Ultra-Wideband technology has attracted interests of the researchers and commercial groups due to its advantage of high data rate, low complexity and low power consumption. The direct-sequence code division multiple access ultra wideband system (DS-CDMA UWB) is one of the proposal of IEEE 802.15.3a standard. By combing the power of both UWB and DS-CDMA techniques, the system could construct multiple access architecture using direct sequence method. In multi-user environment, the major problem of the receiver designing of conventional DS-CDMA system is multiple access interference(MAI). In DS-CDMA UWB system, the transmitted signal were interfered by inter-symbol interference(ISI) and neighbor symbol interference because of the multi-path channel characteristic. In this thesis, we use the training method to get the spreading waveform influenced by multi-path. Based on the information of spreading waveform, we use the block method to reformulate the received signal. We can separate the interference into multiple access interference and neighbor symbol interference. With Combining the interference cancellation, probabilistic data association (PDA) filter and sliding window techniques, we could eliminate the interference. In the computer simulation section, we compare the detection performance of sliding window PDA detector with conventional detector, and the simulation result shows that the improved PDA detector has better performance than others.

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.

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 µm 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 0.5µm process. The resulting differential pair had a constant transconductance that varied by only ±0.35% for rail-to-rail input common mode levels. The input common mode range extended well past the supply levels of ±1.5V, resulting in only ±1% fluctuation in gm for input common modes from -2V to 2V.

The main purpose of this thesis is to combine modified GML algorithm with 2-D simulated annealing for estimation of signal arrival time in the UWB systems.In a dense multipath environment, the generalized maximum-likelihood (GML) algorithm can be used for the time-of-arrival (TOA) estimation. Nevertheless, the GML algorithm usually takes a long period of time, and sometimes fails to converge. Hence, a modified GML (MGML) algorithm is investigated. Two threshold parameters need to be determined in using the estimation algorithm. One threshold is to decide the arrival time range of estimated path, and the other, an amplitude threshold, is to judge whether the estimated path is true. Generally, the decision rule of thresholds may be based on the minimum error probability, which is defined as the sum of false alarm probability and miss probability. To mitigate the effects from noise and dense multipath interference, and to reduce the computational complexity of the algorithm, a method of threshold settings based on the minimum root mean square error (RMSE) criteria is discussed. In this scheme, the RMSE value for each candidate threshold pair in an appropriate region is computed. Constructing an accurate RMSE table and performing a full-scale grid search of adequate threshold settings can be very time-consuming. A 2-D simulated annealing process is adopted for finding the best pair of thresholds for use in the modified GML algorithm. The simulated annealing, different from the gradient descent, can avoid trapping into a local minimum in finding the best threshold pair. The resulting threshold pair makes the modified GML algorithm become more efficient in estimating the signal arrival time with an automatic search manner. Simulation results show that the proposed scheme can achieve better performance than the grid search approaches in UWB environments.

The majority of the UWB radars available on the market today are expensive and often closed forfurther development due to proprietary rights. Therefore it is difficult to fully understand and adaptthe functionality of an available UWB system to fit one’s needs. The consulting-firm Addiva purchasedan UWB radar to be used in a safety system. However, the radar had limitations and the functionalityof it was partly unknown. This master thesis was inspired from this issue to examine the possibilitiesof developing a low-cost UWB radar, with main focus on research of human detection. The systemshould be easy to understand and modify, as well as reporting reliable data from the scanning. Theresults indicate that such a system can be developed. However, further development to the UWB radarneeds to be made in order to have a complete system.

Αντικείμενο αυτής της διπλωματικής εργασίας είναι ο σχεδιασμός και η υλοποιηση ενός ψηφιακού δέκτη τύπου Rake για ασύρματη λήψη UWB. / Subject of this diploma thesis is the design and implementation of a digital Rake receiver for an UWB transmission scheme.

No description available.

