Ultra wideband: applications, technology and future perspectives

Ultra Wide Band (UWB) wireless communications offers a radically different approach to wireless communication compared to conventional narrow band systems. Global interest in the technology is huge. This paper reports on the state of the art of UWB wireless technology and highlights key application areas, technological challenges, higher layer protocol issues, spectrum operating zones and future drivers. The majority of the discussion focuses on the state of the art of UWB technology as it is today and in the near future

Ultrawideband Antenna Distortion Compensation

Abstract-The radiation characteristics of ultrawideband (UWB) antennas vary with frequency, introducing directionally asymmetric bandwidth reduction and waveform dispersion. In this paper, we develop a simple technique to alleviate the distortion due to nonisotropically dispersive antennas, and use indoor channel measurements to verify its performance. The approach is based on multipath direction estimation and therefore involves antenna arrays. We show that antenna distortion can enhance sensor localization ambiguity and introduce errors in its estimate. Antenna compensation mitigates this effect, significantly improving the location estimation accuracy. We further demonstrate that antenna compensation helps reduce the small-scale fading artifacts that arise due to the antennas, thus reducing the channel spatial variability and delay spread. Our technique can also aid empirical channel characterization by providing antenna-independent propagation data

Denoising Two-Photon Calcium Imaging Data

Two-photon calcium imaging is now an important tool for in vivo imaging of biological systems. By enabling neuronal population imaging with subcellular resolution, this modality offers an approach for gaining a fundamental understanding of brain anatomy and physiology. Proper analysis of calcium imaging data requires denoising, that is separating the signal from complex physiological noise. To analyze two-photon brain imaging data, we present a signal plus colored noise model in which the signal is represented as harmonic regression and the correlated noise is represented as an order autoregressive process. We provide an efficient cyclic descent algorithm to compute approximate maximum likelihood parameter estimates by combing a weighted least-squares procedure with the Burg algorithm. We use Akaike information criterion to guide selection of the harmonic regression and the autoregressive model orders. Our flexible yet parsimonious modeling approach reliably separates stimulus-evoked fluorescence response from background activity and noise, assesses goodness of fit, and estimates confidence intervals and signal-to-noise ratio. This refined separation leads to appreciably enhanced image contrast for individual cells including clear delineation of subcellular details and network activity. The application of our approach to in vivo imaging data recorded in the ferret primary visual cortex demonstrates that our method yields substantially denoised signal estimates. We also provide a general Volterra series framework for deriving this and other signal plus correlated noise models for imaging. This approach to analyzing two-photon calcium imaging data may be readily adapted to other computational biology problems which apply correlated noise models.National Institutes of Health (U.S.) (DP1 OD003646-01)National Institutes of Health (U.S.) (R01EB006385-01)National Institutes of Health (U.S.) (EY07023)National Institutes of Health (U.S.) (EY017098

An holistic approach to optimal ultra-wideband wireless communications system design

Ultra-wideband (UWB) wireless systems rely on signals spanning very wide bandwidths, typically several gigahertz, for information transmission. The distinguishing feature of UWB communications technology is the unrivalled data-rates it provides, with other benefits such as fade resistance and spectral reusability. These characteristics render UWB the technology of choice for a gamut of modern wireless communications applications, including multimedia transmission, personal- and body-area networks, imaging devices, and sensor networks. The use of wide bandwidth signals, however, leads to many complications that necessitate specialised design considerations. The propagation channel and system components acquire frequency-selective characteristics, and their nonlinear and dispersive nature, usually innocuous in a conventional setting, causes signal distortion and erroneous detection. This thesis analyses various aspects of the indoor channel and the distortion to a UWB signal propagating through it. The performance of transmitter and receiver sub-systems is evaluated, with an emphasis on the challenges posed by the large operating bandwidth. The significance of incorporating this knowledge into the system design process is demonstrated, and a novel framework for optimising the performance-complexity tradeoff is presented. • The following are the contributions of this thesis to the state of the art in UWB communications. • Experimental characterisation of the indoor UWB channel spanning the FCC band (3.1-10.6 GHz) • Demonstration of the variability of propagation characteristics in the spectral sub-bands • Assessment of frequency-dependent pathless and the consequent signal waveform distortion • Polarimetric analysis of the temporal, spectral and angular channel evolution • Evaluation of rake receiver performance and its dependence on various channel conditions • Investigation of the effect of antenna angular-spectral distortion on signal propagation • A technique for the normalisation of UWB link aberration due to antennas • Performance evaluation of diversity and spatial multiplexing with multiple-antenna systems • Design of gigabit wireless links for high data-rate applications or high user density scenarios • A novel holistic framework for the design of an optimal UWB communications system</p

