Standard to address precise locationing

Ultrawideband is a radio communications technique (with recent Federal Communications Commission unlicensed-spectrum allocation) that may be applied to all manner of communications systems, just as narrowband, carrier-based or spread-spectrum techniques may be used for any type of system. In all cases, there will be some classes of systems that are better-suited to the characteristics of one transmission technique or another. The trick is to find out which classes of applications are particularly well-suited to a given technology.

If ultrawideband (UWB) techniques are compared with existing, established standards, then two particularly interesting areas can be identified. One is very short-range, very high-data-rate systems (as are being standardized in 802.15.3a). The other is longer-range/lower-power, low-data-rate systems. In general, data rate and range can be traded using processing gain.

In November 2002, the IEEE started an activity to investigate "the other end of the UWB spectrum, that being for low-data-rate applications." These low-data-rate systems are the domain of 802.15.4, which is an established, IEEE-published standard adopted by the Zigbee Alliance. Products have already begun shipping for wireless sensor and control applications (www.zigbee.org).

More recently however, the IEEE Study Group 802.15.4a was formed to work on a potential alternative physical-layer (PHY) specification to the 868- and 915-MHz and 2.4-GHz PHYs that have already been defined in the 802.15.4 specification. The new PHY is intended to bring enhancements in features, performance and range to address evolutionary applications.

IEEE begins work

Currently, the focus is on precision-location functions, identified as a key addition to 802.15.4 capabilities, as well as improved nonline-of-sight performance. That said, it must be emphasized that Study Group 802.15.4a is just beginning its work and according to the IEEE standards process must first gain approval to create a task group before starting evaluations of specific PHY technologies. UWB is clearly going to be an important candidate, however, since it readily offers the precision-location capabilities that have already been identified as evolutionary requirements.

For UWB systems, position may be derived from time-of-flight calculations from a device to fixed reference points. The resolution of the position estimate is limited by the width of the intersecting curves, which is in turn a function of the uncertainty in time of arrival of the signal at the reference points. Various mechanisms can be used to provide small uncertainty in this parameter.

Time uncertainty in a system using very short pulses will be proportional to the width of the pulse (a 1-nanosecond pulse is equivalent to approximately 1 foot uncertainty, since this is the distance electromagnetic radiation travels in free space in 1 ns).

UWB signals occupying approximately 2 GHz of spectrum would be short enough for good positioning resolution. Again, a variety of technologies, aside from UWB, may well be proposed. The IEEE open technical-debate procedure will be used to select which technology will form the basis of a future 802.15.4a PHY.

Study Group 802.15.4a has spent the last six months hearing applications and requirements, and the project time line now calls for drafting documents that reflect the technical requirements and selection criteria of the applications presented. Assuming that interest and market motivation continue to build, it is expected that an official task group will be formed next May and it is likely a standard could be ratified by mid- to late 2005.

About the applicants

At the time of this writing, 14 companies representing consumer electronics vendors, systems integrators, semiconductor and technology companies, and two nonprofit organizations have proposed applications to Study Group 802.15.4a.

Specifically, Samsung Electronics and Staccato Communications presented "smart home" applications that encompass a high density of wireless-network controllers, sensors and actuator nodes for environmental control, energy management, security and identification, and emergency monitoring and safety.

These applications are similar to industrial and medical applications presented by Texas Instruments, ST-Microelectronics and General Atomics. Finally, a third set of applications presented by both commercial and public-interest groups, such as the city of Chicago's Office of Emergency Management, require precision location for people tracking, to prevent child abductions and to assist trapped firefighters.

Visit the official IEEE Web page at www.ieee802.org/15/pub/SG4a.html for more information.

Larry Taylor (larry@staccatocommunications.com) is system architect at Staccato Communications Inc. (San Diego) and chairman of IEEE 802.15.4SGa. Jason Ellis (jason@staccatocommunications.com) is manager of marketing and business development at Staccato and vice chair of 802.15.4SGa.

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