Ultra-wideband (UWB) is a revolutionary radio communication system that utilizes a large portion of the frequency spectrum while maintaining low power levels and high data rates. UWB systems can be used both indoors and outdoors within the power-level masks regulated by the Federal Communications Commission, thus making the technology very versatile. One of the main advantages of UWB is its robustness to multi-path diversity. The technology has attracted the interests of research and industry alike, owing to the possibility of implementing low-power, low-complexity, and low-cost devices. A widely recognized method of transmitting UWB signals is the use of Impulse Radio technology to transmit information. Impulse Radio Ultra-Wideband (IR-UWB) uses repetitive pulses of very short duration, low duty cycle, and low power levels within FCC regulations. One implementation of IR-UWB pulses in non-coherent transmission is the use of Differential Code-Shifted Reference (DCSR) pulses. In this technique, one of the main challenges at the receiver is pulse-level synchronization that times the received pulses at the right moments for accurate pulse detection. This thesis will introduce two design proposals in attempt to achieve the pulse synchronization. The first proposal is based on a fast-switch-controlled integrator circuit, while the second focuses on the use of an active low pass filter and phase-locked loop circuits to achieve proper clock timing. Both proposals will be presented, together with schematics, computer-aided simulations, and lab tests results.

Recent years have witnessed a growing demand for broadband wireless communication services such as on-the-go web-browsing, high speed data transfer and streaming of high definition multimedia. In response to this growth, there has been a rapid progress in research and development of technologies supporting high-speed wireless networks offering flexibility and scalability to heterogeneous consumer requirements. A fundamental challenge to the reliable operation of a wireless communication link is the wireless channel which is influenced by time-variant noise, interference, multipath and scarcity of the available frequency spectrum. Due to the wireless nature of the signal transmission and the manner in which energy is distributed or collected, an antenna has a profound influence on an efficient operation of wireless link. Because nowadays an antenna is required to work with many wireless standards, it poses one of the most difficult design and development technological problems. In the past, many antenna designs were concentrated on conventional outdoor applications such as satellite communications, terrestrial point to point communications and cellular base stations. In these applications, the primary design goal was the antenna electrical performance. In case of indoor applications, the designer has to pay attention not only to the electrical performance but also to mechanical, environmental and aesthetic features of antenna. In this thesis, the investigations into design and development of antenna for indoor wireless communication systems that are either currently widespread or quickly entering the consumer market are carried out. First, a single band circularly polarized Radial Line Slot Array antenna covering 2.4GHz ISM frequency spectrum of IEEE 802.11b/g protocol is proposed. Then, an access point antenna for IEEE 802.11a/b/g WLAN applications operating in a dual frequency band covering 2.4GHz and 5.2GHz frequency spectra is described. It consists of a RLSA antenna and a patch antenna combined in one body. During the design stage, in addition to characteristics such as return loss, radiation pattern and polarization, attention is paid to mechanical rigidity, light weight and low visual impact of these radiating structures. A low manufacturing cost is also part of the design strategy. This is important because of competitive commercial market of WLAN applications which is sensitive to the development cost. In theoretical investigations, a Field Matching Method is utilized to achieve a first order approximation to the coaxial-to-waveguide transition forming the feeding element of the RLSA antenna. Next, the full EM analysis (HFSS™) based on Field Element Method is applied to simulate the single and dual band antennas. Both types of access point antennas are manufactured and tested. Experimental results are compared with simulation results. The next part of this thesis presents the investigations into antenna diversity techniques for a wireless communication link in an indoor environment. The design of the automated experimental testbed is presented. This testing facility is used to measure the signal strength levels of a communication link between a mobile wireless device and an access point when they are equipped with multiple element antennas (MEAs). Special attention is given to the benefits of using MEA in a rich scattering environment that is accompanied the experiment. Full design details including electrical and mechanical features are provided. For a given feeding configuration, the testbed allows for measuring the received signal strength when the receiving module is moved over a circular area in an indoor environment. First set of experiments concerns the MEA system that utilizes two single-port transceivers each equipped with either 180º or 90º 3dB hybrid. By using alternatively one of the two input ports of the hybrids to feed a pair of monopole antennas several different transmission or reception modes of the 2x2 MEA communication link are investigated. The next set of experiments focuses on the performances of an indoor wireless system which uses either linearly or circularly polarized antennas at the two sides of the communication link. The overall diversity results indicate that by marginally increasing an overall system complexity (by using simple hybrid circuits and antennas), traditional transceiver systems equipped with MEA can provide significant improvements in the quality of indoor wireless link. The final part of this thesis presents the investigations into the design of planar monopole antennas that offer good return loss and omni-directional radiation pattern characteristics over an Ultra Wide frequency Band (UWB) spanning from 3.1GHz to 10.6GHz. Two types of planar monopole antennas are investigated. First, the ring type square with semi-circular base monopole antenna placed vertically above a finite ground plane is introduced followed by its design, manufacturing and testing. The second UWB antenna which is proposed in this thesis is a printed square with semi-circular base monopole antenna. This antenna is positioned in the same plane as ground and thus offers direct integration with a front-end circuitry of wireless transceiver. Several variations of this type of antenna featuring different outlines are designed, manufactured and tested. The obtained experimental results show a good agreement with the simulation results, as accomplished with the full EM analysis and simulation software HFSS™.

