Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references (leaves 62-65). Also available in electronic version.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 191-196).

published_or_final_version / abstract / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

One of the key building blocks in a direct-conversion receiver is the low noise amplifier (LNA), which needs to provide a sufficient gain with a low noise figure for the RF front-end. However, the wideband nature of the receiver imposes harsh requirements on the LNA. It is difficult to achieve desired performance goals over the wide frequency range without excessive power consumption. To deal with this problem, this thesis proposes a novel band-selective UWB LNA. Utilizing the frequency hopping property of the MB-OFDM system, the proposed method switches the operating frequency of the LNA in real time following the MB-OFDM's hopping pattern so that optimal gain and noise performance can be achieved in each frequency band. Unlike the conventional approach, this LNA does not need to cover the entire band simultaneously, thus excessive power consumption is avoided. Fabricated in a 0.18-mum CMOS process, the proposed LNA achieves a peak power gain of 16 dB and a minimum noise figure of 2.74 dB at a low power consumption of less than 12 mW. / Other challenges in direct-conversion MB-OFDM receivers include ultra-short band switching time and wide LO frequency range. The single-sideband (SSB) generation is an attractive method for a fast-hopping multi-band LO generator. However, it involves LO frequency synthesis in an open-loop architecture, and thus the spurious-tone performance becomes critical in maintaining the LO signal integrity. Since the accuracy of the SSB generation and the spurious-tone power are difficult to control in a high-frequency operation, a 4.5-GHz SSB upconverter system was fabricated in a standard 0.18-mum CMOS process to investigate its performance against process variation. Some precise quadrature signal generation circuits such as divider and polyphase filter are employed. Experimental results show that the fabricated SSB upconverter system achieves image rejection of higher than 48 dB and spurious-tone suppression of higher than 32 dB. / The use of an active downconversion mixer is an alternative to relax the LNA requirements for direct-conversion MB-OFDM UWB receivers. However, its linearity becomes a problem when the bandwidth is ultra wide. In this thesis, the static current bleeding technique is used in the UWB downconversion mixer to improve its linearity. By injecting a DC current to the RF transconductor for linearization, the mixer's transconductance is enhanced while the noise from the LO switches is not affected. As a result, the conversion gain increases and the noise figure improves. Fabricated in a 0.18-mum CMOS process, the UWB downconversion mixer achieves a peak conversion gain of 4.1 dB, a peak IIP3 of --2.5 dBm, and a minimum double-sideband (DSB) noise figure of 11.7 dB at a low power consumption of 6 mW. / Ultra-wideband (UWB) is a short-range, high-data-rate communication system for Wireless Personal Area Networks (WPAN) based on the IEEE 802.15.3a physical layer standard. The allocated frequency range is from 3.1 to 10.6 GHz, in which 14 bands are defined. The first band group, which is assigned to the mandatory Mode 1 devices, consists of three bands. In UWB systems, multi-band orthogonal frequency division multiplexing (MB-OFDM) is the dominant modulation scheme for its high spectral flexibility and its similarity in communication architecture with other existing wireless communication standards, such as IEEE 802.11a/b/g and WiMAX. For practical reasons, the direct-conversion architecture is widely considered the best architecture to implement an MB-OFDM UWB receiver, which has advantages of low power consumption and high integration level. Nevertheless, there are some performance limitations in direct-conversion MB-OFDM UWB receivers. In this thesis, some key building blocks in the RF front-end of the direct-conversion MB-OFDM UWB receivers for use in Mode 1 devices are investigated to overcome such limitations. / Tang, Siu Kei. / "May 2008." / Adviser: Pun Kong Pang. / Source: Dissertation Abstracts International, Volume: 70-03, Section: B, page: 1857. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (p. 161-169). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

This thesis studies the problem of estimating the interior structure of a collapsed building using embedded Ultra-Wideband (UWB) radios as sensors. The two major sensing problems needed to build the mapping system are determining wall type and wall orientation. We develop sensing algorithms that determine (1) load-bearing wall composition, thickness, and location and (2) wall position within the indoor cavity. We use extensive experimentation and measurement to develop those algorithms. In order to identify wall types and locations, our research approach uses Received Signal Strength (RSS) measurement between pairs of UWB radios. We create an extensive database of UWB signal propagation data through various wall types and thicknesses. Once the database is built, fingerprinting algorithms are developed which determine the best match between measurement data and database information. For wall mapping, we use measurement of Time of Arrival (ToA) and Angle of Arrival (AoA) between pairs of radios in the same cavity. Using this data and a novel algorithm, we demonstrate how to determine wall material type, thickness, location, and the topology of the wall. Our research methodology utilizes experimental measurements to create the database of signal propagation through different wall materials. The work also performs measurements to determine wall position in simulated scenarios. We ran the developed algorithms over the measurement data and characterized the error behavior of the solutions. The experimental test bed uses Time Domain UWB radios with a center frequency of 4.7 GHz and bandwidth of over 3.2 GHz. The software was provided by Time Domain as well, including Performance Analysis Tool, Ranging application, and AoA application. For wall type identification, we use the P200 radio. And for wall mapping, we built a special UWB radio with both angle and distance measurement capability using one P200 radio and one P210 radio. In our experimental design for wall identification, we varied wall type and distance between the radios, while fixing the number of radios, transmit power and the number of antennas per radio. For wall mapping, we varied the locations of reference node sensors and receiver sensors on adjoining and opposite walls, while fixing cavity size, transmit power, and the number of antennas per radio. As we present in following chapters, our algorithms have very small estimation errors and can precisely identify wall types and wall positions.

