Recently, ultra-wideband (UWB) technology based on the transmission of short duration pulses has gained much interest for its application to wireless communications. This thesis covers a range of topics related to the analysis of indoor UWB channels for communications and to system level design issues for UWB receivers. Measurement based UWB small scale modeling and characterization efforts as well as UWB communications system analysis and simulation are presented. Relevant background material related to UWB communications and wireless channel modeling is presented. The details of the small scale channel modeling work, including statistical characterization and potential models, are discussed. A detailed analysis of the CLEAN algorithm, which was used to process all the measurement data, is also given, and some limitations of the algorithm are presented. The significance of the channel impulse response model chosen for the simulation of UWB communications systems is also evaluated. Three traditional models are found to be useful for modeling NLOS UWB channels, but not LOS channels. A new model for LOS UWB channels is presented and shown to represent LOS channels much more accurately than the traditional models. Receiver architectures for UWB systems are also discussed. The performance of correlation receivers and energy detector receivers are compared as well as Rake diversity forms of each of these types to show tradeoffs in system complexity with performance. Interference to and by UWB signals is considered. A narrowband rejection system for UWB receivers is shown to offer significant system improvement is the presence of strong interferers. / Master of Science

The use of ultra-wideband (UWB) signals holds great promise for remote monitoring of vital-signs which has applications in the medical, for first responder and in security. Previous research has shown the feasibility of a UWB-based radar system for respiratory and heartbeat rate estimation. Some simulation and real experimental results are presented to demonstrate the capability of the respiration rate detection. However, past analysis are mostly based upon the assumption of an ideal experiment environment. The accuracy of the estimation and interference factors of this technology has not been investigated. This thesis establishes an analytical framework for the FFT-based signal processing algorithms to detect periodic bio-signals from a single target. Based on both simulation and experimental data, three basic challenges are identified: (1) Small body movement during the measurement interval results in slow variations in the consecutive received waveforms which mask the signals of interest. (2) The relatively strong respiratory signal with its harmonics greatly impact the detection of heartbeat rate. (3) The non-stationary nature of bio-signals creates challenges for spectral analysis. Having identified these problems, adaptive signal processing techniques have been developed which effectively mitigate these problems. Specifically, an ellipse-fitting algorithm is adopted to track and compensate the aperiodic large-scale body motion, and a wavelet-based filter is applied for attenuating the interference caused by respiratory harmonics to accurately estimate the heartbeat frequency. Additionally, the spectrum estimation of non-stationary signals is examined using a different transform method. Results from simulation and experiments show that substantial improvement is obtained by the use of these techniques. Further, this thesis examines the possibility of multi-target detection based on the same measurement setup. Array processing techniques with subspace-based algorithms are applied to estimate multiple respiration rates from different targets. The combination of array processing and single- target detection techniques are developed to extract the heartbeat rates. The performance is examined via simulation and experimental results and the limitation of the current measurement setup is discussed. / Master of Science

yes / A novel miniaturized planar double inverted-F antenna is presented. The antenna design is based on the electromagnetic coupling of two air dielectric PIFA antennas, combined with a broadband rectangular plate feed structure to achieve ultra-wideband characteristics. The computed and experimental impedance bandwidths show good agreement over an UWB frequency band from 3.1 GHz to 10.6 GHz for |S11| < -10dB. The antenna is electrically small, with size 0.31 x 0.16 x 0.09 wavelengths at 3.1 GHz and 1.06 x 0.55 x 0.31 wavelengths at 10.6 GHz. The simulated and measured gain and radiation patterns show acceptable agreement and confirm that the antenna has appropriate characteristics for short range wireless applications. / MSCRC

