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UWB by definition is any RF technology that uses a bandwidth in excess of 500MHz or deviation greater than 25 percent of the center frequency. UWB technology was and continues to be used for impulse applications such as ground-penetrating radar and systems used by military and law enforcement to see behind walls. In the WPAN world, UWB forms the basis for the Wimedia specification.
While Wimedia is also intended to operate in a limited range, think of it as Bluetooth on steroids. Most notably it can operate legally in certain portions of the 3.1GHz to 10.6GHz range, permitting it to offer high bandwidths without the interference issues typical of the more crowded 2GHz spectrum. It is also compatible with current and emerging mobile telephony standards such as Wimax. Because of its ability to transfer data at speeds in excess of current Ethernet networks, but also support voice, video and data, Wimedia could ultimately replace Bluetooth.
Zigbee was born from a later addition to the 802.15 Bluetooth specification called 802.15.4, which created a specification for a low data rate, low power consumption and a more secure network device. In 2004, the Zigbee alliance, a group of over 100 companies, ratified the Zigbee 1.0 specification. While compatible with the former IEEE specification, it improves the functionality associated with applications such as industrial control systems, building/home automation and medical data collection.
Like Bluetooth, it operates in the ISM 2GHz band, but requires significantly less overhead in terms of software code requirements to create an application, hence a savings in power consumption and simpler implementation.
The Zigbee specification supports operation in one of three modes:
- Router works similar to traditional Ethernet routers providing connections based on source destination requirements of the respective devices.
- Zigbee Coordinator is required to form a Zigbee network. The coordinator could be viewed as similar to the Domain Name Server (DNS) in a large network, storing information about the other devices of the network.
- Zigbee End Device is the simplest device on a Zigbee network. It can only communicate to a coordinator or a router, however it can not pass data through. This is used where a simple, inexpensive point-to-point connection is all you need.
Other WPAN technologies
WPAN devices are not limited to various black-boxes. A German company called Ident Technologies has developed a technology called Skinplex, which permits the transmission of data using the human body as a medium. Basically, a person carries a device that uses his skin as the antenna. When he is in close proximity to a receiver, communications can be reliably achieved. One of the current applications for this technology is secure access to buildings, automobiles or other situations that require verification. The system operates at low data rates on a frequency of 195kHz. This is similar to the RFID systems found in most retail stores.
WPANs might present some interesting applications in a broadcast facility. Imagine a studio of WPAN-enabled devices where there are no wires, and where equipment could be moved from studio to studio without rewiring.
McNamara is president of Applied Wireless, Cape Coral, FL.
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