Thesis (Ph. D.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

Indoor localization systems have a variety of applications such as tracking of assets, indoor robot navigation, and monitoring of people (e.g. patients) in hospitals or at home. Global positioning system (GPS) offers location accuracy of several meters and is mainly used for outdoor location-based applications as its accuracy degrades significantly in indoor scenarios. Wireless local area networks (WLAN) have also been used for indoor localization, but the accuracy is too low and power consumption of WLAN terminals is too high for most applications. Ultra-wideband (UWB) localization is superior in terms of accuracy and power consumption compared with GPS and WLAN localization, and is thus more suitable for most indoor location-based applications [1-4]. The accuracy and precision requirements of localization systems depend on the specific characteristics of the applications. For example, centimeter or even millimeter localization accuracy is required for dynamic part tracking, while decimeter accuracy might be sufficient for tracking patients in hospitals or at home. Note that accuracy is not the only aspect of the overall performance of the system. Factors such as cost, range, and complexity should also be considered in system design. In the first part of this dissertation, a centimeter-accurate UWB localization system is developed. The technical challenges to achieve centimeter localization accuracy are investigated. Since all the receivers are synchronized through wire connection in this system, a wireless localization system with centimeter accuracy is introduced in order to make the system easier for deployment. A two-step synchronization algorithm with picosecond accuracy is presented, and the system is tested in a laboratory environment. The second part of this dissertation focuses on reducing the complexity of UWB localization systems when the localization accuracy requirement is relaxed. An UWB three-dimensional localization scheme with a single cluster of receivers is proposed. This scheme employs the time-of-arrival (TOA) technique and requires no wireless synchronization among the receivers. A hardware and software prototype that works in the 3.1-5.1 GHz range is constructed and tested in a laboratory environment. An average position estimation error of less than 3 decimeter is achieved by the experimental system. This TOA scheme with receivers in a single unit requires synchronization between the transmitter and the receiver unit. In order to further reduce system complexity, a new time-difference-of-arrival localization scheme is proposed. This scheme requires multiple units, each operating on its own clock. It avoids synchronization between the transmitter and receivers, and thus makes the development of the transmitter extremely simple. The performance of this system is simulated and analyzed analytically, and turns out to be satisfactory for most indoor localization applications. / Graduation date: 2013

Linearity enhancement, especially within the front end of a wireless receiver IC design, is highly desirable since it allows the front-end to withstand strong interferers from co-existing communication standards or other wireless radiators. We propose an interferer suppression method based on feed-forward cancellation that uses an injectionlocked oscillator (ILO) to extract the interferer from the incident spectrum. The technique is expected to be useful in environments where a strong narrowband interferer appears along with a wideband desired signal, such as ultra-wideband (UWB) and emerging cognitive-radio applications. The ILO is further embedded within a phase-locked loop which provides several advantages including ILO center frequency self tuning and automatic phase alignment between the main signal path and the auxiliary path. An IC that uses this approach is implemented in a UMC 0.18[mu]m RFCMOS process. In measurement, the chip demonstrates 20dB suppression for phase and frequency modulated interferers while maintaining around 18dB power gain and noise figure below 5dB, measured with an off-chip balun for the desired signal. Techniques for canceling amplitude modulated interferers, though not included in the integrated circuit, were also demonstrated with an off chip amplitude control loop. Over 20dB rejection was obtained with AM interferers with properly scaled envelop signal applied to the ILO bias port. A second LNA was connected in cascade with the system to emulate the input stage of a down-conversion mixer and the cascaded P1dB was improved over 16dB with cancellation on. Gain compression above 13dB was also observed when auxiliary path was disabled, at the same input level as the P1dB with cancellation applied. / text

The wide bandwidth employed in the UWB system allows for high data-rate communications, while its broadband nature requires it to coexist with other systems. For instance, several communication systems, such as digital TV, wireless LANs, WiMAX, and satellite receivers, utilize spectrum that is in the UWB band. According to Federal Communications Commission (FCC) regulations, the power spectral density (PSD) of UWB devices for communication applications is limited to less than -41.25dBm/MHz in the 3.1-10.6GHz frequency band, to minimize the impact of UWB on other systems. The impact of narrowband signals on UWB systems can also be significant, even though these signals may occupy a small part of the UWB spectrum, due to their much larger power. The performance and capacity of UWB systems can be significantly degraded by these narrowband interferers. In-band interference can be tolerated by increasing the dynamic-range of the receiver such that the interferers are accommodated within the linear range of the receiver. Alternatively, if the interferers can be avoided altogether, the excessive linearity requirements imposed by the interferers can be relaxed. Such an avoidance mechanism requires the ability to detect interferers. This work presents a low-power and low-cost detector for this purpose that can be employed in multi-band approaches to UWB, including pulse-based schemes, and those employing OFDM. The UWB band is divided into narrower sub-bands in these schemes. During transmission, the carrier hops to a new sub-band every symbol. The detector is designed to provide a profile of interference over the entire UWB spectrum, during each symbol period. This information would be available to the main-path UWB receiver to decide a frequency sequence of sub-band hopping, in order to avoid sub-bands occupied by large interferers. This relaxes the dynamic-range requirement, and hence the power dissipation of the main-path receiver, thus compensating for the extra power dissipation of the detector. The detector is based on a cascade of image-reject downconverter stages. An implementation of the architecture is demonstrated in a 0.13[mu]m CMOS process. / text