Lately, spread spectrum systems are being increasingly used for commercial wireless communications because of their ability to reject various types of interference. This ability allows them to be used in multiple access systems. Direct sequence and frequency hopping systems have been the primary spread spectrum techniques used in practice. One technique which has not received much attention until recently is time hopping. In time hopping, a symbol is transmitted at a random position within the symbol period using a pulse width which is much smaller than the symbol period. Ultra-wideband (UWB) technology is a radar technology which shows promise for an relatively simple implementation of a time hopping system. This thesis looks at the error probability performance of a UWB time hopping multiple access system. Previous work has led to an estimate of the performance using a Gaussian approximation similar to that used for direct sequence systems. Through the use of a fast simulation technique, it will be shown that in certain situations, the Gaussian approximation fails to accurately predict the performance. A numerical analysis which uses characteristic functions is developed and shown to correctly predict the system’s performance under a wide range of situations. This numerical analysis also contributes to the understanding of the system. / Master of Science

In Impulse Radio based Ultra Wide Band (UWB) systems, where sub-nano second pulses are used, synchronization is very challenging because of their short pulse duration and very low duty cycle. Coherent detection of ultra wide-band signals requires complex channel estimation algorithms. In impulse based UWB systems, suboptimal receivers that require no channel estimation are proposed for low data rate applications using non coherent detection of energy. This approach requires integrators that collect energy and detect the incoming stream of bits for detection and synchronization. These techniques yield reasonable performance when compared to coherent detection techniques that require complex hardware and dissipate more energy. Non-coherent detection is a promising technique for low complexity, low cost and low data rate ultra-wideband communication applications like sensor area networks. In the past, several attempts have been made to characterize the performance of the energy collection receivers for synchronization using various metrics that include time of arrival and BER measurements. A comprehensive study of the synchronization problem using Probability of False Alarm is limited. The current thesis attempts to characterize the synchronization problem using Probability of False Alarm and Probability of Detection under various channel models and also discusses the importance of the length of the integration window for energy collection receivers. The current work also focuses on the performance evaluation of synchronization for Impulse based UWB systems using energy capture method and modeling them using the Probability of False Alarm and Probability of Detection under various channel models. In these systems, the integration region of a receiver integrator significantly affects the bit error rate (BER) performance. The effect of the integration window on the performance of the algorithm is also studied. This work also discusses the trade-offs between complexity and precision in using these algorithms for synchronization of Impulse based Direct Sequence Ultra Wideband Systems (DS-UWB). Signal to Noise Ratio vs. Probability of Detection, Probability of False Alarm are plotted for different channel models. / Master of Science

Ultra-Wideband has recently gained great interest for high-speed short-range communications (e.g. home networking applications) as well as low-speed long-range communications (e.g. sensor network applications). Two flavors of UWB have recently emerged as strong contenders for the technology. One is based on Impulse Radio techniques extended to direct sequence spread spectrum. The other technique is based on Orthogonal Frequency Division Multiplexing. Both schemes are analyzed in this thesis and modifications are proposed to increase the performance of each system. For both schemes, the issue of simultaneously operating users has been investigated. Current MAC design for UWB has relied heavily on existing MAC architectures in order to maintain backward compatibility. It remains to be seen if the existing MACs adequately support the UWB PHY (Physical) layer for the applications envisioned for UWB. Thus, in this work we propose a new MAC scheme for an Impulse Radio based UWB PHY, which is based on a CDMA approach using a code-broker in a piconet architecture. The performance of the proposed scheme is compared with the traditional CSMA scheme as well as the receiver-based code assignment scheme. A new scheme is proposed to increase the overall performance of the Multiband-OFDM system. Two schemes proposed to increase the performance of the system in the presence of simultaneously operating piconets (namely Half Pulse Repetition Frequency and Time spreading) are studied. The advantages/disadvantages of both of the schemes are discussed. / Master of Science