Recent years have witnessed a growing demand for broadband wireless communication services such as on-the-go web-browsing, high speed data transfer and streaming of high definition multimedia. In response to this growth, there has been a rapid progress in research and development of technologies supporting high-speed wireless networks offering flexibility and scalability to heterogeneous consumer requirements. A fundamental challenge to the reliable operation of a wireless communication link is the wireless channel which is influenced by time-variant noise, interference, multipath and scarcity of the available frequency spectrum. Due to the wireless nature of the signal transmission and the manner in which energy is distributed or collected, an antenna has a profound influence on an efficient operation of wireless link. Because nowadays an antenna is required to work with many wireless standards, it poses one of the most difficult design and development technological problems. In the past, many antenna designs were concentrated on conventional outdoor applications such as satellite communications, terrestrial point to point communications and cellular base stations. In these applications, the primary design goal was the antenna electrical performance. In case of indoor applications, the designer has to pay attention not only to the electrical performance but also to mechanical, environmental and aesthetic features of antenna. In this thesis, the investigations into design and development of antenna for indoor wireless communication systems that are either currently widespread or quickly entering the consumer market are carried out. First, a single band circularly polarized Radial Line Slot Array antenna covering 2.4GHz ISM frequency spectrum of IEEE 802.11b/g protocol is proposed. Then, an access point antenna for IEEE 802.11a/b/g WLAN applications operating in a dual frequency band covering 2.4GHz and 5.2GHz frequency spectra is described. It consists of a RLSA antenna and a patch antenna combined in one body. During the design stage, in addition to characteristics such as return loss, radiation pattern and polarization, attention is paid to mechanical rigidity, light weight and low visual impact of these radiating structures. A low manufacturing cost is also part of the design strategy. This is important because of competitive commercial market of WLAN applications which is sensitive to the development cost. In theoretical investigations, a Field Matching Method is utilized to achieve a first order approximation to the coaxial-to-waveguide transition forming the feeding element of the RLSA antenna. Next, the full EM analysis (HFSS™) based on Field Element Method is applied to simulate the single and dual band antennas. Both types of access point antennas are manufactured and tested. Experimental results are compared with simulation results. The next part of this thesis presents the investigations into antenna diversity techniques for a wireless communication link in an indoor environment. The design of the automated experimental testbed is presented. This testing facility is used to measure the signal strength levels of a communication link between a mobile wireless device and an access point when they are equipped with multiple element antennas (MEAs). Special attention is given to the benefits of using MEA in a rich scattering environment that is accompanied the experiment. Full design details including electrical and mechanical features are provided. For a given feeding configuration, the testbed allows for measuring the received signal strength when the receiving module is moved over a circular area in an indoor environment. First set of experiments concerns the MEA system that utilizes two single-port transceivers each equipped with either 180º or 90º 3dB hybrid. By using alternatively one of the two input ports of the hybrids to feed a pair of monopole antennas several different transmission or reception modes of the 2x2 MEA communication link are investigated. The next set of experiments focuses on the performances of an indoor wireless system which uses either linearly or circularly polarized antennas at the two sides of the communication link. The overall diversity results indicate that by marginally increasing an overall system complexity (by using simple hybrid circuits and antennas), traditional transceiver systems equipped with MEA can provide significant improvements in the quality of indoor wireless link. The final part of this thesis presents the investigations into the design of planar monopole antennas that offer good return loss and omni-directional radiation pattern characteristics over an Ultra Wide frequency Band (UWB) spanning from 3.1GHz to 10.6GHz. Two types of planar monopole antennas are investigated. First, the ring type square with semi-circular base monopole antenna placed vertically above a finite ground plane is introduced followed by its design, manufacturing and testing. The second UWB antenna which is proposed in this thesis is a printed square with semi-circular base monopole antenna. This antenna is positioned in the same plane as ground and thus offers direct integration with a front-end circuitry of wireless transceiver. Several variations of this type of antenna featuring different outlines are designed, manufactured and tested. The obtained experimental results show a good agreement with the simulation results, as accomplished with the full EM analysis and simulation software HFSS™.