For any communications technology to be widely deployed, it must be cost-effective and highly reliable. Two new global wireless standards, IEEE 802.15.4 and ZigBee™, promise to deliver the high reliability and low price points necessary to achieve volume deployment worldwide across a wide range of power devices in commercial markets.

IEEE 802.15.4 - A Standard Hardware Platform

Ratified in May 2003, IEEE 802.15.4 is the first wireless standard designed specifically to address the unique needs of a variety of industries. IEEE 802.15.4 is a simple but powerful packet data protocol that provides high reliability through acknowledgement, error checking, prioritized communications, direct sequence spread spectrum, the ability to change frequencies to avoid interference, and user-selectable security levels. IEEE 802.15.4 specifies the physical (PHY) and media access control (MAC) layers, and defines three license-free frequency bands, including 2.4 GHz, 915 MHz, and 868 MHz, making it a truly global standard.

ZigBee -- A Standard Software Platform

The ZigBee Alliance (www.zigbee.org), a global nonprofit consortium of over 50 industry leaders, is defining the Network, Security, and Application layers that reside above the IEEE 802.15.4 PHY and MAC layers. The result of this cooperative effort is a well-integrated, standards-based wireless network platform designed to meet the unique needs of wireless monitoring and control applications.

The ZigBee Alliance is defining multiple network layer topologies, including star, mesh, and cluster-tree (a hybrid star/mesh), key management for AES encryption, and application profiles to provide interoperability among a variety of applications. The IEEE 802.15.4 and ZigBee standards thus form a solid networking foundation to enable reliable and secure wireless communications in power sources that could be sold and installed anywhere in the world.

IEEE 802.15.4 & ZigBee Key Features:

• 2.4 GHz, 915 MHz, 868 MHz frequencies supported.


• High data reliability and network scalability.


• Data throughput of up to 250 KB/s.


• 128-, 64- or 32-bit AES encryption.


• Star, mesh, or hybrid network topologies.


• Interoperability via ZigBee Application Profiles.

Wireless Network Topologies

The logical shape of a network -- its topology -- determines how different nodes in a network are logically connected to each other and how they communicate. Network topologies include star, mesh, and hybrid architectures. Each has its own strengths for various applications.

Star topologies work well for relatively simple or low-power applications. In a star topology, all wireless nodes are connected to a network coordinator or gateway. When physical obstructions or strong RF interference blocks communication, the normal fix is to move the affected node, which is not an acceptable solution for most applications.

Mesh networks utilize a decentralized, multi-hop architecture in which each node is in direct communication with its immediate neighbors. Mesh topologies can provide an extended coverage area by relaying information from node to node. If a single node fails for any reason -- including the introduction of strong RF interference -- messages can be automatically routed along alternate paths. Optimal path selection is usually set by measured signal strength between any two nodes, and the cumulative number of hops required to transmit a message from one node to another. Mesh topologies can provide the industrial-strength reliability required by a variety of building and design applications.

A hybrid cluster-tree configuration combines the power of a mesh topology with the simplicity of a star topology to form a reliable, scalable, and cost-effective wireless network. This is frequently the best solution for low-data-rate applications that require both long battery life at the node and high network reliability. Battery-powered sensors on a single floor of a commercial building could be linked in a star topology to line-powered wireless appliances on each floor, which could then be linked in a mesh topology.

Summary

The emergence of global wireless standards for nonresidential buildings has fundamentally altered the industry landscape, accelerating the demand for wireless monitoring and control applications worldwide. Helicomm is working to integrate IEEE 802.15.4 and ZigBee wireless communications into a wide range of products. These wireless standards will minimize manufacturer risk, differentiate commodity products, enhance product value, and increase customer satisfaction.