Wireless sensor positioning with ultrawideband fingerprinting

Ultrawideband (UWB) systems offer high spatiotemporal resolution and are therefore well suited to sensor localization applications. In this paper, we consider the use of UWB signals for positioning and ranging based on fingerprinting using a channel impulse response database. We use indoor measurements to demonstrate the reduction in the location estimation ambiguity and false alarm probability with an increase in the channel bandwidth

Elements reviews-new books

Book reviews.Network convergence is the topic in the telecommunications arena both from a commercial management and technological perspective. How to combine many different services in one single network is a very strong motivational direction for both research and development. This book provides a very thorough and surprisingly readable guide to the many different subtleties of network convergence. Moreover, it applies its perspective in a very unbiased way, focusing on the technological, historical and standardisation issue

Impact of bandwidth on small-scale fade depth

This paper investigates the impact of channel bandwidth on fading in wireless channels using indoor measurements. The variation of channel energy over a local region is examined for narrowband, wideband and ultrawideband (UWB) channels, and the corresponding fade depth is evaluated. The relation between bandwidth and fade depth is then captured with a simple dual-slope model. The effect of antenna polarization and line-of- sight blockage is also investigated. We observe that the fade depth initially falls rapidly with bandwidth, reaching 4 dB at 1 GHz, but further reduction in fading with bandwidth is much slower

A simple adaptive beamformer for ultrawideband wireless systems

This paper introduces a simple beamformer for ultrawideband (UWB) wireless networks. The architecture consists of a two-element antenna array, a phase shifter and a signal combiner. The performance of the proposed beamformer is analyzed in terms of radiation pattern characteristics over the FCC's defined operating band for UWB communications devices. It is shown that this simple architecture can provide useful interference rejection and range extension capabilities for high data-rate UWB wireless networks. In particular, it is shown that the radiation pattern characteristics of the proposed sub-optimal beamformer remain beneficial over the allocated UWB band, even given its low complexity and implementation cos

nSTAT: Open-source neural spike train analysis toolbox for Matlab

Over the last decade there has been a tremendous advance in the analytical tools available to neuroscientists to understand and model neural function. In particular, the point process – generalized linear model (PP-GLM) framework has been applied successfully to problems ranging from neuro-endocrine physiology to neural decoding. However, the lack of freely distributed software implementations of published PP-GLM algorithms together with problem-specific modifications required for their use, limit wide application of these techniques. In an effort to make existing PP-GLM methods more accessible to the neuroscience community, we have developed nSTAT – an open source neural spike train analysis toolbox for Matlab[superscript ®]. By adopting an object-oriented programming (OOP) approach, nSTAT allows users to easily manipulate data by performing operations on objects that have an intuitive connection to the experiment (spike trains, covariates, etc.), rather than by dealing with data in vector/matrix form. The algorithms implemented within nSTAT address a number of common problems including computation of peri-stimulus time histograms, quantification of the temporal response properties of neurons, and characterization of neural plasticity within and across trials. nSTAT provides a starting point for exploratory data analysis, allows for simple and systematic building and testing of point process models, and for decoding of stimulus variables based on point process models of neural function. By providing an open-source toolbox, we hope to establish a platform that can be easily used, modified, and extended by the scientific community to address limitations of current techniques and to extend available techniques to more complex problems.National Institutes of Health (U.S.) (F31NS058275