Ultra-wideband Devices Research Articles

Production test technique for measuring BER of ultra-wideband (UWB) devices

Ultra-wideband is an emerging standard for short-range high data-rate wireless communication. In a production test environment, ultra-wideband devices are tested for bit error rate (BER) in the presence of an external interferer. As the target BER values are small at low interference levels, it requires a long test sequence for measuring BER, incurring a long test time. This paper describes a novel production test technique for BER testing of orthogonal frequency-division multiplexing transceivers. By adjusting the phase values of the baseband signal, the proposed manufacturing test methodology reduces the overall test time considerably (up to 20/spl times/), while keeping the error vector magnitude and peak-to-average ratio of the transmitted signal unchanged. This method can be extended to any phase modulation scheme to reduce the test time for BER.

Measurement Techniques of Emissions from Ultra Wideband Devices

This paper describes the measurement techniques of emissions from UWB devices discussed in ITU-R task group (TG) 1/8 to study the compatibility between ultra-wideband (UWB) devices and radiocommunication services. This paper also provides the background idea behind the measurement methods, as the final output of the discussion, i.e. ITU-R Recommendation, will not contain any citations to the references, nor any educational description of the theoretical background.

Time-Domain Diversity in Ultra-Wideband MIMO Communications

The development of ultra-wideband (UWB) communications is impeded by the drastic transmitted power limitations imposed by regulation authorities due to the "polluting" character of these radio emissions with respect to existing services. Technical solutions must be researched in order either to limit the level of spectral pollution by UWB devices or to increase their reception sensitivity. In the present work, we consider pulse-based modulations and investigate time-domain multiple-input multiple-output (MIMO) diversity as one such possible solution. The basic principles of time-domain diversity in the extreme (low multipath density) or intermediate (dense multipath) UWB regimes are addressed, which predict the possibility of a MIMO gain equal to the product of the numbers of transmit/receive antenna elements when the channel is not too severe. This analysis is confirmed by simulations using a parametric empirical stochastic double-directional channel model. They confirm the potential interest of MIMO approaches solutions in order to bring a valuable performance gain in UWB communications.

Spectral Analysis of UWB Multiple Access Schemes Using Random Scrambling

With the new release of the Federal Communication Commission on matters of regulation of marketing and operation of ultra-wideband (UWB) devices, an analytical framework to enable tractable analysis of the spectrum shape of these signals is needed. We extend the framework introduced by W. A. Gardner to the case of UWB signals. We introduce a generalized UWB signal model that can be specialized to represent the traditional time-hopping (TH) technique as well as the alternative multiple access technique that we indicate as delay coded sequence (DCS). The DCS technique resembles the traditional direct sequence spread spectrum techniques, but it is not based on pulse polarity inversion. The considered matrix signal formulation allows us to easily evaluate the spectral characteristics of UWB signals under many different operating conditions: continuous or discontinuous transmissions, random or periodic scrambling operations, with or without jitter. We evaluate the spectrum of the general UWB signal under the random scrambling assumption, then we specialize it to the TH and DCS cases and discuss the variability of the spectra to some critical design parameters. We obtain an asymptotic expression of the general UWB spectrum that we use to evaluate the UWB interference power at the output of a generic receiver.

