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Performance Analysis of Improved Selective-Rake on Ultra-Wideband ChannelsWang, Yan-Lun 23 July 2004 (has links)
The Ultra-Wideband (UWB) communication technology has been extensively attended in recent years. In this thesis, we propose the improved selective-Rake receiver and analyze the performance on UWB channels. The UWB transmission channels are modeled with statistical methods and its fading characteristics are discussed. Different impulse radio properties for the UWB communication system are analyzed. The system performance and design complexity issues of selective-Rake receiver (SRake) are studied. Rake receiver has difficulties achieving desired system performance in the dense multipath environment. The main ideas of SRake receiver are to obtain the SNR level on known multipath channel and to determine the desired number of Rake fingers. Matched filters and maximum likelihood detectors are utilized in the implementation of the SRake to estimate the signal time delay. The CLEAN algorithm is then used in selecting the paths with relatively high energy. Furthermore, we also propose a noise cancellation scheme for performance improvement in the SRake receiver. In the noise cancellation scheme, the multiresolution property of wavelet transform is used for filtering the noise interference caused by the rapid fluctuation factor. In addition, a two-stage search is combined with the original CLEAN algorithm to increase the accuracy of path selection. From our simulation results on the UWB channels, the improved SRake receiver, with noise cancellation and two-stage search, indeed has high SRake output SNR and better path accuracy than the original SRake receiver.
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Indoor Positioning and Tracking with NLOS Error Mitigation in UWB systemsLiu, Wei-Tong 01 August 2005 (has links)
This thesis presents mobile positioning and tracking with non-line of sight (NLOS) mitigation using time difference of arrival (TDOA) in biased extended Kalman filter (BEKF) in indoor dense multipath Ultra-Wideband (UWB) environment. The most serious issues which render to influence accuracy for the time-based location system is NLOS problem. Kalman filters (KFs) are used for smoothing range measurement data, and a method with sliding window is proposed to process range data for calculating standard deviation in a hypothesis testing and then identifying NLOS scenarios. When the measured arrival time has been converted to range difference, the biased extended Kalman filter is proposed to mitigate the NLOS error in the certain base stations (BSs) for mobile station (MS) positioning and trajectory tracking. From the simulation results in the indoor positioning environment with measurement and NLOS error, the sliding window algorithm and biased extended Kalman filter have higher accuracy than other related methods for NLOS identification and mitigation in positioning.
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MUSIC Algorithms in Frequency-Space Domain for Time Delay Estimation in UWB Multipath ChannelsChen, Kuan-Hsun 27 July 2006 (has links)
In this thesis, an algorithm based on frequency-space domain MUSIC method is presented for estimating the propagation delay of a wireless multipath channel.For indoor geolocation systems, the time-of-arrival (TOA) is the most popular technique for accurate positioning system. The basic idea in TOA-based techniques is to accurately estimate the propagation delay of the radio signal arriving from the direct line-of-sight (DLOS) path. However, dense multipath environments may cause unresolved paths, and yield an error in the estimation of the DLOS path. UWB (Ultra-wideband) technology provides an excellent means for wireless positioning due to its high resolution capability in the time domain. Its ability to resolving multipath components makes it possible to obtain accurate location estimates. In this thesis, we investigate the use of UWB signals in positioning and combine frequency-domain MUSIC algorithm. At the same time, the structure of time-space-time method is studied.
In addition, we propose a frequency-space domain MUSIC algorithm, called FSF-MUSIC algorithm, and use the spatial smoothing technique to improve the performance of the algorithm. For a two-multipath case, analysis and simulation results of multipath resolvability and the variance of estimation errors of signal arrival time are discussed.