Interest in Ultra-wideband (UWB) has surged since the FCC's approval of a First Report and Order in February 2002 which provides spectrum for the use of UWB in various application areas. Because of the extremely large bandwidth UWB is currently being touted as a solution for high data rate, short-range wireless networks. An integral part of designing systems for this application or any application is an understanding of the statistical nature of the wireless UWB channel. This thesis presents statistical characterizations for the large and small scale indoor channel. Specifically, for large scale modeling channel frequency dependence is investigated in order to justify the application of traditional narrowband path loss models to UWB signals. Average delay statistics and their distributions are also presented for small scale channel modeling. The thesis also investigates narrowband interference cancellation. To protect legacy narrowband systems the FCC requires any UWB transmission to maintain a very low power spectral density. However, a UWB system may therefore be hampered by the presence of a higher power narrowband signal. Narrowband interferers have a much greater power spectral density than UWB signals and can negatively affect signal acquisition, demodulation, and ultimately lead to poor bit error performance. It is therefore desirable to mitigate any in-band narrowband interference. If the interferer's frequency is known then it may simply be removed using a notched filter. It is however of more interest to develop an adaptive solution capable of canceling interference at any frequency across the band. Solutions which are applied in the analog front end are preferable to digital backend solutions since the latter require extremely high rate sampling. The thesis therefore discusses two analog front-end interference cancellation techniques. The first technique digitally estimates the narrowband interference (this is possible because the UWB signal is not being sampled) and produces an RF estimate to perform the narrowband cancellation in the analog domain. Two estimation techniques, an LMS algorithm and a transversal filter, are compared according to their error performances. The second solution performs real-time Fourier analysis using transform domain processing. The signal is converted to the frequency domain using chirp Fourier transforms and filtered according to the UWB spectrum. This technique is also characterized in terms of bit error rate performance. Further discussion is provided on chirp filter bandwidths, center frequencies, and the applicability of the technology to UWB. / Master of Science

Software defined radios have the potential of changing the fundamental usage model of wireless communications devices, but the capabilities of these transceivers are often limited by the speed of the underlying processors and FPGAs. This thesis presents the digital design for an impulse-based ultra wideband communication system capable of supporting raw data rates of up to 100 MB/s. The transceiver is being developed using software/reconfigurable radio concepts and will be implemented using commercially available off-the-shelf components. The receiver uses eight 1 GHz ADCs to perform time interleaved sampling at an aggregate rate of 8 Gsamples/s. The high sampling rates present extraordinary demands on the down-conversion resources. Samples are captured by the high-speed ADC and processed using a Xilinx Virtex-II Pro (XC2VP70) FPGA. The testbed has two components: a non real-time part for data capture and signal acquisition, and a real-time part for data demodulation and signal processing. The overall objective is to demonstrate a testbed that will allow researchers to evaluate different UWB modulation, multiple access, and coding schemes. As proof-of-concept, a scaled down prototype receiver which utilized 2 ADCs and a Xilinx Virtex-II Pro (XC2VP30) FPGA was fabricated and tested. / Master of Science

Increasing interest in ultra-wideband (UWB) communications has engendered the need for a test bed for UWB systems. An FPGA-based software-defined radio provides both post-fabrication definition of the radio and ample parallel processing power. This thesis presents the FPGA design for a software-defined radio targeted to impulse ultra-wideband signals. The system is capable of an effective sampling frequency of up to 8 G-samples/s using time interleaved sampling with eight 1-GHz ADCs. The system is also capable of transmitting UWB pulses using a transmitter board controlled by the FPGA. In this thesis, the FPGA design used to capture and export data from the eight ADCs is presented, along with two systems which make use of the transceiver: a pilot-based matched filter communications system, and a remote vital signs monitor. / Master of Science