Design of a Multiband OFDM System for Realistic UWB Channel Environments

In February 2002, the Federal Communications Commission allocated 7500 MHz of spectrum for unlicensed use of commercial ultra-wideband (UWB) communication devices. This spectral allocation has initiated an extremely productive activity for industry and academia. Wireless communications experts now consider UWB as available spectrum to be utilized with a variety of techniques, and not specifically related to the generation and detection of short RF pulses as in the past. There are many differences between real-world behavior of narrow-band and UWB systems. All wireless systems must be able to deal with the challenges of operating over a multipath propagation channel, where objects in the environment can cause multiple reflections to arrive at the receiver (RX). For narrow-band systems, these reflections will not be resolvable by the RX when the narrow-band system bandwidth is less than the coherence bandwidth of the channel. The large bandwidth of UWB waveforms, instead, significantly increases the ability of the RX to resolve the different reflections in the channel. The UWB channel model developed by the IEEE 802.15.3a standard body is described in this paper. For highly dispersive channels, an orthogonal frequency-division multiplexing (OFDM) RX is more efficient at capturing multipath energy than an equivalent single-carrier system using the same total bandwidth. OFDM systems possess additional desirable properties, such as high spectral efficiency, inherent resilience to narrow-band RF interference, and spectral flexibility, which is important because the regulatory rules for UWB devices have not been finalized throughout the entire world. This paper describes the design of a UWB system optimized for very high bit-rate, low-cost, and low-power wireless networks for personal computing (PC), consumer electronics (CE), and mobile applications. The system combines OFDM modulation technique with a multibanding approach, which divides the spectrum into several sub-bands, whose bandwidth is approximately 500 MHz. The system described in this paper has been selected by several key industry organizations [Mulitband OFDM Alliance, WiMedia, Wireless Universal Serial Bus (USB)] because of its very good technical characteristics for the diverse set of high performance short-range applications that are eagerly anticipated for CE, PC, and mobile applications.

Time-domain measurements of radiated and conducted UWB emissions

This paper summarizes results obtained from time-domain full-bandwidth emissions measurements of selected ultra wideband (UWB) transmitting devices. Brief descriptions of two NIST-developed measurement systems are provided. High-fidelity time-domain waveforms are shown, along with associated amplitude spectra for several devices. Results are shown for both conducted and radiated emissions from UWB devices.

Beamforming array antenna with heterogeneous signal distribution for UWB pulse transmission

AbstractAs ultra‐wideband (UWB) is a technology primarily aimed at short‐range communications, it is expected that in many UWB networks transmitters and receivers are concentrated in close proximity. Mutual interference among UWB devices is therefore a key problem to be overcome. One effective method to achieve this goal is the application of spatial division techniques using array antennas, which can have modified radiation patterns modified adaptively. UWB impulse radio systems, however, employ the transmission of baseband (carrierless) signals. This peculiarity of UWB‐IR systems makes the straightforward application of conventional beamforming methods, which are based on the control of amplitudes and phases of the signals transmitted from each element in the array, a rather difficult problem. In this paper a new beamforming method is proposed, which is based on the control of the power intensity profile of the frequency components shared by signals transmitted simultaneously from several antenna elements. In order to demonstrate the effectiveness of the method, computer simulations are shown which demonstrate that if a monocycle waveform is divided into several signals representing overlapping frequency subband components of the original, each transmitted from a different antenna element, a radiation pattern without sidelobes can be synthesized over the UWB. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 87(11): 1–10, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20074

Ultrawide gap on ultrawideband

Ultrawideband-a technology in which signals are transmitted in the form of billions of extremely short radio pulses spread over a bandwidth totaling several gigahertz-is highly anticipated because it will provide the wireless personal-area-network (WPAN) connectivity of Bluetooth, but at speeds up to 500 times faster. Despite that promise, a growing rift between the backers of separate ultrawideband (UWB) technologies has led to a stalemate within the IEEE 802.15.3a working group for WPAN charged with finalizing a standard for ultrawideband. The two groups at loggerheads are the Multiband-OFDM Alliance and the XtremeSpectrum group. Their main disagreements concern how much UWB devices might interfere with other radio users, how much power they will consume, and how much the chipsets needed to relay UWB signals between devices will cost.

Ultra-Wideband Signal Impact on the Performances of IEEE 802.11b and Bluetooth Networks

This paper presents the results of a coexistence study investigating the impact of ultra-wideband (UWB) interference on IEEE 802.11b and Bluetooth networks. The results are based on the experimental test measurements made at the University of Oulu, Finland. Simple high-power UWB transmitters are used to interfere with victim networks. Preliminary results show that only under extreme interference conditions with thousands of equivalent Federal Communications Commission– (FCC)-compliant devices in close proximity, will the IEEE 802.11b and Bluetooth networks experience significant performance degradation. The impact of the UWB interference on the IEEE 802.11b network was insignificant if the distance to UWB transmitters was greater than 40 cm. The impact on Bluetooth was even less noticeable. In our study, several high-power UWB transmitters that greatly exceed the FCC radiation regulations have been used, and the measurement settings presents the worst case scenario because of the very short distance between the interferers and the victim system. Effectively our study approximates the use of thousands of FCC-complaint UWB devices in the same space.