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An analog approach to interference suppression in ultra-wideband receiversFischer, Timothy W. 17 September 2007 (has links)
Because of the huge bandwidth of Ultra-Wideband (UWB) systems, in-band narrowband
interference may hinder receiver performance. In this dissertation, sources
of potential narrowband interference that lie within the IEEE 802.15.3a UWB bandwidth
are presented, and a solution is proposed. To combat interference in Multi-Band
OFDM (MB-OFDM) UWB systems, an analog notch filter is designed to be included
in the UWB receive chain. The architecture of the filter is based on feed-forward
subtraction of the interference, and includes a Least Means Squared (LMS) tuning
scheme to maximize attenuation. The filter uses the Fast Fourier Transform (FFT)
result for interference detection and discrete center frequency tuning of the filter. It
was fabricated in a 0.18 õm process, and experimental results are provided. This is
the first study of potential in-band interference sources for UWB. The proposed filter
offers a practical means for ensuring reliable UWB communication in the presense of
such interference.
The Operational Transconductance Amplifier (OTA) is the predominant building
block in the design of the notch filter. In many cases, OTAs must handle input
signals with large common mode swings. A new scheme for achieving rail-to-rail
input to an OTA is introduced. Constant gm is obtained by using tunable level
shifters and a single differential pair. Feedback circuitry controls the level shifters
in a manner that fixes the common mode input of the differential pair, resulting in consistent and stable operation for rail-to-rail inputs. As the new technique avoids
using complimentary input differential pairs, this method overcomes problems such
as Common Mode Rejection Ratio (CMRR) and Gain Bandwidth (GBW) product
degradation that exist in many other designs. The circuit was fabricated in a 0.5õm
process. The resulting differential pair had a constant transconductance that varied
by only ñ0.35% for rail-to-rail input common mode levels. The input common mode
range extended well past the supply levels of ñ1.5V, resulting in only ñ1% fluctuation
in gm for input common modes from -2V to 2V.
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Antennas for spectrum efficient wireless communications /Chan, Chiu Lun. January 2003 (has links)
Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 68-72). Also available in electronic version. Access restricted to campus users.
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Compact planar UWB antennas for wireless device applicationsLiu, Li, 劉荔 January 2014 (has links)
The thesis report presents the designs of compact planar ultra-wideband (UWB) antennas for wireless devices applications. Three main designs of UWB antennas are studied, namely, single UWB antennas, UWB multiple-input-multiple-out(MIMO)antennas, and transparent UWB antennas on the screens of mobile phones.
For single UWB antennas, the designs of two compact planar monopole antennas with compact sizes of 26×28 mm2and 30×39.3mm2are presented. The UWB operations of the antennas are achieved using a ground slot under the feed line, offsetting the feed line and the radiator from the middle of the ground plane and smoothly transforming the feed line. Simulation and measurement show that the two antennas can achieve an ultra-wide bandwidth with approximately omnidirectional patterns. A deep notch-band in5.1-5.85 GHz is created in one of the UWB antennas by employing two pairs of meander lines (MLs), one pair being close to the feed line and the other pair along the upper edge of the ground plane. At the notch frequency, the simulated efficiency is only 4%.
Three compact UWB-MIMO antennas with very compact sizes of 26×40 〖mm〗^2, 21×38 〖mm〗^2, and 22×36 〖mm〗^2 are designed. Each of them is designed using two UWB antenna elements perpendicularly or symmetrically placed. Different techniques such as using ground stubs besides the radiators, cutting inclined slots on the ground, and adding a T-shaped protruding from ground are proposed to lower mutual coupling between the two antenna elements. One of the antennas is designed to generate a notched band in 5.15-5.85 GHz using two ground strips. Simulation and measurement results show that these antennas can cover the entire UWB of 3.1-10.6GHz with mutual coupling of less than -15 dB, and envelope correlation coefficient of less than 0.1.
An UWB antenna is designed using a transparent conductive film for applications on mobile phone screens. The effects of a finger touching the screen are studied. Results show that, with the radiator on the bottom side of the screen and a thin film with a thickness of 0.05 mm on the top side to separate the finger and the antenna, the effects of the finger can be minimized.
