Microwave Engineering Europe - March 2008 - (Page 31)

WIRELESS INFRASTRUCTURE 31 Exceeding the standard for wireless sensor networks ZigBee is just one answer for many practical wireless network applications. Other solutions could be easier-to-implement, more compact and use less power. By Rod Morris, Engineering Manager, ANT, www.thisisant.com ireless Sensor Networks (WSNs) are becoming big business. U.S.-based analyst Harbor Research predicts the number of wireless devices and sensors shipped in 2010 will be almost 200 million, while another U.S. analyst ABI puts the number closer to 300 million. If these forecasts are accurate, there needs to be a truly pervasive networking technology that can form networks consisting of hundreds of nodes (even though at present the overwhelming majority of practical wireless networks comprise no more than ten). These nodes need to be capable of communicating with each other at any time without being compromised by interference from other RF sources. Further, the nodes must be reliable, ultra-low power (because nodes will be typically battery-powered and often hard to access) and low cost to purchase, install and maintain. To meet these requirements, engineers are faced with developing their own WSNs (a difﬁcult and time consuming business) or selecting a turnkey solution. ZigBee is W Figure 1: Mesh networks are overly complex for most practical WSN applications. The ANT develoment kit. perhaps the best known. However, in addition to ZigBee, there are some proven proprietary alternatives. ANT’s Practical Wireless Network protocol, for example, is optimised for the star and peer-to-peer networks typical of most WSNs installed to date. More importantly, ANT is a proven technology used in over a million nodes worldwide and employed by several major consumer electronics manufacturers. Let’s compare these two WSN technologies in more detail. In an attempt to mimic Bluetooth’s success as a short-range wireless standard for Personal Area Networks (PANs) in the consumer electronics sector, the ZigBee Alliance has introduced a de facto standard for WSNs. Marketed as “Wireless Control That Simply Works”, ZigBee is backed by many powerful silicon vendors, is based on the IEEE 802.15.4 standard Physical (PHY) and Media Access Control (MAC) layers and supports the Alliance’s own Network (NWK) and Application (APL) layers. Like many standards-based protocols, ZigBee has extra features that creep into consortia specs in order to keep all contributing parties happy and ensure interoperability. This tends to increase the protocol’s size, lower its efﬁciency and consequently increase power consumption. Moreover, ZigBee’s backers envisaged that it should be a universal solution for complex mesh networks. However, it turns out that complex mesh networking, whereby a node can communicate with several other nodes directly (see ﬁgure 1), introduces a level of intricacy that’s difﬁcult to justify for many practical applications. While of interest to academics, engineers appreciate that mesh networks are difﬁcult to set up and demand lots of computing resource and electrical power. ZigBee’s latest stack, ZigBee Pro, addresses some of these issues, but is yet to be ratiﬁed. In reality, practical networks rarely require nodes to communicate with every neighbor. Indeed, virtually all practical networking problems to date have been solved using a pre-determined networking topology such as Microwave Engineering ● March 2008 ● www.mwee.com 031_032-033_034_MWEE.indd 31 22/02/08 12:07:06 http://www.thisisant.com http://www.mwee.com

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Microwave Engineering Europe - March 2008 News Contents Comment Wireless Infrastructure: A Direct Conversion I/Q Demodulatordrives Favorable Basestation Cost-performance Metrics Wireless Infrastructure: Mobile World Set to Reshape the Internet RF Amplifiers: Latest Advances in RF Amplifiers Include a CMOS PA Operating at 77 GHz and Significant Advances in PAs for WiMAX and Broadband Applications Many Applications Still Require Unique Performance Benefits of BeO ACE Automated Circuit Extraction Returns to Real Design by Exploring Design Alternatives and Changes in Seconds Exceeding the Standard for Wireless Sensor Networks Products Calendar

Microwave Engineering Europe - March 2008

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