The Zigbee specification is built on the IEEE standard 802.15.4. Zigbee was created for applications that require low cost and low power, but with the need for a large degree of flexibility. The Zigbee specification was created by the Zigbee Alliance, which is supported by over 200 companies. The goal of the Alliance was to create a standards based protocol that allowed consumers to have access the low cost, low power and highly flexible wireless technology.
2. Strengths and Weaknesses
• Low Cost
• Low Power Consumption
• Flexible Network Architecture
• Support from Many Companies
• Large Number of Nodes (65k)
• Single Point of Failure (Zigbee Coordinator)
• Low Data Rates
• Lack of fully developed devices
3. Technical Specifications
Physical and MAC Specifications
|Frequency||2.4 GHz||915 MHz||868 MHz|
|Data Rate||250 kb/s||40 kb/s||20 kb/s|
Range: 10 - 75 meters (depending on the environment)
Radio Power Requirements: 1mW to 100mW
Modulation Tech: DSSS and CSMA/CA
The Zigbee network layer allows for 3 device types: the Zigbee Coordinator (ZC), the Zigbee Router (ZR) and the Zigbee End Device (ZED).
Zigbee Coordinator: There is only one ZC in any given Zigbee network and its main function is to initiate the network formation by configuring the Channels, PAN ID and Stack Profile).
Zigbee Router: The ZR is an optional network component whose main function is to participate in multi-hop / mesh routing of network messages. It maintains a routing table and manages local address allocation / de-allocation for its assigned ZED’s.
Zigbee End Device: The ZED is also an optional network component who does not participate in routing. It can be optimized for low power operation by taking advantages of sniff and sleep techniques.
For a ZED or ZR to join a network it first selects the highest quality association, based on link quality. It is then given an address on the network and completes authentication using the Zigbee security keys.
Routing: When a request is sent through a router who does not have an entry in its routing table the router will issue a route request, which is broadcast throughout the network. When the destination receives the route request it will then reply with the path that has the lowest “cost” or how many hops it took to reach the destination.
The base for the Zigbee security architecture is the use of 128 bit security keys throughout the network. The keys are distributed from a Zigbee “Trust Center”. The distribution of keys from the Trust Center is one of the most important security elements in the network.
The Trust Center allows outside devices to join the network and distributes new keys. In most networks the Trust Center is assumed to be the ZC, but other devices in the network can be configured to perform the functions of a Trust Center.
The Trust Center has two modes of operations: residential and commercial mode.
In residential mode the Trust Center allows other devices to join the network but does not maintain keys for the new devices. This is great for small applications where memory is a factor.
In commercial mode the Trust Center maintains keys for every network device, which allows the Trust Center to control and update keys in a centralized fashion. In this mode the memory cost does increase based on network size.
ZigBee is built on top of the physical layer and medium access control (MAC layer) defined in the IEEE standard 802.15.4 (2003 version) for low-rate WPAN's. The Zigbee specification then adds to the standard four main components: network layer, application layer, ZigBee device objects (ZDO's) and user-defined application objects which allows for customization and flexibility within the standard.
In addition to integrating two high-level network layers to the underlying structure, the most significant addition is the introduction of Zigbee Device Objects (ZDO's). ZDO’s are responsible for multiple tasks, which include defining device roles, management of requests to join a network, device discovery and security.
By nature, ZigBee is a “mesh network” architecture. In addition to the mesh topology the network layer supports two other types of topologies: star and tree. Every network must have one Zigbee Coordinator device, tasked with its creation, the control of its parameters and basic maintenance. Within star networks, the ZC is the central node. Both tree and mesh networks allow the use of ZigBee Routers to extend communication at the network layer.
Zigbee can be configured as a beacon or a non-beacon enabled network. In a non-beacon network, CSMA/CA is used, and the Zigbee Routers are continuously active. This allows other Zigbee devices to only transmit when an external stimulus is received from a Zigbee Router. The other type is a beacon enabled network. In this configuration the Zigbee routers send periodic beacons to confirm their existence to the rest of the nodes. In between beacons nodes can sleep, which allows for extended battery life. As a result of this the network requires precise timing for transmitting and receiving. This requires more complex devices which can drive up costs.
• Industrial Control and Monitoring
• Environmental and Health Monitoring
• Home Automation, Entertainment and Toys
• Security, Location and Asset Tracking
• Emergency and Disaster Response
• Military/Battlefield Applications
6. Case Studies
|Resolving ZigBee IEEE 802.15.4 PHY Layer Test Challenges Using a WPAN Test Suite Based on NI LabVIEW and RF PXI Instruments|
|Developing an automated PXI-based Zigbee WPAN compliance test suite using National Instruments PXI-5660 RF signal analyzer and PXI-5670 RF signal generator in NI LabVIEW.|
|Accelerating ZigBee and 802.15.4 Module Testing with National Instruments LabVIEW and the NI RF Vector Signal Analyzer|
|Improving throughput, repeatability, and accuracy in the current production test environment at MaxStream using the National Instruments PXI-5660 vector signal analyzer and NI LabVIEW for ZigBee/802.15.4 and proprietary radio RF production test.|
|ZigBee cRIO module By GEOPROTEK TECH INC.|
|GEOPROTEK adopted Wireless Communication Protocol of IEEE 802.15.4 to develop small and portable integrated ZigBee cRIO Module to perform digit and analog signal data acquisition.|