Ultra-wideband technology to offer new opportunities for wireless video, networking - Video

Computer Technology Review, Feb, 2002 by John Santhoff

This article is the first in a two-part series.

Recently, there has been considerable discussion about new wireless technologies and standards that support throughput speeds in the tens-of-megabits per second. Such technologies, proponents claim, are fast enough to stream video wirelessly and robust enough to, in theory, replace or considerably expand today's wired networks. However, many of the wireless networking solutions proposed, in development, or nearing commercial viability are carrier-based technologies that have severe limitations.

A new solution, Ultra-Wideband (UWB), is a wireless communications technology fundamentally different from all other radio frequency communications. In 1998, the FCC recognized the significance of UWB technology and began the process of regulatory review. In May of 2000, the FCC issued a notice of Proposed Rulemaking, accepting comments through the current period Throughout 2001, comments and review from the FCC, NTIA, Department of Commerce, and DOD were received. The formal rule change is expected sometime early this year. Pot-ential UWB applications will be dependent on the spectrum and signal levels that are permitted by the new roles.

Ultra-Wideband technology has a history going back to Marconi and his original spark gap transmitters. The United States military re-invented it under a cloak of secrecy and black projects from the 1960s to the 1990s, where UWB was particularly well suited for modern RADAR and highly secure communications. One hundred years after Marconi's first demonstration of wireless technology across the Atlantic Ocean, we again have wireless history in the making.

How It Works

Unique to UWB technology is the fact that it achieves wireless communications without using an RF carrier. Instead, it uses modulated pulses of energy less than one nanosecond in duration. Techniques for modulating UWB pulses include Pulse Position Modulation and Pulse Amplitude Modulation. The more common approach of PPM, for instance, might assign a digital representation of 0 or 1 to the transmitted and received pulse based on where, in time, the pulse is placed. Each pulse, when applied through a Fourier Transform formula, can be shown to exist simultaneously across an extensive band of frequencies; however, the distributed energy of the pulse at any given frequency exists in the noise floor. This allows UWB to co-exist with RF carriers with no discernable interference, thereby opening up vast new communications territory and possibilities by providing tremendous wireless bandwidth to ease the growing bandwidth crunch.

Ultra-Wideband is only becoming commercially viable now through decreased costs and recent advancements in chip development, the evolution of the marketplace, and FCC recognition. What is driving UWB into the consumer market is the ability to render UWB circuitry into CMOS technology. Therefore, as CMOS scales from .25 to .18 to .13 micron, so does the ISWB circuitry. (As a result some call UWB "Moore's Law Radio.") Up until several years ago the circuitry to implement UWB was power- and form factor-constrained. With UWB now being implemented in CMOS this is no longer the case. We can expect to see smaller and smaller UWB devices over the next few years.

Commercial Viability

Potential commercial applications include distribution of wireless audio, video, and data over local area networks for home and office. In addition UWB has the unique ability to resolve a device's geo-positional location to centimeter accuracy as a by-product of sending and receiving data between multiple UWB devices. Such capability might support wireless Internet and video-capable devices such as smart phones, PDAs, laptop computers, web-pads, digital video cameras, automobiles, and a wide range of consumer electronics and home appliances with extremely precise, GPS-like positioning.

Other advantages of UWB are penetration and signal power. In terms of penetration, an unfiltered pulse of 200 picoseconds duration, when applied through a Fourier formula, demonstrates signal energy throughout the spectrum between DC and 5GHz. Obviously this is not a perfect square wave representation because the pulse is subject to some coloring from the antenna--and antenna technology is an extremely important facet of UWB technology. But with proper antenna implementations the distribution of energy is spread fairly evenly across the spectrum. A UWB receiver detects the presence of the energy of the pulse in time, not at specific frequencies, so absorption of specific carriers such as at 1.8GHz or 2.4GHz has little effect, provided about 50 percent of the spectral energy density of the pulse penetrates whatever obstacles lie in the transmission path. Absorption at any one particular frequency does little to affect the integrity of the actual pulse.

In terms of signal power, the simplest conceptual example would be to think of Morse code. Imagine hooking a microphone to a one-watt transmitter and speaking into it. The voice is being used to generate a complex modulation onto an analog carrier. That same complex modulation must be received and demodulated at the receiver. In order to recover the voice at the receiver, integrity of both the modulation and the carrier must be maintained. Although the carrier is capable of going great distances, the modulation is much more fragile and degrades over distance quickly, so one might be able to recover the voice modulated signal a mile or so away.