Design of field emitter devices for microwave and terahertz applications

Simulations show that photomixing in resonant laser-assisted field emission can cause the emitted current to oscillate at frequencies from dc to over 100 THz, so this technique shows promise for new ultrawideband devices. However, it is necessary to find a means to couple these signals from the apex of the tip to an external load while avoiding the effects of dispersion of the bunched electron beam and the low-pass filter action caused by the series impedance of the electron beam and the shunting capacitance of the electrodes. We have designed a new type of device in which the signal would propagate as a surface wave on the emitting tip itself. The procedures for design are defined, and graphs are given to determine the dimensions. Examples of designs are presented, which include devices to generate signals from 10 GHz to 10 THz, from 100 GHz to 100 THz, and a device that would be simpler to construct for use from 10 MHz to 10 GHz.

Broad is the way

Ultrawideband (UWB) systems, which combine bandwidths in excess of 1 GHz with very low power spectral densities (PSDs), are currently attracting growing interest as a means of wresting additional capacity from the already heavily utilised store of wireless bandwidth. If the emissions from UWB devices are regulated to avoid causing significant interference to licensed services, then it becomes possible to allow UWB systems to operate on an unlicensed basis, enabling UWB technology to support a diverse range of applications. As yet, there are no regulations for UWB devices. However, the US is in the process of setting up a regulatory framework, while within Europe, where matters are not quite so far advanced, possible approaches to UWB regulation are under consideration. The author describes the basic principles and the role of regulation in determining the UWB devices destined for commercial deployment.

Comparison of three different methods for coupling of microwave and terahertz signals generated by resonant laser-assisted field emission

Photomixing in resonant laser-assisted field emission can cause the emitted current to oscillate at frequencies from dc to over 100 THz, and thus shows promise for new ultrawide band devices. The signal occurs at the apex of the emitter, and we consider three methods for coupling this signal to an external load while avoiding the effects of dispersion of the bunched electron beam and the large series beam impedance (≈1 GΩ). These methods are use of (1) a tapered Goubau transmission line, (2) a dielectric transmission line, and (3) traveling-wave log-periodic zigzag antennas. We conclude that each of these methods could give an output power of 100 pW with an oscillating tunneling current of 1 μA at 10 THz. The output power is proportional to the square of the current for 100 μW with 1 mA.

Investigation of intense electromagnetic transient phenomenon and Paschen curves for hydrogen and helium in subnanosecond regime

One of the major drivers of pulsed power innovation is ultrawide-band technology. Subnanosecond risetimes with nanosecond or less pulse durations place this technology in a temporal regime that corresponds to microwave frequencies. These ultrawide-band devices have pushed pulsed power technology into a parameter space where there is little published data on breakdown. This paper describes the experimental determination of the Paschen curve for two gases under the application of intense, transient, electric fields. This experiment utilized the Hindenberg series of hydrogen gas switched pulsers at the Air Force Research Laboratory located at Kirtland Air Force Base. The Paschen curves for hydrogen and helium are presented. For subnanosecond risetime pulses, there are typically very few free electrons in the discharge space generated by external radiation sources such as cosmic rays. The occurrence of cosmic ray ionization in the gap is unlikely in such a short period of time. Therefore, electric field emission plays a very important role in these discharges. However, a small number of discharges are effected by ionization from external radiation, with the resulting data lying along classic Paschen curves. As a verification of this effect, an intense continuous ultraviolet (UV) source was utilized for supplying seed electrons and the expected Paschen curves of hydrogen and helium were obtained.