The work in hand considers energy efficiency of data transmission in wireless networks with low data rate (=sensor networks). Often the network nodes are battery operated thus calling for node lifetimes of months or even years. Thus, energy efficiency becomes an important optimisation criteria when designing hardware as well as for the physical transmission, protocol design etc. In order to meet the tight energy constraints, it is necessary to optimise the system as a whole, not just single parameters. This work first shows a derived analysis model for calculating the energy consumption during data transmission. This model is based on a complex state diagram which is evaluated using Mason rules. Using this model the impact of individual parameters on the energy consumption can be computed. Herein the interference of other nodes is included as well. The individual parameters investigated include detection method, modulation scheme, error correction and channel access. The main conclusion is, that higher transmit power can yield decreased energy consumption if the time, which nodes spend in the energy intense active mode, is reduced. Ultra-Wideband-transmission (UWB) using short pulses (Impulse Radio-IR) is currently developing. The potential of this technology is a very simple power-efficient transmitter. Moreover, due to the short pulses, transmission time is short. These two facts promise an energy efficient operation in transmit mode. Nevertheless, performance of simple receivers is still quite low, especially in multi-path environments. Moreover there is the need of powerful synchronisation algorithms. Sensor networks usually possess multi-hop functionality. However, only in severe (block) fading channels multi-hop is more energy efficient than direct transmission. Supposed the transmit power is the same for all nodes, then the transmit power has to be dimensioned for the weakest link. Then, under certain conditions, cooperative relaying schemes can not capitalize the spatial diversity gain. - (This manuscript is also available - in the form of a book - from Dresden: Vogt (Verlag), ISBN:3-938860-02-2) / Die vorliegende Arbeit beschäftigt sich mit der Energieeffizienz der Datenübertragung in Funknetzwerken mit geringer Datenrate (=Sensornetzwerke). Die Netzknoten solcher Netzwerke sind zumeist batteriebetrieben und sollen Betriebsdauern von Monaten bis Jahren erreichen. Daher ist Energieeffizienz ein wichtiges Designmerkmal sowohl beim Hardwareentwurf als auch bei der physikalischen Übertragung, im Protokolldesign usw. Um den energetischen Beschränkungen gerecht zu werden, sollen nicht Einzelparameter optimiert werden, sondern das System insgesamt. In dieser Arbeit wird zunächst ein Analysemodell zur Berechnung des Energieverbrauchs bei der Datenübertragung entwickelt, welches diesen Forderungen gerecht wird. Dieses basiert auf einem komplexen Zustandsdiagramm, welches mit der Mason'schen Regel ausgewertet wird. Dieses Modell nutzend, kann der Einfluss von Einzelparametern auf den Energieverbrauch unter Berücksichtigung der Interferenzen anderer Netzknoten berechnet werden. Als Einzelparameter werden exemplarisch Detektionsverfahren, Modulation, Fehlerschutzkodierung und Kanalzugriff untersucht. Die Grunderkenntnis dieser Betrachtungenen ist, dass höhere Sendeleistungen zu geringerem Energieverbrauch führen, wenn dadurch die Zeit des Netzknotens im energieintensiven Aktiv-Mode verkürzt wird. Ultra-Wideband-Verfahren (UWB) mittels kurzen Pulsen (IR-UWB) befinden sich noch in einer frühen Entwickungsstufe. Das Potential liegt in einem sehr einfachen Senderaufbau, der sehr leistungseffiziente Sender ermöglicht. Aufgrund der kurzen Pulse ist zudem die Übertragungszeit sehr gering. Diese beiden Gegebenheiten lassen auf einen geringen Energieverbrauch hoffen. Allerdings ist die Leistungsfähigkeit von einfachen Empfängern insbesondere in Mehrwegekanälen sehr gering. Desweiteren gibt es noch intensiven Forschungsbedarf für leistungsfähige Synchronisationsalgorithmen. Sensornetzwerke verfügen im Allgemeinen über Multi-Hop-Funktionalität. Energetisch betrachtet, ist deren Einsatz aber nur in starken Blockschwundkanälen sinnvoll. Wird die Sendeleistung aller Netzknoten als konstant angenommen, muss die Sendeleistung auf die schwächste Verbindung dimensioniert werden. Bei kooperativen Vermittlungsverfahren kann dadurch unter bestimmten Bedingungen der räumliche Diversitätsgewinn nicht genutzt werden. - (Die Dissertation ist veröffentlicht im Verlag Vogt, Dresden, ISBN:3-938860-02-2)