (MAC) layers at the 868MHz (Europe), 915MHz (US) and 2.4GHz (worldwide) ISM bands, enabling regional or global deployment.
The air interface is Direct Sequence Spread Spectrum (DSSS) using BPSK for the 868/915MHz PHY, and O-QPSK for the 2.4GHz PHY. The IEEE 802.15.4 PHY includes receiver energy detection (ED), link quality indication (LQI) and clear channel assessment (CCA).
The IEEE 802.15.4 MAC sublayer controls the access to the radio channel using the CSMA-CA (Carrier Sense Multiple Access with Collision Avoidance) method, and handles network (dis)association and MAC layer security (AES-128 encryption based).
It is also responsible for flow control via acknowledgement and retransmission of data packets, frame validation, and network synchronization as well as support to upper layers for robust link operation.
The ZigBee wireless technology specifies the network, security, and application layers upon the IEEE 802.15.4 PHY and MAC layers. The ZigBee Alliance also provides interoperability and conformance testing specifications.
The ZigBee network layer is responsible for device discovery and network configuration, and supports three networking topologies, i.e. star, mesh (peer-to-peer) and cluster-tree. ZigBee-enabled networks will employ a combination of device types as shown in Figure 2.
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2. Device types in ZigBee networks.
Figure 3 shows the ZigBee network topologies employing these different device types.
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3. ZigBee network topologies.
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