In measurement of monopole antennas with small ground planes, due to the feeding cable used, there are always discrepancies between the simulated and measured results in radiation patterns, efficiencies, and gains at lower frequencies. To verify that the discrepancies in the results of these studies are indeed due to the feeding cable used in measurement, the models of the feeding cables are developed and used for simulation. Results show that, by using the cable model, the simulated and measured results in radiation patterns, efficiencies, and gains agree very well. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy
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Ultra-wideband systems exploiting orthonormal waveformsKim, Youngok, 1971- 12 August 2011 (has links)
Not available / text
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Multicarrier CDMA overlay for ultra-wideband wireless communicationsWong, Tat-tung., 黃達東. January 2003 (has links)
published_or_final_version / abstract / toc / Electrical and Electronic Engineering / Master / Master of Philosophy
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Pre-equalization for pre-Rake MISO DS-UWB systemsTorabi, Elham 05 1900 (has links)
In recent years, ultra-wideband (UWB) communications has gained tremendous
popularity in both research community and industry. The large bandwidth
of UWB systems raises new wireless channel effects and consequently
unique advantages as well as challenges to be dealt with, compared to conventional
wireless systems. One of these advantages is the ability to resolve
dense multipath components and use Rake combining at the receiver in order
to significantly reduce the negative effects of fading. However, implementing
a Rake receiver with a sufficiently large number of fingers to make use
of this advantage is an evident challenge for most UWB devices with limited
signal processing capabilities. A possible approach to overcome this problem
is to move computational complexity from the receiver to the more powerful
transmitter, which is the main focus of the present work.
In this thesis, we propose two novel pre-equalization schemes for multiple-
input single-output (MISO) direct-sequence ultra-wideband (DS-UWB) systems
with pre-Rake combining and symbol-by-symbol detection. The first
pre-equalization filter (PEF) scheme employs one PEF per transmit antenna,
whereas in the second, simplified PEF (S-PEF) scheme all transmit antennas
share the same PEF. For both schemes the optimum finite impulse response
(FIR) and infinite impulse response (IIR) PEFs are calculated based on the
minimum mean squared error (MMSE) criterion. We show that in contrast to
previously proposed schemes for DS-UWB, both our proposed PEF schemes
efficiently exploit the channel shortening properties of the pre-Rake filter.
In particular, our proposed PEF schemes operate at the symbol level. We also
show that under certain conditions the S-PEF scheme achieves the same performance
as the more complex PEF scheme. Finally, we demonstrate that a
single-input multiple-output (SIMO) DS-UWB system with post-Rake combining
and MMSE post-equalization is the dual system to the considered MISO
DS–UWB system with pre-Rake combining and MMSE pre-equalization. This
uplink-downlink duality can be exploited for efficient calculation of the PEFs
and for complexity reduction.
Our simulation results show that the proposed PEF schemes achieve significant
performance gains over pre-Rake combining without equalization even if only
short PEFs are employed, and this is the case even for long UWB channel
impulse responses.
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Realistic Assessment of Novel Wireless Systems with Ray-tracing Based TechniquesSood, Neeraj 23 July 2012 (has links)
Ray tracing based on geometric optics can be utilized for generating propagation models for arbitrary and complex environments. These methods can be employed to determine important wireless channel characteristics such as path gain and the channel impulse response which in turn can be used to deduce channel capacity. In this thesis, a fully vectorial 3-D ray-tracer is developed. The simulator is applied to study novel wireless systems such as ultra-wideband pulse propagation in complex railway tunnels and MIMO systems employing closely spaced low mutual coupling meta-material antennas.
The computational complexity of the ray-tracing algorithm is reduced using optimizations and via the development of a novel hybrid method that combines the efficiency and accuracy of waveguide models with the flexibility of a ray-tracer. The resulting simulator is validated against measured results and demonstrated to show good agreement. Convergence of the solution using the ray-tracing method is also discussed.
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