Ultra-wideband (UWB) radio is a fast emerging technology with many unique attractive features that promotes major advances in wireless communications, networking, radar, imaging, and positioning systems. Research in UWB is still in its infancy stages, offering limited resources in handling the challenges facing the UWB communications. Understanding the unique properties and challenges of UWB communications as well as its application in competent signal processing techniques are vital in conquering the obstacles towards developing exciting UWB applications. UWB research and development has to cope with the challenges that limit their performance, capacity, throughput, network flexibility, implementation complexity, and cost. This tutorial focuses on UWB wireless communications at the physical layer. It overviews the state-of-the-art UWB in channel modeling, transmitters, and receivers of UWB radios, and outlines the research directions and challenges that needs to be overcome. Since a signal processing expertise is expected to have major impact in research and development of UWB systems, emphasis is placed on the DSP aspects.

Ultra-wideband communications: an idea whose time has come

The recent FCC frequency allocation for UWB has generated a lot of interest in UWB technologies. There is 7,500 MHz of spectrum for unlicensed use. The main limitations are provided by the low-power spectral density and by the fact that the transmit signal must occupy at least 500 MHz at whole times. IEEE 802.15.3a is being developed for high-bit-rate PAN applications, and UWB is the most promising technology to support the stringent requirements: 110, 200, and 480 Mb/s. Two UWB multiband systems, frequency hopping and Spectral Keying, have been described in this article. Both systems meet the stringent requirements provided by IEEE 802.15.

Ultra-wideband wireless systems

Local positioning will be one of the most exciting features of the next generation of wireless systems. Completely new concepts and features for wireless data transmission and transponder systems will emerge. Self-organizing sensor networks, ubiquitous computing, location sensitive billing, context dependent information services, tracking and guiding are only some of the numerous possible application areas. This article introduces different concepts of several existing and emerging systems and applications.

Wireless local positioning

Summary form only given. Ultra-wideband (UWB) refers to bandwidths in excess of 2 GHz, whose utilization by radar systems dates back to the late '60s. The renewed and rapidly growing interest for UWB was sparked by the spectral mask released by FCC in February 2002, and is well motivated by the attractive features UWB brings to commercial communications: low-power carrier-free transmissions, ample multipath diversity, enhanced penetration capability, low-complexity transceivers, ability to overlay existing systems, and a potential for increase in capacity. This article outlines features and challenges unique to UWB, with emphasis on timely signal processing issues that focus on synchronization, channel estimation, multiple access, and suppression of interference UWB systems cause to (and suffer from) co-existing narrowband systems. Application areas include shortrange indoor wireless links at home, and in the workplace for low-cost multimedia communications and storage, as well as secure connectivity for ranging, and covert communications.

Highly dispersive nature of ultra-wideband (UWB) channels makes time of arrival (TOA) estimation extremely challenging, where the leading-edge path is not necessarily the strongest path Since the bandwidth of a received UWB signal is very large, the Nyquist rate sampling becomes impractical, hence motivating lower complexity and yet accurate ranging techniques at feasible sampling rates In this paper, we consider TOA estimation based on symbol rate samples that are obtained after a square-law device A normalized threshold selection approach based on the minimum and maximum values of the energy samples is introduced, and optimal values of the thresholds for different signal to noise ratios (SNRs) are investigated via simulations Also, the effect of window size when searching the leading edge prior to maximum energy block is analyzed Theoretical closed form expressions are derived for mean absolute TOA estimation error for a fixed threshold case Performances of different algorithms are then compared via simulations using IEEE 802154a channel models and by choosing appropriate normalized threshold and search-back window parameters

Threshold-based TOA estimation for impulse radio UWB systems

Ultra-wideband (UWB) signals as implemented in our localizers provide a foundation for highly accurate methods of 3D position determination using precise ranging between any two nodes. In a large, distributed network of nodes, the time required for all nodes to acquire each other is of paramount importance. We have developed a method of rapid acquisition that allows two nodes to acquire each other in a fraction of the time afforded by other methods. We utilize a beacon/listener technique using Kasami sequences and divide-and-conquer algorithms to effect acquisitions in less than a second. We discuss our rapid acquisition process in this paper.

G. Roberts

Papers

Rapid acquisition for ultra-wideband localizers