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Ultra-Wideband technology to offer new opportunities for wireless video, networking, Part 2.

This article is the second in a two-part series. The first part appeared in the February issue of CTR.

From an architectural perspective, Ultra-Wideband (UWB) should always cost less than carrier-based technologies. Carrier-based technologies must modulate and demodulate a complex analog carrier waveform, and incorporate the componentry required to do so. UWB, on the other hand, offers a truly binary form of communication that can essentially be boiled down to four components. The first is the UWB transmit receive chip, the second is an UWB antenna. Third is a digital baseband processor that handles things like packetizing data, forward error correction, and so on. Fourth is the embedded firmware and protocols that drive the digital baseband processor. Platform solutions for OEMs are now being created; these solutions deriver the four elements in an inexpensive chipset.

It should be noted that there are claims of potential interference between UWB and carrier technologies. Some of these issues may be overstated based more on competitive corporate interests than technical merit, but there is no question that the potential for such interference exists if appropriate mitigation steps are not implemented.

For example, spurious harmonics might result if pulses are transmitted in a fixed repetition modulation, or if too many pulses are sent out during a fixed interval of time. The energy of multiple pulses from different devices stepping on one another, were they to occur in the same instant in time, can have a cumulative effect and potentially bring their cumulative energy out of the noise floor. It can be easily deduced, however, that collisions of pulses from different UWB devices stepping on one another would also impair Quality of Service (QoS)--and solutions for this problem form a necessary basis for the technology from companies who want to insure QoS and non-interference with other UWB users and with other existing spectrum users.

Another worry suggests that the cumulative effect of wide scale proliferation of UWB devices would have a cumulative effect on the noise floor and raise it to an unacceptable level. Real world experience suggests this scenario untenable, insomuch as every single electronic device regulated by the FCC's Part 15 rules (i.e. personal computers, PDAs, phones, microwave ovens, any consumer electronics, light bulbs, and so on) radiates equal if not more energy into the noise floor. But it is also generally understood that such interference inevitably happens and as a result, the FCC has put roles into place specifically to address these inadvertent emissions.

Much has been stated about UWB interference with GPS. But it is the same properties that unintentional emitters such as cell phones, laptop computers, portable radios, and more possess when radiating into the noise floor--and their widely accepted effect on GPS--that forms the basis for roles demanding that you must turn off electronic devices when taking off and landing on an airplane. Once again, the real world gives us an acceptable basis to accommodate UWB: billions of devices all around us are constantly radiating energy into the noise floor with no appreciable effect, and no one is suggesting that these devices not be permitted as a result.

The issue behind regulatory approval of UWB really comes down to an analyses and revision of the FCC's Part 15 roles for unintentional emitters. Devices such as computers, phones, consumer electronics, and more are all known to radiate energy into the noise floor across broad bands of frequencies. UWB transmits its signals directly into the very same noise floor. The technical issue, as it relates to properly managed UWB systems, is moot. The primary difference is that those other devices are "unintentional" emitters into the noise floor, whereas UWB is an "intentional" emitter. Once again, it is important to note that the very smile issues that are required to provide reliable QoS in UWB also serve to mitigate possible negative interference.

Other Challenges

These issues aside, additional challenges from the standpoint of actually delivering reliable UWB come in several areas. Because UWB pulse signals are resolved in time, the effects of propagation delay of the received pulse over appreciable distance become considerable. Timing and synchronization are critical, particularly as devices become mobile. Multipath also becomes a factor. Near/far issues, received signal strength, spectra shaping, antenna spectral coloring, and antenna ringing must be addressed. Dealing with the effects that other Part 15 devices have on the noise floor (a hair dryer for instance) all pose critical questions. In fact, modulation of binary data using UWB pulses is really one of the easier parts of a UWB solution. Engineering the answers to these issues and doing so in a fashion that derivers broad scalability is really what forms the core intellectual properly of UWB companies.

To achieve broad consumer acceptance of a technology, you cannot ask companies and consumers to toss everything out on its ear. Most UWB companies aim to be part of a logical upgrade path and to facilitate ease of integration based on existing deployed technology. For instance, because UWB companies are at times faced with supporting ease of adoption, most have at one point or another looked at adopting MACs similar or in some cases based on IEEE 802.11x, IEEE 802.15.3x, HiperLAN, and other known, accepted, and deployed carrier-based technologies. To be certain, each case has some merit.

Mac Design

In some cases, while existing standards bring "ease of development" benefits insomuch as they already exist, they may not allow or account for many of the features, functions, or unique characteristics that UWB enables. An ideal MAC for UWB would have guaranteed QoS, low jitter, bounded latencies, contention free access, ad-hoc and central control, low overhead, security, support for many users, and possess optimum scalability. In this case, we refer to scalability in reference to issues of adding users, Quality of Service, bandwidth management and allocation, and security.

Put another way, it is one thing when you have a few people using a few devices in a specialized military application. Now, imagine cellular-like UWB, UWB LANs, a UWB PAN, etc., each widely accepted and deployed in close proximity to one another in a high density urban environment. How do you guarantee bandwidth availability, QoS, security, targeted BER thresholds, and jitter? These are some of the questions and solutions on which UWB companies have been focused.

The question then becomes, "How do we establish an air interface and system management to accommodate optimum scalability?" By way of illustration, imagine that no spectrum whatsoever had ever been allocated to any wireless carrier technology. Now imagine that we were going to--for the very first time--divide the spectrum to accommodate advanced Cellular, TV, Radio, GPS, Satellite communications, LMDS, TV-remotes, garage door openers, and every other conceivable application of carrier technology. Obviously, we would allocate spectrum vary differently than the patchwork system we currently have in order to obtain harmonious peak efficiency for all of these uses.

We have this opportunity with UWB: a clean slate, so to speak. Now, if you simply stake out your turf ha one application or another without considering how to make this fit for maximum harmonious efficiency with other UWB and carrier-based systems, you are simply repeating the mistakes we've made with carrier allocations. To be certain, what we have with spectrum allocations wasn't intentional; we allocated as we innovated. In the final analysis, we must look to the vast possibilities of UWB technology, which has a theoretical capacity of gigabit data rates and transmission ranges approaching several miles. The theoretical capacity of UWB promises a path to multiple applications, users, and devices. It is important to insure a path that supports such capabilities to the benefit of all future applications, devices, and users of UWB, and tiffs too forms the cote of much of the development being done in the field.

John Santhoff is founder and Chief Technology Officer at Pulse-LINK, Inc. (San Diego, CA).
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Title Annotation:Video
Author:Santhoff, John
Publication:Computer Technology Review
Date:Mar 1, 2002
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